Canada’s Special Purpose Dexterous Manipulator (SPDM) robot “Dextre” has reported himself as fit for duty, as the clock ticks down to his debut tasks on the International Space Station (ISS). Meanwhile, preparations are building up for the arrival of the first Japanese HTV (H-II Transfer Vehicle) – which may involve spare robotic work station hardware being flown up on the Russian resupply vehicle Progress 34P.
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.