Author Topic: Upper Stratosphere "near-space" station for "space" tourism?  (Read 27792 times)

Offline ChrisWilson68

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The JP crowd seems to be in denial about basic physics.  You simply cannot have lift from the atmosphere without also having drag, whether that lift comes from buoyancy or aerodynamics.

Go up where the atmosphere is thin and you can have lower drag, but that means lower lift from buoyancy or aerodynamics.  If you add a large surface area, you can get back lift, but drag comes right back along with it.  It's those same gas molecules bouncing off your craft that give both lift and drag.

Who said otherwise?


Anyone who takes the airship-to-orbit concept seriously says otherwise.  The ion engines that gradually accelerate the airship to orbit are supposed to overcome drag through high mach numbers while gravity is being countered by a combination of buoyancy and aerodynamic lift.

Offline QuantumG

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Anyone who takes the airship-to-orbit concept seriously says otherwise.  The ion engines that gradually accelerate the airship to orbit are supposed to overcome drag through high mach numbers while gravity is being countered by a combination of buoyancy and aerodynamic lift.

I'm sorry, but your point is still alluding me. Rocket engines regularly provide sufficient thrust to overcome drag.. that's kinda what they're for.

Human spaceflight is basically just LARPing now.

Offline R7

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[I'm sorry, but your point is still alluding me. Rocket engines regularly provide sufficient thrust to overcome drag.. that's kinda what they're for.

They do, and are, but they also require copious amounts of propellant to do that and they propel slim aerodynamic rigid bodies instead of gargantuan blimps.

May I offer some simple math to further illustrate the challenge here. Have not seen exact schematics of the ATO ship anywhere, but the JPA pdf offers imagery and information (length of the ship 6000ft) from which some crude assumptions can be made (in the attached image).

The pdf says ATO uses buoyancy to climb at 200kft. According to 1976 Standard Atmosphere the air density at that height is 0.000254864 kg/m3

Let's simplify ATO volume calculation by assuming that it is roughly the same as cylinder whose length is twice the diagonal 1.75km line and diameter same as ATO's. So volume is

V = pi * 732 * 1750 * 2 = ~59 million cubic meters, quite a blimp

How much lift force you get from that with buoyancy at 200kft? Let's assume the airship skin and structure is made of 187Nomassnium and is filled with vacuum. AIUI per Archimedes the theoretical ultimate lift force is equal to the weight of displaced fluid

59,000,000m3 * 0.000254864kg/m3 = ~15,000kg

15 tons for airship structure and payload  :-\

How is the drag at that height for such vehicle? Let's use the drag equation with frontal reference area estimated by the 1.33km line. What's the actual drag coefficient for ATO's geometry is beyond me but I SWAG it is somewhere between ball (0.47) and streamlined body (0.05). We'll try relatively good 0.1, small initial velocity of 100m/s and see how that flies.

Fdrag  = 0.5 * 0.000254864kg/m3 * (100m/s)2 * 0.1 * 146m*1330m = ~25,000N

Begin to see the problem here? Only 15 tons of mass to distribute to create the behemoth, and requirement is for 25kN thrust just to get barely moving. Drag is proportional to the square of velocity so at 500m/s you need 625kN and 1000m/s 2.5MN. The thrust requirements are nowhere near current SEP SoA and chemicals are pretty much off the table as too massive.

Did not touch aerodynamic lift, what's the L/D coefficient of such geometry?

AD·ASTRA·ASTRORVM·GRATIA

Offline FutureSpaceTourist

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Here's what JP Aerospace say about drag: http://nextbigfuture.com/2011/10/floating-airship-could-radically-reduce.html

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The 3 remaining potential showstoppers:

1. Scaling active drag reduction.

Active hypersonic drag reduction has been demonstrated in the lab for 30 years. Can we take it out in the real world and scale it up to the airship to orbit requirement?

[...]

So they're very aware of the problem. From other interviews etc I've seen, they think they know what approach(es) to use to solve it but are a long way currently from proving it'll work/scale-up.

Offline gbaikie

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"The final version of JP Aerospace’s first-stage Ascender airship will be among the largest airships ever constructed, with an expected volume (57 million cubic feet) greater than seven times that of the Hindenburg."
http://en.wikipedia.org/wiki/Orbital_airship

There would be quite difference between 59 million cubic meters and 57 million cubic feet

Anyways, what about something like 100 meters in diameter 1 km long.
That's is 7.85 million cubic meters.
Or about 257 million cubic feet.

