What is a GMA? That's the Gas Management Assembly for Gravity Probe B. Its job is to spin up our
gyroscope rotors very soon
after the spacecraft's launch. This is a very important piece of equipment: without it, GP-B's gyros cannot spin and
we cannot do our experiment. The GMA has exceptionally high tolerance requirements. It is a complex assembly
consisting of a large number of components. MOOG designed
and built our GMA in a remarkably short time frame. The GMA took 14 months to complete, from initial contact
(in June 2001) through design (July 2001), fabrication and proto-flight qualification testing to final
acceptance(Aug 2002). This is an impressive accomplishment given the difficulty of the design and the time
required to go through formal flight acceptance procedures.
The Images to the left are:
- The final flight Gas Management Assembly (GMA), photographed at MOOG in East Aurora, New York,
- The engineers at MOOG packing the GMA for shipment
- The Lear jet chartered to fly this space-flight-qualified cargo across the country. Its captain and co-pilot are
pictured here with Marv from Quality Assurance at NASA Marshall Space Flight; Dorrene Ross, Systems
Effectiveness Manager here at Stanford, also made the five-plus hour flight.
- The GMA team, including representatives from MOOG, Stanford University, NASA MSFC & Lockheed Martin.
- The GMA at Stanford University undergoing acceptance testing in FISTOps. The GMA is in a clean tent to
prevent any contamination to the unit.
- A close up of the GMA in the clean tent.
- The mock GMA ("GMOCK") test unit built at Stanford to mimic the GMA in all possible appearances used for
testing the Gyro Suspension Electronics and Software. The GSE and S/W systems must be properly tested
with the mock unit before they are allowed to be connected to the flight GMA from MOOG. The GMOCK will also be
used for flight simulation during the mission if needed.
- This is the Gyro acceptance "facility". There is a gyroscope at the bottom of a long probe inside the blue dewar
(the large blue tank on the left). Long gas lines are sent from the GMA into the probe inlet to do the spin-up testing.
Low speed and then high speed testing of gyroscope spin speeds have been accomplished at Stanford for buy-off of the GMA
(spin speeds of 1 Hz and 57 Hz). These tests and documentation are passed, signed off and completed. The criteria for
success? Spin a gyro with the Gyro Acceptance GSE (the Gyro Acceptance GSE is also used for flight qualification of our
gyros) and spin the gyro with the flight GMA, and make sure you get comparable speeds in time and results. The spin-down
of the gyro has to show no signs of contamination. Because we are in a cryogenic system, so there can be no air or particles
inside the gas lines that could end up between the narrow clearance between the rotor and the housing of the
gyroscope. The GMA passed all criteria successfully.
- The GMA in its clean tent, again. The voltmeter-like gadget to the right of the GMA is actually
a particle counter inside clean tent. It counts the number of particles inside the tent to ensure
no airbourne contamination to the GMA. The wires on left side are sleeved and connect to the
Experiment Control Unit electronics from the GMA.
Gravity Probe B is very proud of the entire GMA team for all outstanding efforts.