Discovery is all set for her Tuesday departure from the International Space Station (ISS), following the reberthing of the Leonardo Multi-Purpose Logistics Module (MPLM) into the orbiter’s payload bay and the hatch closure between to two vehicles. Tuesday’s undocking will be ahead of a new conjunction threat that is being monitored by ISS controllers.
With docked operations now coming to an end, Discovery and her crew can look back on the highly successful completion of transfers and spacewalks for this mission – with the final EVA completed over the weekend.
Overall, all three EVAs managed to complete all their tasks, along with a number of get-heads. Only a handful of “items of interest” were noted via the conclusion of EVA-3 on the Mission Management Team (MMT) documentation.
“EVA Items: EMU water recharge. Following troubleshooting on FD8, water recharge was successfully completed in the ISS Airlock. Water recharge was successful following EVA 3,” noted the latest presentation on L2.
“Node 3 Avionics Cable Routing: Complete except J181/P181 connection would not soft mate. This is primary path for channel 4A power to Node 3; required for activation.
“Temporarily covered with thermal sleeve (planned for use on MT/MBS get-ahead task). GPS Antenna 4 MLI: MLI was loose, would not stay below plane of antenna base. Used two wire ties to achieve acceptable MLI positioning.
“EV2 helmet WVS (Helmetcam) mount separated from helmet near end of EVA3. WVS assembly placed in trash bag for return.”
Water management also became a topic, as the balance between supplying the Station with spare water from Discovery, and the protection of an extra day docking to the ISS, was worked by managers.
“Water Production/Transfer: Water transfer from Shuttle to ISS has been less overall than predicted. In parallel with EVA 3 operations, a proposal was worked to deactivate SSPTS (Station to Shuttle Power Transfer System) on FD10 at crew wake in order to ensure transfer of the expected 3 technical water CWCs (Collapsible Water Container) prior to undocking,” added MMT documentation.
“With nominal SSPTS plan, expect to transfer 1 CWC. This was brought to the ISS and SSP programs for consideration. Would have reduced cryo margins overall and eliminated possibility of +1 docked day. ISS and SSP program management agreed to forego the additional water transfer in favor of protecting the +1 docked day margins.”
The main topic of conversation has been the undocking plan for Discovery, following the issue with thruster F5R – which resulted in the loss of vernier thrusters (or Vernier Reaction Control System – VRCS) ahead of docking. This in turn resulted in a plan being created for Discovery’s departure.
“Attitude Control/maneuver Plans: FD12 Undocking: Prime plan is to maneuver to +XVV undock TEA on PRCS (ALT DAP). Nominal Plan (VRCS failed) – PRCS: NORM Z from undock to 75′, then select LOW Z >75′. If there is an FxD (downward firing) thruster failure, procedures keep the config NORM Z.”
“ISS MER (Mission Evaluation Room) is analyzing loads if NORM Z is required outside 75′. Assessment of current solar array plan – if the current plan will work, no further action required. If the current plan is not acceptable for loads: Updated solar array angle constraints will be provided to the flight control team. Results, and impacts to undock plan.”
Those loading concerns on the Station’s structure should not be an issue, following evaluations by experts on the ground.
“Jacobs and Boeing teams have assessed the loads on the ISS structures given the current procedures for undock (ALT DAP < 75’, Lo-Z > 75’, if another FxD jet fail, NORM Z > 75’) and found them acceptable.”
Although plans for the use of Discovery thrusters for a DAM (Debris Avoidance Maneuver) – relating to a debris source from an expended Ariane 5 upper stage wasn’t required – the ISS is keeping an eye on another conjunction event.
However, this latest threat will not make its closest pass to the Station until after Discovery has undocked.
“Potential conjunction with Fengyun debris (object 30535) at 252:08:37 which is about 13 hours after Shuttle undock. Latest miss data radial: 0.791 km, downtrack: -4.811 km, crosstrack: 17.954 km, Total: 18.6 km,” added Mission Evaluation Room information on L2.
“Undock maneuvers will cause vector permutations that effect predictions Post undock “stand alone” DAM using 35P thrusters is the current plan.”
Once Discovery has undocked, she will be put through a Late Inspection of her Thermal Protection System (TPS) via the Orbiter Boom Sensor System (OBSS). The previous inspections – on Flight Day 2 and 3 – found very few items of interest, which were soon cleared as no concern for re-entry.
Finally, the successful nature of the mission was singled out for comment on by Space Shuttle Program (SSP) manager John Shannon via the latest Shuttle Standup/Integration report.
“Mission is going fantastic, could not be any better. Appreciate all the hard work on debris avoidance maneuver, ALT/DAP work, and the vernier activities. It has been a nice effort by the combined international team.”
L2 members: Documentation – from which the above article has quoted snippets – is available in full in the related L2 sections, now over 4000 gbs in size.