Such a thing would be hard to deploy. Maybe it would deployed in building which is 110 to 120 meters in diameter cylinder, say 100 meters high. Though one might make it much shorter, say 20 meters tall [6 stories high]. And one want very still air deploying it maybe elevation of the mile high city of Denver type elevation. So selecting site which normally has low wind conditions.
So such building with larger than football field "roof" [lacking one or having a temporary one] is pretty expensive. To make a smaller building, one could balloon diameter expand as it gains altitude [as it typical of such balloon launches].
So, perhaps have blimp like inner structure- a balloon within a balloon.
The outer balloon is limited in that it just displaces atmosphere and inner balloon has such strength to enable it take loads.
So inner one could be say 50 meter in diameter, and it is inflated to be blimp-like or rigid and the 25 meter donut surrounding it, only gets inflated at a higher elevation.
This way instead 110 meter diameter building, one limit it to say 60 meter diameter building [still quite large but smaller than football stadium. One might rent such an existing building- if in a good location].

continuing:
So the "inner tube" has everything that one could call a "hard point", such as valves which open. Also it could sectional and accessible. Whereas the donut is just like a very high altitude balloon- minimal load bearing and continuous and not sectional. Though it could be- it could be balloons attached to inner tube and have hundreds of them. This could be easier to deploy [perhaps].
So inner tube could have 50 meters section per the 1 km- so, 20 sections. So first section could inflated and be rigid, and then you inflate lower sections, having entire balloon rises until has enough buoyancy to lift entire balloon structure, and continuing to inflate all the inner tube and the outer donuts as it gains in elevation. 

Edit, continuing:
So maybe the limit of a balloon launch is 1 km in height, or 500 meters or whatever, one could have two or more dock them together. So one could
have very tall structures. So say 5 km by 100 meters in diameter. And connection being inner tube to inner tube. One also remove the sections
every 50 meters so it's continuous open space, which was 1 to 5 km and 50 meters in diameter. And do weird things like have elevators/air tube lifts inside this space, allowing the transporting 1 or 5 km upwards.
So in other words each 50 section is a "hard point" which can start as structural support to allow pressurization [low pressure, but still have quite a load] and once at elevation one doesn't need such pressurization or these membranes separating the space. So you could cut off the 50 meter diameter part and leave the "hard point" ring it was attached to. And attach other stuff to these hard points.
So such "hard points" would be made something strong per it's weight- plastics or titanium alloys and will have considerable weight regardless of what made of, but the inner tube itself would be stronger material than donut, so it might be that hard point is around same mass as 10 meter length/height of this inner tube blimp. Or perhaps it's possible that removed 50 meter diameter sectional membrane is around it's mass/weight.
But in any case it has to be supported, and it's seems it would be tensional in nature- or compressional is implausible. One will be using helium or hydrogen gas and it will be warmer than atmosphere and around same pressure [a vacuum {less than 1 psi}].
But with such large structures even near perfect vacuum condition the gas has some mass, but mass of structure and mass of gas must be equal to the displaced volume of very low density gas of the atmosphere.
And what I am talking about must have less mass at the top than at the bottom [gravity gradient keeps to vertical]. But whole purpose is to have some payload, so having most payload/structural mass at bottom, "resolves this". But if have body of air in gravity, there will be more gas density at bottom than at the top- even if all the gas temperature is the same- and won't be- hot air rises.
Good news about hot air, is that in near vacuum one has very little convection losses of heat- radiant heat loss would be more significant and one would use reflective materials to lower such losses. Anyways lots of details to deal with in terms of thermal control. Of course I am kind of focus on inner tube and most lift and thermal area will be related to donut part of balloon. If donut is comprised of many smaller balloon these balloon can attached to the 50 meter sectional part of inner tube,
and this gives vector of the tensional force. It's not so much vertical as somewhat sideways. I mean it's not combination of vertical loads, but rather each section is being supported individually.

