Aeronautics and astronautics – Spacecraft – Attitude control
Reexamination Certificate
1999-04-30
2001-02-20
Barefoot, Galen L. (Department: 3644)
Aeronautics and astronautics
Spacecraft
Attitude control
C244S158700, C343S909000
Reexamination Certificate
active
06189835
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to an apparatus for controlling angular momentum build up of a spacecraft. More specifically, the present invention relates to an apparatus for controlling angular momentum build up of a spacecraft by tailoring the surface properties of the side mounted antennas.
BACKGROUND ART
Conventional spacecraft designs attempt to minimize the amount of angular momentum build up and therefore minimize the size of the momentum storage system and the number of momentum dumping operations required to dispose of any momentum build up. Spacecraft with larger momentum storage systems are heavier than those with smaller storage systems. Further, momentum dumping operations require utilization of fuel resources and thus increase the operational costs of the spacecraft and its complexity.
These spacecraft designs also use protective devices, such as thermal blankets, on the large side-mounted reflectors to provide thermal protection for the reflectors. Conventional thermal blanket designs utilize carbon-loaded (black) blankets on the back side of the reflectors and a Germanium-coated (reflective) sunshield on the front surface of the reflector. For a spacecraft with the same reflector design on both sides of the spacecraft, the surface properties of each one of the pair of reflectors are symmetric.
FIG. 1
illustrates an example of a conventional spacecraft
10
having a spacecraft body
12
and symmetric right and left reflectors
14
,
16
. Each of the reflectors
14
,
16
are dual surface antennas that have a sunshield on a respective front surface
18
and a black reflective blanket on a respective back surface
20
. As the spacecraft
10
rotates throughout a twenty-four hour period, sunlight illuminates all sides of the spacecraft
10
. The solar pressure acting on the spacecraft
10
is larger on the reflective front surfaces
18
than the black back surfaces
20
. As the designs of the reflectors
14
,
16
are symmetric, the solar-induced torque on the spacecraft
10
is balanced as it rotates over a twenty-four hour period. As the solar pressure is balanced, the resulting net angular momentum build up about the y-axis is zero.
For a spacecraft with asymmetric reflector designs, such as a bare graphite left reflector (black on both surfaces) and a blanketed right reflector (reflective front surface and black back surface), the solar pressure on the reflective front surface of the right antenna is greater than on the black front surface of the left antenna. As the spacecraft rotates over a twenty-four hour period, there is a net build up of angular momentum due to the unbalanced pressure on the front side of the left reflector. With this configuration, the angular momentum can quickly exceed the momentum storage capability of the spacecraft thus requiring more frequent angular momentum dumping operations on-orbit.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide an apparatus for tailoring the surface properties of the front and back surfaces of the side mounted antennas of a spacecraft for controlling angular momentum build up.
It is a further object of the present invention to provide a reflective antenna thermal blanket design that counteracts imbalances in the solar or radiated RF power from the side-mounted antennas.
In accordance with the objects of the present invention, a spacecraft having a pair of side-mounted reflectors that are asymmetrically designed is provided. One of the pair of side-mounted reflectors is smaller in size than the other of the side-mounted reflectors. The other of the side-mounted reflectors is positioned on the opposing side of the spacecraft and has a front surface and a rear surface with the front surface having a Germanium-coated sunshield overlay thereon and the rear surface having an antenna blanket positioned thereon. The antenna blanket has an inner layer attached to the rear surface of the other side-mounted reflector and an outer layer attached to the inner layer which has low solar absorptivity (&agr;) to control the solar pressure on the spacecraft such that over a twenty-four hour period, the angular momentum build up of the spacecraft is approximately a net zero.
Additional advantages and features of the present invention will become apparent from the description that follows, and may be realized by means of the instrumentalities and combinations particularly pointed out in the appended claims, when taken in conjunction with the accompanying drawings.
REFERENCES:
patent: 3225208 (1965-12-01), Wolfe
patent: 4684084 (1987-08-01), Fuldner et al.
patent: 4894125 (1990-01-01), Fenolia et al.
patent: 5305971 (1994-04-01), Decanini
patent: 5373305 (1994-12-01), Pepore, Jr. et al.
patent: 5618012 (1997-04-01), Lehner et al.
patent: 5775645 (1998-07-01), Yocum, Jr. et al.
patent: 6102336 (2000-08-01), Cande
Barefoot Galen L.
Gudmestad Terje
Hughes Electronics Corporation
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