The Evolution of Command and Sequencing at JPL: Origins and Flight Software Core Lineage

Abstract

Since launching the first American satellite Explorer 1 in 1958, NASA's Jet Propulsion Laboratory (JPL) has led the world in robotic space exploration. Throughout the history of the lab, subsequent missions have traveled deeper into space, explored more challenging environments, lasted longer, attempted more ambitious science, and returned orders of magnitude more data. This paper is the first in a planned series to document the history of how JPL has commanded its spacecraft in order to achieve the increasingly daring and demanding goals of its missions. This first effort focuses primarily on the onboard technologies associated with JPL's Flight Software (FSW) Core Product Line (FCPL), the Mars rover missions that preceded it, and the Cassini mission to Saturn. It also provides a brief discussion of pre-Cassini missions in order to provide context. Other JPL sequencing technologies (namely VML and the open source F Prime Flight Software) are not discussed in detail here but will instead be the subject of future work, as will any detailed discussions on ground-based software developed to support JPL projects and the interface between onboard autonomy and sequencing. The paper explores the challenges of the more assembly-like sequencing languages common before the mid-1990s (Cassini), the significant paradigm shift that came with the Faster, Better, Cheaper era and Mars Pathfinder (MPF), the development of conditional sequencing for the Mars Exploration Rovers (MER), the SPAM scripting language of Mars Science Laboratory (MSL) and Mars 2020 (M20), the latest developments in the deep space orbiters Psyche and Europa Clipper, and a preliminary look at Sample Retrieval Lander (SRL). VML is also discussed as needed to contextualize the features in JPL's sequencing architecture that were written in response to it. The paper also explores the broader concept of spacecraft behavior. Modern spacecraft behave in highly complex ways and sequencing is only one place where spacecraft designers and operators can encode that complexity. As such, the trades needed to define a sequencing system must take this broader landscape into account. Other important modes of encoding spacecraft behavior include physical hardware, flight software, and real time commanding. Finally, the paper discusses the flexibility JPL's different command and control solutions give to operators to change behaviors in flight. While some sequencing systems are robust enough to resolve complex anomalies or react to unforeseen circumstances in flight, many are not. Historically, JPL's flight system designers have provided many methods to change behavior outside of the normal cadence of design and test, creating a large trade space to do so in flight.