Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-04-25
2001-09-11
Phan, Dao (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C701S013000, C244S164000
Reexamination Certificate
active
06288671
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to spacecraft attitude control and, more particularly, to beacon-assisted attitude control.
2. Description of the Related Art
Various conventional tracking systems and methods have been described (e.g., see U.S. Pat. Nos. 4,963,890 and 5,926,130) for beacon-assisted spacecraft attitude control. The acquisition range, transient response and offset pointing of these systems and methods, however, has often been found to be less than satisfactory and they typically fail to operate autonomously (i.e., they require assistance from supporting control systems).
SUMMARY OF THE INVENTION
The present invention is directed to the autonomous orientation of a spacecraft to a desired spacecraft attitude A
dsrd
relative to a beacon that transmits a beacon signal. It discloses attitude control systems and methods which make direct use of received antenna powers and a signal modifier S
mod
to facilitate autonomous spacecraft attitude control, enhance conventional acquisition ranges and conventional transient responses and facilitate precise offset attitudes. These systems and methods avoid ambiguities that are introduced when received antenna powers are converted to angular distances.
These goals are achieved with process steps that include:
a) providing the spacecraft with at least three antennas A - - - N that have respective boresights arranged in a fixed angular relationship;
b) from the antennas, receiving the beacon signal with power amplitudes P
A
- - - P
N
that are each a measure of the angular distance between the boresight of a respective one of the antennas A - - - N and the beacon;
c) combining the powers P
A
- - - P
N
in accordance with the angular relationship to generate at least one attitude error signal S
err
whose magnitude is a measure of the attitude difference between a current spacecraft attitude A
crnt
and the desired spacecraft attitude A
dsrd
;
d) generating a signal modifier S
mod
that increases with decreases in a sum power P
&Sgr;
that is the sum of the signal powers P
A
- - - P
N
;
e) modifying the attitude error signal S
err
with a term (1+S
mod
) to form an enhanced attitude error signal S
err
enhd
; and
f) orienting the spacecraft to reduce the enhanced attitude error signal S
err
enhd
.
In one embodiment, the signal modifier S
mod
is set equal to n|P
max
−P
&Sgr;
|
m
wherein n and m are positive numbers and the maximum power P
max
is the sum power P
&Sgr;
when the attitude error signal S
err
=0.
Systems and spacecraft are also described for realizing the methods described above.
The novel features of the invention are set forth with particularity in the appended claims. The invention will be best understood from the following description when read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4963890 (1990-10-01), Perrotta et al.
patent: 5790071 (1998-08-01), Silverstein et al.
patent: 5926130 (1999-07-01), Werntz
patent: 6018315 (2000-01-01), Ince et al.
Chiang Richard Y.
Ketkar Umesh S.
Li Rongsheng
Wu Yeong-Wei Andy
Gudmestad T.
Hughes Electronics Corporation
Phan Dao
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