Combined stationkeeping and momentum management

A method of simultaneous north-south stationkeeping and 3-axis momentum management for a geosynchronous orbiting spacecraft having a first thruster, a second thruster, and at least three momentum wheels mounted on-board the spacecraft, the method comprising steps of:

• in a first-pass of a thruster firing cycle, firing the first thruster at a first point along an orbital path of the spacecraft;
• firing the second thruster at a second point along the orbital path of the spacecraft, wherein a thrust vector at the second point is non-planar with a thrust vector at the first point;
• in a second-pass of the thruster firing cycle, firing the first thruster at a third point along the orbital path of the spacecraft, wherein a thrust vector at the third point is parallel with and on an opposite side of the orbital path from the thrust vector at the second point;
• and
• firing the second thruster at a fourth point along the orbital path of the spacecraft, wherein a thrust vector at the fourth point is parallel with and on an opposite side of the orbital path from the thrust vector at the first point;
• wherein when the first and the second thrusters are fired at the first, the second, the third and the forth points on the orbital path radial components of a change in velocity produced by firing the first and the second thrusters are cancelled and angular momentum stored in the at least three momentum wheels is desaturated.

A method of simultaneous north-south stationkeeping and 3-axis momentum management for a geosynchronous orbiting spacecraft having a first thruster, a second thruster, and at least three momentum wheel mounted on-board the spacecraft, the method comprising steps of:

• defining a point A along an orbital path of the spacecraft wherein the orbital path crosses a line of nodes coplanar with a z-axis of the spacecraft;
• defining a point B along the orbital path of the spacecraft wherein the orbital path crosses the line of nodes and wherein the point B is oriented 180° from the point A;
• in a first-pass of a thruster firing cycle, firing the first thruster at a point A′ along the orbital path of the spacecraft, wherein the point A′ is a first predetermined angle from the point A;
• firing the second thruster at a point B′ along the orbital path of the spacecraft, wherein the point B′ is a second predetermined angle from the point B and a second predetermined time of motion from the point A′, and wherein the point B′ is non-collinear with the point A′ and a point O at the earth's center;
• in a second-pass of the thruster firing cycle, firing the first thruster at a point A″ along the orbital path of the spacecraft, wherein the point A″ is a third predetermined angle from the point A and a third predetermined time of motion from the point B′, and wherein the point A″ is collinear with and on an opposite side of the orbital path from the point B′ and the point O;
• and
• firing the second thruster at a point B″ along the orbital path of the spacecraft, wherein the point B″ is a fourth predetermined angle from the point B and a fourth predetermined time of motion from the point A″, and wherein the point B″ is collinear with and on an opposite side of the orbital path from the point A′ and the point O;
• wherein when the first and the second thrusters are fired at points A′, B′, A″ and B″ on the orbital path, radial components of a change in velocity produced by firing the first and the second thrusters are cancelled and angular momentum stored in the at least three momentum wheels is desaturated.

A system for simultaneous north-south stationkeeping and 3-axis momentum management for a geosynchronous orbiting spacecraft, said spacecraft having a center of mass, a north face, a south face and an anti-earth side facing opposite earth during said geosynchronous orbit, said system comprising:

• a first thruster mounted on said anti-earth side of said spacecraft and adjacent to said north face of said spacecraft, wherein said first thruster is aligned to produce a first thrust vector slightly off from said center of mass;
• a second thruster mounted on said anti-earth side of said spacecraft and adjacent to said south face of said spacecraft, wherein said second thruster is aligned to produce a second thrust vector slightly off from said center of mass;
• and
• at least three momentum wheels mounted on-board said spacecraft for maintaining an orbital attitude of said spacecraft with respect to a corresponding one of three orthogonal spacecraft axes, wherein said at least three momentum wheels are non-planar such that angular momentum of said corresponding one of said three spacecraft axes is independently stored in at least one of said at least three momentum wheels;
• wherein said angular momentum stored in said each of said at least three momentum wheels is desaturated by firing at a given time a single one of said first or said second thruster to desaturate said stored angular momentum, the first thruster and the second thruster being alternatively fired at least at a pair of noncollinear points with the earth's center along an orbital path of the spacecraft.

A method of simultaneous north-south stationkeeping and 3-axis momentum management for an orbiting spacecraft having a first thruster, a second thruster, and at least three momentum wheels mounted onboard the spacecraft for storing angular momentum in a corresponding one of three orthogonal spacecraft axes, the method comprising steps of:

• alternatively firing the first thruster and the second thruster at a first pair of non-collinear points with the earth's center along an orbital path of the spacecraft;
• and
• alternatively firing the first thruster and the second thruster at points along the orbital path of the spacecraft that are collinear with and on an opposite side of the orbital path from the first pair of non-collinear points and the earth's center;
• wherein there is simultaneously provided a desired change in velocity of the spacecraft in the north-south direction and a desaturation of the angular momentum stored in the momentum wheels.