Janus Mission to Explore Binary Asteroids Cancelled by NASA

NASA has officially ended Janus, a mission to investigate binary asteroid systems in the near-Earth region. This decision came after the launch postponement of Psyche, with which Janus was meant to share the ride to space onboard a Falcon Heavy on July 2022.

Due to a postponed launch that made its asteroid targets inaccessible, NASA has decided to conclude the Janus mission. Janus was part of our SIMPLEx program of low-cost, high risk science missions ride-sharing with primary missions. https://t.co/wZEZbxedyw
— NASA Solar System (@NASASolarSystem) July 11, 2023

After a short evaluation, NASA concluded that the mission couldn’t achieve its primary objectives, and different targets were unfeasible. The two twin spacecraft will now be prepared for long-term storage.

A mission to binary asteroid systems

Funded as part of the SIMPLEx (Small Innovative Missions for Planetary Exploration) Programme, Janus was a twin spacecraft mission designed by Colorado Boulder University in collaboration with Lockheed Martin to collect data from two different asteroid systems in the near-Earth region. The name is derived from the Roman God of duality.

*Artistic representation of Janus spacecraft near the binary asteroid system. Credits: Lockheed Martin*

Both spacecraft were planned to launch as rideshare of Psyche mission on an Earth-Mars trajectory. They would have then performed a series of deep space maneuvers, including an Earth fly-by, to encounter 1991 VH and 1996 FG3, respectively, for Janus-A and Janus-B. The objective was to combine visible and infrared observations of the targets developing topographical and dynamically accurate models of binary asteroids to understand their formation and evolution better.

*Janus probe performing scientific operations. Credits: NASA*

Janus should have lasted about four years, with the Earth fly-by taking place in July 2025 and the asteroid encounters in March 2026

The Spacecraft

Both satellites were identical, a SmallSat with less than 45 kg of mass and a CubeSat alike form factor. Two payloads were installed onboard:

A visible imager, specifically an ECAM-M50, with a 2592×1494 pixels CMOS detector with an electronic rolling shutter. This camera was directly derived from OSIRIS-REx and Lucy engineering cameras.
An Infrared Imager, ECAM-IR3a, with an uncooled 640×480 pixels microbolometer sensor.

To lower costs, all subsystems were designed with commercial off-the-shelf components. Two gimbal-controlled solar arrays allowed for achieving power generation in different mission scenarios, while the propulsion unit comprised six electric thrusters. Only four were required to perform deep space or trajectory correction maneuvers; the other two were for redundancy. Moreover, the thrusters also allowed for the desaturation of the inertia wheels installed onboard.

*Janus-A and Janus-B at Lockheed Martin integration facility. Credits: Lockheed Martin*

A specific driver for the selection of the spacecraft’s attitude determination and control subsystem was the slew rate – the time required by the platform to reorient itself from one direction to another. High performance was needed to maximize the data produced during the asteroid systems encounter.

The overall cost of the system was below the 55 million dollar cost cap of the SIMPLEx Programme.

What next?

As stated, NASA will now place both satellites in long-term storage. The hope of seeing them fly lies in the future availability of funds, needed to review the mission and adapt it to alternative targets.