Launch

LISA Pathfinder will be carried into orbit from Europe's Spaceport in French Guiana by an ESA Vega launch vehicle. The lift off is scheduled for 2015. Vega will place the spacecraft in an elliptical parking orbit around the Earth with perigee at 200 km, apogee at 1620 km and an inclination of 5.3°, aligned so that the spacecraft can then use its own expendable propulsion system to transition to its final operational orbit, at L1.

The velocity increment required for apogee-raising and injection into the operational orbit is about 3100 ms^-1. As the spacecraft transfers to the operational orbit, the propulsion module separates from the science spacecraft prior to drag-free operations, to prevent disturbances that would be generated by the residual propellants acting on the inertial sensors.

Operational orbit

LISA Pathfinder transfer and operational orbit. Credit: Astrium

The operational orbit for LISA Pathfinder will be a 500 000 km × 800 000 km Lissajous orbit around the first Lagrange point  (L1) of the Sun-Earth system. The L1 Lissajous orbit has been chosen because it is an intrinsically 'quiet' place in space, far away from massive bodies, which induce tidal forces on the spacecraft; has constant illumination from the Sun; and has a quasi-constant distance from Earth for communication. This orbit fulfils the stringent requirements of LISA Pathfinder concerning thermal and gravitational stability.

This Lissajous orbit, with period of 180 days, is unstable and periodic station-keeping manoeuvres will be required - amounting to about 1.8 ms^-1 per year - which will be performed using the cold gas thrusters that make up the spacecraft's micro-propulsion system.

Ground segment

The LISA Pathfinder ground segment has two operational centres, both provided by ESA:

• The Mission Operations Centre (MOC) at the European Space Operations Centre (ESOC), in Darmstadt, Germany, is responsible for the Launch and Early Operations Phase (LEOP), the transfer phase, and all operations during the routine phase. The MOC is in contact with the spacecraft for eight hours per day through the ground station(s).
• The Science and Technology Operations Centre (STOC), located at the European Space Astronomy Centre, near Madrid, Spain, is the interface to the scientific community and is responsible for the payload scheduling, quick-look data analysis, data processing and archiving.

Communications with the spacecraft will be performed in X-band through a network of ground stations, including Kourou, Maspalomas and Perth, during LEOP. For this the ground station infrastructure has been upgraded to include X-Band acquisition aids mounted on the LEOP stations.

During science operations, communications will be performed using DSA-2, the 35-metre X-band deep-space antenna located at Cebreros, in Spain. Using this station, a communications link will be established for six to eight hours per day. During each pass, the data stored on board will be retrieved, spacecraft tracking will be performed and the command timeline will be uplinked.

Following the initial on-orbit check-out and instrument calibration, the STOC will be responsible for the inflight demonstration of the LISA technology. The major task of the STOC is to plan and validate the use and related configuration of the scientific instruments on board the spacecraft, derive from the mission products the science and technology results, and feed these results back into later planned instrument activities.

LISA Pathfinder's science operations will last six months; split between 90 days for the LISA Technology Package (LTP), and 90 days for the Disturbance Reduction System (DRS). The DRS experiment will be using the European LTP sensor for its measurements.

All of the data accumulated by the LTP, and a subset of the data analysis products, will be archived by the STOC and made available to the wider scientific community. The LTP team have proprietary data rights for the first three months, after which time the archive will be in the public domain.