Slowing Down in Space

<if the space shuttle slows down in space and enters the atmosphere would it still need the ceramic blocks on the bottom?>

- no.

<is this possible?>

- yes, but not with any current technology available that i'm aware of.

<or would the fuel required to perform this slow down procedure be too much to carry>

- yes.

The shuttle must use reaction mass(rocket thrust) to slow down or speed up or make any changes in it's orbital parameters.

If is slows down the height that it orbits will decline and it will enter the stmosphere. There will be heating on all parts of the shuttled as it descends. Most heat on the leading edges, but all parts will get some heating. So the will need all the heat tiles they have

There is no significant propulsion in space because there is no air to push against. It make space travel nearly impossible. Take your hand put in front of your face and lightly blow on it, thats about what is possible as far as propulsion in space goes. Think about how much fuel is expended the launch the shuttle into space with the benefit of the air to push against. Of course it's way more complicated than that but it may give you a comparative instaead of a simple no.

the shuttle does not push against air. It works by reaction mass leaving at high speed and in massive amounts. The only way to move in a vacuum is via mass transfer. you throw mass away and you travel in the opposite direction. Faster mass transfer is more efficient. You need to read up on it.

http://www.nakka-rocketry.net/pvcmot4.html

http://www.nakka-rocketry.net/index.html

A New York Times editorial, from 1921 regarding Robert Goddard's revolutionary work and I quote,

"Professor Goddard does not know the relation between action and reaction and the need to have something better than a vacuum against which to react. He seems to lack the basic knowledge ladled out daily in high schools."

I have, on occasion, read the New York Times. They have not shown significant improvement.

Merkelerk: That's a great quote!

The New Your Times is a wonderful paper. It is just that they have moved their inaccurate publication of non facts from the scientific to the political arena.

This gives us, clear thinkers, something to push againist.

Hay Philip. I didn't write this but could have. Will not be playing golf today. Its raining. But, may take a nap.

There is an interesting quasi-paradox in the question with regards to orbits in general. Like on the earth's surface, gravity keeps drawing everything towards the center of the earth regardless of its height above ground. The effect of gravity on a spacecraft is to accelerate it towards the earth, however its velocity is balanced such that the effect of the acceleration is just to curve the spacecraft's trajectory towards the earth enough that it doesnt go flying off into space or crash into the atmosphere (remember Newton's First Law: A body will stay in constant (straight) motion unless acted upon by an external force [aka. gravity]).

In the case of the space shuttle, if it slows down, its orbit will decay and it will enter the earth's atmosphere like a normal re-entry, and will definately need the ceramic heat shield. Unless the shuttle provides enough rocket thrust towards the earth to balance the force of gravity at the same time as slowing down, it cannot just slow down and maintain its orbital height at the same time. (On the other hand, satellites like those used for GPS and communications are typically in geosynchronous orbit, which effectively means that they appear to be stopped relative to the ground, in which case you could argue that they are 'stopped' but remain at their orbital height. This effect is due to the rotation of the satellite being equivalent to the rotation of the earth, though it is still moving in an absolute sense). If it were able to come to a complete halt (or even just slow down) above the earth, then it would still have to contend with gravity's acceleration towards the earth. Depending on its orbit, this could be a long time before entering the atmosphere, which means that the shuttle could still reach speeds that would require a heat shield.

In short, it is possible to slow down (though highly impractical); however, this will likely still require the use of ceramic heat shield for re-entry.

What about deploying parachutes whilst the atmosphere is still very thin?

'What about deploying parachutes whilst the atmosphere is still very thin?"

I think the shuttle's fairly large belly is as good as a parachute. Secondly, when the air is still thin, the braking effect is not huge, but there is already a lot of heating due to the high speed. I'm pretty sure NASA did look at such ideas and rejected them in favor of the present system.

