Earth to LEO - discuss

C M Edwards · 2005-05-26 09:50:52

There is some work already done on the net about space tethers, even a http://spacetethers.com/spacetethers.html]free java simulator. There are still some important details that I haven't seen so far yet. And the best way to really understand them is to do the basics again and incorporate these details into it.

That's a cool simulator, with lots of pre-programmed options that can be editted for study in depth. I also like the way the central body is represented. It does not appear to be able to model Dick's idea in action, but can compute the necessary dimensions for a spectra (high density polyethylene) tether to spin at a rate high enough do the job.

Fledi, you're probably right about the relative mass ratio. I didn't intend to impune you, just encourage a little depth of discussion. Thanks for the useful link.

As for my personal favorite scheme for Earth-to-LEO, that would have to be:
www.jpaerospace.com]JP Aerospace Airship-To-Orbit Plan

It looks wonderfully simple, and should be re-usable with heavy-lift capability, though I suspect it's more complex than advertised, with a smaller launch window and complex navigation requirements. (My preliminary investigation suggests multiple critical points during the launch, all of which must be overcome for a successful ascent.) While we're on the subject of calculations, I should point out that JP Aerospace won't release any of theirs regarding the ATO. But it flies in spherical coordinates for me just as surely as it does for them, and I believe the thing will work.

publiusr · 2005-05-26 14:32:41

I heard that the company that has the AN-225 is going into bankrupcy--not because of lack of a market--but because they only have that one good plane and the other under construction. If Rutan and Branson want a white Knight--they should come here to Alabama--where we look to be building new Airbus tankers if we win out, and convince them to make the hanger a bit larger. Instead of Gov. Riley giving 2000 million to B'ham for this Domed Stadium--Scaled should get the money.

I would love to see the second AN-225 with a pair of 777 engine replacing the two to either side nearest the fuselage.

Fledi · 2005-05-26 16:54:31

The external tank used aluminum-lithium alloy 1460

Maybe new composite materials would be worth a look too, but they would have to be cheap if you plan to make one way tanks.

No problem, C M, that remark of me wasn't meant to sound that seriously, just funny.
Unfortunately your link is not working, but the concept sounds interesting. Are they planning to use an Airship as a kind of first stage?

Austin Stanley · 2005-05-27 00:31:19

I think I said this before, but it bears repeating. I think entirely to much time and effort is spent on attempting to recover the upper stages of any launch vehicle. It is far more important recover the lower and any intermediate stages. They are both larger, and thus generaly very expensive and far easier to recover than the upper stages. The upper stages are the smallest and have the toughest job to do, so it makes the most sence to make them disposable of all the stages.

If our goal is to lower the cost to orbit, it might be seriously worth looking at various methods of re-using the lower stages of current launch systems, such as the fly-back boosters for the shuttle. It may be worth a high development price and lower performance if the lower stages can easily re-used. I'm worried that most of the SDV and EELV continue to focus any of there re-use upon the upper stages of the vehicle, when it should be focused on the lower stages.

I mean, yes ideal we would like to get the whole vehicle back intact, but if that is not possible, let's keep the lower stages and use disposable uppers. A great deal of our future uplift demand isn't going to be comming back anyways, indeed people or maybe a hundread pounds of samples/science equipment is all that we currently are looking at bringing back anyways, everything else is staying in space. So why all the focus on re-using the most stressed and least used componet of any launch vehicel?

C M Edwards · 2005-05-27 05:30:41

Are they planning to use an Airship as a kind of first stage?

Actually, they're planning to use an airship for the entire ascent. The system uses a rondevous in the lower mesosphere to change vehicles, then goes single stage to orbit riding on an airship. The entire airship makes the ascent from mesosphere to orbit. (No rockoons or further staging.)

Let me find a working link...

http://jpaerospace.com/atohandout.pdf]ATO *.pdf File

Expect it to be a little vague. They like to think they're being secretive. For example, when they first began posting descriptions of their V-airships more than five years ago, they would only show them in profile! :laugh:

Various other links and speculations exist around the internet, including this thread at Newmars:
http://www.newmars.com/forums/viewtopic … 1]Airships To Orbit Thread

As I mentioned, it's performance isn't likely to be what's advertised. However, we should still be interested, if only because its performance is likely to be better on Mars.

