Table C-2: Typical plasma parameters for LEO and GEO
|
Altitude km |
Circular velocity |
Ion Acoustic velocity |
Mach no. |
Mach angle degrees |
|
200 |
7,8 |
1,4 |
5,5 |
10 |
|
500 |
7,6 |
2,1 |
3,7 |
16 |
|
1000 |
7,3 |
3,6 |
2,0 |
29 |
|
1500 |
7,1 |
4,3 |
1,6 |
38 |
|
2000 |
6,9 |
5,7 |
1,2 |
55 |
|
GEO |
3,0 |
30 – 500 |
0 – 0,1 |
n/a |
|
a. Adapted from [10]. b. A range of electron temperatures from 2eV to 2keV is estimated for GEO. |
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C.6.1.2. Effects
It is important to note that the wake effect induces a modified local environment favourable to charging. Because a wake creates a plasma void next to one face of the satellite, there is no low-energy plasma available to neutralize high potentials that can arise. For LEO through the auroral zones, electrons with energies of around 10s keV (described in ECSS-E-ST-10-04) can strike the spacecraft. The ability of such electrons to cause hazardous charging levels is increased by the presence of the wake. This effect can be local, with certain surfaces shielded by booms and other projecting features, due to their orientation relative to the direction of motion.
Wakes present problems to scientific satellites whose goal is to monitor ambient plasma characteristics. When probes enter the wake region near the spacecraft, the plasma they observe is much disturbed.
It is important to note that wakes can be used for extremely pure vacuum applications. NASA has flown the Wake Shield Facility [11] on the Space Shuttle in a proof-of-concept demonstration and it is proposed as a means of generating ultra-pure semiconductors by molecular beam epitaxy and chemical beam epitaxy.