SpaceX conducted its second launch in barely 48 hours on Wednesday, with their Falcon 9 rocket boosting a Dragon spacecraft on the first leg of its cargo run to the International Space Station. Liftoff of the CRS-16 mission took place from Cape Canaveral’s Space Launch Complex 40 at 13:16 Eastern Time (18:16 UTC). The booster lost control during its return to LZ-1, but managed to soft land in the water just off the coast and appears to be intact.

The launch, SpaceX’s twentieth of the year and the nineteenth to use a Falcon 9 vehicle, came just 48 hours and four minutes after another Falcon 9 lifted off from California on Monday to deploy its SSO-A payload. Notably, the CRS-16 Dragon was set to launch just 24 hours after the SSO-A mission, before an unusual issue called for a 24 hour delay.

With CRS-16’s Dragon hosting not just hardware and experiments, but also mice, the food bars set to keep the rodents fed during their mission were found to be moldy. As such, they required changing out, resulting in a rush to fly in replacement food before Dragon could be sealed ahead of being erected at the pad on the Falcon 9.

Dragon’s CRS-16 mission is the eighteenth flight of SpaceX’s cargo spacecraft, which made its debut with a test flight in December 2010 and flew its first mission to the space station in May 2012 – both under NASA’s Commercial Orbital Transportation Services (COTS) program. Subsequent missions have been conducted under a Commercial Resupply Services (CRS) contract, which was initially awarded in 2008.

SpaceX was originally contracted for twelve resupply missions, however this has since been extended twice – CRS-16 will be the first of five missions under the last extension, awarded in December 2015, after which a new CRS2 contract will come into effect.

Aside from the crewed Soyuz, Dragon is the only spacecraft currently servicing the International Space Station that is designed to be recovered at the end of its mission. This has made it invaluable in bringing cargo back to Earth as well as for delivering it to orbit and has also enabled SpaceX to refurbish each Dragon for multiple trips into space.

The CRS-16 mission is the second flight for Dragon C112, which first flew in last year’s CRS-10 mission. On its previous mission, Dragon spent a month in orbit including 23 days berthed to the Harmony module of the space station. The duration of the CRS-16 mission is still to be finalized but is expected to be around five weeks.

The Dragon spacecraft is divided into two sections: a pressurized capsule and an unpressurized trunk section. The capsule contains 1,598 kilograms (3,523 lb) of cargo to be unloaded by the astronauts aboard the space station, while the trunk carries additional payloads for attachment to the outside of the ISS and houses critical vehicle systems including Dragon’s two solar arrays. The capsule is the only part of Dragon that is recovered; the trunk is jettisoned and burns up when it reenters Earth’s atmosphere.

The pressurised cargo aboard Dragon includes 304 kilograms (670 lb) of provisions for the crew, 191 kilograms (421 lb) of hardware for the US and international segments of the station and 11 kilograms (24 lb) for the Russian segment, 40 kilograms (88 lb) of computer equipment, 15 kilograms (33 lb) of hardware to support spacewalks and 1,037 kilograms (2,286 lb) of scientific equipment and new experiments.

In the Dragon’s Trunk are two payloads that will be mounted to the outside of the space station. The Global Ecosystem Dynamics Investigation (GEDI) will use laser ranging to study the three-dimensional structure of features on the Earth’s surface such as forests, snowpacks and glaciers. GEDI consists of a LIDAR instrument which will use the reflection of light pulses to build up a profile of surface elevations. The instrument will be mounted on the Exposed Facility (JEM-EF) of the Japanese Experiment Module, Kibo.

Robotic Refuelling Mission 3 (RRM3) will serve as a demonstrator for future satellite servicing and long-duration space missions. It will test for the first time in orbit the transfer of a cryogenic propellant – liquid methane – between two tanks via a hose attached in space. RRM3 carries 42 liters (89 US pints, 74 Imperial pints) of methane and will attempt to verify that this can be stored for up to six months without any boiloff and that it can be transferred to another, empty, tank without any loss.