Fledi · 2005-05-27 07:10:01

Wow, what a cool thread you linked. Now that is a really unconventional approach, spent the last 2 hours reading through it. So you say it might have less performance as they claim? But it seems like you did quite an effort to take a deeper insight into the concept and were still optimistic about it at the last postings. Did you find out something that changed your mind since?
I wonder whether it would be within the limits of Mars Society budget to build some small-scale version of it, the Ion Engine would probable be a problem, though.

GCNRevenger · 2005-05-27 08:49:10

Its an interesting idea, but I would question the quality of the calculations concerning if it would work or not, it seems to me that there would need to be some pretty optimistic assumptions to guesstimate that it would fly.

There are some pretty serious technical hurdles too, like making thin-film polymer solar cells efficent enough (right now they are poor), the balloon gas bag light enough yet not too fragile, and an ion engine light enough while still having the thrust to overcome drag. It is very possible that such a vehicle is simply beyond our present-day materials science.

C M Edwards · 2005-05-27 12:41:51

Fledi, you wrote:

...you did quite an effort to take a deeper insight into the concept and were still optimistic about it at the last postings. Did you find out something that changed your mind since?
I wonder whether it would be within the limits of Mars Society budget to build some small-scale version of it, the Ion Engine would probable be a problem, though.

Well, the first hurdle is that the technology is not readily scaled down. An airship of any mass must be enormous to even attain mesospheric altitudes in the first place, and carrying enough fuel to attain orbit only increases the size. To even serve as a useful test bed, much less reach orbit, an experimental vehicle would need a size comparable to the largest balloons ever launched.

The ion engines shouldn't be a problem, but we probably shouldn't use them. My own power-vs-thrust analysis suggest that the necessary engine performance is more comfortably met by a set of electric arcjets than the average ion drive. (Lower Isp, but more thrust per watt.)

Garden variety polyethylene could do most of the envelope, although the leading edge of the airship may need reinforcement by something that can go beyond 60 degrees celsius without warping. The supersonic flow does not raise the temperature too high for the average plastic coke bottle, but there's no safety margin.

The biggest problem is navigation. This vehicle has to take advantage of coriolis force, lattitudinal atmospheric variations, and diurnal variations to ratchet itself higher with each pass. As its altitude increases, the magnitude of these variations - up and down - increases because of the thinning atmosphere. By the time the vehicle is entering the thermosphere, upper atmosphere thermal variation is pulling the rug out from under it every time it crosses the day/night terminator. The final ascent is something of a roller coaster ride, and may become quite chaotic.

Getting it nearly to orbit should be easy. Getting it into orbit will depend greatly upon your navigator.

GCNRevenger · 2005-05-27 13:53:08

The weight of the solar cells would also be a problem, you can't afford to bring along silicon cells, they would be too heavy. Polymer solar cells are possible, but their efficency is pretty poor. Energy storage on any scale is not going to happen either, batteries would be much too heavy. Flywheel storage might help a little bit, but I doubt you could attain enough storage without the weight or gyroscopic force would be too great.

Fledi · 2005-05-27 16:49:30

Thin film amorph silicium solar cells have efficiencies of 6% - 9% according to http://en.wikipedia.org/wiki/Solar_cell … ]wikipedia.
The film is only a few micrometers thick and can be placed on many kinds of materials, which can also be elastic. If we go with another 5 microns for the support plate, it should still be interesting from the weight standpoint, I mean half the efficiency of a 300 microns thick full Si cell is still not that bad compared to the mass saved.

Might be still difficult for the airship however, as is energy storage for that one, as you pointed it out.

Getting it nearly to orbit should be easy.

How nearly do you mean? I guess it should not be that much of the problem to go the rest with a conventional rocket powered 2nd stage, if it is just nearly enough.

