altitude. The total time in shadow .during such a passage would be approx. 20% of the flight time. In practice the time in shadown would always be considerably.less than this. Time in shadow could be minimized by proper selection of the initial orbit inclination and orientation (nodal position), considering such factors as thrust levels (flight time), nodal regression rates, and solar position at start of flight (time of year). This time cannot however, be eliminated altogether for the entire flight. 3.6 HIGH-THRUST ORBITAL MECHANICS IN COMPARISON TO LOW THRUST For those phases of construction and repair that require manned operations at geosynchronous orbit, a high thrust system will be required. Low thrust will not be desirable because of long duration flight times which take place in a hostile environment (the radiation belt). Undoubtedly a more conventional level thrust system will be used. Delta V for transfer from 250 NM. LEO to synchronous orbit in-plane is approx. 12,700 fps. Requiring a 28.5° plane change increases this to 13,800 fps. With a high thrust system the plane change is not as costly in delta V as with the lower thrust. However, because of the lower Isp normally associated with higher thrust systems (i.e., <1000 sec), coupled with the fact that the manned operation generally requires a round trip, the added propellant weight due to this plane change is often considerably greater than with the low thrust system.
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