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

by William Graham

SpaceX’s Falcon 9 and Falcon Heavy are the only rockets currently flying worldwide to incorporate reusable components.

Since the company first demonstrated the reuse of a core with 2017’s launch of SES-10, the “flight-proven” Falcon 9 has become a routine fixture on SpaceX’s launch manifest.

Of the twenty Falcon 9 rockets launched last year, eleven incorporated previously-flown first stages. Last February’s test flight for Falcon Heavy used two flight-proven cores which had previously flown as Falcon 9s.

Falcon Heavy side boosters landing at LZ-1 and LZ-2 – via SpaceX

Not including the Falcon Heavy launch, Saturday’s was the sixty-ninth flight of a Falcon 9 rocket. In its previous missions, Falcon has achieved an impressive success rate with only one loss of mission. This failure was the 2015 launch of a Dragon spacecraft for the CRS-7 resupply mission to the space station. A carbon overwrapped pressure vessel (COPV) containing helium used to pressurize the second stage oxidizer tank broke loose and vented, rapidly increasing the pressure within the tank and causing the rocket to disintegrate.

Another anomaly occurred during pre-launch testing several days ahead of a planned mission to deploy Israel’s Amos 6 communications satellite in September 2016 – while the rocket was being fuelled for a static firing an explosion was seen on the second stage and a fireball quickly engulfed the vehicle, destroying both rocket and payload.

This was also traced to the second stage COPVs and an unexpected interaction with the supercold oxidizer in the surrounding tank. Bubbles of oxygen formed between the inner aluminum and outer carbon fiber layers of the COPV, which caused it to rupture when the tank was pressurized. Following these incidents, SpaceX redesigned the COPVs to ensure similar incidents could not occur again.

The only other major issue that occurred during a Falcon 9 launch was a first stage engine failure during one of the rocket’s early launches. While Falcon 9 is designed to continue flying with an engine out and was able to deploy its primary payload successfully, the second stage did not have enough fuel for a planned second burn that would have allowed a second payload to be deployed. These few incidents aside, Falcon 9 has quickly proven itself a reliable workhorse for launching commercial and government space missions.

Crew Dragon missions, as did Saturday’s test flight, will launch from the historic Launch Complex 39A at NASA’s Kennedy Space Center in Florida. LC-39A was originally built in the 1960s for the Apollo program, for which it served as the primary launch pad for the Saturn V rocket. In this capacity, Pad 39A was the point of departure for eight of the nine manned missions to the Moon, including all of the missions that landed. After the end of the Apollo program, LC-39A was used for one more Saturn V launch – its final flight – which deployed the United States’ only space station, Skylab.

39A ahead of the DM-1 launch – via Nathan Barker for NSF

In total, twelve Saturn V launches – including both the first and last – took place from LC-39A. After Skylab, the pad was redeveloped for the Space Shuttle. Columbia lifted off on her maiden flight – and the first flight of the Shuttle program – from Pad 39A on 12 April 1981. This was the first of eighty-two Space Shuttle launches from the pad, which concluded with the final Shuttle mission, STS-135, which was flown by Atlantis in July 2011.

SpaceX leased Launch Complex 39A from NASA in 2014, under a twenty-year agreement, and set about creating a launch facility for their Falcon 9 and Falcon Heavy rockets. Their first launch from the pad was that of a Dragon spacecraft on the CRS-10 resupply mission to the International Space Station, in February 2017. Prior to Saturday’s launch, SpaceX had used the pad for thirteen Falcon 9 launches and last year’s maiden flight of the Falcon Heavy rocket with Elon Musk’s Tesla Roadster aboard.

During the Apollo and Space Shuttle eras Complex 39A – as well as nearby Complex 39B – was served by NASA’s Vehicle Assembly Building (VAB). Saturn or Space Shuttle vehicles would be stacked vertically within the VAB atop a Mobile Launch Platform (MLP). The platform – with its fully assembled rocket – would then be rolled into place on the launch pad.

For Saturn launches the MLP – then known as a Mobile Launcher (ML) – also housed the Launch Umbilical Tower (LUT) that provided access to the rocket and spacecraft and housed swing arms with connectors to service and fuel the rocket. With the advent of the Space Shuttle, the LUT was removed from the launch platform and new Fixed and Rotating Service Structures (FSS and RSS) were constructed at each launch pad.

SpaceX opted not to use the VAB or Mobile Launch Platforms, instead using the same horizontal integration process that Falcon 9 uses at its other launch pads. A hangar was constructed at the base of LC-39A’s launch ramp where Falcon 9’s stages are integrated and placed onto a transporter-erector, known as the Strongback. This is used to transport the rocket into position on the pad, raise it to the vertical, and provide umbilical connections to support Falcon as it prepares for launch.

