Astroscale’s ELSA-d Mission Successfully Completes Complex Rendezvous Operations
Astroscale based at Harwell today announced that, despite several unexpected setbacks, its End-of-Life Services by Astroscale-demonstration (ELSA-d) mission successfully completed further controlled close-approach rendezvous operations between its two spacecraft in orbit. The technologies proven in this demonstration include tracking of an object from a great distance, rendezvous with an uncontrolled object, and handover from absolute navigation to relative navigation for a low-Earth orbit (LEO) servicing spacecraft. These capabilities are essential for rendezvous and proximity operations and in-orbit servicing, and this demonstration is unprecedented for a commercially funded mission in LEO.
“The journey to reunite the servicer and client, along with the successful completion of switching from absolute to relative navigation, have allowed us to prove even more key technologies and operational capabilities required for commercial end-of-life debris removal services,” said Seita Iizuka, ELSA-d Project Manager. “Proving these capabilities gives us, and our partners, greater confidence in our debris removal service developments, and I congratulate the team on this impressive achievement.”
ELSA-d is the world’s first commercial mission to prove the core technologies necessary for in-orbit satellite servicing in LEO. The mission, which consists of two satellites — a servicer designed to safely remove debris from orbit and a client that serves as a piece of replica debris — was launched as a stack into a 550 km orbit from the Baikonur Cosmodrome in Kazakhstan in March 2021. The first demonstration, in which the servicer released the client and manually performed magnetic docking, was completed on August 25, 2021, successfully validating the capture system, on-board sensors and cameras.
Mission operations for an Autonomous Capture demonstration began on January 25. After successful release of the client from the servicer’s magnetic capture system, the servicer successfully maintained a distance of 30 meters from the client through the use of autonomous relative station-keeping algorithms, with input from the servicer’s lower power radio (LPR) sensor. After successfully demonstrating this important rendezvous capability for more than seven hours, anomalous spacecraft conditions were detected. For the safety of the mission, the ELSA-d team decided not to proceed with the capture attempt. The servicer and client were further separated to allow the team to investigate several issues from a safe distance and by doing so, the spacecraft drifted farther apart, to a maximum distance of approximately 1,700 kilometers.
The biggest challenge of the latest demonstration was replanning the rendezvous approach with the use of only four of the eight thrusters on the servicer. This restricted the ability of the servicer to perform detailed rendezvous manoeuvres with the client as originally planned. While a system issue had an impact on three of the thrusters, the root cause for the loss of one thruster is not clear and is under joint investigation by Astroscale and Bradford/ECAPS, the thruster supplier for the ELSA-d mission.
Several carefully planned manoeuvres were conducted over the past two months to prepare the servicer for a controlled close approach rendezvous with the client. On April 7, using the limited set of available thrusters, the servicer successfully maneuvered to a distance of 159 meters from the client, and the ability of the servicer to search for and detect the client was validated, enabling a transition from absolute navigation, which relies on GPS and ground-based observations, to relative navigation, using on-board sensors. This handover has been the most challenging operation of the ELSA-d mission so far and is widely recognised as one of the more difficult capabilities to prove for satellite servicing operations.
With the completion of this critical operation, the servicer has once more been manoeuvred away from the client and will remain at a stable distance for several months. During this time the team will analyse the next phase of the mission, including the potential for a safe and viable magnetic recapture of the client.
Despite not yet being able to complete the autonomous capture demonstration, the ELSA-d mission has proven several key technologies required for capturing orbital debris, including:
- autonomous guidance, navigation and control algorithms,
- closed loop control with on-board navigation sensors,
- autonomous thruster rendezvous maneuvering and attitude control,
- navigation of a servicer spacecraft from 1,700 km to within 160 m of a client using absolute navigation techniques (GPS and ground-based observations),
- transition from absolute navigation to relative navigation using on-board LPR sensor,
- more than one year of servicer and client satellite in-orbit mission operations, and
- magnetic capture mechanism using a docking plate.
As a validation of these pioneering capabilities, ELSA-d has received numerous awards and accolades for breaking new ground for space sustainability and in-orbit servicing, including the Via Satellite 2021 Satellite Technology of the Year and the Minister of State for Space Policy Award, sponsored by the Cabinet Office, Government of Japan. The mission was also key to Astroscale being named to TIME’s List of the 100 Most Influential Companies and Fast Company’s Most Innovative Companies.
“ELSA-d was never going to be easy, even under ideal circumstances, but our global team has overcome numerous challenges and had tremendous successes, which will accelerate the already rapid growth of the in-orbit servicing market,” said Nobu Okada, Founder and CEO of Astroscale. “We are grateful for the recognition our team has received from around the globe, and we thank the international space community for its support.”
Astroscale’s end-of-life services present a proactive way for satellite operators to protect their assets, avoid collision with other satellites and safeguard the orbital environment. Astroscale will harness what it learns from ELSA-d’s technologies and capabilities to deliver the cutting-edge ELSA-M spacecraft, capable of capturing multiple defunct LEO satellites in a single mission. Technology development and planning are well underway to deliver an in-orbit demonstration, with the UK Space Agency, the European Space Agency and OneWeb as key partners, to test ELSA-M’s capabilities with more than one defunct satellite belonging to a constellation operator, such as OneWeb.