SATELLITES AND SATELLITE FLEET IMPLEMENTATION METHODS AND APPARATUS

• US 20080237399A1
• Filed: 03/29/2007
• Published: 10/02/2008
• Est. Priority Date: 03/29/2007
• Status: Active Grant

• Current Assignee: The Boeing Co.
• Original Assignee: The Boeing Co.
• Inventors: Caplin, Glenn N., Rosen, Harold A., Fowler, Harmon C.
• Granted Patent: US 8,016,240 B2
• Time in Patent Office: Days
• US Class Current: 244/158.4
• CPC Class Codes: B64G 1/1085 Swarms and constellations
• CPC Class Codes: B64G 1/242 Orbits and trajectories
• CPC Class Codes: B64G 1/26 using jets
• CPC Class Codes: B64G 1/643 for arranging multiple satellites in a single launcher

Abstract

A method for implementing a satellite fleet includes launching a group of satellites within a launch vehicle. In an embodiment, the satellites are structurally connected together through satellite outer load paths. After separation from the launch vehicle, nodal separation between the satellites is established by allowing one or more of the satellites to drift at one or more orbits having apogee altitudes below an operational orbit apogee altitude. A satellite is maintained in an ecliptic normal attitude during its operational life, in an embodiment. The satellite'"'"'s orbit is efficiently maintained by a combination of axial, radial, and canted thrusters, in an embodiment. Satellite embodiments include a payload subsystem, a bus subsystem, an outer load path support structure, antenna assembly orientation mechanisms, an attitude control subsystem adapted to maintain the satellite in the ecliptic normal attitude, and an orbit maintenance/propulsion subsystem adapted to maintain the satellite'"'"'s orbit.

Claims

1. A method for implementing a satellite fleet, wherein the satellite fleet includes multiple satellites whose orbital planes have separated nodes, and the method comprises the steps of:

launching a first launch vehicle, which contains a first group of the multiple satellites within a first payload fairing of the first launch vehicle;

releasing the first group from the first payload fairing into an initial orbit;

performing a first series of one or more orbit changes to transition a first satellite of the first group from the initial orbit to an operational orbit having an operational orbit apogee altitude that is higher than an initial orbit apogee altitude; and

performing a second series of one or more orbit changes to transition a second satellite of the first group from the initial orbit to the operational orbit, wherein performing the second series includes establishing a first desired nodal separation between the first satellite and the second satellite by allowing the second satellite to drift for one or more first drift time periods at one or more orbits having apogee altitudes below the operational orbit apogee altitude.

2. The method of claim 1, further comprising:

when the first group includes at least one additional satellite, performing at least one additional series of one or more orbit changes to transition the at least one additional satellite from the initial orbit to the operational orbit, until all of the multiple satellites of the first group have been transitioned into the operational orbit.

3. The method of claim 1, further comprising:

prior to launching, stacking the satellites of the first group in the first payload fairing to form a satellite stack, wherein the satellites are stacked so that an outer load path support structure of a lower satellite of the satellite stack bears the load of any higher satellites of the satellite stack.

4. The method of claim 1, wherein:

performing the first series of one or more orbit changes includes firing a booster rocket of the satellite to perform each of the one or more orbit changes.

5. The method of claim 1, further comprising:

imparting an axial rotation to the first group at the initial orbit.

6. The method of claim 1, wherein the first desired nodal separation is in a range of about 10 degrees to about 180 degrees.

7. The method of claim 1, wherein performing the first series of orbit changes comprises:

performing at least some of the orbit changes when the first satellite is in a vicinity of perigee.

8. The method of claim 1, further comprising:

after performing the first series of one or more orbit changes, preparing for system operations by de-spinning a communications payload subsystem of the first satellite.

9. The method of claim 1, further comprising:

after performing the first series of one or more orbit changes, preparing for system operations by adjusting an attitude of the first satellite to place the first satellite in an ecliptic normal attitude.

