Discovery docks with ISS following stunning RPM

by Chris Bergin

Shuttle Discovery has docked with the International Space Station (ISS), following a visually stunning Rbar Pitch Maneuver (RPM), on Flight Day 3 of STS-120.

During the RPM, ISS crew members took photography of Discovery’s belly and TPS (Thermal Protection System), to look for any issues – although so far only one slightly protruding gap filler has been spotted (on Flight Day 2).

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The RPM allows the ISS crew to perform a high resolution photo survey of the lower surface thermal protection system (TPS) tiles to screen for ascent debris damage.

The nine minute maneuver was debuted on STS-114’s Return To Flight mission, following months of planning by shuttle experts at the Johnson Space Center (JSC).

They were tasked with the limitations on crew and sensor visibility, maneuvers conducted about an unstable orbital stationkeeping position, inherently unstable attitude dynamics, thruster plume impingement on the ISS, shuttle propellant limitations, and a very tight set of lighting and geometry constraints for the inspection photography.

Last week, Clay Anderson and Yuri Malenchenko successfully completed a standard 30-min Shuttle RPM skill training exercise, ahead of the arrival of Discovery.

ISS crewmembers used their DCS-760 digital still cameras with 400 and 800mm lenses at SM windows 6 and 8 to take target imagery.

The RPM photography will allow technicians on the ground to take a detailed look at Discovery’s TPS, with only one Protruding Gap Filler at Panel 20R, showing up, following Flight Day 2’s inspections. This process of checking the RPM images will take a couple of days.

The opening RPM images have already been acquired by this site’s L2 section, showing several areas of Discovery in high resolution. No damage is obvious on the images, which include the LH2 umbilical door area. (Cropped sample of the door).

Discovery’s ‘funnies’ (issues)

Hardly any, with Discovery performing like the veteran orbiter she is. A grand total of five ‘funnies’ are listed, one of which being the ice found pre-launch – subsequently falling off at SSME (Space Shuttle Main Engine) ignition. The other related to SSME 1 – which had a LO2 Inlet Temp Erratic reading – though this did not cause any issues during ascent.

The other three issues relate to a laptop connection issue, a slight blip with the Star Tracker and a positional error that was noted with the OBSS (Orbiter Boom Sensor System) grapple position, none of which are a problem for the mission.

‘WIS GFE Laptop Local Timeouts. MER-04 RMS OBSS Grapple Position Delta from Expected. Y Star Tracker Transient BITE,’ noted the Mission Management Team (MMT) overview for the mission thus far. ‘All other systems operating nominally.’

‘When the OBSS was grappled by the SRMS the POR position was different than expected: Y delta – 3 inches. Z delta – 1 inch. Note: OBSS Grapple position was nominal for last flight of OV-103,’ added another MMT presentation.

‘Potential Causes: MPM deploy – Mech reports deploy was nominal. Arm S/N 202 Joint biases – Joint angles were nominal when SRMS was cradled. IBA S/N 203 (first flight) – EFGF on forward transition could be cause. Thermal deflections – being discussed.

‘Impacts: only impacts OBSS ops. OBSS Sensor team assessing impact to TPS inspection coverage.’

Also noted by the MMT are the latest readings from the sensors on Discovery’s wing leading edges, which have only registered two minor readings – during ascent – both well below any cause for a closer evaluation at this stage.

Debris/Foam Loss Update:

As revealed by this site on Wednesday, the main foam loss wasn’t mentioned at the post MMT press briefing, but is internally classed as the biggest foam loss event during the ascent of Discovery on Tuesday.

Information points to the foam ‘popcorning’ off the LO2 Ice Frost Ramp (IFR) at the top of the tank, rather than liberating in one piece. There is no information that points to it then hitting the orbiter.

ET TPS Loss IFR 593: Missing TPS was noted at IFR 593. Preliminary assessment by ET is heavy popcorning or erosion/recession,’ noted NASA information.

Interestingly, images of ET-120 in the Vehicle Assembly Building (VAB) show the foam in question to have a white patch at the top of the IFR. All the other IFRs suffered no foam loss.

Further evaluations are taking place on the images of the IFR, although that is believed to be related to checking ET-125 – which was recently mated in the VAB ahead of December’s STS-122.

L2 members: All documentation and quotes – from which the above article has quoted snippets – is available in full in the related L2 sections, updated live.

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