Power Systems for Planetary Missions
Wednesday, June 24th, 2009, Glenn Research Center – Cleveland, OH
Geoffrey Landis is an expert in the exploration of the planets nearest Earth, namely Mars and Venus. Mars research is ongoing with many successful orbiters and landers and future plans for more elaborate missions. There has been much geological interest in Mars because of the polar cap, large canyons, volcanoes and the slight atmosphere. On the other hand, Venus is a planet where research has just begun. Venus is much different than Earth with a harsh atmosphere that has a large greenhouse effect, which has made it very hard to study.
Dr. Landis began speaking about the various Mars probes from the past. Mariner 4 was the first probe to Mars which caused some disappointment because it showed that Mars was not as Earth-like as many thought. Viking, in 1976, was an orbiter-lander that showed us river valley-like ditches that could mean there was liquid water on the surface in the past.
After this mission, twenty years passed until the Pathfinder and Sojourner rovers went to explore small rocks on the surface. There were also many missions, both NASA and international missions, that failed around this time, including the Mars Climate Orbiter and the Mars Polar Lander.
The next missions launched were the most successful to date, the Spirit and Opportunity Mars Exploration Rovers (MERs). Two rovers were launched and both landed and began to explore. About twice the size of Sojourner, the rovers were able to give a human perspective on the surface and move farther than Sojourner was able to.
Spirit landed in the Gusev Crater, which appeared to be a dry lake bed. Scientists believed that figuring out the story of water on Mars would be the best way to make ground-breaking discoveries. After outliving the 90 days for which it was designed, Spirit went exploring farther and traveled up Martian hills. It traveled to a feature known as “Home Plate” which was white because of the sulfate salt present that might suggest ancient water.
A wheel failed during this transit and the rover was now operating on five wheels instead of six, which caused the rover to upturn some of the top-level soil. This overturn meant that the rover found opaline silica, which is a mineral found in terrestrial hot springs. The mission is still operational today and currently the team is trying to find a way out of a sand trap in which the rover has lodged itself.
Opportunity landed on the opposite side of Mars in the Eagle crater. This gave geologists insight into the history of Mars because many layers of rock were visible and able to be studied. Opportunity also outlasted its expected life and traveled to the crater Victoria, where it spent two years. It is still operational today, and is traveling towards an even larger crater, Endurance. Large sandstorms have threatened the lives of these rovers due to the blocking of the solar arrays by dust, yet the rovers are still operational.
The most recently launched Mars mission was the Phoenix lander, which landed in May 2008 in the North Polar region of Mars. This lander was sent to dig into the subsurface ice on Mars.
Upcoming Mars missions include the Mars Science Laboratory with the Curiosity Rover to study the surface in greater detail. This mission is scheduled for 2012 and will have many new features. It will be twice the size of Spirit and Opportunity and will have new science tools. The MAVEN is also scheduled to study atmospheric gasses in 2013. Future manned missions are desired.
Venus unmanned study has only recently gained interest. The surface is believed to contain continents with vast basins instead of oceans. The days are around 1173 Earth days and the surface is very hot, around 850 degrees Fahrenheit, because of greenhouse effect. The surface pressure is around 92 bar and the clouds are composed of concentrated sulfuric acid. This adds up to a harsh environment that isn’t easily studied. But viable data can still be collected, so a few short-lived missions have been sent and more missions are being developed.
The Pioneer probes were the first missions to Venus. These involved multiple orbiters to get through the atmosphere. Russia actually landed multiple probes on the surface, the longest of which lasted seven hours. They also flew Vega balloons which floated for 72 hours at 54 kilometers of altitude. The Magellan Radar orbiter mapped the surface topography.
More exploration of Venus is desired today. Ways are being devised to explore the atmosphere with orbit and surface operations. An important fact the mission developers are using is that at 60 kilometers of altitude, the temperatures are Earth-like. The mission to Venus that Dr. Landis proposed involves a complex system with a large mission payload. The mission would use nuclear ion thrusters and have multiple rovers and a solar powered plane to fly through the atmosphere, which would use the cooler temperatures to perform most of the computing work. The rovers and plane would be deployed from an orbiter, which would relay information back to Earth and use a Stirling engine with an RTG (radioisotope thermoelectric generator) for power.
Overall, near-planetary study is a field that is opening up because of the new technologies that have been recently developed.