SPACE WEATHER - AGI

More documents

Recommendations

Info

Section I: Residual Atmosphere Effects© SSS Educational Series 2012Section I: Residual Atmosphere Effects1. IntroductionThe saying that “outer space is a vacuum” does not apply to all regions of space.Spacecraft in LEO, especially those below 550 km, are still within the reach of theEarth’s atmosphere and have to carry out their operations successfully whilesubjected to the effects of the atomic and/or molecular atmospheric constituents. Inthis section, the components of the Earth’s atmosphere which spacecraft areexposed to and the different interactions are outlined.2. Earth’s AtmosphereThe neutral thermosphere is the region of the Earth's atmosphere containing neutralgases like Hydrogen, Helium, Atomic Oxygen (AO), 1 and Nitrogen extending from 90km to 600 km [1]. In this region, the absorption of EUV leads to a rapid increase intemperature. Solar activity strongly influences temperature in the thermosphere.Figure 1: Layers of the Earth’s atmosphere (Source: NASA).1 Due to photo-dissociation, oxygen exists predominantly in atomic form.1
© SSS Educational Series 2012Section I: Residual Atmosphere EffectsThis is the part of the atmosphere that most low altitude spacecraft are exposed to.Above 150 km, AO is the main constituent, with 66% at 200 km and 90% at 500 km.The density of the constituent gases varies with altitude and solar activity (due toheating caused by the absorption of solar EUV radiation). Since AO is lighter than theother constituents, its abundance decreases less rapidly with altitude. Figure 2 showsthe number density of the various constituents at different altitudes. It shows that,typically, AO is the constituent of concern in LEO (MAX refers to solar maximum andMIN to solar minimum). The effects of residual atmosphere on spacecraft include;drag, outgassing, contamination, glow, surface degradation/erosion, aerodynamicheating.Figure 2: Number density of the different atmospheric constituents as a function ofaltitude (Source: NASA).3. Atmospheric Effects3.1 DragSpacecraft in LEO pass through relatively dense neutral particles. At relativevelocities of 8 km/s, there is a considerable exchange of impulse and energybetween ambient atmosphere and spacecraft causing an applied drag on thespacecraft. Aerodynamic drag causes orbit decay and induced torques in spacecraftleading to tracking problems. In the long-run, if not compensated for, drag causesspacecraft to slow, lose altitude, and finally re-enter. enter. This aerodynamic drag isdependent on the spacecraft ballistic coefficient 2 (the mass-to-area area ratio), as shownin2 The ballistic coefficient of a body is a measure of its ability to overcome air resistance.2
Page 3: © SSS Educational Series 2012Ackno
Page 8 and 9: Section I: Residual Atmosphere Effe
Page 15 and 16: Section II: Radiation Effects© SSS
Page 27 and 28: Section III: Thermal Effects© SSS
Page 31 and 32: Section III: Thermal Effects5. Miti
Page 35 and 36: Section III: Thermal Effects6. Refe
Page 37: Schwarzenbergplatz 6Vienna A-1030AU

SPACE WEATHER - AGI

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?