[amsat-bb] Re: ARISSat-1 - Dumb Question
Hello All.. A basic rule of the internets is in the discussion of orbits when Hohmann transfers are brought up the easy discussion is over (grin)...but everyone below has the essential points. When a velocity vector modification is made in an orbit the area rule means that the changes to the orbit are increasingly felt as the antipodal or 180 degree point is approached. IN addition of course other factors act on the orbit and as Bob described it in the cares of ARISSAT the main one would be drag as the probe has a lot less mass then the space station...this will quickly remove the satellite from the orbital altitude of the station...although Bob is correct in a perfect world the satellite and ISS would meet again one orbit later. There is a great deal of difference in prox ops and long term orbit modifications. This is not initiative. The closest thing to it is in basic pilot training teaching the notion of a turn around a point. Here the change vector is wind and it takes a bit of instruction to recognize that any changes made now do not really manifest themselves until about 90 degrees later. There are several strange things that celestial mechanics drive. It took sometime to recognize that when the shuttle and station dock, the center of gravity of both vehicles combine to move the CG well outside the combined stack. (think of how the shuttle VRS say how a Progress docks as well as the relative mass of the vehicles). This eventually drove changes in the docking and latching procedure. Robert G. Oler WB5MZO Life Member AMSAT/ARRL and NARA and soon to be 5N something. CC: orbit...@hotmail.com; ko6th_g...@hotmail.com; g0...@aol.com; clintbradf...@mac.com; amsat-bb@amsat.org From: saguaroas...@cox.net Subject: Re: [amsat-bb] Re: ARISSat-1 - Dumb Question Date: Thu, 10 Feb 2011 17:51:12 -0700 To: bruni...@usna.edu This time I'll actually type something before hitting send;) The two burn maneuver is essentially a Hohmann transfer maneuver. The point of the first burn becomes the new apogee or perigee (depending on the direction of the burn). The burn will raise or lower the antipodal point from where the burn occurred. At that point a second burn in the same direction will bring the point of the first burn to the new level. But you all probably already knew that:) If you want to play around with this try this: http://orbit.medphys.ucl.ac.uk/home.php 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
Thank you Greg. Makes sense to me now. Also, just calculated the velocity of a 90 minute LEO orbit and the velocity of a geostationary 24 hr orbit using circumference and time. Found that the velocity at LEO is higher, so presumably the decrease in orbit altitude of Arissat due to decay must also add acceleration. (Gravity) 73 David G0MRF In a message dated 10/02/2011 05:26:00 GMT Standard Time, ko6th_g...@hotmail.com writes: From: g0...@aol.com Date: Wed, 9 Feb 2011 15:45:36 -0500 To: clintbradf...@mac.com; amsat-bb@amsat.org Subject: [amsat-bb] Re: ARISSat-1 - Dumb Question Hmm. This is a bit of a brain teaser... So if the satellite is deployed towards the rear of the ISS, it's velocity will be slightly lower. So does that mean it will go to a lower orbit- (Same as firing retros to reenter)? 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 ? Time for me to have a Tuna sandwich. We all know it's probably full of Dolphin...and they are really clever. David G0MRF 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
Celestial mechanics is a brain teaser...but most of what has been said here is more or less correct. The trick is to realize that the ONLY orbit where the velocities (and energy) are constant is a perfectly circular one...and that really doesnt happen but in theory (although some come very close)...a retrograde manuever will remove ARISSsat from the proximity of ISS very very quickly. Robert G. Oler WB5MZO From: ko6th_g...@hotmail.com To: g0...@aol.com; clintbradf...@mac.com; amsat-bb@amsat.org Date: Wed, 9 Feb 2011 21:12:28 -0800 Subject: [amsat-bb] Re: ARISSat-1 - Dumb Question From: g0...@aol.com Date: Wed, 9 Feb 2011 15:45:36 -0500 To: clintbradf...@mac.com; amsat-bb@amsat.org Subject: [amsat-bb] Re: ARISSat-1 - Dumb Question In a message dated 09/02/2011 06:08:45 GMT Standard Time, clintbradf...@mac.com writes: ... 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. Great, succinct info - MANY thanks! Clint, K6LCS Hmm. This is a bit of a brain teaser... So if the satellite is deployed towards the rear of the ISS, it's velocity will be slightly lower. So does that mean it will go to a lower orbit- (Same as firing retros to reenter)? 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 ? Time for me to have a Tuna sandwich. We all know it's probably full of Dolphin...and they are really clever. David G0MRF 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
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
[amsat-bb] Re: ARISSat-1 - Dumb Question
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
[amsat-bb] Re: ARISSat-1 - Dumb Question
In a message dated 09/02/2011 06:08:45 GMT Standard Time, clintbradf...@mac.com writes: ... 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. Great, succinct info - MANY thanks! Clint, K6LCS Hmm. This is a bit of a brain teaser... So if the satellite is deployed towards the rear of the ISS, it's velocity will be slightly lower. So does that mean it will go to a lower orbit- (Same as firing retros to reenter)? 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 ? Time for me to have a Tuna sandwich. We all know it's probably full of Dolphin...and they are really clever. David G0MRF ___ 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
From: g0...@aol.com Date: Wed, 9 Feb 2011 15:45:36 -0500 To: clintbradf...@mac.com; amsat-bb@amsat.org Subject: [amsat-bb] Re: ARISSat-1 - Dumb Question In a message dated 09/02/2011 06:08:45 GMT Standard Time, clintbradf...@mac.com writes: ... 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. Great, succinct info - MANY thanks! Clint, K6LCS Hmm. This is a bit of a brain teaser... So if the satellite is deployed towards the rear of the ISS, it's velocity will be slightly lower. So does that mean it will go to a lower orbit- (Same as firing retros to reenter)? 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 ? Time for me to have a Tuna sandwich. We all know it's probably full of Dolphin...and they are really clever. David G0MRF 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
Nice article in QST Feb 2011 pretty well spells out what they are doing and how... TK, K7TRK -Original Message- From: amsat-bb-boun...@amsat.org [mailto:amsat-bb-boun...@amsat.org] On Behalf Of Clint Bradford Sent: Tuesday, February 08, 2011 8:22 PM To: AMSAT BB Subject: [amsat-bb] ARISSat-1 - Dumb Question When ARISSat-1 is deployed next week, confirming it will simply be pushed outside the ISS, correct? How closely will it emulate the orbit of the ISS? What is its intended orbit - will it be passing the poles? I apologize if this is covered all over the place already ... Clint, K6LCS ___ 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
[amsat-bb] Re: ARISSat-1 - Dumb Question
... 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. Great, succinct info - MANY thanks! Clint, K6LCS ___ 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
