CRS-6 Dragon successfully completes ISS berthing

by Chris Bergin

While the internet community continues its fascination with the Falcon 9 First Stage landing attempt on the Autonomous Spaceport Drone Ship (ASDS), SpaceX’s primary mission objective – the CRS-6/SpX-6 Dragon – completed berthing operations with the International Space Station (ISS). The spacecraft was grappled by the Station’s “Big Arm” at 6:55am Eastern on Friday, ahead of being attached to the orbital outpost.


The SpX-6/CRS-6 Dragon began her journey to the ISS atop of her Falcon 9 v1.1 partner earlier this week, via another smooth ascent uphill – confirmed by the quick look status report into the rocket’s performance.

Dragon, fast becoming a Station veteran, then completed her on orbit operations and checkouts, including the spreading of her solar arrays shortly after separation.

Per the primary mission objectives, everything went by the book through this first element of the CRS-6 mission. However, a large amount of focus was placed on the First Stage that had been involved in the opening few minutes of the ride into space.

2015-04-16-225157This was due to the stage making another landing attempt on SpaceX’s landing platform vessel sporting the SpaceX’s logo as a target for the landing legs of the core stage.

The first stage made its best landing attempt to date but was unable to remain upright after hitting the deck with too much velocity and at a slight angle, resulting in the loss of the stage.

Another attempt will be made during the CRS-7 launch.

Meanwhile, Dragon continued her orbital journey, conducting numerous burns to position herself for Friday’s arrival, 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.

Dragon had to refine her approach to the Station via an orbital dance that involved the coelliptic (CE) burn, with the 350 second firing resulting in a change of velocity of 96 mph.

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

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

4f5518b15ac4e3ac1c74dff2f7496f32The arrival into the ISS’ back yard involves 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.

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

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.

Dragon through RWS with CUCU support, via L2The 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 to 100 meters distance from the Station was given, where she automatically paused. The next step was to close in on the 30 meters mark.

At all points, the ability to abort could be ordered by controllers on the ground, the Dragon herself and the ISS crew – the latter option 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 and Dragon during proximity operations and a command security between ISS and the spacecraft.

This is a hugely important capability that protects the Station from being impacted by a misbehaving visitor.

Z5Moving on from 30m to the Capture Point – 10 meters out – Dragon automatically held position again, allowing the ISS’ robotic assets – by then already translated to the pre-capture position – to make the move towards the Dragon via controls in the RWS inside the Cupola.

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 – under the control of Italian astronaut Samantha Cristoforetti – translated over the Grapple Fixture (GF) pin on Dragon to trigger the capture sequence ahead of pre-berthing.

Capture occurred at 6:55am Eastern.

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 for 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 was then 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 marked Dragon’s berthing with the ISS.

The operation was completed around 30 minutes ahead of schedule.

2015-04-16-225554With all of the ISS berthing milestones part of the pre-planned schedule, the ISS crew were then left with the decision of when to open the hatch to the Dragon, which can vary depending on the allowances in the crew’s timeline.

They began the operation on Saturday.

The cargo aboard CRS-6 has a total mass of 2,015 kilograms (4,387 lb; 1,898 kg or 4,184 lb without packaging).

This includes 500 kilograms (1,102 lb) of items and provisions for the station’s crew, 518 kilograms (1,142 lb) of station hardware and equipment, 16 kilograms (35 lb) of computer and electronic equipment and 23 kilograms (51 lb) of hardware for EVAs.

The remaining 844 kilograms (1,860 lb) of the Dragon’s payload is taken up by scientific hardware and experiments, including critical materials to directly support about 40 of the more than 250 science and research investigations that will occur during Expeditions 43 and 44.

Also making the trip is a new espresso machine for space station crews and a new team of mousetronauts in the Rodent Research-2 payload.

After five weeks of docked operations, Dragon will return with more than 3,000 pounds of cargo, including crew supplies, hardware and computer resources, science experiments, space station hardware, and trash.

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

(Click here: – to view how you can access the best space flight content on the entire internet and directly support’s running costs)

Related Articles