NASA Glenn Research Center’s Optical Instrumentation and Nondestructive Evaluation (NDE) Branch delivered its Smart Power System to Carnegie Mellon University (CMU). The system was integrated into CMU’s Scarab lunar rover. Scarab is a joint effort between CMU, Glenn’s Space Flight Systems and Research and Technology Directorates, NASA’s In-Situ Resource Utilization Project, and the NASA Ames Research Center to develop an Earth analog for a lunar rover. The Smart Power System is a stand in for more lunar friendly power systems, which might be based on radioisotope heat sources.
Power supply; PWM, pulse-width modulation.
Long description of figure 1.
The Smart Power System integrates a battery bank, a charging system, and a power converter with electrical characteristics similar to that of Glenn’s Stirling Radioisotope Generator (see the diagram). This system also incorporates a microprocessor-based instrumentation package that communicates with Scarab’s central processing unit (CPU) through a serial data link. This system produces a nominal 28-V bus for the general power needs of the robot and a second programmable 720-W supply that can be adjusted by the rover for any voltage between 24 and 48 V. The Scarab rover (see the photograph) currently uses the programmable supply for the wheel drive motors. In addition to providing flexibility, the Smart Power System allows CMU to instantaneously monitor several power system variables during testing and operation. This functionality will allow power-consumption modeling for different mission objectives, which could provide invaluable information for a power-constrained mission such as a lunar exploration.
Scarab lunar rover.
As described in a Pittsburgh Post-Gazette article, “The robotic rover, Scarab, is designed to drill into the ground and obtain core samples a meter long that it also can process and analyze. The eventual goal is finding hydrogen, and possibly water and other chemicals, that can be mined on the moon to produce fuel, water and air essential for supporting lunar outposts” (ref. 1).
Glenn’s Optical Instrumentation and NDE Branch designed the Smart Power System, which is the only noncommercially available subsystem in Scarab (see the following photograph). The Smart Power System gives CMU the flexibility to try different actuators and instruments with varying power requirements. It also monitors the two power buses for voltage and current, calculates instantaneous power and power converter efficiency, and can be set to cut the programmable voltage output at a current level chosen by the Scarab CPU to prevent overload conditions. Thus, CMU has been able to monitor instantaneous power system variables while testing Scarab. The Smart Power System also can initiate communication with the CPU autonomously when an anomalous condition, such as low battery voltage or a current overload, occurs. For mission safety, if the Smart Power System were to fail, Scarab would not lose battery power and the battery voltage would appear on the programmable bus. A system such as this could eventually be extended to flight-level hardware, which would allow for a highly robust power system capable of a high level of autonomy, thus off-loading the spacecraft CPU and increasing performance and reliability.
Power system within Scarab.
Last updated: November 7, 2008
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