Anyways, so one 100 meter by 1 km gives 7.85 million cubic meters
and if had it 5 km it's roughly  7.85 million times 5 or 39.25 million cubic meter, which less than "59 million cubic meters" number, so if asume 15 tons per 59 million cubic meters at 200,000 ft is correct. I have around 50% less payload or less than 8 tons. So according given reference at
150000 feet there is 0.00170221 rather than the 0.000254864 of 200,000 feet. So roughly 6 times more lift. And 5 km is 16400 feet.
So, I guess one probably shouldn't go as high as 200,000 feet.
« Last Edit: 06/18/2013 04:03 pm by gbaikie »

Offline ChrisWilson68

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Anyone who takes the airship-to-orbit concept seriously says otherwise.  The ion engines that gradually accelerate the airship to orbit are supposed to overcome drag through high mach numbers while gravity is being countered by a combination of buoyancy and aerodynamic lift.

I'm sorry, but your point is still alluding me. Rocket engines regularly provide sufficient thrust to overcome drag.. that's kinda what they're for.



Yes, and the rocket engines have to expend some of their thrust to overcome gravity losses.  For that reason, high thrust is needed -- they need to quickly ramp up to orbital speed because every second along the way they're expending energy fighting gravity.

The benefit of the airship-to-orbit concept is supposed to be that a combination of buoyancy and aerodynamic lift counter most of the gravity loss so the engines can use low-thrust, high efficiency engines, such as ion thrusters.

My point is that if the airships are fighting gravity with buoyancy and/or aerodynamic lift, they will inevitably have much, much higher drag than today's launchers, which go up out of most of the atmosphere to avoid drag before picking up most of their speed.

Offline QuantumG

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Yes, and the rocket engines have to expend some of their thrust to overcome gravity losses.  For that reason, high thrust is needed -- they need to quickly ramp up to orbital speed because every second along the way they're expending energy fighting gravity.

The benefit of the airship-to-orbit concept is supposed to be that a combination of buoyancy and aerodynamic lift counter most of the gravity loss so the engines can use low-thrust, high efficiency engines, such as ion thrusters.

My point is that if the airships are fighting gravity with buoyancy and/or aerodynamic lift, they will inevitably have much, much higher drag than today's launchers, which go up out of most of the atmosphere to avoid drag before picking up most of their speed.

Yep, it's definitely a tradeoff. JP seems to think that's a workable tradeoff, but he doesn't show his work (or hasn't even figured out how to work it yet) so we can't evaluate whether or not his solution will work.

That's a far cry from your original claim of being "in denial about basic physics".

In the mean time he's flying student experiments to high altitude, for free. What's not to like?
Human spaceflight is basically just LARPing now.

Offline Vultur

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A few points:

-Ascender is not the same thing as the orbital airship. In the proposed system, Ascender goes from Earth surface to the Dark Sky Station, and the orbital airship goes from the Dark Sky Station to orbit. So the wildly different volumes make sense, since they're totally different vehicles.

-I thought by 200k ft, it was supposed to be supporting itself by aerodynamic + buoyant lift? So the mass could be greater than the ~15 metric tons allowed by buoyant lift alone... right?

However, I still don't think it can possibly work. Even if they have more than 15 metric tons to work with, it probably isn't enough.

And I severely doubt ion engines can give enough thrust to deal with the drag on a vehicle that size even at that altitude.

And can it possibly deal with the heating induced by moving at near orbital velocities even through that sparse atmosphere? It can't really have any kind of shielding at all, given the weight constraints...

Offline QuantumG

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However, I still don't think it can possibly work. Even if they have more than 15 metric tons to work with, it probably isn't enough.

Which is no doubt why you're not working on it.

Quote
And I severely doubt ion engines can give enough thrust to deal with the drag on a vehicle that size even at that altitude.

Who said anything about ion engines?

Quote
And can it possibly deal with the heating induced by moving at near orbital velocities even through that sparse atmosphere? It can't really have any kind of shielding at all, given the weight constraints...

Now you're asking a question that someone could actually answer.. has there been any big hypersonic Mylar balloons flown in the upper atmosphere? Well yeah, with significant challenges overcome.. http://history.nasa.gov/SP-4308/ch6.htm

That doesn't mean JP Aerospace can do it, but nothing will.. until they do it.
Human spaceflight is basically just LARPing now.

Offline ChrisWilson68

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Yes, and the rocket engines have to expend some of their thrust to overcome gravity losses.  For that reason, high thrust is needed -- they need to quickly ramp up to orbital speed because every second along the way they're expending energy fighting gravity.

The benefit of the airship-to-orbit concept is supposed to be that a combination of buoyancy and aerodynamic lift counter most of the gravity loss so the engines can use low-thrust, high efficiency engines, such as ion thrusters.

