초록 ▼

A method for controlling a vehicle may include sensing a position of each of a plurality of stars relative to the vehicle. The method may also include determining an attitude of the vehicle using the sensed positions of the plurality of stars, and the attitude may be determined either with or withou

A method for controlling a vehicle may include sensing a position of each of a plurality of stars relative to the vehicle. The method may also include determining an attitude of the vehicle using the sensed positions of the plurality of stars, and the attitude may be determined either with or without using information from a gyro or sensor for measuring angular velocity. The method may additionally include implementing a set of strategies to optimize determination of the attitude of the vehicle when using only the sensed positions of the plurality of stars, without information from the sensor for measuring angular velocity. The method may further include controlling the vehicle based on the determined attitude of the vehicle.

대표청구항 ▼

1. A method for controlling a vehicle, comprising: sensing a position of each of a plurality of stars relative to the vehicle;determining an attitude of the vehicle using the sensed positions of the plurality of stars, and either with or without using information from a sensor measuring angular velo

1. A method for controlling a vehicle, comprising: sensing a position of each of a plurality of stars relative to the vehicle;determining an attitude of the vehicle using the sensed positions of the plurality of stars, and either with or without using information from a sensor measuring angular velocity;implementing a set of strategies to optimize determination of the attitude of the vehicle when using only the sensed positions of the plurality of stars, without information from the sensor for measuring angular velocity, wherein implementing the set of strategies comprises determining if a lost-in-space (LIS) solution is invalid by applying at least one of a plurality of tests to the LIS solution, the plurality of tests comprising: a trajectory test comprising determining if the LIS solution is inconsistent with a vehicle trajectory, as estimated by two previous LIS solutions, from which an estimated attitude is determined; anda convergence test comprising determining if the LIS solution is inconsistent with a spacecraft attitude and angular velocity estimates, as determined by processing of attitude estimates from multiple previous LIS solutions, or attitude estimates based on other sources; andcontrolling the vehicle based on the determined attitude of the vehicle. 2. The method of claim 1, further comprising determining an angular velocity of the vehicle using only star position information from at least one star sensor captured and stored at different times. 3. The method of claim 1, further comprising determining whether a valid lost-in-space (LIS) solution was found since a previous determination of the attitude of the vehicle, wherein determining the LIS solution comprises finding a star pattern match between star position information captured by at least one star sensor and star position information stored in a star catalogue stored in association with an onboard vehicle processor, the LIS solution being valid when the star pattern match is correct, and leads to an accurate vehicle attitude estimate. 4. The method of claim 3, further comprising: periodically incrementing a no-solution counter in response to a predetermined condition or event; andresetting the no-solution counter to zero in response to the LIS solution being found. 5. The method of claim 4, wherein using implementing the set of strategies to optimize determination of the attitude of the vehicle further comprises: declaring a fault in response to the no-solution counter reaching a preset threshold; andresponding to the fault, wherein responding to the fault comprises at least one of: switching from a single star sensor mode of operation to a multiple star sensor mode of operation; andswitching control of the attitude and angular velocity of the vehicle from one mode of control to another mode of control of a plurality of modes of control. 6. The method of claim 5, wherein the plurality of modes of control comprise: controlling the vehicle by a plurality of thrusters,controlling the vehicle by a plurality of wheels each corresponding to a different axes of rotation of the vehicle,controlling the vehicle by a combination of thrusters and wheels, andallowing the vehicle to drift. 7. The method of claim 5, wherein the multiple star mode sensor mode of operation comprises switching to another star sensor of a plurality of star sensors in response to consistently failing to obtain a LIS solution after a specified time period or a predetermined number of runs of the stellar acquisition module. 8. The method of claim 7, wherein a toggle counter is associated with each star sensor, and wherein the method further comprises: incrementing the toggle counter associated with each star sensor currently being used for the LIS solution each time the LIS solution associated with the star sensor is not obtained; andswitching to another star sensor for capturing star positions for the LIS solution in response to the toggle counter associated with the at least one star sensor currently being used for the LIS solution reaching a preset threshold. 9. The method of claim 3, further comprising determining if the LIS solution is invalid in response to determining the LIS solution. 10. The method of claim 9, wherein determining if the LIS solution is invalid comprises determining if an event occurred causing the LIS solution to be unreliable. 11. The method of claim 1, wherein determining if the LIS solution is inconsistent comprises determining a discrepancy between two attitudes, and evaluating whether the discrepancy exceeds a predetermined threshold value. 12. The method of claim 1, wherein applying the trajectory test is based on whether there have been at least two previous LIS solutions within a specified or predetermined time period. 13. The method of claim 1, wherein applying the convergence test is based on whether there have been a specified number of LIS solutions within a specified or predetermined time period. 