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SpaceX will continue the deployment of its Starlink constellation with the launch of another sixty satellites aboard a Falcon 9 rocket on Sunday. Liftoff from Florida’s Kennedy Space Centre is expected at 08:27 Eastern Time (12:27 UTC).

Sunday’s launch is the thirteenth Falcon 9 mission to deploy operational Starlink satellites, designated Starlink v1.0 L13. This continues the first phase of Starlink deployment, which is aimed at setting up an initial operating capability and allowing SpaceX to begin rolling out its service. To do this, SpaceX expects to require at least 1,440 satellites in the first tranche alone. Since beginning operational launches, 713 Starlink spacecraft have been placed in orbit – with Sunday’s mission expected to add another sixty – although some of the spacecraft launched on earlier missions have already re-entered the atmosphere.

Starlink is a network of satellites which SpaceX intend to use to offer a worldwide commercial satellite internet service, with a particular focus on areas where traditional broadband services provide poor coverage. Unlike previous satellite broadband services, Starlink was designed to employ vast numbers of satellites in low orbits, reducing the round-trip time for signals and therefore the latency of connection compared to spacecraft in geostationary orbit. Beyond the initial 1,440-satellite-strong constellation, SpaceX has plans to launch up to 30,000 more spacecraft, replacing existing ones as they fail and adding new capacity as the system is rolled out worldwide. The company’s factory can produce 120 new satellites every month.

The first operational Starlink satellites were launched at the end of last year, with all operational satellites currently in orbit having been deployed in the last twelve months. Prior to launching the operational spacecraft, SpaceX flew two technology demonstrator spacecraft – nicknamed Tintin A and B – in early 2018 and an entire batch of prototype Starlink spacecraft in early 2019.

Although there are not currently enough satellites in orbit for continuous global coverage, SpaceX has already begun recruiting initial test users for a regional service in the northern United States and Canada. Starlink terminals were also made available to emergency services responding to wildfires in Washington State last month, providing communications for firefighters tackling the blazes and temporary internet connectivity to areas affected. The Starlink terminals were described as being easier to set up and providing more reliable service than other tactical communications systems that responders had used in the past.

SpaceX eventually aims to market Starlink around the world, potentially reinvesting some of the profits in its other programmes.

Each Starlink satellite has a mass of around 260 kilograms (570 lb). The satellites have a flat design allowing them to be stacked closely on the rocket, with a solar panel and sunshades deploying once on orbit. The onboard communications payload uses the Ku and Ka bands of the electromagnetic spectrum, while the purpose of the sunshade is to reduce the amount of sunlight reflected by the satellites following complaints from astronomers that the satellites were harming their observations.

Starlink satellites are designed to be held together on the rocket with tension rods, which release at spacecraft separation allowing all of the satellites to float away from Falcon 9’s upper stage without needing individual deployment mechanisms. On some launches, small third-party commercial payloads can be substituted for individual Starlink satellites, however Sunday’s mission will be carrying a full complement of 60 Starlink birds.

SpaceX carry out Starlink launches using their own Falcon 9 rockets, with Sunday’s launch no exception. First flown in June 2010, the Falcon 9 is a two-stage liquid-fueled rocket with a reusable first stage and an expendable second stage. Prior to Sunday’s launch, the Falcon 9 family – which also includes the larger Falcon Heavy rocket – had carried out ninety-seven missions with only one in-flight failure. All of these launches have been orbital except for one test launch last year, which used a modified Falcon 9 to boost an in-flight abort test of SpaceX’s Crew Dragon spacecraft.

The Falcon 9 which will carry out Sunday’s launch incorporates as its first stage Core 1051.6, a booster which has already participated in five successful launches. Built for the uncrewed DM-1 test flight of the Crew Dragon spacecraft, it first flew in March 2019. For its second mission, the booster flew from Vandenberg Air Force Base as part of the Falcon 9 that deployed Canada’s Radarsat Constellation Mission last June. Its three subsequent launches have all carried Starlink payloads, flying in January, April and August this year.

