SpaceX launches historic DM-1 mission, Dragon 2 on first flight to the ISS

by William Graham

SpaceX took a major step towards ending the United States’ human spaceflight gap Saturday, with the launch of their Crew Dragon spacecraft on its first demonstration flight. Flying without astronauts aboard for its Demo-1 test flight, Crew Dragon lifted off from the Kennedy Space Center at 02:49:03 Eastern Time (07:49 UTC) atop a Falcon 9 rocket.

Saturday’s launch has been years in the making and also represents a step forward¬†for SpaceX’s ambition of taking humans to Mars through the demonstration of a spacecraft that can carry a crew to orbit and return them safely to the Earth – albeit on a smaller scale than the Starship vehicle that SpaceX plans to develop for Mars missions.

Dragon 2 on the pad – via Thomas Burghardt for NSF/L2

In the shorter term, Demo-1 – or DM-1 – will complete qualification objectives for NASA’s Commercial Crew Development program that – subject to a separate test of the spacecraft’s launch abort system – will put Dragon in good stead to carry its first crew to the International Space Station (ISS) later this year.

Crew Dragon – which is also known as Dragon 2 – is an evolution of the current Dragon spacecraft used for cargo and logistics missions to the space station under Commercial Resupply Services (CRS) contracts. In this guise Dragon has already flown eighteen times – making two test flights under NASA’s Commercial Orbital Transportation Services (COTS) program, before beginning operational cargo delivery flights under CRS.

Dragon’s first flight occurred in December 2010, when the spacecraft completed three orbits around the Earth before a successful splashdown in the Pacific Ocean. Seventeen months later, the C2+ demo flight saw Dragon fly to the International Space Station for the first time. CRS missions began in October 2012 and will continue until next year, when a cargo version of Dragon 2 will take over under the next phase of the CRS contracts.

Dragon is named after Puff the Magic Dragon, referencing skepticism that SpaceX would be able to realize its ambitions – in the words of founder Elon Musk “people said I was high if though [sic] it could work, so I named it after their insult”. The Falcon rocket that carries it is named after the Millennium Falcon from Star Wars.

Like the existing version of Dragon, Dragon 2 consists of a pressurized capsule and an unpressurized trunk. The capsule can seat up to seven astronauts and can be reused for future missions after a successful landing. Although SpaceX considered land-based landings during the early stages of Crew Dragon’s development, they have settled on splashdown and recovery at sea, like the current version of Dragon.

Power is generated by solar panels mounted on the outside of the Trunk. This differs from the current Dragon, which uses deployable solar arrays. Another difference between the two spacecraft is the nosecone, which on Dragon 2 hinges open to provide access to the spacecraft’s docking port. Earlier Dragons jettison their nosecones to reveal a Common Berthing Mechanism (CBM).

Crew Dragon’s use of the NASA Docking System (NDS) instead of the Common Berthing Mechanism allows it to dock with and undock from the space station directly, under its own control. The berthing process used with the CBM requires Dragon to hold position close to the station, where it is captured and positioned by the station’s robotic arm. For a crewed spacecraft, which may need to facilitate a quick exit for its crew should an emergency occur, docking is preferred to berthing.

Dragon V2 also incorporates eight SuperDraco thrusters – liquid-fuelled engines which serve as a launch escape system to carry Dragon clear of its Falcon 9 carrier rocket should an anomaly occur before it reaches orbit.

Saturday’s launch began a six-day flight that will provide an end-to-end test of Crew Dragon on a mission to the International Space Station. This will allow key spacecraft systems to be tested on-orbit, including Dragon’s avionics, communications, telemetry, environmental, electrical and propulsion systems.

The guidance, navigation and control systems of first the combined Falcon 9/Dragon stack and later Dragon itself are demonstrated, while internal and external loads, vibration levels and acoustics are monitored and recorded. During the launch phase of the mission, SpaceX was able to test systems designed to trigger the spacecraft’s launch escape system automatically should an emergency be detected on future missions.

Dragon 2 Super Dracos in action during the Pad Abort test – via NASA

Dragon’s planned docking with the International Space Station will also provide an opportunity to test the spacecraft’s docking systems and procedures. Although not a primary objective of its mission, Dragon has been loaded with 180 kilograms (400 lb) of cargo that can be unloaded by astronauts aboard the complex. Dragon will then demonstrate undocking and its return to Earth.

As well as the cargo, Dragon is carrying mass simulators to mimic the presence of astronauts, and an anthropomorphic test device (ATD) – an instrumented mannequin named Ripley fitted with instrumentation to record the conditions that a crewmember would experience during the flight.

The completion of the Demo-1 mission, as well as an in-flight abort test in the coming months, will leave SpaceX ready to begin ferrying astronauts to and from the International Space Station. If all goes well, the Demo-2 mission will be the first to carry a crew, with astronauts Douglas G. Hurley and Robert L. Behnken expected to fly to the space station later this year.

