Cassini Spacecraft-DSN Communications, Handling Anomalous Link Conditions, and Complete Loss-of-Spacecraft Signal

Abstract

Once spacecraft are launched, it is impossible for engineers to physically repair anything that breaks onboard the vehicle. Instead, remote solutions must be employed to address spacecraft anomalies and fault conditions. To achieve this goal, telemetered data from the spacecraft are collected and assess by ground personnel to resolve problems. However, if the ground-to-spacecraft communication system breaks down, or the vehicle delivers an anomalous signal, a rigorous protocol must be employed in order to re-establish or fix the telecommunications link. There are several factors that can contribute to link problems, such as malfunctions or mishandling of the ground station equipment, onboard failures of the spacecraft's flight software coding, or even mishaps caused by the space environment itself. This chapter details the anomaly recovery protocols developed for the Cassini Mission-to-Saturn project, to resolve anomalous link problems as well re-acquisition of the spacecraft should a complete Loss of Signal (LOS) condition occur.

Robotic Autonomous Spacecraft Missions: Cassini Mission-To-Saturn Example

“…These onboard running sequences (that execute continuously for weeks to months) consist of hundreds of commands to perform activities such as earth, sun, and star tracking, monitoring celestial references for attitude targeting, performing maneuvers to fine-tune the trajectory when required, science calibration and collection; all of which are all subject to human-induced glitches which can potentially cause serious faults. As an example, should the transmitter or receiver onboard the spacecraft be accidentally commanded off, the condition would cause an inability of the ground station to communicate with the spacecraft [5]. Too many components commanded on at the same time could exceed the spacecraft's power allocation, leading to a spacecraft-wide "under-voltage power-outage" condition.…”