This standard provides requirements relative to various plasma interactions that can result when a high-voltage system is operated in the Earth's ionosphere and standard practices to eliminate or mitigate such reactions.

Purpose

The purpose of this standard is to provide a design standard for high-voltage space power systems ( 55 volts (V)) that operate in the plasma environment associated with LEO (altitude from 200 and 1000 km and latitude between -50 and 50 degrees). Such power systems, particularly solar arrays, are the proximate cause of spacecraft charging in LEO; and these systems can interact with this environment in a number of ways that are potentially destructive to themselves as well as to the platform or vehicle that has deployed them.

High-voltage systems are used in space for two reasons. The first reason is to save launch weight. First of all, for the same power level, higher voltages enable use of thinner wires (lighter cabling). This is true because P = IV, and V = IR, so P = I2R (where P is power, I is current, R is resistance, and V is voltage). If I is decreased by use of higher V, then thinner wires can be used with no increase in power loss due to cabling. Of course, if one uses the same cable mass, higher voltages will enable higher efficiencies, since less power will be lost to resistance in the cables. For very large power systems, the decrease in cable mass can be substantial.

Second, some spacecraft functions require high voltages. For example, electric propulsion uses voltages from about 300 V (Hall thrusters) to about 1000 V (ion thrusters). For low-voltage power systems, conversion of substantial power to high voltages is required for these spacecraft functions to operate. The weight of the power conversion systems, power management and distribution (PMAD), can be a substantial fraction of the total power system weight in these cases. It is more efficient, and can save weight, if the high-voltage functions can be directly powered from a high-voltage solar array, for instance. If the high-voltage function is electric propulsion, we call such a system a direct-drive electric propulsion system.

Because of these and other reasons for using high voltages in space, spacecraft designers and manufacturers are using high voltages more and more. However, the use of high voltages entails risk; in particular, spacecraft charging in LEO, in contrast to that in geosynchronous earth orbit (GEO), is caused by exposed high voltages, and can lead to arcing, power drains, power disruptions, and loss of spacecraft coatings. Thus, system designers need a standard to show them how to mitigate the spacecraft charging effects of using high voltages in LEO. In addition to system designers, this document should be useful to project managers, solar array designers, system engineers, etc.

This document is intended as a standard for design applications and can be used as a requirements specification instrument.

Applicability

This standard is applicable to high-voltage space power systems that operate in the plasma environment associated with LEO.

This standard is intended for space systems that spend the majority of their time at altitudes between 200 and 1000 km (usually known as LEO applications) and at latitudes between about and -50 degrees — that is, space systems that do not encounter GEO (geosynchronous orbit) charging conditions, that do not (often) encounter the auroral ovals of electron streams, and that do not fly through the Van Allen belts. For the extreme radiation protection that is necessary for orbits in the Van Allen belts, exterior spacecraft charging will likely be a secondary concern. However, internal charging will be very important. It is not in the purview of this document to deal with internal charging.

Some of the design standards for LEO are at variance with good design practice for GEO spacecraft. If your spacecraft will fly in both LEO and GEO conditions, be careful to use design solutions that are applicable in both environmental regimes.

This standard may be cited in contract, program, and other Agency documents as a technical requirement. Mandatory requirements are indicated by the word "shall." Tailoring of this standard for application to a specific program or project shall be approved by the Technical Authority for that program or project.