Alongside Dragon, the Commercial Crew Development program has seen NASA task Boeing with development of another spacecraft, Starliner, which will share ISS crew rotation flights with SpaceX. Starliner’s first test flight – equivalent to Dragon’s DM-1 mission – is due to lift off aboard an Atlas V rocket in late April or early May. Whichever spacecraft reaches the outpost first with a crew aboard will claim the right to “capture the flag” left in orbit by the crew of Space Shuttle Atlantis during her STS-135 mission.

Starliner and Dragon 2 – via Nathan Koga for NSF/L2

STS-135 was the final flight of the Space Shuttle, and the landing of Atlantis on 21 July 2011 marked the beginning of a “gap” in US human spaceflight capabilities which Commercial Crew aims to close.

At over seven and a half years, this has already surpassed the interval between 1975’s Apollo-Soyuz mission and the Space Shuttle’s maiden flight in 1981 as the longest gap between two crewed missions in the US space program.

During this time, NASA has been reliant on Russia’s Soyuz spacecraft to transport its astronauts to the ISS, making the space station reliant on a single type of spacecraft for crew access and emergency escape.

The lack of other spacecraft capable of carrying crew to the space station was highlighted after the launch failure of last year’s Soyuz MS-10 mission, which raised the prospect that the station might have to be de-crewed temporarily if Russia could not return Soyuz to flight before the vehicle then on orbit had to return. As it was, Soyuz was quickly returned to service and no such contingencies were necessary, however having multiple crewed spacecraft available improves the program’s ability to handle unexpected circumstances.

Beginning its test flight ahead of Starliner, Crew Dragon remains in pole position to capture the flag aboard the space station.

Dragon launched atop SpaceX’s Falcon 9 rocket. First flown in June 2010, Falcon 9 is a two-stage rocket which is frequently used to deliver payloads for NASA, the US military and commercial customers. Falcon’s first stage is powered by nine Merlin-1D engines, while a tenth Merlin-1D provides thrust for the second stage. The second stage engine is optimized for the vacuum of space and is known as Merlin Vacuum or MVac.

Dragon 2 and her Falcon 9 – via NASA

Falcon 9 was the second rocket to be developed by SpaceX, following the much smaller Falcon 1 which allowed the company to cut its teeth before moving on to more powerful rockets. SpaceX was founded by Elon Musk in May 2002 with the goals of providing affordable, reliable access to space and of eventually helping humans to reach Mars. Musk previously founded software company Zip2 and online payment provider PayPal.

SpaceX’s first launch, in March 2006, failed to reach orbit and two more Falcon 1 missions failed before success was achieved at the fourth attempt. After a fifth launch, which successfully deployed Falcon’s first commercial payload, Falcon 1 was retired and SpaceX refocussed its efforts on the Falcon 9.

In order to meet NASA’s requirements for human-rating the Falcon 9, SpaceX needed to freeze the design of the Falcon 9, ending a pattern of incremental upgrades that had been made over the original design. This has resulted in the Block 5 version of Falcon 9, which is expected to represent its final evolution. It is considerably longer and more powerful than the rocket that made the type’s maiden flight back in 2010.

A major driver for SpaceX’s upgrades to the Falcon 9 design has been a desire to re-use as many parts of individual rockets as possible, rather than discarding them as is typically done with most expendable rockets. The foremost aspect of this was the plan to recover and reuse the entire first stage of the rocket – also known as the booster or core.

While initial attempts to recover the first stage relied upon parachutes, and proved unsuccessful, from the sixth flight onwards SpaceX began taking steps in a new direction – towards a controlled, powered landing. The first significant upgrade to the Falcon 9 design, the Falcon 9 v1.1, incorporated more powerful engines and stretched first and second stages that gave the rocket enough extra performance that it would have leftover fuel to try and recover the first stage. Falcon 9 v1.1 also debuted the OctaWeb – the octagonal arrangement of engines at the base of Falcon 9 – which replaced a square grid layout used on earlier versions of the rocket.

A further upgrade came in December 2015 with the Falcon 9 Full Thrust, or v1.2, which was further stretched and began the use of supercooled liquid oxygen – a practice which SpaceX has continued with later versions of Falcon 9, and which allows more oxidizer to be carried relative to the size of the rocket’s tanks by storing it at an increased density.

The Block 3 and Block 4 upgrades that followed were more minor, implementing changes that would lead to today’s Block 5 configuration. Block 5 itself was introduced last May when SpaceX launched Bangladesh’s Bangabandhu-1 satellite, implementing changes required by NASA to human-rate the rocket and building on the incremental upgrades that had come before it. Block 5 is also designed to facilitate multiple reuses of each core – whereas earlier rockets could only fly twice – and reduce the amount of refurbishment required between launches.

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