micro re-entry vehicle challenge

hmmmmm, I wonder what they define as "low earth orbit"

The Rutan Voyager did a low earth orbit :)

and do we need to deploy it from low earth orbit, or just prove it can be done?

I'd guess achiving and maintining orbital velocity (~7.8km/s) within the region from 100km to 1000km or so. (Not sure where the LEO/HEO boundry is). 100km would last for about two orbits before atmospheric drag slowed it down enough to reenter, so that might work...but the profile would be very shallow.

Hardly. It was nither in space or at orbital velocity.

I havn't looked, but the way the challenge is worded, I suspect it will hitch a ride on another rocket (ala nano-sats on D4H) and be dropped of just short of orbital velocity. They could fake it with a big blowtorch, perhaps, but it wouldnt' be very realistic.

Anyway, getting it down shouldn't be too difficult, keeping the eggs intact might be. Thick balsa (several inches) would actully make a decent ablative heat shield, but the egg capsule and eggs would need to endure the 7-8Gs of a ballistic reentry. Once you do that, its just a matter of recovery.

i'd nitpick, low earth orbit does not imply a spacefaring object. (yes i am tugging at your chain)

and name a vehicle that WAS at orbital velocity. the early space vehicles were fast, btu they coudl not sustain their orbit beyond their missions by much(ok, it might take a year, but....)

nor would the PR be as good :)

I was thinking of areogel, the stuffs got amazing insulative properties. balsa would be my next bet, but with a ceramic outer coating, a-la shuttle.

wonder how big a device such as that would be?

While, in theory, you could orbit lower than 100km, there is no way you could sustain it without constant thrust, the drag is just too great. The orbit would decay before you even complete one orbit. You'd also be encased in a ball of plasma.

Way too many to mention.

Orbits decay because gravity peturbations or atmospheric drag slow them down. Your car will coast to a stop if you put it in neutral because of friction, but that doesn't mean you wern't previously going 55.

The trouble with aerogel is its very expensive. You can use a ceramic outer coating over balsa, but IIRC balsa itself will work fine. Of course, you'd want to test it to make sure.

I probobly should have worded this better. 100km isn't some magical line where drag stops. In fact, you'd probobly have trouble sustaining orbit for more than one or two orbits below 200km. The ISS, at over 300km, needs periodic reboosts to keep its orbit from decaying. When your working with satillites in LEO, atmospheric drag is a pain in the arse. ;)

I'm curious as to whether water/ice wouldn't make a good ablative. When I took my HVAC training water was described as the "perfect coolant" because it's chemically inert, non-toxic, and absorbs huge amounts of heat. Maybe something like a double shell spherical capsule, where the water would sloosh to the "front" of the capsule and boil/ablate there. If there was a means to assure starting re-entry with frozen water you'd could also gain the change of state "bonus" as heat is absorbed as it melts.

I guess the biggest trick isn't re-entry as much as finding the thing. With a whole planet to randomly chose from, talk about a needle in a haystack search, even with tracking devices!

Chuck

Balsa wood as an ablative re-entry heat shield? I strongly disagree. Re-entry from LEO has stagnation temperatures over several thousand degrees, and exposed surfaces reach about 3000K. Take a blowtorch (which is actually more gentle than re-entry) and you can burn through several inches of balsa in seconds. I guarentee that NASA does not have balsa wood on their list of tile repair materials.

Dave

You may be right. Balsa came from an older discussion of heat shield materials. It was pointed out that some chinese RV designs used a balsa heat shield, but I can't seem to find any supporting evidence now. Some sites list cork, but the majorty seem to agree that oak was used.

I guess thats what I get for assuming someone isn't pulling facts out of their arse. ;)

John, I found this while Googling...

"I have a faint memory of a photo of a technician filling honeycomb cells in an Apollo heatshield with a slurry of balsa powder and resin, possibly epoxy. Now that I know it wasn't going to have to do a re-entry at 25,000 mph, I can see how they were able to cut corners like this."

...Rick

John Bowles wrote: