CRS-4: SpaceX Dragon returns back to Earth

by Chris Bergin

SpaceX’s Dragon spacecraft has concluded her successful mission to the International Space Station (ISS) with a return to Earth on Saturday. The EOM (End Of Mission) events began with an unberthing and release of the CRS-4/SpX-4 spacecraft from the orbital outpost, ahead of a parachute-assisted splashdown in the Pacific Ocean at around 15:38 Eastern.

CRS-3 Dragon – EOM:

Launched early on Sunday, September 21 atop of SpaceX’s Falcon 9 v1.1 launch vehicle, Dragon has enjoyed another successful stay at the ISS.

This is the fifth time the commercial vehicle – that has aspirations of becoming crew-rated into an advanced version known as Dragon V2 (or simply Dragon 2 as now referred to internally) – has paid a visit to the Station.

4f5518b15ac4e3ac1c74dff2f7496f32Grabbed by the tail by Canada’s Space Station Remote Manipulator System (SSRMS), Dragon was carefully translated towards her orbital on the Earth facing port of the Harmony module.

(Animation created by Artyom Zharov, via L2′s huge collection of Dragon arrival hi res images)

Riding uphill with the Dragon was a cargo compliment of almost 5,000 pounds of supplies and experiments to the International Space Station during a month-long stay.

The Dragon also contains 20 mice have now taken up residency on the orbital outpost.

2014-09-18 04_30_18-habitat.jpg (1280×1024)The “Mousetronauts” rode uphill in a new hardware system designed to carry rodents safely from Earth to the orbiting laboratory and provide long-term accommodation aboard the station.

The rodent research system enables researchers to study the long-term effects of microgravity on mammalian physiology.

Also delivered alongside the multitude of food, clothing, equipment, experiments and supplies for the ISS and her crew was a 3D printer and new EMU batteries that have since been used on the two recent US spacewalks.

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The ISS crew removed and stored the cargo, before refilling Dragon with downmass. Dragon is the only American vehicle capable of returning downmass since the retirement of the Space Shuttle fleet.

2014-10-25 10_54_14-CRS-4 RapidScat removal - Google SearchShe also provided the Station with a payload that was launched in her Trunk section.

Known as the ISS-RapidScat, the experiment was attached on the end of the Station’s Columbus laboratory, via the use of the Station’s robotic assets that are now well-versed in removing and installing hardware from the Dragon’s trunk.

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

The experiment – now studying Earth’s ocean surface wind speed and direction, returns a lost capability when the SeaWinds scatterometer aboard NASA’s then 10-year-old QuikScat satellite experienced an age-related antenna failure – is a low cost project, assembled from spare components left over from the development of QuikScat and ADEOS II.

To kick off the homecoming, the long sequence of events – that will ultimately lead to Dragon safely bobbing up and down in the Pacific Ocean – saw the ISS crew initiate 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 was under the firm grip of the SSRMS, which arrived back in the location of the spacecraft, following its role with Dextre and the Trunk payload removal tasks.

With the SSRMS holding on to the Dragon – and the bolts released through the opposite process that saw first and second stage capture – the ISS crew will used the “big arm” to pull Dragon away from the port, controlled from the Robotic Workstation (RWS) in the panoramic-viewed Cupola.

Dragon was then maneuvered 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, via a squeeze of the trigger on the Rotational Hand Controller (RHC) on the RWS.

This was initiated by the release of the snares holding the SSRMS Latching End Effector (LEE) to the Dragon Flight Releasable Grapple Fixture (FRGF) – effectively “letting go” of Dragon.

This process concluded with a 09:56 Eastern release of SpaceX’s Dragon.

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

This departure towards the edge of the ISS’ neighborhood will be monitored by the COTS UHF Communication Unit (CUCU) Crew Command Panel (CCP), which was successfully checked out ahead of the departure events.

The third burn will be the larger of the firings, which will send Dragon outside of the approach ellipsoid, at which point SpaceX controllers inside MCC-X at SpaceX’s Californian facility will take full control of the mission.

Dragon Flying on orbit, via L2Dragon then enjoyed a free-flying phase on-orbit for around five hours, during which time she completed a critical action – closure of the GNC bay door, to which the FRGF is mounted – before conducting the de-orbit burn at 14:43 Eastern.

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

The umbilical between Dragon and her Trunk then disengaged, prior to the Trunk separating from the Dragon capsule.

As the spacecraft moved into Entry Interface (EI) she was protected by the 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 deployed, followed by Dragon’s main parachutes, easing the vehicle to a splashdown in the Pacific Ocean off the coast of California at around 15:38 Eastern.

Three main recovery boats soon arrived on station, with fast boats racing to meet the Dragon shortly after she hit the water, allowing for the recovery procedures to begin.

The vehicle was powered down and then hooked up to the recover assets.

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

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

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