What would happen if...? my son asked - I dunno!

[ChrisV (Chris)]

This question brings back the horrors of my son doing the HSC over the past few weeks !!!!

He did physics and virtually the same question was in a past paper that he did for practice, except it was something heavier. And one object was released from a moving space station over the equator. And another dropped from one at the same height over the pole.

Ahhhhh. Chris

[Neutronstar (T)]

Alex,

I wondered if you have shown your son Felix Baumgartner's Space Dive?
There is some video's of it on Youtube and a NatGeo documentary on Netflix - called "Space Dive".
While this is not as high up as the ISS it is close to the edge of the atmosphere.

I kind of imagine that he and his space suit made it that the paper plane would as well.

Tim

[pluto (Hugh)]

Originally Posted by Neutronstar

Alex,

I wondered if you have shown your son Felix Baumgartner's Space Dive?
...
I kind of imagine that he and his space suit made it that the paper plane would as well.

Apart from the difference in altitude, Felix wasn't travelling at orbital speed which for the ISS is about 27600km/h.
Even an orbit with it's apoapsis around that of the ISS and its periapsis within the atmosphere would still have a velocity of over 27000km/h and Felix only reached a top speed of ~1300km/h.

Good doco that one on Netflix though, very interesting

As for whether the paper plane would survive, I think it would burn - there's just too much energy to dissipate - but I don't have the knowledge to answer that using physics.
However if one was able to control the planes attitude then maybe there would be a way to slow it enough slowly enough by skimming, or bouncing, off the top of the atmosphere multiple times before actually re-entering. Then again probably not as there are good reasons why the Shuttle never did it that way.

[mental4astro (Alexander)]

I'll show him the space jump, for sure.

I've been thinking about the re-entry scenario some more. While my maths may be a little, well, wanting, logic is helpful...

Momentum is a function of mass and velocity, and a cousin of kinetic energy. Take the recent Russian (?I think it was?) satellite that was in a decaying orbit and eventually re-entered. It had a huge mass, and not a streamlined structure. High altitude drag was what was slowing it down. The burn up did not happen until it reach a certain altitude where the density of the atmosphere overwhelmed the heat dissipation that the very thinnest of the atmosphere would have been generating. But because of its momentum, this slowing of the orbit was very gradual, but drag would have eventually slowed it enough to for it to fall into the denser atmosphere, but not enough to slow it significantly enough, and it burnt up.

Now take a paper plane. While it is moving at the same rate of knots, its momentum is considerably less as its mass is tiny. And, as a function of its surface area, the drag it would experience at the same altitude of the thinnest of the atmosphere, the effect on the plane's momentum would be significantly greater than the above satellite. The result would be a much faster rate of deceleration than the satellite, yet it is still at the very highest and thinnest levels of the atmosphere. It would slow down faster. But it would also not be dropping down through to denser atmosphere either. Drag would also serve to slow down its vertical decent. It may well be that the plane just does't burn up.

It could well be that the initial drag may have a catastrophic affect on the structure of the plane, and there may be some ionization effects, but I somehow doubt that it would incinerate.

The proverbial 'dust' particles that burn up on re-entry have a couple of things going against them - Their mass to density to volume ratio is greater than a paper plane; They enter the atmosphere at a steeper angle than the plane would, even for those that are skimming the atmosphere (the plane is initially running parallel to the atmpsphere).

Now, all of this is all just hypothetical. Everything that is written here is!

What we really need is someone to hurl a plane out of the goddamn ISS airlock!

Thank you for the discussion, girls and boys. I am enjoying the debate,

[sharptrack2 (Kevin)]

One aspect that stands out in my mind is that there would be no shock wave in front of a paper airplane... assuming standard "dart" folding. Therefore, no matter what speed, the heat build up would be greater than can be dissipated and the plane would simple turn to ash as fast as it could enter the upper atmosphere. I don't think that there would be enough structural strength to withstand a "flaring" manoeuvre and the plane would always present a knife edge as it fell toward the earth.

I found a very interesting document on the FAA website, on re-entry design...

https://www.faa.gov/other_visit/avia...om%20Space.pdf

[jenchris (Jennifer)]

The structure of paper means it would be dismantled quite quickly by molecules that have a relative velocity of 17500 mph.
The resulting strands of cellulose would be heated by impactas they swapped v for heat. The temperature rises to white heat quite quickly and destruction to molecular level dissipates the remains

[mental4astro (Alexander)]

Thanks for that link, Kevin. Interesting read.

Combining the information of that FAA link, and the high velocity impact of the air on the material structure of the paper as mentioned by Jen, I know see that a paper plane would not survive re-entry if its initial velocity is the same as that of the ISS. There is just too much energy involved and the paper is too fragile.

