Formulation and characterization of one-way radiometric tracking with the Iris radio using a Chip Scale Atomic Clock

The Iris software defined radio is increasingly being used by deep space CubeSats for commanding, telemetry, and communications because of its small mass and power requirements and its compatibility with the Deep Space Network (DSN). The Iris ability to coherently transpond DSN signals enables traditional two-way Doppler and (either regular or regenerative) range tracking that can be used by the operations team to navigate the spacecraft. Because of the proliferation of these small spacecraft, their need to minimize power usage, and the potential for onboard autonomous navigation, the Iris radio has recently been updated to be able to measure and collect one-way Doppler and range. Traditionally, one-way Doppler and range have found limited use because a radio’s typical oscillator did not possess sufficient stability to collect precise radiometric data suitable for deep space navigation. However, Iris has also been paired with a space-qualified Chip Scale Atomic Clock (CSAC) via an input 1PPS signal. A CSAC’s superior long-term stability relative to a radio’s usual thermally controlled crystal oscillator (TCXO) has the potential to provide tracking data with sufficient precision and accuracy to support a CubeSat with modest navigation requirements (as compared to the increased navigation accuracy required for many larger deep space missions). In this paper, we develop models and characterize performance of one-way Doppler and range as collected by the Iris radio with these updates. We also compare this theoretical performance with measured data taken from lab tests of Iris. This has all been preparation for a space-based test of this capability by NASA’s CAPSTONE mission, launched in June 2022 and now in orbit at the Moon, which has manifested the Iris with the one-way radiometric tracking capability and plans to demonstrate this capability as one of its mission objectives.