NASA has announced the Augustine panel, and the Sentinel got it right. Give ’em hell, Jeff.
Category Archives: Space
Space Solar Powerballs
Trevor Brown proposes spherical solar power satellites.
This isn’t a new idea. I wrote a paper on it back in the early nineties for an SPS conference, and I think that Geoff Landis has done some work on it as well (for instance, here’s a report of a talk that he gave on it at the 1996 ISDC, which was the last one that I attended prior to by going to Dallas two years ago — ctrl-F for “spherical”). It does vastly simplify the design issues, because it is no longer necessary to point the panels at the sun. One of the comments there needs some elaboration:
While the surface area of the sphere facing the Sun matches your calculations, the whole side would not be available for power generation. The so-called Beta angle, or the Sun angle, affects the total amount of power converted. Also, while a sphere would not need rigid station-keeping and attitude control to collect solar energy, the transmitter back to Earth certainly will. Also, a large spherical structure would be more taxing on a station-keeping/attitude control system than a more planar design. These caveats in mind, this is a creative alternative.
With regard to the needed area, the beta-angle effect means that at any orientation, you’re only getting the effective solar panel area of the cross-section of the sphere. That is, while the hemisphere has twice the area of the circular cross section, the non-zero beta angle of all points except that at the center of the illuminated area means that you need twice the solar panel that would be necessary if it were a flat circle. Add to this the fact that you have just as much area on the side in shadow, and it means that you need four times the total solar panel area to get the equivalent collection capacity of a pointed flat plate. So you have to postulate very cheap panels for this to make economic sense. But if you can get them, the simplification of the design is worth a lot.
As for pointing the transmitter, that’s actually not so tough a job. You hang it down below the sphere, and it will remain vertical, due to gravity gradient restoring torques. You could point it with control cables all around its circumference, attached to the sphere. In addition to inflating it, I also considered putting a charge on its surface to keep it spherical, but it would take a lot of ions, particularly for a big one, and inflating is probably a better solution, though subject to leaks, and the need for gas resupply.
One other point. I actually considered a fleet of them in MEO, continuously switching from one rectenna to the next as they orbit, to reduce the size of the transmitter antenna, which gets kind of humungous out at GEO.
DIRECT Rebuttal Thoughts
I had missed this when they were posted, but the Chair Force Engineer had some thoughts on DIRECT a couple weeks ago, here and here.
“Wow.” Are we to believe that ESAS was designed with little or no consideration of what the supporting infrastructure would cost? It would certainly explain why we’re stuck with the unaffordable Ares I and Ares V.
I’d like to say that I’m surprised, but sadly, I’m not.
Further NASA statements such as “Ares I + Ares V uses 15 SRB segments, while two Jupiter 232’s use 16 segments” also reveal an incredibly simplistic approach to cost estimation. Such simple methods might be appropriate for pre-algebra students. Professional cost estimators ought to know better. That’s why cost estimation is so difficult; there may literally be thousands of dependent and independent variables that make up the true cost of the system over its lifetime. Saving a few million in rocket hardware may have bigger reprocussions with development dollars, standing army costs, and infrastructure costs. It’s best summed up on Slide 26, where Jupiter’s higher launch costs (measured in tens of millions per launch) are offset by the savings of billions in development costs.
We’d have to see a full life-cycle cost accounting with assumptions to know whether or not it’s a good saving to cut development cost at the price of higher ops costs. It depends on how much you’re going to fly. But I suspect that it probably is, because the up-front costs are in expensive near-term dollars whereas the flight costs are down stream and discounted, and the flight rate will probably never get big enough to justify spending more on development to reduce marginal cost per flight. That’s always the problem with expendables.
I really need to write up my talk on marginal costs from Space Access.
A Brief Tutorial On Lunar Resources
From Paul Spudis, who unfortunately (at least for us, if not for him) was not in attendance at the ISDC.
The New Administrator Will Have His Hands Full
I missed it because I was too busy traveling and attending and covering the ISDC, but I had a piece at Pajamas Media yesterday on the challenges facing Bolden, if confirmed.
More ISDC Coverage
But Other Than That, It’s Great
Some criticism (to put it mildly) of Constellation over at SpaceVidCast, in comments.
I agree with the commenter over at Clark’s place, though, that the purpose of the program should not be to create jobs, and layoffs at NASA centers are a feature, rather than a bug, if we want to get more for the taxpayers’ money. Of course, if NASA could come up with something useful for those people to do in advancing the goal of becoming a spacefaring nation, and keep them on, that would be even better.
Suborbital Technology Panel
Marine Lt. Col. Paul Damphousse talking about SUSTAIN, a concept for delivering marines anywhere in the world on short notice. Recognizes it as a stretch goal, but use it to drive nearer-term suborbital point-to-point technologies, which are interesting in their own right, including commercial sector, that will eventually support that goal. Continue reading Suborbital Technology Panel
Rocketplane Resurrection?
I talked to George French briefly last night at the bar. He hasn’t given up on raising funds not only for Rocketplane XP, but is still hoping to revive Kistler itself. It wasn’t clear whether or not this was contingent on another bite at the COTS apple, but he’s hoping to have money reraised by August. Good luck with that in this economy. It would be nice, though, to see at least one reusable system going to orbit, after all these years.
The Greason Pick
…assuming that he really will be on the commission, of course.
Jeff Foust has a report on an aspect of Jeff’s talk yesterday that I missed because I was late to the session. It provides an interesting context for his commission duty, if it occurs.