Dextre Checkout:

Following the engineering resolution of a potential failure mode in the SPDM Power Switching Init (PSU), which saw the Canadian robot ‘grounded’ at the end of last year, Dextre is now back on track to assist with operations outside the orbital outpost.

His role will be vital for the long-term health of the ISS, with his capabilities including the removal and replacement of dexterous compatible Orbit Replaceable Units (ORUs), along with the servicing of scientific payloads.

Supporting EVA-based maintenance is also part of its role, along with the preposition of ORUs or Integrated Assemblies, the provision of lighting and camera support, actuating external mechanisms, performing inspection tasks, and extending the reach of the SSRMS (Space Station Remote Manipulator System). The Station will also gain its own Orbiter Boom Sensor System (OBSS) from the final shuttle mission.

The robot arrived on the International Space Station (ISS) during STS-123, following his lift to orbit in Endeavour’s Payload Bay.

Engineers have now successfully completed the key roadmap checkout test, ahead of his first job on the ISS – which will involve the removal and replacement of the RPCM (Remote Power Control Module), scheduled for later this year.

“Checkout of the SPDM continued on the road to performing the first R&R operation with a RPCM this fall. Robotics ground controllers operated the Special Purpose Dexterous Manipulator (SPDM) via ground control,” noted a minutes from the Space Station Program Control Board (SSPCB), on L2.

During the checkout, Dextre’s fine-alignment maneuvering capabilities were tested, although with cameras and video downlinks.

“With the SPDM held on the end of the Space Station Remote Manipulator System (SSRMS) (clear of the Lab window), SPDM Arm1 fine-alignment maneuvering capabilities were checked out in auto-sequence mode.

“The ground teams also checked out the Arm1 On-orbit Replacement Units (ORU) and Tool Change out Mechanism (OTCM) camera as well as the ground system developed to display alignment overlays with downlink video.”

The checkout marked the first time a dexterous arm was aligned with a dexterous grapple fixture and target on ISS, and was deemed to be a full success.

“These operations were successful, demonstrating that maneuvers over distances as small as 2mm can be performed with control and precision. System performance was nominal.”

Preparing for HTV arrival:

Eight years after its planned debut launch, the Japanese HTV is closing in on its debut mission to the ISS.

The HTV is currently scheduled to launch on September 1 from Tanegashima Space Center on an H-IIB vehicle – into an initial 200 km x 300 km orbit.

The JAXA cargo vehicle is capable of supplying a total of six tons of pressurized and unpressurized cargo to the ISS at an altitude of 407 km. Pressurized cargo can be received at the rack level (an International Standard Payload Rack (ISPR)) or sub-rack level; such as Cargo Transfer Bags (CTBs).

Sub-rack level cargo is integrated into HTV resupply racks (HRRs). All HRRs and ISPR equivalents are integrated into the HTV Pressurized Logistics Carrier (PLC). Unpressurized cargo is integrated onto an exposed pallet and, subsequently, into the HTV Unpressurized Logistics Carrier (UPLC).

After the HTV has delivered cargo to the ISS, waste cargo from the ISS is loaded into the HTV; and is destroyed upon reentry into the Earth’s atmosphere.

“Resupply volume: The PLC is capable of carrying 8 ISPR (or equivalent structural interface) racks. The water resupply subsystem inside of the PLC is capable of supplying up to 600 kg of water. The water tanks (8) are located in the standoff area of the PLC,” noted an expansive 130 page presentation on the HTV, available on L2.

The type I exposed pallet can support as many as three payloads (maximum 500 kg each). The type III exposed pallet can support up to six FRAM type payloads/cargo with a total mass of no more than 1500 kg.

“Disposal Capacity: The HTV PLC, including the water resupply system, has disposal capacity equivalent to the resupply capacity. The HTV UPLC is capable of disposing of two unpressurized payloads/cargo with a combined mass of up to 1500 Kg; depending on the type of Exposed Pallet used.”

The HTV PLC accommodates passive cargo only. Conditioned (active) cargo cannot be accommodated.

The following kinds of pressurized cargo are anticipated for HTV missions: Crew supplies (Foods storable at room temperature, Clothing and CHeCS (Crew Health Care System)). System Orbital Replacement Units (ORU)s. Experiment equipment (ISPR). Experiment ORUs (experiment materials, specimens, samples, replacement hardware etc.). Water.

