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Brilliant idea for re-entry

Posted by: SuperShuki - Fri Aug 26, 2005 8:50 am
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Brilliant idea for re-entry 
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Post    Posted on: Tue Sep 06, 2005 3:25 pm
Ekkehard Augustin wrote:
I still don't see why an ion drive can't have similar results for a vehicle as it would have in orbit.
The difference is that in orbit you can stay at an altitude where drag is negligible, significantly below orbital speed you can't.
If you turn off the ion engine thrust in orbit then assuming you are orbiting at an appropriate altitude (which might be about 200km) you won't immediately start to drop in altitude, but that is the case all the time up until you are very close to orbital speed.
Before you reach orbital speed there won't be enough thrust to remain at any altitude significantly above 60km without extra lift. If that lift is being made at the expense of drag (which if it is made aerodynamically will be the case) then that drag will be a large fraction of the engine thrust.
Ekkehard Augustin wrote:
The vehicle won't achieve an orbit at an altitude less than 100 km - because the required velocity at such an orbit is too high.
You can orbit at almost any height you want, and increasing orbital altitude with ion engines in the ATO isn't an objection of mine. ATO however cannot orbit at 100km or below because it is such a low density vehicle that it would encounter very excessive drag, any small increased velocity needed is secondary.
Ekkehard Augustin wrote:
What is the direction the impulse got by the ion engine will go to? Parallel to Earth's surface?
Ion engines thrusting almost parallel to the Earth's surface, matching the climb angle of the vehicle. This isn't a difficult decision as this adds the most mechanical energy to the system for a given amount of thrust and is the only sensible thing to do until you are very close to achieving orbital speed.
Ekkehard Augustin wrote:
There is no base to predict failure or impossibility - because there are too much degrees of freedom.
There are many degrees of freedom which affect possibility, but most have no affect on a proof of impossibility for a general scheme. The engine thust direction is a good example, if it was done terribly wrongly it would prevent possibility but someone trying to prove something impossible would always assume the details were as conducive to sucess as could be possible.

As long as you are significantly below orbital speed you need aerodynamic lift and as long as you need aerodynamic lift you produce drag. The drag may only be fraction of the lift, but this fraction has a lower limit at high speed. If the ion engine test produces very high thrust to weight (maybe using already ionised air) at very high ISP then there's a small chance it can work. That said it would need to be a miraculously large improvement as thus far ion engines have very low thrust to weight.

Everything comes back to the lift/drag ratio.

Of greatest importance in a feasibility study here are the two ratios lift/drag and thrust/weight at various different velocities. If the product of these two numbers is not greater than the fraction of weight not taken by either centrifugal force or buoyancy at any time (which is almost 1 for most of the time) then the concept can't work. This is just one of the major reasons I think this concept can't work.
I simply cannot imagine what they think will get them high enough lift to drag at hypersonic speed, or high enough thrust from an ion engine to sustain any great speed or altitude. They could be relying on extremely high performance ion engines (though they said it was not needed in the Space Access presentation) or some unknown levitation technology (though they said it was just old fashioned aerodynamics). Without levitation they would at least need major breakthroughs in power generation, aerodynamics and ion engine thrust. I haven't seen evidence for any of these.

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Post    Posted on: Tue Sep 06, 2005 4:50 pm
I am wondering a little bit.

My remarks about the degrees of freedom were meant to say that as lons as there are no concrete informations about material, angle, geometry of wings, direction of impulse, thrust, pressure inside the wings or abot the question if the wings are massive there is no chance to find exactly those formulars and numbers JP aerospace used. It can be compared to the situation I was faced to before I could get insight into Virgin Galactic's costs in the Financial Barriers section: I needed the informations about their price policy as well as the informations about some of the specific fixed costs. Previous to the availability of those informations an infinite number of formulars and functions etc. were possible - no chance, to get insights. After the informations were made available I still had to recognize that Break-Even-Point-Analysis is applicable.

Do you assume that the ion engine will be shutdowned before orbital velocity of around 28,000 km/h is achieved? I don't think so - they will be kept working until the vehicle is at 28,000 km/h, they will be working permanently. This means permanent acceleration - the vehicle will become faster and faster and this way achieve more and more altitude. The acceleration will be so that it is larger than the deceleration caused by drag - which of course is required. The number not available here is the power of the ion engine JP Aerospace will use.

I understand the logic of your argumentation - but what you say sounds as if you are assuming something I don't assume regarding how the engine etc. will be used.



