Canada’s Dextre meets SpaceX’s Dragon to demo CRS operations

by Chris Bergin

With Dragon now installed and ingressed on the International Space Station (ISS), Canada’s Dextre robot took an opportunity to greet the new spacecraft on Sunday. The SPDM (Special Purpose Dexterous Manipulator) was translated to the SpaceX vehicle to practise the removal of cargo from the trunk, a key element of future Commercial Resupply Services (CRS) missions.

Dragon and the Canadians:

It was the CSA’s “big arm” on Station – the Space Station Remote Manipulator System (SSRMS), or Canadarm2 – that enjoyed a staring role during Dragon’s arrival at the ISS, reaching out to grapple the new spacecraft, prior to carefully installing it on the Node 2 Nadir port.

Preparations for the SSRMS’ role begin in April, as it conducted a “double walk off” from its previous location at the Mobile Base System (MBS) Power Data Grapple Fixtures -1 (PDGF-1) to Node 2′s PDGF. The Mobile Transporter (MT) also translated to its supporting position.

As with a lot of the Station’s robotic operations, the translation was conducted by ground teams, avoiding the ISS’ crew from being interrupted from their important science work on the National Laboratory.  As noted by Expedition 30 astronaut Don Pettit in response to’s Philip Sloss, the inspection of Dragon’s trunk is also a task for teams on Earth.

“The robotic arm can be operated from the ground, as there are a lot of routine tasks that the flight controllers on the ground do with the arm to save crew time, as we (ISS crews) do science and payload operations,” said Dr Pettit. “During the time Dragon is docked, they plan to walk-off the arm and translate the Mobile Transporter for the robotic operations.

“Everything will then be put back to where it needs to be by the time we do the unberth and release of Dragon.”

For Sunday’s operation, Dextre was used to perform a survey of the Dragon trunk using the SPDM at the end of the SSRMS, after the big arm retrieved its Canadian cousin from the Mobile Base System at Work Station 5 (WS5).

Dextre is capable of robotic execution of ISS external maintenance tasks, such as the removal and replacement of dexterous compatible Orbit Replaceable Units (ORUs), and the servicing of scientific payloads.

Supporting EVA-based maintenance is also part of its role, with the preposition of ORUs (Orbital Replacement Units) or Integrated Assemblies, the provision of lighting and camera support, and is it is also capable of actuating external mechanisms, performing inspection tasks, and extending the reach of the SSRMS.

The robot arrived on the International Space Station (ISS) during STS-123 and has already enjoyed a star role in ISS operations and evaluations into future projects, not least the Robotic Refueling Mission (RRM) tests.

Pre L2 documentation, Dragon’s trunk was surveyed using Dextre’s own LEE and Camera Light Pan Tilt Assembly (CLPAs), under the control of MCC-Houston.

This task will allow for teams on the ground to assess viewing and lighting conditions to aid in operations planning for future trunk cargo extraction/insertion operations that will play a resupply role during future missions.

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. Such payloads will be removed from the trunk – mainly by Dextre – and translated to staging points on the ISS, such as the External Platforms, ahead of installation via a Stage EVA (spacewalk).

Careful planning – including a vast amount of hardware that arrived during the final Space Shuttle missions to stock up the orbital outpost – means the smaller capability of Dragon is sufficient for any potential spares that will need to head uphill over the years to come.

Notably, SpaceX CEO and Chief Designer Elon Musk noted that they could make the trunk “bigger”, should NASA requested it.

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Once the survey has been completed, the SSRMS will return Dextre to the MBS, which will then carry the robot back to Work Station 2 (WS2).

It is likely to re-grapple Dragon, holding on to the new spacecraft until un-berthing day, an operation that will be a near reverse of the operations seen to install the Dragon on the ISS.

(Images: NASA, CSA, SpaceX and via L2’s SpaceX Dragon C2+ Mission Special Section – Containing presentations, videos, images, interactive high level updates and more, with additional images via NASA, SpaceX). 

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