SpaceX’s Dragon spacecraft returned to flight Friday with the CRS-8 resupply mission to the International Space Station: a mission which also carries a prototype inflatable module for the outpost. The first Dragon mission since a launch failure last June, Friday’s mission lifted off from Cape Canaveral at 16:43 EDT (20:43 UTC), followed by a historic first stage landing on the ASDS.
The CRS-8 mission is the tenth flight of the Dragon spacecraft, which was developed by SpaceX to participate in NASA’s Commercial Orbital Transportation Services (COTS) program and subsequently to compete for resupply missions under the Commercial Resupply Services (CRS) program.
Dragon first flew in December 2010 – with the C1 mission; a short free-flying demonstration which completed two orbits before returning to Earth for a landing in the Pacific Ocean. The next mission, C2+, became the first to deliver cargo to the space station in May 2012.
With these demonstrations complete, six successful operational CRS missions visited the station between October 2012 and April 2015.
The seventh, and most recent, CRS mission lifted off last June however the Dragon was lost during ascent after its Falcon 9 carrier rocket suffered a structural failure of its second stage.
Falcon returned to flight last December with the successful deployment of eleven Orbcomm communications satellites.
Further launches in January and March carried the Jason-3 satellite for an international partnership of weather and scientific research organisations and the SES-9 commercial communications satellite.
Orbital Sciences’ Cygnus was also developed for the COTS program and shares CRS duties with Dragon, while a cargo version of Sierra Nevada Corporation’s Dream Chaser spacecraft is under development to enter service when the second round of CRS contracts begin at the end of the decade.
In addition to being Dragon’s return to flight, the CRS-8 launch is the first time it had flown in conjunction with the Falcon 9 “Full Thrust” version, which has replaced the Falcon 9 v1.1 that had been used previously.
Friday’s launch was the third flight of this configuration, which was previously used for December’s Orbcomm mission and the SES-9 launch in March. Overall it was the twenty-third flight of a Falcon 9.
The Full Thrust model is a further enhancement of the Falcon 9 design over the v1.1 – which was discontinued after the Jason launch.
The second stage of the vehicle has been stretched, the rocket’s engines have been uprated and the temperature at which liquid oxygen is stored has been decreased to around -207 degrees Celsius (55 Kelvin, -341 Fahrenheit), increasing its density and allowing more to be loaded into the tanks. Liquid oxygen is used to oxidise RP-1 propellant in both stages of the vehicle, producing the reaction which powers the vehicle.
These changes are geared towards increasing the rocket’s performance margins so that attempts to recover the first stage can be made on more missions, including flights to geostationary transfer orbits.
SpaceX continued its attempts to land the first stage both on land and at sea, with Friday’s launch targeting a landing atop the Autonomous Spaceport Drone Ship (ASDS) barge named “Of Course I Still Love You” in the Atlantic Ocean.
SpaceX had yet to complete a controlled landing on the barge from four attempts, until Friday.
However, this time it all went to plan as the Falcon 9 first stage completed its boostback, re-entry burn and landing burns without issue and calmly landed on the deck of the ASDS.
Slightly off center, but firmly in place, teams will next secure the stage to the deck and return the duo back to port.
The Falcon launched from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station. A former Titan III and IV launch pad, SLC-40 has hosted all but two of the Falcon 9’s launches.
The other two launches came from Space Launch Complex 4E at Vandenberg Air Force Base, a site which allows for launches into more highly-inclined orbits.
A third launch pad is being commissioned a few miles north of SLC-40, Kennedy Space Center’s Launch Complex 39A, which is expected to see its first Falcon launch later this year.
SpaceX also holds the lease to the former Launch Complex 13 to the south of SLC-40. Designated Landing Zone 1 (LZ-1) this facility is equipped for land-based recovery attempts.
The final stages of Friday’s countdown began with a poll of flight controllers to determine readiness for fuelling operations thirty-eight minutes before launch.
With controllers go to proceed, loading of RP-1 propellant and liquid oxygen began three minutes later. Loading of liquid oxygen continued throughout the countdown to replenish the oxidiser as it boils off.
The last ten minutes of the countdown were an automated sequence during which the clock cannot be stopped without resetting to the start of the sequence. At the start of this period, chilldown of the rocket’s engines began.
Seven minutes before liftoff the spacecraft was placed onto internal power with the rocket also switching to internal power shortly afterwards.
Activation and arming of the flight termination system (FTS), explosive charges used to destroy the rocket should it go off course, took place three and a half minutes in advance of liftoff.
The US Air Force’s Range Control Officer and the Launch Director gave their final approval for launch on behalf of the Eastern Range and SpaceX respectively, two minutes and a minute and a half before the end of the countdown.
At the one-minute mark the rocket’s computers were commanded to begin their final preprogramed checks, the rocket’s propellant tanks were pressurised and the launch pad water deluge system, or “Niagara”, was armed and subsequently activated.
Three seconds before launch the flight computer sent a command to the first stage’s nine Merlin-1D engines to begin their ignition sequence.
Approximately a second later the engines, arranged in an octagonal or “OctaWeb” pattern, roared to life and begin building to full thrust.
