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Oberg: "The real significance of the ISS thruster test failure"
Henry Spencer wrote:
There's always an orientation which puts the radiators edge-on to both the Sun and the air, although perhaps it might be one that ISS can't use because of something like gimbal limits. To keep the solar arrays edge-on to the air, alas, you'd have to accept less-than-ideal Sun angles much of the time, and a penalty on power output as a result. (Mind you, it might have been preferable to just make the arrays somewhat bigger and plan to operate this way, to save reboost fuel; there was a nice little paper by Landis&Yu in 1991 suggesting this.) Amazing. I wasn't aware that anybody had ever read that paper. Our conclusion had been that you could gain a noticible amount of drag-reduction (not huge, but it adds up) if you simply feather the arrays when you're in the Earth's shadow. (If you don't need full power, you can feather them all the time, and just accept that your power is down by something like a factor of pi.) -- Geoffrey A. Landis http://www.sff.net/people/geoffrey.landis |
#82
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Oberg: "The real significance of the ISS thruster test failure"
"Geoffrey" wrote in
ups.com: Henry Spencer wrote: There's always an orientation which puts the radiators edge-on to both the Sun and the air, although perhaps it might be one that ISS can't use because of something like gimbal limits. To keep the solar arrays edge-on to the air, alas, you'd have to accept less-than-ideal Sun angles much of the time, and a penalty on power output as a result. (Mind you, it might have been preferable to just make the arrays somewhat bigger and plan to operate this way, to save reboost fuel; there was a nice little paper by Landis&Yu in 1991 suggesting this.) Amazing. I wasn't aware that anybody had ever read that paper. Our conclusion had been that you could gain a noticible amount of drag-reduction (not huge, but it adds up) if you simply feather the arrays when you're in the Earth's shadow. And ISS does exactly that - they call the mode "Night Glider". -- JRF Reply-to address spam-proofed - to reply by E-mail, check "Organization" (I am not assimilated) and think one step ahead of IBM. |
#83
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Oberg: "The real significance of the ISS thruster test failure"
On Sun, 21 May 2006 12:27:55 -0700, Geoffrey wrote:
Our conclusion had been that you could gain a noticible amount of drag-reduction (not huge, but it adds up) if you simply feather the arrays when you're in the Earth's shadow. "Feather"... (The zapkitty has a vision of ISS circling the globe with the solar arays windmilling freely in the breeze... -- Chuck Stewart "Anime-style catgirls: Threat? Menace? Or just studying algebra?" |
#84
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Oberg: "The real significance of the ISS thruster test failure"
"Jorge R. Frank" wrote:
And ISS does exactly that - they call the mode "Night Glider". If the arrays are at an angle to direction of travel (with the sun in the back), do they provide any lift at all ? Once the truss os fully deployed, if they were to put one side at 45° and the other at -45°, would it create sufficient force to actually put the station into a spin ? Will the surfaces be large enough that they could use the arrays/truss to help desaturate the CMGs ? |
#85
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Oberg: "The real significance of the ISS thruster test failure"
Geoffrey wrote:
Our conclusion had been that you could gain a noticible amount of drag-reduction (not huge, but it adds up) if you simply feather the arrays when you're in the Earth's shadow. How practical is/was it to make PV arrays consisting of independently rotated slats, like a venetian blind? Paul |
#86
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Oberg: "The real significance of the ISS thruster test failure"
In article , John Doe wrote:
And ISS does exactly that - they call the mode "Night Glider". If the arrays are at an angle to direction of travel (with the sun in the back), do they provide any lift at all ? They'd generate a little, I would think, but hypersonic L/D ratios are generally poor and these would be no exception, i.e. you'd pay for that added lift with quite a bit of added drag. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#87
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Oberg: "The real significance of the ISS thruster test failure"
In article ,
Paul F. Dietz wrote: How practical is/was it to make PV arrays consisting of independently rotated slats, like a venetian blind? There's nothing impossible about it, but it would add many moving parts (and many rotating joints with power transmission across them), and could reasonably be expected to reduce reliability as a result. It would be done only if there was some big important reason to do it. -- spsystems.net is temporarily off the air; | Henry Spencer mail to henry at zoo.utoronto.ca instead. | |
#88
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Oberg: "The real significance of the ISS thruster test failure"
Jorge R. Frank wrote:
"Geoffrey Landis" : Our conclusion had been that you could gain a noticible amount of drag-reduction (not huge, but it adds up) if you simply feather the arrays when you're in the Earth's shadow. And ISS does exactly that - they call the mode "Night Glider". Yep. Cheng-Yi Lu and I invented that (back when the space station power systems package was at Lewis Research Center). G. Landis and C-Y Lu, "Solar Array Orientation Options for a Space Station in Low Earth Orbit," Journal of Propulsion and Power, Vol. 7 No. 1, 123-125 (1991). John Doe wrote: If the arrays are at an angle to direction of travel (with the sun in the back), do they provide any lift at all ? Sure. Once the truss os fully deployed, if they were to put one side at 45° and the other at -45°, would it create sufficient force to actually put the station into a spin ? Yep. Slowly, though, since the station has a lot of mass. Will the surfaces be large enough that they could use the arrays/truss to help desaturate the CMGs ? Yep, probably could do that. You could also do it with drag, putting one array panel edge-on and the other flat on. Pioneer Venus-Mercury did that trick with solar arrays, using solar pressure, to extend the mission lifetime. -- Geoffrey A. Landis http://www.sff.net/people/geoffrey.landis |
#89
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Oberg: "The real significance of the ISS thruster test failure"
Paul F. Dietz wrote:
How practical is/was it to make PV arrays consisting of independently rotated slats, like a venetian blind? Not terribly practical. If you do that, you can feather the arrays ok, but you can't track, since each array shadows the one next to it. Unless you space them out. (The full-up ISS essentially does that, with several parallel wings. There's also a solar-power satellite design nick-named "abacus" with that technique). -- Geoffrey A. Landis http://www.sff.net/people/geoffrey.landis |
#90
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Oberg: "The real significance of the ISS thruster test failure"
On Sun, 21 May 2006 23:08:58 +0000, Henry Spencer wrote:
There's nothing impossible about it... ...It would be done only if there was some big important reason to do it. NASA would wind up needing funding from states that happen to make gimbal bearings... NASA PAO flack at a press confrerence: "No one has ever done this before! It will be a huge leap in space solar power applications that will undoubtedly have many spinoff effects for life on Earth... and also we're using RMS technology engineered for the shuttle/ISS program so costs will be reduced by a factor of 10!" Ayup... -- Chuck Stewart "Anime-style catgirls: Threat? Menace? Or just studying algebra?" |
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