10. The method of claim 9, wherein preparing for the system operations further comprises:

orienting an antenna assembly of the first satellite in a direction to support downlink signal transmission into a desired coverage area using at least two control axes, wherein a first control axis is a primary axis, and wherein a second control axis is an elevation adjustment axis that is substantially orthogonal to the primary axis.

11. The method of claim 10, wherein orienting the antenna assembly comprises:

orienting the antenna assembly with respect to the primary axis using a despin control mechanism adapted to provide a 360 degree range adjustment around the primary axis.

orienting the antenna assembly with respect to the elevation adjustment axis using an elevation adjustment mechanism adapted to provide about a 90 degree range adjustment around the elevation adjustment axis

12. The method of claim 1, further comprising:

after performing the first series of one or more orbit changes, actively performing satellite orbit maintenance to correct for orbital deviations using a plurality of axial thrusters, radial thrusters, and canted thrusters.

13. The method of claim 1, further comprising:

after performing the first series of one or more orbit changes, actively performing satellite orbit maintenance to maintain the first satellite in a Molniya orbit with an orbital period of about 12 hours, an angle of inclination of about 63.4 degrees, and a desired nodal separation of the first satellite, with respect to other satellites within the satellite fleet, of 360 degrees divided by a total number of satellites in the satellite fleet.

14. The method of claim 1, further comprising:

launching a second launch vehicle, which contains a second group of the multiple satellites within a second payload fairing of the second launch vehicle;

releasing the second group from the second payload fairing into the initial orbit;

sequentially transitioning each satellite of the second group of satellites to the operational orbit so that desired nodal separations are established between satellites of the first group and satellites of the second group.

15. A satellite comprising:

an outer load path support structure, which includes a substantially cylindrical structure having an interior cavity adapted to contain at least one satellite subsystem.

16. The satellite of claim 15, and wherein the outer load path support structure is further adapted to couple to a second outer load path support structure of a second satellite and to bear a load of the second satellite, when the second satellite is stacked above the satellite.

17. The satellite of claim 15, further comprising:

one or more solar cell assemblies attached to the outer load path support structure.

18. The satellite of claim 15, further comprising:

a payload subsystem; and

a bus subsystem coupled to the payload subsystem and to the outer load path support structure, wherein the bus subsystem includes at least one booster rocket and one or more fuel tanks.

19. The satellite of claim 18, wherein the outer load path support structure is rigidly coupled to the bus subsystem, and the satellite further comprises:

a despin control mechanism adapted to couple the bus subsystem to the payload subsystem, wherein the despin control mechanism is further adapted to allow the bus subsystem to spin around a primary axis of the satellite at a rate wherein the payload subsystem appears substantially stationary, with respect to earth.

20. The satellite of claim 15, further comprising:

a plurality of axial thrusters, radial thrusters, and canted thrusters adapted to perform satellite orbit maintenance to correct for orbital deviations.

21. A satellite comprising:

a payload subsystem;

a bus subsystem coupled to the payload subsystem;

an outer structure that substantially surrounds the payload subsystem and the bus subsystem;

one or more solar array panels attached to the outer structure; and

an attitude control subsystem adapted to maintain the satellite in an ecliptic normal attitude during an operational life of the satellite so that the one or more solar array panels are approximately perpendicular to the sun throughout a year, resulting in a thermal boundary that is approximately constant throughout the operational life of the satellite.

22. The satellite of claim 21, wherein the attitude control subsystem includes a plurality of axial thrusters, radial thrusters, and canted thrusters.

23. The satellite of claim 21, further comprising:

one or more mechanisms adapted to point an antenna beam produced by the satellite in a desired direction.

24. The satellite of claim 21, further comprising:

a despin control mechanism adapted to couple the bus subsystem to the payload subsystem, wherein the despin control mechanism is further adapted to allow the bus subsystem to spin around a primary axis of the satellite at a rate wherein the payload subsystem appears substantially stationary, with respect to earth.

