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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: Fri Sep 02, 2005 1:07 pm
There are reasons why being very large at very high altitude helps with power generation, it helps you dump waste heat radiatively at lower temperatures which is kind of interesting and maybe even relevant to this thread. JP's proposal was at the very least thought provoking, even if those thoughts didn't end up with something I could believe would work.

There's no question that JP Aerospaces concept would have to work at altitudes where buoyancy is not an issue. It's best to say that not too far above 60km the buoyancy is largely gone, but regardless of the details it just doesn't make *that* much difference to the analysis. It must operate at altitudes well above 60km because a simple calculation shows that the drag experienced at that altitude is utterly overwhelming at high speeds, this does not realistically depend on how it makes lift or is propelled.

How does it get to higher altitude given that buoyancy is not enough? If JP's being straight about things then at least at high speeds it is meant to accelerate under ion thrust and uses aerodynamic lift to increase altitude. It *is* meant to be working as an aeroplane for most of the time...under somewhat unusual conditions but ones which are still understood. This is explicit in its shape which loosely resembles a wave rider.

There is no very sharp cut-off point where a air plane of suitable construction could not fly, you could fly above 42 km if you really had to - but given the limitations would you really want to?
A rocket powered aircraft can fly level above 42km for some time before its fuel has run out. And yes, another candidate for an extreme altitude plane is an inflatable one that has some significant contribution of lift due to buoyancy. At lower speeds it will be operating in the same way as Zeppelin where the majority of the lift is due buoyancy. Needless to say there's no way to sneak past the physics by moving inbetween categorizations of existing flying vehicles.

One of the crucial points in this matter is that to actually work it will have to generate lift under hypersonic conditions, waaay above 60km were there is no useful buoyancy effect. There is no known way of generating aerodynamic lift without very significant drag at these speeds. It has to generate almost all its weight in lift for days at high altitude against a large force of drag. There is no way around this.

Decades of Hypersonic research show that it would be extraordinarily optimistic to think this drag could be a tenth of the weight of the vehicle in a vacuum for most of this time. This is completely independent of the scale of the vehicle or the fact that it may contain helium. If you calculate how much Delta-V you need to keep up this performance it is so far beyond any non-nuclear form of rocket propulsion, let alone an ion thruster that it causes incredulity. You have to ask yourself, why should I believe in a plan that does not appear to follow known laws of physics? Whatever trick is needed to make this work must at least be some form of secret because no-one has given a convincing explanation of what it might be.

There are many other arguments as to why it can't work, but it becomes boring after a while.

Simplifying things, you can draw an analogy with a sea-plane lifting its belly out of the water using the power of its engines. What I am trying to say is that in this instance it would be a sea-plane that never could reach enough speed to lift its belly completely out of the water and would run out of fuel trying. And it wouldn't be a close thing.

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Post Hydrogen and Helium Atmosphere   Posted on: Fri Sep 02, 2005 6:00 pm
By the way, the "Atmosphere" at extreme altitude consists mostly of Hydrogen and Helium (no longer primarily of Nitrogen and Oxygen) so no lighter gass exists to produce boyant lift. A significant percentage of even lighter monatomic Hydrogen is also present!


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Post    Posted on: Fri Sep 02, 2005 6:47 pm
This and the thermosphere might be enough to push speeds out of the hypersonic region into the supersonic region. Don't have very good data data on this but it might be worth a second look.


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Post    Posted on: Sun Sep 04, 2005 11:00 am
In between I am asking myself if teh ATO will have a vacuum inside its wings.

Regarding th buoyancy the .pdf of JP Aerospace explicitly says that it will be used for going up from 42 km altitude to 60 km altitude without using the ion engines. They agree that buoyancy can't be used above 60 km without using the ion engines.

But even in the vacuum of space a vehicle can go up to a higher orbit without buoyancy simply by using its engines to get acceleration. Since that's possible this should be possible too under near-vaccum conditions above 60 km altitude within the atmosphere.

The topic should be discussed with jpowell now urgently - I'll initiate a thread in the General JP Aerospace Forum now.



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

EDIT: Initiated thread to ask jpowell: Doubts If ATO will be working


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Post    Posted on: Mon Sep 05, 2005 8:39 am
Just this moment I had a look into JP Aerospace's .pdf - it said that the ion engine for the ATO is going to be tested five months after the .pdf is published. The document has been published at 9th of May 2005 and so the test will take place after 9th of October 2005.

