The latest SpaceX Dragon – and her crew of “Mousetronauts” – arrived at the International Space Station (ISS) on Tuesday. The orbital ballet between the giant orbital outpost and the commercial spacecraft resulted in the CRS-4 Dragon being captured by the Station’s “big arm” at 06:52 Eastern, ahead of berthing operations that were completed a few hours later.



Day of the CRS-4 Dragon:

The SpX-4/CRS-4 Dragon began her journey to the ISS atop of her Falcon 9 v1.1 partner on Sunday morning, a rocket that was launching just a fortnight after the previous SpaceX launch from SLC-40 at Cape Canaveral.

The “quick look” review of the duo’s performance during the ride uphill showed no major issues, with only inertial measurement problem on the Dragon noted as failed during ascent, per a NASA Mission Management Team (MMT) meeting.

With built-in redundancy, Dragon has merrily continued her orbital journey to catch up with the ISS, with the MMT praising the performance of the spacecraft.

The Dragon has been conducting numerous burns to position herself for Tuesday’s big day, with her propulsion system – a set of four “quads” of thrusters – successfully completing a priming phase, ahead of bringing the thruster systems up to operation via the pressurizing the fuel tanks and injection of gaseous helium.

The first burn completed was the coelliptic (CE) burn, with the 350 second firing resulting in a change of velocity of 96 mph.

An “Out Of Plane” burn was followed by the first Height Adjustment burn (HA1), with the 218 second firing resulting in a 34 mph change to the delta velocity.

Another coelliptic burn (CE1) was followed by two shorter burns, as Dragon chased down the ISS.

The arrival into the ISS’ back yard involved a whole series of thruster firings, each taking her closer to the station; holding at distances of 2,500, 1,200, 250, 30 and 10 meters, before finally being grappled by the Canadarm2 Remote Manipulator System, and attached to the nadir port of the Harmony module.

The initial series of finite maneuvers brought Dragon to just 2.5 km below ISS. A Go/No-Go was performed for the HA2/CE2 burn pair bringing Dragon to 1.2 km below ISS.

The HA3/CE3 burn pair, using RGPS and configured with the ISS’ own GPS system, was then conducted, followed by the HA4 (Ai) burn, taking Dragon inside the corridor where the crew began to monitor the spacecraft’s approach.

The approach was aided by Dragon’s LIDAR system, a key element of hardware that has a heritage of testing via the Space Shuttle Discovery during her STS-133 mission.

With both SpaceX mission control (MCC-X) in California, and NASA’s ISS Flight Control Room (FCR) in Houston monitoring, Dragon continued her approach and held at 250 meters distance from the Station.

With all systems proving to be nominal, a “Go” to approach 100 meters distance from the Station was given where she automatically paused. The next step was to close in on 30 meters distance.

At all points, the ability to abort could have been made by controllers on the ground, the Dragon herself and the ISS crew – via the Commercial Orbital Transportation Services (COTS) Ultra High Frequency (UHF) Communication Unit, or CUCU, which rode in the middeck stowage locker on Atlantis during STS-129 late in 2009, before being handed over to ISS crew members ahead of the Dragon flights.

The CUCU provides a bi-directional, half-duplex communications link between Dragon and ISS using existing ISS UHF Space to Space Station Radio (SSSR) antennas, which provides a communication path between MCC-X (SpaceX) and Dragon during proximity operations and a command security between ISS and Dragon.

Proceeding from 30m to the Capture Point at 10 meters out, Dragon automatically held position again, allowing the ISS’ robotic assets – already translated to the pre-capture position – to make the move towards the Dragon via controls in the RWS inside the Cupola, which was fully operational for this event, despite it’s recent MMOD strike.

Upon receiving the “Go for Capture” call from Houston, the ISS crew armed the SSRMS capture command and began tracking the vehicle through the camera on the Latching End Effector (LEE) of the SSRMS, as overviewed in a detailed presentation available in L2 – Link).



With the ISS’ thrusters inhibited and Dragon confirmed to be in free drift, the arm’s LEE was translated over the Grapple Fixture (GF) pin on Dragon to trigger the capture sequence ahead of pre-berthing.

Capture occurred at 10:52 GMT.

The Dragon, secured by the SSRMS, was then carefully translated to the pre-install set-up position, 3.5 meters away from the Station’s module, allowing the crew to take camcorder and camera footage of the vehicle through the Node 2 windows.

This footage will be downlinked to the ground for engineers to evaluate the condition of the Dragon spacecraft.

The SSRMS translated to the second pre-install position, at a distance of 1.5 meters out. Desats were inhibited prior to the translation of the Dragon into Common Berthing Module (CBM) interface to begin the securing of the spacecraft to the ISS.

A “Go” at this point was marked by all four Ready To Latch (RTL) indicators providing confirmation on the RWS panel.

As has been seen with previous Dragon arrivals – and indeed new additions to the Station itself – the spacecraft was put through first stage capture tasks, allowing the SSRMS to go limp, ahead of second stage capture that officially mark Dragon’s berthing with the ISS.

Berthing operations were complete at 13:21 GMT.

With all of the ISS berthing milestones part of the pre-planned schedule, the ISS crew will decide when to open the hatch to the Dragon, which can vary depending on the allowances in the crew’s timeline.

Along with carrying two Extravehicular Mobility Unit (EMU) Long Life Batteries (LLBs). The Dragon is also delivering the ISS-RapidScat, inside her unpressurized Trunk compartment.

The experiment will be attached to the Station’s Columbus laboratory, via the use of the Station’s robotic assets.

The Dragon also contains 20 mice that will take residence on the orbital outpost.

The “Mousetronauts” – which have earned some fame in the mass media coverage of the mission – are housed 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 being delivered alongside the multitude of food, clothing, equipment, experiments and supplies for the ISS and her crew is a 3D printer.

The printer was set to be launched on CRS-5/SpX-5 mission, but achieved all of its required NASA checks to earn a ticket on the upcoming Dragon.

3D Printing is a maturing technology and should eventually provide the ISS with the ability to “print” a select amount of replacement parts, in situ.

This technology will be vital for future explorers in deep space, where ISS-style cargo runs won’t be readily available.

SpaceX is also a big fan of 3D printing, with parts for the SuperDraco thrusters on the Dragon V2 “printed” in this manner. L2 sources also note that parts for SpaceX’s next generation engine, the Raptor, are currently being 3D printed at the company’s Hawthorne base in California.

(Images: SpaceX, NASA and L2’s hundreds of unreleased hi-res Dragon ISS mission photos.)

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