14. The method of claim 1, further comprising determining if ready to request star position information from a star sensor currently selected from a plurality of star sensors mounted to the vehicle, for use in determining an attitude of the vehicle, wherein determining if ready to request the star position information comprises at least one of: determining if the star position information is available from the star sensor currently selected;determining if a new attitude has just been determined and system adjustments need to be completed before determining another attitude; anddetermining that the star position information is only being captured at certain fixed time periods and determining whether a current fixed time period has elapsed. 15. The method of claim 1, further comprising: determining if a sufficient number of stars have been tracked for determining an attitude of the vehicle; anddetermining if a sufficient number of pairs of the tracked stars meet a predetermined criteria. 16. The method of claim 1, further comprising: determining whether a currently selected star sensor for capturing star position information for determining an attitude of the vehicle needs to be steered to track a different star; andgenerating and sending a command to the currently selected star sensor to cancel tracking of a dimmest star and to establish tracking on a brighter star in response to determining that the currently selected star sensor needs to be steered, wherein the star sensor is capable of tracking multiple stars simultaneously. 17. The method of claim 1, further comprising determining the attitude of the vehicle at predetermined time intervals. 18. The method of claim 17, further comprising overwriting an existing attitude maintained by a component of the vehicle with a predetermined number of initial determinations of the attitude of the vehicle. 19. The method of claim 18, further comprising metering the determinations of the attitude of the vehicle into the existing attitude maintained by the component after overwriting the existing attitude with the predetermined number of initial determinations of the attitude of the vehicle to avoid any sudden transients that could destabilize control of the vehicle. 20. The method of claim 17, further comprising overwriting an existing angular velocity maintained by a component of the vehicle with a predetermined number of initial determinations of the angular velocity of the vehicle. 21. The method of claim 20, further comprising metering the determinations of the angular velocity of the vehicle into the existing angular velocity maintained by the component after overwriting the existing angular velocity with the predetermined number of initial determinations of the angular velocity of the vehicle to avoid any sudden transients that could destabilize the attitude or angular velocity estimates, or control of the vehicle. 22. A system for controlling a vehicle, comprising: a processor;a module operating on the processor to determine an attitude of the vehicle using a sensed position of each of a plurality of stars relative to the vehicle, and either with or without using information from a sensor measuring angular velocity, wherein a set of strategies are used to optimize determination of the attitude of the vehicle when using only the sensed positions of the plurality of stars, without information from the sensor measuring angular velocity, wherein the set of strategies comprises determining if a lost-in-space (LIS) solution is invalid by applying at least one of a plurality of tests to the LIS solution, the plurality of tests comprising: a trajectory test comprising determining if the LIS solution is inconsistent with a vehicle trajectory, as estimated by two previous LIS solutions, from which an estimated attitude is determined; anda convergence test comprising determining if the LIS solution is inconsistent with a spacecraft attitude and angular velocity estimates, as determined by processing of attitude estimates from multiple previous LIS solutions, or attitude estimates based on other sources; andan attitude control module, operating on the processor, to control the vehicle based on the determined attitude of the vehicle. 23. The system of claim 22, further comprising a module to determine an angular velocity of the vehicle using only star position information captured and stored at different times by a star sensor. 24. The system of claim 22, further comprising a star catalogue including a plurality of star identities and associated star position information, wherein a lost-in-space (LIS) module matches star position information sensed by at least one star sensor to the star position information in the star catalogue to provide a LIS solution. 25. The system of claim 24, further comprising a no-solution counter, wherein the no-solution counter is periodically incremented and wherein the no-solution counter in reset in response to obtaining the LIS solution. 26. The system of claim 24, further comprising a switch means to switch to another star sensor of a plurality of star sensors for capturing star position information in response to the no-solution counter reaching a preset threshold. 27. The system of claim 26, further comprising a toggle counter associated with each star sensor, wherein the toggle counter associated with the star sensor currently being used for the LIS solution is incremented each time the LIS solution is not found and switching to another star sensor for capturing star positions for the LIS solution in response to the toggle counter associated with the star sensor currently being used for the LIS solution reaching a preset threshold. 28. The system of claim 25, wherein the set of strategies to optimize determination of the attitude of the vehicle comprises: declaring a fault in response to the no-solution counter reaching a preset threshold; andresponding to the fault, wherein responding to the fault comprises at least one of: switching from a single star sensor mode of operation to a dual star sensor mode of operation; andswitching control of the attitude and angular velocity of the vehicle from one mode of control to another mode of control of a plurality of modes of control. 