So there may be more and more detailed informations about the ATO and how it will work soon. These informations may be interesting for the topic of this thread.



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Post hypersonic conditions   Posted on: Mon Sep 05, 2005 12:32 pm
On second look, with guessed at parameters and a poor model - 5Km/sec I think corresponded with not much more than 110km of altitude, and it shouldn't need to get very much higher operating under aerodynamic lift. This seems to be roughly in line with some other peoples calculations. The temperature at 110km isn't starting to warm up much, so any supersonic/hypersonic difference doesn't come into play even if it were mostly hydrogen and helium. That said any pure Mach number distinction seems a practically meaningless under these conditions. Molecules breaking apart is assured at these speeds and very much higher the mean free path becomes too close to the vehicle size and the amount of lift possible even with extremely low density vehicles becomes negligible.

I haven't looked at the numbers, but possible extension of de-orbit times though lift generation is probably is pretty significant under such conditions *if* you can get a reasonable L/D. The big benefit would appear to be that you can radiate heat away without temperatures being as great, but it is quite possible that a greater fraction of heat reaches the vehicle surface because of the greater mean free path. This would require further investigation to be sure of.

You can't do anything comparable with devices which just produce drag which can only hasten your decent. We should probably be thinking of de-orbit proper only occurring when speed is below ~7.7km^s-1 for nearly circular orbits unless the reduction is it is happening rapidly, anything else might be better considered simply altitude reduction.

Ekkehard, I'm not sure JP Aerospace want to talk about this much. If there is a secret which makes their plan work (and depending on your interpretation, they have practically said as much) then I don't think we will make some progress. I just don't think it can work in the way it seemed to be described. Even with some secret detail I don't think it could work very close to how has described in seven years, not unless it's a really special secret. If there is some fault with my arguments (I make numerous mistakes or errors each and every day) they may want to correct some of these, but these issues have been raised elsewhere and were not all settled publicly which again is fine - I don't want to create ill-feeling over this. I'm quite happy to be proved wrong in the future if their concept just works, it would be a shock and I would have to adjust to the reality of it but I'm not against that. Hopefully the folks at JP Aerospace wouldn't hold it against me that I didn't think their idea would work. In the meantime - even while I am very sceptical about ATO, the DSS does look both interesting and viable and I hope they continue to build and do good things.


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Post    Posted on: Mon Sep 05, 2005 1:01 pm
The only thing I don't like currently is to talk about someone else's concept and project without involving him into that talk. To do so tends to substitute him or his potential answer by interpretations, opinions and the like which all will be within the borders of the interpretator while the author of the concept and project may have thoughts and ideas ouside those borders.

I prefer to keep the question marks about his thoughts etc. instead of substituting by interpretations.

Even if the author is keeping secrets this is valid (it has to do with the question of correct and incorrect behaviour) - the author and constructor surely will have done calculations etc. himself and have got results on which his decisions are based. I am sure that he has done this because he is investing a lot of financial ressources - even those of sponsors. And there will be no sponsor who hasn't had a look into calculations.

This is why I caused the new thread in the General JP Aerospace Forum and asked jpowell.

What can be said perhaps currently exactly is that it wouldn't work based on the thoughts others than the author and constructor have

Regarding the airplane-comparison - what I consider to be an airplane and what not depends on the engine and the technology the vehicle uses too. This means that I can't consider a vehicle which is driven by a rocket-engine as an airplane. Of course that vehicle is capable of all what you say. I could consider it to be a hybrid vehicle which partly is an airplane and partly is a rocket.

This is valid for SSO for example - I consider it to be an airplane as long as it is gliding simply and the engine is shutdowned but after the engine is ignited and before it is shutdowned again I merely consider it to be a rocket.

It will be interesting what jpowell answers in the new thread.



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Post    Posted on: Mon Sep 05, 2005 2:39 pm
Ekkehard Augustin wrote:
The only thing I don't like currently is to talk about someone else's concept and project without involving him into that talk. To do so tends to substitute him or his potential answer by interpretations, opinions and the like which all will be within the borders of the interpretator while the author of the concept and project may have thoughts and ideas ouside those borders


Ordinarily I would agree, but these are well known objections outside of this forum. I'm not the first person to arrive at them. For whatever reasons, JP hasn't publicly addressed them all - at least not to many's satisfaction. I am not regulating opportunities for this to occur. I agree that I am speculating about ATO rather than working with details, this isn't desirable but with secrecy it is inevitable. If peoples speculation would upset them noticably much I doubt JP Aerospace would have made information about ATO public at all. If ATO involves some crucial secret we can't make progress unless it is revealed, if it doesn't I'm unlikely to believe it can work without superior knowledge.

