Data processing: vehicles – navigation – and relative location – Vehicle control – guidance – operation – or indication – Aeronautical vehicle
Reexamination Certificate
2002-07-02
2004-04-20
Chin, Gary (Department: 3661)
Data processing: vehicles, navigation, and relative location
Vehicle control, guidance, operation, or indication
Aeronautical vehicle
C701S004000, C244S171000
Reexamination Certificate
active
06725133
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an attitude detection system for an artificial satellite and, more particularly, to an attitude detection system for detecting the attitude angle of an artificial satellite in a ground station, which is capable of accurately detecting fluctuation of the attitude angle of the artificial satellite over a broad frequency band. The present invention also relates to a method for detecting the attitude angle of the artificial satellite.
2. Description of the Related Art
The attitude of an artificial satellite residing in the space is generally observed from a ground station.
FIG. 1
shows an example of the conventional attitude detection system, which includes an attitude-angle calibration sensor
11
for sampling the attitude angle of the artificial satellite at a low frequency to generate an attitude-angle calibration signal
14
, an angular-velocity sensor
12
for detecting the angular velocity of the artificial satellite to generate an angular-velocity signal
15
and a sequential Kalman filter
13
for estimating the attitude, i.e., the attitude angle of the artificial satellite by integrating the angular-velocity signal
15
with respect to time while calibrating the integrated data based on the attitude-angle calibration signal
14
at a specified time interval.
Examples of the angular-velocity sensor
12
include a gyroscope, and examples of the attitude-angle calibration sensor
11
include a start tracker. In the sequential Kalman filter
13
, the noise characteristics of the attitude-angle calibration sensor
11
and the angular-velocity sensor
12
, which are mounted on the artificial satellite, are modeled by using a probability model technique, thereby estimating and removing the noise included in the angular-velocity signal
15
and the attitude-angle calibration signal
14
.
The attitude detection system shown in
FIG. 1
has a relatively simple structure, and is originally developed as an on-board processing system, i.e., a real-time processing system on the artificial satellite. However, since the ground station can also extract time-series data of the angular-velocity signal
15
and the attitude-angle calibration signal
14
from the telemetry data received by the ground station, the attitude detection system of
FIG. 1
is generally and widely used as an on-board processing system as well as a ground processing system.
In the conventional attitude detection system of
FIG. 1
, although the attitude-angle calibration sensor
11
generally has a higher accuracy compared to the angular-velocity sensor
12
, the attitude-angle calibration sensor
11
has a longer measurement cycle which is, for example, more than 10 times longer compared to the measurement cycle of the angular-velocity sensor
12
. Accordingly, even if the measurement cycle of the angular-velocity sensor
12
may be significantly improved, the frequency band of the final attitude-angle signal
16
obtained thereby is relatively limited due to the waste time caused by the characteristics of the attitude-angle calibration sensor
11
.
It may be considered that the angular-velocity sensor
12
alone is used for obtaining the attitude-angle signal
16
to improve the measurement cycle. However, in this case, there arises a problem that the noise involved in the angular-velocity signal
15
largely affects and degrades the accuracy of the calculated attitude-angle signal
16
, although it is possible to detect the fluctuation of the attitude angle of the artificial satellite itself in a higher frequency range.
JP Application 2000-265553 proposes an attitude detection system for an artificial satellite which can solve the above problem in the conventional technique. The proposed system includes an on-board high-frequency attitude-angle sensor, in addition to the attitude-angle calibration sensor
11
and the angular-velocity sensor
12
shown in
FIG. 1
, thereby generating a broad-band attitude-angle signal.
FIG. 2
shows the proposed system, which includes a telemetry data memory
220
for storing the telemetry data received from the artificial satellite, a first data extractor
201
for extracting attitude-angle calibration data
209
as time-series data from the telemetry data memory
220
, a second data extractor
202
for extracting angular-velocity data
210
as time-series data from the telemetry data memory
220
, and a third data extractor
205
for extracting high-frequency attitude-angle data as time series data from the telemetry data memory
220
.
An angular displacement sensor using a liquid is used as the on-board high-frequency attitude-angle sensor
205
, whereby the attitude angle of the artificial satellite can be detected at a higher frequency compared to the angular-velocity data
210
. The high-frequency attitude-angle signal, stored in the telemetry data memory
220
, is extracted by the third data extractor
205
as a high-frequency attitude-angle signal
213
.
The sequential Kalman filter
203
generates an attitude-angle signal
211
based on the attitude-angle calibration signal
209
and the angular-velocity signal
210
extracted by the first data extractor
201
and the second data extractor
202
, respectively, from the telemetry data memory
220
. The attitude-angle signal
211
generated by the sequential Kalman filter
203
is passed by a low-pass filter
204
, interpolated in an interpolator
207
, and then delivered to an attitude data adder
208
as a low-frequency interpolated signal
215
.
The high-frequency attitude-angle signal
213
extracted by the third data extractor
205
is passed by a band-pass-filter
206
and then delivered to the attitude data adder
208
as a high-frequency attitude signal
214
. The attitude data adder
208
adds both the low-frequency interpolated signal
215
and the high-frequency attitude signal
214
together to generate a high-accuracy broad-band attitude-angle signal
216
.
In the proposed system of
FIG. 2
, as described above, the low-frequency attitude signal
212
obtained by the sequential Kalman filter
203
and the low-pass filter
204
is interpolated in the interpolator
207
, and then added to the high-frequency attitude signal
214
in the attitude data adder
208
to obtain the high-accuracy attitude signal
216
.
In the above operation of the sequential Kalman filter
203
, the angular-velocity signal
210
is sampled at a specified time interval corresponding to the measurement interval of the angular-velocity sensor, and integrated with respect to time while being calibrated based on the attitude-angle calibration signal
209
. In general, a shorter step interval for the integration provides a higher accuracy. However, in the proposed system, the step interval in the integration is determined by the frequency, or the measurement cycle, of the angular-velocity sensor which has a relatively limited performance as to the measurement cycle, and thus an accurate broad-band attitude-angle signal by the system is difficult to expect.
SUMMARY OF THE INVENTION
In view of the above problems in the conventional attitude detection system and the proposed attitude detection system proposed in JP Application 2000-265553, it is an object of the present invention to provide an attitude detection system for an artificial satellite, which is capable of detecting a broad-band attitude-angle signal for the artificial satellite with improved accuracy.
It is another object of the present invention to provide a method for detecting a broad-band attitude-angle signal for the artificial satellite with improved accuracy.
The present invention provides an attitude detection system for an artificial satellite including a telemetry data memory for storing telemetry data received from the artificial satellite, a first data extractor for extracting attitude-angle calibration data from the telemetry data memory as time-series data, a second data extractor for extracting angular-velocity data from the telemetry data memory as time-series data, an interpolato
Chin Gary
NEC Corporation
Ostrolenk Faber Gerb & Soffen, LLP
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