Atmospheric Burn-Up vs. Rogue Bolts

I understand there is an enormous amount of space junk .Why wouldn't it be practicle to send out a space dustpan to scoop up all that stuff and solve the problem

The "space dustpan" would have to be in an orbit in order to "stay up". It would have to have a huge "capture area" in order to actually catch anything (remember, space is a pretty big place). However, the closing speeds (the speed of your car plus the speed of the oncoming car) would necessitate (if even practical) that the support structure be extremely hefty (and heavy; a problem for the lift vehicle). Also, orbital mechanics (different orbits at different altitudes) would mean that the dustpan would have to have a propulsion system (with limited life) to move it from one orbit (assume it has cleaned up its current orbit) to another orbit. Then there's the problem of cleaning up the space junk without capturing (and destroying) the current in-use satellites. It has been thought of and studied but not pursued due to technical and cost prohibitions.

Quoting JavaHead: "What would the formula be to solve for mass?"

Although it's a bit unrealistic to work from a zero velocity initial condition, lets stick to the question as asked. I doubt if there is a simple formula as you requested, because you will have to numerically integrate the equation of motion all the way from space, with negligible air density, down to ground level, with changing air density, just to get the instantaneous speed of the object.

Inside the algorithm, you can then stick the calculation for burn-up and check numerically when the object disappears. I know how to do the velocity part, but not the burn-up part!

Jorrie,

I know this is an old thread, but I still have some renewed interest in it. But as I stated in the original post, I have little to no knowledge in this area.

In your response, you stated you knew how to calculate the velocity facet. Without giving me the answer, could you possibly give me the components of the calculation, or maybe the steps used to solve and the name of the mathematical process used at each step? I'll then do the research on my end to try and put something together.

Thanks,

JavaHead

There are other factors as well. Surface finish, hardness, grain structure, etc. can affect the oxidation of carbon steel. For example a highly polished surface will take longer to oxidize than a rough surface. The smooth surface has less exposed area than the rough surface which has peaks, valleys, craters, cracks, etc.

If the microstructure contains large inclusions of carbon, these will oxidize much faster than iron, leaving behind huge pits, with more surface area for oxidation, and more friction to generate heat, which speeds oxidation as well. Finely dispersed carbon will leave a smoother surface when it oxidizes. Not being a metallurgist, there may be other factors as well, of which I am not aware.

Because of so many factors, questions like yours often require experimental data to answer, with any kind of statistical probability of being correct. Given the expense/impracticallity of such an experiment, THE WORLD MAY NEVER KNOW!

Besides which, how much space junk (the dangerous kind) is made of 10XX carbon steel? I would expect most of it is Stainless Steel, Titanium, or other exotic metal alloys which, by design, have very low oxidation rates and very high temperature resistance.

I think you would need to define "at initiation of gravitational pull." Where in space does that occur? If you pick a point, let's say 5000 miles above the surface, then the velocity is easy to calculate to the point at which atmosphere begins to impede progress. So given an entry velocity and a mass and a set of materials properties, I think you could model the re-entry fairly reliably. I'd think you could run a few simulations through a CFD program, and then come up with a reverse-engineered simple formula, given and entry speed at a particular altitude and a material.

Given that mass increases with the cube of sphere size and surface area with square, I'd expect big things to fair better. Therefore, the case would not be that 75% (etc.) of the original mass would be lost, but that the curve would be more parabolic.