As Perseverance makes tracks, NASA must plan its next Mars move

March 10, 2021, 3:00PMNuclear News

NASA’s Mars 2020 Perseverance rover took its first drive on the surface of Mars on March 4, traversing 21.3 feet and executing a 150-degree turn in about 33 minutes. The drive was one part of an ongoing check and calibration of every system, subsystem, and instrument on Perseverance, which landed on Mars on February 18.

The NASA team has also verified the functionality of Perseverance’s instruments, deployed two wind sensors, and unstowed the rover’s 7-foot-long robotic arm for the first time, flexing each of its five joints over the course of two hours.

With relatively little fanfare, the functionality of Perseverance’s radioisotope thermoelectric generator (RTG)—assembled at Idaho National Laboratory and fueled by the decay of plutonium-238—is also being proved. It is reliably providing the power that Perseverance’s mechanical and communication systems require.

Plan now, NASEM says: Perseverance’s primary mission is slated for one Martian year, or 687 Earth days. According to the National Academies of Sciences, Engineering, and Medicine (NASEM), which released a consensus study on February 12, NASA should commit within one Earth year to an extensive and objective assessment of the merits and challenges of using different types of space nuclear propulsion systems and make significant technology investments during this decade. Preparing nuclear propulsion to support a human mission to Mars in 2039 will require an aggressive technology development program, according to Space Nuclear Propulsion for Human Mars Exploration. The study was undertaken by the NASEM Space Nuclear Propulsion Technologies Committee.

A successful nuclear propulsion system will require more than just a functional, compact, and efficient nuclear device. NASA’s program would need to include subsystem development, prototype systems, ground testing, and cargo missions as a means of flight qualification prior to its first crewed use, the report says.

Thermal or electric? The NASEM study assessed the primary challenges, merits, and risks for developing a nuclear thermal propulsion (NTP) system and a nuclear electric propulsion (NEP) system for a human mission to Mars. NTP would use the thermal energy from a nuclear reactor to heat hydrogen propellant and create thrust, while NEP would convert that thermal energy into electrical energy that would generate thrust by ionizing inert gas propellants (such as xenon and krypton) and accelerating the ions using a combination of electric and magnetic fields or an electrostatic field.

According to the NASEM study, detailed comparisons of NEP and NTP systems are needed to assess the viability of each system for a crewed mission to Mars. While the fundamental challenge facing an NTP system is the ability to heat its propellant to about 2,700 K, the fundamental challenge for an NEP system is scaling up the operating power for each subsystem.

Nuclear space: NASA, which sponsored the NASEM study, has other work on space nuclear applications underway. NASA has signed a memorandum of understanding with the Department of Energy on research, development, and testing of nuclear propulsion systems and a lunar based power supply and grid system; has sought industry input for nuclear propulsion; and continues ongoing research, including the testing of high-assay low-enriched uranium fuel elements that could fuel NTP systems.

“Safely transporting astronauts to and from Mars will require advances in propulsion systems to develop spacecraft that are up to the challenge,” said Roger Myers, cochair of the report committee. “Nuclear propulsion systems have the potential to substantially reduce trip time compared to nonnuclear approaches. Synergy with other space mission applications and terrestrial power programs is also significant and will bring about added value.”

Between planned lunar missions that can be supported by nuclear propulsion and nuclear surface power, the development of dynamic radioisotope power systems, and NASEM’s recommendations on the development of nuclear propulsion technologies, it is clear that NASA’s future will be nuclear powered.

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