Following Falcon 9 Saturday launch, CRS-17 Dragon arrives at the ISS

by William Graham

SpaceX’s Dragon spacecraft – on its CRS-17 resupply mission to the International Space Station – has arrived at the orbital outpost on Monday. Dragon launched on a Falcon 9 rocket from Cape Canaveral at 02:48 Eastern Time (06:48 UTC) on Saturday.

Dragon’s CRS-17 mission is being flown as part of NASA’s Commercial Resupply Services (CRS) program, which uses commercial spacecraft to deliver cargo to the space station. SpaceX and Northrop Grumman carry out these missions for NASA, using the Dragon and Cygnus spacecraft respectively.

SpaceX was originally contracted for twelve missions under the first phase of CRS in 2008, and several extensions have since increased this to twenty resupply flights. These Phase 1 missions use the original version of Dragon: additional missions awarded since 2016 under the second phase of CRS will use a cargo configuration of the Dragon v2 spacecraft.

First flown in 2010, Dragon has successfully flown sixteen missions to the International Space Station to date: a demonstration flight under NASA’s Commercial Orbital Transportation Services (COTS) program, and fifteen operational CRS flights. The CRS-7 mission, launched in 2015, failed to reach the station after the Falcon 9 rocket carrying it disintegrated during its ascent to orbit.

Dragon consists of a pressurized capsule housing most of its cargo and an unpressurized Trunk section. The Trunk, attached behind the capsule, houses the spacecraft’s solar arrays and other vehicle systems. Unpressurized cargo stored within the Trunk can be accessed in orbit from the rear of the spacecraft, using the space station’s robotic arm.

The Dragon capsule is reusable and is recovered by parachute at the end of each mission. The Dragon that flew this mission, numbered C113.2, is the same capsule that was used for the CRS-12 mission in 2017. During that mission, Dragon spent a month berthed to the space station before returning to Earth for a splashdown in the Pacific Ocean. C113 was the final first-generation Dragon spacecraft to be built and all flights since CRS-12 have used previously-flown Dragons.

Only Dragon’s capsule is recovered. The Trunk is jettisoned after Dragon completes its deorbit burn, and is left to burn up as it reenters the atmosphere.

The CRS-17 launch had been scheduled to take place on Wednesday but slipped – initially to Friday – to give NASA time to resolve electrical issues that had been affecting the space station.

Dragon provides capacity to transport both pressurized and unpressurized cargo to the International Space Station and is the only vessel currently capable of returning pressurized cargo to Earth from the outpost.

For this launch, the spacecraft’s pressurized capsule is loaded with 1,517 kilograms (3,344 lb) of equipment and supplies, while a further 965 kilograms (2,128 lb) of unpressurized cargo is stored in the spacecraft’s trunk section, for a total of 2,482 kilograms (5,472 lb).

The pressurized cargo includes 726 kilograms (1,601 lb) of scientific equipment and experiments. Research that CRS-17 will deliver to the station includes Tissue Chips in Space – an investigation that will use three-dimensional cultures of human tissue to study how cells respond to factors such as drugs or diseases in the microgravity environment.

The experiment launching to the station aboard CRS-17 is the second in this series, the first having flown aboard CRS-16 last December.

Another experiment, Photobioreactor, will study the feasibility of using biological processes as part of the life support system on future long-duration space missions.

The experiment will cultivate microscopic algae, Chlorella vulgaris, aboard the space station’s Destiny laboratory. The algae consume carbon dioxide and give off oxygen, while also producing nutritional biomass that could be consumed by astronauts.

Dragon has also delivered the Hermes Facility to the space station. Hermes is a ground-controlled laboratory which will allow scientists on Earth to conduct research aboard the space station. Experiments can be installed in the Hermes Facility via interchangeable “cassettes” which scientists can control remotely. The first experiment to use this facility will be a materials and microgravity study exploring how particles interact in the regolith of small asteroids.

As well as science, the CRS-17 mission delivered 338 kilograms (745 pounds) of supplies and provisions for the space station’s crew, 357 kilograms (787 lb) of hardware for the US and International segments of the station, 75 kilograms (165 lb) of computer equipment, 10 kilograms (22 lb) of hardware to support EVAs and 11 kilograms (24 lb) of hardware that is being flown on behalf of the Russian Federal Space Agency, Roskosmos.

