Needle in a Haystack: Finding Two S-band CubeSats in a Swarm of 64 Within 24 Hours

In the past few years we have witnessed the ascension of rideshare missions, breaking records again and again for the total number of satellites released on a single launch. Such large swarms of spacecraft make it difficult for the Combined Space Operations Center (CSpOC) to identify satellite orbits until days to weeks after launch. For the SSO-A launch in December 2018, it took 11 days to catalog all 64 objects. While satellites should be designed to survive without ground contact for that long, for most missions, making contact and assessing vehicle state of health during early orbit operations is critical, and waiting for object cataloging is simply too risky. Furthermore, as CubeSats take on more operational roles, the amount of data needed to both uplink and downlink requires moving away from the traditional L-band frequencies to S-band and higher. While higher frequency bands allow faster data transmission it comes at a cost of smaller ground antenna footprints, requiring an order of magnitude better pointing knowledge in order to establish communications lock. With typical canister ejection speeds, spacecraft can drift away from the launch vehicle, whose orbit is typically known and provided by the launch integrator. Depending on ground antenna size, this implies the spacecraft will no longer be in the ground antenna field of view within a day or so of launch. This makes establishing communications with the spacecraft within the first 24 hours after launch paramount. This paper discusses how the ORS-7/DHS Polar Scout mission successfully achieved contact with its two 6U CubeSats and determined their orbital ephemerides in less than 24 hours after launching on the SSO-A mission on December 3, 2018. We present our spacecraft acquisition plan, which encompassed a number of different strategies that can be employed depending on the capabilities and equipment at the ground site