Bad popularizing article, doesn't cover the actual conclusion:
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
It's a shame there's not a more substantial colony in space than the ISS with its own stock of throwaway microcontrollers and paper. If there were someone could make a few transmitters with paper airplanes, fling them out on the next space walk, and we could have a pretty good idea of what actually happens.
Once you have a vehicle made from heat resistant paper that can survive re-entry, with a GPS receiver and a couple of control surfaces you can drop it within a few meters anywhere along your orbital path. If the weather cooperates. "Hi Mom, I'm up in space!"
"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.
I feel like the news article doesn't emphasize that you aren't "launching" the plane any more than you would by setting it on the roof. So it's really surprising that it all happens in <4 days.
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.
Isn't the windtunnel test completely different from actual conditions? Mach 7 at 1 bar is wildy different than Mach 7 at very low pressure, isn't it?
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.
Just minddumping here but I think that basically high velocity is bad because it leads to high friction and high temperatures. Velocity has two components, downwards and tangential. Tangential velocity is both good and bad. It increases velocity, but it also makes the trajectory more orbitlike, with less downwards acceleration. A gliding plane will both fall slower both due to the above, but also because thats just how gliding works. But if it tumbles it will not glide.
Hmm... the paper plane has an initial kinetic energy of (0.004 kg) * (7800 m/s)^2 / 2 = 121.6 kJ. But it is supposed to experience 10^5 W of heating for several minutes? The atmospheric heating comes from converting the kinetic energy to thermal energy. What am I missing?
This is the best answer. The area of the plane is 0.0196 m^2, so the heating of 10^5 W/m^2 is actually around 2 x 10^3 W, which seems much more reasonable.
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.
Not that the paper was clear, but I assume that is the maximum heat rate across the entire airplane. If only 1/4 of the plane sees the heating (say wings), that adds up about right vs the kinetic energy.
That adds roughly (6.674e-11(m^3)(kg^-1)(s^-2) * 5.972e24kg * 0.004kg) / (6380km + 420km) = 234kJ. So 355kJ total. That's 5.9kW over 1 minute, or 590W over 10 minutes, etc. It's 10^5W over 3.55s, not several minutes. So either the power is incorrect or the time is incorrect.
I wonder if there is a paper treatment or paper like substance that could manage those temperatures without issues? Certainly a little “styrofoam” glider carved out of foam heatshield material, which would be cool enough, but lacks the “I found a paper airplane and it was signed by an astronaut “ appeal.
Looks like cotton has a self ignition temperature almost twice as high as paper. Considering it is already in use for dollar bills, we know that it already has a paper like feeling. So maybe this could be achieved with this material?
> Combustion or pyrolysis is expected due to aerodynamic heating.
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?
If you had 250 miles of wire (only about 400 pounds), could you unroll it all the way down to the surface of earth and drag it across the world? I guess at some point it would melt from friction with air. But what if the source was geostationary??
No. Any type of metal wire would break under its own weight.
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.
If you want true insanity there's a way it could be done.
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.
Asking some follows up to ChatGPT it was interesting to hear that if the plane was made out of copper it would orbit significantly longer than the paper airplane because it has a lower surface-area-to-mass ratio. Estimated to orbit months, before mostly being burned up due to coppers melting point.
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.
Rather than an airplane, what about a paper helicopter? Paper airplanes can get into an unrecoverable dive, but the helicopters start rotating on their own (one of these: https://www.wikihow.com/Create-a-Paper-Helicopter)
You have air molecules blasting it, which causes heat which burns the paper up. If you aren't going to read the article, at least read the other comments which talks about this.
Bad popularizing article, doesn't cover the actual conclusion:
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
So, in other words make it a tinfoil plane (or Mylar or something else) and it might survive?
This is definitely something that should be tested before the ISS deorbits. For science.
>105 W/m2 (or 10 W/cm2)
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 :)
It's a shame there's not a more substantial colony in space than the ISS with its own stock of throwaway microcontrollers and paper. If there were someone could make a few transmitters with paper airplanes, fling them out on the next space walk, and we could have a pretty good idea of what actually happens.
Once you have a vehicle made from heat resistant paper that can survive re-entry, with a GPS receiver and a couple of control surfaces you can drop it within a few meters anywhere along your orbital path. If the weather cooperates. "Hi Mom, I'm up in space!"
Answer: it would most likely burn up
Original paper: https://www.sciencedirect.com/science/article/pii/S009457652...