Now, a 'geo-static' re-entry, that is, the plane's relative velocity to Earth is 0m/s, a simple lift and drop, that's another matter.

Thanks for the discussion. I'll now present this info my son

[N1 (Mirko)]

Originally Posted by mental4astro

Now, a 'geo-static' re-entry, that is, the plane's relative velocity to Earth is 0m/s, a simple lift and drop, that's another matter.

That's got to depend on the distance from the surface. And to a certain degree (no pun intended), latitude. While perhaps not a great factor at astronomical speeds, the Earth's atmosphere does move at about 460m/s at the equator at ground level releative to a fixed point in the sky (fixed relative to background stars), even more at higher altitude. Obviously that's not the case for geosyncronous objects, but for them, altitude is just as cricitcal.

I'm suspecting any wisdom derived from high altitude balloon flights tells us very little in this regard. Baumgartner for instance was nowhere near space. His ascent relied on the very thing that makes the Earth's surface a "non-space" environment. Give an object enough time to be accelerated by Earth's gravity in a negligible atmosphere and see what happens when it does hit the air...

Edit - I just re read the original question. A geostationary/syncronous paper object falling from ISS altitude very well could survive I suppose.

[RobinClayton]

I love this debate so far.

My vote is for the paper plane to survive "intact". One problem is that the ISS is in orbit, so anything released from ISS would also be in orbit. However if it was thrown towards Earth, then it should eventually reach the outer atmosphere. Here I think it should be slowly drifting downwards and friction would not build up sufficiently to damage the paper. The shape of the plane may start to crumble, but not until much lower altitude.

If you are able to contact ISS, then you may want a controlled experiment with several planes of different shapes and thrown in several different directions. Do we know how much paper they have on board?

[pluto (Hugh)]

Originally Posted by RobinClayton

I love this debate so far.

My vote is for the paper plane to survive "intact". One problem is that the ISS is in orbit, so anything released from ISS would also be in orbit. However if it was thrown towards Earth, then it should eventually reach the outer atmosphere. Here I think it should be slowly drifting downwards and friction would not build up sufficiently to damage the paper. The shape of the plane may start to crumble, but not until much lower altitude.

If you are able to contact ISS, then you may want a controlled experiment with several planes of different shapes and thrown in several different directions. Do we know how much paper they have on board?

Knowing what direction to throw the plane from the ISS to de-orbit it is easy - throw it in a backwards direction to reduce its orbital energy and lower its periapsis (opposite to the direction of travel). You would have to throw the plane at a relative velocity of over 300km/h if you wanted it to re-enter on the current orbit, however a paper plane in an orbit similar to that of the ISS will de-orbit, due to atmospheric resistance, after a couple of weeks(?) anyway.

A few years ago a cosmonaut hit a 3 gram golf ball from the ISS in a direction opposite to the direction of travel. A super quick google hasn't found much detailed info but it would be interesting to see if there's any data on what happened (though I know it was too small to be tracked by radar).

I like the thinking in your latest post Alex, but I still think that there's too much heat to dissipate and, to my highly untrained mind, I don't think a paper plane is a very good radiator of heat. It's gonna burn!

[mental4astro (Alexander)]

IF such an experiment could be allowed on the ISS, the simplest payload would be a "sheet of paper" and the smallest 'Sputnik' beep-beep transmitter possible - the primary outcome we want to know is 'Will the plane survive re-entry'. We don't need to retrieve it, and a beep-beep transmitter will allow ground based amateur astronomers and radio hams to follow its progress. If the transmitter survives, the plane's survived. Simple.

Then other scenarios could be looked at such as initial orbital speed, materials, plane design; many things.

Not a flippant idea either. A lot of money goes into designing re-entry mechanisms. Why not look at an idea from left field?

[bugeater (Marty)]

Originally Posted by RobinClayton

One problem is that the ISS is in orbit, so anything released from ISS would also be in orbit. However if it was thrown towards Earth, then it should eventually reach the outer atmosphere.

I'm not sure it would reach the atmosphere. Throwing it towards the earth would put the paper plane on a different orbit to the ISS, but it would still stay in orbit, at least over the medium to long term (most stuff in low earth orbit will come down eventually due to atmospheric drag). You would basically put it on an elliptical orbit. Indeed, strangely, I think it would spend part of its orbit above the ISS now.

A fun way to play with orbit mechanics and indeed build space rockets is to purchase the game Kerbal Space Program. It's great fun.

[N1 (Mirko)]

I don't think throwing anything (as in: using your arms) from the ISS, regardless of direction, would provide that object with a trajectory sufficiently different from that of the space station itself to allow a scenario that was different to the fate of the ISS if left to drift. Even the fastest cricket bowl is mind crushingly slow compared to the 8km/s of the ISS. The object would deorbit and burn up. A little sooner or a little later, depending on direction.

