Practicality and Cost of an Interstellar Probe

You'll need a substantial nuclear reactor, and an ion drive - both of these have been build and flown inside the solar system. There are other drives as well - the Daedalus Drive for instance, but that would require a lot of research and development, and I gather you want do this right away.

I don't think you can get much faster than about .1C with anything currently on the drawing boards - it takes a lot of energy to move that fast. But you might look into the Heim Drive.

If you're really interested in this sort of thing, there's a forum at www.nasaspaceflight.com that talks about advanced concepts.

Would it be OK if we go back to exploring the solar system after we launch this thing? Somehow I think that 8 years of interstellar weather reports might get a little boring.

You indicate .1c as a top limit. Why? Do you have some links or equations or reasons?

To put it another way, would 2g acceleration for 60 days be impossible?, because that gets you past .2c. If its impossibe, why?

How much fuel would it take to sustain a 2g acceleration for 60 days? Obviously the acceleration would be easier to maintain as the trip continued and the weight of the fuel decreased (significantly).

Anybody have an idea regarding this?

I think the current limits are with the speed of the propellant. Your craft can never exceed its own exhaust velocity.

That means at current ion drive exhaust speeds of 30 km/second, you top out. Throwing more ions out the tail does nothing, so you might as well shut the engine off and coast. Someone else can do the math and determine how long that trip would take.

One of the biggest problems with ion drive is that their acceleration rates are very, very low. One of the latest probes we launched last year has an acceleration rate of 0 to 60 mph in 4 days! Compare that to my car which can go 0 to 60 in 4 seconds.

The beauty of ion drive is that it can theoretically run for years. Whereas my car can only run for a few hours and I have to get out to pee.

So what have we left. We need power and lots of it to generate acceleration. Chemical rockets are good at generating acceleration, but their impulse times are very limited.

The only thing I can think of is nuclear propulsion; probably fusion. I think we could generate high enough exhaust velocities (sort of like a particle accelerator) and enough of it to generate realistic thrust. Dr. Bussard was working on such a breakthrough just before he passed away last year. The process was called inertial electrostatic confinement fusion. Unlike cold fusion, this may actually work. I know there were some experiments performed that actually looked like they could (if scaled up) produce more power than what they put into to start the process. Dr. Bussard's dream was that this would provide a viable solution for space travel locally and interstellar. More tests are scheduled this year. I only hope that this is really a break though, but we will have to wait and see.

Anyone have any other ideas?

Ok... I'm bad at maths..but I think you have a flaw in your assertion that the speed tops out..

Your craft can never exceed its own exhaust velocity.

Exhaust velocity relative to what???

Say you get upto 30Km/sec relative to the Earth and turn the engine off.
You are now going at a constant velocity...this is your new inertial frame of reference and can be considered as 'zero velocity' .
After all the space craft has no 'knowledge' of the relative velocity of Earth Mars or anyother object. e.g. At constant velocity you (and the engine) can't tell if you are moving back/forwards or stationary..

Thus when you start the engine again you are effectively starting up from stationary.

And will start to accelerate again.

Hopefully someone will enlighten me if I have got the wrong end of the stick...(or fuel rod)

Del

Good point. Jorrie also corrected this as well. The exhaust speed doesn't limit the velocity of the projectile or rocket. As long as you are throwing mass out the back you will get thrust and therefore acceleration.

However, exhaust speed and exhaust mass do impact thrust.

Excellent point Del,

You said "Exhaust velocity relative to what???"

I think I remember this point being brought up in an earlier thread. I'm not sure what the exact context of the thread was however. It is a fascinating idea.

It really goes back to the idea that there is NO absolute motion. Motion must always be relative to something else. AE confirmed this if I remember, and I think Jorrie will bear me out on this but if not, please correct me Jorrie.

So, it seems that acceleration, as you describe it, must be relative to some "object(s)" in the universe, otherwise, you are correct. There is no motion, no acceleration at all.

Could it be, maybe, that the craft is accelerating relative to photons being emitted? No, that can't be, since they emanated from said craft. What next?

Suppose, our craft, through some means, manages to travel vast interstellar distances such that eventually it lands in a "void" (as recently discovered) somewhere in the nether region of the observable universe. Does it have relative motion, say relative to the CMB itself or do we reach a singularity where motion takes on an different form?

-John

-John

Hi John, you asked:

"Suppose, our craft, through some means, manages to travel vast interstellar distances such that eventually it lands in a "void" (as recently discovered) somewhere in the nether region of the observable universe. Does it have relative motion, say relative to the CMB itself or do we reach a singularity where motion takes on an different form?"

It can surely measure its velocity relative to us, provided it is still in radio contact. Failing that, it can measure the redshifts of some known bright galaxies in the vicinity, with known peculiar velocities relative to our Earth frame and calculate it's velocity relative to us. The CMB frame itself is also available, but that's a really tough measurement!

BTW, voids were not recently discovered. They are known to exist since the 1930's...

Jorrie

"BTW, voids were not recently discovered. They are known to exist since the 1930's..."

Sorry about that Jorrie. I should have researched before posting. I probably should have said "recently discovered by me, i.e., since discovering and joining CR4.

-John

Here are a couple of links for you;

http://www.grc.nasa.gov/WWW/bpp/1997-J_AIAA_SpaceDr.pdf

http://www.grc.nasa.gov/WWW/bpp/2005-J_ANYAS_AssessBPP.pdf

Ok, so here goes nothing. Lets say we want to go 4 light years away.

If we launch from orbit and produce a continuous thrust of 2g for 60 days we should reach a speed of roughly .3c.

So how much fuel would be required?

The space shuttle uses about 1 million kg of solid propellant for launch. If we could make our probe 1000 kg, how much solid propellant would it need to sustain 2g thrust for 60 days?

I know a simple equation would be:

Thrust= F= -uR where R=ΔM/ΔT and u is the exhaust velocity (2000 m/s is reasonable).

F=a x M(probe) = 2(9.8 m/s2) x 1000kg = 19600 N

plugging it into the equation:

FxΔT/u = -ΔM

gives

19600 N x 5184000 sec / 2000 m/s = -ΔM

50 million kgs of fuel. Roughly.

Is that possible? Would it be possible to fly that much fuel up into orbit?

Shuttle Payloads are around 20,000 kg, meaning it would take 2500 shuttle missions to bring up that much fuel up into low orbit where the probe could be assembled and launched. Yikes.

The Saturn five rocket could bring 100,000 kg to low earth orbit, meaning 500 launches. Yikes, still a lot.

Of course, if you could somehow make the probe 1/10th the weight we're down to 50 launches, but that would be difficult. At least 50 launches sounds possible if extremely expensive. I'm not even sure if my math is close above.

Nice work, Roger. However, I think that the final velocity any object (or space craft) can obtain is limited to less or equal to the exhaust velocity it generates.

Am I wrong?

Also, initially, you are also trying to propel 5 X10^7 kg of fuel at 2 Gs, so that mass needs to be factored into the equation along with the trivial mass of the probe, yes?

Jorrie,

Are we sure about the not carrying fuel thing. I ask because it seems like it might be done. I'm thinking it's a one way trip for the probe, and I'm also thinking that it could be fuel for 3/4's and then some other kind of drive. I think this idea that it has to be an exotic drive is what makes it seem unlikely.

If we cut back on weight, made 25 or so launches of fuel compartments into low orbit, assembled the ship in low orbit and then launched it, I feel like a reasonable speed could be obtained. As far as I can see, the major difficulty seems to be getting the fuel into low earth orbit.

Is there a way, instead of launching the fuel up there, that we instead could make a fuel processing ship up there that siphons off atmosphere to create propellant? Essential pump and filter oxygen (or whatever) out of the atmosphere into a tank in orbit, which then processes the fuel and then distributes it to tanks (rocket sections) that we launch. Is this physically possible?

Or rather than that, can you tell me, would there be much relativistic effects at .3c?

"As far as I can see, the major difficulty seems to be getting the fuel into low earth orbit."

That is one hurdle, but it is also like loading up your car with bricks when you finally leave earth orbit. You have to carry and accelerate all that mass as you accelerate towards escape velocity.

Your equation F=a x M(probe) = 2(9.8 m/s2) x 1000kg = 19600 N does not seem to contain the mass of the fuel, which I think it should. The propellent needs to go along for the ride, so you have to accelerate it as well.

