STS-131: Discovery closing in on ISS docking – RSB liberation during ascent

by Chris Bergin

Discovery is continuing to close the gap between herself and the International Space Station (ISS) for a Flight Day 3 rendezvous that will result in docking at 02:44am Central time. Bar the Ku band failure, Discovery is in great shape, and enjoyed a nominal ascent on Monday morning, according to opening MMT (Mission Management Team) reviews – which included one early debris event, relating to a potential tile liberation from the Rudder Speed Brake (RSB).

STS-131 Status:

Despite the loss of the Ku band Forward and Return links, Flight Day 2’s opening inspections of Discovery’s Reinforced Carbon Carbon (RCC) and Thermal Protection System (TPS), were completed within a nominal timeline.

Engineers on the ground followed the process via still images sent down on the S-Band link, while the Damage Assessment Team (DAT) will start their review once around six tapes – each containing several gigabytes of converted video footage – is downlinked to the ground via the ISS’ Ku assets.

Other tasks completed included EMU checkouts for the three EVAs of the mission, the Orbiter Docking System (ODS) centerline camera installation, NC-3 rendezvous OMS engine firing, and the ODS (Orbiter Docking System) extension and rendezvous tools checkout – prior to crew sleep, which began at 11:21 Central on Tuesday morning.

Flight Day 3 begins with crew wakeup scheduled for 19:21 Central, followed by several burns – including the TI burn scheduled for 00:08 Central time. Discovery and her crew will arrive below the ISS for the initiation of the R-bar Pitch Maneuver (RPM) at around 01:42 Central.

The RPM – Rbar denoting along the radius vector of the ISS, downward – allows the ISS crew to perform a high resolution photo survey of the lower surface TPS tiles to screen for ascent debris damage.

The nine minute maneuver – which involves the orbiter being commanded through a 360 degree back-flip – was debuted on STS-114’s Return To Flight mission, following months of planning by shuttle experts at the Johnson Space Center (JSC) and has been hailed as one of the major steps forward in ensuring the health of an orbiter prior to clearance being given for re-entry.

STS-131 Specific Articles:

Opening DAT item of interest:

Even without the vast amount of imagery that would nominally be flooding down into the DAT office by now, the highly efficient team have still managed to clear several areas of the orbiter already.

“Full Coverage and Cleared Items: Starboard T0. Port OMS Black Tile Region. Starboard OMS Black Tile Region. Starboard Upper Carrier Panels 1, 5-9, 13-22. Port Upper Carrier Panels 1-13, 18-19, 21-22. Starboard Lower Carrier Panels 3, 6, 8-22. Port Lower Carrier Panels 1-6, 12-22,” noted a Tuesday DAT presentation – available on L2.

“TPS Items Missed/Partial Coverage but will be Picked up During RPM: Lower Starboard Carrier Panels 1-7. Lower Port Carrier Panels 7-11. Upper Starboard Carrier Panels 2-4, 10-12. Upper Port Carrier Panels 14-17, 20.

“TPS Items Requiring Look at Downloaded Video after Docking: Starboard Forward Fuselage. Port T0. Port Forward Fuselage.”

Ascent footage has also resulted in the first item of interest for evaluation, relating to what appears to be a liberation from the RSB, observed at 42 seconds into flight – as the vehicle was going supersonic.

“Debris event during accent at 42.229 MET (Mission Elapsed Time)  from port upper RSB trailing edge. Appears to be tile loss,” added the DAT presentation which provided several slides on the RSB event.

“RPM imagery may provide some detail from aft views. Identified station assets with access to damage site. Two cameras have visibility to area.”

With RPM footage scheduled to arrive on the ground during Wednesday morning, a full evaluation of the area will be conducted by DAT.

They will also have a potential view of the liberation via the Solid Rocket Booster (SRB) cameras that face aft during ascent. Footage will be available once the recording devices have been removed from the recovered boosters later this week.

“SRB Retrieval Status: Liberty Star and Freedom Star are in tow and expected at the dock Wednesday at 0800 and 1000 EDT respectively,” noted the NASA Test Director (NTD) report on L2. “Open Assessment is expected to begin on Thursday at 0700 EDT.”

It is unlikely a tile liberation on the RSB would be a problem for entry, given they are mainly used to provide ascent heating protection.

Opening Ascent Report:

The veteran orbiter’s performance during ascent was completely nominal, per the opening ascent report – one of several reports which review the propulsion systems used for the eight and a half minute ride to orbit.

“The STS-131 mission was launched at 095/10:21:24.992 GMT on April 5, 2010, on the thirty-third Space Shuttle Program (SSP) mission to the ISS, and the 38th flight of the OV-103 (Discovery) vehicle,” noted the ascent report (L2).

“SRB separation was visible. A nominal Orbital Maneuvering System (OMS) assist maneuver was performed following SRB separation. Ignition occurred at 095/10:23:41.0 GMT (00/00:02:16.0 Mission Elapsed Time (MET)), and cutoff for the maneuver was 095/10:25:25.6 (00/00:04:00.6 MET). The maneuver was 104.6 sec in duration. 

“MECO occurred at 095/10:29:49 GMT (00/00:08:24 MET). The ET separated from the Orbiter at 095/10:30:10 GMT (00/00:08:45 MET).”

Once on orbit, Discovery continued to perform well, bar a transducer on the Main Propulsion System (MPS) Liquid Hydrogen (LH2) inlet pressure measurement failing Off Scale Low (OSL). This issue holds no mission impact.

“A nominal OMS-2 maneuver was performed at 095/10:58:39.6 GMT (00/00:37:15.6 MET). The maneuver was a dual engine firing that was 128.4 sec in duration with a differential velocity (ΔV) of 196.9 ft/sec. The achieved orbit was 31.6 by 123.6 nmi,” the report continued.

“Just prior to Space Shuttle Main Engine (SSME) 3 start, the MPS LH2 inlet pressure measurement began behaving erratically at 095/10:21:15 GMT and eventually went to Off-Scale Low (OSL) (on orbit). The loss of these data remains no concern for the remainder of the flight.

“The payload bay doors were opened at 095/11:52:01 GMT (00/01:30:36 MET). The Ku-Band antenna was deployed and the self-test was performed. The approval for On-Orbit operations was given the crew at 095/11:53 GMT (00/01:32 MET).”

This article will be updated during the Flight Day, with another article outlining the specifics of the Fuel Cell 2 and Ku Band MER (Mission Evaluation Room) findings.

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