Nuclear-powered Perseverance begins seven-month journey to Mars

July 30, 2020, 2:56PMNuclear News

An Atlas V rocket with NASA’s Mars 2020 Perseverance rover on board launches on July 30. Photo: NASA/Joel Kowsky

The launch of the Mars 2020 Perseverance rover went ahead as scheduled on July 30, lifting off from Space Launch Complex 41 at Cape Canaveral Air Force Station in Florida at 7:50 a.m. (EDT) . The rover was onboard a United Launch Alliance Atlas V 541 rocket.

Minutes later, NASA reported that all flight milestones were being met as planned. There are several more milestones to reach before Perseverance—the fifth rover that NASA has sent to Mars—lands on the Red Planet in seven months.

This illustration depicts NASA’s Mars Perseverance rover on the surface of Mars. Image: NASA

The mission: Equipped with 23 cameras—more than have been deployed on any interplanetary mission in history—and instruments designed to analyze the suitability of Mars for future human exploration, Perseverance is tasked with finding signs of ancient microbial life and collecting rock and soil samples for potential return to Earth in a future mission.

Only radioisotope thermoelectric generators (RTG) can provide the long-lasting, compact power source that Perseverance needs to carry out its long-term exploratory mission. The rover’s multi-mission RTG consists of a plutonium-238 heat source and thermocouples that use the plutonium’s decay heat energy and the contrasting cold of space to generate electricity.

Staff at INL assembled and tested the power source for the Mars 2020 Perseverance Rover. Photo: INL

The power: Department of Energy laboratories have built nearly 50 RTGs that have powered more than two dozen U.S. space missions, including the Curiosity rover, which landed on Mars in 2012 and is still going strong.

Pu-238’s half-life of nearly 88 years is ideal for deep-space travel, but the nation’s supplies have been dwindling. In 2015, Oak Ridge National Laboratory began U.S. plutonium production for the first time in nearly three decades. The lab has been consistently increasing its Pu-238 production capabilities and aims to produce 1.5 kg per year by 2026 to support a partnership between the DOE and NASA to ensure an ample supply of domestic plutonium to support future missions.

While ORNL provided the plutonium oxide and fuel cladding for the Perseverance power system, staff at Los Alamos National Laboratory manufactured the fuel, and Idaho National Laboratory’s Space Nuclear Power and Isotope Technologies Division assembled and tested the unit.

Working inside a hot cell, INL staff placed the fuel pellets into graphite components to form general purpose heat source modules, and then inserted those modules into a converter that houses thermocouples to form the radioisotope power system.

The specs: The RTG weighs about 99 pounds (45 kg) and contains 10.6 pounds (4.8 kg) of plutonium dioxide. It was designed to produce about 110 watts of electrical power at the beginning of the mission, a power output that will decrease predictably by a few percent each year. While the system has a design life of 17 years, it can be expected to produce power for much longer.

Two lithium-ion batteries, charged by the RTG, are available to meet peak demands of rover activities when the demand temporarily exceeds the RTG’s electrical output levels. (Perseverance’s power demand can reach 900 watts during science activities, according to NASA.) The RTG also provides a source of heat for the rover’s instruments and onboard systems.

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