If the mass of the fuel is supposed to be included, then we will need even more propellent than you calculated (by a huge margin). This would shore up the idea that we need something other than a chemical rocket to get to the stars. Nuclear seems like the most promising choice because we grasp the physics and it provides a long-term fuel source.

Perhaps we should think Titan for it's methane. Hydrogen is a excellent source of deuterium and tritium for a thermonuclear engine. Nitrogen makes a good moderator for the reaction.

As far as the reaction itself He3 is a very effective fusion reaction fuel. There are approximately 90 lbs of He3 per square mile and to a depth of three feet in the regalith on the moon.

If you think that is an inconsequential amount, that would power the city of Milwaukee for over a year.

So if we want to get to stars perhaps stopping by the moon to fuel up might be a good idea. Oh, yes, that would mean going back to the moon and building a base there. I know it's "old hat". But you see it is not "old" if it was not done right the first time. Or continued when we had the momentum.

You see the problem is not so much ability as will. If humanity was threatened by complacent extinction they might decide that the effort to spread out humanity might be worth it.

Oh, wait they are threatened.

Dragon

I was thinking more about mining Earth's atmosphere from a low Earth orbit. Basically I think all we need is a lot of liquid Hydrogen and liquid Oxygen.

You could set up a large tank space craft in a highly elliptical low Earth orbit. As the craft (The high ellipticity allows the craft to "dip" into the atmosphere and collect gas. Since H2 is relatively light, this will be found more readily in the upper atmosphere, meaning the mining should be possible (by mining I mean "scooping up" or pumping up to the space craft). Once the craft has the Hydrogen, it can have a compression unit that creates liquid Hydrogen. In essence it would be an orbiting gas station for rockets.

Getting the oxygen may not be possible in this approach since it is heavier and tends to be found below 100km, however, even if we launch the oxygen the more traditional way, we've significantly reduced payload weight.

Please notice that this idea doesn't require anything new. You basically put a craft with a pump into low Earth orbit and compress the gas you get and store it in a tank. I'd also like to point out the filtering for the H2 shouldn't be too bad, since it is so much lighter than everything else you might get, you need only set your pump so that its strong enough to pull Hydrogen and too weak to pull the heavier elements. Plus I'm sure theirs all kinds of filters that could be used. The pump could be solar powered.

Why wouldn't this work?

Roger, The concept is a good one, however the problem I see is there is not enough hydrogen (if any) in earth's upper atmosphere. The solar radiation and solar wind will push any hydrogen that has sufficient energy to reach the upper atmosphere off into space.

I personally think that we need a permanent presence on the moon. Then we could take advantage of the moon's lighter gravity,(one sixth g) and use solar powered linear launch facilities, (no atmospheric resistance), and sunlight for two weeks at a time.

The lunar regalith could be mined for HE3, for safe and efficient fusion to power a facility while in the dark.

As for a source of hydrogen, there is compelling evidence that there is water ice on the moon.

Dragon

I'm sorry Dragon but your wrong, there are lots of Hydrogen particles

http://books.google.com/books?id=GKS5pI3feW4C&pg=PA31&lpg=PA31&dq=heterosphere+hydrogen&source=web&ots=RDob5-7op_&sig=rbn4y7IyszXfSqRiGtnhtYnroNw

Actually a low Earth orbit (200km) is much closer than the region where the atoms escape into space and actually there is a lot of hydrogen in our atmosphere, just not by percentage in the lower atmosphere.

Upon further review, this is a bad idea, the difference between 0 km/s and 7 km/s (LEO) is negligible when compared to 300,000 km/s (speed of light). It doesn't make much difference to launch from LEO. Also, its quite impossible to get speeds much higher than a couple 100 km/s with a traditional engine.

Hi Roger,

"If we cut back on weight, made 25 or so launches of fuel compartments into low orbit,..."

Sorry for interrupting your request to Jorrie, but the biggest, and perhaps, most insurmountable problem to the entire venture is that of acquiring funding for such a long range return project. Narrow minded politicians will object mightily I'm afraid.

However, as an academic exercise, it is fascinating.

-John

Hi Roger, first your last question: "... would there be much relativistic effects at .3c?"

Not much, only some 6% or so. Your 0.3c after 60 days of 2g acceleration is very close.

As far as carrying the fuel - I think the best path would be to have rocket fuel to escape the Sun's gravity-well (utilizing gravity assist were possible) and then some form of sustained hi-efficiency (perhaps exotic) propulsion to get up to your 0.3c outside the solar system.

I don't think ion thrusters have a chance - they are extremely inefficient in terms of energy required for a given delta-V. For 0.3c, the nuclear reactor will have to be massive with a lot of fuel, and remember, most of that mass must be accelerated as well. That's why I back Gavilan's field reaction propulsion, or something similar, where all the mass don't have to be carried with you. Mining Pluto or some other Kuyper belt object, as far from the Sun as possible, could perhaps be considered.

Jorrie

There is a good discussion of the exit velocity issue and how it affects the efficiency of your engine in one of those papers I cited above.

Dear Roger, Please also reference the work of John Searle and T.T. Brown.

Dragon

If I remember my physics correctly to double your acceleration in the same amount of time you have to square your force.

So to go far fast you need efficient and powerful.

I would suggest a nuclear ion engine with a magnetic wiggler accelerator to add velocity to the reaction mass.

2bits from

Brad

Use some chemical boosters to start off, a nuclear powered ion drive as needed, but a lot of speed could be gotten by using the gravity whip idea and a lot of free power from solar sails. Boost it around Venus and extend the solar sails. When too far out for the sails, furl them and use the nuclear ion drive to continue a slow but steady acceleration. Halfway small chemical rockets could turn it 180 degrees and it would start slowing down. The onboard computer would analyze the star system and steer a course that would provide as much information as possible before settling into a permanent orbit and sending back information all the while.

The size of the payload would depend on how much information was wanted and redundancy. I'd settle for visuals, spectrographic analysis, radio propagation and gravitational analysis. I want to see what it sees and if it hears radio signals I want to hear them. If there are planets I want to know their size and what their atmosphere is like.

Short-sighted, bleeding hearts will insist on turning inward toward Earth and its problems will fight spending money on what they consider a waste, learning new things. No research or exploration in history has been a waste, except to the wrong-heads who view any change at any time as bad.

I move that we boldly go where no man has gone before. Yes, I am a sci-fi fan.

Now we're talking. I'm liking your idea. I've made some adjustments, tell me what you think.

The probe will have several drives. First fire the probe close to the sun (as close as is safe) and when the probe slingshots by, deploy solar sail. The closer you are to the sun, the higher the velocity and concentration of solar wind particles. By deploying the solar sail when so close to the sun, we are in essence maximizing the thrust we can get out of that drive. Conservation of momentum insures that whatever we gained we keep, because we didn't deploy the sail until we were moving AWAY from the Sun.

Once we are far enough away from the Sun that the sails aren't helping much, we fire the chemical thrust for a nice long burn. Since the solar sail components were on the boosters, as we shed the boosters, the weight from these sails are shed as well. Now we're left with just a nuclear power system and the probe with an ion drive.

Once burnout is complete and boosters are spent and shed, use ion drive for the rest of the trip.

This would work great only if the Solar Sail is able to accelerate the ship significantly. If the ship is close to the sun I would think this ought to be possible. I did the solar sail portion before the thrusters to maximize the amount of time the sails were exposed to the dense fast moving particles closest to the sun. If we fired the thrusters first, the probe, though lighter, would fly past the sun to fast to exploit the solar wind with its sails.

Does anybody know an equation for a rough estimate of the kind of thrust a solar sail can produce?

It occurs to me that we could deploy the sails as you first suggested BEFORE we get past the Sun, catching the solar wind the same way as sail boat tacking into the wind. I guess the hard part would be getting the boosters to remain in sound working order so close to the sun, but it could be done I think.

I would really like to get a number to go with this solar sail idea. How can we calculate the thrust produced by a solar sail?

You Wrote: "AFAIK, the flux will change with the inverse square law, so one could calculate what you would get nearer to the sun."

I'm going to take that assumption and run with it (if it turns out to be wrong, please let me know).

