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Astroscale’s ELSA-d Mission
Successfully Completes Complex Rendezvous Operation
May 4, 2022
Astroscale Holdings Inc. 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 on-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 on-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 maneuvers 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 maneuvers
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 recognized 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
maneuvered away from the client and will remain at a
stable distance for several months. During this time the
team will analyze 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 on-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 on-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 on-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.
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