Sent from my iPod Rick Tejera Editor, SACnews Saguaro Astronomy Club www.saguaroastro.org K7TEJ
On Feb 10, 2011, at 17:17, "Bob Bruninga" <bruni...@usna.edu> wrote: >> a retrograde maneuver will remove ARISSsat from >> the proximity of ISS very very quickly. > > It is interesting that any such one-thrust (arm throw) maneuver will then > intersect the ISS exactly one orbit later. In theory that is. But the > difference in drag at that low altitude will usually be enough to have a > safe miss distance on the next and subsequent orbits. > > I think that is why most space maneuvers require two burns. One to start a > new orbit (but it will still intersect the original orbit on every orbit. > Then a second burn somewhere else in the orbit to get rid of that > intersecting point? > > Bob, WB4APR > >>>>> ... Clint. When ARISSAT is released it will stay in the "Plane" of > ISS >>> orbit...they will toss it retrograde meaning in the opposite direction > of >>> the velocity vector and with its slightly lower velocity the orbit will >>> start to decrease...this is done so that very quickly the orbits will > stop >>> being "prox ops" reasonably fast. >>> >>> If so, then I believe as the orbit altitude is reduced, the apparent >>> velocity increases.....(??) which will cause ARISsat-1 to 'move ahead' > of the >>> ISS over a few hours >>> >>> But didn't we say the velocity would be less than the ISS due to the > method >>> of deploying it against the velocity vector ? >>> >> >> Interesting puzzler, eh? From what I have read in the past, I think this > their logic. >> >> What they are trying to do is to separate the orbits of the ISS and > ARISSat as quickly as possible, to avoid the potential for a collision. > Consider the options: >> >> 1. Throw it sideways to the ISS orbit. The result is that twice per > orbit the two spacecraft's paths will cross, side to side. Bad idea. >> >> 2. Throw it ahead of the ISS (faster orbit speed). This will raise the > orbit, slightly, and also make it a bit elliptical (up and down). The > higher orbit makes the satellite go behind the ISS, but the elliptical shape > also means that the orbits will cross every orbit (but out of phase, so they > won't be at the same place when they do). But, then as the ARISSat orbit > decays, they will get closer and closer, potentially getting back to the > same place. Not good, either. >> >> 3. Throw it behind the ISS (slower orbit). As you note, this will lower > the orbit (and make it a bit elliptical), and initially the apogee of the > orbit will intersect that of the ISS. Being in a lower orbit, ARISSat will > move ahead of the ISS, and over time, as the ARISSat orbit decays, the two > will diverge even farther. So, this is the safest. >> >> At least, I think that's the logic. If not, pass me some of that tuna... >> >> Greg KO6TH > > _______________________________________________ > Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. > Not an AMSAT-NA member? Join now to support the amateur satellite program! > Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. Opinions expressed are those of the author. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://amsat.org/mailman/listinfo/amsat-bb
