SpaceX conducts doubleheader with Starlink mission followed by launch for SES

by William Graham

Hot on the heels of Tuesday’s successful CRS-27 launch, SpaceX’s Falcon 9 was in action again for a pair of back-to-back missions from both coasts Friday, tasked with deploying communications satellites into orbit.

The first of Friday’s two launches occurred at 12:26 PM PDT (19:26 UTC) from Vandenberg, California, with the 52 satellites of Starlink Group 2-8 aboard. Just over four hours later, the second lifted off from Cape Canaveral at 7:38 PM EDT (23:38 UTC) carrying a pair of satellites for commercial operator SES.

These are SpaceX’s 18th and 19th missions of 2023, with Starlink Group 2-8 marking the company’s ninth Starlink launch of the year – and the fifth of the year going to the second shell of the first-generation constellation. The deployment of SES-18 and 19 was SpaceX’s third commercial geostationary launch of the year and continued a long-running relationship with European satellite operator SES.

Both missions launched aboard flight-proven Falcon 9 rockets, and both completed booster recoveries aboard SpaceX’s Autonomous Spaceport Drone Ships (ASDS) downrange of their respective launch sites. The Starlink launch saw the booster land aboard Of Course I Still Love You in the Pacific Ocean, while Just Read The Instructions was positioned in the Atlantic to support the SES mission.

Starlink Group 2-8

The Starlink Group 2-8 mission was the sixth deployment of satellites into the second shell of the first-generation Starlink constellation — the numbers are out of sequence, with the Group 2-2 and 2-3 missions having not yet launched. 

The first-generation Starlink system consists of five different orbital shells, with multiple planes per shell and multiple satellites in each plane. Shell two satellites operate in orbits at an altitude of 570 kilometers, inclined at 70 degrees.

SpaceX is developing Starlink to offer high-speed satellite internet access around the world, with a focus on rural areas where terrestrial broadband is unavailable. The company intends to launch all of its Starlink satellites via its own rockets, with the task currently falling to Falcon 9 to fit in around its customer payload commitments. Future missions may also be flown aboard Starship. 

By leveraging its reusable rockets and gaps in its launch manifest, SpaceX aims to minimize the costs of deploying one of the largest constellations of satellites ever envisioned.

The majority of Starlink missions are carried out using flight-proven boosters, including some with the highest flight numbers in the fleet. Group 2-8 launched aboard B1071-8, a veteran of seven previous missions including its first in February 2022 with the NROL-87 mission.

Its second flight was also for the National Reconnaissance Office, NROL-85, while subsequent launches have deployed the German SARah-1 radar imaging satellite and the multinational Surface Water and Ocean Topography (SWOT) ocean research satellite. Friday’s mission is its fourth flight in support of Starlink and deployed another 52 satellites for the constellation.

Falcon 9 is a two-stage rocket. While the booster can be recovered and re-used, the second stage is expendable, meaning that whenever a flight-proven booster is used, the mission flies with a mixture of old and new hardware. The payload fairing that encapsulates the satellites at the nose of the rocket is also designed to be reusable, with the two halves parachuting back to Earth for a seaborne recovery after separating during ascent.

The Starlink mission lifted off from Space Launch Complex 4E (SLC-4E) at Vandenberg Space Force Base in California. SLC-4E is a former Atlas-Agena and Titan launch pad that has served as the West Coast home of Falcon 9 since the launch of CASSIOPE in September 2013.

B1071 lands at LZ-4 during its previous NROL-87 mission. (Credit: Michael Baylor for NSF)

Its nearby sister pad, SLC-4W, is now Landing Zone 4 (LZ-4) and is used to recover boosters on Return To Launch Site (RTLS) missions; however, since Friday’s launch featured a drone ship landing, LZ-4’s services were not required.

It took Falcon 9 about eight minutes and 43 seconds to reach orbit, with spacecraft separation taking place another six minutes and 41 seconds after orbit has been achieved. The launch began with the ignition of the nine Merlin-1D engines powering Falcon 9’s first stage a few seconds before the countdown reached zero.

At T0, Falcon 9 lifted off and began its climb toward orbit with B1071-8 powering ascent for the first two minutes and 27 seconds. After shutdown, there was a four-second delay before the first stage separated.

About six seconds after stage separation, Falcon 9’s second stage took over. Its single Merlin Vacuum (MVac) engine – a version of the Merlin-1D optimized to operate at peak efficiency in the vacuum of space – fired for a little over six minutes to reach low Earth orbit. 

While it is burning, Falcon 9’s first stage executed its own series of maneuvers to set up its landing on Of Course I Still Love You, which took place a few seconds after second stage engine cutoff.

