New Sweet way to reenter?

[chosen_silver]

Maybe some are missing the point of my post. I am curious what it would take with future technology to effective lose all your velocity say within half an orbit. I understand we would not want to use a method that needs fuel as the cost in fuel would be too great. I suppose some very advanced engine would be required. Are there any theoretical engines that exist (as a theory of course) that might work for something like this?

Is it possible for someone to make some sort of changes in orbitor to give the DGIV are very unrealistic thrust that could be used from orbit to nearly stop the craft to see what sort of temps it sees falling back down through the atmosphere?

 

[Linguofreak]

When we have enough delta-V to have a spaceship land on its thrusters from orbit down, we'll have a no-heat reentry, until then we'll have to feel the heat.

Thrusters with enough ISP and thrust to do that will probably produce as much or more heat than a traditional reentry.

 

[joiz]

You are aware of the fact that the heat generated during re-entry is the vehicle's kinetic energy being converted into the aforementoned heat? And that is the only way to slow down from orbital velocity? When we have enough delta-V to have a spaceship land on its thrusters from orbit down, we'll have a no-heat reentry, until then we'll have to feel the heat.

yeeeeeessssss but what about reentering for hours in stead of minutes?

---------- Post added at 09:54 PM ---------- Previous post was at 09:53 PM ----------

oh, and for propulsive reentry: what about a reverse thrust scramjet?

 

[TSPenguin]

oh, and for propulsive reentry: what about a reverse thrust scramjet?

Now that makes no sense. A scramjet would not work at all if you try to reverse thrust (no matter how). All you would do is create more surface that breaks you.

 

[Urwumpe]

oh, and for propulsive reentry: what about a reverse thrust scramjet?

Does not work - SCRAMS require extremely clean airflow in their inlet, you can't poison this airflow with it's own airflow.

Also, turning the airflow by 180° while supersonic, would require a HUGE curve.

 

[Linguofreak]

yeeeeeessssss but what about reentering for hours in stead of minutes?

The heat shield doesn't have to absorb energy as quickly, but it also has to absorb more energy than otherwise. Also, it gives more time for heat to bleed from the heat shield to the frame of the craft.

 

[tblaxland]

The heat shield doesn't have to absorb energy as quickly, but it also has to absorb more energy than otherwise.

Because of a weaker shock front? Otherwise, why? You are converting the vessel's kinetic energy which is the same at initial and final conditions, so the overall energy transfer from kinetic energy to heat should be the same. I can see that the ratio between heat-added-to-vessel and heat-added-to-atmosphere would not stay the same.

Also, it gives more time for heat to bleed from the heat shield to the frame of the craft.

Therefore requiring either bigger structure or active cooling of structure = extra weight = reduced payload performance.

 

[Hielor]

Is it possible for someone to make some sort of changes in orbitor to give the DGIV are very unrealistic thrust that could be used from orbit to nearly stop the craft to see what sort of temps it sees falling back down through the atmosphere?

Just use the scenario editor.

It will pick up a whole lot of downward vertical speed, and if it doesn't burn up once it gets to the lower atmosphere it'll disintegrate when it hits the ground.

 

[Linguofreak]

Because of a weaker shock front? Otherwise, why? You are converting the vessel's kinetic energy which is the same at initial and final conditions, so the overall energy transfer from kinetic energy to heat should be the same. I can see that the ratio between heat-added-to-vessel and heat-added-to-atmosphere would not stay the same.

I'm not entirely sure what the mechanics are, but I do know that softer reentries result in more total heat load.

 

[TSPenguin]

If you go fast enough, you create a buffer zone between the actual plasma and your heatshield. At least if you use an ablative heatshield system. Might even be true for thermal soak systems as the shuttle has.

http://en.wikipedia.org/wiki/Atmospheric_reentry

 

[tblaxland]

If you go fast enough, you create a buffer zone between the actual plasma and your heatshield. At least if you use an ablative heatshield system. Might even be true for thermal soak systems as the shuttle has.

It is true. That is the shock front I was referring to earlier.

 

[joiz]

The heat shield doesn't have to absorb energy as quickly, but it also has to absorb more energy than otherwise. Also, it gives more time for heat to bleed from the heat shield to the frame of the craft.

the concorde spent four hours in 100 degrees c. and the only that crashed did so on takeoff. the blackbird spent similar amounts of time in much higher temperatures.

 

[garyw]

the concorde spent four hours in 100 degrees c. and the only that crashed did so on takeoff. the blackbird spent similar amounts of time in much higher temperatures.

Incorrect. Maximum temperature on the tip of Concordes nose was 107 degress C. The nose rarely got about 80 or 90. The rest of the airframe was at much lower temperatures.

 

[Andy44]

How can you compare something like the Concorde to the Space Shuttle? The former is slow as a slug while the latter zips along at mach 25.

And yes, the shuttle does use a detached bow shock to stand itself off from hot plasma. That is why its nose is rounded, not pointed (like Concorde), and why it enters at a high angle of attack. Same reason why capsules re-enter blunt-end first. The trick is to keep all parts of the vehicle from touching the shockwave. If the Concorde was shoved through the stratosphere at mach 25 the first thing that would happen is the pointy nose would melt right off as it poked through the shockwave into the hottest part of the plasma.

 

[garyw]

There is a DTO on STS-119 to examine what happens when the boundary layer is tripped.

See "Boundary layer Transition DTO" on this link:
http://www.nasaspaceflight.com/2008...anning-special-thrust-oscillation-test-added/

 

[RisingFury]

well that's sort of my point. I'm pushing towards no heat reentry, if indeed it is possible.

You'll always get *some* heating, but to keep heating at comfortable levels, you'd have to cruise through the upper atmosphere for a LONG time... and that's far more dangerous then just putting a heat shield on it and ride it out.

Besides, any weight savings you might get on a heat shield will be nulled by the extra weight of high aspect ratio wings allowing you to cruise in the first place.

 

[Sky Captain]

Seems that Skylon designers are planning to use soft reentry since Skylon wikipedia article say peak heating will be only 1100 Kelvin and less thermal protection will be needed. Also because Skylon is larger and lighter than Space Shuttle it will slow down at higher altitude.

 

[garyw]

*IF* Skylon ever flies and that's very unlikely.

 

[joiz]

How can you compare something like the Concorde to the Space Shuttle? The former is slow as a slug while the latter zips along at mach 25.

AHHHHHHH IM NOT!!! im saying what if we reentered in a way that allowed us to stay at mach two as the air is hugely thin in the upper atmosphere. and could someone please tell me how doing that is more dangerous than going through a furnace? maybe true about high aspect ratio wings giving extra weight.

 

[Urwumpe]

AHHHHHHH IM NOT!!! im saying what if we reentered in a way that allowed us to stay at mach two as the air is hugely thin in the upper atmosphere.

OK, in gas dynamics, I have to give you an F.

Lower density -> lower speed of sound.

http://www.aerospaceweb.org/question/atmosphere/q0112.shtml

As you can see, the speed of sound is about the same in 100 km altitude, than at 8 km altitude - the effect of higher temperature in the thermosphere (higher agility of the gas molecules) is offset by lower density.