NASA's Psyche spacecraft was photographed at JPL in July 2021, during its assembly, test and launch operations phase. The spececraft will be propelled by hall thrusters to reach its target in the main Asteroid Belt. Credit: NASA/JPL-Caltech
NASA's Psyche spacecraft will be able to propel itself through deep space using more brain power than brute force when it is time. The quiet and efficient power of electric propulsion, once the stuff of science fiction will propel the Psyche spacecraft to the main asteroid Belt between Mars and Jupiter. The orbiter's target is a metal-rich asteroid, also known as Psyche.
The spacecraft will launch on August 20, 2022. It will travel approximately 1.5 billion miles (2.4 million kilometers) over three years to reach the asteroid. Scientists believe it may be part the core of a planetesimal. This is the building block for a rocky planet's early days. The mission team will use the unique payload of science instruments once in orbit to explore what this target can tell them about the formation of rocky worlds such as Earth.
To launch off the launchpad, and escape Earth's gravity, the spacecraft will use the Falcon Heavy rocket engine. The rest of the journey will be powered by solar electric propulsion once Psyche has separated from the launch vehicle. This propulsion uses large solar arrays to convert sunlight into electricity. The spacecraft's thrusters are powered by this form of propulsion. These are known as Hall thrusters and will be used by the Psyche spacecraft beyond the orbit of the moon.
Left, xenon plasma emits a bright blue glow from an identical electric Hall thruster to the ones that will propel NASA’s Psyche spacecraft into the main asteroid Belt. A similar non-operating thruster is shown on the right. Credit: NASA/JPL-Caltech
Psyche will be carrying tanks filled with xenon as propellant. This neutral gas is used in plasma TVs and car headlights. Four thrusters on the spacecraft will use electromagnetic fields to accelerate or expel charged atoms (or ions) of that xenon. They create thrust which gently propels Psyche across space and emits blue beams of ionized xenon.
The thrust is actually so gentle that it exerts roughly the same pressure as if you held three quarters of your hand in your hands. It's sufficient to propel Psyche through deepspace. The spacecraft will eventually accelerate to speeds of up 200,000 miles an hour (320,000 km per hour) without any atmospheric drag.
Because they are so efficient, Psyche could run its Hall thrusters almost nonstop for many years without running out. Psyche will be carrying 2,030 lb (922 kg) of xenon in its tanks. Engineers estimate that it would use about five times as much propellant if it used traditional chemical thrusters.
"Solar electric propulsion was an integral part of our mission plan from the very beginning. It would have been impossible to create the Psyche mission without it," Lindy ElkinsTanton from Arizona State University, who is the principal investigator of the mission. It's become part and parcel of the mission's character. To calculate orbits and trajectories using solar electric propulsion, it takes a skilled team.
A gentle maneuver
Psyche will launch at NASA's Kennedy Space Center's historic Pad 39A. The Falcon Heavy will position the spacecraft so that it can fly to Mars seven months later in May 2023. The delicate task of getting the spacecraft in orbit around asteroid Psyche will be performed by the thrusters. They will use a little ballet to return the craft to its target orbit.
This task will be difficult because scientists don't know much about the asteroid. It appears in telescopes as a small dot of light. Ground-based radar indicates it is approximately 140 miles (226 km) wide and potato-shaped. Scientists won't be able to determine how its gravity field functions until then. Navigation engineers will use electric propulsion thrusters to propel the spacecraft through a series of orbits to bring it closer to Psyche as the mission's science investigation continues over 21 months.
NASA's Jet Propulsion Laboratory, in Southern California manages the mission. It used a similar propulsion system for Deep Space 1. The mission launched in 1998, and passed by an asteroid before it was stopped in 2001. Dawn was next, using solar electric propulsion to orbit and travel to the asteroid Vesta. The protoplanet Ceres followed. Dawn was the first spacecraft to orbit extraterrestrial targets. It lasted 11 years and ended in 2018, when it ran out of hydrazine propellant.
Propulsion partners
Maxar Technologies has used solar electric propulsion for commercial satellite communications since the 1970s. Psyche needed super-efficient Hall thrusters for deep space flight. That's when JPL engineers were able to help. Both teams believe that Psyche will push the boundaries of solar electric propulsion by using Hall thrusters beyond lunar orbit.
Steven Scott, Maxar’s Psyche program manager, stated that solar electric propulsion technology offers the right combination of cost savings, efficiency and power. He believes it could be an important part in future science missions to Mars.
Maxar's Palo Alto team, California was also responsible for the building of the van-sized chassis. This housed the electrical system and propulsion systems as well as the guidance and navigation system. Psyche, once fully assembled will be moved into JPL's large thermal vacuum chamber to test the environment in deep space. The spacecraft will be launched from Cape Canaveral by JPL next spring.
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