Would it be possible to design a tiny satellite, such as a femtosatellite or a chipsat, with such a shape and ballistic coefficient, that it would survive reentry without a heat shield? A bit like this feathery question except that our chipsat wouldn't be made of quite the same material. Somewhat of the opposite of this question.
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1$\begingroup$ I'm assuming you mean re-entry into Earth's orbit from LEO. The trick is to find a way to non-destructively dissipate 30 Joules of kinetic energy for every milligram of mass. $\endgroup$– uhohMay 17, 2017 at 0:12
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1$\begingroup$ @uhoh I do. Not sure how it could reentry from any higher orbit as there wouldn't be any drag, unless it's a highle elliptical orbit. $\endgroup$– gerritMay 17, 2017 at 0:24
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2$\begingroup$ I suppose you are familiar with shooting stars :) $\endgroup$– AntziMay 17, 2017 at 9:47
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1$\begingroup$ Small meteorites do not survive the entry into the atmosphere, larger ones do, at least partially. The ratio between surface and volume is getting worse for smaller particles, therefore a satellite has to be large enough to survive a reentryy at least partially. $\endgroup$– UweMay 18, 2017 at 14:10
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1$\begingroup$ About all meteorites arrive into the atmosphere from outside of the Earth system, on trajectories that bring them deep into the atmosphere immediately. It doesn't matter so much how many Joules you have to dissipate, as - how many Watts. So the reentry timescale is essential: put the chipsat into a trajectory that loses altitude slowly enough and it will be fine. $\endgroup$– SF.May 19, 2017 at 7:54
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2 Answers
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A correctly prepared (shielded) nanosat could survive the reentry.
A satellite the scale of cubesat around Kármán Line would experience about 1 kilowatt of heating. This is not what a cubesat electronics can survive - but this is something a layer of aerogel can stop from conducting in, a mirror-coated foil from radiating in, and a few centimeters of light ablator to dissipate for a couple minutes. So if you package your femtosat of, say, 10cm^3 in a cubesat form factor (1000cm^3) of lightweight thermal shielding, it should survive just fine.
Locating it on the ground after reentry is an entirely different matter...
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$\begingroup$ What about balsa wood, I guess four centimeters at each side should do it. $\endgroup$– UweMay 20, 2017 at 20:37
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1$\begingroup$ @Uwe: I don't know, but I believe cohesion is important; the ablator must ablate, not get ripped apart. TLA is a corkwood based ablator, really light, and probably more mechanically durable than balsa wood. The pieces of balsa wood I had in my hands, you could literally grind/smash it with your fingers. $\endgroup$– SF.May 20, 2017 at 22:21
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$\begingroup$ Shielding is not necessary solarsystem.nasa.gov/docs/p390.pdf $\endgroup$ Mar 10, 2018 at 18:32
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I think it's an interesting question, The way I see it is your satellite stays in orbit because of it's high speed but it also burns up because of it's high speed. If you can get it traveling slow enough by the time it reaches the atmosphere you should be able to use atmospheric drag without burning up. So you would need a way to slow it between the orbit height and speed and the atmosphere.
I think it could be interesting do the math for trying to slow a chipsat by using a collection of tethers using drag generated by geomagnetically induced current, so using the magnetic field of the earth to slow down before hitting the atmosphere. But I wouldn't know where to begin with running those sorts of calculations.
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$\begingroup$ That's not an answer, but a new question. Feel free to create a new question for this. $\endgroup$– HobbesMay 19, 2017 at 7:25