Makes sense, the ISS is moving at ~Mach 25 relative to a fixed point on the ground.
Not much survives at those speeds, in an atmosphere, without careful engineering.
Is Mach the correct way to describe the speed of something traveling in (near) vacuum? Easier to say orbital velocity ~17,500mph or so.
> Mach 25
The SR-71 story should be updated with an ATC speed request from the ISS.
Which was submitted (a paper has a less catchy headline) https://news.ycombinator.com/item?id=44513900
That is a cool paper.
"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.
Speed of sound is much lower at low pressure.
I feel like the news article doesn't emphasize that you aren't "launching" the plane any more than you would by setting it on the roof. So it's really surprising that it all happens in <4 days.
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...
Isn't the windtunnel test completely different from actual conditions? Mach 7 at 1 bar is wildy different than Mach 7 at very low pressure, isn't it?
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.
Just minddumping here but I think that basically high velocity is bad because it leads to high friction and high temperatures. Velocity has two components, downwards and tangential. Tangential velocity is both good and bad. It increases velocity, but it also makes the trajectory more orbitlike, with less downwards acceleration. A gliding plane will both fall slower both due to the above, but also because thats just how gliding works. But if it tumbles it will not glide.
Hmm... the paper plane has an initial kinetic energy of (0.004 kg) * (7800 m/s)^2 / 2 = 121.6 kJ. But it is supposed to experience 10^5 W of heating for several minutes? The atmospheric heating comes from converting the kinetic energy to thermal energy. What am I missing?
It's supposed to be 10^5 W heating per square metre, and the aeroplane's cross-section is much smaller than a square metre.
This is the best answer. The area of the plane is 0.0196 m^2, so the heating of 10^5 W/m^2 is actually around 2 x 10^3 W, which seems much more reasonable.
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.
Not that the paper was clear, but I assume that is the maximum heat rate across the entire airplane. If only 1/4 of the plane sees the heating (say wings), that adds up about right vs the kinetic energy.
You are missing the potential energy.
That adds roughly (6.674e-11(m^3)(kg^-1)(s^-2) * 5.972e24kg * 0.004kg) / (6380km + 420km) = 234kJ. So 355kJ total. That's 5.9kW over 1 minute, or 590W over 10 minutes, etc. It's 10^5W over 3.55s, not several minutes. So either the power is incorrect or the time is incorrect.
I wonder if there is a paper treatment or paper like substance that could manage those temperatures without issues? Certainly a little “styrofoam” glider carved out of foam heatshield material, which would be cool enough, but lacks the “I found a paper airplane and it was signed by an astronaut “ appeal.
This stuff might work https://www.amazon.co.uk/Wallrock-Fireliner-20m-x-0-55m/dp/B... Wallrock Fireliner ?
Looks kinda paper dart capeable https://youtu.be/YBpd2StDP_o?t=522
fire resistance https://youtu.be/amQFBYjOQ4w?t=47
Looks like cotton has a self ignition temperature almost twice as high as paper. Considering it is already in use for dollar bills, we know that it already has a paper like feeling. So maybe this could be achieved with this material?
I'm thinking maybe graphite foil?
I'm not sure how well it holds together though.
> Combustion or pyrolysis is expected due to aerodynamic heating.
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?
A black surface can re-radiate 1E5W/m^2 at ~1100C (assuming I calculated correctly).
So, paper is out, but maybe glass would work ok :)
If you had 250 miles of wire (only about 400 pounds), could you unroll it all the way down to the surface of earth and drag it across the world? I guess at some point it would melt from friction with air. But what if the source was geostationary??
No. Any type of metal wire would break under its own weight.
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.
If you want true insanity there's a way it could be done.
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.
NASA once tried a little something along those lines:
https://pwg.gsfc.nasa.gov/Education/wtether.html
Asking some follows up to ChatGPT it was interesting to hear that if the plane was made out of copper it would orbit significantly longer than the paper airplane because it has a lower surface-area-to-mass ratio. Estimated to orbit months, before mostly being burned up due to coppers melting point.
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.
Rather than an airplane, what about a paper helicopter? Paper airplanes can get into an unrecoverable dive, but the helicopters start rotating on their own (one of these: https://www.wikihow.com/Create-a-Paper-Helicopter)
You have air molecules blasting it, which causes heat which burns the paper up. If you aren't going to read the article, at least read the other comments which talks about this.
?
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.
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