DM-1/Falcon 9 on the T/E heading to 39A – via NASA

Pad 39’s Rotating Service Structure was dismantled in 2017, as this was no longer needed to support Falcon 9 rockets. Although Falcon 9 does not require the pad’s Fixed Service Structure either, SpaceX has retained it to facilitate crew access to the Dragon spacecraft. A new crew access arm has been installed near the top of the FSS, replacing the one that was used during the Shuttle program.

Although Saturday’s launch did not carry a crew itself, it demonstrated the launch procedures for a crewed mission and will, therefore, be the first to make use of the access arm.

Ahead of Saturday’s launch, Falcon 9 and Dragon rolled out to LC-39A on Thursday.

Saturday’s countdown was controlled from Firing Room 4 at NASA’s Launch Control Center, where a team of SpaceX and NASA personnel will supervise operations.

Fuelling of Falcon 9 followed a similar timeline to a regular launch, except that the Launch Director gave authorization to proceed with the process earlier than normal, at about T-45 minutes. This was give time for the Dragon’s launch abort system to be armed before propellant begins flowing. In the event of a major problem during fuelling – like the one that occurred during the Amos 6 static fire – Dragon can carry itself and any crew aboard to safety.Loading of propellant into both stages of the Falcon 9, and of oxidizer into the first stage, commenced thirty-five minutes before liftoff. Second stage oxidizer loading began slightly later, at the sixteen-minute mark in the countdown.

With about seven minutes to go the first stage engines chilled-down to prepare them for oxidizer flow at ignition, and at the five minute mark Dragon went to internal power. Shortly after this, arms on the Strongback opened and this structure moved to its pre-launch position, rotated slightly away from Falcon 9. It fell back further as the rocket began to lift off.

In the final minute of Saturday’s count, Falcon’s onboard computers undertook their final prelaunch checks while the rocket’s propellant tanks were brought up to flight pressure. With forty-five seconds remaining until liftoff, the Launch Director gave the final confirmation that the rocket was “go” for launch.

Falcon’s nine Merlin-1D engines were commanded to begin their ignition sequence three seconds before the countdown reached zero, roaring to life moments later. These built up to full thrust and at the zero mark Falcon and Dragon lifted off.

Taking a north-easterly trajectory out over the Atlantic Ocean, Falcon passed through the area of maximum dynamic pressure – Max-Q – fifty eight seconds into flight. At about the same time Falcon’s speed exceeded Mach 1, the speed of sound, and the rocket entered supersonic flight.

The first stage – Core 1051 – powered Falcon 9 for the first two minutes and 35 seconds of Saturday’s launch. After this, Main Engine Cutoff (MECO) occurred and the nine Merlin engines shut down. Stage separation occurred three seconds later.

Falcon 9 and Dragon 2 staging – via Nathan Koga for NSF/L2

Core 1051 then began its journey back to Earth while Falcon’s second stage and Dragon continued on towards orbit. The second stage Merlin Vacuum engine ignited four seconds after staging, burning for six minutes and 17 seconds to insert Dragon into orbit.

While the second stage burns, Falcon’s first stage made a series of maneuvers to bring itself back to Earth for future reuse.

Core 1051 landed on the Autonomous Spaceport Drone Ship (ASDS), Of Course I Still Love You, which is stationed downrange in the Atlantic Ocean. This called for Core 1051 to continue initially on the same trajectory it was following at separation – reaching apogee and beginning to fall back to Earth, before it made two more engine burns. The first of these burns began five minutes and five seconds after stage separation, reducing the forces and heating the rocket experiences as it enters the atmosphere.

Core 1051’s landing burn began at approximately nine minutes and 24 seconds mission elapsed time – shortly after the end of the second stage’s burn. Landing itself took place about twenty eight seconds later.

Eleven minutes after lifting off from LC-39A – and 121 seconds after second stage cutoff – Dragon separated from Falcon 9’s second stage to begin its own mission. Following a series of maneuvers it is expected to arrive at the International Space Station around 11:00 UTC on Sunday.

Dragon 2 approaches the ISS for docking – via Nathan Koga for NSF/L2

Dragon will dock to Pressurized Mating Adapter 2 (PMA-2) on the station’s Harmony module – the same docking port that was used during most of the Space Shuttle’s visits to the space station. Dragon is expected to remain docked to the outpost for five days. After departing the space station on Friday, Dragon will return to Earth and splash down in the Atlantic Ocean.

A successful demonstration flight will pave the way for SpaceX to begin crewed missions to the International Space Station later this year. Before these flights start, SpaceX plan first to test Dragon’s launch abort system by launching it uncrewed atop a Falcon 9 first stage and simulating an in-flight emergency at one of the most critical points in the flight.

SpaceX has two more launches planned for March – with a Falcon 9 due to deploy three Canadian Radarsat spacecraft from Vandenberg Air Force Base and a Falcon Heavy mission with the Arabsat 6A communications satellite slated to fly from the Kennedy Space Center towards the end of the month. The next Dragon mission, CRS-17 – using the older cargo version of the spacecraft, is scheduled to lift off in late April.

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