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Part 1: Project Objectives

The primary objective of this SBIR project was to deliver NASA a flight prototype of an efficient, economical spacecraft charge monitor of novel design - the Spacecraft Charge Monitor (SCM). The SCM will be the first device to use high energy-resolution spectroscopy to determine spacecraft floating potential. Our electron-spectroscopic technique (Goembel and Doering, 1998) has enabled the production of a small, lightweight, easily deployed instrument to monitor a spacecraft's "absolute" (spacecraft chassis) floating potential. To date, Goembel Instruments is the sole provider of a spacecraft charge monitor based on high energy-resolution electron spectroscopy. Goembel Instruments also holds the patent on the 'heart' of the Spacecraft Charge Monitor.1 Its highly efficient electron analyzer has enabled us to build a powerful and accurate, yet simple, device. Our instrument achieves an astounding 300-fold increase in sensitivity per unit weight over the only comparable instrument that has flown 2.

Although some instruments have been used in the past to gauge spacecraft floating potential, none has offered the advantages of the instrument we have delivered to NASA. In low Earth orbit (LEO), Langmuir probes are the most commonly used charge monitor. They are used on the International Space Station. It is not really known how accurately they can determine spacecraft charge. It is known that their accuracy degrades over time, and they certainly cannot be used to determine the charge of spacecraft that are not in low Earth orbit. That means that Langmuir probes cannot be used to determine charge on, for instance, spacecraft en-route to Mars or science probes located far from the Earth. The SCM can be used on such missions.

Outside of low earth orbit other techniques have been used to gauge charge. Typically the spacecraft's electric field is measured by the potential difference between two probes mounted on booms. The booms are typically meters in length. All methods used to determine floating potential in the solar wind have been complicated by orbit-attitude considerations, lack of confidence in the measurement, etc., but one of the more promising techniques (electron spectroscopy) could be exploited by the SCM to determine spacecraft charge in the solar wind. In fact, the SCM would be far lighter, smaller, cheaper, and better able to determine spacecraft charge than the instruments now used to determine spacecraft charge in the solar wind 3.

Now that the SCM flight prototype has been delivered to NASA, it is available for a flight opportunity to prove its utility in space.