Attitude determination and control system (ADCS)
An attitude determination and control system (ADCS) may include relatively large momentum wheels (i.e., reaction wheels) for improved momentum storage and magnetic torque rods that enable low power sun pointing and dissipate angular momentum imparted during deployment or by differential drag on the space vehicle. The momentum wheels, magnetic torque rods, or both may be algorithmically selected and driven to perform various maneuvers.
1. An attitude determination and control system (ADCS) for a space vehicle, comprising:
a plurality of momentum wheels;
a plurality of magnetic torque rods arranged in a perpendicular orientation with respect to one another, the plurality of magnetic torque rods each configured to generate torque when a current is applied thereto; and
a processing card comprising a processor, the processing card configured to algorithmically select and control at least one of the plurality of momentum wheels, the plurality of magnetic torque rods, or both, to execute a desired maneuver, wherein
the processor of the ADCS is different from a processor of another processing card of the space vehicle that performs command and data handling (C&DH) for the space vehicle, and
the processing card comprises at least one recess through which at least one respective momentum wheel of the plurality of momentum wheels extends, thereby improving compactness of the ADCS.
2. The ADCS of claim 1 , wherein the processing card is configured to control the plurality of magnetic torque rods to perform de-tumbling, static sun pointing, nadir pointing operations, or any combination thereof.
3. The ADCS of claim 1 , wherein
the processing card comprises a processor and a field programmable gate array (FPGA),
the processing card is controlled by the processor paired with the FPGA, and
the FPGA is configured to provide a memory-mapped interface to other devices of a space vehicle.
4. The ADCS of claim 3 , wherein the FPGA comprises watchdog timers that reboot the processor when a system fault occurs.
5. The ADCS of claim 1 , wherein the plurality of momentum wheels are arranged in a pyramid configuration with an elevation angle of 20° or more.
6. The ADCS of claim 1 , further comprising:
a momentum wheel carriage that houses the plurality of momentum wheels; and
a gyroscope mounted on the momentum wheel carriage, wherein
the processing card is configured to control the gyroscope to propagate an attitude solution when another mechanism for doing so is not available.
7. The ADCS of claim 6 , further comprising:
a frame to which the processing card and momentum wheel carriage are attached.
8. The ADCS of claim 1 , further comprising:
an independent motor for each of the plurality of momentum wheels, each independent motor configured to drive a respective momentum wheel, wherein
the processing card comprises a processor and a field programmable gate array (FPGA), and
the FPGA of the processing card is configured to control each independent motor by running a proportional-derivative (PD) control loop.
9. The ADCS of claim 8 , wherein after determining an attitude error angle between a command attitude and a current attitude solution, the FPGA is configured to apply the PD control loop to the attitude error angle to generate a desired torque setting and drive at least one momentum wheel of the plurality of momentum wheels to a desired speed, apply an appropriate current to at least one of the plurality of magnetic torque rods to generate a requested torque, or both.
10. The ADCS of claim 1 , wherein
the ADCS is part of a space vehicle that comprises a top section comprising a high gain helical antenna, a middle section comprising the ADCS, and a bottom section comprising a power subsystem, and
the ADCS is configured to orient the space vehicle based on pointing requirements of the high gain helical antenna with an accuracy of 15° or better.
11. The ADCS of claim 1 , wherein the processing card is configured to control the plurality of torque rods in accordance with
τ= Dω+sKq e
where τ is command torque, ω is an angular velocity of a space vehicle, q e is a quaternion error vector between a command and a determined attitude, s is a sign of the scalar quaternion error term, and D and K are proportional and derivative gains of a control system, respectively.
12. The ADCS of claim 11 , wherein after deriving the command torque, the processing card is configured to:
calculate a dipole moment using
m
req
=
B
×
τ
❘
"\[LeftBracketingBar]"
B
❘
"\[RightBracketingBar]"
2
where m req is a dipole moment, B is the modeled Earth's magnetic field, and τ is the command torque; and
deliver a corresponding current command from the dipole moment to be delivered to one or more of the plurality of torque rods.
13. The ADCS of claim 12 , wherein the processing card is further configured to use a proportional-derivative (PD) control loop to apply current to one or more of the plurality of torque rods.