Hi, I'm Alex head of Aerosoft Research and Development Division: we, together with CIRA, (Italian Aerospace Research Center) are just now researching about a new reentry profile (that will lower the heating) and new thermal protection (that will protect the "cold" structure). This effort is made in order to improove safety and increase the life of reentry vehicle structure.

Alex

This is a question to Alex or somebody who knows about the emergency case of the space vehicles.

Is there a device to eject the capsul to bring the astronouts in a safe landing when there is a heating problem in a vehicle structure in the reenttry process.

I think this is fairly common knowledge for the Space Shuttle. NO, there is no device to eject the capsule, there is no capsule. Earlier programs (Mercury, Gemini, and Apollo) had a means to separate the capsule from the booster rockets in an emergency after liftoff, with a parachute landing in the ocean, but this still required that the astronauts had suffiicient warning and time to make a decision to abort. Unfortunately, on re-entry all they had was their capsule with its heat shield and parachutes.

The shuttle doesn't even have that protection. The first four shuttle missions (all two person missions) had fighter plane style ejection seats. These were subsequently taken out. See the Wikipedia article for more information on Ejection Escape Systems, part of a larger article on Space Shuttle abort modes.

Interestingly, NASA does (now) have a contingency plan for rescuing Shuttle crews in orbit and returning the un-manned Shuttle to earth by remote control. If it was determined that the Shuttle was unsafe to re-enter the atmosphere, the crew would transfer to the International Space Station (ISS) and a rescue mission would be sent up within 40 days. The ISS has provisions and oxygen to support both Shuttle crews for 80 days. In addition, ISS keeps a Russion Soyuz capsule docked as a "lifeboat".

Of course all of this is only possible if a problem is detected before re-entry is attempted.

I heared something about ejection capsul, but nothing really developed(that is what I know).

Anyway cosider the following: Where the reentry vehicle encounters heating problems the speeds are that high that if a capsule would be ejected it would immediately burn. So we need the capsule itself to be all of heating protection. And more, would the astronauts surveiw the accelerations the capsul will be subjected?

Finnaly: the hevier the vehicle is, bigger are the lounch problems and less payload can it carry.

Quote: "I heard something about ejection capsule, but nothing really developed (that is what I know)."

AFAIK, the ejection capsule or escape tower idea is just for emergencies during the liftoff and shortly afterwards. I agree that they are of little use during re-entry. Maybe ejection during approach for landing could be feasible again?

Just throwing this out there as my perspective

Typical shuttle flight in LEO travels at aproximatly 200 statute miles above the earth with a velocity magnitude over 17,000 miles per hour. Assume the shuttle's payload bay is mostly empty so Orbiter mass is roughly 200,000lbm. Do a little math to find the sum of potential and kinetic energy; then write an energy ballance equation to get altitude to zero and velocity to what ever the earth's surface velocity is, and figgure out how to dissapate ALL of that energy. That's how I look at it.

The other option I would like to see is instead of dissapating it, just transfer it. Maybe use a 400+ mile long cable with a pulley up at geosychronous orbit, and do like the old trains used to do on steep mountain hills. Pull the next train up as the first one goes back down. Ain't that a silly solution!

Quote: "The other option I would like to see is instead of dissapating it, just transfer it. Maybe use a 400+ mile long cable with a pulley up at geosychronous orbit, and do like the old trains used to do on steep mountain hills. Pull the next train up as the first one goes back down. Ain't that a silly solution!"

Not so silly - this sort of idea is called the 'space elevator', not practical today, but who knows... Search Wikipedia.

http://science.howstuffworks.com/space-elevator.htm

Any decrease in orbital (tangential) velocity results in decrease in altitude, and therefore a conversion of potential energy into kinetic energy, increasing the linear speed, and velocity vector toward the earth. However, this does raise another question: why couldn't retro-rockets be fired after the shuttle enters the atmosphere to reduce linear speed, reducing friction and the heat load on the ceramic tiles?

Is this not practical because the extra fuel required to make any significant difference would be impossibly great?