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)


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Post    Posted on: Tue Sep 06, 2005 7:07 pm
Ekkehard Augustin wrote:
Do you assume that the ion engine will be shutdowned before orbital velocity of around 28,000 km/h is achieved?

Maybe in recognition of its futility? In any conceivable working scheme you would run the engines all the way to orbital speed or until they run out of fuel or power - I'm not assuming anything strange. I keep having to put in caveats like 'almost orbital speed' instead of orbital speed when talking about needing lift, because once you are very close to orbital speed you will have some freedom to sustain or increase altitude without the help from aerodynamic force just using the ion engines. There's a similar caveat regarding need for lift at low altitudes because of the buoyancy you can get there. There's probably a much neater way to word things but it has eluded me. Everywhere between these two extremes the required behaviour seems very easily defined and troubling.

Ekkehard Augustin wrote:
This means permanent acceleration - the vehicle will become faster and faster and this way achieve more and more altitude.
It is quite simple to show that with a constant value of thrust to weight and a buoyant vehicle there is a limiting value below which orbit cannot be achieved regardless of the duration of the thrust. i.e. the vehicle would reach a limiting altitude and speed. With sufficient thrust the vehicle can achieve orbit, but this isn't even vaguely consistent with the thrust to weight of existing ion engines even if the power supply and fuel took up no weight. With existing ion engines the speed would be so low that the altitude would barely register above 60km. Realistically you need ion engine thrust to weight approaching 0.5 for this concept to achieve orbit - the power consumption at this level of thrust is getting close to the full theoretical amount of sunlight falling on the vehicle. That just isn't plausible for technology available in seven years. JP aerospace seem to be assuming drag will reduce to negligible levels at high altitudes. If this is the case then they are wrong, it will remain substantial while the vehicle is supported aerodynamically. Tellingly JP has said that they think what they are doing can be accomplished by a large margin. That could signify some kind of breakthrough - but it *really* sounds like a mistake.

Ekkehard Augustin wrote:
My remarks about the degrees of freedom were meant to say that as lons as there are no concrete informations about material, angle, geometry of wings, direction of impulse, thrust, pressure inside the wings or about the question if the wings are massive there is no chance to find exactly those formulars and numbers JP aerospace used.

If they don't do things optimally within what is known about ATO then there may be additional reasons why it will not work, this is true of any concept. To be frank I'm not looking for reasons for it to not work, I haven't been for some time, they may exist - I believe there are too many likely ones already, reasons that I believe don't depend on the implementation details in any foreseeable way. Unless the information given about ATO were just a distraction, a way to mislead people about how it works I can't see it working. If it is a distraction - and I really don't believe it is, then there isn't much to be gained talking about it. Either way, I'm more than willing to wait and find out much later.

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Post    Posted on: Wed Sep 07, 2005 10:28 am
I am recognizing specific or special signs or points in your post I sometimes recognized in posts of others which obviously have a significant impact on view etc. - you say:

Quote:
thrust to weight of existing ion engines
and

Quote:
With existing ion engines the speed would be so low


What you - and some others - say seems to be based on what already exists or was there. This will be justified in development and construction of vehicles - for reasons which I would call economic ones and thus do understand. Your arguments seem to be experience-kind and the theories you and others make use of partially a descriptions of experiences - this too I understand.

But experiences and theories describing them never mean that something beyond these experiences and the theories describing them is impossible. This is an philosophical issue which is required here for a simple reason - in Political Economics (my Science) nothing must be based on experiences because experiences allways are special cases while Political Economics is interested in general theories. This doesn't mean that Political Economics doesn't make use of experiences - but their meaning is different. Each economic theory based on experiences fails or is tending to fail. So in Political Economics first there are theories based not on experiences but on logical and mathematical connections and links (for example) and then looks on the real world, on experiences, empirical research and statistics is done to find out if the predictions of the theories meet the experiences.

General theories like those Political Economics are interested in are provided by Physics, by Newton, by Einstein, by Planck, by Heisenberg, Bor and the like. Kepler's theory is a descripting one - such theories do exist in Political Economics too. And of course I know that they are used in Engineering too.

Arguments using properties and data about "existing ion engines" necessaryly are specific and special ones which can't have results that are valid in general.

I am not that sure that JP Aerospace is going to use ion engines like existing ones regarding the data about thrust etc. I wouldn't wonder if they have done all their calculations completely correct and without mistakes but looked for ion engines meeting their requirements, didn't find any and decided to develop a new one which didn't exist previously that provides the required thrusts etc. They are inventing and innovating - this increases the probability that it is misleading toassume the use of existing engines etc.



