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Doubts If ATO will be working

Posted by: Ekkehard Augustin - Sun Sep 04, 2005 11:37 am
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Doubts If ATO will be working 
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Post Doubts If ATO will be working   Posted on: Sun Sep 04, 2005 11:37 am
Hello, jpowell,

in the Technology section there is the thread [url=http://www.xprizenews.org/forum/viewtopic.php?t=1426]
Brilliant idea for re-entry [/url].

In that thread serious doubts have been expressed regarding the ATO from Friday, 2nd of Septmber 2005 to Sunday 4rth of September if the ATO would work.

The doubts say that there is no sufficient buoyancy to lift the ATO from the DSS at 42 km to 60 km and that it is possible to go up to orbit by using electric drives beginning at 60 km altitude.

This part of that thread has to do with slow days long reentry the ATO would be capable of in the undertsanding of the initiator of that thread and me myself. The ATO is considered to be a supersonic airplane which can't get lift or sufficient lift to do a days long renetry. I myself mentioned that the large wings of the ATO could be filled by Helium or may contain a vacuum which other vehicles don't as far as I know. I may be wrong in thinking that this provides lift to the ATo at all or at reentry but I think that you have your reasons why you trust ATO will work, use buoyancy from 42 km to 60 km, enter space and orbit by electric drives and can retrun to DSS slowly and safely at 42 km altitude.

How does it work really?



Dipl.-Volkswirt (bdvb) Augustin (Political Economist)[/url]


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Post Re: Doubts If ATO will be working   Posted on: Thu Sep 15, 2005 9:23 pm
Ekkehard Augustin wrote:
The doubts say that there is no sufficient buoyancy to lift the ATO from the DSS at 42 km to 60 km and that it is [im]possible to go up to orbit by using electric drives beginning at 60 km altitude.

This part of that thread has to do with slow days long reentry the ATO would be capable of in the undertsanding of the initiator of that thread and me myself. The ATO is considered to be a supersonic airplane which can't get lift or sufficient lift to do a days long renetry. I myself mentioned that the large wings of the ATO could be filled by Helium or may contain a vacuum which other vehicles don't as far as I know. I may be wrong in thinking that this provides lift to the ATo at all or at reentry but I think that you have your reasons why you trust ATO will work, use buoyancy from 42 km to 60 km, enter space and orbit by electric drives and can retrun to DSS slowly and safely at 42 km altitude.


My two cents:

I love the ATO concept. Analysing it has been great practice for me in my studies as an engineering student. And I can tell you that even though I still have serious doubts about its practicality, none of those doubts still center around whether it can get the bouyancy to go from 42km to 60km or worries about its supposed lift-to-drag ratio.

The "huge balute" re-entry concept has been proposed before, independently of JP Aerospace. For example, look at the Archimedes Project.

And development is still ongoing.

Quote:
How does it work really?


John Powell has repeatedly made it clear that he isn't going to tell us.

So, do the math and find out! 8)

If you've had high school physics, you're probably at least as capable as I was when I first got curious about the idea. Don't just look at the equations or plug in a few numbers - try to derive them.

As a good start, get a dictionary of aeronautical engineering jargon (online or at your local library) and look up the difference between the terms "aerodynamic vehicle" and "non-aerodynamic vehicle". (Forget "poor aerodynamics"; look for "non-aerodynamics".) Then go find the derivation of lift-drag ratio and actually try to replicate it using the characteristics of a non-aerodynamic vehicle.

Eventually, you will realize why the derivation won't work, and you'll get your first glimpse of why an ATO possibly could. :wink:

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Post    Posted on: Fri Sep 16, 2005 6:54 am
Hello, C M Edwards,

I personally don't share the doubts about JP Aerospace's concept. You say
Quote:
Don't just look at the equations or plug in a few numbers - try to derive them.
- and that's what I am thinking too.