25. The satellite of claim 21, wherein the outer structure comprises:

an outer load path support structure that includes a substantially cylindrical structure.

26. The satellite of claim 21, further comprising:

an orbit maintenance subsystem adapted to maintain the satellite in a Molniya orbit with an orbital period of about 12 hours, an angle of inclination of about 63.4 degrees, and a desired nodal separation of the satellite, with respect to other satellites within a satellite fleet, of 360 degrees divided by a total number of satellites in the satellite fleet.

27. A satellite having a primary axis and an outer cylinder, the satellite comprising:

a payload subsystem;

a bus subsystem coupled to the payload subsystem, wherein the bus subsystem includes at least one booster rocket and one or more fuel tanks;

at least one booster rocket adapted to impart impulses substantially parallel to the primary axis; and

an orbit maintenance subsystem adapted to correct for orbital deviations during an operational life of the satellite, wherein the orbit maintenance subsystem includes a plurality of axial thrusters, radial thrusters, and canted thrusters.

28. The satellite of claim 27, wherein the axial thrusters are positioned at a bottom of the satellite between the primary axis and the outer cylinder, wherein the axial thrusters are oriented to impart impulses substantially parallel to the primary axis, and wherein the axial thrusters are adapted to provide a velocity increment in a direction of the primary axis and to re-orient the primary axis.

29. The satellite of claim 27, wherein the radial thrusters are positioned around the outer cylinder, wherein the radial thrusters are oriented to impart impulses that are substantially perpendicular to the primary axis, and wherein the radial thrusters are adapted to increase and decrease a rate of spin around the primary axis and to provide a velocity increment in a direction perpendicular to the primary axis.

30. The satellite of claim 27, wherein the canted thrusters are positioned around an outer surface of the satellite, wherein the canted thrusters are oriented to impart impulses that substantially intersect a center of gravity of the satellite, and wherein the canted thrusters are adapted to provide a velocity increment in the direction of the canted thruster.

31. The satellite of claim 30, wherein a first set of the canted thrusters are positioned above a plane that bisects the center of gravity and is perpendicular to the primary axis, and wherein a second set of the canted thrusters are positioned below the plane.

32. The satellite of claim 31, wherein a cant angle between impulse vectors of the first set and the plane is in a range of about 30 degrees to about 60 degrees.

33. The satellite of claim 31, wherein a cant angle between impulse vectors of the second set and the plane is in a range of about 30 degrees to about 60 degrees.

36. The satellite of claim 27, wherein the attitude control subsystem is further adapted to maintain the satellite in an ecliptic normal attitude.

37. The satellite of claim 27, wherein the orbit maintenance subsystem is further adapted to maintain the satellite in a Molniya orbit with an orbital period of about 12 hours, an angle of inclination of about 63.4 degrees, and a desired nodal separation of the satellite, with respect to other satellites within a satellite fleet, of 360 degrees divided by a total number of satellites in the satellite fleet.

38. A satellite comprising:

a payload subsystem, which includes a downlink antenna adapted to produce an antenna pattern that is a figure of revolution;

a bus subsystem coupled to the payload subsystem, wherein the bus subsystem includes at least one booster rocket and one or more fuel tanks;

an outer load path support structure coupled to the bus subsystem, wherein the outer load path support structure substantially surrounds the payload subsystem and the bus subsystem, wherein the outer load path support structure includes a substantially cylindrical structure, and wherein the outer load path support structure is adapted to couple to a second outer load path of a second satellite and to bear a load of a second satellite stacked above the satellite;

at least one booster rocket adapted to impart impulses substantially parallel to the primary axis; and

an attitude control subsystem adapted to maintain the satellite in an ecliptic normal attitude during an operational life of the satellite; and

an orbit maintenance subsystem to correct for orbital deviations during an operational life of the satellite, wherein the attitude control subsystem and the orbit maintenance subsystem includes a plurality of axial thrusters, radial thrusters, and canted thrusters.