Dark Sky Station
Now there is a now to conjure up a super-villain image.
Where is that white Persian cat got to now!
Inventors in America are claiming an altitude record for airships after a recent test flight in which an unmanned electrically-propelled helium dirigible successfully manoeuvred under power at 95,085 feet above the Black Rock Desert in Nevada. The "Tandem" craft is intended to demonstrate the first stage of radical plans which …
Be interesting to see how they solve that particular problem. When USAF aircrews fly above 60Kft (U-2s), they wear dosimeters. So, if some crew were going to work up there for an extended time, they'll need shielding of some kind, which is (so far) always heavy.
...mine's the one with the lead liner...
The magnetic fields themselves aren't heavy, but there are 2 basic flaws in your argument:
1. Something needs to generate that magnetic field, adding weight. Also the bigger and/or stronger the magnetic field required the bigger and heavier the equipment required to generate said field.
2. Magnetic fields won't stop all types of radiation.
I can't see why you'd need crew up there. In addition to the heavy radiation shielding, they'd need heavy air supplies, heavy food, heavy sanitary facilities, heavy temperature regulation ...
Use a robot. Steer it from the ground. Even at this altitude, it is less than a light-millisecond away so even a hard-core gamer would have trouble noticing the latency.
Not sure that statement holds water...
Companies are already developing photovoltaic fabrics that allows for the creation of flexible, cloth-like gas envelopes/structures that can generate (at least a portion of) their own electricity.
For example, a company called ShadePlex, LLC in Toledo, Ohio, has developed a process that binds thin-film solar cells to architectural fabric:
-- -- http://www.shadeplex.com/products.html
Other organisations are developing solar fabrics where the fibres of the fabrics themselves are photovoltaic in nature:
-- -- http://dvice.com/archives/2009/07/solar-fabric-yo.php
I would think that a monster-sized, orbital, semi-rigid, lighter-than-air vessel would have a gas envelope with enough surface area to make the use of solar fabric a reasonably practical solution.
The issue may be power consumption, I get the idea they intend to use a higher thrust version of VASMIR, which currently produces 5N of thrust for 200Kw of electrical power, with respectable fuel efficiency.
They will need significantly more thrust than 5N, and so probably significantly more power for the engine.
Maybe they can compromise fuel efficiency to reduce power consumption, but increase thrust.
Well, they're talking about platforms that are a "mile wide." Not sure this relates to the gas envelope, or the platform itself, but if airship history is a guide, the human-habitable section of an airship tends to be quite a bit smaller than the envelope.
So, for sake of argument, let's conclude that the gas envelope is "a mile wide," and is shaped like a thick disc, or an extremely oblate spheroid.
This means that if the sun were shining perpendicularly on the upper surface of said photovoltaic envelope, there would be (at minimum) about 0.785... square miles of incident area:
-- -- A = pi (r^2) = pi * (0.5 mi ^ 2) = 0.785398163 square miles
-- -- -- -- (It's a "mile wide," which means 0,5 mile radius.)
(Probably more, since the "top" of the envelope "disc/spheroid" would probably have a noticeable curved "bulge" in the middle, increasing surface area, but to keep things simple, we'll presume it's perfectly flat.)
0.785... square miles translates into 2.034... * 10^6 square meters:
-- -- 0.785398163 square miles * (2,589,988.11 square metres / square mile) = 2,034,171.9 square metres
Let's subtract, say, 7% of that area to factor for zones that can't be used for solar collection (seams between cloth sections, cabling, envelope expansion control bladders, etc.) and we're left with about 1.892... * 10^6 square meters of photovoltaic area:
-- -- 2,034,171.9 square metres - 7% = 1,891,779.87 square metres
If each square metre produces just one watt of power, our photovoltaic balloon-disc generates almost 1.9 **megawatts** of electricity at its relative "high noon" point, well in excess of the 200 kilowatts needed to drive a VASIMR engine.
So, the problem isn't available power; rather, it's the weight of everything else that goes into getting that power to the ion drive, like cabling, control systems, and other-and-sundry components.
Making a cloth photovoltaic envelope that generates the necessary amount of electricity isn't the issue. It's getting that power to the engine in a manner that still allows enough lifting capacity for useful cargo...
This is awesome. Thanks for doing the maths for us :-)
However, consider the name of the project (Dark Sky)... was it chosen because it sounds cool? PV may not always be appropriate. Low orbits are fast, after all.
Because 17000 MPH is bloody fast. How much petrol does it take your car to accelerate to that speed? :)
In comparison, I believe that the fuel needed to get high enough that wind resistance is minimised is not so much (not when you consider how much weight it has to get up there, with the payload and all the fuel needed to accelerate it to orbital velocity)
We are just starting our re-entry into earth atmosphere. We will complete our re-entry and dock at Upper Atmosphere Transfer Base One in eighteen hours, after which you will transfer to the atmosphere descent craft.
Mind you I suppose if you've just come from Mars or something then another two days doing thelast twenty five miles vertically probably won't hurt that much...