I suppose that JP Aerospace are doing so - while the doubting ones perhaps don't - and that to do so is one requirement to be able to achieve innovations and inventions.

The reason to initiate this thread were doubts by others who discussed JP Aerospace based on those doubts without at all trying to ask John Powell and thus ignoring him and his company - this thread is meant to repair this.

So Thank You Very Much for your answer.

I want to continue and to keep the question to John Powell - simply to keep the chance to get an answer open. To get an answer is less probable if nobody asks - to ask increases the chances to get an answer.



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


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Post    Posted on: Sat Sep 17, 2005 12:05 am
It's a balancing act, what to give out and what to hold back. On one end is Scaled that don't give any technical details, (it's still hard to find out the thrust of Spaceship One), and on the other end is John Carmack who's open about everything.

Where we've settled on is showing what we've done and what were going to do but not how it works.

We even have competition now, the Russian program (and a few others) on the ATO side and about 50 companies on the airship side. We want to keep the community informed but we don't want to get burned in the process.

JP


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Post    Posted on: Sat Sep 17, 2005 2:38 pm
jpowell wrote:
We even have competition now, the Russian program (and a few others) on the ATO side and about 50 companies on the airship side. We want to keep the community informed but we don't want to get burned in the process.

JP


If AKC's any indication, you may be overestimating some of your competition. :?

Better safe than sorry, though.

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Post    Posted on: Sat Sep 17, 2005 7:47 pm
Hmm that sounds like a physics problem worthy of someone better than me. I'd probably waste my time on it. In fact, I'm not really sure what your discussion of the subject means. But it seems that the real question is if the ATO can be neutrally buoyant at such an altitude that it's thrusters can get up significant orbital velocity despite the atmospheric drag. If the ship can go fast enough, then the centrifugal force on it will begin to lift it above it's bouyancy level, which will allow the ship to go faster (due to lower drag), and the ship will be home free. (I suppose this also depends on the ISP and thrust levels of the ship's engines. I assume they will be some sort of rocket engines or ion engines, rather than propeller or jet engines due to the thin atmosphere. But I could be wrong.) (Oh, another thing I assume is that there won't be any aerodynamic lift or vertical component to the engine thrust. It just doesn't seem like a useful strategy for a balloon.)

At any rate, I might begin to get a grip on the math if I tried, but I doubt I will try.


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Post Propulsion   Posted on: Sun Sep 18, 2005 5:52 am
LukeSkywalker wrote:
I assume they will be some sort of rocket engines or ion engines, rather than propeller or jet engines due to the thin atmosphere. But I could be wrong.) .


You're right, they use Ion engines, it says so on a pdf on their website. And also the engines are pointed horixontally.

All you really need are the concepts. Everything else can be proven logiically. I've learned through experience that it's amazing what you can discover when you don't underestimate yourself.


Question for John Powell: What's the timeline 'till orbit? Or is it allready on the website?

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Post    Posted on: Sun Sep 18, 2005 3:16 pm
The PDF describes "an airship/dynamic vehicle" which "dynamically climbs. Over several days it reaches orbital velocity". They do not use the word "lift". There is also a picture of the orbital vehicle with the caption, "Five day climb to orbit". The PDF also mentions "solar/electric" propulsion but only mentions "ion engine" once where it says, "The ion engine 120,000 foot flight test for the orbital airship will be flown in the next five months". I believe that this PDF is already over 5 months old, so either the schedule has slipped or the test was done in secret.


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Post    Posted on: Sun Sep 18, 2005 4:07 pm
From what I've gathered conventional ion engines are not the only nor even the first choice for ATO. Presumably whatever could replace them would still be an electric engine.


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Post    Posted on: Sun Sep 18, 2005 9:44 pm
LukeSkywalker wrote:
Hmm that sounds like a physics problem worthy of someone better than me. I'd probably waste my time on it. In fact, I'm not really sure what your discussion of the subject means. ...