The radius of the orbit of mercury varies but is sometimes 1/3 (perihelion)the size of Earths orbit. That means the intensity at such an orbit would be 9 times (inverse square law) as compared to Earth (1.4 kW/m² x 9 = 12.6 kW/m²). Using the quick and dirty equation from that link Jorrie provided:

(Power/m²)/c = Force/m² we get

12.6 kW/m² / 3 x 10⁸ m/s = 4.2 x 10^-5 N/m²

This means that it would take a perfect sail sized approximately 155m by 155m to generate 1 Newton of force.

To put this in perspective. Lets say our ship with sails weighs 1000 kg. The acceleration produced by 1 Newton of force would be;

a=F/M
a=1/1000= .001 m/s² = 10^-4 g

Yuk, solar sail isn't looking so good.

Lets go extreme and say an orbital radius of 1/100th AU.

So F/m² = .5 N/m² so with the same 154 m by 154 m (perfect) sail we would get roughly 12,000 N of force.

a=F/M = 12 m/s = 1.2 g

At 1/100th AU from the sun, roughly 1 billion meters from the sun (mercury is 46,000 billion meters from the sun) the craft would melt I'm sure or be completely damaged by the radiation.

Looks like there isn't much hope for solar sails to get us enough velocity to get up to near c values. Though to be fair I'm only calculating radiant force (light), I'm ignoring solar particles because I have no idea how to include them in the calculation. Those things are like bullets and are more likely to go straight through the ship then they are to be harnessed for power. Thats a lot of power though.

Assuming my calculations are correct, which is always a big assumption with me.

Though another solution would be to make a giant reflective sail. If a sail was made that was say 1000 meters by 1000 meters, that would be a 10⁶ m² sail. Such as sail at Mercury would produce accleration of:

4.2 x 10-5 N/m² x 10⁶ = 42N

a = F/M = .042 m/s = .004 g

At that rate of accleration it would take:

V_f=Vi + at = 0 + at = at

t = 10⁸ m/s/.042 m/s² = 2,380,952,380=75 years

Yikes, doesn't look like this is going to help.

Hi again Roger. You wrote:

"Since the solar sail components were on the boosters, as we shed the boosters, the weight from these sails are shed as well. Now we're left with just a nuclear power system and the probe with an ion drive."

I made a few computations for the nuclear powered ion drive with a whopping 100 km/s exhaust velocity. You will still need a prohibitive 10¹⁶ kg of ions to reach 1% c. The most efficient engine from a reaction mass point of view will be a linear particle accelerator, achieving ve ~ c. This will need only 30 kg of reaction mass and 30,000 kg of nuclear fuel, which sounds feasible. So where is the catch? The mass of the linear accelerator and the nuclear powerplant...??

No wonder NASA has once considered a pulsed nuclear explosion drive. No need for a big controlled nuclear powerplant and accelerator!

Jorrie

Sobering, Jorrie.

Jorrie,

Can you provide the equation you used, I'd be interested in seeing / using it. I'm having a lot of fun with this discussion.

If you haven't yet, please check my response regarding the rocket fuel calculation you provided. You'll see that with a little change I've made it much more reasonable but I'm not convinced the math I used is right because the answer seems....light.

Roger

Hi,

look at:

http://nextbigfuture.com/2007/11/vasimr-engines-plus-200-mw-of-nuclear.html

this may take one or two persons and an additional separate payload to mars in 40 days - if if if we will have a nuclear 10MW generator to feed the electric accelerator.

So to go to one of the next solar neighbours we would need about 10GW and the distance will not be 8 to 12 light-minutes but 4 to 8 light-years.

No chance today to have a guess about technology and cost.

And: if really there is a civilisation there, maybe they don't like us and wipe us out to nonexisting. If we are much bigger than they are, they will fear us. If we are much smaller, they will think us to be ants or worms or bacteria that should be treated with advanced DDT. If they live submerged below the sea they may think us as fierce and rough enemies on the wrong side of culture?

So before thinking this exotic field of galactic travel it would be advisable:

Build an ultrabig (VLBI) very long baseline interferometric telescope residing in the libration points of 4 of our planets. (Maybe we see them)

Solve the energy requirements of the future by extracting oil, coal and gas, then go to uranium und thorium (CANDU), then fusion if possible and then ultra-mirrors(5km diameter) as satellites and concentrating sunlight onto a boiler on earth. (Maybe we learn how to build a big spaceborn reactor)

All this is possible today (with adequate funding). Look for some deep drilling to make real sense of geothermal energy, look for some distributed seawater desalination to give people what they need.

And most important: establish a net of linked natural reserve areas, saveguarded and protected as military restricted areas so that really nobody without authorisation will get into that real wildlife refuge. We will only survive if a significant part of wildlife will survive!

Today it is likely that we will not be able to establish minimum survival necessities
- not global warming or cooling- so the next generation of intelligent creatures in some million years will do some excavations and find our fossilised bones and relics and think again our thoughts (considering us as not too intelligent dinos).

RHABE

Sorry Rhabe, but I still believe we can use a chemical rocket. Everyone seems to just assume this is possible. From the math I've seen, it isn't. It just is difficult to get the fuel in orbit.

Dear Roger;

Working with the basic rocket equation solve for the fuel mass required to achieve .1 C.

Also, what challenges do you see regarding scavenging your fuel mass from the upper atmosphere? At what rate would the orbital energy of the collector be lost to dynamic and collection drag?

Perhaps producing and launching the fuel mass from the lunar surface may have less practical challenges? Would magnetic launching of ionized fuel mass, un-contained, directly to the collection orbit intercept and then scavenging from that point be a possibility?

But again, I think it would be helpful if we knew the total estimated fuel mass required to achieve a small fraction of C. Perhaps solving from the basic rocket equation would support your position?

Gavilan

You Wrote:

"Working with the basic rocket equation solve for the fuel mass required to achieve .1 C."

I already used a basic rocket equation in an earlier post which showed it works. If you want to disagree I suggest you do the math and show me.

You Wrote:

Also, what challenges do you see regarding scavenging your fuel mass from the upper atmosphere? At what rate would the orbital energy of the collector be lost to dynamic and collection drag?

I said a highly elliptical orbit, that means it will be out of the atmosphere for most of the orbit so drag would be minimize. Of course, since the orbiting tank would be gaining mass, thrust would have to be fired to maintain its orbit periodically, but that shouldn't be too much of a problem since its a FUEL tank.

You Wrote:

Perhaps producing and launching the fuel mass from the lunar surface may have less practical challenges? Would magnetic launching of ionized fuel mass, un-contained, directly to the collection orbit intercept and then scavenging from that point be a possibility?

What fuel are you going to get from the moon? It has no atmosphere. The oxygen availible is locked up in oxides. Even launching the fuel from the moon would take more fuel than it would take to launch from Near Earth Orbit. Not to mention there is no delay for adjustments and the moon is relatively far away. No, the moon wouldn't be even close to better.

You Wrote:

But again, I think it would be helpful if we knew the total estimated fuel mass required

Again, I've already done this calculation, look at my responses.

"I already used a basic rocket equation in an earlier post which showed it works."

If the total mass of the fuel is zero.

AH,

I've redone the equation in response to Jorrie in the post where he says that the mass of fuel required would be infinite.

It turns out he's right if we launch from Earth, but I haven't been suggesting we launch from Earth for that very reason. When we launch from Low Earth Orbit (LEO), the amount of fuel needed is greatly diminished. This is because at LEO you are already traveling at 7800 m/s. So ΔV/Ve is much smaller (which is important as this value is the exponential in the rocket equation).

Now the equation isn't called the "ideal" rocket equation for nothing. Obviously in real life it would take more than 25000kg of fuel from LEO. But considering the Saturn V rocket had a payload of 100,000 kg, I think I'm being reasonable in saying its possible.

I'm hoping that Jorrie will check my math and either confirm it or correct it. Or anybody else for that matter.

Roger

I'll keep checking in. This is getting interesting. Great post, eh?

Do you know what the escape velocity for the Sun is? This is getting more complex than I am able to manage, but I think this is a good academic study to better understand what the real issues and hurdles are.

AH,

Jorrie was right, I made a simple mistake in my calculation. It does appear that chemical fuel alone to achieve .3 c is impossible. I'm checking to see how much ΔV is bought with 1 million kg of fuel.

Hi Roger. You wrote:

"I already used a basic rocket equation in an earlier post which showed it works. If you want to disagree I suggest you do the math and show me."