It's also true that JP Aerospace must have done some calculations, my belief is that they have made some mistakes in those calculations or based them on things which turn out not to be physically valid. I'm not saying this because I have a low opinion of them, or that it was an opinion I rapidly formed, but given the information at hand it seems much the most likely answer - I am not alone in this belief. The only thing that seems likely to change that is information, either from JP Aerospace or elsewhere. Simply telling me there is some secret involved will not alter my disbelief measurably in this case, this level of extraordinary claim requires verification. If ATO turns out to not work, I will not be demanding explanations.


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Post Re: Hydrogen and Helium Atmosphere   Posted on: Mon Sep 05, 2005 3:54 pm
rpspeck wrote:
By the way, the "Atmosphere" at extreme altitude consists mostly of Hydrogen and Helium (no longer primarily of Nitrogen and Oxygen) so no lighter gass exists to produce boyant lift. A significant percentage of even lighter monatomic Hydrogen is also present!


So make it a hot gas ballon - same principle as a hot air balloon, they contain the same gas as outside the envelope, but hotter and less dense, which is where the lift comes from but maintaining pressure to prevent ballon collapse. Needs to be extremely large, as JP's design is, to ensure that the bouyancy exceedes mass, but possible I think.

This principle has been suggested for Jovian exploration (and Mars I think). Since Jupiter has a hydrogen atmosphere (I think), there are no lighter gases, so the only option is a hot air ballon.

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Post    Posted on: Mon Sep 05, 2005 3:57 pm
Hello, nihiladrem,

I should clarify something - it was me myself who used the term secret but NOT JP Aerospace or John Powell themselves. They haven't been using that term never.

What has been said is "i can't speak about the propulsion system currently" or something similar in one of the younger threads - about a Pongsat flown at the recent Away-mission if I remember correct.

They aren't the first ones nor the only ones who are acting like this - Scaled Composites are doing so too. And JP Aerospace have revealed the Ascender as well as the DSS by some photos.

What you say is looking to me like a political and psychological way to urge JP Aerospace to provide more or better informations. It would be are way a lot of people are using to get the informations they want and even other things. A lot of consultants, experts etc. are teaching people to do so by courses, books and workshops. I personally don't like those ways and find them very negative: I refuse to do so and prefer the way I am going currently. But this is not meant to criticise you.

There are a lot informations we don't have: What's the material the ATO will me made of? What shape will the wings have exactly? How thick will their walls be? How much thrust will the ion engines generate and what will be their size and weight? Will they contain a vacuum? and much more..Answers to each of these questions may be required here - JP Aerospace would unveil nearly all their business and development secrets. They can't and mustn't be expected to do so. Why consider them like The da Vinci Project have been considered?

I didn't know that there is that much dissatisfaction regarding JP Aerospace's information policy.



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Post    Posted on: Mon Sep 05, 2005 4:54 pm
Ekkehard Augustin wrote:
Hello, nihiladrem,

I should clarify something - it was me myself who used the term secret but NOT JP Aerospace or John Powell themselves. They haven't been using that term never.
Alfred Differ wrote:

The details everyone probably wants to know are probably covered by a trade secret or two right now, so I'm sure readers will groan when I try to dodge talking too much about them. There are a lot of bright people out there, so I'd rather not loose all our best stuff to Boeing until they offer us huge sums of money so I can retire to the South Pacific. Very Happy


I think he was talking about ATO, I took this to mean there were reasonable limits to their openness.

Ekkehard Augustin wrote:
What you say is looking to me like a political and psychological way to urge JP Aerospace to provide more or better informations.

Nothing could be further from the truth, if they don't want to explain *everything* about how it works I'm really ok with that, if it's partly a secret that's understandable - they should expect some people will not believe in it.. There are concepts you just couldn't guess at as an individual with much chance of success, this could be one of those. But from my point of view, even if they have a very clever idea, that still doesn't mean it is bound to work.


Ekkehard Augustin wrote:
I didn't know that there is that much dissatisfaction regarding JP Aerospace's information policy.