At any rate, I might begin to get a grip on the math if I tried, but I doubt I will try.


That's a pity. You seem to have a lot of legitimate questions about this concept, and no other legitimate way to get answers.

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Post    Posted on: Thu Sep 22, 2005 2:01 am
Well, I stay pretty busy, that's part of the problem. I'm just studying calculus 1 right now, as a senior in highschool, so my skillz aren't complete. But really, I have no idea what you were getting at with that non-aerodynamic business. I suppose I ought to take your advice and look it up. But saying that failing to derive the equation is going to show how the concept works, you sort of lost me on that. Were you trying to say that you can show that aerodynamic lift wouldn't be useable, and that's why the ATO won't utilize it? Or am I missing the point?


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Post    Posted on: Thu Sep 22, 2005 6:46 pm
The only way I know of to get an airship in space is to fly it above as much drag as you could--and have it catch some kind of tether of a larger object in space. The so called "Single Stage To Tether" concepts do not work well with mini spaceplanes, where an airship has more surface area to snag lines--like an upside down NAVY carrier with its hooks up top.

The airship would have to be very strong to survive--either that or the tehter would have some give to it to allow more steady acceleration to and from orbit.

A Captured asteroid--or even an asteroid on a near pass might be enough to do a clean and jerk with tethers that do not have to be as long as 22,500-60,000 miles.

A NEO within 1,000 miles allows for a modest cable. What is more--is that a large NEO could yank a large floating/flying platform right out of the water (or some other large base) and as it accelerated the asteroid slows. Therefore both go into orbit and they spin like a cycler.

All you need is to build a base on the ground, a few thousand miles of tether, and a small net with pitons to snag the asteroid.


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Post    Posted on: Thu Sep 22, 2005 7:34 pm
I wouldn't count on catching any asteroids, they'd probably destroy whatever you are using to catch them, if you ever found any big enough to be useful. THe DSS as a taking-off point for a spinning tether isn't half-bad though.


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Post    Posted on: Wed Oct 12, 2005 4:26 pm
Thank you. I am wondering about beamed energy propuslion for the concept. If an ion wind effect can get you high enough, how much energy will be needed to push the craft as it would a solar sail. Also-if there are these magnetic vortex phenom--could it be possible to get a craft in space without the need fro great speed--perhaps getting it entrined inside some type of loop.

If it gets high enough, sunlight may be enough to keep it aloft as a statite--and it will be high enough for beamed energy to supply the ion drive with enough power for Earth escape.

Upon return, it reverses the process.


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Post    Posted on: Wed Nov 09, 2005 8:15 pm
Time to resurrect an old thread :). I read the other thread in the Technology section some time ago (and this one as well), and I found the arguments unconvincing. Most specifically, nobody gave any numbers, it was all a lot of magic handwaving and proof-by-authority. I'm not a rocket scientist, but the question of whether an airship can get to 60 km on bouyancy should be solvable even by a lowly computer science student such as myself I figured. And I can speculate on the rest :).

First, some data. I looked up atmospheric density and temperature as a function of altitude. Second, the heterosphere starts at 100 km according to Wikipedia, so at these lower altitudes we are still dealing with an oxygen/nitrogen atmosphere, that is, air. The average molecular weight of air is 29 g/mol. Third I assume the airship is filled with helium, which has a molecular weight of 4.0 g/mol, at zero overpressure (like in the Away 28 vehicle) and at the same temperature as the environment. Finally, let's set the weight of the whole contraption to 100 ton, or 10^8 kg.

Airships rise because they are lighter than air. According to Archimedes' Law, the upward force is equal to the weight of the displaced mass of air. To lift 10^5 kg, we need to displace 10^5 kg of air, which at 29 g/mol equals 3.4 * 10^6 mol.