The Dextre manipulator, attached to the space station’s robotic arm, will be used to prepare and connect the two tanks for the refueling demonstration, including attaching a hose. RRM3 builds on the success of two previous demonstration missions which tested techniques for refueling, without transferring propellant.

Dragon is also carrying several small satellites – CubeSats – which will be deployed from the space station using a NanoRacks deployer and the airlock of the Kibo module. CubeSat Assessment and Test, or CATSat, will use two CubeSats to conduct a communications technology experiment. The satellites are being operated by the Applied Physics Laboratory at Johns Hopkins University on behalf of the US Government.

Delphini 1, also known as AUSAT-1, is a single-unit CubeSat built by students at Denmark’s Aarhus University using a kit provided by GomSpace. The satellite carries a camera to record images of the Earth from space, however its primary objective is to give the university’s students experience in building and operating their spacecraft.

The University of Southern Indiana’s Undergraduate Nano Ionospheric Temperature Explorer (UNITE) satellite is also aboard CRS-16. This is a three-unit CubeSat carrying temperature sensors, a Langmuir probe and a GPS receiver. The satellite will be used to build and validate models of plasma densities and temperatures in the lower regions of Earth’s ionosphere. By tracking the satellite’s orbit, the mission will also help to improve models of orbital decay for small satellites.

TechEdSat-8 is a partnership between NASA, the San Jose State University and the University of Idaho, using a six-unit CubeSat in the uncommon 10 by 10 by 60 centimeter (3.9 x 3.9 x 23.6 inches) form factor. The satellite will test a device called Exo-Brake, which is designed to increase – and control – the rate of orbital decay for the satellite by controlling its drag profile.

Another payload, SlingShot, is designed to aid future CubeSat deployments. This will be attached to the berthing mechanism of a Northrop Grumman Cygnus spacecraft – another cargo vehicle which performs CRS resupply missions to the station – and used to release up to eighteen small satellites from the Cygnus after it departs from the space station.

The CRS-16 launch was the sixty-fifth flight for SpaceX’s Falcon 9 rocket. First flown in 2010, Falcon 9 is a two-stage, partially-reusable, liquid-fuelled rocket. Falcon 9 launched from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station on Florida’s Space Coast.

Complex 40 is a former Titan launch pad which was built in the 1960s for the Titan IIIC rocket, and subsequently supported Titan III(34)D, Commercial Titan III and Titan IV launches before being leased to SpaceX in 2007 for the Falcon 9. It is one of two Falcon launch pads on the East Coast, alongside Launch Complex 39A (LC-39A) at the nearby Kennedy Space Center.

A third Falcon 9 launch complex is located at Vandenberg Air Force Base on the West Coast, facilitating missions to more highly-inclined orbits than can be safely reached from Florida.

Falcon is assembled horizontally in a hangar near its launch pad, with the first and second stages being mated before the rocket is rolled out for a static fire test, which tests fuelling and countdown processes up to and including a brief test-firing of the rocket’s first stage engines. This was conducted successfully on Friday night, after which Falcon returned to its hangar to allow Dragon to be attached.

A Transporter-Erector (T/E), or Strongback, is used to transport Falcon to its launch pad, raise it to the vertical and provide umbilical connections up until liftoff.

While Falcon 9 is designed to be partially reusable, with the first stage capable of making multiple launches, this launch will use a newly-built rocket. The first stage, Core 1050, was expected to return to Cape Canaveral after separating from the second stage, allowing it to be flown again with other payloads in the future.

Fuelling the Falcon for the launch began 35 minutes before liftoff with loading of RP-1 propellant into both the first and second stages and of liquid oxygen – which is the oxidizer – into the first stage tanks. Liquid oxygen began to be loaded onto the second stage sixteen minutes before launch.

