Well, at least this much is clear: NASA’s propulsion system for its Psyche spacecraft looks a lot cooler than previous probes. The thrusters (known as Hall thrusters) emit a futuristic blue glow. The thrusters will be reliant on solar arrays that convert sunlight into electricity and will carry the probe 1.5 billion miles (2.4 billion kilometers) to its intended destination: an asteroid.
The treasure in the sky
The craft’s ultimate goal is the metal-rich asteroid 16 Psyche. Located in the main asteroid belt between Mars and Jupiter, it will take Psyche, the spacecraft, three and a half years to reach Psyche, the asteroid.
The spacecraft will also rely on the large chemical rocket engines of the Falcon Heavy to blast off Pad 39A at NASA's Kennedy Space Center and to escape the planet's gravity. But the rest of the journey, once Psyche separates from the launch vehicle, will rely on solar electric propulsion. This form of propulsion starts with large solar arrays that convert sunlight into electricity, providing the power source for Psyche's thrusters.
"Even in the beginning, when we were first designing the mission in 2012, we were talking about solar electric propulsion as part of the plan. Without it, we wouldn't have the Psyche mission," said Arizona State University's Lindy Elkins-Tanton, who as principal investigator leads the mission. "And it's become part of the character of the mission. It takes a specialized team to calculate trajectories and orbits using solar electric propulsion."
For propellant, the spacecraft will carry tanks of xenon, the same noble gas you see in plasma TVs and those bright headlights which blind the traffic on the other side of the road. Psyche’s four thrusters will use electromagnetic fields to accelerate and expel charged atoms, or ions, of the gas. As ions from the xenon are expelled, they create thrust that smoothly propels the craft through space, emitting blue beams of ionized xenon in the process. It’s actually so smooth that the scientists that built it say that its pressure is about that which you would feel holding three quarters in your hand. However, despite the gentleness of it, the Hall thrusters would be forceful enough to accelerate Psyche to speeds of up to 200,000 miles per hour (320,000 kilometers per hour).
While this will be the first time that Hall thrusters have been used beyond the orbit of the Moon, it's not the first of its kind to use solar electric propulsion. NASA's Jet Propulsion Laboratory, which manages the mission, used a solar electric propulsion chassis with the agency's Deep Space 1, which launched in 1998 and flew by an asteroid and a comet before the mission ended in 2001.
Next came Dawn, which used it to travel to, and orbit, the asteroid Vesta and then the protoplanet Ceres. The first spacecraft ever to orbit two extraterrestrial targets, the Dawn mission lasted 11 years, ending in 2018 when it used up the last of the hydrazine propellant used to maintain its orientation.
The spacecraft was built by Maxar Technologies and includes a multispectral imager, magnetometer, and a gamma-ray and neutron spectrometer. Its ultimate goal is to determine whether the asteroid is a core, or if it is an unmelted material; the ages of regions of the surface; whether small metal bodies incorporate the same light elements as are expected in the Earth's high-pressure core; if Psyche was formed under conditions more oxidizing or more reducing than Earth's core; and to characterize the asteroid’s topography.
Researchers believe that the 140-mile wide (226-kilometer) asteroid could be made entirely of iron and nickel. If true, its value could reach $10,000 quadrillion, more than the entire economy of Earth.
"Solar electric propulsion technology delivers the right mix of cost savings, efficiency, and power and could play an important role in supporting future science missions to Mars and beyond," said Steven Scott, Maxar's Psyche program manager.
The mission is set to launch in August 2022.