Dragon’s cargo includes components for the space station’s new water storage system, filters for a new waste management system, wire harnesses and depressurization indicators that will be used to support future commercial crew flights and the POLARS system that will facilitate transportation of scientific experiments at low temperatures.

Once Dragon’s cargo has been unloaded, the capsule will be filled with equipment to be returned to Earth. Because its capsule is designed to be recovered, Dragon provides NASA and their international partners with the ability to return failed hardware to Earth for investigation, experiments for further analysis, and equipment to be refurbished and reflown.

Dragon’s unpressurized Trunk contains hardware that will be mounted on the outside of the space station. This includes the Orbiting Carbon Observatory 3 (OCO-3) payload, which will use three spectrometers to measure the density and distribution of carbon dioxide in Earth’s atmosphere.

OCO-3 uses an instrument that was built as a backup for the stand-alone OCO-2 mission, fitted to a pallet that can be mounted on the Kibo module’s exposed facility and expected to operate for three years.

OCO-3 – via NASA

OCO-3 will join the OCO-2 satellite, which was launched aboard a Delta II rocket in 2014, in collecting data that is vital to understanding Earth’s carbon cycle and its impact on the climate. OCO-2 was a replacement for the original OCO satellite, lost at launch in 2009 after its Taurus carrier rocket’s payload fairing failed to separate.

The Trunk also contains Space Test Program – Houston 6 (STP-H6), a package of eight technology development and demonstration payloads for the US Air Force’s Space Test Program (STP). STP-H6 includes experiments that will test instruments for ionospheric and plasma research, demonstrating computing resources for in-orbit image processing, validating the use of modulated X-rays for communications and testing systems for future satellites.

STP-H6 will be attached to one of the ExPRESS Logistics Carriers (ELCs) fixed to the space station’s truss.

Dragon launched atop SpaceX’s Falcon 9 rocket, flying from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Air Force Station in Florida. Like Dragon, the Falcon 9 was designed with reusability in mind, and the rocket’s first stage can be recovered and reflown on subsequent missions. Falcon 9 is the only reusable rocket currently flying that is capable of reaching orbit.

Falcon 9 is a two-stage rocket which first flew in its original form in June 2010. SpaceX has refined the design several times since its debut, resulting in the Falcon 9 Block 5 vehicle that is flying today. Introduced one year ago, Block 5 is the ultimate culmination of SpaceX’s upgrades to the rocket, benefiting from the experience that SpaceX gained with earlier iterations to produce a vehicle with a greater payload capacity, facility for recovery and reuse of its first stage, and meeting NASA’s requirements for human-rating ahead of planned Crew Dragon missions starting later this year.

The launch was the seventieth flight of Falcon 9, not including two launches of the closely-related Falcon Heavy which clusters three of the rocket’s first stage boosters together to accommodate missions with larger payloads or to higher orbits than the standard Falcon 9 can reach.

For the CRS-17 mission, a newly-built Falcon 9 was used. Core 1056.1 made its first flight but has been recovered after this launch for use of further missions. After separation, the booster performs a series of additional engine firings for a controlled, powered, landing either on a concrete pad back at the launch site or aboard a floating platform – an Autonomous Spaceport Drone Ship (ASDS) – located downrange.

The choice between return to launch site (RTLS) and ASDS is normally driven by mission requirements – launches with heavier payloads or targeting higher orbits, where more of the rocket’s performance is needed to boost the payload towards orbit – typically call for recovery to occur downrange.

While normally Falcon is able to return to the launch site after CRS launches, an incident that occurred during testing of SpaceX’s Crew Dragon spacecraft late last month means that the Landing Zone is currently out of action. On 20 April, during a series tests on its propulsion system, the Dragon capsule that had previously flown the DM-1 mission was destroyed by an apparent explosion.

Dragon’s test stand is located as part of the same complex as the two Falcon landing pads, and SpaceX has opted not to attempt the landing there while they ensure that all pieces of debris from the accident are cataloged and recovered to aid the investigation.

Instead, the Autonomous Spaceport Drone Ship (ASDS) Of Course I Still Love You was deployed a few miles off the coast of Florida. Falcon’s first stage performed a boostback maneuver to turn back towards land after separating as it would for a return-to-launch-site mission, for recovery offshore using the drone ship. This differs from a normal drone ship recovery, where no boostback burn occurs and recovery happens far out in the Atlantic along the stage’s established trajectory.

