STS-131: FD2 inspections completed smoothly despite lack of KU capability

by Chris Bergin

Veteran orbiter Discovery is closing in on the end of Flight Day 2 on orbit, following her launch at the first attempt on Monday morning, kicking off the STS-131 mission. Inspections of Discovery’s Reinforced Carbon Carbon (RCC) and other parts of her Thermal Protection System (TPS) have been completed, although footage of the surveys won’t be downloaded until after ISS docking on Flight Day 3, due to a failure of the Ku band antenna system.

STS-131 FD2 Tasks:

Flight Day 2’s main events are the TPS and OMS pod surveys via the OBSS (Orbiter Boom Sensor System). EMU (EVA Suit) checkout and Centerline camera installation. ODS (Orbiter Docking System) ring extension and Rendezvous tools checkout.

Two course correction burns – known as NC2 and NC3 burns – are also being undertaken, as Discovery continues to close in on the International Space Station (ISS) for docking on Flight Day 3.

Current status shows three Mission Evaluation Room (MER) items, although only one – an issue with the Ku band antenna system – is being worked on.

“(Pre-launch) MER-01 FC 2 (Fuel Cell 2) H2 Pump Motor Controller Voltage Increase. MER-02 MPS (Main Propulsion System) Engine 3 LH2 Inlet Pressure 3 OSL (Off Scale Low). MER-03 Ku-Band Forward & Return Link Failures,” noted L2 information.

With FC2 performing nominally throughout the remainder of the countdown, and only a transducer on the MPS triggering MER-02 1 hour 40 minutes into flight, evaluations on the health of the Ku band currently shows it has likely failed for the duration of the mission.

The Ku band antenna – which provides the live video from Discovery when on orbit, along with the ability for high bandwidth downloading and uploading between the ground and the orbiter, and radar range for rendezvous and docking – undergoes activation after the Payload Bay Doors (PLBDs) are opened on Flight Day 1.

The hardware on the antenna system is then put through a self test checkout, which failed. Commands to power cycle the two black boxes on the hardware failed to correct the problem, which has resulted in the Ku band antenna being unable to work on both the forward and return links.

Its ability to provide a role on the black box which relates to radar range for rendezvous when Discovery closes in on docking with the ISS on Flight Day 3, won’t be fully known until the crew attempt to use it for that purpose.

The confirmed loss of the forward and return links has resulted in a change of plan for the downloading of ascent data – such as the WLE IDS (Wing Leading Edge Impact Detection System), and hi res photographs of the External Tank – and the ability to send the footage taken by the OBSS during FD2 inspections.

This collection of data will instead be sent down on Flight Day 3, after docking with the ISS, using the Station’s own Ku band assets. During FD2, the crew will create footage of the inspections via a Windows Movie Maker program on one of the orbiter’s laptops.

Although the Ku will now be unable to make up for patches in communication via the S-band and UHF assets on Discovery – resulting in additional levels of “ratty comm” – the mission will be able to proceed as planned for the bulk of the flight.

Yet to be decided by managers will be if they need to carry out Late Inspections whilst still being docked with the ISS – allowing for the footage to be sent down to the ground via ISS Ku. The potential to add an additional docked day on Station is available in the mission timeline options.

MMT presentations have started to arrive into L2, and an article based on their content will be published on Tuesday.

STS-131 Specific Articles:

FD2 Inspection Tasks:

Normally, the handheld photography and ET Umbilical Well imagery would already be in the process of being downloaded to the ground for the Damage Assessment Team (DAT) to begin their evaluations into any foam liberation events.

Given the Ku antenna problem, that footage – along with the FD2 inspections of the health of Discovery’s heatshield – won’t arrive at the DAT office until later of FD3.

With the NC2 and NC3 Rendezvous burns planned into the flight day, the main role for the crew was the unberthing of the OBSS via the RMS (Remote Manipulator System), in order to carry out surveys of Discovery’s wing and nose cap, before heading to the OMS Pods to check for any tile damage or protruding blankets.

“TPS Surveys: All RCC (Reinforced Carbon Carbon) is inspected during the OBSS Starboard Wing, Nose Cap, and Port Wing surveys. The two wing surveys also cover most of the areas of the crew cabin. The OMS Pod is inspected using a handheld camera to take pictures from the aft flight deck windows,” noted Flight Readiness Review (FRR) mission outline documentation (L2).

The OBSS survey procedures incorporate the use of supplemental IDC (Digital Camera) images during LDRI (Laser Dynamic Range Imager) scans, thus reducing the likelihood of needing Focused Inspection. The OBSS unberth procedure incorporates the LDRI 3D calibration and the starboard survey the flat field calibration.

Three crewmembers are required continuously during the surveys, two for the SRMS/OBSS ops and one to operate the situational awareness cameras and sensors. Only two crewmembers are required during unberthing and berthing operations (non-laser ops).

Scans of the entire starboard wing are scheduled first, given they are not easily performed, or are impossible to perform while docked – providing a challenge should a docked late inspection be required. The surveys are scheduled to continue through the night passes, but the crew may elect to pause if the night time visuals are not sufficient.

“The LDRI survey attitude requires no sun within a +/-20 degree field of view (FOV) of the laser bore-sight. Additionally, no sun can be within a 10 degree half-cone directly behind the instrument; however it is highly desired to keep the sun at a 90 degree half cone behind the instrument as long as it’s not directly behind,” added the FRR overview.

Although Flight Day 3’s RPM (Rbar Pitch Maneuver) – carried out ‘underneath’ the ISS ahead of docking – will provide a near-complete overview of Discovery’s heatshield, the OBSS inspections will give the opening insights into the extent of any damage sustained during the ride uphill.

A level of review is already been undertaken by engineers on the ground, who are able to review ground-based camera and radar footage relating to debris events.

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