Space/Reentry Question?

[GTFlow]

For all you Space gurus.......I've seen a lot of good topics about space and astrology in this forum and just wanted to ad another one.

Temperatures in space are freezing....so do during reentry of a space vehicle or object why do they come in as a "ball of flame"? Maybe I missed something while in school but You would think that with the subzero temperatures in the outer space/atmosphere and elements that exist if any it would be impossible.

 

[qachargh]

The friction as the object moves from a near absoloute zero vacuum into the much warmer atmosphere.

 

[Double"O"]

friction against our atmosphere

ever use a cutting wheel???? same thing essentially

 

[motoman991]

That happens because earth has an atmosphere. The very high speed with friction from the air causes that. Jim Snover (hope I got that right) knows everything space related. He will probably chime in.

 

[wizbangdoodle]

Because you go from no atmosphere to atmosphere. The fact there is air causes friction and creates heat. Hence a "ball of flame".

 

[Double"O"]

The SR71 would leak fuel like a siv on the ground but the heat caused from friction at mach 3+ caused the metal to expand and seal the tanks

 

[qachargh]

ever use a cutting wheel???? same thing essentially

That's a pretty good analogy. And the correct term is astronomy, not astrology. Astrology is horoscopes, planetary alignments, and reading goat entrails and other such methods of divining the future.

 

[GTFlow]

friction against our atmosphere

ever use a cutting wheel???? same thing essentially

I did think that......but I wasn't sure.

 

[James Snover]

You guys all got it right. The resulting plasma is a result of the energy pumped into the air coming in contact with the shuttle and having to be pushed out of it's way. So its better than -60, then this brick the size of several city busses comes barreling through, and now because you had to get out of the way to let it pass you are really really hot.

The friction is actually a necessary thing, as far as getting back on the ground in one piece, goes. All that rocket fuel expended tossing the shuttle in orbit means there is a huge energy surplus in the shuttle that has to be gotten rid of to get it back on the ground in one piece. In addition, ther eis also the energy gravity is pumping into it as it descends. This combined energy surplus is dumped into the atmosphere, making that thin air go from -60 to a plasma. That is what is slowing the shuttle down so it can land on it's tires, and not make a big hole in the ground at Mach 25.

Or rather, the friction is a good thing as long as you can keep the heat on the outside of the spacecraft, and _not_ let it get in the main gear wheel wells, for example. This is where the shuttles infamous tiles come in: they reflect this heat from the surface of the tile back into the atmostphere. As long as they are in place.

Double "O", you're talking about my favorite plane. As if that's news to anyone here. And you're 100% correct. Until they go tit in the air and heated up, it leaked fuel like crazy. So they made a fuel that was very hard to ignite. Everyone knows the Blackbird refueled several times in the course of a mission. What most don't realize is that there was a very tight window to get the refueling done. If they took too long, the airframe cooled too much and started leaking again. Take too long, and by the time they got unhooked and hot, they had lost so much they needed to refuel yet again to replace what had leaked while refueling.

Jim Snover

 

[GTFlow]

Cool thanks fellas!

Jim as for the heat tiles on the shuttle....we use similar tiles on our (B-2) aircraft for different reasons of course. Oh yeah and seeing the SR-71 in person I'll agree it is an awesome aircraft.

 

[GTFlow]

double post......Sorry.

 

[Double"O"]

Cool thanks fellas!

Jim as for the heat tiles on the shuttle....we use similar tiles on our (B-2) aircraft for different reasons of course. Oh yeah and seeing the SR-71 in person I'll agree it is an awesome aircraft.

LOL i got pulled over on Whiteman AFB for 27 in a 25 (on the far side on the runway away from the B2 hangars lol)...in a duty vehicle lol

all i wanted to do was preflight our P-3 so we could fly home lol

 

[thomas91169]

the SR71 is a badass aircraft. Two ****ing big ass engines strapped to the first titanium airframe (aluminum couldnt be used as it would melt under the heat and stresses), and a insanely aerodynamic and sleek body.

