16 Psyche is the heaviest known M-type asteroid, and is thought to be the exposed iron core of a protoplanet, the remnant of a violent collision with another object that stripped off its outer crust. Radar observations of the asteroid from Earth indicate an iron–nickel composition. On 4 January 2017, the Psyche mission was selected for NASA's Discovery #14 mission.
Psyche was submitted as part of a call for proposals for NASA's Discovery Program that closed in February 2015. It was shortlisted on 30 September 2015, as one of five finalists and awarded US$3 million for further concept development. One aspect of selection was enduring the "site visit" in which about 30 NASA personnel come and interview, inspect, and question the proposers and their plan.
On 4 January 2017, Lucy and Psyche were selected for the 13th and 14th Discovery missions, respectively, with launch for Psyche set for 2023. In May 2017, the launch date was moved up to target a more efficient trajectory, launching in July 2022 aboard a SpaceXFalcon Heavy launch vehicle and arriving on 31 January 2026 with a Mars gravity assist on 23 May 2023.
Data shows asteroid 16 Psyche to have a diameter of 222 km (138 mi). Scientists think that 16 Psyche could be the exposed core of an early planet that could have been as large as Mars and lost its surface in a series of violent collisions.
Its composition and density match mesosiderite meteorites and it is likely their parent body.
It was proposed that the rocket launch might be shared with a separate mission named Athena, that would perform a single flyby of asteroid 2 Pallas, the third-largest asteroid in the Solar System. In May 2020, it was announced that the Falcon Heavy carrying Psyche would include two smallsat secondary payloads to study the Martian atmosphere and binary asteroids, named EscaPADE (Escape and Plasma Acceleration and Dynamics Explorers) and Janus respectively, but in September 2020, the EscaPADE Mars atmosphere probe was removed from the plan.
Science goals and objectives
An illustration depicting the target of NASA's Psyche mission: the metal-rich asteroid Psyche, in the main asteroid belt between Mars and Jupiter.
A 3D model of 16 Psyche based on light curve data.
The science questions this mission will address are:
Is 16 Psyche the stripped core of a differentiated planetesimal, or was it formed as an iron-rich body? What were the building blocks of planets? Did planetesimals that formed close to the Sun have very different bulk compositions?
If 16 Psyche was stripped of its mantle, when and how did that occur?
If 16 Psyche was once molten, did it solidify from the inside out, or the outside in?
The Psyche's electric propulsion system uses SPT-140 Hall-effect thrusters powered by its solar panels. An early SPT-140 Hall-effect thruster used for ground testing is shown in the top right of this picture.
This mission will use the model SPT-140 engine, a Hall-effect thruster utilizing solar electric propulsion, where electricity generated from solar panels is transmitted to an electric, rather than chemically powered, rocket engine. The thruster is nominally rated at 4.5 kW operating power, but it will also operate for long durations at about 900 watts. Psyche will be the first mission to use Hall-effect thrusters beyond lunar orbit.
The SPT-140 (SPT stands for Stationary Plasma Thruster) is a production line commercial propulsion system  that was invented in Russia by OKB Fakel and developed by NASA's Glenn Research Center, Space Systems Loral, and Pratt & Whitney since the late 1980s. The SPT-140 thruster was first tested in U.S. as a 3.5 kW unit in 2002 as part of the Air Force Integrated High Payoff Rocket Propulsion Technology program. Using solar electric thrusters will allow the spacecraft to arrive at 16 Psyche (at 3.3 astronomical units) much faster while consuming only 10% of the propellant it would need using conventional chemical propulsion.
Electricity will be generated by bilateral solar panels in an X-shaped configuration, with five panels on each side. Prior to the mission being moved forward with a new trajectory, the panels were to be arranged in straight lines, with only four panels on each side of the spacecraft.
Launch and trajectory
The launch is planned for August 2022 on a Falcon Heavy vehicle. The cost of the launch, including secondary payloads, is US$117 million. Psyche will be launched on a trajectory that will perform a gravity assist maneuver past Mars on 23 May 2023, toward the asteroid belt, and intercept the asteroid Psyche.
Psyche will encounter 16 Psyche asteroid and enter orbit on 31 January 2026. The spacecraft would orbit at decreasing altitudes or regimes. Its first regime, Orbit A, will see the spacecraft enter a 700 km (430 mi) orbit for magnetic field characterization and preliminary mapping for a duration of 56 days. It will then descend to Orbit B, set at 290 km (180 mi) altitude for 76 days, for topography and magnetic field characterization. It will then descend to Orbit C, at 170 km (110 mi) altitude for 100 days to perform gravity investigations and continue magnetic field observations. Finally, the orbiter will enter Orbit D, set at 85 km (53 mi) to determine the chemical composition of the surface using its gamma-ray and neutron spectrometers. It will also acquire continued imaging, gravity, and magnetic field mapping. The mission is planned to orbit the asteroid for at least 21 months.
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