14. A space vehicle, comprising:
a top section comprising a high gain helical antenna;
a middle section comprising an attitude determination and control system (ADCS); and
a bottom section comprising a power subsystem, wherein
the ADCS comprises:
a plurality of momentum wheels,
a plurality of torque rods, and
a processing card comprising a processor, the processing card configured to control the plurality of momentum wheels and the plurality of torque rods, wherein
the processor of the ADCS is different from a processor of another processing card of the space vehicle that performs command and data handling (C&DH) for the space vehicle,
the processing card comprises at least one recess through which at least one respective momentum wheel of the plurality of momentum wheels extends, thereby improving compactness of the ADCS, and
the ADCS is configured to orient the space vehicle based on pointing requirements of the high gain helical antenna with an accuracy of 15° or better.
15. The space vehicle of claim 14 , wherein
the processing card is configured control the plurality of magnetic torque rods to perform de-tumbling, static sun pointing, nadir pointing operations, or any combination thereof.
16. The space vehicle of claim 15 , wherein the processing card is configured to control the plurality of torque rods in accordance with
τ= Dω+skq e
where τ is command torque, ω is an angular velocity of a space vehicle, q e is a quaternion error vector between a command and a determined attitude, s is a sign of the scalar quaternion error term, and D and K are proportional and derivative gains of a control system, respectively,
after deriving the command torque, the processing card is configured to:
calculate a dipole moment using
m
req
=
B
×
τ
❘
"\[LeftBracketingBar]"
B
❘
"\[RightBracketingBar]"
2
where m req is a dipole moment, B is the modeled Earth's magnetic field, and τ is the command torque, and
deliver a corresponding current command from the dipole moment to be delivered to one or more of the plurality of torque rods, and
the processing card is further configured to use a proportional-derivative (PD) control loop to apply current to one or more of the plurality of torque rods.
17. The space vehicle of claim 14 , wherein
the processing card comprises a processor and a field programmable gate array (FPGA),
the processing card is controlled by the processor paired with the FPGA, and
the FPGA is configured to provide a memory-mapped interface to other devices of the space vehicle.
18. The space vehicle of claim 14 , wherein
the ADCS further comprises an independent motor for each of the plurality of momentum wheels, each independent motor configured to drive a respective momentum wheel, wherein
the processing card comprises a processor and a field programmable gate array (FPGA),
the FPGA of the processing card is configured to control each independent motor by running a proportional-derivative (PD) control loop, and
after determining an attitude error angle between a command attitude and a current attitude solution, the FPGA is configured to apply the PD control loop to the attitude error angle to generate a desired torque setting and drive at least one momentum wheel of the plurality of momentum wheels to a desired speed, apply an appropriate current to at least one of the plurality of magnetic torque rods to generate a requested torque, or both.
19. An attitude determination and control system (ADCS) for a space vehicle, comprising:
a plurality of momentum wheels;
a plurality of magnetic torque rods arranged perpendicular to one another along an x-axis, a y-axis, and a z-axis, the plurality of magnetic torque rods each configured to generate torque when a current is applied thereto; and
a processing card comprising a processor, the processing card configured to algorithmically select and control at least one of the plurality of magnetic torque rods to execute a desired maneuver, wherein
the processing card is configured to control the plurality of torque rods in accordance with
τ= Dω+sKq e
where τ is command torque, ω is an angular velocity of a space vehicle, q e is a quaternion error vector between a command and a determined attitude, s is a sign of the scalar quaternion error term, and D and K are proportional and derivative gains of a control system, respectively,
after deriving the command torque, the processing card is configured to:
calculate a dipole moment m req using
m
req
=
B
×
τ
❘
"\[LeftBracketingBar]"
B
❘
"\[RightBracketingBar]"
2
where B is the modeled Earth's magnetic field,
use a proportional-derivative (PD) control loop to apply current to one or more of the plurality of torque rods, and
deliver a corresponding current command from the dipole moment to be delivered to one or more of the plurality of torque rods,
the processor of the ADCS is different from a processor of another processing card of the space vehicle that performs command and data handling (C&DH) for the space vehicle, and
the processing card comprises at least one recess through which at least one respective momentum wheel of the plurality of momentum wheels extends, thereby improving compactness of the ADCS.