The basic rocket equation requires a initial mass (payload + fuel) of:

m₀ = m₁ e^Δv/v_e, where m₁ is the final mass, Δv your required velocity change and v_e your exhaust velocity. Putting in the values that you used, my spreadsheet overflows. Bringing down the velocity to 0.1% c, it still requires more mass than there is in the observable universe! So reaction mass propulsion cannot work for your mission.

To send a rocket from Earth straight to the Sun requires a Δv of greater than 30,000 m/s. According to the (optimistic) rocket equation, it requires an initial mass of greater than one billion kg. That's not feasible with today's technology, so Jupiter must be used for a slingshot to achieve that.

Jorrie

Jorrie,

Thanks for this. I agree it appears impossible if you assume an initial velocity of zero, but please consider this:

At Low Earth Orbit, the craft is already moving at 7800 m/s. Putting this into the equation you mentioned and assuming an exhaust velocity of 4000 m/s (typical value for a burn) and a final velocity of 10⁸ m/s (1/3 c) we get:

ΔV= Vf - Vi = (1 x 10⁸ m/s) / (7.8 x 10³ m/s)= 1.3 x 10⁴ m/s

m₁e^(ΔV/Ve)=m₀
(1000kg)e^(1.3 x 10⁴ m/s/4x10³ m/s) = m₀
26,000 kg = m₀

So we can launch the fuel into low earth orbit (the Saturn V rocket had a payload of 118,000 kg), assemble the space craft in orbit and launch it from orbit.

Now I have to admit, 26,000kg seems pretty small and I'm not sure I trust the answer, but I used the equation you gave to do it and I'm not seeing any mistakes.

Anybody else, can you please check my math and correct me if I'm wrong?

Hi Roger, I do not follow your ΔV calc: "ΔV= Vf - Vi = (1 x 10⁸ m/s) / (7.8 x 10³ m/s)= 1.3 x 10⁴ m/s". Why do you divide the two numbers?

If you subtract 7.8E3 from 1E8, the answer is still 1E8...

If I'm right, that will destroy your scheme, sorry! LEO's energy is negligible compared to c/3 energy...

BTW, the overflow occurs because of e^1000, not a division bt zero!

Jorrie

Dear Jorrie,

I'm an idiot. Yes, of course you are correct. Thank you for checking it and correcting it, I don't know what I was thinking.

So back to the drawing board. Let me try the reverse approach. How much speed would 1 million kg of fuel buy us?

ΔV=V_exln(m₀/m₁)=(4800 m/s) ln(10⁶/10³) = 33 km/s

So how about completely unrealistic yet techniquely possible, in other words, a 1 Kg probe with an exhaust velocity of 10 km/s and 10 million kg of fuel.

ΔV=V_exln(m₀/m₁)=(10000 m/s) ln(10⁷/1) = 161 km/s (.05%c (c=300,000 km/s))

Wow, that's depressing (though I'm glad I know the truth). Clearly a traditional drive alone is unrealistic.

I guess I'd better start reading about the relative speeds of nearby stars to see if one of them can help me out. This was a tough blow (though I appreciate Jorrie taking the time to tell me).

Well, another way to look at it is that the energy of getting to LEO is pretty much the sum of the energy expended with all of the launch vehicles.

Hi Gavilan,

You said "Would magnetic launching of ionized fuel mass, un-contained, directly to the collection orbit..."

Do you mean something like this?

-John

I was making a mistake when I was calculating using Tsiolkovsky's rocket equation. Jorrie has pointed it out and I see now that you are correct, reaching such speeds only by chemical means is completely unrealistic. I'll be launching a discussion on the whether or not Photon based drives are a possible solution for ramping up to large velocities.

Hi Roger.

Photon rockets are unfortunately very power-hungry. The most efficient conventional method seems to be heating a mass by nuclear means and somehow beam the black-body radiation all rearward. Due to massive fuel requirements, you are looking at 0.1 milli-g at best.

There is some hope for matter-anti-matter annihilation that can create gamma waves to be much more efficient. Good luck with this endeavour!

Jorrie

Jorrie,

Good timing, I've started a new thread on photon drives. I agree with your take, though there is an approach where you "reuse" photons to squeeze more thrust out of them by bouncing them between mirrors on two ships. Check out the thread and comment if you have time.

Roger

Hi Roger,

I just ran across Burkhard Heim's theories for interstellar space travel, i.e., a hyperdrive system that apparently has some merit. NASA, the military, and others have looked into this. Heim, who is now deceased was very well respected in the physics community.

You may already be aware of his research, but if not, check out these links:

Prepare for ludicrous speeds.

Take a leap into hyperspace.

.pdf file detailing Heim Quantum Theory (HQT).

Some really interesting stuff here. The math in the pdf file is way beyond me, but you and Jorrie may very well appreciate it. I'd be most interested in your, and Jorrie's, comments about this.

-John

Hi John. I'm sceptical of Heim's work - it claimed to have included general relativity into quantum physics, but it is clearly not true - nobody has been able to do that yet. I scanned the pdf that you referenced (not quite interested in reading it as a whole) and read the conclusion, starting with:

"The authors are aware of the fact that the current paper contains shortcomings with regard to mathematical rigor, and also proposes two highly speculative concepts. It should be kept in mind, however, that any type of field propulsion necessarily must exceed conventional physical concepts."

I expect the quantum-gravity problem to be cracked sometime in the future, but I'll rather watch the mainstream papers for that, not the "fringe". Anyway, thanks for the reference - I did not know about the recent paper that appeared on it.

Jorrie

Hi Jorrie,

Thanks for the reply.

You said "I expect the quantum-gravity problem to be cracked sometime in the future..."

I believe Heim, or maybe it was Dröscher, called them "gravitophotons" or something like that, resulting from manipulation of interactions of higher dimensions. What really made me take notice was this comment "At the moment, the main reason for taking the proposal seriously must be Heim theory's uncannily successful prediction of particle masses. Maybe, just maybe, Heim theory really does have something to contribute to modern physics. "As far as I understand it, Heim theory is ingenious," says Hans Theodor Auerbach, a theoretical physicist at the Swiss Federal Institute of Technology in Zurich who worked with Heim. "I think that physics will take this direction in the future."

"The general consensus seems to be that Dröscher and Häuser's theory is incomplete at best, and certainly extremely difficult to follow. What is needed is a step-by-step introduction, beginning at modern physical concepts," he says."

I wonder if any current physicists are deciphering, or working on completing, their work?

-John

IF I get my rocket engine design to work (still Theory). It is chemical sort of. Then the probe would be easy(not cheap). Lots of work to do until then.

Brad

Unlike Rhabe I am not afraid of finding alien life. Any probe must be programmed to self-destruct if intercepted and avoid revealing where it is sending its information, just in case. However if a probe finds aliens it will be many years before they can get here. We would have time to prepare.

He would have us solve every problem on Earth before venturing to the stars, but there will always be problems here we have not solved, so his way would have us never try. Making wildlife areas high security military reservations reveals his authoritarian view of how to protect wildlife, just shoot everyone who goes near a wilderness area. Then he says we will make ourselves extinct by not doing what he thinks is right to protect ourselves by solving all our problems.

The best way to assure the survival of humanity is by spreading ourselves and our plants and animals to as many places as possible. Technically it would be possible to hollow out a reasonably sized asteroid with multiple tunnels and chambers, add some spin to simulate gravity and send some thousands of people and their plants and animals on a generational trip to the planet of another star and land them from orbit. But first we need to find a suitable planet.

Rhabe does not consider the possibility that aliens have already found us and are sending their own probes and/or piloted scouts to check us out. If so, we should hurry to establish ourselves somewhere else.

Voyager 1 and Voyager 2 both contain a wealth of information about who we are and where we are located.

So, if you are worried about aliens finding us and attacking us you may be watching too much TV. ;-)

Dear Taganan,

there seems to be some misunderstanding: I do not fear finding alien life but I see the possibility that "they" are hostile.

Ans as they will be far advanced (probability tells us) they will see our spaceship long before we will detect them. So they will know where it comes from!

And I would try to solve only those problems that I think necessary for human survival.

We are far from establishing a permanent station on our moon.

We are very far from going to mars.

We are not at all near any ability to go to the next sun. We don't know where the next habitable planet may be.

