SpaceX’s CRS-11 Dragon captured by Station for a second time

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For the first time since 2011, a previously-flown spacecraft has arrived at the International Space Station.  The CRS-11 Dragon from SpaceX – which was previously used on the CRS-4 mission in Sept.-Oct. 2014 – was capture and berthed to the ISS following a flawless 41-hour orbital rendezvous.  The capture came ahead of schedule at 09:52 EDT to be followed by berthing a few hours later.

After six years, a reused spacecraft arrives at the Station:

A stated goal of SpaceX has always been to reuse their Dragon capsules, helping the company continue to march toward its plan of introducing reusability into all aspects of spaceflight – something that will not only reduce costs and increase access to space but also greatly aid humanity’s quest of not only sending people to Mars but colonizing the planet as well.

The milestone reached Saturday afternoon when SpaceX successfully relaunched a previously flown Dragon aboard a Falcon 9 rocket toward the International Space Station marked the commencement of Dragon reuse operations – an event that will prove its merit in full over the next month as the vehicle delivers and removes thousands of pounds of supplies to and from the ISS.

With Dragon’s arrival at the Station this morning, NASA will also mark the first time that a previously flown spacecraft has berthed to the orbital outpost since the Space Shuttle Atlantis docked on the STS-135 swansong mission for the Shuttle Program on 10 July 2011.

Since the conclusion of the Shuttle Program, the ISS has been resupplied by a series of Russian Progress, European Space Agency Automated Transfer Vehicles, Japan Aerospace Exploration Agency HTVs, SpaceX’s Dragons, and Orbital ATK’s Cygnus spacecrafts.

Crewed missions have solely used the Russian Soyuz vehicles.

Notably, all of those vehicles except Dragon are designed for one-time use only.

While all Dragons were/are technically designed and built with reuse in mind, not all of them will be reused, and in the early days of Dragon flights to ISS, it was not known exactly which Dragon would be the first to be reused.

To this end, when the CRS-4 Dragon successfully completed its flight in October 2014, the milestone of reusing a Dragon was very much an in-progress goal, with SpaceX and NASA not realizing at the time that the CRS-4 Dragon would in fact be the first capsule to be reused… let alone which CRS mission it would re-fly on.

In this way, it’s worth noting that the mission patch from SpaceX for CRS-4 contained 11 stars in its backdrop – an unintentional foreshadowing of the capsule’s eventual reuse on CRS-11.

Rendezvous and berthing:

Following a flawless launch Saturday evening from LC-39A at the Kennedy Space Center, the Falcon 9 rocket successfully inserted the CRS-11 Dragon into a 51.6 degree inclination orbit and sent the spacecraft on a 41-hour rendezvous profile toward the International Space Station.

Dragon enjoyed several hours of non-propulsive flight before controllers in Hawthorne, California, commanded the vehicle to perform the Coelliptic burn, a thruster firing that altered the craft’s velocity by 44.9 m/s and fine tuned its orbit to better match that of the Station’s.

The Coelliptic burn occurred on Sunday morning and set up for two more burns Sunday afternoon, the HA1 and CE1 burns – which changed Dragon’s velocity by 10.6 m/s and 11.7 m/s, respectively.

Early Monday morning, Dragon performed the HA2 and CE2 burns in rapid succession, altering its velocity by a combined total of 4.9 m/s.

By 05:21 EDT Monday morning, Dragon was within 28 km of the International Space Station, with the craft performing the HA3 burn at 06:00 EDT, followed by two successive HA3 burns, dubbed HA3-MC1 and -MC2 burns, at 06:16:40 EDT and 06:33:20 EDT.

The CE3 burn at 06:46:10 EDT brought Dragon within 6 km from the ISS at 07:01:10 EDT.

The HA4 burn, known as the Approach Initiation burn, occurred at 07:16 EDT to begin Dragon’s final approach sequence to the Station by altering its velocity by 0.3 m/s.

Dragon then performed the minor correction HA4-MC1 and -MC2 burns at 07:32:40 EDT and 07:49:20 EDT, respectively, to continue to fine tune its approach to the Station.

The capsule arrived at the 350m hold point at 08:04 EDT, where Dragon’s thrusters matched the craft’s speed with the Station and hold Dragon in place relative to the Station – a maneuver called station-keeping.

During this time, Dragon performed a 180-degree yaw maneuver to properly orient it for grappling by the Space Station Remote Manipulator System (SSRMS) arm.

With all systems healthy aboard Dragon, the vehicle departed the 350m hold point at 08:11 EDT and reached the 250m hold point at 08:19 EDT.

Dragon remained at this location for 15 minutes before continuing its slow approach to the Station at 08:34 EDT. However, Dragon began to advance on the pre-planned timeline.

Under a nominal approach timeline, Dragon was to cross the 100m mark from the ISS at 08:51 EDT. During CRS-11, this milestone was reached ahead of schedule.

Dragon then arrived the 30m hold point just before 09:00 EDT, where held position for 20 minutes as mission controllers in Houston and Hawthorne assessed final health checks of the Dragon and issue a “go” for Dragon to proceed to its Capture Point.

Dragon was expected to depart the 30m hold point at 09:27 EDT, arriving at the 10m Capture Point at 09:44 EDT. However, these milestones were reached at 09:20 EDT and 09:37 respectively. 

Once at the Capture Point, Dragon’s thrusters fired to hold the craft in station-keeping while astronauts Peggy Whitson and Jack Fischer performed final preparations for capturing the craft with the SSRMS.

Mission Control Houston gave the “go for capture” call at 09:42 EDT, again ahead of schedule, aided by good light conditions from the orbital sunrise.

Whitson and Fischer then captured Dragon in the snares at the end of the Station’s arm at 09:52 EDT.

Had for some reason Dragon not been captured within the prime window, a backup capture window opened at 10:31:14 EDT and closes at 11:47:46 EDT.

As with all approaches to the Station, Dragon itself, the ISS crew, Mission Control Houston, or Mission Control Hawthorne could have also issued an abort to safely move Dragon away from the ISS should a problem arise.

While approach aborts are rare, one was needed during the CRS-10 approach of Dragon when the spacecraft recorded a “bad value” in an ISS State Vector and a relative GPS error inside its flight computer.

Once Dragon is safely berthed to the Station, the ISS’s three-person crew will spend the next month conducting numerous time-sensitive experiments brought up on the spacecraft.

Many of these experiments, including those with the mice and fruit flies, have to be performed while Dragon is berthed with the Station so they can return to Earth for safe recovery after Dragon splashes down in the Pacific Ocean in early July.

In all, the CRS-11 Dragon is carrying 1,069 kg (2,357 lb) of science investigations, 242 kg (534 lb) of crew supplies, 199 kg (439 lb) of vehicle hardware, 56 kg (123 lb) of spacewalk equipment, 27 kg (60 lb) of computer resources, a 325 kg (717 lb) Roll-Out Solar Array, a 372 kg (820 lb) Neutron Star Interior Composition Explorer experiment, and a 305 kg (672 lb) Multiple User System for Earth Sensing system.

Notably, the mission is lite on crew supplies, with NASA stating after CRS-11’s successful launch that the Station currently has enough consumables on board in each major category to last six months – thus allowing this Dragon to focus on science delivery and return.

(Images: SpaceX; NASA)

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