Collision Avoidance and Debris Mitigation for Spaceflight’s SSO-A Mission

Providing affordable rides to low Earth orbit for a large number of small spacecraft, as we’re doing on the SSO-A mission, also introduces some unique engineering challenges. In particular, deploying a pack of spacecraft into the same orbit raises natural concerns about potential collisions between spacecraft causing orbital debris. To that end, we wanted to take this opportunity to share a bit about the approach we’ve taken to mitigate some of these risks for the SSO-A mission. This isn’t an an exhaustive list by any means, but it offers some insight into our commitment to a safe space environment.

One step we took was to design and rigorously analyze a strategy for how to deploy the spacecraft on this mission while minimizing the probability of a collision. To do so, we built and validated an in-house, six degree-of-freedom dynamic simulation of the mission to test out the effects of different orders, timings, and directions of spacecraft deployments. This simulation carefully models the complex physics of each and every single object on this mission and their interactions during deployment operations. In essence, we can fly the mission with this computer simulation.

Starting from the launch vehicle’s initial insertion into the sun-synchronous orbit, this simulation runs through the successive deployments of every spacecraft, tracking their trajectories over time and checking for collisions. The simulation is then used to run computational algorithms known as Monte Carlo analyses that help us understand how successful a particular deployment strategy is in the presence of uncertainties, and to iterate our strategy based on the results. Using this approach we ran the experiment with many, many thousands of deployment strategies.

Once we had a viable deployment strategy in hand, we next set out to discuss the mission and vet our approach with various external stakeholders.

One such stakeholder was the NASA Orbit Debris Office. As the name implies, this is the NASA office that studies and helps develop mitigation measures for orbital debris. Through our conversations, we confirmed that the types of low-velocity collisions our simulations showed are possible (although very unlikely)  but they are not a big concern for generating orbit debris. This is because any such collision would occur with very low relative velocity – around one meter per second in the worst-case, it is roughly equivalent to the velocity of an object hitting the ground after being dropped from a height of less than one foot on the Earth.

Another important stakeholder that we’ve been working with is the 18th Space Control Squadron (18 SPCS). This is the part of the U.S. Air Force responsible for tracking space objects, predicting close approaches, and supporting collision avoidance operations between spacecraft operators. By initiating discussions with the 18 SPCS, we’ve been able to provide them with the information they need to minimize risks to currently orbiting space objects.

At Spaceflight, we strive to be good stewards of space so everyone can continue to enjoy the benefits that space-based technologies bring. We thought a lot about the issues of potential collisions and debris as we prepared the SSO-A mission, and kept our commitment to a safe space environment throughout the process.

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