Tech Briefs

Guidance and Control System for a Satellite Constellation

A distributed guidance and control algorithm was developed for a constellation of satellites. The system repositions satellites as required, regulates satellites to desired orbits, and prevents collisions.

  1. Optimal methods are used to compute nominal transfers from orbit to orbit.
  2. Satellites are regulated to maintain the desired orbits once the transfers are complete.
  3. A simulator is used to predict potential collisions or near-misses.
  4. Each satellite computes perturbations to its controls so as to increase any unacceptable distances of nearest approach to other objects.
  1. The avoidance problem is recast in a distributed and locally-linear form to arrive at a tractable solution.
  2. Plant matrix values are approximated via simulation at each time step.
  3. The Linear Quadratic Gaussian (LQG) method is used to compute perturbations to the controls that will result in increased miss distances.
  1. Once all danger is passed, the satellites return to their original orbits, all the while avoiding each other as above.
  2. The delta-Vs are reasonable. The controller begins maneuvers as soon as practical to minimize delta-V.
  3. Despite the inclusion of trajectory simulations within the control loop, the algorithm is sufficiently fast for available satellite computer hardware.
  4. The required measurement accuracies are within the capabilities of modern inertial measurement devices and modern positioning devices.

This work was done by Jonathan Lamar Bryson, Chadwick James Cox, Paul Richard Mays, James Christian Neidhoefer, and Richard Ephrain Sacks of Accurate Automation Corp. for Goddard Space Flight Center.

In accordance with Public Law 96-517, the contractor has elected to retain title to this invention. Inquiries concerning rights for its commercial use should be addressed to:

Accurate Automation Corp.
7001 Shallowford Road
Chattanooga, TN 37421

Refer to GSC-14990-1, volume and number of this NASA Tech Briefs issue, and the page number.