Spacefaring tech discussions; CSI and space tugs; Ignoring NASA's in-space skills

Jon Goff's posting yesterday on the essential technologies for spacefaring got lots of interesting comments here, here, and here.
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I'll point out in particular the comment from Ben Muniz of Constellation Services International about how the CSI COTS proposal took good advantage of a space tug approach.
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If one looks over the Shuttle era, the area in its human spaceflight program where I think NASA shined brightest was in orbital operations involving EVAs and other spacecraft. The retrieval of satellites, repair and refurbishment of the Hubble Telescope, and the various ISS assembly missions have generally gone extremely well. (Hope I'm not jinxing next week's mission!) Those successes also highlight the tremendous capabilities provided by human participants. The tasks required specialized skills, dexterity, and on-the-spot problem solving abilities that are decades ahead of what any robotic system can do.

So it's a bit puzzling why NASA management is so intent on minimizing in-space assembly for future space projects. The delays in the ISS were not caused by problems "in space" but by the Shuttles, which flew infrequently and were grounded for long periods. With smaller but much more reliable vehicles capable of frequent, low cost flights, assembly of large space systems from modest sized components would seem a great way to take advantage of the tremendous amount of in-space operations knowledge and skills that the agency has accumulated over the years.

Posted 08/24/06 | 09:59:57 by TopSpacer | Filed under: Space Technology

Comments

The discussion of in-space assembly leaves out the important factor of increased design costs. Building the International Space Station in stages increased its complexity because each component had to be able to operate in the absence of all the components to be delivered after it. I think the ISS would have been less massive, easier to maintain, and less costly and time-consuming to design if it had been either launched in one piece or left uninhabited until it was more or less complete. Of course neither of these options were possible with the Shuttle's limitations. In-space assembly makes much more sense when there is some existing infrastructure, like a space station in the desired orbital inclination.

Posted by Matt Wronkiewicz at 08/24/06 10:31:34

Hi Matt,
But that still assumes an old style space transport paradigm, e.g. pieces delivered over a multi-year time span separated by long and indefinite pauses in between. In that scenario it makes sense to operate what you have while waiting for more parts to be delivered.

However, if you can launch every week or two, which is quite feasible with the COTS type transports (with multiple vehicles), the system can wait to be switched on until all or at least the core pieces are in place.

If, say, a habitat module needs a second life support module, you could attach the habitat but wait to activate it until after the support module was delivered. This would be no big deal if the wait time was just a few weeks.

- C.

Posted by TopSpacer at 08/24/06 11:14:21

Feasible, maybe, but not economical. The only people talking about a flight rate that high are building suborbital vehicles.

I agree that it makes more sense to build smaller vehicles with a higher flight rate and then complete the assembly before turning it on. Especially if you have a space tug. I think at NASA they're comparing Skylab and ISS, discounting high flight rates and space tugs, and concluding that big boosters are the way to go. It isn't going to work out well for them, but at least they're starting to learn from direct experience.

Posted by Matt Wronkiewicz at 08/24/06 14:28:53

Institutional experience doesn't count for much if your engineers die of old age between projects.

Posted by Patrick at 08/24/06 15:24:54

Actually, as I noted recently in a comment on another posting, papers available on the Kistler site
http://www.kistleraerospace...
say that a fleet of five vehicles could provide one flight per week. At that rate, a flight would cost $17M according to a 2004 Kistler paper. (For 4500kg to 200km at 45 degrees that is about $3800/kg or $1700/lb)

The usual response is that there is not enough demand to justify such a rate. But that is a chicken and egg problem. There has never been a launch system capable of providing such a launch rate at anywhere close to that price. (For sake of brevity I'm ignoring the Falcon at the moment but I assume that SpaceX will always have a system capable of similar or better performance.)

If the lunar program was re-configured to use orbital assembly that would certainly add to the demand. Smallsat demand would certainly grow with lower launch costs. The K-1 will have a passenger option so it would be delivering passengers not only to the ISS but to a Bigelow habitat.

So high flight rates are not out of the question at all. It's just a matter of time and the bootstrapping process.

- C.

Posted by TopSpacer at 08/24/06 16:51:28

It's the early 1960s: I've seen the B-58 in sustained turbojet-powered flight at Mach 2+, and the X-15 in rocket-powered bursts at Mach 6+.

So fleets of supersonic bombers/transports "are not out of the question at all. It's just a matter of time and the bootstrapping process."

We've been round this block before, Clark. My point is not that it can't be done, not that it won't be done. My point is that you haven't shown me why the market for orbit (from a starting point of some hundreds of tons per year) should bootstrap any more briskly than the much, much larger market for point-to-point travel on earth.

(Other than that it would make us both very happy.)

Posted by Monte Davis at 08/25/06 07:11:37

Hi Monte,
I don't think your examples are comparable to the K-1/Dragon systems. The latter will be operational systems that will significantly lower the price on getting to space. The X-15 was an important developmental project but far from an operational system. (I don't know anything about the Mach 2+ B-58 so I won't comment on it.)

Also, we are not choosing between a slow, conventional way to get to space and a way that can get you there really, really fast. We are simply trying to get to space as cheaply as possible. I don't think anyone has ever tried to sell supersonic transport as a cheaper way to get from A to B.

On the other hand, I certainly agree with you that I cannot prove that the market will respond strongly to the availability of low cost access. I think I can make a good case for significantly increased government and commercial demand (not room for that here) but a good case is not proof.

This is why I think COTS is an appropriate action by the government. If it works out, it will benefit both the govt and the commercial sector (which will pay back the money via taxes). If it doesn't work out, the govt will have lost a small fraction of what it is spending on other projects like Ares/Orion.

Elon's long term commitment to SpaceX being the exception, most investors want proof of the market before they will put up hundreds of millions of dollars.

I hope and expect that when we actually have systems capable of low cost access we both will be happy at the response.

- C.

Posted by TopSpacer at 08/25/06 09:38:46

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