NASA Scientific and Technical Aerospace Reports

distribute across the spacecraft and how rapidly charge imbalance will dissipate. To understand these processes requires
knowledge of how charge is deposited within the insulator, the mechanisms for charge trapping and charge transport within
the insulator, and how the profile of trapped charge affects the transport and emission of charges from insulators. One must
consider generation of mobile electrons and holes, their trapping, thermal de-trapping, mobility and recombination.
Conductivity is more appropriately measured for spacecraft charging applications as the ‘decay’ of charge deposited on the
surface of an insulator, rather than by flow of current across two electrodes around the sample. We have found that
conductivity determined from charge storage decay methods is 102 to 104 smaller than values obtained from classical ASTM
and IEC methods for a variety of thin film insulating samples. For typical spacecraft charging conditions, classical
conductivity predicts decay times on the order of minutes to hours (less than typical orbit periods); however, the higher charge
storage conductivities predict decay times on the order of weeks to months leading to accumulation of charge with subsequent
orbits. We found experimental evidence that penetration profiles of radiation and light are exceedingly important, and that
internal electric fields due to charge profiles and high-field conduction by trapped electrons must be considered for space
applications. We have also studied whether the decay constants depend on incident voltage and flux or on internal charge
distributions and electric fields; light-activated discharge of surface charge to distinguish among differing charge trapping
centers; and radiation-induced conductivity. Our experiments also show that ‘Malter’ electron emission occurs for hours after
turning off the electron beam. This Malter emission similar to emission due to negative electron affinity in semiconductors is
a result of the prior radiation or optical excitations of valence electrons and their slow drift among traps towards the surface
where they are subsequently emitted. This work is supported through funding from the NASA Space Environments and Effects
Program.
Author
Charge Transfer; Dissipation; Insulators; Conduction Electrons; Spacecraft Charging
20040111091 QinetiQ Ltd., Farnborough, UK
ECSS-E-20-06 Draft Standard on Spacecraft Charging: Environment-Induced Effects on the Electrostatic Behaviour
of Space Systems
Rodgers, D. J.; Hilgers, A.; 8th Spacecraft Charging Technology Conference; March 2004; 12 pp.; In English; See also
20040111031; No Copyright; Avail: CASI; A03, Hardcopy
ECSS (European Cooperation on Spacecraft Standardisation) is an initiative to develop a coherent, single set of
user-friendly standards for use in all European space activities. One part of this initiative has covered environment-induced
effects on the electrostatic behaviour of space systems, including spacecraft charging. This has resulted in a draft standard,
ECSS-E-20-06, that describes the performance and verification requirements needed to control these effects. Contributions to
the standard have come from European governmental agencies, the European Space Agency and industry. Before adoption,
the standard will be subject to wider circulation and amendment as a result of feed-back. This draft standard attempts to bring
together good practice and de facto standards, from a wide range of sources, into a single reference document. In addition,
it provides an explanation of the main physical processes of spacecraft electrical interactions and their effects, covering sheath
effects, wakes, tethers, electric propulsion, internal and surface charging, and discharges and transients. Requirements are
given for surface materials, solar arrays, internal materials, tethers and electric propulsion systems. Finally, useful information
is provided into ways of carrying out the required tests and simulations.
Author
Standardization; Electrostatics; Spacecraft Charging; Propulsion System Performance; Electric Propulsion; Aerospace
Systems
20040111096 Air Force Research Lab., Hanscom AFB, MA, USA
Onset of Spacecraft Charging in Single and Double Maxwellian Plasmas in Space: A Pedagogical Review
Lai, Shu T.; 8th Spacecraft Charging Technology Conference; March 2004; 12 pp.; In English; See also 20040111031; No
Copyright; Avail: CASI; A03, Hardcopy
This paper reviews some recent advances in the onset of spacecraft charging. Current balance determines the spacecraft
potential. The electron flux intercepted by an object in a plasma exceeds that of ions by orders of magnitude because of the
ion-electron mass difference. Negative voltage charging occurs when the incoming electron flux exceeds the outgoing
secondary and backscattered electron flux. The secondary electron emission coefficient depends on the surface material,
typically exceeds unity at about 40 to 1800 eV of primary electron energy, and falls below unity at higher energies. Beyond
a critical temperature T*, the incoming electron flux exceeds that of the secondary electrons, thereby negative charging occurs.
Scarce evidence of T* was observed on ATS-5 and ATS-6 satellites. Recently, abundant evidence was observed on the Los
Alamos National Laboratory geosynchronous satellites. The existence of T* enables accurate prediction of spacecraft charging
316