After completing its role in a Falcon 9 mission, the first stage is recovered through a powered landing – either on a concrete pad near the launch site, or an Autonomous Spaceport Drone Ship (ASDS) – a large converted barge – at sea. A return-to-launch-site (RTLS) landing is typically executed on missions with lighter payloads targeting lower orbits, where there is enough fuel remaining for the booster to turn its trajectory around and head back to land. Missions like with heavier payloads, including Sunday’s launch, use the drone ship so this extra performance can be put towards getting the payload into orbit. B1051.6 will be targeting a landing aboard the drone ship Of Course I Still Love You, 633 kilometres (393 miles, 342 nautical miles) in the Atlantic Ocean, downrange of the Kennedy Space Centre, following Sunday’s mission.

Starlink mission 14 has begun with the departure of Of Course I Still Love You and Finn Falgout bringing her out to the northern LZ. Launch is currently NET 10/18. #SpaceXFleet #FleetCam pic.twitter.com/YgzzhGOGto

— Julia (@julia_bergeron) October 14, 2020

As well as recovering and re-using the first stage of Falcon 9, SpaceX have begun recovering and re-flying the rocket’s payload fairing. A pair of ships, Ms Tree and Ms Chief, have been equipped with large nets to maneuver underneath and catch each half of the fairing as it descends under parachute. Both halves of the payload fairing for Sunday’s launch have made two previous launches, and the fairing recovery ships are in position downrange to recover them again following this flight.

Falcon will lift off from the historic Launch Complex 39A at Florida’s Kennedy Space Center. Originally constructed during the Apollo programme of the 1960s, this is the same launch pad from which men first lifted off to go to the Moon. LC-39A supported all of the Apollo lunar missions except Apollo 10, which flew from the nearby backup pad, LC-39B. At the end of the Apollo programme, LC-39A hosted the 1973 launch of the Skylab space station using a leftover Saturn V rocket, after which the pad was rebuilt for the Space Shuttle programme.

In the Shuttle era, LC-39A hosted eighty two launches – including the maiden and final flights of the programme: Columbia’s STS-1 in 1981 and Atlantis’ STS-135 in 2011. NASA announced in 2014 that it had signed a twenty-year agreement to lease the pad to SpaceX, which led to the pad’s conversion for Falcon 9 and Falcon Heavy rockets. The first Falcon 9 launch from the pad took place in February 2017. LC-39A is one of three launch pads from which SpaceX can operate the Falcon 9 – alongside Space Launch Complex 40 at the nearby Cape Canaveral Air Force Station and Space Launch Complex 4E at California’s Vandenberg Air Force Base. Of these three pads, however, only LC-39A can also be used by the Falcon Heavy.

SpaceX’s modifications to Launch Complex 39A included the construction of a large hangar at the base of the launch ramp, where Falcon rockets are assembled horizontally – in contrast to the vertical integration profile previously used by NASA. The completed rocket is then rolled to the launch pad by the Transporter-Erector, or Strongback, which is used to raise it to the vertical and to provide umbilical connections while it is at the pad. For Sunday’s launch Falcon rolled out on Friday and underwent a successful static fire on Saturday, igniting its nine first-stage engines for a brief test burn.

On launch day, fueling of the Falcon 9 will commence thirty-five minutes before liftoff. Both stages of the rocket burn RP-1 propellant – rocket-grade kerosene – and liquid oxygen. To increase the density of the liquid oxygen, allowing more to be carried in the rocket’s tanks, it is subcooled to a lower temperature than that used by other rockets. While this has improved Falcon 9’s performance, it means that propellant must be loaded just before liftoff, so the temperature does not increase – and too much oxygen boil off – while the vehicle is sitting on the launch pad. At the thirty-five minute mark, following a poll of flight controllers a few minutes earlier, RP-1 will begin flowing into both stages of the rocket, and oxygen into the first stage. Second stage oxidizer loading will begin sixteen minutes before launch.