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Post    Posted on: Wed Sep 07, 2005 4:32 pm
Hi Ekkehard,
In engineering what might be called the state of the art is an important reference point. If not something that imposes physical limits in itself, it does reasonably point out what can be accomplished without new technology. I suppose I'm making the assumption that the laws of physics will be the same in seven years, I mean - I'm talking about existing physical laws. In the event that isn't true then anything is possible in seven years. It's possible no-one will remember hearing about ATO in seven years, if I announce this theory do you think I can get anyone to believe it?
Maybe orbit won't mean what it does now in seven years, that's another way ATO can work. Do you see where this is going?

All sound opinions are based in some way on experience, even for those inventing new concepts. The mechanism by which they are connected may not be an obvious one, but if there's isn't one what is formed is purely speculation. Speculation that cannot by definition be justified except by new experience. I've speculated myself about how ATO might try to work, and nothing but new experience could justify it.

You will be aware that I have not limited any analysis of ATO to using existing ion engines even if they were part of the original concept. What I have said is that to work realistically, ie. with enough confidence to talk about things like payload without outright derision you need ion engine thrust to weight approaching 0.5. Do you fail to see how unrealistic this is while maintaining a high ISP? I'll go out on a limb, there's definitely more than one order of magnitude of thrust to weight improvement (at a high ISP) possible in ion thrusters, reaching out further there may be two orders of magnitude improvement possible. Most of it won't be easy or inexpensive nor available outside a laboratory in seven years. And it still isn't enough. Long before that point you have to wonder if ion thrusters are even the right kind of technology to be using.

But that's ok, because it seems that high ion engine thrust isn't part of the ATO concept, if it were there would be no good reason to reach orbit over several days and no way to even power the ion engines for that long before they had long ago run out of fuel, or in any event become non-functional.

I can only assume the revealed parts of their plan were designed to cause maximum doubt among the space community, either that or they made a believable mistake.

In my view, given what is known any public speculation that ATO will work is a gamble. What exactly is it that leaves you with a tenuous hope that ATO will work as described? It can't be what we actually know about it because that's a terrible disadvantage to start from. Is it hard to believe JP Aerospace have made a mistake? I don't know that they have, but it isn't that hard to think it is possible. What makes the unknown any more probable than the likely?

Ekkehard Augustin wrote:
I am not that sure that JP Aerospace is going to use ion engines like existing ones regarding the data about thrust etc.

Comments have been made to the effect that ATO would at least work with existing ion engines, these comments inevitably created the impression that it would work with very low thrust to weight. These impressions have seemed to be confirmed, ie. that existing engines we actually know about - not something hidden in a secret laboratory should work. without drag this would match Really Well with orbit being made in about three to nine days. It's such a close match it would be considered by reasonable people to be a most likely scenario.

Using only low thrust ion engines makes ATO completely impossible without levitation due to simple lift/drag and thrust/weight reasoning.
Alfred Differ has made a comment to the effect that ATO does not use levitation but aerodynamic lift. I believe him.

Notwithstanding that levitation looks Very Hard technologically, with both electric or magnetic flavours. The magnetic kind won't work on Mars which has been said would work well with ATO. I can't see the electric kind working anywhere. I could be wrong.
You could speculate that there is extreme drag reduction going on, or some kind of forcefield to deflect gas without drag. Apart from being fanciful, it also disregards things we have been told about ATO. It's just aerodynamics.

JP has made comments that ATO would work by a large margin, that is a mistake. There are no large margins involved except those preventing ATO working. Without drag ATO would work by a large margin, unfortunately without levitation drag isn't going to go away.

What seems highly probable, and I don't see why your not noticing it is that if you just think - drag is reducing as altitude increases(!) you could be fooled into thinking drag won't be a problem. The problem is that lift is also decreasing with increasing altitude(!) and to keep enough lift to maintain any altitude with increasing speed, the drag can at best remain about constant or increase at high speed. Hypersonic flow dictates that the lift generating mechanisms at very high speed are poor and that there is no real way round it. If JP Aerospace were busy trying to solve other aspects of the problem (and there are a several big ones) then there is a chance they never put this under proper scrutiny. Forget my earlier statement about ATO resembling a waverider, that was ridiculous optimism - I briefly hoped it would be changing shape with Mach number. That was unfounded, looking closer in the pictures provided, if they are anywhere close to accurate ATO will have really bad hypersonic aerodynamics.


