Page 102 - Intro to Space Sciences Spacecraft Applications

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Spacecraft Environment
The Atmosphere. A chapter on space environment may seem like a
strange place to include a discussion of the earth’s atmosphere, but the
atmosphere is a factor in the operation of spacecraft in many ways. The
following sections describe the atmosphere, along with its interaction with
the sun’s electromagnetic radiations.

Composition of the Atmosphere. It is believed that the atmosphere was
created as a result of the exhausting of materials from the interior of the
earth by volcanic activity. Nitrogen, being relatively inert, remains as the
most common atmospheric element. Diatomic oxygen was mainly pro-
duced via the photosynthesis of water and carbon dioxide by plant life
over millions of years. Argon and other trace elements make up the
remainder of the earth’s atmosphere as shown in Table 4- 1.

Table 4-1
Composition of the Earth’s Atmosphere (blow 100 km)

Constituent Content (fraction of total molecules)
Nitrogen (N2) 0.7808 (75.51% by mass)
0.2095 (23.14% by mass)
Oxygen (02)
Argon 0.0093 (1.28% by mass)
Water vapor (H20) 60.04 (variable)
Carbon dioxide (C02) 325 parts per million
Neon (Ne) 18 parts per million
Helium (He) 5 parts per million
Krypton 1 part per million
Hydrogen (H) 0.5 parts per million
Ozone (03) 0-12 uarts Der million

Higher in the atmosphere, monatomic oxygen (single oxygen atoms) are
created through photodissociation (splitting) of molecular oxygen by the
sun’s radiation. Monatomic oxygen is highly reactive, and some of these
atoms combine with diatomic oxygen to produce the ozone (0,) found in
the atmosphere. Ozone is particularly important to life on earth because it
absorbs much of the harmful ultraviolet radiation emitted by the sun.

Temperature Variation. The variation of temperature with altitude up to
about 700 km through the atmosphere is shown in Figure 4-6. These val-
ues are for a “standard” atmosphere which represents typical conditions at