The HTV is not capable of transporting active racks requiring utility interfaces such as electric power or avionics etc.

In preparation for the docking of the HTV later this year, ISS managers have been working on contingencies relating to the Station’s Robotic Work Stations (RWS), and the potential need for “hot backups” – which fall under the tag of Orbital Replacement Units (ORUs) – being flown up on a Progress resupply vehicle.

“ORU Pre-Positioning Plan in Support of Free Flyer Robotics Ops: This was a discussion of what ORUs are required to provide fault tolerance for HTV track and capture,” noted MOD’s 8th Floor ISS News on L2.

“The Central Electronics Unit (CEU) is the primary computer for the Robotics Workstation (RWS), and the DCP is the display and control panel for the RWS. Two RWS’s are required to provide a ‘hot backup’ capability for HTV capture.”

After separation from the H-IIB, the HTV’s automated guidance and control system flies the HTV to the point where it will be grappled by the Space Station Remote Manipulator System (SSRMS), thus the involvement of ISS robotics.

The area directly below the ISS, within which the HTV guidance and control systems stops the HTV motion with respect to ISS motion, is known as the berthing box. At this point the ISS crew will grapple the HTV using the SSRMS. Once the ISS crew grapples the HTV, the HTV is attached to the Node 2 Nadir port.

The 8th Floor update went on to explain the need for “hot backup” – with the worst case scenario resulting in the HTV “windmilling” itself free from the SSRMS. Backups are already in place to protect the SSRMS itself.

“Hot backup is considered to be a mission success capability from an ops perspective. For example, if there are any SSRMS failures during capture and berth, the crew could use the alternate RWS.

“If a failure occurs as the snares close, you could have a snared but not rigidized HTV which leads to ‘wind milling’ – where the HTV could rotate about the snare point.

“There is an ability to separate the grapple fixture from the HTV via HTV command, so if this situation occurs, we can safely separate the HTV from the SSRMS.”

The final decision on potential inclusions on the Russian Progress – due to launch on July 24 – will be taken over the next few weeks, with the current status classed as a “recommendation”.

“Although there was no decision as of this time, the board recommended that the CEU and DCP be prepped for possible launch on 34P if there is an on board failure prior to that point.”

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.

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The performance of Discovery continues to impress, with only two new issues – both very minor and with no mission impact – noted as of Wednesday morning.

Known as “Funnies” – the Mission Evaluation Room (MER) list now has a total of 11 items of interest, which is extremely low, with only a slight communications issue being added to the list, along with transient dropouts on the Laser Dynamic Range Imager (LDRI) on the Orbiter Boom Sensor System (OBSS).

On the ground, the DAT (Debris Assessment Team) worked through the hundreds of images gained from Flight Day 3′s RPM (10s of mbs of photos available on L2), in order to clear Discovery from a Focused Inspection.

So far 138 Regions Of Interest (ROI) have been found via the inspections that have taken place on Discovery’s TPS, which is slightly above average. During this stage of STS-126′s mission, Endeavour had 85 ROIs listed by DAT engineers.

No concerns were raised with any element of the heatshield, which has resulted in clearance for re-entry – via a call to remove the need for a Focused Inspection – being given during Flight Day 4.

The MMT did take a closer look at one tile at the aft of Discovery (port elevon) which has suffered some damage, but it is not a cause for concern.

Already cleared earlier in the day by the DAT engineers were all areas of Discovery’s RCC (Reinforced Carbon Carbon) panels on both wings of the orbiter.

“138 ROI’s required PRT disposition. All ascent threats cleared,” noted DAT. “One region of missing coverage has been addressed. As a result of this review the LESS is GO for entry. FD2 results will serve as the baseline for late inspection.”

The performance of Discovery’s External Tank during ascent will once again be highlighted as a major contributor to the healthy TPS, as the mitigation of foam liberation threats show a continuing trend of improvement.

However, it may never be known just how clean ET-127 was after the eight and a half minute ride to orbit, due to a problem with Discovery’s umbilical well camera flash, which was needed due to the dark conditions during ET sep.

