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| Testing the first server sky thinsat arrays may be challenging - they don't belong in a common orbit, they won't last long below 2000 km altitude due to ram drag. It would be nice to deploy the first tests at M288, but that will require a custom launch. | Testing the first server sky thinsat arrays may be challenging - they don't belong in a common orbit, they won't last long below 1000 km altitude due to ram drag. It would be nice to deploy the first tests at M288, but that will require a custom launch. |
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| But there's a trick. | If we dispensed thinsats from a GTO transfer orbit with a 622 km perigee ( 7000 km radius ), MORE LATER |
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| Thinsats can be tested in a highly elliptical orbit above LEO and below GEO. Deploying them as hitchhikers from a GTO bound upper stage would work - except that the perigee of the GTO orbit would be too low. | |
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| What if we used a tether? Ivan Bekey proposed sending shuttle back from the space station by lowering it on a tether, first. The combined two-mass-and-a-string system would orbit around the center of gravity, with shuttle pulled down and ISS pulled up by tides. ISS moves up, going faster than natural orbital velocity, and shuttle is slower. When the tether is released (twang!) the ISS orbit rises, and shuttle reenters with somewhat less velocity than it would otherwise. Spool the tether back into ISS, and do the same thing for the next visit. This could significantly reduce the amount of propellant needed to raise orbit. |
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| Well, it might not ''really'' work because that would jerk ISS around, and subject it to "milligravity" that it isn't designed for. And the released tether will get frisky, might break something or even puncture a hole. | |
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| But a tether between the GTO stage and a server sky experiment package? We want to reenter the GTO stage, and raise experimental perigee. Doesn't have to be much. | === But there's a trick. === |
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| Let's assume the experiment weighs 50 kg, and the empty stage weighs 500 kg. | Thinsats can be tested in a highly elliptical orbit above LEO and below GEO. Deploying them as hitchhikers from a GTO bound upper stage would work - except that the perigee of the GTO orbit is too low. Raise it, just enough to make 92 5 gram thinsats (V = 3 array) last a month or two - lets assume that is 1322 km altitude perigee (7700 km radius). Start with a GTO transfer orbit with a perigee of 622 km altitude (7000 km radius), with an apogee velocity of 1640.7 m/s. The test orbit has an apogee velocity of 1708.7 m/s, for a delta V of 68 meters per second, an impulse of 31 Newton-seconds. That is similar to one Estes E9-4 model rocket engine (30 N-s, 57 grams, 2.8 seconds). Of course, we would want a custom engine with a much slower burn, lighter casing, etc. Perigee velocity is 5.53 km/s. Let's assume that we are in full area ram drag for 80% of the orbit perigees, and edge-on for 20% of the orbit perigees, and that drag occurs within 200 km of perigee; a 42 degree arc, 0.73 radians, 5600 kilometers at an apogee velocity of 9357 m/s, 600 seconds. Air drag - Larson and Wertz tells us that mean density at 1250 km is 1.11e-15 kg/m^3^, and 5.21e-16 kg/m^3^ at 1500 km. Let's assume 1e-15 kg/m^3 at 1322 km altitude, edge on for 20% of the orbits, and ram drag for 80% of the orbits. The average drag through perigee is $ 0.8 A \rho V^3 $, or $ 0.8 * 0.025 * 1e-15 * 9357^3^ or 1.64e-5 N, decellerating the 5 gram thinsat by 3.3e-3 m/s^2^, or 2 m/s per orbit. Circular orbit velocity at that altitude is 7195 m/s, 2162 m/s less than GTO, so we would get about 1000 experimental orbits before the altitude starts decaying fast. |
Hitchhiker Server Sky Test
Testing the first server sky thinsat arrays may be challenging - they don't belong in a common orbit, they won't last long below 1000 km altitude due to ram drag. It would be nice to deploy the first tests at M288, but that will require a custom launch.
If we dispensed thinsats from a GTO transfer orbit with a 622 km perigee ( 7000 km radius ), MORE LATER
But there's a trick.
Thinsats can be tested in a highly elliptical orbit above LEO and below GEO. Deploying them as hitchhikers from a GTO bound upper stage would work - except that the perigee of the GTO orbit is too low. Raise it, just enough to make 92 5 gram thinsats (V = 3 array) last a month or two - lets assume that is 1322 km altitude perigee (7700 km radius). Start with a GTO transfer orbit with a perigee of 622 km altitude (7000 km radius), with an apogee velocity of 1640.7 m/s. The test orbit has an apogee velocity of 1708.7 m/s, for a delta V of 68 meters per second, an impulse of 31 Newton-seconds.
That is similar to one Estes E9-4 model rocket engine (30 N-s, 57 grams, 2.8 seconds). Of course, we would want a custom engine with a much slower burn, lighter casing, etc.
Perigee velocity is 5.53 km/s. Let's assume that we are in full area ram drag for 80% of the orbit perigees, and edge-on for 20% of the orbit perigees, and that drag occurs within 200 km of perigee; a 42 degree arc, 0.73 radians, 5600 kilometers at an apogee velocity of 9357 m/s, 600 seconds.
Air drag - Larson and Wertz tells us that mean density at 1250 km is 1.11e-15 kg/m3, and 5.21e-16 kg/m3 at 1500 km. Let's assume 1e-15 kg/m3 at 1322 km altitude, edge on for 20% of the orbits, and ram drag for 80% of the orbits. The average drag through perigee is $ 0.8 A \rho V3 , or 0.8 * 0.025 * 1e-15 * 93573 or 1.64e-5 N, decellerating the 5 gram thinsat by 3.3e-3 m/s2, or 2 m/s per orbit.
Circular orbit velocity at that altitude is 7195 m/s, 2162 m/s less than GTO, so we would get about 1000 experimental orbits before the altitude starts decaying fast.