Spacecraft to iron asteroid Psyche

[lpetrich]

The Psyche spacecraft is on its way to its namesake asteroid  16 Psyche That asteroid has lots of iron on its surface, much like some iron meteorite, and it will be the first such asteroid ever to be visited by a spacecraft. It is about 220 km (140 mi) in diameter, though with a rather irregular shape, and it orbits at about 3 times the Earth's distance from the Sun, with a period of about 5 years.

•  Psyche (spacecraft)
• Psyche - NASA Science
• Psyche at JPL

It will fly by Mars on May 2026, and arrive at the asteroid on Aug 2029, and then do several sizes and orientations of orbits over the next two years.

The spacecraft carries a multispectral imager, gamma-ray and neutron spectrometers, and a magnetometer. Spacecraft tracking will be used to measure the asteroid's mass and find its surface-gravity variation. How much of that asteroid is iron and how much is rock?

 

[lpetrich]

The spacecraft was originally scheduled to launch in 2022. From Wikipedia,

In June 2022 NASA found that the late delivery of the testing equipment and flight software for the Psyche spacecraft did not give them enough time to complete the required testing, and decided to delay the launch, with future windows available in 2023 and 2024 to rendezvous with the asteroid in 2029 and 2030, respectively.

...
An independent review of the delays at JPL reported in November 2022 found understaffing, insufficient planning, and communications issues among engineers and with management. The VERITAS Venus mission was delayed to free up staff to focus on Psyche.

 VERITAS (spacecraft) - delayed from 2027 to 2031.

The delay of Psyche meant the cancellation of  Janus (spacecraft) - a pair of small spacecraft that were to be passenger spacecraft for the Psyche launch, spacecraft that were to fly by asteroids. They were put into storage for future launch opportunities.

 

[lpetrich]

Psyche was launched on October 13.

Complete launch video: Psyche Launches to a Metal Asteroid (Official NASA Broadcast) - YouTube - has lots of talking about the mission that some of you may want to skip over.

Most of the launch action: SpaceX Falcon Heavy launches NASA Psyche to weird metal asteroid, nails landings - YouTube - 9 minutes

Both of the rocket's side boosters successfully returned, while the first stage did not try to return. The first stage is between those boosters and extends a little higher.

Signal Acquired – Psyche Begins Its Journey of Discovery – Psyche Mission

Psyche mission controllers on Earth have received full acquisition of signal from the spacecraft, and the solar arrays are fully deployed. The spacecraft will be propelled by solar electric propulsion. The five-panel, cross-shaped solar arrays provide around 800 square feet of solar collecting surface and make the spacecraft about the size of a singles tennis court when fully deployed.

The solar arrays will produce more than 20 kilowatts of power when the spacecraft is near Earth, but they will generate just over 2 kilowatts of power – just a little more power than a hair dryer – when it reaches the asteroid Psyche, which is far away from the Sun. However, this will be more than enough power to meet the spacecraft’s needs on its journey, including running science instruments, telecommunications, equipment that controls the spacecraft’s temperature, and the spacecraft’s superefficient solar electric propulsion engines.

 

[lpetrich]

The spacecraft is propelled by four SPT-140 Hall-effect ion engines, the first such use of that kind of engine for interplanetary flights. Ion engines have been used in other interplanetary spacecraft, but those ones are gridded electrostatic ones.

 Hall-effect thruster

The essential working principle of the Hall thruster is that it uses an electrostatic potential to accelerate ions up to high speeds. In a Hall thruster, the attractive negative charge is provided by an electron plasma at the open end of the thruster instead of a grid. A radial magnetic field of about 100–300 G (10–30 mT) is used to confine the electrons, where the combination of the radial magnetic field and axial electric field cause the electrons to drift in azimuth thus forming the Hall current from which the device gets its name.

Hall-effect engines were developed by the Soviet Union for satellite stationkeeping, and Psyche's engines are derived from those engines.

Spacecraft	Make/Model	Type	Number	Isp	Thrust	Dry mass	Launch mass
Dawn	NSTAR	Electrostatic	3	3,100 s	90 mN	747.1 kg	1,217.7 kg
BepiColombo	QinetiQ-T6	Electrostatic	4	4,300 s	145 mN	2,700 kg	4,100 kg
Psyche	SPT-140	Hall effect	4	1,800 s	280 mN	2,608 kg	1,648 kg

Isp is the exhaust velocity divided by the Earth's surface gravity, taken to be 9.81 m/s^2. The masses are for the spacecraft.

It is evident that there is a tradeoff between exhaust velocity and thrust. The Space Shuttle Main Engines -  RS-25 - have Isp 421 s and thrust 1.0331 MN (meganewtons) - some 10 million times more than the thrust of these ion engines, but with much less exhaust velocity. Those engines use H2 and O2, and easier-to-store propellants have less Isp.

Greater exhaust velocity means less propellant needed to make some velocity change (delta-V), so that's why it's desired.

 

[Loren Pechtel]

So it's going to use heat and steam to smooth the surface?