Session
Technical Session IV: New Mission Concepts I
Abstract
The next phase of Mars exploration will utilize a network of small low-cost landers, penetrators, microrovers and other surface devices to provide site-diversity. Direct Earth communications link, if required for these landers, will drive the lander design for two reasons: a) mass and complexity of a steerable high-gain antenna and b) electric power supply for high-power X-band amplifier (solar panel and battery mass). Total mass of the direct-Earth-link hardware for several recent small-lander designs exceeded mass of scientific payload. Alternatively, local UHF communication link via a relay spacecraft can be used. Resource requirements of this link are comparatively trivial; a simple whip antenna and less than 1 Watt power. Clearly, using a Mars Relay Space craft (MRS) is the preferred option if MRS can be accomplished in an affordable and robust way. Our paper describes a point design of such mission. We have asked the following question: What is the lowest-cost MRS spacecraft design that can be used for relaying scientific data from stations on Martian surface to Earth as well as for commanding these stations? Specifically, requirements for our MRS study were based on the latest IMEWG mission model for post-2001 era. The typical data return is total 65 Mbit/sol from six landers to be relayed in one 4-hour DSN contact using 34-m subnet. The mission design assumes dedicated MRS launch on the NASA Small Expendable Launch Vehicle to LEO parking orbit. Small spin-stabilized upper stage (Star-27) will inject the space craft to the Mars transfer orbit. The capability of this configuration is 98 kg (to C3 = 10.2 kg2/m2 ). The spacecraft provides all propulsion after injection: trajectory corrections, Mars orbit insertion and maintenance, and attitude control. The simple blowdown monopropellant hydrazine system has Δv capability of 1850 m/sec. The spacecraft is spin-stabilized, with the high-gain antenna pointing towards the Earth. Solar panel is behind this optically transparent (mesh) antenna and is sized for continuous transmitter operation under the worst-case conditions. Highly-integrated electronics is contained in a single unit with the exception of RF hardware and attitude sensors. The attitude determination is performed with a simple V-slit star and sun crossing sensors. Standard X-Band Small Deep-Space Transponder (SDST) is used for the DSN communications and UHF transceiver is used for the in-situ communications at 400 MHz. No antenna switching nor reconfiguration is required. Estimated spacecraft dry mass of 42 kg has 20% margin. Power requirement is 23 W for spacecraft housekeeping and 17-40 W DC for high-power transmitter (depending on orbit geometry). This MRS point design requires no post-launch deployments, has no moving parts and its full functional redundancy and expendables budget is compatible with five year lifetime in Mars orbit. The estimated life-cycle cost of this mission is less than $50M (including launch and mission operations).
Mars Relay Spacecraft Low-cost Approach
The next phase of Mars exploration will utilize a network of small low-cost landers, penetrators, microrovers and other surface devices to provide site-diversity. Direct Earth communications link, if required for these landers, will drive the lander design for two reasons: a) mass and complexity of a steerable high-gain antenna and b) electric power supply for high-power X-band amplifier (solar panel and battery mass). Total mass of the direct-Earth-link hardware for several recent small-lander designs exceeded mass of scientific payload. Alternatively, local UHF communication link via a relay spacecraft can be used. Resource requirements of this link are comparatively trivial; a simple whip antenna and less than 1 Watt power. Clearly, using a Mars Relay Space craft (MRS) is the preferred option if MRS can be accomplished in an affordable and robust way. Our paper describes a point design of such mission. We have asked the following question: What is the lowest-cost MRS spacecraft design that can be used for relaying scientific data from stations on Martian surface to Earth as well as for commanding these stations? Specifically, requirements for our MRS study were based on the latest IMEWG mission model for post-2001 era. The typical data return is total 65 Mbit/sol from six landers to be relayed in one 4-hour DSN contact using 34-m subnet. The mission design assumes dedicated MRS launch on the NASA Small Expendable Launch Vehicle to LEO parking orbit. Small spin-stabilized upper stage (Star-27) will inject the space craft to the Mars transfer orbit. The capability of this configuration is 98 kg (to C3 = 10.2 kg2/m2 ). The spacecraft provides all propulsion after injection: trajectory corrections, Mars orbit insertion and maintenance, and attitude control. The simple blowdown monopropellant hydrazine system has Δv capability of 1850 m/sec. The spacecraft is spin-stabilized, with the high-gain antenna pointing towards the Earth. Solar panel is behind this optically transparent (mesh) antenna and is sized for continuous transmitter operation under the worst-case conditions. Highly-integrated electronics is contained in a single unit with the exception of RF hardware and attitude sensors. The attitude determination is performed with a simple V-slit star and sun crossing sensors. Standard X-Band Small Deep-Space Transponder (SDST) is used for the DSN communications and UHF transceiver is used for the in-situ communications at 400 MHz. No antenna switching nor reconfiguration is required. Estimated spacecraft dry mass of 42 kg has 20% margin. Power requirement is 23 W for spacecraft housekeeping and 17-40 W DC for high-power transmitter (depending on orbit geometry). This MRS point design requires no post-launch deployments, has no moving parts and its full functional redundancy and expendables budget is compatible with five year lifetime in Mars orbit. The estimated life-cycle cost of this mission is less than $50M (including launch and mission operations).