If you put aside everything you have been told about ATO, then you can come up with concepts which work. As soon as you add a few of the critical elements it fails to reach orbit.

We're stuck here, I don't believe ATO can work and nothing I can think of can make it work or get close to working.

I've spent about 1% of the time looking for problems with it and 99% of the time trying to think of ways to fix them so it can work. I've found nothing that helps enough even with extreme optimism, neither in the ATO concept as described nor in anything that is close to resembling it. They have picked out a region of design which is not conducive to working, if ATO were close to working I might have been able to fool myself that there was a way it could work, but whatever would be required to make it work doesn't seem to be on anyone's radar. Look on http://www.islandone.org/LEOBiblio/ for several schemes which appear to stand a better chance of success.

I am saying that what I know can only justify scepticism. You on the other hand may be telling me that I can't justify my scepticism because of unknowns. While no-one here needs to achieve complete belief or non-belief about ATO, this would invalidate ever being sceptical and I can't agree with that.

My best guess is that JP aerospace have all the necessary information as to why the concept they described doesn't reach orbit and cognitive dissonance is at work. Again I could be wrong.

I have made similar kinds of errors, usually I eventually realise where I've gone wrong, most often without involving other people in my ideas first. Sometimes even after work even the good ideas turn out to not work, not always by enormous margins but enough to not be worthwhile. I think ATO fits the earlier category, it was an idea which had an error in it - but it built up way too much inertia before the problems were pointed out. It can take a long time to move on from these kind of ideas if you've got something at stake in it. This has happened before, just not with JP Aerospace. Maybe this isn't what has happened, going over and over just a fraction of the available arguments is wearying. I would prefer to be free of the burden of thinking about ATO, if it works - that's great. I'll get to see why I'm wrong - not an unusual event in itself but I feel that I must have put some credibility at stake here even if that wasn't an explicit intention.

We have talked so much that I actually believe strongly in my own arguments, that's not the exact situation I started from and it may mean I should not continue to talk about ATO on this forum. I would like to throw fresh doubt on what I now believe, but I have very little left. One does not merely walk to orbit.


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Post    Posted on: Wed Sep 07, 2005 5:34 pm
We do seem to have strayed from the topic, which is re-entry. Propulsion is not even part of the question, only drag and lift. And maybe buoyancy. The only way to make re-entry take more than a half orbit is with lift of some kind. The lift (or maybe buoyancy) supports the vehicle as is slows due to drag. But for a week long re-entry you need drag to be very small compared to lift. In other words L/D has to be high.


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Post    Posted on: Wed Sep 07, 2005 8:03 pm
Ah--but propulsion is part of the mix. The reason we have an external tank to begin with is to reduce the amount of spacecraft that must be exposed to re-entry.

It all matters.

SSTOs are basically orbiters which have swallowed their External Tanks--and must therefore have more surface area covered with heavy shields--and landing gear rated to take the weight of the whole vehicle. It can all get out of hand pretty fast. It is not about private vs. public--it is about physics.

TSTO craft have double the wing weight, double the landing gear, etc.

In many ways, STS is the perfect shape for physics. Side mount reduces pitch loads. Side staging keeps all engines on the ground where they are visible--and not hidden by fairings and such. The aeodynamic purists don't like it--but better control authority can be had over in-line designs--tho' they are more clean. By leaving tankage off--you don't have to shield as much.

With cpasules--you need even less shielded area--and the tankage just has to be rated to handle simple axial loads and the like.

It is easy to bash shuttle--but when you try to do one better and re-enter more slowly--it just doesn't work. Yes, wider re-entry envelopes are nice--but the ultra thin construction of Ascenders limits their ability to withstand any real heating or stress.

I would try to find a cheap spacecraft design that emulates the STSs good points and avoids its bad points.

As I see it--the orbital version of Dream Chaser with the AMROC boosters and the mini-Buran design philosphy is what we need. Large airships might be a good base for Space Elevators--to fly above weather and above most icing loads--that will hurt airships and elevator cars just like it would hurt orbiters--thus the foam.

So you see--many of NASA's problems are not solved with the simple "gov't is incompetant' hand waving. STS's biggest enemy is icing. That will be true with Airships and esp. elevator cars.

Little changes.


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Post    Posted on: Wed Sep 07, 2005 11:12 pm
Well publiusr, I see you have mentioned Buran again without addressing the topic under discussion, which is how to keep the vehicle from dropping into the atmosphere as it spends many days circling the Earth at suborbital velocity.