RobertDyck · 2005-05-27 17:48:44

Space rated tripple junction GaInP2/GaAs/Ge solar cells now have beginning of life (BOL) efficiency of 28.3% at maximum power, and 28.0% at load voltage. End of life (EOL) efficiency is 24.3% at maximum power. Panels >2.5m^2 at 28°C produce 350W/m^2. A 5.5 mil thick cell with 3 mil ceria doped cover slide masses 1.76kg/m^2. This isn't thin film. There is a patent to grow thin film GaAs on a silicon substrate, but I don't know of one on a germanium substrate.

The new material is indium gallium nitride. (In1-xGaxN) covers the full solar spectrum, but it requires layers. Notice the formula has "x"s; this varies the absorption spectrum. For x Ga atoms you must include 1-x In atoms. A two junction cell could theoretically convert 50%, but the best I read about so far is 30%. Most importantly, with 36 of layers this could convert 72%. As of 2002, the issue to implement this is control of p-type doping.

Fledi · 2005-05-27 18:59:21

That amorph Si film I was talking about, I've seen a 6µm layer on top of a glass plate about one millimeter thick. Also heard it can be placed on top of some sort of plastic, even onto a steel plate.
I see no reason why the supporting plate would have to be any thicker than a few µm itself. So if you go with a total thickness of 10µm and an average density of 3000 kg/m^3, you get a mass of 0.03 kg/m^2. Also the method of getting that film on is '80s tech, for that cell I've seen is from then and is still working.
But maybe it still doesn't work that way for some other reason.

RobertDyck · 2005-05-27 20:48:21

True, instead of glass you can use a fluoropolymer film. Both Tefzel and Teflon FEP have been used. In space you need something very resistant to UV damage. Tefzel is stronger and lighter but Teflon FEP is more resistant to UV. There are a couple other fluoropolymers that could be used, but other plastics can't handle the heat, cold, mono-atomic oxygen, vacuum, or UV of space.

Thin film amorphous silicon on thin stainless steel sheet has already been tested by Russians on Mir. It works. Amorphous silicon may not have the conversion efficiency of more modern photovoltaics, but the fact it's so thin makes it very light. Weight to power ratio is everything, it doesn't matter if high efficiency cells have a small area if they're heavy.

srmeaney · 2005-05-27 21:06:50

This space taxi would be launched from the back of a 747, one of the two that NASA already owns. It's small enough that the empty tank could be lifted onto the 747 with a mobile construction crane, and the orbiter could also be lifted with that crane. You don't need the dedicated crane structure used for the current Shuttle. Fuel could be delivered with semi-trucks (tractor/trailer) and pumped through hoses directly from the truck tanks to the spacecraft fuel tank on the 747's back. Fuelling would have to be done at a safeing area, but that's just a piece of airport tarmac away from any buildings. The tank could be delivered by a flat bed semi-truck, and the orbiter could be delivered by a flat bed medium truck with dual rear axle. This means the space taxi could take off and land from any airport capable of servicing a 747.

Mass colonization requires a hundred passengers a week. That means a Space Plane the Size of the Air Bus (Mostly Fueltanks) with possibly a big turtle shell heat shield made from tiles siting on top (So it can make reentry upside down).

And Even More fun, free to any Space Station.

In fact all passenger service infrastructure will ultimately be free.

RobertDyck · 2005-05-27 21:56:15

Mass colonization requires a hundred passengers a week. That means a Space Plane the Size of the Air Bus (Mostly Fueltanks) with possibly a big turtle shell heat shield made from tiles siting on top (So it can make reentry upside down).
And Even More fun, free to any Space Station.
In fact all passenger service infrastructure will ultimately be free.

Uh huh! Free! And investors would spend billions of dollars developing this, why?!

Colonization will be relatively expensive, but middle class people could afford a trip to Mars by selling their house and spending their life savings. After all, emigration is for the purpose of living there. I expect a ticket to Mars will cost double the price to an orbital hotel. Another way of saying the same thing is that a ticket from Earth orbit to Mars will cost as much as a ticket to Earth orbit plus a few weeks in an orbital hotel.

