Shallow reentries and heat shields

[agentgonzo]

Knowing every trick in orbiter and getting from KSC to AA in 20 minutes does NOT make you a rocket scientist. There are thousands of people who work for various space agencies and aerospace engeneering companies and frankly it's an insult to their combined intelligence to suggest that they didn't think of "soft reentries".

I didn't say that I was a rocket scientist, nor did I say that they hadn't considered it (in fact my original post says exactly the opposite - that they have and have rejected it). This thread was a quest so that I could understand why. Stop looking for an argument where one does not exist.

Thank you to to those of you who have provided scientific reasons and explanations to answer my question. I now understand spaceflight a bit better (the reason I asked the question). To the rest of you, please find something better to do than trawling the internet looking for an argument and shouting down everyone who does not possess whatever qualifications you think should be relevant to ask a question.

---------- Post added at 04:31 PM ---------- Previous post was at 04:21 PM ----------

What about deorbiting a newspaper at a shallow angle? (Remember that?) Will it just burn then?

I do (and got reminded of that question when I was thinking about this one). I don't think that we came to a useful answer either way.

 

[Ark]

I do wonder if NASA has a flight plan for a soft reentry stashed away somewhere. It would have been a smart move to try it with Columbia, it certainly beats the strategy they decided on (aka: Let's pretend there is no problem). Someone must have thought of it, it's pretty rediculous to think that nobody in JPL ever stood up and said "Hey, how about a real long and shallow reentry angle?"

 

[garyw]

I do wonder if NASA has a flight plan for a soft reentry stashed away somewhere. It would have been a smart move to try it with Columbia, it certainly beats the strategy they decided on (aka: Let's pretend there is no problem). Someone must have thought of it, it's pretty rediculous to think that nobody in JPL ever stood up and said "Hey, how about a real long and shallow reentry angle?"

Because it is impossible. To reduce peak heating on Columbia they would have had to dump as much as possible overboard. That was investigated and it wouldn't have helped much. The best Columbia strategy would have been a high alpha entry.

There is no such thing as a "shallow entry" for a shuttle. it's been covered in the previous replies.

 

[T.Neo]

The best Columbia strategy would have been a high alpha entry.

What constitutes a high alpha reentry?

 

[garyw]

What constitutes a high alpha reentry?

High-Alpha = 60-degress pitch up, allow more heat to impact on the belly, try to protect the damaged wing as much as possible. No one was sure if it would work though. it was largely a paper excercise.

 

[RisingFury]

This whole debate goes far beyond just knowledge.

To even think that Orbiter can be applied to any realistic reentry scenario with accuracy is worthless.

In Orbiter, or any other program / simulator, the positions, velocities, orientations,... are known for every body being simulated. The response to certain scenarios is 100% predicable with 100% accuracy. You don't have that in reality.

A real-time simulator such as this will only be capable of simulating realistic scenarios when computers become as powerful as today's supercomputers and someone is willing to spend a lifetime building the software.

 

[garyw]

Here is a bit more information on high-alpha -> http://forum.nasaspaceflight.com/index.php?topic=17437.msg470894#msg470894

---------- Post added at 06:05 PM ---------- Previous post was at 06:03 PM ----------

A real-time simulator such as this will only be capable of simulating realistic scenarios when computers become as powerful as today's supercomputers and someone is willing to spend a lifetime building the software.

Sure but it does wonders for promoting what-if questions, scenarios and actively engaging the imagination of those of us who can't do this for real. We can then ask questions here in a friendly environment and learn from those that do know more. Everybody wins. :thumbup:

 

[Calsir]

If you compensate a weight of 1N, you will produce 1/1.6 N drag as well, and altogether have the whole (1N+1/1.6N) * velocity as power, which you will get by aerodynamic friction. At 8000 m/s at this point initially, this will mean a needed aerodynamic heat flux of 13000 W. For a weight of 1N.

I may be nitpicking, and I may very well be utterly wrong, but should Lift, by definition, dissipate no power?

Since [math] P = \mathbf{F} \cdot \mathbf{v}[/math] and [math] \mathbf{L} \cdot \mathbf{v} = 0[/math], then the only dissipated power should be due to drag. Or am I completely and utterly wrong?

 

[Mindblast]

From what i read, the peak temperature of air in a normal shock can be eyeballed by taking the speed in m/s and use that as the temperature in Kelvins.. so at ~8000 m/s reentry you'd have plasma temperatures of up to 8000K in the shockwave. As Urwumpe already explained, the only thing that helps to keep this shockwave at a good distance from the spacecraft skin is having very blunt shapes.. those in turn yield bad lift/drag ratios. So if you want to do a shallow reentry you'd have to use pointier/edgier shapes to get better L/D ratio resulting in much more direct contact with the plasma and thus probably much higher hull temperatures.
Also the longer the whole operation takes, the more heat leaks through to the interior.

I think most of the orbiter addons with heat displays probably use very simplified ways of calculating the hull temperatures like using something along the formula airdensity * velocity^3 that orbiter uses for the reentry flame texture. So they are really misleading when it comes to shallow reentries.

 

[RisingFury]

Sure but it does wonders for promoting what-if questions, scenarios and actively engaging the imagination of those of us who can't do this for real. We can then ask questions here in a friendly environment and learn from those that do know more. Everybody wins. :thumbup:

Indeed, but people need to understand that the implementation of aerodynamics in Orbiter is far from reality, because Orbiter uses a relativelly simple model.


I mean... when you think about "outside the box" solution for problems like these, you have to realize that TPS is usually dead weight and if they could remove it, they would. There's usually a good reason why spacecraft are designed the way they are.

It's like saying: "What if you tried voodoo instead of chemotherapy?" to a cancer pacient...

 

[Urwumpe]

Or am I completely and utterly wrong?

Not utterly wrong, but remember the most important rule of physics: TANSTAAFL.

Producing lift produces drag as well.

 

[Calsir]

Not utterly wrong, but remember the most important rule of physics: TANSTAAFL.

Producing lift produces drag as well.

I never said otherwise. However, induced drag is already included in the L/D parameter, hence my remark. Even without lift, the power dissipation due to heat is considerable nonetheless.

Actually, there are free lunches: let someone else do the work, then consider your system as "closed". You then have invented a perpetual motion machine :lol:.

 

[Ghostrider]

It's like saying: "What if you tried voodoo instead of chemotherapy?" to a cancer pacient...

Zombie with no hair?

Sorry. That was evil. But couldn't help myself. It's like dead babies' jokes: you know they're in bad taste but you can't help.

 

[agentgonzo]

Indeed, but people need to understand that the implementation of aerodynamics in Orbiter is far from reality, because Orbiter uses a relativelly simple model.

We do. What you need to understand is that we are asking questions to understand spaceflight more (the reason why this technique wouldn't work), rather than saying it should be done this way because it works for our computer game.

 

[garyw]

Thread closed at the request of the original poster as the question has been answered and it's going off-topic.