Spacecraft momentum management
View Patent ↗Three-axis spacecraft momentum management is performed for a spacecraft traveling along a trajectory, by an actuator including at least one thruster disposed on a single positioning mechanism. As the spacecraft travels along the trajectory, a desired line of thrust undergoes a substantial rotation in inertial space. When the spacecraft is located at a first location on the trajectory, the single positioning mechanism orients the thruster so as to produce a first torque to manage stored momentum in at least one of a first and a second of the three inertial spacecraft axes. When the spacecraft is located at a second location on the trajectory, the single positioning mechanism orients the thruster so as to produce a second torque to manage stored momentum in at least a third of the three inertial spacecraft axes.
1. A method for managing momentum of a spacecraft traveling along a trajectory, the method comprising:
determining a respective momentum storage error (MSE) in each of three inertial spacecraft axes, said respective MSE comprising a difference, for each axis, between a momentum value actually stored on the spacecraft and a desired momentum value;
reducing each respective MSE by producing, with at least one thruster disposed on a single positioning mechanism, a plurality of torques, by:
orienting the thruster, with the single positioning mechanism, so as to produce a first torque that reduces the respective MSE of either or both of a first and a second of the three inertial spacecraft axes when the spacecraft is located at a first location on the trajectory, and,
orienting the thruster, with the single positioning mechanism, so as to produce a second torque that reduces the respective MSE of at least a third of the three inertial spacecraft axes when the spacecraft is located at a second location on the trajectory; wherein,
the single positioning mechanism is configured to orient the thruster so as to simultaneously (i) accelerate the spacecraft along a line of thrust and (ii) produce a torque around at least one of two axes substantially orthogonal to the nominal thrust vector; and
as the spacecraft travels along the trajectory, a desired line of thrust undergoes a substantial rotation in inertial space.
2. The method as recited in claim 1 , wherein spacecraft acceleration and MSE are simultaneously controlled by the at least one thruster disposed on the single positioning mechanism.
3. The method as recited in claim 1 , wherein the thruster is a low thrust electric propulsion device.
4. The method as recited in claim 3 , wherein the thruster is a Hall effect thruster.
5. The method as recited in claim 1 , wherein, as the spacecraft travels along the trajectory, the substantial rotation is approximately ninety degrees.
6. The method as recited in claim 1 , wherein the single positioning mechanism has two degrees of freedom.
7. A spacecraft comprising:
at least one thruster;
spacecraft control electronics configured to:
(i) generate a desired orbit transfer profile for the spacecraft; and
(ii) determine a respective momentum storage error (MSE) in each of three inertial spacecraft axes, said respective MSE comprising a difference, for each axis, between a momentum value actually stored on the spacecraft and a desired momentum value; and
a spacecraft steering apparatus, comprising the at least one thruster disposed on a single positioning mechanism, that, responsive to signals from the spacecraft control electronics:
controls the attitude of the satellite so as to follow the desired orbit transfer profile; and
reduces each respective MSE by producing, with the at least one thruster, a plurality of torques, by:
orienting the thruster, with the single positioning mechanism, so as to produce a first torque that reduces the respective MSE of either or both of a first and a second of the three inertial spacecraft axes when the spacecraft is located at a first location on the trajectory, and,
orienting the thruster, with the single positioning mechanism, so as to produce a second torque that reduces the respective MSE of at least a third of the three inertial spacecraft axes when the spacecraft is located at a second location on the trajectory; wherein,
the single positioning mechanism is configured to orient the thruster so as to simultaneously (i) accelerate the spacecraft along a line of thrust and (ii) produce a torque around at least one of two axes substantially orthogonal to the nominal thrust vector; and
as the spacecraft travels along the trajectory, a desired line of thrust undergoes a substantial rotation in inertial space.
8. The spacecraft as recited in claim 7 wherein the at least one thruster comprises an electric propulsion thrusters.
9. The spacecraft as recited in claim 8 wherein the at least one thruster comprises a Hall effect thruster.
10. The spacecraft as recited in claim 7 , wherein, as the spacecraft travels along the trajectory, the substantial rotation is approximately ninety degrees.
11. The spacecraft as recited in claim 7 wherein the spacecraft control electronics comprises a profile generator configured to compute a desired orbit transfer profile such that perigee, apogee and inclination of the spacecraft are adjusted simultaneously in a mass-efficient manner.
12. The spacecraft as recited in claim 7 wherein the desired orbit transfer profile includes:
placing the spacecraft in an Earth-pointed attitude when the spacecraft is at a predefined point in the trajectory;
slewing the spacecraft from the Earth-pointed attitude to a desired orbit raising attitude; and
steering the spacecraft according to the desired orbit transfer profile while changing a spacecraft velocity.
13. The method as recited in claim 7 , wherein the single positioning mechanism has two degrees of freedom.
14. A method comprising:
dynamically computing an optimal steering profile for a spacecraft, based on position of the spacecraft on a trajectory, the spacecraft comprising at least one thruster disposed on a single positioning mechanism and an inertial reference sensor;
dynamically computing the spacecraft's actual position;
steering the spacecraft according to the computed optimal steering profile such that the at least one thruster imparts a change in velocity of the spacecraft along a desired direction;
periodically shutting down the at least one thruster and reorienting the spacecraft;
restarting the at least one thruster;
autonomously repeating the above steps until the desired orbit is reached wherein three axis momentum management of the spacecraft is performed by:
determining a respective momentum storage error (MSE) in each of three inertial spacecraft axes, said respective MSE comprising a difference, for each axis, between a momentum value actually stored on the spacecraft and a desired momentum value;
reducing each respective MSE by producing, with at least one thruster disposed on a single positioning mechanism, a plurality of torques, by:
orienting the thruster, with the single positioning mechanism, so as to produce a first torque that reduces the respective MSE of either or both of a first and a second of the three inertial spacecraft axes when the spacecraft is located at a first location on the trajectory, and,
orienting the thruster, with the single positioning mechanism, so as to produce a second torque that reduces the respective MSE of at least a third of the three inertial spacecraft axes when the spacecraft is located at a second location on the trajectory; wherein,
the single positioning mechanism is configured to orient the thruster so as to simultaneously (i) accelerate the spacecraft along a line of thrust and (ii) produce a torque around at least one of two axes substantially orthogonal to the nominal thrust vector; and
as the spacecraft travels along the trajectory, a desired line of thrust undergoes a substantial rotation in inertial space.
15. The method as recited in claim 14 , wherein the at least one thruster comprises a Hall effect thruster.
16. The method as recited in claim 14 , where the inertial references sensor comprises a gyro that is reset to remove any drift when the spacecraft is in an Earth pointed orientation, using a calculated position of the Earth relative to the spacecraft, spacecraft orbital information and Earth sensor data.
17. The method as recited in claim 14 , wherein the single positioning mechanism has two degrees of freedom.