Falcon 9’s first stage is powered by nine Merlin-1D engines, arranged in an octagonal pattern known as the OctaWeb. The engines began their ignition sequence three seconds before launch, with liftoff timed for the zero mark in the countdown.

For this flight the launch window was instantaneous, so had Falcon not been able to lift off at the exact T-0, the opportunity would have been scrubbed and pushed back by at least a day.

After clearing its launch pad, Falcon maneuvered onto a north-easterly track out over the Atlantic Ocean, passing through the area of maximum dynamic pressure, or Max-Q, fifty-eight seconds into the mission. Two minutes and 23 seconds into flight the first stage – Core 1050 – shut down its engines.

Three seconds later the two stages separated from each other, with the first stage beginning its return to Earth while the second continued towards orbit with Dragon.

Seven seconds after stage separation, Falcon’s second stage ignited its single Merlin Vacuum (MVac) engine. A variant of the Merlin-1D optimized to operate in the vacuum of space, this made just one burn to place Dragon into its target orbit. This burn lasted six minutes and 19 seconds, with Dragon separating from the second stage one minute after cutoff. Deployment of Dragon’s solar arrays commenced sixty-nine seconds after spacecraft separation.

While the second stage was still burning, the first stage will fired its engines three more times to control its return to Earth. The first of these firings was the boostback burn, beginning thirteen seconds after staging to change the vehicle’s course and take it back towards Cape Canaveral. Three minutes and 56 seconds later an entry burn slowed the stage as it passed back into the atmosphere, limiting damage from heating.

Finally, about ninety seconds after the entry burn, a restart of its center engine for a landing burn to ensure a soft touchdown at Landing Zone 1 (LZ-1) is usually the case.

The landing pad at Cape Canaveral was built on the site of former Atlas-Agena Launch Complex 13 (LC-13). It was the site of the first successful recovery of a Falcon 9 core in December 2015 and has supported numerous successful landings since. Landing Zone 1 is typically used where Falcon is deploying a relatively small payload to a low orbit, where the rocket has sufficient fuel reserves to fly back to the coast. For higher-energy missions SpaceX can deploy an Autonomous Spaceport Drone Ship (ASDS) – a converted barge – downrange as a floating landing pad.

However, a problem with a grid fin saw the stage lose control of its return to LZ-1, but still managed to slow down enough to land softly in the water. Elon Musk noted they are looking to recover this booster via ships.

Dragon will arrive at the International Space Station at around 11:00 UTC on Saturday. European Space Agency astronaut Alexander Gerst will use the space station’s CanadArm2 robotic arm to capture the spacecraft and attach – or berth – it to the Harmony module. Dragon will be berthed to the nadir (Earth-facing) port of Harmony for the duration of its stay at the ISS. Upon its departure, CanadArm2 will again be used to unberth Dragon and to release it for the return to Earth.

The launch was the 102nd of 2018 but owing to two failures in October if it is successful it will be the hundredth to reach orbit. Falcon 9 has contributed nineteen launches – including that of CRS-16 – to the year’s total, while SpaceX’s Falcon Heavy rocket, which is based on the Falcon 9, also made its first flight this year.

An increase in commercial satellite launches, spearheaded by SpaceX, along with China launching more satellites than in previous years has led to an increase in the worldwide launch rate over the last few years, with Monday’s liftoff of Soyuz MS-11 taking the yearly global launch count over 100 for the first time since 1990. Because only launches that reach orbit are cataloged or assigned international designators, upon reaching orbit Dragon will be assigned the designation 2018-100A.

The CRS-16 launch is expected to be SpaceX’s penultimate mission of the year, with another Falcon 9 slated to loft the US Air Force’s first Block III Global Positioning System (GPS) satellite towards the middle of December.

Dragon’s next CRS mission is currently scheduled to lift off in mid-February, however before this SpaceX plan to conduct their first unmanned test flight of a new version of Dragon that will carry astronauts to the space station. This Crew Dragon demonstration flight is expected no earlier than mid-January.

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