Zac Manchester Engineer, Rocket Scientist, Bass Player

Quaternion Variational Integrators Paper

I was just notified that my first journal paper, “Quaternion Variational Integrators for Spacecraft Dynamics,” which was accepted for publication in the AIAA Journal of Guidance, Control, and Dynamics back in April of last year, will be appearing in print in the next issue. In the paper I develop special-purpose numerical integration algorithms for simulating spacecraft attitude dynamics. The algorithms are derived by discretizing Hamilton’s Principle (also known as the “Principle of Least Action” or “Principle of Stationary Action”) and have several interesting properties, including long-term energy and momentum conservation (for conservative systems). Here’s a plot from a simulation of a tumbling rigid body comparing the energy drift between the 2nd order midpoint rule, MATLAB’s ODE45 integrator, and the variational integrator in the paper:

EnergyError

If you’re still with me after all of that jargon, you can check out the paper on the journal’s website or download a preprint here. I’m also posting MATLAB implementations of the integrators and some demos on GitHub.

AIAA SciTech 2016 Plenary

I was recently invited to speak on a panel as part of the plenary series at the 2016 AIAA SciTech conference in San Diego. The topic of the discussion was, “Lessons learned from a half century of innovation in aerospace technology.” It was a huge honor to be on stage with former Apollo astronaut Bill Anders, who flew around the moon on Apollo 8 and took the famous “Earthrise” picture.

I tried to bring a positive perspective on where new technologies are taking the aerospace industry, including the rise of small satellite startups and the faster pace of design iteration enabled by CAD software and rapid prototyping tools. Here’s a video of the discussion:

KickSat-2 Deployment Test

Here’s a test of the new deployment mechanism on KickSat-2, which was developed to meet more stringent safety requirements. On KickSat-1, the mechanism was triggered by a single burn wire. On KickSat-2, we have two “inhibits” triggered by two independent burn wire circuits. The primary inhibit is a nylon screw that is threaded through the entire assembly. The secondary inhibit is a monofilament tie-down that is secured to the main spacecraft structure. Both the primary and secondary inhibits must be cut in order to trigger deployment. During the mission, the secondary tie-down would be cut first, followed by the primary. The following video shows the opposite - the nylon screw is cut first, followed by the tie-down - to demonstrate that everything works as it should.

Ph.D. Dissertation

My Ph.D. dissertation just came in from the printer. It documents a lot of my work on KickSat over the past four or five years, along with some stuff on variational integrators, feedback control for flat spin recovery, and spacecraft inertia estimation. You can read the PDF here if you’re interested.

Thanks to everyone at Cornell and NASA Ames who helped me along the way!

Dissertation