Also the fact that it's a paper plane (as opposed to an unfolded sheet of paper) would appear to be counter productive when we want the piece of paper to spread its energy over as large an area as possible. The plane's streamlined shape might make it travel much faster into and through the critical area than it otherwise would.

[pluto (Hugh)]

Originally Posted by N1

I don't think throwing anything (as in: using your arms) from the ISS, regardless of direction, would provide that object with a trajectory sufficiently different from that of the space station itself to allow a scenario that was different to the fate of the ISS if left to drift. Even the fastest cricket bowl is mind crushingly slow compared to the 8km/s of the ISS. The object would deorbit and burn up. A little sooner or a little later, depending on direction.

I agree. As mentioned previously the paper plane, or anything else on an orbit similar to the ISS, would need to decelerate by over 300km/h to enter the atmosphere at the next periapsis.

[mental4astro (Alexander)]

Flight stability - One thing I don't think the plane will do is be gliding in a steady, nose-first direction, when released from the ISS. I think it will be tumbling, even if only slowly - air flow over the plane is what keeps it stable. So to my mind it will initially be behaving like a sheet of paper. I don't think it will achieve a nose-first steady flight position until air density becomes high enough, and then the plane's design needs to be such that it self-corrects. It is a good point you make, Mirko,

Mind you, this could also be self defeating if it self-corrects too soon,

[mental4astro (Alexander)]

Here's another curve ball: elevators on the wings?

As it enters the atmosphere, and drag takes effect, elevators on the wings would act to raise the nose and lift the craft. It's nose would then drop again, descend, and rise up again, doing a constant dip-and-dive action. This would also act to slow the plane.

Something more to ponder...

[N1 (Mirko)]

Originally Posted by mental4astro

Here's another curve ball: elevators on the wings?

As it enters the atmosphere, and drag takes effect, elevators on the wings would act to raise the nose and lift the craft. It's nose would then drop again, descend, and rise up again, doing a constant dip-and-dive action. This would also act to slow the plane.

Something more to ponder...

The wing nuts on here might be able to help, but I think it would depend on whether air density and air speed can be treated as being inversely proportional for the purposes of flying at these speeds, so that this familiar pattern could still occur. I also understand the speed would change periodically in this scenario and each lift and drop of the nose would depend on a certain air speed:air density ratio. Each lifting of the nose would require an increase in speed to occur first, and we'd have to ensure the preceeding deceleration from lifting the nose does not disrupt the paper craft by throwing it into some other position than what is required for the next cycle, or outright destruction. I'm also having trouble imagining how exactly it could even accelerate again once the atmosphere starts to slow it, but while it's still travelling at enormous speed. I'm thinking the plane's encounter with the atmosphere might not involve any acceleration at all, just a change in the rate of slowing - until the process is driven purely by aerodynamics.

[pluto (Hugh)]

Originally Posted by mental4astro

Here's another curve ball: elevators on the wings?

As it enters the atmosphere, and drag takes effect, elevators on the wings would act to raise the nose and lift the craft. It's nose would then drop again, descend, and rise up again, doing a constant dip-and-dive action. This would also act to slow the plane.

Something more to ponder...

This is what I was hinting at in my first post, but I think the plane would still burn up as it's unable to radiate the heat built up during each "dip" into the top of the atmosphere. From what I understand this is one of the reasons the Shuttle wasn't designed to re-enter this way, even though it would have resulted in a lower speed during descent into the thicker parts of the atmosphere.

[AstralTraveller (David)]

Everyone talks about thing burning up in the atm but no one has mentioned that every day tonnes and tonnes of material falls to Earth from space. Dust-particle sized material can make it through the atm but something the size of a pea will burn up. So there is a size limit below which drag in the upper atm will slow the object soon enough to stop it burning up in the lower atm. However I doubt this will slow the paper plane enough - especially if it is loaded down with grams of sensors. Also, as Jen has noted, paper is more combustible than minerals.

A subsidiary question is, assuming the paper plane is on the night side of the globe, could the plane's demise be observed as a meteor?

[pluto (Hugh)]

Originally Posted by AstralTraveller

Everyone talks about thing burning up in the atm but no one has mentioned that every day tonnes and tonnes of material falls to Earth from space.

The debris objects, both human-made and natural, that reach the surface after re-entering are what's left of a larger object that has partly, or mostly, burnt up. Nothing that I know of, except for the tiles on the Shuttle, X37B, and Buran, survive re-entry from orbital speeds or above without losing part of their mass through ablation.