A Statistical Approach To Payload Energy Management For Nasa'S Europa Clipper Mission

Constraining and managing energy for spacecraft and their payloads has often posed a challenge for systems engineers, since, by its very definition, energy has two dimensions, time and power, and thus changes can occur along either or both axes at any point in time. The challenge is even greater for missions which have highly dynamic power generation and consumption profiles, and harder still for those which also have a multitude of instruments with unique, episodic, observation profiles. Indeed, that is the very challenge faced by the systems engineers on the Europa Clipper project and its ten instruments.Past solutions to such problems have relied on a variety of metrics: average or maximum energy utilization, peak power utilization, a worse case energy balance, battery state of charge, and many others. In this paper, we will describe why none of the previous approaches were found to be sufficiently suitable and why that led to a novel approach which defines a representative energy usage in statistical terms. This resulted from the need to concurrently satisfy five separate criteria: 1) the payload allocation must be used to size the spacecraft power generation and storage system; 2) the payload allocation must be suballocated to each instrument; 3) instruments must be able to verify and report against their allocations without the need to run observation profile simulations; 4) the payload allocation must be based on the Europa Clipper Design Reference Mission; 5) allocations must be reasonably immune to variations in future tour designs. While the need to meet each of these criteria may seem obvious, ensuring that a single metric can satisfy all five simultaneously is not.In addition to describing the method and the thinking behind it, the paper will also show how it was applied to the Europa Clipper project, with a focus on the payload, and how it successfully met all the criteria in the presence of changing observation profiles and tour designs.