The flash was programmed to trigger 22 times during separation. However, it is understood that it only flashed once.

“The Camera/Flash System did not appear to function within expected norms,” noted one outline to the Mission Management Team (MMT). “The Tank Centerline Camera appears to show some flash actuations, but the Main Bus B telemetry does not indicate flash operation.

“Additionally, the crew has been unable to establish contact between the Camera and the PGSC (Payload and General Support Computer) laptop. Subsequently, the images have not been downloaded.”

Alternative options for acquiring images of the tank post-sep are also unavailable due to the dark conditions for this particular launch.

“The only other possible source of images of the ET is the movie camera in the umbilical well and the photographs taken by the crew from inside the crew cabin. Given that this was a night launch it is doubtful that either the movie camera or the crew photographs will yield any useful images.”

S6 Transition:

During Wednesday’s robotic work, the Canadarm2 or Space Station Remote Manipulator System (SSRMS) grappled and unberthed the S6 Truss from Discovery’s Payload Bay (PLB). Canadarm2 then completed a handoff of S6 Truss to the Shuttle Robotic Arm (SRMS).

Whilst Discovery’s robotic arm held S6, Canadarm2 translationed to the S6 installation worksite along the Mobile Transporter (MT), before the SRMS passed the S6 Truss back to Canadarm2.

Due to lack of SRMS clearance with JEM Module and length of the ISS truss, robotics ops for S6 maneuvering are complex, as seen via the robotic movements as laid out in the Flight Readiness Review (FRR) documentation.

“SRMS uncradles and maneuvers out of the way to an S6 unberth viewing position. With SSRMS on MBS PDGF-1 (MT WS 6), SSRMS unberths S6 from Orbiter PLB. SSRMS maneuvers S6 to the handoff position,

“SRMS grapples S6. MT Translates to WS 1. SRMS maneuvers S6 to the hand-back position. SSRMS grapples S6 at the hand-back position and maneuvers to the overnight park position.”

The process of installing S6 will be focused on EVA-1 tasks on Flight Day 5, prior to the deployment of the arrays – which may take place on Flight Day 6, should managers decide against the need for a Focused Inspection on Discovery.

The importance of smooth robotics throughout the task ahead of installation are paramount, as outlined in the FRR documentation.

“Robotic failures during maneuvers to S6 install could lead to Inability for ISS to sustain Docking Loads,” noted the FRR. “Zero-failure tolerant during SRMS maneuver to S6-to-SSRMS handback

“SRMS is 0FT to achieving S6 handback position. SSRMS has capability to grapple S6 given any SRMS joint failure and allow the shuttle to depart. ISS unable to sustain subsequent Docking Loads unless S6 structurally mounted.

“Several of the cases result in inability to Press to Install due to robotic clearance issues. Minimal verification that resolution options are viable. Feasibility assessment associated with ability to either Press to Install or Safe S6 for subsequent loads (or Jettison) if RMS joint fails has gaps suggests that S6 can either Press to Install or Return to PLB.”

Also a late item of interest for the robotic operations – specially with the SRMS – was noted via an early release of the Shoulder Brace that holds the Shuttle Robotic Arm in a stable configuration during launch.

The arm is healthy and working within is required parameters. However, engineers have been working on models to ensure this remains the case, especially during high load operations, such as the S6 transition out of the Payload Bay.

“Analytical effort undertaken to verify structural health for launch with shoulder brace out. Confirmed Installation Issue,” noted a Flight Day 4 MMT presentation – which has been updated since Flight Day 2.

“Successful RMS Checkout, Direct Drive Test. Loads Comparison between TPS inspection and S6 Grapple/Hand-off. 1993 structural analysis with 6.0 loads showed positive margin.”

“All hardware remained within load indicator limits. As expected the shoulder inner sleeve load indicator showed the greatest increase in load due to the brace-out condition – 84 percent of its indicator load limit.”

As protection, it is understood that managers requested a slight decrease in the transition rates for the S6 operation with the SRMS. However, engineers are mainly utilizing time on issues – such as above – to refine their lessons learned to aid their understanding in the event of a more serious issue on a future flight.

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. STS-119 L2 Section includes same collections of all MMT presentations, images and video, now over 3,000 mb in total.

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