Since the radioisotope power system (RPS) is an electric-current generator, its operation produces its own magnetic field. Therefore, limitations on the strength of magnetic field produced by the radioisotope thermoelectric generator (RTG) are specified. If unknown or too strong, this magnetic field can have serious negative consequences to certain scientific objectives such as fly-by mapping of the magnetic fields emanating from planets and interference with scientific instrumentation on board the spacecraft that are frequently based on some magnetic phenomenon.
The magnetic field that is measured and characterized at SSPSF is generally three to four orders of magnitude (1/1,000th to 1/10,000th) less than the strength of the earth's magnetic field, between about 5 and 40 nanotesla. To characterize fields this small accurately, great care must be taken to remove the background magnetism. Since magnetic fields cannot be effectively shielded (unlike electric fields, magnetic fields penetrate everything) they must be compensated for in other ways. The tri-axial digital fluxgate magnetometers are used to do this. Other measures are also taken -- the magnetic field that is measured is disturbed by such things as personnel walking by several meters away, opening and closing of doors, or vehicle movement outside the building, as well as things that cannot be controlled, such as variations in the sun's magnetic field. It often takes many runs to obtain measurements that are accurate and precise enough to be used for NASA's purposes. Actual measurements on the RTG are taken at the quietest times possible -- and being located in the remote areas of the Idaho desert contributes greatly to our ability to make these measurements.
Magnetic testings are part of several steps in ensuring proper assembly and finished product quality of the RPS. The magnetic testing area is used to verify the magnetic field of an RPS is appropriate. The limitations on the strength of magnetic field produced by the RTG are specified.
Equipment capabilities include:
4 tri-axial digital fluxgate magnetometers
Nonmagnetic rotation platform
Field measurement range: -65,000nT to +65,000nT
Sensitivity 28 bit at 4096 sample averaging