News Airships to orbit

[agentgonzo]

An interesting notion:
http://www.theregister.co.uk/2011/11/02/space_airships/

 

[SiberianTiger]

I'm kind of intuitively afraid that mounting an ion engine on a high-floating blimp might only result in reaching some speed at equilibrium point between thrust and drag.

 

[agentgonzo]

I'm kind of intuitively afraid that mounting an ion engine on a high-floating blimp might only result in reaching some speed at equilibrium point between thrust and drag.

The guy in the article states that the American military got high altitude weather balloons to fly at Mach 10 in the 70s. I cannot find any evidence of this (yet?) from looking on the web. But that was my main thoughts on it. If you've got a large enough airship to support its own weight at 100-200kft how do you get around the massive drag:weight ratio? Especially when using ion thrusters and a 5-10 day to-orbit time? I'll be mightily impressed if they get it working but remain very sceptical.

 

[SiberianTiger]

An airfoil shape, maybe?

 

[orb]

Discovery News: Airships Offer Alternative Stairway to Space

 

[N_Molson]

Depends what you call "space". Here they state that 200,000 feet (60.960 meters) above the sea level is space. I don't agree on that.

 

[Cras]

I agree, 200,000 is way to low for Space.

NASA calls 76NM space. Europe says 100km is space. The United States Air Force calls anyone who flies over 50 NM an Astronaut.

I tend to go with NASA even though the 100km border has a good reason for it, that this is the height where in order to get enough air over the airfoils for good aerodynamics of flight, one needs to exceed orbital velocity.

But I go with NASA.

 

[cymrych]

Hmm, 76NM? What's that, 140km-ish? Seems kind of arbitrary. Do you know their reasoning for such a figure?

 

[Cras]

76NM is when "Entry Interface" occurs according to NASA.

 

[orb]

76NM is when "Entry Interface" occurs according to NASA.

"Entry Interface" is 400000 feet, which calculates to me as 121 km, and not 140 km, which would be 76 nmi.

 

[cymrych]

"Entry Interface" is 400000 feet, which calculates to me as 121 km, and not 140 km, which would be 76 nmi.

Yep, that's what I was getting too. Guess the 76NM must have something to do with molecular density or pressure reaching a certain minimal limit.

 

[Cras]

No, I mispoke (mistyped), is what i did. It is 76 statute miles, 65 NM miles according to NASA.,

 

[Wishbone]

[ame="http://en.wikipedia.org/wiki/Karman_line"]Kármán line - Wikipedia, the free encyclopedia[/ame]

 

[Sky Captain]

I'm wondering how are they going to prowide power to those ion rockets. They would need fairly high thrust to overcome the drag and maintain acceleration. High thrust high ISP engines by definition are power hogs. Chemicaly stored energy is out of question - the recquired fuel tanks would be too big and heavy and converting chemical energy into electricity and then into ion thrust sounds very inefficient.

 

[MaverickSawyer]

Solar panels and batteries are far too heavy in their current form to be effective.
Nuclear reactors are too heavy.
Not enough O2 for an air-breathing APU, which would negate the need for ion engines.
:beathead: anyone else hitting the proverbial wall?

 

[Sky Captain]

I just thought about beamed power from ground or from their dark sky platform, but realized that also won't work because orbital airship would quickly get out of line of sight and it would have to circle the Earth several times before it achiewed enough speed to reach LEO.

 

[Cairan]

Nah, they're just going to strap a couple of cats in the balloon with buttered bread attached to their backs so they would be in a state of quantum levitation... Cats can't fall on their back but buttered toast falls buttered-side first to the ground, hence instant perpetual anti-gravity device is created...

 

[agentgonzo]

I'm wondering how are they going to prowide power to those ion rockets. They would need fairly high thrust to overcome the drag and maintain acceleration. High thrust high ISP engines by definition are power hogs. Chemicaly stored energy is out of question - the recquired fuel tanks would be too big and heavy and converting chemical energy into electricity and then into ion thrust sounds very inefficient.

I have lost one of the links I was reading originally, but it did say that power-to-weight ratio was one of the two remaining technical hurdles they needed to solve before it was viable. Early designs used fuel cells, but from memory (which may not be accurate) I think they were hoping on future batteries (which is not infeasible given the research being put into it for laptops/phones/tablets these days). They also were planning on spray-coating the outer hull of the airships with solar-cell-paint, which while not very efficient can use their massive surface area to generate a not-insubstantial amount of power at a relatively low weight.

 

[jedidia]

The blog "A place to stand" has taken up the article, and a commenter claims that the Mach 10 reference was relative to ground, not relative to air, and that an airship of the size in question could not accelerate to significantly faster speeds relative to the air it's in.

Interestingly enough, John Powell himself joined the fray and made allegations that this was not correct and that the tests in question were indeed rocket propelled balloons accelerated to Mach 10 relative to their surrounding air:

The Mach 10 weather balloon referred to WERE traveling at that velocity relative to the air they were in. This was done during the Project Shot Put, a precursor program to the Echo Balloon satellite. These balloon were release from sounding rockets at 300,000 to 400,000 feet and zoomed 3/4 the way around the world before failing. This is the exact altitude the airship to orbit vehicle will be conducting there primary acceleration to orbit. This work continued to missile decoys and other hypersonic balloons and inflatables.

I can't find any references to a project Shot Put, at least none that would have to do with wheather balloons. The only reference google provides is a link back to Powells comment, so the claim seems a bit thin (there are a few archive images of a "Shotput lift-off" that are connected to the ECHO-balloons). I'll keep an eye on the blog to see if Powell posts again to reveal some more tangible information. After all, Powell HAS to be considered an expert on high-altitude balloons, so his sources are bound to be a bit wider than wikipedia.

EDIT: Looks like I actually found something usefull. Shotput seems to have been an early launch vehicle with which most of the tests for the ECHO satelite were made, before switching to the Delta for the actual launch (the first of which failed).

It was majorly used for testing the ejection system, so it seems quite possible that they released their baloon payload at Mach 10.

Which leads me to conclude that Powell has been misinterpreted, or has been vague on purpose: This would serve to show that it should be possible to build an airship that can handle the stress. It does NOT go to prove that an airship could reach that speed on its own, in inflated state, as all the stuff about Shotput seems to indicate that the balloons were RELEASED at that velocity and then inflated.

 

[Sky Captain]

I have lost one of the links I was reading originally, but it did say that power-to-weight ratio was one of the two remaining technical hurdles they needed to solve before it was viable. Early designs used fuel cells, but from memory (which may not be accurate) I think they were hoping on future batteries (which is not infeasible given the research being put into it for laptops/phones/tablets these days). They also were planning on spray-coating the outer hull of the airships with solar-cell-paint, which while not very efficient can use their massive surface area to generate a not-insubstantial amount of power at a relatively low weight.

For batteries to work they would need to have energy density significantly better than hydrogen fuel. Is it even physically possible? Maybe some sort of combination with batteries and solar panels might be possible - solar panels during day charge the batteries and power the engines to eccelerate the ship and batteries during night at least keep the ship from loosing speed and altitude it gained during the day, still ir likely would require batteries and solar cells far more weight efficient than anything available today.

Since the orbital airship would be very large structure it would also have high drag. A small ion engine like used on space probes won't do it. They would likely recquire multi megawatt systems, something like proposed for WASIMR driven Mars mission.

Another idea - would it be possible to use atmosphere as reaction mass in some sort of ram/scram jet type system to eliminate the need to carry onboard propellant?