**4. Deleterious effects of plasma interactions with spacecraft**

While interactions with space plasma can sometimes change material properties in a beneficial way (see succeeding section), these interactions also often have deleterious effects on spacecraft performance, often related to a change of electrical potentials on either internal or surface materials. If the local electric field becomes larger than some threshold value, electrostatic discharges (sometimes called arcs) will occur. Spacecraft arcs have been seen to have the following effects:


Due to these and other issues, efforts are usually made to prevent arcs by choosing appropriate materials and power system engineering. Elaborate computer codes are used to see where and when spacecraft charging is likely to occur and to adjust surface and interior materials where arcing susceptibility is found. If material properties change dramatically due to the space radiation, however, these models are invalidated, as they rely on pristine material characteristics, and unwanted surprises are likely to occur.

wavefunction overlap arising from the positional and orientational distribution of these hopping sites [38]. It is our hypothesis that the radical sites created due to bond-specific rupture during electron bombardment can act as electron hopping sites, which are not present in the

238 Plasma Science and Technology - Basic Fundamentals and Modern Applications

Finally, it has been commonly assumed that exposure to air would be deleterious to understanding how materials recover in a vacuum. However, since PI is very stable under normal conditions a small amount of air exposure is accepted as necessary and largely unavoidable in the majority of studies that have been published [40–42]. Data presented here show that air exposure dominates the post-irradiation chemistry of PI and that even limited air exposure (less than 10 min) will cause dramatic and unwanted effects that will obscure experimental studies. This fact illustrates the necessity of in-vacuum characterization methods as well as a careful examination of material handling techniques when reviewing the

While interactions with space plasma can sometimes change material properties in a beneficial way (see succeeding section), these interactions also often have deleterious effects on spacecraft performance, often related to a change of electrical potentials on either internal or surface materials. If the local electric field becomes larger than some threshold value, electrostatic discharges (sometimes called arcs) will occur. Spacecraft arcs have been seen to have

**1.** Large and rapid current spikes, which can cause latchups or even destroy sensitive elec-

**3.** Electromagnetic interference (EMI), which can interfere with communications, and so on. **4.** Contamination of surrounding surfaces, which can affect optical transparency (usually

**5.** Short-circuits between individual solar cell junctions, causing the loss of power from indi-

**6.** Sustained arcing between adjacent solar array strings or from solar array strings to spacecraft ground, which can lead to permanent short-circuits and power loss in one or all

Due to these and other issues, efforts are usually made to prevent arcs by choosing appropriate materials and power system engineering. Elaborate computer codes are used to see where and when spacecraft charging is likely to occur and to adjust surface and interior materials

thermal, but maybe solar cell current output) and electrical properties.

**4. Deleterious effects of plasma interactions with spacecraft**

pristine material.

literature.

the following effects:

vidual cells.

tronic components.

**2.** Transients in spacecraft power.

strings (total loss of power).

Unexpected, unexplained slow and pernicious power loss has been consistently observed in GPS satellites [43]. Although the loss was quickly determined to be due to the contamination of the solar array surfaces, a seemingly exhaustive search for sources of the contamination turned up no suspects. Confronted with the challenge, engineers decided to oversize the solar arrays by 25%, such that the deteriorated solar arrays would still provide adequate power at the end-of-life. This was an expensive and difficult solution because it led to increased spacecraft weight and volume, important launch considerations. Recently, it has been discovered that GPS solar arrays have been undergoing extensive arcing and gradually contaminating their own surfaces, decreasing the amount of sunlight that can reach the active parts of the solar cells [18, 43]. The arcing had gone undetected because of heavy filtering of electrical transients in the power system. Ground-based testing has shown that the power loss can be explained by the contamination produced by thousands of solar array arcs seen on orbit. In this case, a change in material properties due to the space plasma environment led to an unexpected and deleterious result.

As with changes in human DNA, changes in spacecraft materials properties may be beneficial but are usually not. If, however, the materials properties changes can be quantified and predicted, engineering can achieve a survivable spacecraft throughout its anticipated life. In the case of GPS, understanding the cause of solar array power degradation is leading to designs that can prevent the cause of the degradation, and in the end, provide a more reliable, cheaper, lighter, and smaller satellite that can still fulfill its mission.
