Torque control for balloon coupling

1. A system comprising:

a flexible coupling configured to reduce effects of a balloon envelope tilting on a payload;

a sensor configured to measure rotational displacement of the flexible coupling;

a despin mechanism including a motor configured to rotate the payload; and

a controller configured to:

receive the measured rotational displacement; and

use the despin mechanism to rotate the payload towards a preferred orientation based on the measured rotational displacement.

2. The system of claim 1 , wherein the payload includes a solar panel, and the preferred orientation corresponds to the solar panel being oriented towards the sun.

3. The system of claim 1 , wherein the payload includes a communications system, and the preferred orientation corresponds to the communications system being oriented in a particular direction to send and receive information with a network target.

4. The system of claim 1 , wherein the flexible coupling includes a first end and a second end, and wherein the sensor is configured to measure rotational displacement between the first end and the second end.

5. The system of claim 1 , wherein the controller is further configured to control the despin mechanism based on the amount of torque in order to attempt to maintain zero torque at the flexible coupling.

6. The system of claim 1 , wherein the sensor is a magnetic encoder.

7. The system of claim 1 , wherein the sensor is an optical encoder.

8. The system of claim 1 , wherein the sensor is a potentiometer.

9. The system of claim 1 , wherein the sensor is a strain gauge.

10. The system of claim 1 , further comprising a thermometer configured to measure temperature of the flexible coupling, and wherein the controller is further configured to use the despin mechanism further based on the temperature measurement.

11. The system of claim 1 , further comprising a thermometer configured to measure ambient temperature near the flexible coupling, and wherein the controller is further configured to use the despin mechanism further based on the ambient temperature.

12. The system of claim 1 , further comprising the payload.

13. A method of orienting a payload of a balloon, the method comprising:

identifying, by a controller, a preferred orientation of the payload;

receiving, by the controller, displacement information from a sensor configured to measure rotational displacement of a flexible coupling;

determining, by the controller, a control action based on the received displacement information; and

sending, by the controller, a signal to a despin mechanism to cause the despin mechanism to rotate the payload according to the control action and towards the identified preferred orientation of the payload.

14. The method of claim 13 , further comprising the balloon envelope.

15. The method of claim 14 , further comprising receive, by the controller, orientation information from an orientation sensor identifying a current orientation of the payload, and wherein the control action is determined further based on the received orientation information.

16. The method of claim 14 , wherein determining the control action includes determining an amount of torque based on the measured rotational displacement.

17. The method of claim 16 , wherein the amount of torque is determined based on stiffness of the flexible coupling.

18. The method of claim 17 , further comprising:

receiving temperature information from a thermometer; and

using the temperature information to determine the stiffness of the flexible coupling, and wherein the amount of torque is determined further based on the determined stiffness.

19. The method of claim 18 , wherein the temperature is a temperature of the flexible coupling.

20. The method of claim 14 , further comprising, controlling the despin mechanism in order to attempt to maintain zero torque at the flexible coupling.