Page 113 - Intro to Space Sciences Spacecraft Applications

100 Introduction to Space Sciences and Spacecraft Applications
(22,000 mph). Such hypervelocity collision with particles as small as 1 cm
in diameter can cause significant impact damage, and shielding for parti-
cles much larger than this becomes impractical. This subject has become
one of great concern in the design of the international space station. It is
estimated that at least one impact with an object 1 cm in diameter or larg-
er will occw every 2.5 years for a space station sized vehicle, and about
50,000 impacts with particles 0.01 cm or less would occur each year.

As mentioned earlier, the earth’s atmosphere extends thousands of kilo-
meters above the surface, albeit in thinner and thinner proportions. Besides
the potentially damaging interactions with atmospheric elements, the drag
on spacecraft in this region is also not negligible and may affect spacecraft
lifetimes and attitude control. This was graphically exemplified by the
reentry of the huge Skylab space station after only six years in orbit. Solar
effects on the atmosphere (such as from solar flares and changes in the
amount of UV radiations) can cause changes in the atmospheric density,
affecting the drag on orbiting spacecraft dramatically and unpredictably.

Sensors

Sensors used in spacecraft are usually very sensitive to particular radi-
ations. Direct exposure to solar radiation may result in unwanted signal
reception and possible sensor damage. If the purpose of a system is to pick
up the weak radiations of a faraway planet or star, and the sensor happens
to inadvertently “look” in the direction of the sun (or a reflection of some
of its energy), the desired signals may be obscured in the sun’s radiations
and the sensor itself may be damaged. Additionally, the sensors must be
protected from the general effects of the space environment described
above or else performance may be adversely affected.

Spacecraft Performance

The operability and performance of a spacecraft may also be affected
by the space environment through which it must operate. Remote sensors
must peer through an atmosphere of changing properties (heat, cold, rain)
and conditions (night, day), and the transmission of information to ground