Despin and rotational control architectures for lighter-than-air high altitude platforms

1. A method of operating a lighter-than-air high altitude platform (HAP) in the stratosphere, the method comprising:

calculating, by one or more processors of the HAP, an offset to achieve a selected lateral propulsion target heading for a lateral propulsion assembly of the HAP;

determining, by the one or more processors, whether to adjust the selected lateral propulsion target heading to an adjusted lateral propulsion target heading based on an accuracy threshold of the offset;

spinning down a propeller of the lateral propulsion assembly when a rotation amount in accordance with the offset exceeds a gyroscopic force threshold of the HAP; and

controlling rotation, by the one or more processors, of a stepper motor of the lateral propulsion assembly according to either the selected lateral propulsion target heading or the adjusted lateral propulsion target heading.

2. The method of claim 1 , wherein calculating the offset is based on a target heading for a despin mechanism of the HAP.

3. The method of claim 2 , wherein calculating the offset is further based on a location of the lateral propulsion assembly relative to the despin mechanism and a payload of the HAP.

4. The method of claim 1 , further comprising adjusting the offset upon a determination that the lateral propulsion assembly would rotate through a hard stop structure.

5. The method of claim 1 , further comprising, upon determining that the selected lateral propulsion target heading is achieved according to controlling the rotation, resuming actuation of the propeller at a selected rate of rotation.

6. The method of claim 1 , wherein calculating the offset is based on a difference between a rotor position measured by an encoder and a position set by a stepper driver of the lateral propulsion assembly.

7. The method of claim 6 , further comprising performing a calibration routine of the stepper motor against the encoder.

8. The method of claim 7 , wherein performing the calibration routine includes

driving the stepper motor to a set of locations;

at each location, injecting random noise into the stepper motor;

and averaging a position read by the encoder

at each location.

9. The method of claim 1 , wherein controlling the rotation of the stepper motor is performed in accordance with a motor current limit.

10. The method of claim 1 , further comprising performing a despin operation using a despin mechanism disposed between an envelope and a payload of the HAP.

11. The method of claim 10 , wherein the despin operation is performed according to a voltage control mode, and controlling the rotation of the stepper motor is performed according to a current control mode.

12. The method of claim 11 , further comprising:

setting, in the voltage control mode, a voltage setpoint as a function of a mechanical load associated with the despin mechanism; and

setting, in the current control mode, a current setpoint as a function of a mechanical load associated with the stepper motor.

13. The method of claim 1 , wherein controlling rotation of the stepper motor is further performed based on a target heading of a directional communications module of the HAP.

14. A lighter-than-air high altitude platform (HAP) configured for operation in the stratosphere, the HAP comprising:

an envelope configured to hold lift gas;

a connecting member operatively coupled at a first end thereof to the envelope, the connecting member having a connecting axis along a length thereof;

a payload coupled to a second end of the connecting member;

a lateral propulsion system rotatably engaged with the connecting member, the lateral propulsion system including:

a propeller assembly having a propeller, and

a control assembly operatively coupled to the propeller assembly and configured to rotate the propeller in a clockwise or counterclockwise direction about a propeller axis, the control assembly also being configured to rotate the lateral propulsion assembly along the connecting axis of the connecting member; and

one or more processors configured to control operation of the lateral propulsion system, the one or more processors being configured to:

calculate an offset to achieve a selected lateral propulsion target heading for the lateral propulsion system;

determine whether to adjust the selected lateral propulsion target heading to an adjusted lateral propulsion target heading based on an accuracy threshold of the offset;

control rotation of a stepper motor of the control assembly according to either the selected lateral propulsion target heading or the adjusted lateral propulsion target heading; and, perform a despin operation using a despin mechanism, wherein the despin operation is performed in a voltage control mode according to a voltage setpoint set as a function of a mechanical load associated with the despin mechanism; and wherein the control of the rotation of the stepper motor is performed in a current control mode according to a current setpoint set as a function of a mechanical load associated with the stepper motor.

15. The HAP of claim 14 , wherein calculation of the offset is based on a difference between a rotor position measured by an encoder of the lateral propulsion system and a position set by a stepper driver of the lateral propulsion system.

16. The HAP of claim 14 , wherein rotation control of the stepper motor is further performed based on a target heading of a directional communications module of the payload.

17. The HAP of claim 14 , wherein the despin mechanism is configured to adjust for a relative rotation of the envelope with respect to the payload.

18. The HAP of claim 17 , wherein calculation of the offset is based on a target heading for the despin mechanism.