TAMPA, Fla. — Astroscale said May 4 it made another close-approach rendezvous between its two ELSA-d spacecraft last month but ongoing thruster problems continue to hold up a capture demonstration delayed from January.
Astroscale’s ELSA-d servicer spacecraft, a 175-kilogram satellite designed to demonstrate orbital debris removal technologies, lost the use of four of its eight 1-newton thrusters in January.
Despite the setback, Astroscale successfully commanded ELSA-d’s servicer craft to close within about 159 meters of the much smaller client satellite on April 7 from a starting distance of 1,700 kilometers.
The rendezvous put the 17-kilogram client craft within range of the servicer’s low power radio (LPR) sensors, enabling it to take over navigational controls from the ground, Astroscale chief technology officer Mike Lindsay told SpaceNews.
Lindsay said the successful hand-off to the servicer’s onboard sensors was a significant technical achievement — and not one Astroscale had planned to test before ELSA-d’s propulsion problems prompted the team to rethink the mission.
Astroscale was getting ready for a Jan. 25 capture demonstration when ELSA-d’s propulsion anomaly occured, prompting the company to move the servicer to a distance beyond the range of its onboard sensors.
The servicer craft is equipped with eight 1-newton High Performance Green Propulsion (HPGP) thrusters supplied by Swedish propulsion specialist ECAPS, which is owned by U.S.-based Bradford Space.
Bradford Space CEO Ian Fichtenbaum told SpaceNews last month that ELSA-d’s thrusters are not at fault. “These issues do not relate to and are not a result of the design or build of the thrusters and we have full confidence in our products,” he said.
In a May 4 news release describing the April 7 rendezvous operation, Astroscale said a “system issue” was to blame for the loss of three thrusters but “the root cause for the loss of the fourth thruster is not clear and is under joint investigation by Astroscale and Bradford/ECAPS.”
Lindsay said Astroscale does not expect to bring any of the four thrusters online. Because the failed thrusters are not all on one side of the servicer, the craft remains maneuverable.
The ELSA-d servicer did not lose any propellant when thrusters failed, Lindsay said, leaving the spacecraft with enough fuel to capture and de-orbit the client craft if Astroscale decides to attempt that part of the mission.
Although the servicer successfully used its magnetic mechanism last August to release and recapture the client, Astroscale had planned to make another attempt with less direct support from flight operators on the ground.
Before tests in January were called off, Lindsay said Astroscale validated the servicer’s LPR sensor for the station-keeping it would need for this semi-autonomous capture demo.
“At that point, the spacecraft essentially says, I know where the client is, I know what I need to do to bring myself closer to the client and complete the rendezvous,” Lindsay said.
Ground operators would still be required to conduct various safety checks if Astroscale proceeds with a semi-autonomous capture attempt.
The servicer would also be approaching the client craft from a greater distance than the August capture mission if its next capture attempt goes ahead.
After completing its April 7 rendezvous, ground operators took control of the servicer’s navigation to move it about 300 kilometers away from the client to an orbital position where it can remain stable for several months.
The servicer and client, which were launched as a stack to low Earth orbit in March 2021, were never more than 30 meters apart for the August capture mission.
Astroscale is discussing its options with partners, regulators and other groups.
Lindsay said engineers still need to assess the servicer’s capabilities to decide the timing and nature of the mission’s next steps.
He noted it is particularly important for Astroscale to avoid risks when it is building a debris-removing business built around the safety and sustainability of the space environment.
“The ability of the team to overcome this anomaly and still succeed is really an amazing confidence boost for our capabilities here, so I think it bodes very well for our mission and our success in the future,” he added.