Canada’s Dextre completes payload removals from CRS-3 Dragon

by Chris Bergin

Canada’s SPDM (Special Purpose Dexterous Manipulator), or Dextre as it’s commonly known, has completed the removal of payloads from the Trunk of the SpaceX CRS-3 Dragon spacecraft, which recently arrived at the International Space Station (ISS) with an array of supplies and equipment. Two major payloads rode uphill in the unpressurized aft of the Dragon, with Dextre tasked with carefully removing and installing the hardware.

Dragon CRS-3 Trunk Operations:

The latest Dragon to set sail for the orbital outpost enjoyed a smooth April 18 ride to orbit atop of SpaceX’s Falcon 9 v1.1 launch vehicle.

4f5518b15ac4e3ac1c74dff2f7496f32Dragon’s tally-ho with the Station occurred two days later, as the commercial spacecraft closed in on the huge space laboratory for berthing operations.

(Animation created by Artyom Zharov, via L2’s huge collection of CRS-3 arrival hi res images)

Grabbed by another of Canada’s robotic assets, the Space Station Remote Manipulator System (SSRMS), Dragon was carefully translated towards her port of call on the Earth facing port of the Harmony module.

Following routine checks, the ISS crew opened the hatch to the pressurized array of upmass brought uphill by the spacecraft.

This consisted of 476 kilograms (1,050 pounds) of supplies for the crew, 715 kg (1,600 lb) of equipment for scientific research, 204 kg (450 lb) of replacement parts and hardware for the space station, 123 kg (270 lb) of equipment for conducting extra-vehicular activities, 600 grams (1.3 lb) of computer equipment.

Cargo removal ops have been proceeding to plan, ahead of the eventual transition into reloading Dragon with downmass, which – unlike Orbital’s Cygnus spacecraft – will return to Earth via Dragon’s eventual splashdown and recovery from the ocean.

Z77Dragon also brought 571 kilograms (1,260 lb) of equipment in the spacecraft’s trunk.

The trunk is an unpressurized element of the Dragon, allowing for additional cargo – such as Orbital Replacement Units (ORUs) – to ride uphill with the spacecraft.

For CRS-3/SpX-3, the High Definition Earth Viewing (HDEV) package – which is comprised of four high-definition cameras to be placed on the Station’s exterior for use in streaming live video of Earth for online viewing – was joined by the OPALS payload – which aims to demonstrate free-space optical communications technology.

Removing these payloads from the Dragon’s Trunk is the responsibility of Canada’s amazing space robot, Dextre (SPDM).

The SPDM features two arms, both with shoulder, elbow and wrist joints, although only one arm can be used at any one time.

Both arms are terminated with ORU Tool Changeout Mechanisms (OTCMs), which include “jaws” to grasp objects, a retractable socket drive, a camera and light, and an umbilical connector to provide and receive power, data and video to and from a gripped object.

The OTCMs also include Force/Moment Sensor (FMS) technology, giving the arms a “sense of touch”.

RRM OpsBoth arms are connected to a central body which features a Power & Data Grapple Fixture (PDGF) at one end, which enables the SPDM to be grappled and controlled by the SSRMS, and a Latching End Effector (LEE) at the other end, which enables the SPDM to grapple and attach to other PDGFs on the ISS.

Dextre is multi-talented and has already been used in Robotic Refuelling Mission (RRM) tasks.

Dextre and the Dragon spacecraft are no strangers to each other, after an initial meeting during the spacecraft’s debut mission to the Station, testing out clearances and camera views ahead of the future payload removal role.

Grapple Bars removed from Dragon TrunkThe first hardware to be removed from Dragon’s Trunk came during the previous CRS-2/Spx-2 mission.

However, this only involved the SSRMS, tasked with the removal of two Heat Rejection Subsystem Grapple Fixtures (HRSGFs) – which are essentially bars each featuring two Flight Releasable Grapple Fixtures (FRGFs) – from Dragon’s Trunk.

These “grapple bars” are used to aid in the handling of a stowed ISS radiator in a potential future replacement scenario, by adding grapple fixtures to the radiator for the Station’s arm to interface with.

The CRS-3/SpX-3 Trunk payload removal tasks are being spread over two days, based on a complex series of procedures created by ground teams.

With the Dragon secure on the Common Berthing Mechanism (CBM), the MT (Mobile Transporter) translated along the Station’s backbone from Work Site 2 to Work Site 6 to support removing the two sets of research hardware.

The SSRMS then released its grip on the Dragon, and collected Dextre from its staging point and translated over to the aft of the Dragon.

The spacecraft’s Trunk was then surveyed using Dextre’s own LEE and Camera Light Pan Tilt Assembly (CLPAs), under the control of MCC-Houston.

Z3This task allowed for teams on the ground to assess viewing and lighting conditions, along with clearances, ahead of the cargo extraction tasks.

With a GO to proceed, Dextre was carefully eased into the open aft of the Dragon, with its sights set on first removing the HDEV package.

Taking grip, the payload was eased out of the Trunk and translated over to Columbus’ External Payload Facility (EPF) where it was installed successfully late on Wednesday.

Z5The HDEV visible HD video cameras are a fixed payload camera system that requires no zoom, no pan or tilt mechanisms.

One camera is pointed forwards, into the ISS’ velocity vector, with two cameras aft (wake), and the other one camera pointing nadir.

Stunning views from this hardware have already been sent down to Earth.

Dextre was then returned to the Trunk to grab hold of the second payload to be removed, the OPALS package from JPL.

Z5While maintaining lock on the uplink beacon using a closed loop control system and a two-axis gimbal, the OPALS flight system will downlink a modulated laser beam with a formatted video.

The payload consists of a gimbal-mounted optical head, and a sealed container to hold the electronics, laser and motor drivers. The optical head houses a camera to track the beacon and a lens collimator system to transmit the data laser.

Dextre is currently preparing to remove OPALs, ahead of being translated and installed on Dextre’s EOTP (Enhanced ORU Temporary Platform.

OPAL’s home will be the Nadir ExPrESS Logistics Carrier (ELC) from where it will conduct its operations. The task is expected to be completed on Monday.

However, this operation was delayed on Friday as teams on the ground check alignments.

“An experiment attached inside the SpaceX Dragon’s trunk will stay inside commercial cargo craft a little longer as robotics controllers go over very precise measurements necessary to remove the new laser study,” noted NASA. “The Canadarm2 with the Dextre in its grasp will stay in a stable position before removing the OPALS hardware to ensure a proper alignment for the fine robotics work.”

This payload was finally removed this week following troubleshooting.

(Images: via L2′s SpaceX Special Section, which includes over 1,000 unreleased hi res images from Dragon’s four flights to the ISS. Other images via NASA and Cosmonaut Oleg Artemyev and ISS FD Royce Renfrew)

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