What about the so-called "Space Plane" in development? Will it also require similar ceramic shielding, or is its speed and sub-orbital flight so much less than the Shuttle that conventional materials are adequate?

Is the typical Sci-Fi depiction of Spacecraft landing at low-to-zero horizontal speeds and firing retro-rockets to slow vertical descent to zero simply impossibly wrong?

What about using ramjet or scramjet technology (which only works at high velocity) to power "thrust reversers" such as are used on commercial jets, or even simpler retro-jets? This could be much more fuel efficient than retro-rockets, possibly allowing the required amount of fuel to be carried on-board.

Just a few thoughts. Might be a bit more practical than the "Space Elevator"!

I'm not certain, but from an energy balance stand point (again) it seems that it would take roughly the same amount of rocket or jet trust energy to slow the spacecraft's normal velocity (or at least keep it below some important level through most of decent) as it would take to launch it. This is a uselessly theoretical approach, but the energy used to lift the spacecraft and get it up to speed needs to be countered somewhere to get it back down to sea level and stopped realative to earth's surface at that point. If using the Shuttle as an example; one could take into account that the mass of the 2 SRBs and H2O2 tank and contents will nolonger be along for the ride increasing the force created by gravity on the vehicle during decent. That may not make any sence at all...

If that does make sence then that gives a feel for the ammount of fuel that would be required to slow her down, AND have to haul around while completeing objectives.

That would be the conventional argument against the use of retro-rockets. However, since ramjet or scramjet technology uses the very air that is causing friction heat in the first place, the combustion and resultant force is much more efficient as compared to mass-reaction rocket engines. Plus, only the weight of the fuel is required, not an oxidizer like LOX or H₂O₂. Read the Wikipedia article on "Ramjet"

Also, we don't need to get the speed down to zero, as it was at the time of launch, only down to a speed where conventional materials can be used on the fuselage and wing undersides instead of ceramic tiles.

Another advantage, less ceramic tiles, less weight, more fuel can be carried for ramjet retro-thrusters!

Good point.

Would want to be able to reposition the ramjet nozzel or intake (diffuser?) so that it could be used for both asent and desent...

Exactly. Ascent and descent. Makes sense?

The spaceplane are the most possible next generation reenter vehicle that will be developed. One of the many problems to be solved is that the heating is still there because of the very high speed (hypersonic flight in plasma).

Something is actually known about this kind of flight, but much is fully theoretical with little experimental data compared to the amount of data available for supersonic or subsonic flight.

The goal is to lower the temperature and improove the the termal shield.

Lots of words from lots of people, but the real reason may not be apparent.
I think you mean that rockets simply stop all forward motion and the shuttle "drop
" back to earth. NASA actually toyed with this idea long before the shuttle was even an idea. The conclusion they came up with was that you would need just as much if not more than the same amount of fule to land as you would to lift off and enter orbit. First you would have to fire forward rockets very hard to enter what is known a "geo-syncronous orbit" (stay in the same spot above earth). When the shuttle begins to drop, remember there is nothing (no atmosphere) to slow it down. It goes faster and faster until it contacts the atmosphere and burns up. Okay, so why not use rockest on the bottom? They would have to fire far above the atmosphere and continue doing so until it actually touches the ground. It would have to mantain a speed low enough so little to no heat would be building up on its bottom (including rocket exaust. Since this method would add siginificant cost and risk to the missions, the better solution was and is to use a heat shield and the atmosphere as a breaking mechanism for the shuttle. Hope this answers your question.

Dear Guest

If shuttle slows down , orbital force also will slow down and gravitational force will take over and pull the space craft down towards earth centre. The trajectory of descend will be decided by the angle of entry of the space craft,and resultant vector and it will not be VERTICAL FALL.

In this process of descend, the VELOCITY WILL KEEP ON INCREASING as a result enormous heat will be generated, due to friction caused by air.

Hence heat shield or tiles are required to protect from burn out of space craft.

DHAYANANDHAN.S, INDIA