SpaceX launched Bulgaria’s first communications satellite on Friday – the first of two Falcon 9 launches in the space of two days – via the company’s second flight-proven rocket – which also landed a second time. Liftoff from Launch Complex 39A at the Kennedy Space Center was at 15:10 Eastern Daylight Time (19:10 UTC).

SpaceX Launch:

The payload of Friday’s launch, BulgariaSat-1, was a 3.7-tonne geostationary communications satellite.

The launch was the second of three missions SpaceX plan to fly in June, setting up a weekend double-header with the third, which is scheduled to depart from Vandenberg Air Force Base on Sunday carrying eight Iridium satellites. The BulgariaSat mission was also the third launch to take place on Friday, with Indian and Russian rockets lifting off ahead of it.

Constructed by Space Systems/Loral, BulgariaSat-1 is based around the SSL-1300 bus. With a total mass at launch of 3,669 kilograms (8,089 lb) the satellite is designed for at least fifteen years of service but is carrying sufficient fuel for a minimum of eighteen years in orbit. The spacecraft will be operated by Bulgaria Sat, a company affiliated with Bulgarian television provider Bulsatcom.

Friday’s launch carried BulgariaSat-1 into a geostationary transfer orbit, with the satellite using its R-4D-11 apogee motor to circularize its orbit. Once in geostationary orbit, BulgariaSat-1 will be positioned at a longitude of 1.9 degrees East.

From this location, it will be able to provide direct broadcasting and fixed satellite services to much of Europe, and parts of North Africa and the Middle East. A second beam has a smaller footprint, providing additional coverage of the Balkans.

The communications payload aboard BulgariaSat-1 consists of thirty-three Ku-band transponders. Thirty of these will be used for broadcasting, while three will provide fixed satellite services (FSS).

BulgariaSat-1 is the first Bulgarian satellite to launch in almost thirty-six years and only the country’s second spacecraft. Bulgaria’s only previous spacecraft was Bulgaria-1300, or Interkosmos-22, a modified Soviet weather satellite outfitted with scientific instruments.

Constructed and launched under the Soviet Union’s Interkosmos program – aimed at helping promote space science and achievement within other Warsaw Pact countries – Bulgaria-1300 was launched from the Plesetsk Cosmodrome in August 1981 aboard a Vostok-2M rocket.

Friday’s launch was the second time SpaceX has used what they term a “Flight-Proven” Falcon 9 vehicle – that is, one whose first stage has already been used for a previous launch.

A unique aspect of Falcon 9’s design is the ability for the first stage to return to Earth via a powered descent after completing its role in Falcon’s ascent to orbit, instead of burning up in the atmosphere or falling into the ocean as with most – expendable – launch systems.

SpaceX sees reusability as a way to bring down launch costs and reduce vehicle production times, allowing launch rates to increase.

The first “flight-proven” Falcon 9 carried the SES-10 communications satellite into orbit in March, with a first stage – Core 1021 – which previously flew in 2016 as part of the rocket which delivered the CRS-8 Dragon mission into orbit.

After the SES-10 launch, the first stage was once again recovered and SpaceX intends to put it on display at Cape Canaveral. Prior to Falcon 9, the only rocket to achieve partial reusability was the Space Shuttle.

Friday’s launch made use of Core 1029, which previously flew from Vandenberg Air Force Base in January, delivering ten Iridium-NeXT satellites into low Earth orbit. That launch, which was the first successful first stage recovery for a West Coast launch, took place on 14 January and marked Falcon’s return to flight following an explosion during a pre-launch test last September which destroyed both a rocket and its Amos 6 payload.

The Iridium launch was the first of a multi-launch deal to deploy most of Iridium’s second-generation constellation of low Earth orbit communications satellites – the second launch of this contract is expected to occur on Sunday.

From the inception, SpaceX has worked towards making its rockets reusable.

Since the CRS-8 mission, all but one of SpaceX’s attempts to land Falcon 9’s first stage have been successful. The only exception was June 2016’s launch of the Eutelsat 117 West B and ABS-2A satellites, where one of the three engines used for the landing burn did not generate sufficient thrust. The booster was destroyed on touchdown.

