InSight/MarCO Opportunistic Multiple Spacecraft Per Antenna (OMSPA) Demonstration

As smallsats become increasingly capable, longer-lived, and have more secondary payload launch opportunities to beyond-GEO destinations, they are expected to play an increasing role in deep space science investigations. This expectation is borne out by several relatively recent NASA Science Mission Directorate solicitations regarding smallsat studies and small innovative missions. With the potential for these smallsats to substantially add to the number of spacecraft operating in deep space, we need to be thinking about ways to support communications with all of them without the huge expense of trying to build a commensurate number of deep space antennas. One approach to this challenge might involve making greater use of beam-sharing techniques that allow all the spacecraft within the beamwidth of a single ground antenna to simultaneously downlink to the antenna. One of these techniques, Opportunistic Multiple Spacecraft Per Antenna (OMSPA), may be particularly suited to smallsats. In the concept for this technique, smallsats within the scheduled ground antenna beam of some other spacecraft, make opportunistic use of that spacecraft's beam by transmitting “open-loop” to a recorder associated with the antenna. These transmissions get captured on the recorder and can be later retrieved, demodulated, and decoded so that the smallsats can recover their data – all without them having to schedule the antenna itself and compete with larger missions for antenna time. Widespread use of such a technique could lead to more efficient use of receiver antenna resources and result in a dramatic increase in downlink throughput. An opportunity to demonstrate the technique occurred in May 2018, when the Mars CubeSat One (MarCO) mission, consisting of two nanospacecraft (MarCO-A & B) launched alongside InSight, a NASA Mars lander mission. To demonstrate the capabilities of OMSPA for this launch window opportunity, X-band downlink telemetry was recorded for all three spacecraft (InSight, MarCO-A, and MarCO-B) at both the Deep Space Network (DSN), using its 34-m antennas, and at Morehead State University (MSU) using its 21-m antenna – with all of the involved antennas pointed at InSight. Open-loop recordings were collected at the DSN using wideband very long baseline science receivers and at MSU using Universal Software Radio Peripheral (USRP) devices operated using GNU Radio. All the recordings were then processed at the Jet Propulsion Laboratory, California Institute of Technology (JPL) using an OMSPA Software Receiver, a signal processing/communications tool used to extract telemetry transfer frames from baseband samples. The results of extracting telemetry data from InSight/MarCO recordings collected by the DSN and at MSU are described in this article. In particular, details pertaining to the processing chain used by the OMSPA Software Receiver to demodulate the DSN and MSU recordings are presented, from carrier/symbol synchronization, to frame alignment using attached sync markers (ASMs), followed by error correction code decoding. Validation results with closed-loop data obtained by the DSN are also presented in order to highlight the viability of OMSPA for future multiple spacecraft demodulation opportunities.