TABLE 2.
Physical conditions prevailing in the interplanetary space environment and in low Earth orbit
| Parameter | Interplanetary space | Low Earth orbit (≤500 km) |
|---|---|---|
| Space vacuum | ||
| Pressure (Pa) | 10−14 | 10−6–10−4a |
| Residual gas (particles/cm3)a | 1 H | 105 H, 2 × 106 He, 105 N, 3 × 107 O, spacecraft atmosphere |
| Solar electromagnetic radiation | ||
| Irradiance (W/m2) | —b | 1,360 |
| Spectral range (nm) | Continuum | Continuum |
| Cosmic ionizing radiation | ||
| Annual dose rate (Gy/yr) | ≤0.1c | 400–10,000d |
| Temperature (K) | >4b | Wide rangeb |
| Microgravity (g) | <10−6 | 10−3–10−6 |
a
Values in Earth orbit depend on outgassing of the spacecraft. Sources of contamination include waste dumping (H2O and organics) and thruster firing (H2O, N2O, and NO).
b
Values differ depending on orientation and distance to the Sun.
c
Depending on shielding; highest values at mass shielding of 0.15 g/cm2.
d
Depending on altitude, orbit, and shielding; highest values at high altitudes and mass shielding of 0.15 g/cm2.