Any idea of colonisation is absurd. You would try to start colonisation of a foreign world? With a totally different biologic and genetic environment, genetic code, may be other type of biologic information coding and for sure "ours" not being able to detect with certainty if there is an alien civilisation or not.

Wait for 100 more years and the picture will be a little bit clearer. Build the ultra large interferometric telescope - with a basis of 100 to 200M km - and try to see what is going on.
Are you sure where to search for "their" communication? Which electromagnetic frequencies? Which modulation and coding?

Regarding the protected zones I saw many protected areas deteriorate as being not protected well. But I did see not many military areas trespassed by non-authorized people. And if they intruded there was a good likelihood that they got some fine of 500 to 5000$ to pay and or some days in jail. (No one in a civilised military region would shoot if not intruding into inner areas!)

There are really some urgent problems to solve for mankind.

For the first time in our existence there are no more wild-life people that can take over or renew civilisation if ours will fail. (The barbarian tribes of all ancient civilisations that were strong enough for some time, coming in after breakdown of local civilisations and continuing with or without some break.)

That's why I am arguing hard towards some necessary (to survive a severe crisis) achievements.

RHABE

Hostile aliens are so remote that they are hardly worth considering. A probe coasting though space is nearly impossible to detect and the telemetry is aimed away from any possible aliens. Sure, you could program the probe to do a melt-down so as to be untraceable if intercepted, just to be safe. Since the probe is receiving and observing rather than actively searching it is not likely to be spotted, even by an advanced race. I do not believe it is so probable that an alien race would be so far advanced, it is just as likely they are less advanced.

The problems facing human survival will never be solved to the satisfaction of people like yourself.

We do not need a lunar station or to go to Mars to send a probe to the nearest star. Those things can be done all at the same time. We may not have all the hardware for a stellar probe, but we have the technology. Planets have been detected at Alpha Proxima so why not go and look, whether they are habitable or not doesn't matter.

Regarding colonization as "absurd" is a sign of a closed mind. I would expect atoms. molecules and chemicals to be very much the same throughout the universe and to react the same also. Similarity is more likely than extreme difference. Civilization generally would be detected as structures and use of technology.

Your descendant 100 years from now will still be yelping to wait for more information, without going to look. Detecting more planets around more stars will not be enough for him, he will caution waiting to see more from home, where it's safe, rather than take any risk by going to see up close.

It is likely they would use about the same communications frequencies we do and for the same natural physical reasons. A scan of both AM and FM for signals with patterns would work over time, which computers have a lot of.

Civilized countries do not need militarized wildlife zones as their citizens do not go out and slaughter animals for money and food. Is your country so uncivilized so that it requires this? I am all for conservation of wildlife for the generations to come. They taste good and I want animals around to be hunted and eaten in the future.

Again, there will always be urgent problems to solve for mankind. I say that one of them is getting us off this ball of rock and settled elsewhere, giving our species a greater chance of survival. Those barbarians of the past are now us and if civilization crumbles, the survivors will be the new barbarians to begin a new cycle. Even today there are plenty of barbarians to go around.

Work for your goals, let others work for theirs. I see space as a new frontier into which we can expand and it should not be put off because Earth is not perfect.

Hi Taganan,

"Hostile aliens are so remote"... as remote as William the Conqueror, the Reconquista, the colonisations of Europe all over the world, Napoleon, the opium wars, the war that brought Florida to the US, Germany starting WW1, Hitler starting WW2, China ? Korea ? India, France - Indochina - US, and many more older and newer.

Nearly impossible to detect? If we are transmitting with the technology of 1920 and they do a survey with the technology of 2020?

Receiving and observing ... same did the early soviet satellites and were tracked and heard wit a big ear by the US although there was only microwave transmission 300km to the ground. If the probe is executing a melt down it will still tell where it came from.

"do not believe that an alien race would be so far advanced"... It took 3,000,000,000 years to get our technology ready. This is now able to do telecommunication since 100 years. So we have a chance of less than 1:30,000,000 to arrive there in the gap of development of 100 years and much less if you think of todays advanced communication and much less if there is another timescale of development.

So we will find millions of alien technologies that are advanced and then we may find one or none in our status of development. And many more biologically interesting living communities that do not have our intelligence or that we do not recognise as we are too stupid.

You are right that we will not solve our problems to satisfaction, it is sufficient to solve the problems as far as the solutions allows us to survive.

"lunar and martian station and visit" ... ask NASA or ESA they know."

"atoms, molecules and chemicals" are the same in our universe, we have a positive proof from spectroscopy.

But encoding life will be different; see the differences in the genetic codes that survived from early evolution here on earth.

"it is likely that they use the same frequencies...AM...FM ..." If you watch the development from first Marconi transmissions to todays GHz and lightwave communication it is more than likely that "they" may use frequencies and/or modulations we cannot detect nor decipher.

Civilised countries may not slaughter big animals (our ancestors did this until there are no more), but some bad guys are stealing eggs from protected falcon and other nests, they come in with lots of people -never enough fence or guard- and walk above rare plants, nests, other habitats, chase off parents so predators can easily catch the offspring, and and and...

I have no idea of banning hunting but I really would work hard to preserve most of wildlife. Not malaria and similar.

I am living somewhere in Europe but the problems are similar worldwide.

There will be no new frontier in colonisation. There is simpy not enough energy here, see Jorries posts.

If you can achieve the best possible education for most people worldwide and establish a stable community (we do not have one now) then there may come up a new Einstein... who may tell us how to build a Schwazschild-Generator where a small black hole is suspended and fed with some material of any type to release more energy than usable. I fear this will never happen.

So awake from your dreams. Last time when similar dreams on a much smaller scale became actual politics we had Hitler and Stalin with results you know. Both wanted to colonize the whole world according to their weird ideas. Please do not try a third time.

RHABE

There is no sensible connection between any possible natives of another planet and "William the Conqueror, the Reconquista, the colonisations of Europe all over the world, Napoleon, the opium wars, the war that brought Florida to the US, Germany starting WW1, Hitler starting WW2, China ? Korea ? India, France - Indochina - US" all of which were NOT aliens.

But we are not using the technology of 1920 and using tight beam transmission at preset times is much different than orbiting the Earth with a microwave transmitter broadcasting a signal for all receivers to pick up. There is no way to know where some lumps of molten metal and debris came from, so there is no way for it to tell its origins.

Since there are both younger and older stars there are probably both older and younger planets, but if you plot the estimated ages the majority of them are close to the age of our Sun and it is also likely that many planets are going to be about the age of the Earth. So it is just as likely that we would find less advanced alien life as advanced alien life. The advancement of a civilization proceeds by fits and starts and is affected by many variables. Ours was and it is likely any other alien civilization would be too. Yet you insist that millions of the possible aliens would be more advanced and almost none near us, which reveals your phobia and fear of alien contact. A biologically interesting, but unintelligent, living community would be animals. And to top it all of you have decided that humans are too stupid to recognize civilization.

"encoding life will be different; see the differences in the genetic codes that survived from early evolution here on earth", the genetic codes affect the way living organisms are put together and they certainly have made many strange and complex creatures, yet the simplest are likely to be similar. We still have some very primitive genetic materials within our own cells. But what worked well here in terms of amino acids, sugars, cellulose and proteins is likely to work anywhere. Life elsewhere may have differences, but the similarities are much more likely.

Radio waves are electromagnetic and in certain ranges for certain purposes some work better than others. They would have started at the same type of spark-gap transmission and would use whatever was best suited to the purpose. There is no reason to assume any aliens would be more or less likely to use many of the same methods we use for at least some things nor that we could not detect them.

Why are the bad guys stealing eggs from falcons and not from chickens? Since it is illegal they must be 1. desperately hungry or 2. making a lot of money. There are two simple solutions, stop the money by clamping down and educating and just shoot the poachers.

Given a very long time for the journey colonization could be done, perhaps we don't have the energy source now for even much of a probe, but I am optimistic that better sources of energy or travel will be found. It is not necessary to have the best possible education for all nor a stable [stagnant] community to produce a genius. Peace and stability are periods of little technical or social progress. War and risk bring on periods of great progress

DO NOT EVER COMPARE ME TO HITLER OR STALIN!!!! MY dreams are nothing like theirs. If there was now a way for any group who wanted to go anywhere in the galaxy and set up on their own I would cheer their freedom.

Dear Taganan,

I feel a need to object:

"There is no sensible connection between any possible natives of another planet and..."

