SAES Getters has announced the conclusion of the pressure modeling of the interferometer inertial sensor head, commissioned by Carlo Gavazzi Space within the frame of the LISA Pathfinder project, the precursor to the ESA-NASA LISA mission due for launch in 2015. LISA (Laser Interferometer Space Antenna) is being developed to detect gravitational waves from sources involving galactic binaries and extra-galactic massive black holes, and so will study the death spirals of stars, ripples in space-time and echoes from the early universe.
The ESA-NASA mission involves three identical spacecraft in orbit around the Sun and flying approximately 5 million kilometres apart in an equilateral triangle formation. This spacecraft constellation acts as a Michelson interferometer to measure the distortion of space caused by passing gravitational waves. On board lasers will be used to measure minimal changes in the separation distances of free-floating masses within each spacecraft.
The LISA space-based interferometer is planned for launch in 2015 and, after a 13-month transfer to its operational orbit, it will stay in orbital phase for two years. The ultimate target of the project is the detection of gravitational waves, whose existence was predicted in Einstein's general relativity theory, and that are thought to be generated by massive objects, such as black holes.
The LISA mission will depend on critical concepts and technologies needed for highly accurate formation flying and precise measurement of the separation between very distant spacecraft. Prior to LISA's launch, the necessary technologies will be tested by the LISA Pathfinder mission. Planned for launch in 2009, this will put two test masses in a near-perfect gravitational free-fall and will control and measure their motion with unprecedented accuracy. This is achieved through state-of-the-art technology comprising the inertial sensors, the laser metrology system, the drag-free control system and an ultra-precise micro-propulsion system.
SAES Getters has been in charge of modelling the inertial sensor head of the interferometer, in order to set the vacuum pressure requirements necessary to support the space mission. Pressure stability and its uniform distribution inside the vacuum enclosure of the inertial sensor head is fundamental for the success of the project: an inadequate level of pressure might cause the shifting of the sensor inertial mass, directly effecting the experimental results and impacting on the whole mission.
The model realized for Carlo Gavazzi Space at SAES Getters' laboratories in Lainate shows that pressure in the vacuum chamber of the inertial sensor head needs to be at least as low as 10-7 mbar for two years. This vacuum level will ensure the sensor correct operation also by avoiding that possible pressure gradients in the vacuum chamber interfere with the experiment.
Data obtained from this modeling also indicate that the mission vacuum requirements can be best addressed by the zirconium non-evaporable getter (NEG) technology. SAES Getters' porous NEGs have enhanced sorption capacity thanks to their high porosity and large surface area, and are planned to be mounted on the interferometer sensor. Their porous structures allow the gases to diffuse through the pores inside the getter mass, thus involving the inner parts of the getter body in the sorption process and delivering a dramatic increase in sorption for nitrogen, hyrogen, carbon monoxide and other oxygenated gases.
The results of the modeling will ultimately be confirmed through extensive dedicated experimental tests, which will also enable the suitable number of NEGs to be determined and their most appropriate distribution inside the sensor head chamber.
