Reentry without a heatshield possible on Earth?

[Savage117]

Did some quick digging and found out there are spacecraft that use active cooling (Liquid cooling systems) and passive cooling (Heatsinks) techniques during re-entry so they are possibilities, add those to a special space suit ,possibly made to be specialy aerodynamic, and they might just survive a straight up and down fall into the atmosphere without using an ablative heatshield. Sorry im kinda stuck on this idea of space diving.

[Tommygun]

Did some quick digging and found out there are spacecraft that use active cooling (Liquid cooling systems) and passive cooling (Heatsinks) techniques during re-entry so they are possibilities, add those to a special space suit ,possibly made to be specialy aerodynamic, and they might just survive a straight up and down fall into the atmosphere without using an ablative heatshield. Sorry im kinda stuck on this idea of space diving.

I'm curious, how are they removing that much heat or are you referring to the interior cabin heat?

[Savage117]

I'm curious, how are they removing that much heat or are you referring to the interior cabin heat?

All I could find was some quick little entries on how some early ICBMs and unmanned entry capsules used liquid cooling and/or heatsinks to shed heat on the entry parts nose during re-entry, as far as I know it wasn't used with manned craft. I’m not sure how effective it would be over the ablative side of things, I assume we chose ablative for most re-entry craft because it was more efficient at heat dissipation, lighter, less complex, and cheaper to replace afterword.

I can see how liquid cooling would be effective but a heatsink requires some sort of heat dissipation itself. In an atmosphere a heatsink transfers heat from a its origin to its outer flanges/vanes and then uses a fan to push that heat out into the air, effectively dissipating the heat away from whatever you are cooling. That would not be possible in a vacuum since there is no place to transfer the heat from the heatsink outside the craft, so they would act kinda like heat capacitors, storing the heat until they could be cooled by the atmosphere, doesn't sound like it would work well for a manned re-entry vehicle of any type. Liquid on the other hand uses pumps to move the heated liquid from the hottest part to the coolest part of what ever you are trying to cool, and since liquid dissipates heat much faster than air its an effective alternative, but because of the pump and other moving parts, it would probably be too unsafe to use in a manned spacecraft, due to higher chance of failures.

I work with computer hardware on a daily basis so I understand passive vs active cooling methods pretty well. But fluid dynamics don't really enter that realm except to understand which way your liquid cooling or air cooling system is going to flow. Plus ablative cooling would be extremely inefficient for cooling a computer.

[TwoHedWlf]

I'd imagine one possible way would be with something along the lines of a glider. Large enough wings and low enough wing loading that it can skim along where the air is thin enough to minimize heating and structural forces but thick enough to create enough lift to maintain altitude. Then you just slowly descend as you scrub off speed.

[K^2]

I'd imagine one possible way would be with something along the lines of a glider. Large enough wings and low enough wing loading that it can skim along where the air is thin enough to minimize heating and structural forces but thick enough to create enough lift to maintain altitude. Then you just slowly descend as you scrub off speed.

No. Anything dense enough to give you lift is dense enough to torch your glider. It's about the worst configuration you can come up with. The idea itself is not stupid, though. I had to do some math before I realized it wasn't going to work.

[Tommygun]

Could generating a strong plasma field be a substitute to a heat shield "in theory".

I realize that the equipment would be heavier than the shield with existing technology.

[K^2]

Could generating a strong plasma field be a substitute to a heat shield "in theory".

I realize that the equipment would be heavier than the shield with existing technology.

You might not even need to. The ship passes through ionosphere, where it does a great deal of braking. For reference, ionosphere starts at about 85km, while Space Shuttle lost most of its orbital speed between 30 and 120km. I can't say exactly where most of the heating is going to take place, but it seems to be close to the ionosphere boundary.* So if you have a strong enough magnetic field, you can brake against ionosphere without exposing your ship to the flow. This can dramatically cut on the heatting of the ship during re-entry. In part, because you can brake at higher altitude where density is lower.

Unfortunately, I was able to do only very rough estimates, but it still seems like the weight of the magnets is going to be too big of a problem. HTC superconductors just can't take these kinds of fields, and resistive magnets will require the kind of power you can't reasonably produce on the ship we can launch to space. So you'd be stuck with standard superconducting magnets, which are very heavy and have to be kept at 2K, which requires cooling systems that make them way heavier still.

It's a really neat idea, and if we learn to generate huge magnetic fields with something much lighter, it'd be the way to go. One potential I can see here is trying to use charged plasma flows to generate even stronger magnetic fields. Unfortunately, my brain can't handle this sort of E&M/Plasmodynamics problem.

Edit: * Ok, I looked into the wrong column. Peak heating is actually between 40km and 70km. Velocity is down to half at about 50km. So this is quite a bit bellow ionosphere, but like I said bellow, with a magnetic field, you can start braking at a much, much lower density without worrying about burning up. So I still think this is workable, pending super-magnets.

Edit2: Damn, this chart is weird. You know what, can somebody double check my numbers? Here is the chart.

Edited November 10, 2013 by K^2

[SFJackBauer]

Edit2: Damn, this chart is weird. You know what, can somebody double check my numbers? Here is the chart.

That's correct, although there is a deviation between the predicted and actual as shown in the graph. You follow the vertical lines of PEAK HEATING to the Altitude curve, and then to the left in the vertical ALTITUDE axis line.

[Mr Shifty]

So if you have a strong enough magnetic field, you can brake against ionosphere without exposing your ship to the flow. This can dramatically cut on the heatting of the ship during re-entry. In part, because you can brake at higher altitude where density is lower.

In this scheme, where does the heat go? You have to transfer the energy somewhere. If you're using a coil to generate the field, the power requirements would be massive, and you'd be heating your coil.

[K^2]

In this scheme, where does the heat go? You have to transfer the energy somewhere.

Same as it does during normal reentry. Into the atmosphere. The trouble is that during normal reentry, your ship has to be in close contact to the air flows it superheats, so some of the heat rubs off. If you brake against plasma using magnetic fields, density of plasma anywhere near your ship can be almost zero. Make the ship shiny to reduce absorption of the radiated heat, and you don't have to worry about it.

And like I said, magnets would have to be superconductive. No heating there.