I think there is if you want to colonise the foreign planet. To send an ambassador would be ok if "they" agree. To colonise would either be damaging to them or to our party or very likely to both.

"much different than orbiting the Earth with a microwave transmitter broadcasting a signal for all receivers to pick up"

This was a highly directed microwave transmission with no chance to get some radiation of the primary beam. But any antenna has back lobes, and those distributed energy radially out from earth. A very tiny amount was strayed back from the moon. Then using (or may be deciding to build and using) the very big antenna of Arecibo they captured these signals.

"There is no way to know where some lumps of molten metal and debris came from"

Anybody who knows about mechanics of moving bodies can do this.

You are right with the likelihood that we may find also less advanced civilisations.

But if you think of a lifetime of a scientific or technical civilisation of estimated 1 million years, then it is very unlikely to get there in the first 500 or 1000 years where we are now. So if there is a considerable lifetime of a civilisation (no sure about this) then we will very likely encounter them in a much later stage then we are.

"to top it all of you have decided that humans are too stupid to recognize civilization." My intention was to express that we may not see them, either because they may hide themselves below surface (sea or land) or because they are much smaller than we are or?

"We still have some very primitive genetic materials within our own cells." I agree, and this is showing us that in these early times of living on earth there have been different genetic codes. Same amino-acids, sugars ... also DNA!, as you state but different encoding for a protein! The major survivor of these different codes are the mitochondria.

"Radio waves are electromagnetic..."

OK, but would you see the today transmission with a sophisticated receiver of the 40ies?, 60ies?,80ies?

If you think about FSK (frequency shift keying) or about spread spectrum communication, or burst transmission, if you think about now using microwaves up to Tera-hertz frequencies and modulated light and very low amplitude detection circuits then I conclude that they would use some other technology and other encoding that we may not see nor be able to demodulate or understand.

To stop stealing eggs from falcon nests is not so easy. Protectors are not allowed to shoot at intruders, and some falcons nest in not so easy accessible areas. Protection needs weeks of permanent surveillance, stealing only hours. Money is coming from other states so governments will not really be harsh to stop any trade.

I do not think a stable community be stagnant, this would be the first step towards instability. I think stability as first nor big oscillatory movements, no big excursions (black Friday on the stock exchange) and no long time over-stressing resources because of ever growing demands.

I did not want to compare you to these mass murders. But they had the drive that their ideas should be brought to all other countries: colonisation. And if the others are not willing then to be killed. Any colonisation was that way.

Today we should know better.

RHABE

Colonization is only acceptable when the planet does not have intelligent life. There are likely to be many planets without intelligent life. A planet in its equivalent of the times of dinosaurs or very early mammals would be suitable. A colony would ensure that an asteroid would not wipe us out.

If their communications are so different from ours that we are unlikely to detect them, the converse holds true, if theirs are all using advanced techniques that we don't have they are just as unlikely to be watching primitive types of communication methods.

I believe I mentioned that the probe would have to do some maneuvering, slight but enough that its path could not be traced as it could if it came in directly, in order to run a course through the systems gravity wells.

It is no more likely that any aliens would be more advanced than they would be less advanced. Man has thousands of years of tool using, language, clothing and such. Lets give Man 100,000 years of this type of civilization and assume that alien races would have this range of development in time. Then 49.9% would be less advanced and 49.9% more advanced. I agree that the chances of finding one even near our present level would be only about .2%. The age of the star systems we explore would give a rough indication of the possibility of civilization.

Civilizations use tools and build things and using the mere speculation that a civilization may hide underground or that a race living in the water [not using the land that we would want] and probably not technological at all or are small, is no reason not to go and find out. If they are there and are of any real level of civilization I would say we should maintain contact if possible, but not colonize.

You are thinking of colonization in modern Leftist political terms of one country having control of another. The entire history of man on Earth has been one of colonization as tribes and whole peoples moved from place to place, often displacing or absorbing the previous residents or being absorbed by them. The Visigoths were absorbed by the native Spanish and the Roman colonists in Romania absorbed those who invaded them. Every person who moves from one country to another is a colonist. When the Vikings went to Iceland they did another kind of colonizing. They settled where there were no other people, which is the kind of colonizing I am talking about when I say I want to see Man colonize other planets. There would be no other civilization there, no one to kill. So it is not true that "any colonization was that way", because the Vikings, Amerindians and the Polynesians colonized uninhabited places.

Stability means lack of change, no stress, no worry, no need to innovate. Stability would reject new things, new scientific discoveries, because they would cause change and change is instability, therefore stability equals stagnation. "Black Friday" was a result of fear on the part of investors who panicked and sold at a loss rather than just hang on. To stabilize that would require socialism and being a free market capitalist I reject that type of "stability".

I am going to to chime in on extraterrestrial life because I think that some of these thoughts have overlooked some fundamental ideas.

1) Any self-aware intelligent society will ponder the question, "Are we alone?" The rules of survival pretty much guarantee that question. Curiosity makes a species grow, so I would expect that to be an innate function.

2) Any society that ponders the question will consider what the most likely methods a civilization would communicate. Physics dictates a few likely possibilities that make sense. This means that anyone sending blanket signals will make the message easy enough to decode and find. Mathematics gives us some clues where we would likely choose for frequency and the message type. Any message will be clear that it is not simply natural phenomena, but obvious that it was sent on purpose. I will skip the details, but Google SETI and you will find a wealth of information.

Then there is the probability of finding a message. The universe has been around for nearly 14 billion years. Our own civilization has been around for 20,000 or so years and only technically cognizant to even attempt to listen and transmit for about 100 years. We teeter on self destruction (I am an optimist that we will survive), and we could wink out in the next 100 to 1,000 years.

Even if we continue another 1,000 years, 1,000 years is a cosmic wink in time in a universe so mind boggling vast. If this is not atypical development for a culture, having two cultures in close enough proximity in time and space is statistically small. There is no rule that states that every society will evolve and become technically able to communicate at the same sliver of time in the universe.

As for colonizing other worlds that have life, even if it is technologically and biologically feasible, Green Peace and the UN will prohibit it.

Well, as Jorrie and some others have pointed out to me (thank you all for your feedback) the equation for an ideal rocket is:

ΔV=V_exln(M₀/M₁) where M₀ is the starting mass and M₁ is the final mass (probe and rocket fuel tank), ΔV is Vf - Vi (increase in speed acheived), and V_ex is the exaust velocity.

Exhaust Velocity is governed by this equation:

All of this means that at very best we can't get more than a few 100 km/s of velocity. Which means that reaching speeds of 300,000 km/s (c) is pretty much impossible with a traditional rocket.

Great work Roger. Although it was not what we had hoped for, I think we all have learned a lot and now can better understand the challenge ahead.

I think technology is on the cusp of doing this, but it is unclear exactly what that will be. I still find it fascinating to dream and wonder and Roger you have at least stoked my imagination.

Very interesting Roger,

I'm still interested in what you (and others) think about the magnetic launch aspect, as I indicated in this reply to Gavilan. Seems like it would, at least, get rid of the initial fuel requirement problem if it could be exploited.

I don't know if anyone has brought this up yet, but is there any research into using Earth's magnetic field (short term), and even magnetic fields of other galactic objects to aid in velocity acquisition? (assuming this is even possible).

Seems like if most planets exude a magnetic field, the supposed Black Hole at the galaxy's center would exude an enormous magnetic field(?). There MUST be a way to utilize it.

Other than Gavilan's post, I haven't heard anything concerning magnetic propulsion (maybe I just missed it).

Just a little 2 cents worth.

-John

Hi Johnjohn,

there will not be magnetic propulsion as there is only an ultrafaint magnetic field in our planetary region and much smaller in interstellar space.

The only possibility is to have a big nuclear power plant feeding a big ion drive (search for "vasimr") and gathering the material to be accelerated with big collectors that act like a vacuum cleaner to suck in most particles, accelerate these and exhaust backwards.

Unless somebody inwents a wharp drive or a black-hole-Schwarzschild-generator as un ultimate power plant there will not be interstellar travel. Alas but reality.

RHABE

I think its a bit of a jump to go from "Chemical or Solar Sail Propulsion is not practical" to "interstellar travel is not possible with current technology". There seems to be many more avenues to investigate before we turn to science fiction.

I said that Chemical Propulsion and Solar Sail Propulsion were not practical (with math) so we could move on, not end the discussion.

