Janus

Mission type	Asteroids flyby
Operator	University of Colorado Boulder, NASA
Mission duration	4 years (planned)
Spacecraft properties
Spacecraft	Janus Serenity and Mayhem
Manufacturer	Lockheed Martin
Launch mass	36 kg (×2)[1]
Power	2 solar arrays and batteries[2]
Start of mission
Launch date	TBD
Rocket	TBD
Launch site	Kennedy Space Center, LC-39A
Contractor	SpaceX
Instruments ECAM-M50 Visible camera ECAM-IR3a Infrared camera
Small Innovative Missions for Planetary Exploration (SIMPLEx) Program ← LunaH-Map Lunar Trailblazer →

Janus is a planned NASA mission that will send dual space probes, Serenity and Mayhem,^[3] to visit asteroids that will be chosen prior to launch date. The mission is part of NASA's SIMPLEx program and was expected to be launched in October 2023 as a secondary payload on Falcon Heavy together with the Psyche spacecraft, but it was removed due to an inability to reach its target from that launch date.^[4] On 3 September 2020, Janus successfully passed Key Decision Point-C and was approved for the final design of hardware. The mission budget is limited to US$55 million.^[5] Currently the new launch date and new launch vehicle is yet to be confirmed.

Spacecraft

The two small 36 kg spacecraft —which fall under the 180 kg mass limit for SIMPLEx missions — will conduct stand-alone planetary science missions. The spacecraft is jointly developed by two teams, based at the University of Colorado Boulder (led by Daniel Scheeres) and at Lockheed Martin (led by Josh Wood). The two spacecraft, Janus A and B, also go by Serenity and Mayhem.^[3][6]

Instruments

The Janus team plans to image the two asteroids in visible and infrared light, using the ECAM-M50 (visible) and ECAM-IR3a (infrared) cameras. These cameras were developed by Malin Space Science Systems and successfully used on the OSIRIS-REx asteroid sample return mission.^[7]

Mission

Initial plan

In 2020, NASA gave approval for the Janus mission to proceed to the next phase of development.^[5] The mission is managed by the Planetary Missions Program Office at NASA's Marshall Space Flight Center in Huntsville, Alabama, as part of the Solar System Exploration Program at NASA Headquarters in Washington, D.C. The program conducts space science investigations in the Planetary Science Division of NASA's Science Mission Directorate at NASA Headquarters, guided by NASA's agency priorities and the Decadal Survey process of the National Academy of Sciences. Janus is led by the University of Colorado Boulder, where the principal investigator (PI) is based, which will also undertake the scientific analysis for the mission. Lockheed Martin will manage, build and operate the spacecraft.

After riding along with the launch of NASA's Psyche mission in October 2023, the Janus twins will separate and complete an orbit around the Sun, before heading back toward Earth for a gravity assisted sling-shot, each going their separate ways to the two asteroids, (175706) 1996 FG3 and (35107) 1991 VH.^[5]

Delay and new targets

Because Psyche's launch date was moved from August 2022 to late September, new targets have to be chosen as Janus would be unable to visit the initially chosen asteroids (175706) 1996 FG3 and (35107) 1991 VH.^[8] Psyche's launch was again delayed on June 24, 2022, to an unspecified date after the end of 2022.^[9][10] It was removed from the Psyche mission on 18 November 2022, after an assessment determined that Janus would not be on the required trajectory to meet its science requirements as a result of Psyche’s new launch period.^[11]