My point is that if the airships are fighting gravity with buoyancy and/or aerodynamic lift, they will inevitably have much, much higher drag than today's launchers, which go up out of most of the atmosphere to avoid drag before picking up most of their speed.

Yep, it's definitely a tradeoff. JP seems to think that's a workable tradeoff, but he doesn't show his work (or hasn't even figured out how to work it yet) so we can't evaluate whether or not his solution will work.

That's a far cry from your original claim of being "in denial about basic physics".

I stand by my claim that they're in denial of basic physics.  If they're getting enough lift from either buoyancy and/or aerodynamics to have any significant affect on gravity losses, the drag will be overwhelming.  There's no way their low-thrust engines will get them going even a few hundred mph with that kind of drag, let alone to orbital speed.  Buoyancy comes from having enough gas molecules striking your vehicle to prop it up.  So does aerodynamic lift.  Those same gas molecules cause drag.

Offline ChrisWilson68

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Quote
And I severely doubt ion engines can give enough thrust to deal with the drag on a vehicle that size even at that altitude.

Who said anything about ion engines?

JP Aerospace says "electric propulsion":

http://www.jpaerospace.com/atohandout.pdf

Quote
The third part of the architecture is an airship/dynamic vehicle that flies directly to orbit. In order to utilize the few
molecules of gas at extreme altitudes, this craft is big. The initial test vehicle is 6,000 feet (over a mile) long. The
airship uses buoyancy to climb to 200,000 feet. From there it uses electric propulsion to slowly accelerate.

Note that it says "electric propulsion" and "slowly accelerate".  The obvious interpretation of that is an ion engine, with low thrust but high efficiency.

They could be leaving open to tethers, too.  That would push against the Earth's magnetic field and it's another form of electric propulsion.  But it has the same key properties as ion engines: high efficiency but low thrust.

I think all the points about ion engines apply to any low-thrust electric engine.

Quote
And can it possibly deal with the heating induced by moving at near orbital velocities even through that sparse atmosphere? It can't really have any kind of shielding at all, given the weight constraints...

Now you're asking a question that someone could actually answer.. has there been any big hypersonic Mylar balloons flown in the upper atmosphere? Well yeah, with significant challenges overcome.. http://history.nasa.gov/SP-4308/ch6.htm

That doesn't mean JP Aerospace can do it, but nothing will.. until they do it.

The link you gave is about project Echo.  That was an inflatable satellite system.  It was launched deflated and only inflated once in orbit, and out of essentially all atmospheric drag.  That's not really a hypersonic balloon.

Offline QuantumG

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I think all the points about ion engines apply to any low-thrust electric engine.

Not at all.. ever heard of plasma thrusters?

Quote
The link you gave is about project Echo.  That was an inflatable satellite system.  It was launched deflated and only inflated once in orbit, and out of essentially all atmospheric drag.  That's not really a hypersonic balloon.

You actually have to read the link.. there was a whole test program which involved deployments in the upper atmosphere.

Human spaceflight is basically just LARPing now.

Offline FutureSpaceTourist

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I stand by my claim that they're in denial of basic physics.

Lots of people said that about JPA's claim that they could use propellers at 100k ft altitudes. Then they demonstrated propellers working at c 100k ft! Of course they don't break the laws of physics, people had misunderstood/mis-applied their knowledge to what JPA were doing.

There are plenty of crackpots who propose perpetual motion machnes etc. But given what they've achieved I give JPA a lot of credit that they're not crackpots. They clearly understand about drag and are not in denial about it. They may be wrong about whether they can get the technology to work, or even if the technology in principle gives them the drag reductions they need, but it seems pretty unlikely to me that they've missed a basic physics gotcha.

Offline FutureSpaceTourist

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http://nextbigfuture.com/2011/10/floating-airship-could-radically-reduce.html

Quote
Question: For the airship going to orbit, would the engines be chemical, ion, or some sort of hybrid?
The engines would be a hybrid, employing both ion thrusters and chemical propulsion. At certain points we will be using ion thrust, and at other points we will be using chemical. There is a tradeoff between efficiency and time to orbit, the more efficient you are, the longer it takes to achieve orbital velocity. Rockets are measured in terms of specific impulse, which provides an indication of the efficiency of the system, with higher being better. The specific impulse of our hybrid is about 1100, which compares to about 450 for chemical rockets and 30,000 for ion thrusters. So this hybrid can either be viewed as being the most efficient chemical rocket ever, or the least efficient ion rocket.

