LISA Pathfinder (LPF), ESA’s demonstrator for spaceborne observations of gravitational waves, is ready to leave for Europe’s Spaceport in Kourou, French Guiana, where it is scheduled for launch on a Vega rocket later this year, having completed extensive testing and final integration at IABG’s test center in Ottobrunn, near Munich, Germany.
LISA Pathfinder project manager, César García Marirrodriga, described the recent testing to Aerospace Testing International: “LPF has been tested like any other spacecraft. Environmental tests at unit, sub-system or system level included static load, sine vibration, random loads, vibro-acoustic loads, thermal vacuum, thermal balance (with solar simulator), etc. The test loads are defined, at each level of integration, using the expected environment and applying adequate qualification and/or acceptance margins. We also performed EMC (electro-magnetic compatibility) and radio transmission tests. But LPF is special on many accounts; so we also tested for magnetic cleanliness of all spacecraft components or for high-vacuum outgassing of materials around the ‘test-mass’.
“On the test-mass itself, we also measured quantum yield (electrons emission when subject to UV photons), magnetic susceptibility, homogeneity and inner voids … The testing of the optical metrology subsystem was also a challenge, as we want to discriminate pico-metres and the lab environment must be tightly controlled.”
However testing such a unique piece of equipment here on Earth has its limits: “In LPF we have replicated the planned in-orbit experiments and measurements with similar or identical equipment,” says Marirrodriga. “But one cannot have a 2kg free-floating mass or a spacecraft subject to micro-Newton thrusters on Earth!”
LISA Pathfinder will conduct inflight testing of the concept of low-frequency gravitational wave detection. It will put two test masses in a near-perfect gravitational free-fall, and control and measure their motion with unprecedented accuracy. To do this, it will use inertial sensors, a laser metrology system, a drag-free control system and an ultra-precise micro-propulsion system.
The mission aims to demonstrate, in a space environment, that free-falling bodies follow geodesics in space-time, by more than two orders of magnitude better than any past, present, or planned mission. This requires extraordinary measurement techniques using lasers, with the test masses flying freely in space, each shielded by a surrounding spacecraft from all extraneous influences, such as the solar wind.
September 11, 2015