Start Date

4-1968 8:00 AM

Description

Round trip missions to Mars have been investigated to define representative launch windows and associated AV requirements. The 1982 inbound and the 1986 outbound Venus swingby missions were selected for analysis and serve to demonstrate the influence of the characteristics of the heliocentric trajectories on the launch window velocity requirements. This report presents results indicating the effects on the launch windows of velocity capability, transfer technique, and of the inclination, eccentricity, and insertion direction of the orbit. The analysis assumed a circular parking orbit at Earth and considers both circular and elliptical parking orbits at Mars. Use of one-, two-, and three-impulse transfers were investigated. The three-impulse transfer employs an intermediate elliptic orbit of 0,9 eccentricity. For all cases, insertion at planet arrival was into an orbit coplanar with the arrival asymptote and any required plane change was performed during the planet departure phase.

The minimum AV requirement to transfer from a circular parking orbit to a hyperbolic asymptote occurs when the orbits are coplanar and the maneuver is performed at periapsis of the hyperbola. The study indicates that, using a three-impulse transfer, the AV penalty for non-coplanar departures, is no more than 5-10% above the minimum coplanar requirements. Therefore, use in mission analysis of the coplanar AV requirements would not result in large errors if threeimpulse transfers are acceptable. Use of fewer impulses significantly increases the error. Similar characteristics occur for elliptical parking orbits. However, due to the low coplanar AV's, they provide a longer launch window for a given total AV capability.

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Apr 1st, 8:00 AM

Launch Window Analysis for Round Trip Mars Missions

Round trip missions to Mars have been investigated to define representative launch windows and associated AV requirements. The 1982 inbound and the 1986 outbound Venus swingby missions were selected for analysis and serve to demonstrate the influence of the characteristics of the heliocentric trajectories on the launch window velocity requirements. This report presents results indicating the effects on the launch windows of velocity capability, transfer technique, and of the inclination, eccentricity, and insertion direction of the orbit. The analysis assumed a circular parking orbit at Earth and considers both circular and elliptical parking orbits at Mars. Use of one-, two-, and three-impulse transfers were investigated. The three-impulse transfer employs an intermediate elliptic orbit of 0,9 eccentricity. For all cases, insertion at planet arrival was into an orbit coplanar with the arrival asymptote and any required plane change was performed during the planet departure phase.

The minimum AV requirement to transfer from a circular parking orbit to a hyperbolic asymptote occurs when the orbits are coplanar and the maneuver is performed at periapsis of the hyperbola. The study indicates that, using a three-impulse transfer, the AV penalty for non-coplanar departures, is no more than 5-10% above the minimum coplanar requirements. Therefore, use in mission analysis of the coplanar AV requirements would not result in large errors if threeimpulse transfers are acceptable. Use of fewer impulses significantly increases the error. Similar characteristics occur for elliptical parking orbits. However, due to the low coplanar AV's, they provide a longer launch window for a given total AV capability.

 

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