ClearSpace-1

ClearSpace SA.

Overview

ClearSpace-1 is a servicer spacecraft being developed under the Active Debris Removal and In-Orbit Servicing cornerstone of the European Space Agency’s Space Safety Programme, to rendezvous with, capture and de-orbit an existing non-cooperative and unprepared object in low Earth orbit. OHB System AG and ClearSpace SA develop it for ESA, with the platform supplied by OHB Sweden on the InnoSat product line and the payload, comprising the capture system and the rendezvous and proximity operations guidance, navigation and control, supplied by ClearSpace[1].

The capture system is four multi-degree-of-freedom robotic arms that encompass and grasp the client and secure it to the servicer with enough force to hold it through subsequent stack maneuvers without damaging it and generating new debris [1], [5]. ClearSpace describes the product line behind it as a claw capture system together with an agile robotic arm and end effector for dexterous manipulation, contact dynamic simulation for on-orbit multi-body interaction, and embedded control for fully autonomous capture [6]. The arms close around the client rather than grappling a fixture, because the client has no cooperative interface of any kind [1].

The program was contracted in 2019 with ClearSpace SA, a start-up from a team at the Ecole Polytechnique Federale de Lausanne, against a target of the VESPA Vega secondary payload adapter of about 100 kg left in an approximately 800 by 660 km orbit by the second Vega flight in 2013 [4]. The target was changed to PROBA-1 after a technical and programmatic review with ESA in April 2024, following a collision between VESPA and untraceable debris in 2023 [3]. The industrial arrangement was restructured at the same time, with OHB SE leading the consortium and providing the bus, system integration and launch, and ClearSpace retaining close-proximity and capture operations.

Specifications

Properties of the machine. Flight-specific figures are under Mission profile.

Parameter	Value
Capture system	4 multi-degree-of-freedom robotic arms
Capture method	arms enclose the client without contact, then close onto it
Client tumble rate the GNC is designed for	up to 3 deg/s
Platform	OHB Sweden InnoSat, COTS components
Platform attitude sensors and actuators	magnetorquers, gyros, star trackers, magnetometers, sun sensors, reaction wheels
Propulsion	full chemical system, 6 degree-of-freedom capable
Thruster layout	provides force-free torque and torque-free force
Propellant load	about 90 kg
Solar array	6 body-fixed panels of about 1 m2 each, hexagonal layout, no drive mechanism
Rendezvous sensors	narrow-angle camera, ranging device, wide-angle camera
Downlink	S-band for housekeeping and selected images, X-band for rendezvous data
Spacecraft mass	under 1 t

Source: [1].

The guidance, navigation and control function is split between platform and payload. The platform performs classical attitude and orbit control and orbital maneuvers; the payload performs the rendezvous and proximity operations GNC. Payload units are integrated on three dedicated panels so the payload can be integrated and tested independently of the platform before mating[1].

The solar array configuration is a consequence of two constraints acting together. A solar array drive mechanism does not demise on re-entry, so it was excluded, leaving body-fixed panels in plane with the bottom plate; and the payload sensors must point at the client while the client is well illuminated, which puts the arrays opposite the payload deck and means they are frequently off sun [1]. The array is therefore larger than a sun-pointing design would need. The equivalent constraint on the earlier VESPA baseline was handled in the close-proximity operations design by scheduling illumination-dependent phases against the go/no-go decision points [2].

Mission profile

Parameter	Value	Source
Client	PROBA-1
Client mass at launch	94 kg	[1]; 95 kg in [5]
Client dimensions	0.6 by 0.6 by 0.8 m	[1], [5]
Client launch date	2001-10-22
Client orbit, predicted semi-major axis at encounter	6900 to 6925 km
Client orbit, predicted eccentricity	0.0049 to 0.0058
Client orbit, inclination	98 degrees
Planned launch	2028	[1]; 2029 in [5]
Mission duration	1 year
Post-mission decay	uncontrolled, within 5 years
Total mission delta-v	almost 300 m/s
Capture rehearsals and attempts budgeted	1 rehearsal, 3 attempts, 1 collision avoidance maneuver per attempt
Launch vehicle class	European microlauncher, direct transfer to the client orbit

Rows with no marker are from [1].

PROBA-1 was still operational in 2024, making it ESA’s longest-running operational satellite against a two-year design life [1]. ESA classes it as unprepared and uncooperative for the purposes of this mission [5]. It will be deactivated before capture regardless of its condition [1]. Its suitability as a client rests on being close to symmetric with no complex appendages, solar panels on five of six faces giving good reflectivity, and no propulsion system and therefore no residual propellant. Its orbit at the time of the encounter is not known today because the propagation depends on solar activity over the intervening years, so a range of client orbits was computed for minimum and maximum solar activity.

The earlier VESPA baseline was the subject of a published close-proximity operations design and validation study, which covers client phasing, far rendezvous, close rendezvous and capture, and which defines the keep-out zone, the approach zone, the approach corridor and the go/no-go criteria used to assess passive safety [2]. That work notes that the full mission includes station keeping strategies and co-rotation capture strategies for high-angular-rate targets that the published simplification omits.

Concept of operations

Phasing ends with the servicer 30 km behind the client at the switch point [1], where control passes from the platform absolute navigation to the payload relative navigation. Three relative navigation regimes follow [1].

Regime	Range	Sensing
Far range	30 km to a few hundred meters	angles-only, narrow-angle optical camera
Mid range	a few hundred meters to 50 to 100 m	narrow-angle camera plus ranging device
Close range	from the initial proximity point to capture	wide-angle camera, pose estimation, continuous 6 degree-of-freedom control

The far-range closing uses a passively safe impulsive guidance strategy on angles-only navigation in the visible spectrum. Fly-around orbits are established with the same guidance concept, augmented with range measurements to reduce the error in the relative navigation, and the client is observed and characterized during them.

