Two-axis attitude correction for orbit inclination
First Claim
1. A method of orienting a spacecraft payload of a momentum biased spacecraft orbiting the earth in essentially a geosynchronous orbit in order to maintain the payload pointed at a desirable pointing profile on the earth in the presence of orbit inclination, said method comprising the steps of:
- determining the inclination and phasing of the spacecraft'"'"'s orbit;
calculating a coning motion in inertial space traced out by a pitch axis defined by the spacecraft payload as the payload is maintaining a desirable pointing profile throughout the orbit;
orienting the spacecraft bias momentum at substantially the center of the cone traced out by the pitch axis by applying external torque to the spacecraft;
offsetting the spacecraft payload sinusoidally in a yaw direction with respect to the nominal direction of the bias momentum, the offset having a period of once per day, an amplitude substantially equal to the radius of the cone, and a phase such that the payload pitch axis passes through a plane defined by the spacecraft and the spin axis of the earth when the spacecraft passes through the equatorial plane, wherein the amplitude and phase are determined from the orbit inclination and spacecraft phasing; and
pointing the spacecraft at the earth by means of a sensor and applying calculated payload pitch and roll attitude offsets to maintain the payload pointing direction.
2 Assignments
0 Petitions
Accused Products
Abstract
The attitude corrections required to remove attitude errors induced by orbit inclination deviations from the normal orbit plane, as well as the residual errors, are minimized by placing the satellite bias momentum at an inertial attitude lying substantially between the normals of the nominal and actual orbits, and using a payload reorientation means to adjust the payload attitude about three axes based on a combination of sensor data and offsets computed from the known orbit kinematics. In one embodiment, a momentum bias satellite is in an orbit slightly inclined from the geostationary orbit. The desired angular momentum vector attitude is chosen based on the orbit, the desired payload attitude, and the gimbal capabilities, and executed using thrusters. This reorientation limits the required gimbal travel. Based on this information, time-varying payload offsets in yaw, pitch and roll are computed from the nominal attitude produced by nulling earth sensor errors in roll and pitch, and using momentum bias and yaw estimation to control yaw. These offsets are implemented by a 3-axis gimbal between the momentum bias and the payload. Other sensors, actuators, or orbits could be used, including beacon sensors, star sensors, magnetic torquing, solar torquing, electronic steering, and other gimbal arrangements.
-
Citations
19 Claims
-
1. A method of orienting a spacecraft payload of a momentum biased spacecraft orbiting the earth in essentially a geosynchronous orbit in order to maintain the payload pointed at a desirable pointing profile on the earth in the presence of orbit inclination, said method comprising the steps of:
-
determining the inclination and phasing of the spacecraft'"'"'s orbit; calculating a coning motion in inertial space traced out by a pitch axis defined by the spacecraft payload as the payload is maintaining a desirable pointing profile throughout the orbit; orienting the spacecraft bias momentum at substantially the center of the cone traced out by the pitch axis by applying external torque to the spacecraft; offsetting the spacecraft payload sinusoidally in a yaw direction with respect to the nominal direction of the bias momentum, the offset having a period of once per day, an amplitude substantially equal to the radius of the cone, and a phase such that the payload pitch axis passes through a plane defined by the spacecraft and the spin axis of the earth when the spacecraft passes through the equatorial plane, wherein the amplitude and phase are determined from the orbit inclination and spacecraft phasing; and pointing the spacecraft at the earth by means of a sensor and applying calculated payload pitch and roll attitude offsets to maintain the payload pointing direction. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
-
-
13. A method of orienting a payload of a momentum biased spacecraft in an orbit perturbed in inclination from its nominal orbit in order to maintain payload pointing with respect to an orbited body close to that obtained in a nominal orbit, said method comprising the steps of:
-
determining the inclination and phasing of the spacecraft orbit; determining a desired payload orientation time history over the orbit; calculating a coning motion in inertial space traced out by a pitch axis defined by the spacecraft payload as the payload is maintaining a desirable pointing profile throughout the orbit; orienting the spacecraft bias momentum at substantially the center of the cone traced out by the pitch axis by applying external torque to the spacecraft to optimize the spacecraft'"'"'s ability to implement the desired payload orientation time history; and offsetting the payload axes from the bias momentum to the desired payload orientation based on the determined time history by means of offset corrections calculated from the steps of determining the inclination and phasing wherein the offsets include time-varying corrections in the yaw direction. - View Dependent Claims (14, 15, 16, 17, 18, 19)
-
Specification
-
- Resources
-
Current AssigneeHughes Electronics Corporation (AT&T, Inc.)
-
Original AssigneeHughes Aircraft Company (Rtx Corporation)
-
InventorsFowell, Richard A.
-
Primary Examiner(s)BAREFOOT, GALEN L
-
Application NumberUS07/733,783Time in Patent Office568 DaysField of Search244/164, 244/165, 244/171, 244/169, 364/434, 364/459US Class Current244/165CPC Class CodesB64G 1/285 using momentum wheelsB64G 1/36 using sensors, e.g. sun-sen...B64G 1/365 using horizon or Earth sensorsG01S 3/7867 Star trackers navigation us...
