When it’s time for NASA’s Saiki spacecraft to power itself through deep space, it will be using more of a brain than just the courage to do so. Once like a science fiction novel, the efficient and quiet power of electric propulsion will provide the power to propel the Pushke spacecraft to the major asteroid belt between Mars and Jupiter. The Orbiter’s Target: A metal-rich asteroid, also known as Psyche.
In August 2022, it will travel approximately 1.5 billion miles (2.4 billion kilometers) over three and a half years to reach the asteroid. Scientists believe that asteroids may be part of the core of planetesimals, which are components of early rocky planets. Once in orbit, the mission team will use the payload of scientific instruments to investigate what this unique target can reveal about the formation of rocky planets like Earth.
The spacecraft will use the Falcon Heavy Rocket’s large chemical rocket engine to blow past the launch pad and escape the Earth’s gravity. But once Psyche leaves the rocket, the rest of the journey relies on solar electric propulsion. This form of propulsion begins with a large solar array that converts sunlight into electricity and powers the spacecraft’s thrusters. They are known as Hall thrusters, and the Saiki spacecraft will be the first to use them beyond our lunar orbit.
As a propellant, Psyche carries a tank full of xenon. Xenon is the same neutral gas used in car headlights and plasma TVs. The spacecraft’s four thrusters use an electromagnetic field to accelerate and emit their xenon-charged atoms or ions. When those ions are released, they create a thrust that gently propels Psyche into space, emitting a blue beam of ionized xenon.
In fact, the thrust is very gentle, applying about the same amount of pressure as you feel if you have three-quarters in your hand. But it’s enough to accelerate Psyche in deep space. With no atmospheric drag to curb it, the spacecraft will eventually accelerate to speeds of 200,000 miles per hour (320,000 kilometers per hour).
They are so efficient that Psyche’s Hall thrusters could operate almost non-stop for years without running out of fuel. Psyche carries 2,030 pounds (922 kilograms) of xenon into the tank. Engineers estimate that if the mission had to use conventional chemical thrusters, it would burn about five times that amount of propellant.
“From the beginning, when we first designed the mission in 2012, we were talking about solar electric propulsion as part of the plan, without it, there would be no psychic mission,” said Lindy Elkins Tanton of Arizona State University. “And it has become part of the mission’s character. It takes a dedicated team to calculate orbits, and orbits using solar electric propulsion.”
Psyche will be launched from the historic Pad 39A at NASA’s Kennedy Space Center. Seven months later, in May 2023, Falcon Heavy will place the spacecraft in orbit. In early 2026, thrusters will use a little, to do the delicate task of putting the spacecraft into orbit around the asteroid Psyche, a ballet, to return to orbit around that target.
This task requires special attention, as scientists know very little about asteroids that can only be seen as small spots of light with a telescope. Ground radar suggests that it is about 140 miles (226 km) wide and has the shape of a potato. That is, scientists do not know how the gravitational field works until it reaches it. When the mission conducts scientific research over 21 months, navigation engineers will use electric propulsion thrusters to fly the spacecraft through orbital progression that gradually brings the spacecraft closer to Pushke.
NASA’s Jet Propulsion Laboratory in Southern California, which manages the mission, uses a propulsion system similar to Deep Space 1 in the engine, launched in 1998 it flew by asteroids and comets before the mission ended in 2001. The first spacecraft to orbit two extraterrestrial targets, the Dawn Mission, lasted 11 years and in 2018 ran out of the last hydrazine propellant used to maintain its orientation.
Maxar Technologies has been using solar electric propulsion to power commercial communications satellites for decades. But for Psyche, they needed to adapt their ultra-efficient Hall thrusters to fly in deep space, where JPL engineers came in. Both teams are using solar electric propulsion, by using the Hall thruster for the first time when Psyche crosses the lunar orbit.
“Sun electric propulsion Technology has the potential to play a key role in achieving the right combination of cost savings, efficiency and power to support future scientific missions beyond Mars, “said Steven, McDonald’s Pushke Program Manager.
In addition to supplying thrusters, Maxar’s team in Palo Alto, California was responsible for building a van-sized chassis for the spacecraft that houses electrical, propulsion, thermal, and guidance and navigation systems. When fully assembled, Psyche moves to JPL’s huge thermal vacuum chamber for testing, simulating a deep space environment. By next spring, the spacecraft will be shipped from JPL to Cape Canaveral for launch.