Written in collaboration with Dr. Simon Barke of the Precision Space Systems Laboratory
The Precision Space Systems Laboratory (PSSL) at the University of Florida aims to develop instrumentation and measurement techniques for gravitational science and satellite navigation. In collaboration with the NASA Ames Research Center, the PSSL works on multiple missions for laser communication in space and measures the time difference between ground and space clocks. However, the most significant project the PSSL is involved in is the Laser Interferometer Space Antenna (LISA), a mission to detect and measure gravitational waves from slow-moving astronomical sources by the European Space Agency (ESA) in partnership with NASA. 1
The measurement of gravitational waves can reveal information about the locations of binary stars, details about the properties of black holes, and even the collision and merger of galaxies, giving insight into our cosmic history. Recently, the PSSL hosted ANCORP engineering interns to discuss the lab’s role in the LISA mission and how their custom vacuum chamber system from ANCORP is helping achieve that goal.
The Laser Interferometer Space Antenna (LISA) system will comprise three spacecraft in a triangular formation separated by millions of kilometers and equipped with laser technology and sensors that will allow each spacecraft to detect minuscule changes in position relative to one another. The sensors on the spacecraft that record will be sensitive to distance fluctuations of just a few picometers. This data can then be translated into gravitational wave signals of certain amplitude, frequency, and direction of origin.
However, to make measurements this precise, establishing a gravitational reference point is critical for the mission as position deflections caused by interferences such as noisy solar radiation would drown out the desired gravitational wave signals. The Precision Space Systems Laboratory has been awarded a NASA contract to complete a subsystem for the mission responsible for maintaining the gravitational reference for the sensors: the charge management device.2
The gravitational reference on board each spacecraft is a free-floating gold-platinum alloy test mass. The main measurement of distance fluctuations that allow for the detection of gravitational waves happen between those test masses. The charge management device in development at the University of Florida will utilize the photovoltaic effect through deep ultra-violet (DUV) light-emitting diodes (LEDs) to manage and influence the test mass electrical charge. Through this charge control, position changes of the test masses can effectively be attributed to gravitational effects alone, and it becomes possible to remove the influence of external environmental disturbances from the data for a clean gravitational wave signal.
ANCORP manufactured the custom cylindrical vacuum chamber, featured on the top of the page, outfitted with optical and electrical feedthroughs and viewports to support data collection, UV light transmission, and temperature control. The PSSL has been using the system for a couple of years, qualifying the DUV LEDs for space flight in a variety of precise tests under realistic conditions. Members of the lab proudly shared that the development and testing of any flight hardware for a mission is an incredible feat for a university lab. The Precision Space Systems lab is fortunate to work with their industrial partner, Fibertek, to qualify their technology for integration in the LISA mission.
1 Precision Space Systems Laboratory, https://pssl.mae.ufl.edu/#home/main/
2 Laser Interferometer Space Antenna, ESA, NASA, https://lisa.nasa.gov/
3 LISA mission moves to final design phase, The European Space Agency, https://www.esa.int/Science_Exploration/Space_Science/LISA_mission_moves_to_final_design_phase