As the countdown continues to tick away, SpaceX will run through the steps to check out Falcon and prepare her for flight. This will include chilling the first stage engines about seven minutes before liftoff, arming the flight termination system and moving the Strongback to its pre-launch position. This step involves opening the arms that hold Falcon 9 in place and rotating the structure about 1.5 degrees away from the rocket. At liftoff, the Strongback will rapidly move to its fully-retracted position as Falcon climbs away from the launch pad.

The final minute of the countdown will see further checks carried out by Falcon 9’s onboard computers to verify that the rocket is ready to launch. Falcon 9 will enter startup, switching to autonomous onboard control and pressurizing its propellant tanks. Around this time the launch director will give final approval to launch the rocket. At the three-second mark in the countdown, the nine Merlin-1D engines at the base of the first stage will begin their ignition sequence, with liftoff occurring at the zero mark in Sunday’s countdown.

Climbing away from LC-39A, Falcon will pitch downrange and establish a north-easterly trajectory that will take it over the Atlantic Ocean. About a minute into flight Falcon 9 will reach Mach 1 and go supersonic, passing through the area of maximum dynamic pressure – or Max-Q – at the seventy-two second mark.

Core 1051.6 will power Falcon 9 for the first two minutes and 32 seconds of flight, before the mission reaches Main Engine Cutoff (MECO). The nine Merlin-1D engines will shut down and four seconds later the first and second stages will separate. After another seven seconds, the second stage’s Merlin Vacuum (MVac) engine – a version of the Merlin-1D optimized to operate in the vacuum of space – will ignite and take over propelling the Starlink satellites into orbit. This is the first of two burns that will be required to place the satellites in their initial deployment orbit and is expected to last for six minutes and five seconds. The payload fairing will separate early in this burn, about thirty-nine seconds after ignition.

While the second stage continues to orbit in pursuit of the primary mission, Core 1051.6 will prepare for its return to Earth. Shortly after separation it will deploy grid fins to help stabilize and guide it as it re-enters the atmosphere. The stage will coast to the apogee – or highest point – of its trajectory and then begin to fall back to Earth. At around six minutes, 20 seconds mission elapsed time the stage will make an entry burn to slow itself as it passes back into the atmosphere – this is expected to last about twenty seconds. The booster will fire its centre engine again for a landing burn as it approaches the drone ship and deploys its landing gear, with touchdown expected eight minutes and 24 seconds after liftoff.

The first stage will land a few seconds before the second stage reaches orbit. Following insertion into its initial parking orbit the MVac engine will shut down at eight minutes, 48 seconds time elapsed, a mission event designated Second Stage Engine Cutoff 1 (SECO-1). After SECO-1, the stage will coast for 33 minutes and 38 seconds. A brief second burn, lasting just two seconds, will raise the orbit’s perigee. Spacecraft separation will occur eighteen minutes and 56 seconds after the end of the second burn.

According to pre-launch orbital elements published by satellite tracking website Celestrak, Sunday’s launch will be targeting a 263 by 279 kilometre (163 by 173 mile, 142 by 151 nautical mile) orbit, inclined at 53.1 degrees. After separating from the carrier rocket the satellites will use onboard ion engines to raise themselves into operational 550 kilometre (340 mile, 300 nautical mile) orbits.

Following deployment of the Starlink satellites, the second stage is expected to perform an additional burn to deorbit itself. Hazard areas published ahead of launch suggest the stage will reenter on its second orbit, as it passes to the south of Australia. As the second stage is not designed to be recovered, it will break up in the atmosphere with any debris falling harmlessly into the ocean.

Sunday’s launch is the second of three Starlink missions being carried out in quick succession, coming twelve days after the Starlink v1.0 L12 mission lifted off. The next launch, L14, could come as early as Wednesday with another sixty satellites expected to take flight on another Falcon 9, this time flying from SLC-40. The L13 mission is the twelfth Starlink launch of 2020, with multiple further launches expected in November and December. This is in addition to Falcon 9’s other duties, with several commercial, scientific and military satellite deployments on the books for the end of the year in addition to two Dragon missions for NASA: a CRS flight to deliver cargo to the International Space Station, and the Crew-1 mission which will carry four astronauts to the outpost.