Five of the eleven successful landings have taken place at Landing Zone 1, five aboard Of Course I Still Love You in the Atlantic Ocean and one – the previous flight of Core 1029 – aboard the second Just Read the Instructions in the Pacific.

With Friday’s launch targeting a first stage landing aboard Of Course I Still Love You, a successful landing made Core 1029 the first core to land aboard both drone ships.

SES-10’s Core 1021 was technically the first booster to fly from two different launch sites, because it made its first flight from Space Launch Complex 40 at the Cape Canaveral Air Force Station and its second from Launch Complex 39A at the Kennedy Space Center – an adjacent, but separate, facility, but the BulgariaSat launch will make Core 1029 the first reusable vehicle to lift off from both East and West-coast launch sites.

West Coast Space Shuttle missions were planned, using Vandenberg’s Space Launch Complex 6 (SLC-6). However these were canceled before the first mission – STS-62-A, which would have been flown by Discovery in 1986 – could launch.

Friday’s launch was the thirty-sixth flight of the Falcon 9, and the sixteenth to use a Falcon 9 v1.2 vehicle – which surpasses the v1.1 as the most-launched version of the rocket. Prior to the BulgariaSat launch, the Falcon 9 v1.1 and v1.2 had made fifteen launches apiece, while the original Falcon 9, or the v1.0, made five. It will be the seventh SpaceX launch from Launch Complex 39A (LC-39A) at the Kennedy Space Center.

Formerly the home of NASA’s Saturn V moon rocket and later the Space Shuttle, LC-39A is one of the world’s most historic launch complexes.

It was from this pad in December 1968 that the crew of Apollo 8 departed to become the first humans to fly around the Moon. Seven months later, Apollo 11 lifted off from the same launch pad on the first mission to land men on the Lunar surface. Twelve of the Saturn V’s thirteen launches – including all of the Apollo missions to land on the Moon – were flown from pad 39A. Following the end of the Apollo lunar program, the final Saturn launch from Complex 39A and the final flight of the Saturn V carried the first US space station, Skylab, into Earth orbit.

The Space Shuttle made its maiden flight in April 1981: flying from Launch Complex 39A, Columbia orbited the Earth for two days with astronauts John Young and Robert Crippen aboard. Seven months later Joe Engle and Richard Truly took Columbia up again for the STS-2 mission, marking the first reuse of an orbital spacecraft.

In total, eighty-two of the Space Shuttle’s 115 missions lifted off from pad 39A, including the first twenty-four and the last eighteen missions of the program. The final Space Shuttle launch, of Atlantis on STS-135, took place from Pad A on 8 June 2011.

SpaceX agreed a twenty-year lease of Pad 39A from NASA in 2014, building a hangar at the foot of the pad’s launch ramp for vehicle assembly.

Falcon 9 launches from Pad 39A began earlier this year with the deployment of a Dragon spacecraft on the CRS-10 mission to the International Space Station. SpaceX had intended to use LC-39A for US government missions and Falcon Heavy launches, with commercial flights continuing to depart from Cape Canaveral’s Space Launch Complex 40 (SLC-40). However, the KSC pad is temporarily being used for all launches while SLC-40 is repaired.

The damage that has kept pad 40 out of action was sustained last September when a Falcon exploded during fuelling ahead of what was supposed to be a static fire test in the launch campaign for Israel’s Amos 6 satellite. The Amos spacecraft was destroyed in the explosion.

Falcon returned to flight in January, with the successful Iridium launch from Vandenberg, followed by the CRS-10 launch from Kennedy. The CRS-11 launch earlier this month was the 100th from Complex 39A. SLC-40 is expected to return to service later this year, allowing LC-39A to then be taken offline to finish work that needs to be completed ahead of the maiden flight of the Falcon Heavy rocket.

In preparation for the BulgariaSat launch – which was then scheduled for last Monday – SpaceX conducted a successful static fire on Thursday 15 June. The launch attempt would have followed four days later, but was delayed after SpaceX opted as a precaution to replace a faulty valve in the fairing separation system. The delay means that BulgariaSat-1’s launch will now take place only two days before the next Falcon 9 launch, which is being conducted by a second launch team out of Vandenberg.