Now, according to the image linked above, at 64 km air pressure is about 0.1 millibar, which equals 10 Pa. Temperature is about 240 K. According to the universal gas law the volume V then becomes

V = n * R * T / P

with n the amount of air, R the universal gas constant, T the temperature and P the pressure. Plugging in the values we get

V = 3.4 * 10^6 mol * 8.3114 J/mol/K * 240 K / 10 Pa = 6.7 * 10^8 m^3

That would be a spherical balloon with a diameter of about 1.1 km. Alternatively, two cylinders of about 450m diameter and 2100m long would also do. That looks like the images of the ATO in the PDF on the JPA website. It would also be about 2000m (6000 feet) long, but the cylinders would be much thicker than in the images. Of course, we do not know whether the images show a 100 ton design.

Now, assuming the whole thing is filled with helium at zero overpressure and ambient temperature, we need 3.4 * 10^6 mol * 4.0 g/mol = 14 tons of helium. At 140000 feet (a little over 42 km), where the DSS is from which ATO leaves, air pressure is about 2.5 millibar, or 25 times as much as at 64 km, and ATOs volume would be 25 times less. Perhaps the arms will collapse to reduce the volume at lower altitutes? On the other hand, the images don't show this (perhaps intentionally though).

At any rate, we're up to 64 km using buoyancy alone, and we haven't even used solar heating. Now we still need to get into orbit. I'm moving onto thin ice now, because I don't really know much about this part. But at least we can try something.

I don't know enough about hypersonic vehicles to think about drag and lift, but I'm wondering whether, if there were no air resistance, it would be possible to accelerate a 100 ton vehicle from a speed of 0 (relative to the earth) and 60 km into orbit, using ion engines and a week or so of time. JP talks about several days, so let's take a week and give him the benefit of the doubt.

Let's say we want to end up at 150 km and 7800 km/s. That's about the absolute minimum for LEO.You get about 450 m/s for free from earth rotation, so that leaves about 7350 m/s, and you need another 90 km of altitude, which is another 1350 m/s (or a bit less) equivalent for a total of 8700 m/s. Ion engines use relatively little fuel, so I'll ignore the difference in mass between fully loaded tanks and empty tanks.

Now, using simple Newtonian mechanics (when the only tool you have is a hammer...:)) we get

F * dt = m * dv
or
F = m * dv / dt

With m = 10^5 kg, dv = 8.7 * 10^3 m/s, dt = 6.0 * 10^5s (almost exactly a week) we get F = 1.2 kN. If this post is correct, that requires 1.2 kN * 2.75 * 10^4 W/N = 34 MW. That is a lot of energy. Then again, we have a huge vehicle, so plenty of room for solar cells. Amorphous thin-film solar cells do about 60 W/m^2 so we'd need 34 MW / 60W/m^2 = 5.7 * 10^5 m^2 of cells.That will easily fit onto our 2 km-long cylinders. I don't want to know what it's going to cost though :).

That sounds nice, but I'm skeptical about drag and lift during acceleration. The X-43 flew at about 30 km, where the air is about 100 times denser than at 64 km, but the ATO is big. Really big. Really really big. I just don't see how ion drives are going to push it through that.

Another option would be to fill the thing with hydrogen rather than helium, and to add more than you really need for a zero-overpressure balloon. During the ascent to 60 km, use solar power to liquify the part of the hydrogen from the balloon that you don't need anymore, and oxygen from the atmosphere (is that realistic? The air is awfully thin up there). After arriving at 60 km, light your H2/O2 rocket to get into orbit. The problem with that is that it requires almost as much fuel as an ordinary rocket would. It's also not consistent with going into orbit over the course of several days.

Other exotic option: this thing is 2 km long. Could you put a linear particle accelerator along it, to accelerate ions to much higher speeds than an ion engine can achieve? And if you could,could you get the mass-flow rate high enough for it to be useful? Could that give enough thrust to accelerate at a relatively low altitude, so you still have a lot of buoyancy, and then make a steep jump into orbit?


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