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Post    Posted on: Thu Sep 08, 2005 1:36 am
It seems to me that what we should be trying to do is to reduce orbital speed as fast as possible while the craft in question is still above the majority of the atmosphere. The reason this isn't the way reentry is done today is that it takes way too much fuel. If a way could be found that reduces speed rapidly that doesn't require launching the fuel in the first place the thermal and aerodynamic loading on the craft could be dramatically reduced.

For example, deorbit a packed parachute on a tether and unfurl it in the stratosphere. If you can generate enough drag (without breaking the tether) to decelerate at 3G's, in about 35 minutes you will have reduced orbital speed to approximatly 0. Reentry at this point would be doable with a variation on Scaled's feathering.

Just a thought.


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Post    Posted on: Thu Sep 08, 2005 7:38 am
Hello, nihiladrem,

first a last remark about your look on JP Aerospace's concept, my own look and the differences between them and then second the return back on the topic which I personally should have in mind urgently and really have in mind.

1. The remark on the looks at JP Aerospace.

You say
Quote:
In engineering what might be called the state of the art is an important reference point.
.

I know that and say that explicitly - I assist it and it is reasonable. This is valid regarding construction - in the meaning that you, nihiladrem, should do so if you yourself are constructing something. You have your methods you prefer, you know best and you can work most efficiently by. Please remark - this is so when and if you yourself construct something and talk about that work and task.

Here we are talking about what the people at JP Aerospace, John Powell and so the company JP Aerospace are doing. As far as I understand you yourself aren't working at JP Aerospace and so not involved in the constructions there. This logically and necessaryly means that your experiences and skills regarding construction etc. can't be a source of insight into JP Aerospace's doings, failures and so on. Construction methods are no research instruments - but we are talking about JP Aerospace's concept here without being involved or even being part of that company which means that we are trying to look at and into them from outside and this is reseach and not construction.

I can say this because my science or discipline contains both research and construction methods. The construction methods Political Economics and Enterprise Economics include are the instruments Political Economics have developed for federations, governments, parliaments, the FED and other agencies and institutions as well as methods of organisation and reorganisation, balancing policies, marketing and the like for companies and trusts. Really non of these instruments can be used to understand the american economic policy trying to look at or into it from Germany - to do so the reserach instruments developed have to be used which are no way similar to the political instruments and methods developed. Of course Economists are stuying and researching special companies - but the results never can applied to other companies. In contrary ecah company has to be studied itself then the results can be compared and something can be seen they have in common - by research methods but their organization and marketing etc. instrument may be quite different, contradictory and the like.

You should use state of the art for doing your own construction work but it can't be applied to research the construction work of another company - this requires something different to any state of the art.

This isn't meant to critize you or anyone else but to show up how to look cautiously and without unintended prejudices.

2. On-topic

Long-time-reentry as concepted especially by JP Aerospace would increase safety for example. I am thinking about probes like Genesis this moment. The ATO or even any other vehcile capable of long-time-reentry could have taken the probe aboard - after it has been decelerated sufficiently (may be by ballutes) - and carried if slowly down into the atmosphere. The ATO could simply deliver it to a DSS where it can be moved to an Ascender. The Ascender would go down to the surface slowly and the probe would have a very soft landing this way - it's a pity that there wasn't that concept when Genesis returned.

I do not know when the first martian sample retrun mission is going to return but it could be useful if JP Aerospace's concept would be completely and successfully ready then and used to deliver the sample to the earthian surface.



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Post It looks like one of the Xprize teams had the same idea . .   Posted on: Thu Sep 08, 2005 10:44 am
http://www.tour2space.com/x-prize/xconcept.htm

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Post    Posted on: Thu Sep 08, 2005 1:29 pm
Interesting link SuperShuki, but that vehicle would re-enter much faster than your proposed "a few days, or weeks". Your link says it would have a peak deceleration of 2.8 g's. That is about the same as the space shuttle.


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Post    Posted on: Thu Sep 08, 2005 3:34 pm
BitBanger,

Did you mean 0.3g? Deceleration time at 3g total is only around 5 minutes. In some ways your scheme seems similar to the kite but taken up a few levels, the lift part of that scheme seems only necessary if you need to keep the maximum line length minimal. Otherwise pure drag devices like ballutes/parachutes should be possible. In that scheme which was to reduce orbital altitude over a day or two, you could lower the orbit of a 20tonne vehicle by several hundred km and cause reentry to then occur using just several kgf of drag. Ordinarily just the fuel needed to do that would weigh 250kg or more unless you use ion thrusters. There's a fair bit of mass to play with for any drag scheme because of this. Even with just several kg of line tension the weight of the line over several hundred km is dominant. It is particularly bad for perhaps the lower 100km of the line where the environment is a bad one for low gauge materials moving at high speed. One of the biggest objections is that it might not be compact, it's certainly much more complex than ordinary altitude lowering and it causes concerns about the line hitting things which in the future may be overwhelming. These are all valid objections to it. It can however be easily stored for very long durations.

