The main points emerging from the combined simulation and experimental study on atmospheric entry of the paper plane are: • Orbit: The paper space plane de-orbits from LEO extremely quickly due to its very low ballistic coefficient. Atmospheric entry from a 400 km circular orbit occurs within a few days. • Attitude: In the free-molecular portion of atmospheric entry, above ∼120 km altitude, the paper space plane maintains a stable flow-pointing attitude. Small-amplitude oscillations occur in pitch and yaw. Although the coupled simulator is not designed for application at lower altitudes, the results suggest the onset of uncontrollable tumbling at ∼120 km altitude. • Heating: Based on the hypersonic wind tunnel test results and simulation, surface forces acting on the space plane during atmospheric entry are not expected to cause significant deformation. However, the paper space plane experiences severe aerodynamic heating in the order of 105 W/m2 (or 10 W/cm2 ) for several minutes. Accordingly, combustion or pyrolysis is expected during atmospheric entry
This is definitely something that should be tested before the ISS deorbits. For science.
105 W/m2 = 0.0105 W/cm2..
10W/cm2 is 100kW/m2?!
Edit: from the paper its 10^5W/m^2 which is 10W/cm^2 :)
I'm not sure how well it holds together though.
Looks kinda paper dart capeable https://youtu.be/YBpd2StDP_o?t=522
fire resistance https://youtu.be/amQFBYjOQ4w?t=47
My gut feeling tells me the paper plane doesn't have enough mass to "power through" the thickening atmosphere with enough force to substantially heat up.
Also, if it starts tumbling or not is not very relevant, it's still flying. Surely it could recover at some point, maybe at low altitude with higher air pressure and random turbulences.
So, paper is out, but maybe glass would work ok :)
I thought atmospheric effects were much lower at that altitude, but apparently even the ISS loses about 3km every month (enough to deorbit in ~15 months).[1]
The ballistic coefficient of the ISS is a whopping >500 times greater than the plane so the plane drops really fast.
[1]: https://space.stackexchange.com/questions/9482/how-long-woul...
My naive impression is that this would not be possible. I would expect that a very light object with large sail area would be driven so easily by air flow that it would experience negligible heating from friction. What is the physical reasoning behind thinking it could burn up?
I mean, I'm not using the term "heat" correctly in a technical sense, but just in a way that the average person would understand.
If I made a mistake, I would like to know so that I can learn and not make the same mistake again.
What you're describing is essentially a space elevator. Interestingly, such a system wouldn't actually end at geostationary orbit - its center of mass needs to be in geostationary orbit, so the top end would need to be significantly higher up. It might be possible to construct such a structure using exotic materials such as carbon nanotubes, but even that would have to be tapered to achieve the needed tensile strength. Ordinary materials like steel are out of the question.
As you say, the span is too great for anything to be strong enough to hold itself up without the taper becoming completely impossible. You have to break it up into much smaller chunks--impossible, you say? No. Build a ring around the Earth at the equator inside an evacuated tunnel. Spin the ring at a speed sufficient to generate an outward force (maglev setup to transfer the force) sufficient to put supports in tension. Do the same thing again a bit farther out. Again and again. I haven't done the math on it but as the strength requirement goes to zero as the towers/rings go to infinity it's simply a matter of building enough of them. Yes, orbiting rings are unstable, but this is tethered.
And you can also build the Ringworld that way--no super materials, just an extremely massive stationary track underneath to provide the support. But, not being tethered it has the same instability problem. You can't make the walls but you can slope it without undue forces.
It’s getting even more interesting if the plane was made out of titanium. It would orbit for years potentially before having a 30-40% of surviving reentry. It’s fascinating sometimes physics is the opposite of what you think intuitively. You’d think heavier metals would orbit for less time than a paper airplane. Ballistic coefficients are the key.
Also, I noticed that I missed that the plane is made from 4 sheets of A4 paper. Table 1 lists the mass as 4 grams, but 4 grams is typical for a single sheet of A4 paper, so the listed mass is probably for a single sheet. The actual plane mass is likely 16 grams. This means that the kinetic energy is likely closer to 480 kJ.
Thank you to afeuerstein for pointing out that I was missing the potential energy! However, that is not enough to make a huge difference. A quick estimate because I'm lazy is 9.8 m/s^2 * 480 km * 0.016 kg = 75.2 kJ. Yes, gravity decreases slightly as you get farther out, so this is an over-estimate.
So a total of around 550 kJ, and a power around 2 x 10^3 W gives a duration of 275 seconds or... a couple of minutes. I feel much better about the numbers now.
peterlk•7mo ago
Original paper: https://www.sciencedirect.com/science/article/pii/S009457652...
NortySpock•7mo ago
Not much survives at those speeds, in an atmosphere, without careful engineering.
kylehotchkiss•7mo ago
thebruce87m•7mo ago
The SR-71 story should be updated with an ATC speed request from the ISS.
WJW•7mo ago
"However, the paper space plane experiences severe aerodynamic heating in the order of 10^5 W/m^2 for several minutes."
I can see how that might be a problem for something made of paper. Interestingly, deformation from flying through a (thin) atmosphere at hypersonic speeds was not a large issue according to the paper.
xattt•7mo ago
WJW•7mo ago
Most paper airplanes I ever built would not stand up to 500 m/s airspeeds, I can tell you.
gnabgib•7mo ago