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Part 3.1: Goembel Instruments Functional Tests

The SCM has passed all tests for function performed in our Electron Spectroscopy Laboratory. At no time during the extensive tests of the SCM in various stages of development have we encountered any problems that could impact the SCM's ability to determine spacecraft charge. In fact, the SCM is such a rugged, high performance electron spectrometer that we would like to introduce the SCM to the scientific community as an off-the-shelf, inexpensive, low maintenance alternative to existing electron spectrometers.

Figures 3.1.01 and 3.1.02: Goembel Instruments SCM test apparatus (full chamber and close-up)

The ability of the SCM to collect electron energy spectra is extraordinary. The patented large-geometric-factor optics makes the collection of spectra easy compared to other electron spectrometers I have used in the laboratory. The SCM is indeed a very sensitive charged particle spectrometer. The following spectrum is typical of those collected with the SCM.

Figure 3.1.03: Electron energy spectrum of 50eV electrons scattered by Helium (collected by SCM delivered to NASA)

The spectrum shown above was collected by SCM flight prototype SN001 (the device delivered to NASA at the completion of Phase II). The extraordinary energy resolution, high sensitivity and low background are evident in the spectrum. The data displayed of a 200-point spectrum collected over 100 seconds (100, 200 step scans of one second each, 5ms dwell at each data point). The electron counts that appear on the y-axis are the average of 100, 5 ms counts. The Goembel Instruments high-energy-resolution electron gun produced a narrow bandwidth beam of ~50 eV electrons for the experiment. A dedicated turbo-pump pumped the collision center.

Figure 3.1.04: Apparatus used to collect scattering spectrum; "C.C." marks collision center

A detailed description of a "helium scattering spectrum" appears in the Phase I final report and is excerpted in the footnotes of this report. 5 The flight-prototype SCM has retained all of the extraordinary qualities exhibited by its Phase I laboratory-prototype. The spectrum shown on the previous page has special significance: as far as I know the collection of a laboratory-quality scattering spectrum by a flight-qualified instrument is unprecedented. The SCM is the only flight-qualified spectrometer available today that is capable of collecting such a high quality spectrum. Furthermore, such performance is required to determine spacecraft floating potential through electron spectroscopy.

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