The kite in this scheme is throwing off kW's of heat radiatively - glowing at a low level. The system is still only dumping about 10% of the original orbital energy over a day or more.
Back to your idea, if you make the line tension thousands of times higher than in the kite system till the line tension exceeds the weight of the vehicle then the gauge limitations lessen and possibly you won't need several hundred of km of length - but that could still leave the recovery system equal to the weight of the vehicle you intend to recover. This will improve as material properties do, though there may be hard practical limits. Without actually calculating anything, the length of line you need will depend on how long you need to decelerate over. To do much it will need to be at least in the hundred km range. If you take too long, which could mean if you take longer than a few minutes, you will fall in regardless as you will be dropping in altitude all the time. This just reinforces the idea that you can't make reentry very gentle without really good lift/drag. The big benefit of course is that the parachute and line take almost all the abuse.
[EDIT - this concept actually seems to hurl the vehicle downward into the atmosphere rather aggressively]

With any scheme that generates drag but not significant lift like with a parachute close to the vehicle that keeps a constant size, or a equally low density vehicle, because of the way the atmospheric density changes with altitude the reentry deceleration does not depend to a great extent on the ballistic coefficient. i.e. it doesn't matter greatly what altitude range you lose most of your velocity over, with a constant ballistic coefficient the deceleration curve will be at least roughly the same, maybe even until just before you run out of air and actually start lithobreaking.

If you change the ballistic coefficient as you go, you can increase the time when the rate of energy loss is large (which is a really important thing with regard to heating) but not by very much, especially compared to what you can do with lift. Maybe just enough to make heat-soak a slightly bigger problem.

For vehicles utilising buoyancy, the buoyancy lift itself won't directly figure in the reentry acceleration because at a theoretical level, it's very much smaller than drag forces until below sonic speed. When that point occurs practically all the energy has already gone. Again, lower density should largely make things happen at a higher altitude without any other huge differences to the deceleration. For schemes where reentry doesn't have mechanical lift (like you do in a space-elevator) lift/drag seems to be the only realistic thing left. If you have a low density vehicle and a lifting scheme that works it could plausibly allow you to radiate heat at relatively low temperatures. Because of the fourth power temperature dependency of radiative loss you need to be talking about things with really low density before this argument gets close to convincing. That looks very demanding from a technical point of view and it doesn't appear to be something you can simply bolt-on to an existing vehicle and fly from Earth.


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Post    Posted on: Thu Sep 08, 2005 8:05 pm
campbelp2002 wrote:
Well publiusr, I see you have mentioned Buran again without addressing the topic under discussion, which is how to keep the vehicle from dropping into the atmosphere as it spends many days circling the Earth at suborbital velocity.


:oops:

I did too address heating--saying that a compact object is more likely to survive than a balloon--or a balloon tank upon re-entry. As it turns out--with bigger wings (and only payload and not tankage) being returned--you also get less wing-loading than smaller winged designs.

So the more you have a craft with those dimentions (or a simple capsule) the less the heating problems.

Ballutes are fine--but are too heavy to loft. Perhaps some type of beamed energy propulsion and some weird field entanglement might be used. Probably not.


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Post Re: Brilliant idea for re-entry   Posted on: Fri Nov 18, 2005 1:39 pm
SuperShuki wrote:
Instead of taking a few hours to re-enter, why not take a few days, or weeks? Also, Use a huge parachute in the upper atmosphere. You can use a low angle of approach that way.

Anybody?


GE developed, back in the 60's, a space station escape pod technology, in one man and 3 man modules, that used an inflatable Rogallo wing of steel fabric (as is used in car airbags), coated with silicone, for reentry. Their calcs showed the wing loading was sufficiently low to minimize reentry heating to well within the limits of the steel fabric.

I believe they tested the one-man module, unmanned, with a Thor rocket. Astronautix.com has more on this.

I've been considering this possibility for an ASP entry.... This might be quite popular, esp with the extreme sport set: hang-gliding from orbit anyone?


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