The period between ignition and liftoff allows for an automated abort to be initiated should a problem be detected at startup. With no such abort is called the Falcon lifted off when the countdown reached zero.
Climbing East out over the Atlantic Ocean, the Falcon passed through the area of maximum dynamic pressure, or Max-Q, seventy-one seconds into flight. It achieved the speed of sound, Mach 1, at around the same time. First stage powered flight lasted two and a half minutes before first stage engine cutoff.
Stage separation occurred four seconds later with second stage ignition taking place after a further seven seconds. The second stage’s single Merlin Vacuum engine made one burn to attain Dragon’s target deployment orbit.
Following its separation, the first stage made three further burns; a boostback burn approximately four minutes into the mission put it on course for the Autonomous Spaceport Drone Ship and entry burn at around the seven-minute mark slowed the stage as it reenters Earth’s atmosphere.
With all going well the final burn resulted in a powered descent onto the landing barge.
While the first stage was attempting its landing, the second continued to burn as it accelerated Dragon towards orbital velocity.
Cutoff was around ten minutes after launch with separation of the Dragon spacecraft at around the ten-and-a-half-minute mark in the flight.
A minute and a half after separating from the Falcon 9, Dragon deployed its solar arrays.
For two days following launch, Dragon will make a series of engine burns to facilitate rendezvous with the International Space Station.
With the OA-6 Cygnus mission currently berthed at the nadir port of the Unity module, it will be the first in-orbit meeting for the two CRS resupply vehicles.
The pressurised cargo being delivered to the space station by CRS-8 comes to a total mass of 1,723 kilograms (3,799 lb).
This includes 640 kg (1411 lb) of scientific equipment, 547 kg (1,206 lb) of supplies and provisions for the crew, 108 kg (238 lb) of computer equipment, 12 kg (26 lb) of hardware to support EVAs using the US Extravehicular Mobility Unit (EMU) spacesuits, 306 kg (675 lb) of hardware for the US segment of the outpost and 33 kg (73 lb) for the Russian segment.
Other experiments being carried by Dragon include Rodent Research 3, which has been funded by Eli Lilly and Co and the Center for the Advancement of Science in Space (CASIS), to study the effects of spaceflight on the musculoskeletal structure of rodents in order to test drugs which could potentially help crews on future long-term missions.
The Microchannel Diffusion experiment will study how molecules of fluids behave at a microscopic level in microgravity as an analogue to how they would behave at an atomic level on Earth.
Another experiment aboard CRS-8 is Protein Crystal Growth 4 for CASIS.
The unpressurised Trunk section of the Dragon houses the 1,413-kilogram Bigelow Expandable Activity Module, or BEAM, an inflatable module which will be attached to the station for two years to see how the technology performs in conjunction with the space station.
The module will not regularly be manned however crew will venture inside from time to time.
Developed by Bigelow Aerospace, BEAM builds upon technology demonstrated by Bigelow’s two unmanned demonstration missions, Genesis I and II, which were launched by Dnepr rockets in July 2006 and June 2007 and completed successful missions, with both spacecraft remaining in orbit.
Following the arrival of the CRS-8 spacecraft at the International Space Station, BEAM will be extracted from the Trunk section by the station’s robotic arm and berthed at the aft port of the Tranquillity module; connecting to the space station via a Common Berthing Mechanism.
Following berthing, the module will be inflated to its full size; increasing from 2.16 metres to 4.01 metres (7.09 to 13.2 feet) in length and 2.36 to 3.23 metres (7.74 to 10.6 ft) in diameter. Expanded it will have a total volume of sixteen cubic metres (565 cubic feet).
BEAM is the first pressurised module to be added to the International Space Station in over five years; the last being the Leonardo module which was delivered by Space Shuttle Discovery’s final mission, STS-133, in February 2011. Russia’s Nauka module, which was originally slated for launch in 2007, has been continually delayed and is now not expected to join the outpost until next year at the earliest.
CRS-8 is scheduled for a four-week visit to the space station. Towards the end of this time it will be loaded with items for return to earth, including completed scientific research and samples, unwanted hardware, trash and a faulty spacesuit – EMU-3011 – which NASA hope to investigate following a water leak that occurred while Tim Kopra was making a spacewalk in January.
Dragon is the only resupply craft designed to survive reentry into Earth’s atmosphere and be recovered, so it provides the ISS program with its only opportunities to return large items of cargo to Earth.
After hatches are closed, Dragon will be unberthed using CanadArm2 and released from the station. Following a series of separation burns it will be deorbited and the expendable trunk section jettisoned.
The pressurised module will reenter the atmosphere before descending under parachute for recovery in the Pacific Ocean off the coast of California.
Friday’s launch was the third of the year for SpaceX and its Falcon 9. The next Falcon launch is expected to take place late this month with the JCSAT-14 communications satellite, while a launch next month will carry Eutelsat 117 West B into a geostationary transfer orbit.
The next CRS mission is currently scheduled for 24 June. However, Orbital Sciences’ next Cygnus mission is also targeting this date and it is unlikely that both would launch on the same day. A further Dragon launch is expected around August.
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