Hi again RHABE,

You said "there will not be magnetic propulsion as there is only an ultrafaint [emphasis added] magnetic field in our planetary region and much smaller in interstellar space."

You may very well be right, but just suppose we think outside the box for a moment. We can amplify many things, current, light, sound, you name it. Just suppose we could amplify magnetism! I have no idea how this could be done, but if we could come up with a way, we could overcome the "ultrafaint" field that you refer to.

The other option would be to amplify gravity (since it is a universal property). Gravity seems to be the last force not yet really accounted for, seems like it would be the one to pounce on. Maybe that's far-reaching but again, we gotta go outside the proverbial box.

Bottom line:

Any currently proposed methods: chemical, ion, nuclear, solar, vasimir, etc., etc., are simply doomed to failure as far as traveling anywhere close to distances outside our own galaxy are concerned (at least within a reasonable human time frame). Solar power obviously gives diminishing returns as you travel farther and farther from a solar source. Sorry Roger, but that's just how I see it. At this point we really need "Scotty": "She just won't take anymore Captain!" But, indeed, someone like Scotty will eventually be there, and there will come a point where she will take it, and she'll shine to boot!

-John

Erratum to post #55,

Roger, I missed

your post #54. Sorry if I jumped the gun.

-John

The "very ultra-faint magnetic field" for which Rhabe refers is not so faint as to not protect us from intense ionizing radiation. It is also not so faint as to be the field source for inducing several thousand volts of EMF into a long tether as shown in the space shuttle tether experiments.

Solar field, specifically induced Lenze braking, may well be the cause of the Pioneer Position Anomalies.

The Heliopause extends well out beyond the orbit of Pluto. If we ever get well beyond the Heliopause with the instrumentation to sense it, I am confident we will discover significant galactic field.

The Standard International Ampere is defined by magnetic force. Infinitely large currents will create infinitely large fields. Even infinitely small reaction fields become usable when the action fields become infinitely large.

The issue isn't reaction field strength; it is action field strength and power.

Saying "there will not be magnetic propulsion" may not be an accurate absolute.

If this thread is still active when I get back to my library I will give some reference to space based experiments using Earth field as a reaction field in Satellite Attitude Determination and Control.

Gavilan

Hi Gavilan,

the magnetic field of the earth is around 0.1mT (millitesla) near the surface - up to 600 km where the first two radiation belts are there is not much less than this value.

So please tell me how you want to orient a coil or a magnetic field to get some force out of it.

The coil will be immersed in a uniform magnetic field. So the force in any point of the coil will be equal in magnitude but opposite in direction (because the current there has the opposite direction). So if the magnetic flux vector is perpendicular to the plane of the coil you will get a torque around one coil diameter. And if you orient the magnetic flux vector on a diameter of the coil you will get an expansion or compression along this diameter.

So I would like to know how to get a force from a coil and the magnetic field.

And I want to know the magnetic flux density on this interstellar travel route.

(In a voice coil you have a radial magnetic field interacting with a coil that is wound circumferentially giving an axial force.)

RHABE

Thanks Rhabe;

Your comments are appreciated.

Do you have some supporting links or references to - "The coil will be immersed in a uniform magnetic field."?

Are you suggesting that magnetic field behaves like a liquid or ether? That the uniformity of field is analogous to the pressure in a liquid? How is polarity explained?

Could you comment a bit further on -

"So if the magnetic flux vector is perpendicular to the plane of the coil you will get a torque around one coil diameter. And if you orient the magnetic flux vector on a diameter of the coil you will get an expansion or compression along this diameter."

I don't understand what is being said there. I have always believed that field was incompressible. The "expansion and compression" of field is a fundamental contradiction with what is stated in my text books.

Also; I have always believed "flux" to be a function of "rate of change" associated with a varying field or movement through a constant field.

Perhaps the magnitude of the force vectors will be a trigonometric function of the relative field angles between the action and reaction field sources where the sum of the three axis force vectors will approximate the force at the magnetic equilibrium position for any given fixed distance between the field sources.

Gavilan

Dear Gavilan,

the magnetic field of our earth is a permanent magnetic field like the field that is generated by a permanent magnet (bar like) with one pole near north and the other near the south pole of our earth.

In reality it is not truly constant, it is very slowly cycling with typically reversing polarity every 80,000 years.

The field will be weaker far outside as the field from any permanent magnet vanishes with distance.

Polarity is like a vector (the field strength or the flux density) pointing from north to south, the length of the vectors thought according to field strength. If two fields are superposed on each other (from two magnets) these vectors add to the total field strength.

If you have a current flowing in a wire or as free moving charged particles and if these move perpendicular to the magnetic field a force is generated perpendicular to field vector and current vector.

So if you put a circular coil with its symmetry axis aligned with the magnetic field then this force will be radial to outside or inside (depending on current direction). So the net force is zero.

If you orient the coil-axis perpendicular to the field vector then there are two quarters where there is the current nearly parallel to the magnetic field, there will be no force. (The coils being thought to consist of 4 quarters each extending 90 degrees). And there will be two other segments with anti-parallel forces that is in sum a torque.

So I do not know how the people that are talking about magnetic propulsion in space want to orient the coil to get some force.

The force you can feel if you put two permanent magnets aligned -one parallel to the other- either attraction or repulsion depending on parallel or anti-parallel orientation, this force is not usable inside a field that is not changing its magnitude in usable dimensions (in the length of the total spacecraft there will be no change of the magnetic field of the earth or sun).

If you think of flux as alternating that is the flux of a rotating (rotation axis perpendicular to magnet axis) permanent magnet or a coil fed with AC.

The magnetic field of the earth is nearly constant as from a stationary permanent magnet or DC driven coil.

The force increment dF (in Newtons N) is equal to the vector product of current I (in Amperes A) times flux density B (in Tesla T) times length increment dL (in meter m):

dF = (I x B)* dL

so only the component of the current that is perpendicular to the flux will generate a force.

So please think or search to find an arrangement that will generate some force from a current loop in a spacecraft, I did not find one.

RHABE

Dear Rhabe:

Your patience and thoughtfulness is appreciated.

You stated:

"If you orient the coil-axis perpendicular to the field vector then there are two quarters where there is the current nearly parallel to the magnetic field, there will be no force. (The coils being thought to consist of 4 quarters each extending 90 degrees). And there will be two other segments with anti-parallel forces that is in sum a torque.

So I do not know how the people that are talking about magnetic propulsion in space want to orient the coil to get some force."

My reply:

Are you assuming the coil design is that of a toroid? Of course the force sum vectors would cancel in this case. The coil design is that of a bar magnet, not a toroid.

Rhabe stated:

"The force you can feel if you put two permanent magnets aligned -one parallel to the other- either attraction or repulsion depending on parallel or anti-parallel orientation, this force is not usable inside a field that is not changing its magnitude in usable dimensions (in the length of the total spacecraft there will be no change of the magnetic field of the earth or sun)."

My reply:

When a compass needle is deflected by Earth Field is the only force acting on the needle translated to torque about the pivot point or is there also two other very small force vectors? How can we explain the needle deflection in light of your statement if there "is not usable force inside a field that is not changing its magnitude in usable dimensions?" Have we begun to confuse Induced Electro Motive Force with static field repulsion or attraction?

Gavilan

Dear Gavilan,

"you assuming the coil design is that of a toroid?"

Better call it a cylindrical coil wound circumferentially.

(A toroidal coil can be formed by bending a long cylindrical coil to a circle.)

"The coil design is that of a bar magnet"

I do not understand, if the coil is a cylindrical coil it will generate a dipole field and the length will change this a little. I do not see any other type so please explain or post a sketch.

"compass needle is deflected by Earth Field is the only force acting on the needle translated to torque about the pivot point"

This is not translated to torque but is generated as torque (attraction of the south-pole of the needle and repulsion of the north-pole on the northern hemisphere of earth).

The laws of magnetism are the same in motors or space. But in motors you can design the geometrical shape of the field and the current carrying coils. In space you have only a coil fro the current that is immersed in a very large magnetic field. So from any coil you will get a torque or nothing depending on orientation.

RHABE

Dear Rhabe:

Here is some reference.

Referencing Ap. I (Spacecraft Attitude Systems) - Spacecraft Attitude Determination and Control by - Edited by James R Wertz ISBN 90-277-1204-2.