29. A vehicle, comprising: a processor for controlling operation of the vehicle;a plurality of star sensors each for capturing star position information relative to the vehicle;a module operating on the processor to determine an attitude of the vehicle using the star position information, either with or without using information from a sensor measuring angular velocity, wherein a set of strategies are used to optimize determination of the attitude of the vehicle when using only the sensed position of each of the plurality of stars, without information from the sensor measuring angular velocity, wherein the set of strategies comprises determining if a lost-in-space (LIS) solution is invalid by applying at least one of a plurality of tests to the LIS solution, the plurality of tests comprising: a trajectory test comprising determining if the LIS solution is inconsistent with a vehicle trajectory, as estimated by two previous LIS solutions, from which an estimated attitude is determined; anda convergence test comprising determining if the LIS solution is inconsistent with a spacecraft attitude and angular velocity estimates, as determined by processing of attitude estimates from multiple previous LIS solutions, or attitude estimates based on other sources; anda module to control the vehicle based on the determined attitude of the vehicle. 30. The vehicle of claim 29, further comprising: a stellar attitude acquisition module running on the processor;a LIS module for determining the LIS solution, wherein the stellar attitude acquisition module determines whether a valid LIS solution was found since a previous running of the stellar attitude acquisition module and modifies an estimate of an attitude of the vehicle using the LIS solution in response to the LIS solution being determined to be valid, and wherein the LIS solution is determined using only star position information relative to the vehicle from at least one star sensor of the plurality of star sensors mounted on the vehicle. 31. The vehicle of claim 30, further comprising a star catalogue including a plurality of star identities and associated position information for each of the stars, wherein the LIS module matches the star position information captured by the at least one star sensor to star position information in the star catalogue to provide the LIS solution. 32. The vehicle of claim 29, further comprising a no-solution counter, wherein the no-solution counter is periodically incremented in response a predetermined condition or event and wherein the no-solution counter in reset in response to the LIS solution being found. 33. The vehicle of claim 32, further comprising: a plurality of thrusters mounted to the vehicle to control the attitude and angular velocity of the vehicle;a plurality of wheels mounted to the vehicle, each wheel corresponding to a different axis of rotation of the vehicle for rotating the vehicle about the respective axes, wherein a fault occurs in response to the no-solution counter reaching a preset threshold, and wherein the fault is responded to by at least one of: switching from a single star sensor mode of operation to a dual star sensor mode of operation; andswitching control of the attitude and angular velocity of the vehicle from one mode of control to another mode of control of a plurality of modes of control, wherein the plurality of modes of control comprise: controlling the vehicle by a plurality of thrusters, controlling the vehicle by a plurality of wheels each corresponding to a different axes of rotation of the vehicle, controlling the vehicle by a combination of thrusters and wheels, and allowing the vehicle to drift. 34. A computer program product comprising a hardware computer readable storage medium having computer usable program code embodied therewith for controlling a vehicle, the hardware computer readable storage medium comprising: computer usable program code configured to determine an attitude of the vehicle using a sensed position of each of the plurality of stars, and either with or without using information from a sensor measuring angular velocity;computer usable program code configured to use a set of strategies to optimize determination of the attitude of the vehicle when using only the sensed position of each of the plurality of stars, without information from the sensor for measuring angular velocity, wherein computer usable program code configured to use the set of strategies comprises computer usable program code configured to determine if a lost-in-space (LIS) solution is invalid by applying at least one of a plurality of tests to the LIS solution, the plurality of tests comprising: a trajectory test comprising determining if the LIS solution is inconsistent with a vehicle trajectory, as estimated by two previous LIS solutions, from which an estimated attitude is determined; anda convergence test comprising determining if the LIS solution is inconsistent with a spacecraft attitude and angular velocity estimates, as determined by processing of attitude estimates from multiple previous LIS solutions, or attitude estimates based on other sources; andcomputer usable program code configured to control the vehicle based on the determined attitude of the vehicle. 35. The computer readable storage medium of claim 34, further comprising computer usable program code configured to determine an angular velocity estimate of the vehicle using only star position information from the at least one star sensor captured and stored at different times. 36. The computer readable storage medium of claim 34, further comprising computer usable program code configured to determine whether the LIS solution was found, wherein the LIS solution comprises finding a star pattern match between the star position information captured by the at least one star sensor and star position information stored in a star catalogue. 37. The computer readable storage medium of claim 36, further comprising computer usable program code configured to periodically increment a no-solution counter in response to a predetermined condition or event and to reset the no-solution counter to zero in response to the LIS solution being found. 38. The computer readable storage medium of claim 37, further comprising: computer usable program code configured to declare a fault in response to the no-solution counter reaching a preset threshold; andcomputer usable program code configured to respond to the fault, wherein responding to the fault comprises at least one of: switching from a single star sensor mode of operation to a dual star sensor mode of operation; andswitching control of the attitude and angular velocity of the vehicle from one mode of control to another mode of control of a plurality of modes of control.