Technology to make mass colonization possible is the SCRAM jet. That could propel an SSTO RLV into LEO. And you don't want to re-enter up side down. Imagine all the passengers hanging from ceiling by their seat belts. No, a lifting body with a belly entry like the Space Shuttle is more practical.

GCNRevenger · 2005-05-27 23:53:17

No no, if you are going to build a giant megaballoon space/airship, you ought to abandon conventional inorganic solar cells. Instead, use polymeric solar cells (plastic), which you can make huge areas of them with extremely light weight, down to the grams per square meter. Everything about such an air/space ship will have to be extremely light weight, the ion drive and storage flywheels are bad enough, I don't think you'll go anywhere if you have to drag along some tonnes of solar cells. Polymer cells are also inherintly flexible so they are easy to make and apply in any shape, rather then complicated blankets of extremely brittle and fragile silicon cells. The trouble is, they lack efficency at the moment to do the job, but that is changing with the advent of a few nanotech tricks...

As far as a passenger vehicle, an SSTO "Shuttle-III" regenerative scramjet is the only game in town for "everyman" space travel. Either that or an honest-to-no-crap space elevator. And airship is too slow to ever have a high enough flight rate to be practical for anything but cargo.

dicktice · 2005-05-28 17:33:59

What are your ideas regarding re-entry, or not, of the dirigible?

srmeaney · 2005-06-04 03:35:14

I realy considered the Japanese Passenger carrier "Kankoh-maru" to be the better option. The proposed million tourists into space each year through the mass production of a tranport vessel capable of carrying fifty passengers looks superior to anything else on the drawing board. With that level of passenger overkill, their rivals are unsustainable.
http://uk.geocities.com/osaka2015/kankohmaru.JPG]The Kankohmaru http://www.spacefuture.com/archive/the_ … .shtml]JRS Report
japanese_rocket_societys_symposia_1995_2001.1.jpg
Certainly the passenger terminal looks better than that offered by a six passenger shuttle.

Mitsubishi and Kawasaki heavy industries are on a Winner.

Fledi · 2005-06-04 06:43:44

Hmm looks interesting from the drawing, can you actually give some link with a description?

C M Edwards · 2005-06-05 15:45:12

GCNRevenger, I can't unreservedly endorse any single photocell structure for airship-to-orbit, except to say that some suitable inorganic cells are available. The solar panels needed would weigh several tons regardless of structure. The parameter of interest is not their weight, but their power-to-weight ratio, where organic cells do not exactly shine. I am also leary of organic cells because I don't know their performance at the temparatures involved.

The ascent trajectory can be chosen to place the ship in shadow as little as possible, but some power storage is necessary. It does not need to be 24 hours worth, and can be further reduced by halting the ascent during dark hours. That's still major power use, though. Electric rocket engines are always power hungry, even on a diet.

I have little data to suggest ATO is either "too fast" or "too slow". It's minimum possible turnaround is two weeks, since that's the amount of time it would probably take to get to orbit and back. Make of that what you will.

Speaking of getting to orbit and back: Dick, re-entry is going to be a dream. IMHO, every low earth orbit satellite should have a humongous parachute to ease it smoothly down into the mesosphere without all those messy burn-ups. There's just one catch - that big envelope may not be intact by the time the ATO needs to come down again. It's more fuel efficient to dump it once orbital velocity is attained. (Anything that's still giving the ship lift is still giving it drag, too.) Also, the lower thermosphere - the atmospheric region where an ATO sans envelope could hope to attain orbital velocity - is the region where atmospheric protection from micrometeorites starts fading away. Leaks would not be severe at the gas pressures involved, but would be inevitable. There might be problems with gas loss due to micrometeorite strikes. Anything short of complete rupture still wouldn't cause the ship to burn up, and maybe not even that - the balloon is just too big. But it might not be able to remain airborne once it gets back down, which would destroy it just as surely.

