fm 44-100 us army air and missile defense operations

Appendix C
Space Support
This appendix gives a summary of space support to air and missile
defense operations. It is not intended as a comprehensive guide. FM 100-
18 establishes doctrine for the Army's use of space, describes current
space system capabilities, and provides guidance for the use and
application of space-based assets in support of Army operations.
SPACE FUNDAMENTALS
C-1. Understanding space fundamentals will aid the user in selecting the best
space support. Orbital characteristics and space system limitations are two of
the fundamentals.
ORBITAL CHARACTERISTICS
C-2. Generally, the orbital characteristics of a space system are related to the
function of the satellite. Satellites may be in circular or elliptical orbits that
vary in altitude from 200 miles to over 22,500 miles from the earth's surface.
Low orbits, being closer to the earth, best support-sensing requirements. The
disadvantages of a low orbit are a limited field of view of the earth and a
short station time over any given earth area. As altitude increases, so do the
field of view and station time, but the ability to resolve a small object
decreases at higher altitudes.
C-3. The time it takes to complete one complete revolution of the earth is
known as the orbital period. The period relates directly to the orbit's average
distance from earth and is a function of the satellite's velocity. The greater
the velocity imparted to the satellite during orbital insertion, the greater the
orbital period and average distance from earth. Orbital periods range from 90
minutes for the lowest orbits to 24 hours or more for deep space orbits.
C-4. Another element of a satellite's orbit is its inclination, which is the angle
at which the satellite's orbital plane crosses the equator. A higher inclination
generally means that more of the earth's surface is covered. A polar orbit,
with an inclination of 90 degrees, crosses all latitudes, while lesser or greater
inclinations only provide coverage for increasingly higher latitudes,
particularly for satellites in low earth orbits.
C-5. The length of time between satellite coverage of a particular earth
location, that is, the satellite's revisit time, depends upon a number of factors.
For any given satellite, revisit time depends upon both orbital period and
inclination. For earth coverage by like systems, revisit time also depends
upon the number of satellites in the constellation, the capabilities of the
satellites' payloads, and the footprints of the various onboard sensors.
C-1