Proximity maneuvering runs through waypoints, rehearsed incrementally, always returning to a sufficiently safe point [1]. The formation keeping point is about 150 m along track and is held on mid-range navigation. Waypoint sequencing of this kind is what the published close-proximity operations method formalizes as approach-zone and keep-out-zone decision points [2]. The switch to close-range navigation cannot be made there, so the servicer hops to the initial proximity point, where the wide-angle camera initializes close-range navigation [1]. After a go from ground it moves to the final approach point using motion synchronization to account for client rotation. That sequence must run with the client illuminated and with ground contact, because ground supervises the approach and gives the final go.

The mandate for the mission was given by ESA and eight member states in 2020, to remove an ESA-owned derelict object [6], and the industrial lead passed to OHB SE in 2024 [3], [5]. A full rehearsal of the entire sequence without capture is flown before the capture attempt; the servicer then returns to the formation keeping point and captures in the next proximity slot [1]. The rehearsals also have to demonstrate that the collision avoidance maneuver is correctly computed and triggered without firing the thrusters.

Capture

At motion synchronization the servicer reaches a point at which the client is inside the volume of the opened arms [1]. When the proximity trigger fires, the GNC switches off and the capture system starts closing its phalanges; the arms enclose the client without touching it, then contact it as they continue to close, and finally secure it against relative motion. Capture runs fully autonomously, with selected images and all housekeeping data downlinked over S-band during it, which is also how ClearSpace describes the capability it is building [6].

The capture system has four functions: start closing at the right time, enclose the client without touching it so it cannot escape, absorb the contact loads without damaging client or servicer, and secure the client so its motion does not disturb the servicer attitude control. PROBA-1 can be captured from either of two opposite directions, on the launch adapter ring face or on the opposite face, which gives flexibility against illumination conditions [1]. The GNC is designed to capture a non-cooperative PROBA-1 tumbling at rates up to 3 deg/s. After capture the stack detumbles and the new configuration is characterized, after which the platform attitude control, which is sized to control the full stack, takes over.

Safety and design constraints

Two requirements dominate the design: re-entry safety and the prohibition on creating further debris [1], both of them ESA requirements rather than mission choices [1], [5].

Re-entry casualty risk must be below 1e-4 [1]. A controlled re-entry would require DAL A software development standards and a redundancy concept covering everything involved, which does not fit the design-to-cost approach, so an uncontrolled re-entry was selected early and the vehicle is designed to demise. The consequences are direct: tanks do not demise, so the design follows a maximum tank count or propellant mass approach; solar array drive mechanisms do not demise, so body-fixed panels and a more complex concept of operations were adopted; and non-demisable materials are avoided across the design[1].

Keep-out zone geometry, approach corridor and go/no-go criteria are the formal apparatus by which that prohibition is turned into trajectory constraints [2]. Collision avoidance is the second driver. In naturally stable orbits there is no collision risk, but close approach puts the servicer on trajectories that would collide if not actively controlled [1]. A collision avoidance maneuver breaks the formation and must move the servicer to a position that is passively safe for at least seven days. Recovering from one requires restarting the whole rendezvous approach, and one maneuver plus the return to a capture attempt takes more than 10 percent of total mission delta-v [1].

ESA states the mission demands highly precise close proximity operations [5]. The named engineering constraints on the servicer are high power draw during capture from running the capture mechanisms and proximity sensors in parallel, the client pointing required for optical observation constraining the orientation relative to the sun, high delta-v demand for nominal maneuvers and collision avoidance provisions, accommodation of a large payload whose capture system geometry sets the size of the spacecraft, and the demise requirement [1].

Avionics

Platform avionics hardware, flight software, fault detection isolation and recovery, and the attitude and orbit control system are InnoSat reuse, with minor additions to the control system for the added complexity of this mission. InnoSat components are commercial off-the-shelf parts selected under a design-to-cost approach. Four InnoSat-based satellites were in orbit at the time of the design review with nine more expected within two years, and the catalog components have flight heritage outside the InnoSat program [1].

Status

The mission passed its system requirements review and entered phase B2 to conclude the preliminary design [1]. Launch is expected in 2028 according to the design paper; the ESA program page gives 2029 [5]. ESA’s 2019 announcement of the contract gave a 2025 launch against the VESPA target [4], so the schedule has moved by three to four years across the target change.

Technologies developed

The mission is intended to produce a versatile capture system able to take objects of several shapes and sizes with minimal modification, which is the condition for active debris removal to work commercially under a design-to-cost approach [1]. The close-proximity operations framework developed around it, covering keep-out zone and approach corridor definition, go/no-go criteria, passive safety assessment and active safety strategies, is published as a contribution towards standardizing non-cooperative rendezvous [2]. That framework was validated by model-in-the-loop Monte Carlo campaigns run across a prototyping simulator and a high-fidelity simulator. ESA lists the mission as its first to remove a piece of space debris from orbit [5], and ClearSpace presents it as the reference mission for its in-orbit servicing line [6].

Source limitations

One document, the 2025 ESA Space Debris Conference paper by the OHB, ESA and ClearSpace design team, carries most of the engineering content here [1]. No other open publication describes the servicer or its capture system at that level. The close-proximity operations study [2] predates the target change and is written for the VESPA baseline. Mass, power, joint-level arm design, actuator specification, sensor part numbers and thermal ranges are not published anywhere obtained.