OK, matybe the re-entry won't take that long, but that would spoil the joke..
And yet not *entirely* impossible.
The puzzle is.
With near zero drag and low acceleration (IE Acceleration *force* > drag force) you could take as long as you like to reach orbital velocity.
But near zero aerodynamic drag -> near zero aerodynamic *lift* -> *very* big gas bags.
At some point you rising *not* due to density differences between the bag + payload and the atmosphere but the increase in the kinetic energy of the vehicle.
Can your increase in KE outpace the loss in lift so you don't loose all the KE (and hence velocity) you gained as you sink back into the (relatively) denser air you just left at *much* higher velocity and start to cook?
B****ed if I know.
"... slowly fly themselves into orbit over a period of days using hybrid ion drive propulsion."
Cargo yes, but people too? Days? 'Ships' indeed!
How fortunate then the description "ugly giant bags of mostly water" ... and ions! "We need more speed! Give me some more of those salted nuts, I have something to fill up..."
1. Structural integrity
Contrary to the statement made about not needing heat shielding, when accelerating up to orbital velocity there will be a period where the ship will be in the upper atmosphere (as it needs the lift from the helium to maintain the altitude!), at a high but not orbital velocity e.g. 12,000mph.
The atmosphere is not very dense at these altitudes, but at that speed you're covering a huge distance in a small amount of time, compressing the low pressure gas against the ship and causing friction heating. While the temperatures will be lower than those experienced by the shuttle, this still requires protection.
There will be a transition point, basically there needs to be enough thrust to overcome the aerodynamic drag in the upper atmosphere and also enough thrust to keep the ship up when the velocity is such that it will 'pop' out of the atmosphere and not fall back as it loses buoyancy.
Otherwise it'll just end up skipping along the atmosphere not gaining any speed as it will slow down (And heat up!) as it drops back into the drag of the atmosphere.
Sure you know what you are talking about?
"compressing the low pressure gas against the ship and causing friction heating."
And, where exactly is that heating energy coming from? Presumably, your engine will either accelerate you, dissipate its power internally or cause you to heat up by the drag you are talking about. If you heat up, its because the engine overcame enough air drag that the air being pushed aside heats up your envelope.
If you have a low power ion-type engine, it's not going to succeed much at overcoming air drag.
Yes, on re-entry you do have heating to worry about, but that's also because you start out with a high speed and have plenty of kinetic energy to bleed off as you decelerate. Nothing similar on acceleration.
Seems like one's pontifications require a bit of thermodynamics common sense.
"NASA has already generated electrical power by dragging a long thin wire through the atmosphere. Maybe that's an option since no additional power would be needed to obtain lift?"
No. The Shuttle flights were about more than 99% of the Earth's atmosphere.
It's called a tether and it was dragged through the Earth's *magnetic* field. It's a pure demonstration of EM theory (current flow at right angles to motion at right angles to magnetic field).
Could work here but a trade off. Tether *might* be lighter than solar cells or might not and the *drag* is another matter entirely.
Every new technology is immediately glommed onto by the military/security state.
Forget for a moment using it as a platform for launching rockets. Rather, think in terms of using fleets of these units instead of orbiting surveillance satellites over a nation's own territory and also over the open seas. (Perish the thought that one country would violate another country's air space, right?)
Cameras, radio receivers and other sensors at 100,000 feet would be far smaller and lighter in weight than equivalent devices on a geostationary satellite at ~23,000 miles. They could be launched on a just-in-time basis. Without the need for a ground-launched rocket and a launch facility, they would be dirt cheap, too.
The total surveillance world is about to gain a "neat" new enabling toy.
("The spawn of satan" icon is appropriate, right?")
They already have it. Planes are much better at it; at lower altitudes, lift is easy to achieve, and you are even closer to what you are spying on, so the optics give better performance.
The new trials are even starting to use purely solar power, so it can stay up for months on end.
This tech is not really ideal for that. (However for launching military satellites, yes)
The bigger it gets, the more there is for meteorites to hit. Wouldn't it be better to go for many smaller balloons than one large one, in case it gets popped? Even if the large one has many separated gas chambers, there could be knock-on effects from an impact to one of them.
Many modern airships have multiple independent bladders enclosed by the main envelope, to allow for things like attitude control. For example, if the nose of the airship is pitching upward, you could pump out (or, if price is no object, release outright) helium from the forward bladder to return the airship to level flight.
I would expect that the hypothesised mile-wide balloon-spaceship would be constructed in a similar fashion, to allow for such eventualities.
It is only the US strategic Helium reserve in Amarillo that is running out in about 15 years time, but there are vast reserves of Helium rich natural gas in Qatar, Siberia, Algeria, Iran, Poland, Canada, Australia, China and Indonesia. Some new Helium rich natural gas fields are also under development in the US and there will be no shoratage until after all the natural gas has run out.
Regards JB (Airship & Blimp Consultant and Gasbags lighter than air comedy site:
3w dot airship dot me)
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