Falcon 9 is a two-stage rocket, burning RP-1 propellant oxidized by liquid oxygen. Fuelling takes place in the last seventy minutes of the countdown, following a poll of flight controllers to proceed with tanking three minutes beforehand.

The RP-1 propellant, a rocket-grade form of kerosene, will be loaded first, with liquid oxygen loading starting forty-five minutes ahead of liftoff. SpaceX has recently moved oxidizer loading later in the countdown, using a new, faster, process – although for Friday’s launch the older process was used because Core 1029 was built before this process was devised and lacks the hardware to support it.

In the final minutes of the countdown, Falcon began chilldown of its engines and transfered to internal power. The strongback structure, used to transport the rocket to the launch pad, erect it and provide umbilical connections, rotated slightly away from the vehicle in preparation for liftoff, when it was retracted rapidly away from the rising rocket. A minute before launch Falcon’s propellant tanks were pressurized and the onboard computer began its final prelaunch checks.

The nine Merlin-1D engines that power the Falcon 9’s first stage ignited three seconds before the countdown reached zero. At zero the rocket lifted off, beginning a mission which lasted just under thirty-five minutes to spacecraft separation. After lifting off, Falcon maneuvered onto the preplanned trajectory for its ascent to orbit. Seventy-nine seconds into the mission, the rocket passed through Max-Q, the area of maximum dynamic pressure.

Core 1029 powered Friday’s mission for the first two minutes and thirty-six seconds of flight, up until main engine cutoff, or MECO. Four seconds after cutoff, the first stage separated from the second stage, with the former beginning its return to Earth while the latter continues on towards orbit.

Seven seconds after stage separation, the second stage ignited its vacuum-optimised Merlin-1D engine for the first of two planned burns.

This first burn lasted five minutes and 51 seconds, with Falcon’s payload fairing separating 53 seconds into the burn. After an 18-minute, 30-second coast, the second stage restarted for its second burn, lasting one minute and five seconds. Six minutes and 42 seconds after cutoff, BulgariaSat-1 separated from the rocket, completing Falcon’s mission.

While the second stage was making its first burn, several flight events occurred for the first stage. This involved the stage reorienting itself for reentry, with its entry burn – to slow the core as it reenters the atmosphere – beginning at six minutes, 19 seconds mission elapsed time, or three minutes, 39 seconds after stage separation. The stage landed aboard Of Course I Still Love You at about eight minutes, 31 seconds after liftoff, making a short landing burn to arrest its descent just before landing.

If the landing is successful, Core 1029 will be secured on the deck of the drone ship for the journey back to Port Canaveral. Aerial photographs of the ASDS in port have shown an unmanned tracked vehicle being tested which appears to be designed to secure the core without needing to send people onto the barge.

In the absence of an official announcement or name from SpaceX, the device has earned the nickname Roomba, after the robotic vacuum cleaner. It is unclear whether the Roomba – also internally nicknamed as the OctoGrabber – will play a role in recovery operations after Friday’s launch.

SpaceX has also begun experimenting with the recovery of the Falcon 9’s payload fairing. On some flights, each half of the fairing will be fitted with an attitude control system and a parachute to slow its descent.

This will allow either a surface or airborne recovery to take place. SpaceX hopes that by reusing the fairing they can shave a few million dollars further off of the Falcon 9’s launch cost. It is not known whether Friday’s launch is carrying this hardware.

Friday’s launch was the eighth of the year for SpaceX and its Falcon 9 rocket. It was the fourth SpaceX launch of 2017 to be targeting a geostationary transfer orbit and the second, after SES-10, landing aboard Of Course I Still Love You.

Falcon’s next launch is currently scheduled to occur just over two days after the BulgariaSat launch, with a launch from Vandenberg Air Force Base carrying ten Iridium-NeXT low Earth orbit communications satellites. The Iridium launch, which is being conducted by a second launch team, is scheduled for 13:25 Pacific Time (20:25 UTC).

Falcon 9 was the third rocket to lift off worldwide, bound for orbit on Friday. India’s Polar Satellite Launch Vehicle launched at 03:59 UTC (09:29 local time), while Russia’s Soyuz-2-1v rocket launched just over an hour before Falcon’s launch.