Last Thursday, NASA’s newest rover, Perseverance, landed successfully in the Jezero Crater on Mars, bringing with it a whole suite of new technologies. While the successful landing was a feat in and of itself, the real work for Perseverance has yet to begin.
The Perseverance rover runs on electrical power with an on-board power source. Image used courtesy of NASA
Now alone on the Red Planet, the rover will require electrical power to move, communicate, and utilize all of its new equipment. How do you keep something working that requires indefinite power when it’s 130 million miles away with no hope for human intervention?
In this article, we’ll explore the issues with solar power on Mars, the electrical engineering that went into powering the Perseverance rover, and how NASA engineers plan on keeping it alive on earth’s neighboring planet.
Opportunity’s Death: The Case Against Solar
The seemingly obvious approach to this problem would be to slap a bunch of solar panels on the rover and call it a day. This idea has its merits, and even NASA agrees as it famously used solar to power the Opportunity rover. However, the untimely death of Opportunity occurred because of dust storms creating issues with solar power.
The air before and after a dust storm on Mars. Image used courtesy of NASA
In 2018, Mars experienced one of the most severe dust storms ever recorded. The storm lasted for months and grew so big that it eventually encompassed the entire planet, meaning that virtually no point on the planet’s surface had access to sunlight.
Naturally, Opportunity lost its power because its solar cells couldn’t generate electricity. Without power, the rover couldn’t turn its heaters on, making it susceptible to the harsh conditions of Mars. Eventually, Opportunity could no longer endure the storm, losing contact with NASA for good.
Multi-Mission Radioisotope Thermoelectric Generation
While this storm was certainly an anomaly, these missions have too much money invested in them and too much at stake to leave up to chance.
Following a similar concept to the Curiosity rover, Perseverance rejects solar power in favor of a technique called multi-mission radioisotope thermoelectric generation (MMRTG). As the name implies, the power generation system consists of thermoelectric generators placed near a radioactively decaying piece of plutonium-238.
The plutonium undergoes radioactive decay, which releases a substantial amount of heat as a byproduct. The thermoelectric generators then utilize the Seebeck effect to convert this heat into electricity to power Perseverance. The system also has two lithium-ion batteries to provide peak power to the rover as needed.
Model of an MMRTG. Image used courtesy of NASA
At launch, the MMRTG system for Perseverance produced about 110 W of electrical power, although this number will decline with time (due to the half-life of plutonium). The system has an expected lifespan of 14 earth years, which has required about 10.6 pounds of plutonium and $75 million.
Keeping the Lights On
Having a self-sustaining form of energy production has more added benefits than just protection from weather events. Since the MMRTG allows the rover’s power system to be self-contained, Perseverance can explore previously restricted terrains without fear of losing power (e.g., while scouting a cave or a shadowy valley).
While an expensive solution and not one that will likely find much value here on earth, MMRTGs may be an effective power solution on Mars. Thankfully, it looks like Perseverance is well prepared for the long journey ahead.
Featured image used courtesy of NASA