Until the F22 came into the picture, the Blackbird was my favoritest aircraft. Makes me wonder what we have today that could be its predecessor that we dont even know about yet. Lockheed Skunkworks FTW. One of my other favorites being the A-10 Warthog, or as i like to think of it, the flying tank (its nickname is also "Tank Buster" due to its 30mm cannon and ability to hold shitloads of ammo, and being probably the most heavily armored plane evar.

 

[97WHITEVENOM]

You guys all got it right. The resulting plasma is a result of the energy pumped into the air coming in contact with the shuttle and having to be pushed out of it's way. So its better than -60, then this brick the size of several city busses comes barreling through, and now because you had to get out of the way to let it pass you are really really hot.

The friction is actually a necessary thing, as far as getting back on the ground in one piece, goes. All that rocket fuel expended tossing the shuttle in orbit means there is a huge energy surplus in the shuttle that has to be gotten rid of to get it back on the ground in one piece. In addition, ther eis also the energy gravity is pumping into it as it descends. This combined energy surplus is dumped into the atmosphere, making that thin air go from -60 to a plasma. That is what is slowing the shuttle down so it can land on it's tires, and not make a big hole in the ground at Mach 25.

Or rather, the friction is a good thing as long as you can keep the heat on the outside of the spacecraft, and _not_ let it get in the main gear wheel wells, for example. This is where the shuttles infamous tiles come in: they reflect this heat from the surface of the tile back into the atmostphere. As long as they are in place.

Double "O", you're talking about my favorite plane. As if that's news to anyone here. And you're 100% correct. Until they go tit in the air and heated up, it leaked fuel like crazy. So they made a fuel that was very hard to ignite. Everyone knows the Blackbird refueled several times in the course of a mission. What most don't realize is that there was a very tight window to get the refueling done. If they took too long, the airframe cooled too much and started leaking again. Take too long, and by the time they got unhooked and hot, they had lost so much they needed to refuel yet again to replace what had leaked while refueling.

Jim Snover

First time I have ever heard anyone use a potential/kinetic enegry balance to explain the heat energy released upon re-entry.:beer:

 

[UFGatorGuy20]

It's not friction... but the result of an incredible pressure differential.

I wasn't aware of this until I took an aerodynamics class senior year of undergrad...

It's usually assumed that the mechanism of heating in re-entry is by friction or atmospheric drag. But, this is the predominant mechanism only at lower altitudes, as air density increases. Upon re-entry the shuttle develops a very energetic pressure wave at its leading surfaces. The energy density is sufficient to cause atmospheric molecules to dissociate, and their component atoms to become ionized. The vehicle thus descends in a superheated shroud of incandescent plasma.

There are loads of internet sources that may be able to explain in more detail.

 

[Ry_Trapp0]

wow, thats really interesting! so, if im understanding this correctly, its not actually the atmosphere moving against the surface of the craft, but the extreme energy(from the entry speed) of the craft being dissipated into the air that is being forced around the it.

 

[UFGatorGuy20]

wow, thats really interesting! so, if im understanding this correctly, its not actually the atmosphere moving against the surface of the craft, but the extreme energy(from the entry speed) of the craft being dissipated into the air that is being forced around the it.

That's correct! Great way to think about it without going deep into hypersonic flight aerodynamics.

 

[Uncle Meat]

I was lucky enough to be stationed at Kadena AB in Okinawa back in the early '80's when they still had 3 Habu's (SR-71's) on rotation there out of Beale. There is absolutely nothing, except maybe the space shuttle, more impressive at night than an SR71 at full AB as it rockets damn near vertical from the end of the runway!!!! On a clear night you could watch those dual blue flames quickly disappear as the aircraft climbed out of sight.... yet you still heard its engines rumbling along for a while after...

U.M.

 

[wizbangdoodle]

I learn something new everyday. So if that is the case, theoretically if you could slowly re-enter the atmosphere there would be no "burn"? Like easing your way into the atmosphere?

 

[97WHITEVENOM]

I learn something new everyday. So if that is the case, theoretically if you could slowly re-enter the atmosphere there would be no "burn"? Like easing your way into the atmosphere?

yup