Though I wouldn't describe the general situation as dissatisfaction, there are people who would like to know more. There are certainly quite a lot of people who are sceptical about this, I didn't realize there weren't so many of them here. Anyway, I thought my scepticism would be taken at face value, the idea of an argument in or close to JP's forum seems to be in somewhat bad taste to me.


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Post    Posted on: Tue Sep 06, 2005 1:04 am
ATO is a very interesting concept anyway when you get down to it. One of the very attractive points about this concept of achieving orbit is the stage approach. Assuming that it does work (and I certainly can't say one way or the other) then it would appear to be possibly the safest way to get into orbit.

Another observation that I'd like to make is the amount of work going into the concept. JP have invested a lot of time and effort and money into real hardware, not just drawings and reports, and so I say good on them, best of luck and good riddance to the doubters. Scaled, no doubt, were advised how impossible their efforts would be as well yet they managed to achieve their goal and they used a 'radical' new approach to the problem of reducing entry speed. Of course once the method was exposed everyone agreed that they could have thought of that.

Another thought - even if they only get to the DSS stage, then I would think that there's a whole world of opportunity for lauching conventional ships from that stage. And don't forget the tourism aspects of the DSS. The view from 140,000 feet would certainly be a puller not to mention a leisurly cruise up to the station and then back down.

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Post    Posted on: Tue Sep 06, 2005 1:45 am
I have just one question for nihiladrem,
you said;

[ Decades of Hypersonic research show that it would be extraordinarily optimistic to think this drag could be a tenth of the weight of the vehicle in a vacuum for most of this time.]

wanna explain where the drag comes from in a vacuum, because i cant see the issue with an airship going fast enough under ION propulsion when it is out of any discernable atmosphere?

Andrew


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Post    Posted on: Tue Sep 06, 2005 12:26 pm
I can't seriously believe there were all that many people saying what Scaled were doing was impossible, at least not genuinely meaning it unless they were hopelessly uninformed. Rutan was expected to win the X-Prize a few months after he announced taking part - even before he was known to be competing.
Scaled were doing things a little unconventionally but even at first glance you could see it was clearly not impossible, there might be some difficulties but impossibility requires several whole new levels of wrongness. I can't flatly state ATO is impossible, everything I know tells me that even with the most wildly optimistic assumptions it doesn't seem realistic to me unless I'm missing something crucial. The Dark Sky Station looks like a good idea, I hope they can pull it off.

Andrew, 'Weight in a vacuum' refers to the true weight of the vehicle without any reduction due to buoyancy. Most of the time this is close to the weight at elevated altitude which must be supported aerodynamically as additional lift due to buoyancy is so small. Without this lift the vehicle would drop back to near 60km. This lift must be produced almost the whole time while trying to reach orbit at the expense of drag. The ion engines are operating somewhere above 60km, were not told explicitly at what point because other electrical engines like a ducted propeller might be working at lower speeds. But 25Km is around the maximum jump in altitude you are likely to get with ducted engines. For a vehicle that only has low thrust, the only time drag stops being a large force while in motion is when the centrifugal force is very close to the whole weight of the vechicle. That only happens once you have practically reached orbital speed.

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Post    Posted on: Tue Sep 06, 2005 12:51 pm
Hello, nihiladrem,

I still don't see why an ion drive can't have similar results for a vehicle as it would have in orbit.

In orbit an ion drive causes the vehicle to climb to a higher orbit if it gives accelerating impulse while it causes the vehicle to go down to a lower orbit if it gives decelerating impulse.

At and above 60 km altitude the pressure and the density of air are more similar to the conditions in orbit in space than to the conditions between 0 and 30 km altitude. So acceleration by an ion engine should have results more similar to those in orbit than to those at or below 30 km altitude. This means that the lift got by wings will be less than at or below 30 km while the lift got by accelerating impulse should be more than at or below 30 km altitude. This should be valid for decelerating impulse too.

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. But the impulses got by a permanently working ion engine can make the vehicle to go up - there is an open question I forgot to list yesterday: What is the direction the impulse got by the ion engine will go to? Parallel to Earth's surface? Or will it go diagonally away from the surface to leave into space or diagonally own to the surface at reentry? If there is such a diagonality then the angle could be very small - for example. So the list of parameters unknown has become a row longer.

The open question allow for a large amount of combinations of numbers most of which may lead to a failure while a few lead to success. This means that each specific combination used for calculations may be far from the numbers valid in JP Aeropsace's project. There is no base to predict failure or impossibility - because there are too much degrees of freedom.



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



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