Propulsion Subsystem for LISA Mission

Thales Alenia Space and OHB System AG are cooperating to design, integrate, and test the propulsion subsystem for the Laser Interferometer Space Antenna (LISA) mission, a European Space Agency (ESA) project to deploy a space-based observatory for gravitational wave detection. The cooperation focuses on delivering a key spacecraft subsystem that enables drag-free operation and precise formation flying for the mission’s three-satellite constellation.

Context of the Cooperation
Thales Alenia Space, a joint venture between Thales and Leonardo, and OHB System AG, acting as prime contractor for the LISA spacecraft, are addressing the technical challenge of maintaining near-perfect free-fall trajectories and precise inter-satellite positioning in deep space. LISA’s scientific objective is to measure gravitational waves—minute ripples in space-time—across low frequencies that cannot be detected from Earth-bound observatories. This requires a constellation of three spacecraft separated by 2.5 million km in heliocentric orbit with interconnecting laser interferometry links.

ESA’s approach necessitates integration of a propulsion subsystem capable of compensating non-gravitational forces, such as solar radiation pressure, while enabling formation control and drag-free conditions. Cooperation between Thales Alenia Space and OHB is essential due to the scale of the mission, the precision needed for gravitational wave measurement, and the integration of multiple complex subsystems across international industrial partners.

Technical Solution and Responsibilities
Under a €16.5 million Phase B2 contract, Thales Alenia Space is responsible for the design, manufacture, assembly, integration, and testing of LISA’s propulsion subsystem for one or more spacecraft. This subsystem will form part of the larger drag-free and attitude control system (DFACS) required to maintain the spacecraft’s position relative to free-falling test masses. The DFACS uses micro-thrusters and precise control algorithms to counteract external forces without imparting disturbance to the measurement axes.

The propulsion subsystem’s function at the system level is to provide minute thrust adjustments, measured in micro-newtons, to maintain formation geometry and align laser links between the satellites. The subsystem interfaces with spacecraft avionics, control software, and the telecommunication system, all supplied or integrated by Thales Alenia Space as per the OHB prime contract.

Deployment and Implementation
The cooperation begins with the Phase B2 contract, with Phase C and D execution expected to follow, increasing the total contract value to €89.5 million. Thales Alenia Space’s UK facilities will execute the propulsion subsystem development, assembly, and verification activities. These activities are conducted in compliance with ESA’s space-qualification standards and include integration with existing avionics and DFACS elements.

LISA’s three spacecraft are scheduled for launch on an Ariane 6 vehicle in 2035, after which propulsion and DFACS systems will support orbit insertion, constellation acquisition, and maintenance of the triangular formation in an Earth-trailing heliocentric orbit.

Applications and Expected Impact
The primary application of the cooperation is scientific: enabling the first operational space-based gravitational wave observatory. For industrial automation and system engineering, the project exemplifies complex subsystem integration involving drag-free navigation, precision propulsion, and distributed spacecraft control. By distributing responsibilities—OHB as prime contractor and Thales Alenia Space as propulsion subsystem provider—each partner leverages domain-specific expertise to meet stringent performance and reliability criteria required for deep-space missions.

Technical and Operational Value
Although specific performance figures for the propulsion subsystem were not disclosed, the design must achieve thrust stability and control precision sufficient to maintain geodesic motion of test masses, with acceleration noise and disturbance rejection conforming to ESA mission specifications. The cooperation’s technical value lies in the integration of high-precision control mechanisms, adherence to space standards, and the delivery of subsystems that collectively support LISA’s scientific objectives.

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