dicktice · 2005-06-06 09:44:51

Buoyancy will increase more rapidly than the area of the photoelectric collection surface increases--say one-third of an ideal cylindrical surface adjusted for lamda, etc. (Just thought I'd throw that in.)
The ascent trajectory towards a polar orbit would expose the dirigible to constant sunlight for a useful portion of Earth's orbit around the Sun. Space platforms in polar orbit will be much more useful in the long run, once equitorial launching is not longer an economical essential.
Reentry, the way you describe it, is more of a nightmare than "a dream," as you cterm it. Let's have more discussion on just that aspect.
Personally, I'm against returning anything, except crew flyback vehicles, back to Earth. Accumulate, as well as occupy and manage, vast retrofit conglomerations of tethered materials and consumables, sustained in orbit by judicious use of gravity gradiant tethers--useful, also, as the bases from which Earth-escape tether launching can be accomplished.
I'm still in a quandry as to how the returns to Earth orbit are to be accomplished, short of aero-braking, which I abhore.

C M Edwards · 2005-06-06 14:23:26

Buoyancy will increase more rapidly than the area of the photoelectric collection surface increases...

Indeed. This is one reason that solar panel total weight is less critical than power-to-weight ratio. It's progressively more difficult to increase the wingplane for more collector, but not as difficult to add a little more mass.

I'm still in a quandry as to how the returns to Earth orbit are to be accomplished, short of aero-braking, which I abhore.

Why, they're accomplished by aerobraking, of course! :;): Aerobraking trajectories have many possible profiles. Not every conceivable trajectory requires the vehicle to withstand exposure to 3000 degree plasma for three minutes. The ATO's trajectory is notable because it's conceivable to accomplish the entire descent and not have the vehicle's skin temperature exceed the boiling point of water. High temperatures are required when a lot of counterpressure is needed to slow the vehicle (as suggested by Charles's Law of gases). The ATO's wing plane area is so large than a tiny counterpressure can do the same job as long as it's distributed over the entire wing. An ATO's re-entry would be slow and stately by comparion to anything else flying, without a trace of plasma.

srmeaney · 2005-06-06 18:29:03

What are your ideas regarding re-entry, or not, of the dirigible?

While Atmospheric departure for a dirigible would require burning whats in the baloon as fuel to to achieve obit, although you would probably have to 'burn' the hydrogen into subatomic particles because fuel oxidizer will be dead weight.
Or if the fuel/lift gas was protons then you could burn it with atmospheric electrons to achieve hydrogen as the final product.

Return is tricky but a baloon could sit on the outer edge of the atmosphere and reinflate with the hydrogen (or is it anti protons out there?) that is directed outwards into space. That would allow a very slow re-entry on a scale of many months. If it could be done, you might have a reusable space lifter with a turn around time of a year?

dicktice · 2005-06-07 06:11:35

I meant: How to get from orbital speed to sitting speed?

C M Edwards · 2005-06-07 10:48:10

I meant: How to get from orbital speed to sitting speed?

Ah.

Well, the ATO's answer is still the same: aerobraking.

Aerobraking is just the use of atmospheric drag to change a vehicle's velocity. The drag force can be used to stop the ship and land it, or "skip out of the atmosphere" and change its orbit.

Thanks to Apollo, the Space Shuttle, and other manned spacecraft, we're in the habit of thinking of aerobraking as its own distinct part of the mission (e.g., launch, orbit, aerobraking, landing, debriefing, etc.), rather than as a physical effect employed for navigation. That's not necessarily true for an ATO mission.

The vehicle could conceivably experience substantial drag during its entire flight. This drag would work constantly to slow the vehicle, just as it does for a typical airplane. When we start using that drag force to steer or change speed, that's technically aerobraking. Nobody thinks it's unusual when an airplane pilot throttles back or raises his flaps. He's just flying the plane. Likewise, it's no more unusual for an ATO vehicle to use aerobraking as well.

"Landing" an ATO vehicle would be very similar to landing an airplane using just the throttle. You turn the engines on, and the runway gets smaller. You turn the engines off, and the runway gets bigger.

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