Page 188 - Intro to Space Sciences Spacecraft Applications

Spacecraft Systems
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The ARC subsystem takes its most important cue from the pointing
accuracy of the single most demanding payload. This determines the avail-
able ARC architectures capable of achieving this accuracy: greater than or
equal to 5 degrees for gravity gradient, 1 degree for spin, 0.1 degree for
three-axis bias momentum or dual-spin, and less than 0.1 degree for three-
axis zero-momentum. Having selected an ARC architecture, the designer
matches the selected architecture with the minimum components required
for implementation as indicated in the example shown in Table 8-2. The
mass for the components, required to implement the selected ARC, is
arrived at by a Combination of table look-up and calculation. The table
look-up mass values are shown in an ARC database such as the one shown
in Table 8-3. The contribution to the ARC subsystem mass is simply:

(mass of the component) x (number of components)

As indicated in Table 8-3, the mass for many of the components, such
as the reference sensors, is represented by values based on current tech-

Table 8-2
ARC Components Required

~~ ~~~
Stab Method Reaction Momentum MagTor IRU Sun Star Earth Mag
1 3-axis,
zero-momentum 4 0 2 0 3 0 2 2
2 3-axis,
bias-momentum 1 0 2 0 3 0 2 2
3 Dual-spin 0 1 2 0 3 0 2 2
4 Spin 0 0 2 0 3 0 2 2
5 Gravity gradient 0 0 0 0 2 0 0 2

Table 8-3
ARC Components Mass (kg)

~ ~~~
S/CMass(kg) Wheels Magtor IRU Earth Momentum Sun Star Mag
~ ~~
200 2 1 3 2.5 2 0.5 8 1
500 4 1 7 4 4 0.5 8 1
900 6 2 11 5 6 0.5 8 1
1,200 8 3 14 6 8 0.5 8 1
2,000 10 4.5 17 7 10 0.5 8 1