Start Date
4-1968 8:00 AM
Description
Several deorbit maneuver strategies for unmanned Mars soft landers are evaluated in terms of propulsive efficiency, targeting capability, communication link geometry, and sensitivity to system uncertainties. These strategies include (1) minimum deorbit impulse, (2) minimum entry condition uncertainties, (3) minimum variation in the lander antenna aspect angle during entry, (4) minimum communication range from the lander to the orbiting spacecraft during entry. The selected maneuver strategy is a combination of the above which restricts orbiter lead angles to the range between 0 deg and -10 deg. The analysis covers a range of elliptical orbits with periapsis altitudes of 500 to 2500 KM and apoapsis altitudes of 10,000 to 20,000 KM. The nominal orbit which is selected in order to best satisfy all mission considerations is 1300 KM by 12,500 KM (hp x hA) .
Mission considerations include orbit orientation of the orbiting spacecraft for planet surface mapping, landing site location between 15 to 30 degrees from the terminator for entry TV imaging, and orbit characteristics which insure a 50-year orbit lifetime and non-occultation of either the Sun or Star Canopus for 30 days after encounter. These constraints, coupled with the uncertainties introduced by trans-Mars navigation uncertainty and orbit insertion maneuver uncertainties, are used in the definition of minimum targeting flexibility required to land at a preselected location (latitude and longitude) and the regions of Mars which can be selected for landing. The selection of a landing site after surveillance from orbit where as much targeting flexibility as possible is desired is also considered.
Two aspects of the error analysis are considered. The first deals with the range of orbits relative to a preselected nominal which might be experienced. The sources leading to this range uncertainty include cruise navigation, orbit insertion maneuver, and orbit trim maneuver. The deorbit maneuver strategy must be capable of compensating for these orbit uncertainties if a preselected landing site is to be acquired.
Deorbit Maneuver and Targeting Strategy for Unmanned Mars Landers
Several deorbit maneuver strategies for unmanned Mars soft landers are evaluated in terms of propulsive efficiency, targeting capability, communication link geometry, and sensitivity to system uncertainties. These strategies include (1) minimum deorbit impulse, (2) minimum entry condition uncertainties, (3) minimum variation in the lander antenna aspect angle during entry, (4) minimum communication range from the lander to the orbiting spacecraft during entry. The selected maneuver strategy is a combination of the above which restricts orbiter lead angles to the range between 0 deg and -10 deg. The analysis covers a range of elliptical orbits with periapsis altitudes of 500 to 2500 KM and apoapsis altitudes of 10,000 to 20,000 KM. The nominal orbit which is selected in order to best satisfy all mission considerations is 1300 KM by 12,500 KM (hp x hA) .
Mission considerations include orbit orientation of the orbiting spacecraft for planet surface mapping, landing site location between 15 to 30 degrees from the terminator for entry TV imaging, and orbit characteristics which insure a 50-year orbit lifetime and non-occultation of either the Sun or Star Canopus for 30 days after encounter. These constraints, coupled with the uncertainties introduced by trans-Mars navigation uncertainty and orbit insertion maneuver uncertainties, are used in the definition of minimum targeting flexibility required to land at a preselected location (latitude and longitude) and the regions of Mars which can be selected for landing. The selection of a landing site after surveillance from orbit where as much targeting flexibility as possible is desired is also considered.
Two aspects of the error analysis are considered. The first deals with the range of orbits relative to a preselected nominal which might be experienced. The sources leading to this range uncertainty include cruise navigation, orbit insertion maneuver, and orbit trim maneuver. The deorbit maneuver strategy must be capable of compensating for these orbit uncertainties if a preselected landing site is to be acquired.
Comments
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