NASA required a robust and reliable power source for the Mars Curiosity Rover on its mission to investigate Martian climate and geology. Previous Mars landers were much smaller and used Photo-Voltaic (PV) power (solar cells) and batteries for power. The environment on Mars is dusty. Over time, the PV panels became covered with dust and produced a fifty percent reduction in power to charge the batteries. In addition, the batteries degraded over time, holding less charge. Seasonal changes due to Mars’ orbit also reduce the intensity of the available sunlight and the associated power. Since the Mars Curiosity mission length was one Martian year (687 days), the PV power solution was not acceptable. A continuous power supply was necessary.
The average temperatures on Mars are in the range of negative 80 degrees Fahrenheit (negative 60 degrees Celsius), with winter temperatures reaching negative 195 degrees Fahrenheit. The additional capability of generated heat became an important factor for NASA as they were able to transfer the waste heat from the MMRTG through heat transfer tubes to the items within the rover that needed supplemental heat to properly function in the extreme temperatures on the Martian surface.
The power system needed to provide 110 watts at the beginning of the mission, with a minimum lifetime of 14 years, and be capable of operation in both outer space (Vacuum) and planetary atmospheres. In addition to surviving the harsh Martian environment, the power system also needed to survive the stresses of the rocket launch from Earth, transit to Mars and the EDL – Entry, Descent and Landing. This EDL was a unique sequence of pyroshocks (mini explosions) required to separate components at precise times to enable a safe reverse thrust landing for the jeep-sized Curiosity rover on the surface of mars.
The Multi-Mission Radioisotope Thermoelectric Generator (MMRTG) was chosen by NASA as the power source for the mission, based on its proven reliability and efficiency. Radioisotope Thermoelectric Generator (RTG) technology converts thermal energy from plutonium-238’s radioactive decay to electrical energy using thermoelectric modules. The MMRTG design was based on previous Teledyne Energy Systems, Inc. technology used on SNAP-19 RTG, which was successfully used to power the Pioneer 10 and 11 spacecraft in 1972 and 1973, respectively, and the Viking 1 and 2 Mars Landers in 1975. The RTG’s for the Pioneer 10 operated successfully for over 30 years, and the Pioneer 11 for over 22 years, until the communications link with the spacecraft was lost. In addition to providing the necessary power, the excess heat would be able to maintain the temperature of the rover and the sensitive instruments in its science bay.
NASA commissioned the US Department of Energy (DOE) to supply a Radioisotope power system. DOE awarded the MMRTG project to the Boeing Company’s Rocketdyne Propulsion and Power Division in June of 2003. Teledyne Energy Systems, Inc. teamed with Boeing and was responsible for providing the MMRTG. Teledyne Energy Systems, Inc. provided the housing and all internals, including the proven PbTe/TAGS thermoelectric modules. Rocketdyne supplied the cooling tubes and emissive coating external paint. The MMRTG was fueled at Idaho National Laboratory. After the initial fuelling, the MMRTG was producing about 120 watts power output.
The Success Story
The Mars Curiosity was launched at 10:02 a.m. EST on November 26, 2011 and successfully landed in Gale Crater at 1:32 a.m. EDT, August 6, 2012 after a 9 month cruise. To date, the mission has completed 501 Sol (Martian Days) and has achieved the goal of determining if Mars could ever have supported microbial life. The Mars rover instrumentation confirmed that there is clay on the Mars site called Yellowknife Bay, meaning there was once water there and a habitable environment. Also, channels have been found on the surface which exhibit evidence of water flow. Now, NASA scientists, as well as scientists from around the world, are benefiting from the power provided by Teledyne Energy Systems, Inc. thermoelectric generator to continue to explore other aspects of the Martian planet in preparations for future missions. Since the half-life of plutonium-238 is 87 years, and other Teledyne RTG units have successfully provided power for more than 20 years, there is potential to power systems on Curiosity longer than the planned mission time.
Teledyne Energy Systems, Inc. demonstrated its expertise not only in thermoelectric generators, but the ability to work as a power systems integrator on a space qualified system. The mission to Mars required meeting critical flight deadlines and Teledyne Energy Systems, Inc. met that challenge. Several Teledyne employees also earned the NASA Group Achievement Award for working so well with the many different laboratories and companies required to test and qualify the MMRTG for flight readiness.
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