I counted 23 satellites launched between the late 1960's and late early 1980's that used magnetic stabilization or magnetic attitude control or both.

Of special interest is AZUR-1 also called GRS-A, a German research satellite that used "Passive Magnetic" for stabilization and "Two fixed magnets such that the resulting dipole moment points in the direction of the z-axis with an accuracy of 8 minutes" for attitude control. Its pointing accuracy is given as "Angle between the geomagnetic field vector and the z-axis was less than 12 degrees." It used a sun sensor and two-axis magnetometer" for attitude sensing. It weighed 71.3 kg and was launched to an elliptical orbit inclined at 102.9 degrees. Perigee was 239 KM Apogee was 1955 KM. It was launched on Nov 8, 1969.

There are no notations as to mission success, but as you can see; there have been numerous space based applications of technology closely related to electromagnetic propulsion.

I have a more modern text that addresses these applications further; but right now I want to crawl into the sack with this book again. I am finding myself able to understand a few more bits and pieces now than when this book was given to me a decade or more ago by a very fine gentleman who also gave me his typed and bound notes from his Space Studies at UCLA back in the late 1950's.

Gavilan

Dear Gavilan,

attitude control is angular alignment to a wanted direction: star tracker, solar panels and antennas have to have a near optimum orientation that is achieved by either rotating the spacecraft or the antenna with respect for the spacecraft. These rotators are called BAPTAs (bearing and power transmission-assemblies) and were often prone to early failure.

That's why a direct control of minimum one direction is necessary, in addition any radial orientation of an elongated satellite is more stable than other orientations.

Angular alignment can be done magnetically as I stated in my post: if the magnetic field is oriented along a diameter of a coil then there will be a torque around the diameter that is perpendicular to the magnetic field.

So no problem with a torque but I do not see how to generate a force. In other words: how to bring back the current in an extended magnetic field without generating the opposite force? (in an elongated coil).

As I know todays attitude control is either by momentum wheels: gyroscopic torques act perpendicular to the spin axis of a fast spinning heavy ring-wheel. If you command an input torque along one axis it will rotate around the other axis (the third axis is the rotation- or spin-axis.)

Or it is by reaction wheels where spin-up and spin-down is used to generate reaction torques in the satellite.

If the limits of the range of these is near there have to be additional thrusters to be fired (until exhaust of fuel is limiting life.)

So please find or invent a possible coil to generate a force in a large extended and substantially constant magnetic field - I would be happy if existing.

If existing then the calculation of necessary current and cross section is leading to the same result: Impossible because of weight and necessary power.

RHABE

Dear Rhabe:

Thank you for your reply.

Your statement:

"So please find or invent a possible coil to generate a force in a large extended and substantially constant magnetic field - I would be happy if existing."

A couple rudimentary long electro bar magnets will work fine. No need to re-invent the wheel. By the way, how would you best describe the needle of a compass and its relationship to earth field? We still have not discussed all of the vector forces acting on a compass needle yet. I thing this would help me to grasp your analogy of field to fluid.

"If existing then the calculation of necessary current and cross section is leading to the same result: Impossible because of weight and necessary power."

First off, cross section is not a variable in the force equation; it is however, a variable in the resistance of the coil windings and a variable of the core as it determines the length of each single wrap of the conductor.

Current, of course, as I pointed out earlier, is defined as a magnetic force.

And power, ahh yes, power. I described that in the BASIC algorithm I posted earlier. About 39 gigawatts to accelerate 1000kg to 1/4 C in one year; ignoring relativity.

I'm not trying to invent a starship here buddy. I'm merely trying to use reaction fields to increase the specific orbital energy of satellites and space craft without the use of propellants.

I will ask again; are you suggesting that magnetic field is analogous to a liquid?

Gavilan

Dear Gavilan,

"couple rudimentary long electro bar magnets"

If this is an elongated piece of iron or steel and has wound around a coil of n turns then at the ends there will be magnetic poles, one north one south.

If the north is looking to a uniform (earth or solar or very large compared to this bar-magnet) magnetic field to the south pole it is attracted the south is repelled.

As the field strength of south and north are the same and as the strength of the large field is the same from north to south of the bar the two forces cancel.

If the bar is oriented with an angle to the field lines of the large field then the two forces give a torque: this is the torque that aligns the compass needle. (Any DC electromagnet can be replaced by a permanent magnet and vice versa.)

"are you suggesting that magnetic field is analogous to a liquid"

If you only think about the analogy of the streamlines of a fluid with no inertia, but with some viscosity but without viscous losses, then this analogy is ok. (there is a limit at the saturation flux density and at the apparent viscosity that can be translated to 1/permeability). Any force-gradient along a streamline, generated by pressure in the fluid, will be equivalent to magnetic field strength (A/m).

Any flow per unit of area ((volume/sec)/m²) will be equivalent to flux density (T or V*sec/m²)

Another analogy is better: Analogy to electric current in a volume of conducting material. Conductivity being analog to permeability. Electric field strength will be analog to magnetic field strength. Electric current density will be analog to magnetic flux density. Also this analogy is not modeling the "no loss" situation of a constant magnetic field.

Only the analogy to an electric field will model this lossless situation in a correct manner.

So once again: how to wind a coil or orient a permanent magnet to generate a force from a uniform magnetic field?

RHABE

Here is a thought, there is a classic Physics question that says if you're on a sailboat and have a fan, can you use the fan to make the boat move. The answer is no because of conservation of momentum.

So what about a space craft with an array of lasers that is pointed at a solar sail? Would it work the same way? Would their be no propulsion because of conservation of momentum?

I think that you have the same issue with the fan. The laser source has to emit the beam.

Hi Roger. You wrote: " if you're on a sailboat and have a fan, can you use the fan to make the boat move. The answer is no because of conservation of momentum."

Wrong, you can make the boat move! If you can arrange the sail so that near all the air from the fan hits the sail (spinnaker), most of it will be directed back and past the fan. The nett effect can be a movement into the direction that the fan is pointed.

In an ideal case, if the momentum change of the air by the fan is P, then the momentum change of the "reflected" air is -2P. Add the two and the nett momentum change of the air is -P. In order to conserve momentum, the boat will gain momentum P.

Since there will be losses, it is best to just point the fan backwards and lower the sail. The same for laser propulsion in free space. Point it backwards and you'll get the best acceleration, albeit still at a feeble thrust/input energy ratio.

Jorrie

Interesting take on the problem. The classical problem I was referring to is a fan directly into the sail, not with the air reflecting back which would, as you say resut in movement. Good point though, and you could reproduce the "spinnaker" with a photonic crystal waveguide, not that it makes much sense since a better idea is to just turn the laser around and use that as propulsion as you suggested.

A laser drive has been mentioned several times now. I think I can figure out how to do a rough calculation for it, I'll give it a try just to see how far it is from realistic. As always, thanks for the feedback Jorrie.

To all, If you are interested, a description and operation of a "photon drive" can be found in a short story by author Larry Niven called "The Warriors", it also bring to light another thought discussed on this thread: Hostile Aliens.

Dragon

Hi Roger,

Just tuned in to this thread, and scanned over it. Let me suggest a 'momentum' engine. If you kneel on a chair and jerk yourself around, you can propel the chair across the room by your momentum. So in the rocket you have a mass that you pull slowly forward and then jerk it suddenly back, then repeat. Of course you will need a power source, that's the big problem.

To speed up the launch, say of an ion propelled ship, how about starting from the moon and shooting it from some kind of linear accelerator. Maybe more comments after I have read more.

S

from Wikipedia:

"The nearest known star to the Sun is Proxima Centauri, which is 4.23 light-years away. The fastest outward-bound spacecraft yet sent, Voyager 1, has covered 1/600th of a light-year in 30 years and is currently moving at 1/18000 the speed of light. At that rate, a journey to Proxima Centauri would take 72,000 years. Of course, this mission was not specifically intended to travel fast to the stars, and current technology could do much better. The travel time could be reduced to a few millennia using lightsails, or to a century or less using nuclear pulse propulsion (Orion)."

The dream of getting there in 8 years is just that - a dream, unless there is a major breakthrough such as a wormhole or anti-gravity.

S

We have to start sometime, so it may take centuries for the first probe, so what! Later and better designs, better technology, may get later probes there first. If not at least the original will finally send back its findings.