Question: So this rocket is half ion and half chemical?
Yes, it is almost always half and half. The final insertion is all chemical. The chemical rocket will use wax/nitrous oxide. That is what we are currently testing. With sufficient R&D, I am confident that we could get a hybrid engine up to 2,000 specific impulse. That would obviously have a beneficial effect on payload capacity, perhaps as much as a quarter increase in payload.

Offline ChrisWilson68

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I think all the points about ion engines apply to any low-thrust electric engine.

Not at all.. ever heard of plasma thrusters?

Plasma thrusters are a subset of ion thrusters.

Quote
The link you gave is about project Echo.  That was an inflatable satellite system.  It was launched deflated and only inflated once in orbit, and out of essentially all atmospheric drag.  That's not really a hypersonic balloon.

You actually have to read the link.. there was a whole test program which involved deployments in the upper atmosphere.

Yeah, in the upper atmosphere in the same sense the ISS is in the upper atmosphere.  The ISS needs periodic reboosting because of the drag of the tiny bit of atmosphere up there.

But the ISS is also considered to be in orbit.  All the balloon deployments mentioned in the link involved first putting the balloon into orbit, then inflating it.  A part of the motivation was to watch the decay of the orbit of the balloon satellites to learn about drag in that region.

But I still think it's not really accurate to call that "big hypersonic Mylar balloons flown in the upper atmosphere" any more than it would be accurate to call the ISS a hypersonic vehicle.  People generally don't consider objects in orbit to be engaging in hypersonic travel even though there is a small amount of atmosphere that is slowly decaying their orbits.

Offline ChrisWilson68

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I stand by my claim that they're in denial of basic physics.

Lots of people said that about JPA's claim that they could use propellers at 100k ft altitudes. Then they demonstrated propellers working at c 100k ft! Of course they don't break the laws of physics, people had misunderstood/mis-applied their knowledge to what JPA were doing.

Whoever said propellers couldn't be used at 100k ft was clearly wrong.

But I didn't say that.  And the fact that someone else was wrong in criticizing claim A really has no logical bearing on my criticism of claim B.

There are plenty of crackpots who propose perpetual motion machnes etc. But given what they've achieved I give JPA a lot of credit that they're not crackpots. They clearly understand about drag and are not in denial about it. They may be wrong about whether they can get the technology to work, or even if the technology in principle gives them the drag reductions they need, but it seems pretty unlikely to me that they've missed a basic physics gotcha.

You think they have a secret technology that they won't tell anyone about and have never demonstrated to anyone that would re-write every basic textbook on drag?  Good luck with that.

Offline FutureSpaceTourist

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And the fact that someone else was wrong in criticizing claim A really has no logical bearing on my criticism of claim B.
 

It does when criticisms of both claim A and claim B imply the same claim C (that JPA don't understand basic physics). I was giving counter evidence to claim C.

As I'm sure you're aware, by the law of logic known as the contra-positive that means criticisms of both claims A & B are invalid. :)

To re-iterate, I'm not saying it'll work - I'm saying they're more competent than you appear to give them credit for.

Edit: fixed typos and improved wording
« Last Edit: 06/19/2013 06:52 am by FutureSpaceTourist »

Offline ChrisWilson68

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And the fact that someone else was wrong in criticizing claim A really has no logical bearing on my criticism of claim B.
 

It does when criticisms of both claim A and claim B imply the same claim C (that JPA don't understand basic physics). I was giving counter evidence to claim C.

As I'm sure you're aware, by the law of logic known as the contra-positive that means criticisms of both claims A & B are invalid. :)

Actually, in the specific quote I was responding to, you were using the fact that someone had erroneously criticized claim A as evidence claim B was also suspect, which does not logically follow.

Offline QuantumG

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Plasma thrusters are a subset of ion thrusters.

No they're not. Plasma is not ions, by definition.

Quote
All the balloon deployments mentioned in the link involved first putting the balloon into orbit, then inflating it.

Seeing as you're disinterested in actually reading what was linked, can you please stop commenting on it like you have?
Human spaceflight is basically just LARPing now.

Offline QuantumG

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You think they have a secret technology that they won't tell anyone about and have never demonstrated to anyone that would re-write every basic textbook on drag?  Good luck with that.

Not at all.. we're saying you made a claim about John Powell and his supporters that was completely unsubstantiated.
Human spaceflight is basically just LARPing now.

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