GP-B Post-Flight Analysis—Final Report - Gravity Probe B - Stanford ...

4.2.1.1 The Operations Concept for Mission PlanningPart of the overall Operations Concept for the Gravity Probe-B was to divide the work of the crucial In-OrbitCheckout, or IOC phase of the mission into daily cycles. This is what a typical day would look like.1. The overall plan for what the spacecraft would d—detailed down to the individual instruction—wascreated over years before the mission launched, and was called the Baseline Timeline.2. Each day, project engineers, scientists, and managers would submit changes to the Baseline in the formof Timeline Change Requests, or TCRs.3. Mission Planning would spend every morning receiving these TCRs and readying its products for reviewat the upcoming meeting.4. Every day at 11:00 AM local time, a Timeline Meeting immediately after the Daily Status Meeting. At thetimeline meeting, overall timeline strategy would be discussed, and TCRs would be dispositioned. Agraphical version of the load for the day would be displayed to the group via laptop projection, andAdobe Acrobat software was used to mark up the timeline with requested changes in real time.5. Also, at the Timeline Meeting Mission Planning would present the loads for the next day, and review thestrategy for the next several days, so that major changes could be caught as early as possible—at least aday in advance. In any case, at the end of the meeting, Mission Planning would have its marching ordersfor the day in the form of TCRs, and also a visual representation of the changes.6. Mission Planning would then begin the work of building the two loads for that day. Spacecraft memorywas partitioned into two areas capable of holding executable instructions—what we called storedprogram command (SPC) loads, each of which could consist of several hundred SPC commands, eachcarefully timed down to the second. These two memory areas were called Ping and Pong.• The Ping load would carry out the bulk of the instructions designed to check out the payload andready the experiment.• The Pong load would be the place where attitude and thruster control (ATC) initialization wouldoccur, and other spacecraft systems would be initialized and fine-tuned.7. Changes to the spacecraft SN and GN schedules would be implemented on a “best possible” basis. SinceGP-B’s priority among other extant missions was middling, this often took a great deal ofcommunication with elements at White Sands which manage the overall TDRSS and GN schedules.Furthermore, any change to the schedule had implications to the timeline, so once the final changes weremade to the schedule, the revisions would need to be applied and accounted for by the Planner workingon building the loads.8. Once Mission Planning had a working draft of the Ping and Pong loads, they would be published to theOperations web site, “gpbops”, and a notification page would be sent to all the engineers, scientists, andmanagers responsible for approving the load so they could review the load as soon as possible, and reportproblems and errors.9. At 4:30 PM local time (or whenever possible), a Final Review Meeting involving MP, mission managers,engineers, and scientists would occur. In this meeting, the final product was graphically reviewed, andcompared to the TCRs and to the visually-marked-up baseline shown in the morning meeting. Inaddition, complete load packages would have been assembled and presented for approval. These printedGravity Probe B — Post Flight Analysis • Final Report March 2007 99