Hi Ed and list, I don't consider this an off topic theme (please correct me if I'm wrong Bart), so I'm posting my input to the list. > Now that Mir is history, and with the ISS project in full swing, the > following question comes to mind: what is the determining factor of > the orbital height of these two space stations? > > Are these relatively low heights dictated by: > > (1) Launch vehicle capabilities, > and/or > (2) The height of the inner radiation belt? The optimum height of Mir, ISS and any other satellite which must be frequently visited is determined by a careful trade-off between launch vehicle lifting capability which favours a low altitude and residual air drag which favours a high altitude. Launch vehicles can obviously carry more payload to a lower orbit, but the density of the residual atmosphere decreases with height and this reduces the amount of fuel required to maintain the orbit. As far as I know, the inner radiation belt doesn't come into the equation, although the "South Atlantic Anomaly" is an area where the belt reaches down to even the lowest orbital altitudes and is a factor in Shuttle missions since it affects communications. The necessity of the frequent reboosts of Mir was obvious when looking at the history plot of its orbital height on Heavens-Above. We intend to offer a similar chart for the ISS. Chris Chris Peat, Heavens-Above GmbH E-Mail: chris.peat@heavens-above.com Web-site: www.heavens-above.com ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www2.satellite.eu.org/seesat/seesatindex.html
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