HST SM4 Status Report 4:
HST SM 4: Planning Shift - Flight Day 5, 6
A servicing mission calls for 24-hour support and the ESA Hubble team has been diligent since flight day 1. Splitting into two 12-hour shifts, the ESA team members work either on the “orbit shift” (03:00 - 15:30) or the “planning shift” (15:00 - 03:30). So whether they are morning people or a night people, it matters little since they get some of both during their shifts.
During the planning shift, the astronauts are in their sleep period and functional verification testing is being carried out from ground on HST’s newly installed/repaired instruments and spacecraft subsystems. The point of the functional tests is to validate the correct performance of the HST hardware after repair. When anomalies have occurred during the orbit shift, their impact is being assessed and where necessary, a planning update for the next day’s orbit shift with corrective actions is being defined. Whenever ESA hardware is involved, the team provides engineering support for the re-planning.
Apart from the direct monitoring of the mission progress, potential upcoming issues are discussed online with our NASA interface colleagues in order to assure that no activities will be carried out during the mission that could jeopardize the ESA provided hardware or that might pose any risk to the hardware itself and subsequently to the mission.
During the planning shift on 15 May, the following activities were performed:
The HST ESA Planning Shift Team followed all activities linked to EVA-2 (spacewalk 2) operation, planning, handling and slewing of the solar array and monitored available Solar Array Drive and Electronics (SADE) housekeeping data. Between 20:00 and 23:00 GMT, two solar array slews (turns) were performed from 0 to 90 degrees and back to 0 degrees to charge the new set of batteries and to check their correct function.
A typical example for an activity checked closely during the planning shift was the investigation of a potential inadvertent solar array angular slippage during airlock depressurisation activities prior to EVA activities due to the associated airflow acting on the solar array. Flight rules require that during airlock depressurisation activities, the solar array is monitored by a camera to allow for quick intervention in case of excessive inadvertent solar array rotation.
Another typical planning investigation performed was based on a NASA request to monitor and document micrometeorite damages on the solar array wings. The solar arrays, being external to the spacecraft, are subjected to the severe environment of space, including: radiation, thermal cycling (as Hubble moves from Sun exposure to Earth shadow) and other space hazards such as debris and micrometeorites. Solar array slewing outside its typical operational range had been suggested for adequate view by the on-board camera. Together with the NASA computer aided design (CAD) team, a configuration was found which allows monitoring of the relevant wing impact area by two cameras and remaining within the mission typical solar array slew angle.