OCISLY – Via SpaceX

Both stages of the Falcon 9 consume RP-1 kerosene propellant and liquid oxygen. Loading of the propellant and oxygen into the rocket’s first stage, and of propellant into the second stage, began about 35 minutes before liftoff. Second stage oxidizer loading began nineteen minutes later. Once the tanks reached their fill levels, topping off continued until the final minutes of the countdown to replace oxygen as it boils off.

Dragon transferred to internal power just under eight minutes before launch, while at the seven-minute mark in the countdown Falcon’s first stage engines chilled down in preparation for flight. A few minutes later the arms of the Strongback, or Transporter-Erector, which was used to transport Falcon to the pad and raise it to the vertical position, opened and the Strongback rotated 1.5 degrees away from the rocket. The Strongback remained in this position until liftoff, when it rapidly moved to its fully-retracted position.

The last minute of the countdown saw Falcon’s propellant tanks brought up to flight pressure and the rocket’s onboard computers conduct their final automated checks. SpaceX’s Launch Director gave a final “go” for launch at the 45-second mark. Three seconds before liftoff the first stage’s nine Merlin-1D engines began their ignition sequence and Falcon left her launch pad at the zero mark in the count.

Climbing away from Cape Canaveral, Falcon 9 took about one minute to reach the speed of sound – Mach 1. Twelve seconds later it encountered the area of maximum dynamic pressure – Max-Q – where experienced peak loads due to aerodynamic forces. The first stage burned for two minutes and seventeen seconds before Main Engine Cutoff (MECO), where its engines shut down having completed their role in boosting Dragon into space.

CRS-15 launches from SLC-40 – by Nathan Barker for NSF/L2

Stage separation occurred four seconds later, and while the second stage continued towards orbit with Dragon, the first stage reoriented itself for the first maneuver on its journey back to Earth. Seven seconds after separation, the Merlin Vacuum (MVac) engine on Falcon’s second stage ignited for its first and only burn of the mission.

Falcon’s first stage landed on the drone ship before the second stage reaches orbit. The first step in accomplishing this is the boostback burn, which reverses the booster’s course back towards Florida. As soon as it separated, Core 1056 turned around to orient itself for this burn, which began thirteen seconds after staging using three engines.

With its boostback complete the core deployed gridfins that help guide its descent through the atmosphere. Its next major event was reentry into the atmosphere, with an entry burn beginning at six minutes and 39 seconds mission elapsed time to protect the stage from heating as it passes back into the dense layers of the atmosphere.

Landing aboard Of Course I Still Love You occurred around eight minutes and 27 seconds after liftoff, following a short landing burn of the core’s center engine. This burn arrested the stage’s descent and guide it to a soft touchdown aboard the drone ship. After landing the stage will be secured and the ASDS towed back to Port Canaveral.

Twelve seconds after the booster’s planned landing time, Falcon’s second stage concluded its six-minute, 11-second burn. Now in low Earth orbit, Dragon separated fifty-nine seconds later at the nine-minute, 38-second mark in the flight.

The spacecraft deployed its solar arrays two and a half minutes later, followed by its guidance, navigation and control (GNC) bay doors about two hours and ten minutes after separation.

Dragon used a series of thruster firings to adjust its orbit, setting up a rendezvous on Monday. After matching velocity with the space station and maneuvering within range of the CanadArm2 robot arm, Dragon was grappled by the space station and berthed at the nadir port of the station’s Harmony module.

It will remain berthed until then end of May when CanadArm2 will again be used to unberth the spacecraft and release it away from the station. Dragon will use its thrusters to perform a deorbit burn before jettisoning its trunk section, while the capsule heads for splashdown off the coast of California.

CRS-17 was the fifth launch of the year for SpaceX, following three previous Falcon 9 missions and last month’s launch of a Falcon Heavy rocket. SpaceX’s next launch is expected in less than a fortnight, when a Falcon 9 will deploy the first group of satellites for the Starlink communications constellation which SpaceX are developing in-house. The next launch to the Space Station is currently expected to be SpaceX’s CRS-18 mission, slated to fly on 8 July.

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