Dragon Splashdown concludes SpaceX’s CRS-2 mission

by Chris Bergin and Pete Harding

SpaceX’s Dragon spacecraft has successfully splashed down in the Pacific Ocean on Tuesday, following its departure from the International Space Station (ISS). Known as End Of Mission (EOM) operations, Dragon’s safe return completed the second mission under NASA’s Commercial Resupply Services (CRS) contract.

SpaceX CRS-2 EOM:

Following a nominal launch from Cape Canaveral’s SLC-40with the launch vehicle showing no signs of repeating it’s Engine 1 issue from the previous ride uphill – Dragon begin its journey to the ISS.

However, a challenging issue was noted – just moments after it separated from the Falcon 9’s Second Stage – relating to the spacecraft’s propulsion system – which consists of a set of four “quads”, each hosting thrusters on the Dragon, vital for attitude control and required burns en route to the Station.

Although SpaceX, NASA and even the US military assets all worked together to resolve the issue, Dragon missed the key Coelliptic Burn, resulting in a one day delay to its rendezvous and berthing with the ISS.

All proceeded to plan during Dragon’s arrival at the orbital outpost, successfully berthing and delivering its cargo.

With its troubles behind it, Dragon was also part of a first for a commercial spacecraft at the ISS – as the Space Station Remote Manipulator System (SSRMS) carefully removed a pair of grapple bars from the spacecraft’s trunk.

Future Trunk/ISS Ops, via L2Dragon’s trunk is designed to carry additional cargo outside of its pressurized cabin – such as Orbital Replacement Units (ORUs).

These payloads will be – for the most part – removed by the Dextre (SPDM) robot over the course of the CRS contract, prior to being translated to staging points on the ISS, such as the External Platforms, ahead of installation via a Stage EVA.

During the debut operation on CRS-2, the SSRMS was 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” will be 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.

SSRMS visits Dragon on CRS-2The HRSGFs were successfully removed from Dragon’s Trunk robotically by the SSRMS, whereupon they were installed onto the Payload ORU Accommodation (POA) on the Mobile Base System (MBS) on the ISS Truss, where they will each await respective installation onto the S1 and P1 Truss radiators during a US spacewalk in July.

Dragon still has another important payload task to complete – albeit one day later than planned due to high seas in the splasdown zone – as 2,668 pounds of “downmass” was packed into the spacecraft for its return to Earth. With the hatch closed, the focus will again return to the ISS’ robotic assets.

To kick off the homecoming, the long sequence of events that will ultimately lead to Dragon safely bobbing the Pacific Ocean began with the unberthing of Dragon from the Node 2 Nadir CBM, via the release of 16 bolts around the CBM berthing collar on the ISS side, performed in four sets of four bolts to ensure even unloading on the CBM interface.

Dragon Unberthing, via L2Once complete, the ISS crew pulled Dragon away from the ISS via the use of the Space Station Remote Manipulator System (SSRMS) – which grappled Dragon at the end of last week – controlled from the Robotic Workstation (RWS) in the panoramic-viewed Cupola.

Dragon was then be manouvered to the release position approximately 30 feet below the ISS.

Once in the release position, the time came for Dragon and the ISS to part ways, Expedition 35 Flight Engineer and NASA astronaut Tom Marshburn squeezed the trigger on the Rotational Hand Controller (RHC) on the RWS to release the snares holding the SSRMS Latching End Effector (LEE) to the Dragon Flight Releasable Grapple Fixture (FRGF) – effectively “letting go” of Dragon.

With Expedition 35 Commander Chris Hadfield of the Canadian Space Agency backing up Marshburn by monitoring Dragon’s systems, this process concluded with a 06:56 Eastern release.

CRS-2 Dragon and the SSRMS, vla L2With the SSRMS retracted safely clear, Dragon then conducted a departure burn to depart to vicinity of the ISS, edging away from the orbital outpost, with two small thruster firings to push down the R-Bar.

A larger burn will then conducted to send Dragon outside of the approach ellipsoid, at which point SpaceX will take full control of the mission.

This was a key test of the propulsion system – although a repeat of the issues with the check valves in the helium pressurization lines is not expected. The three burns were classed as nominal.

Dragon Flying on orbit, via L2Dragon the conducted a free-flying phase on-orbit for around five hours, during which time it completed a critical action – closure of the GNC bay door, to which the FRGF is mounted – before conducting a de-orbit burn at 11:40 Eastern.

The 10 minute deorbit burn was conducted by the spacecraft’s Draco thrusters.

The umbilical between Dragon and its Trunk was disengaged, prior to the Trunk separating from the Dragon capsule.

As the spacecraft enters Entry Interface (EI) it was protected by its PICA-X heat shield – a Thermal Protection System (TPS) based on a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material – designed to protect the capsule during Earth atmospheric re-entry, and is even robust to protect Dragon from the high return velocities from Lunar and Martian destinations.

Dragon under chutesOnce at the required velocity and altitude, Dragon’s drogue parachutes were deployed, followed by Dragon’s main parachutes, easing the vehicle to a splashdown in the Pacific Ocean off the coast of California at 12:34 Eastern.

Three main recovery boats soon arrived on station, with fast boats racing to meet the Dragon shortly after it hits the water, allowing for the recovery procedures to begin. The vehicle was powered down and then hooked up to the recover assets.

Dragon was transported to the port of Los Angeles, prior to a trip to Texas for cargo removal.

The cargo return – otherwise known as the downmass capability – is one of Dragon’s star roles following the retirement of the Shuttle fleet.

Click here for more Dragon Articles: http://www.nasaspaceflight.com/tag/dragon/

Although the spacecraft doesn’t get close to the capability of the orbiters, it will still return about 2,668 pounds (1,210 kilograms) of science samples from human research, biology and biotechnology studies, physical science investigations and education activities.

(Images: via L2’s SpaceX Dragon Mission Special Section, which includes over 1,000 unreleased hi res images from Dragon’s three flights to the ISS. Special section also contains presentations, videos, images (Over 3,500MB in size), space industry member discussion and more.)

(Click here: http://www.nasaspaceflight.com/l2/ – to view how you can support NSF and access the best space flight content on the entire internet).

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