Spacecraft separation took place at 15 minutes and 24 seconds mission elapsed time. The satellites will now undergo initial checkouts before maneuvering to their operational orbits. If any fail checkout, they will be left in a lower orbit so that they will re-enter the atmosphere sooner.

SES-18 and 19 launch

While the Starlink launch was conducted out of SpaceX’s own interests, the company’s second launch of the day carried a pair of customer payloads. Namely, these are SES-18 and SES-19, which were built by Northrop Grumman on behalf of Luxembourg-based SES.

These satellites make up half of a four-satellite order that SES announced in June 2020, with Northrop Grumman and Boeing each being awarded contracts for two spacecraft. The Boeing-produced satellites, SES-20 and 21, were successfully launched aboard a United Launch Alliance Atlas V rocket last October. Prior to shipping to Cape Canaveral ahead of their launch, SES-18 and 19 were built, tested, and stored at Northrop Grumman’s facility in Dulles, Virginia.

The decision to procure these new satellites came in response to rules set out by the US Federal Communications Commission (FCC), requiring satellite operators to discontinue using certain C-band frequencies to make this part of the spectrum available for terrestrial 5G internet services. The deadline by which this is to be completed is currently set for Dec. 5, 2023.

Ordered in 2020, much of the satellites’ construction took place during the COVID-19 pandemic. Speaking to NASASpaceflight, a Northrop Grumman spokesperson said the company was “proud of the way […] Northrop Grumman and [its] supply chain partners stepped up to this challenge.”

SES-18 and SES-19 are both equipped with only C-band transponders, operating in parts of the spectrum that are still available for satellite use. This will allow SES to transition customers from the frequencies that are to be discontinued onto their replacements without needing to change their equipment.

Each satellite is designed to operate 10 C-band transponders in support of television and radio broadcasting and data transmission services, although backup transponders are also carried to ensure their capabilities are not degraded in the event some of the primary transponders become non-operational.

The two satellites are based on Northrop Grumman’s GEOStar-3 satellite bus, which was developed by Orbital ATK as a successor to its successful GEOStar-2 platform, and first flown in January 2018. Northrop Grumman acquired Orbital ATK later in 2018, with satellite manufacturing falling under the purview of its Innovation Systems, and later Space Systems divisions.

Steve Krein, the company’s Vice President for Civil and Commercial Satellites, describes the GEOStar platform as “an affordable and reliable option for a diverse set of commercial and government customers”.

GEOStar-3 satellites have typical design lives of at least 15 years, with their twin solar arrays – consisting of multi-junction gallium arsenide cells – generating up to 8,000 watts of power. The bus is designed to be launched both individually – in which case up to 1,000 kilograms of communications payload can be fitted – or in a dual-launch configuration as is being used for SES-18 and 19.

In their dual-launch configuration, GEOStar-3 satellites are stacked one on top of the other, without needing a separate dual-payload adaptor. As a result, although SES-18 and 19 are otherwise essentially identical, SES-18’s omnidirectional antenna is of a fixed tripod design, whereas SES-19 has a deployable antenna so SES-18 can be mounted on top of it for launch.

SpaceX conducted the SES launch from Space Launch Complex 40 (SLC-40) at the Cape Canaveral Space Force Station. Like SLC-4E, this is also a former Titan launch facility and is one of two Falcon 9 launch pads on the East Coast, alongside Launch Complex 39A (LC-39A) at the nearby Kennedy Space Center. SLC-40 was first used by SpaceX in 2010 for Falcon 9’s maiden flight and is today used primarily for commercial and Starlink launches.

Booster B1069-6 makes up the first stage of the rocket that performed the launch. This booster first flew on the CRS-24 mission in December 2021 and already had five launches under its belt before Friday’s flight.

The early phases of the SES mission were similar to the Starlink Group 2-8 launch, with early flight events occurring at roughly the same times on most Falcon 9 missions targeting drone ship recovery. First stage cutoff and stage separation took place about five seconds later than on the Starlink mission, and the coast between separation and second stage ignition was about two seconds longer.

The SES-18 and SES-19 satellites prior to launch. (Credit: SES)

Second stage engine cutoff (SECO-1) came around eight minutes, 17 seconds mission elapsed time: earlier than on the Starlink launch and a few seconds before the first stage begins its landing burn. For the SES mission, the first stage landed aboard Just Read The Instructions, stationed in the Atlantic.

Unlike the Starlink launch, SECO-1 did not mark the end of powered flight for the SES mission. After an 18-minute coast phase, the MVac engine was restarted to raise the upper stage and its payload into geostationary transfer orbit (GTO). This second burn lasted about 47 seconds, with its corresponding shutdown event designated SECO-2.

At 32 minutes, 15 seconds after liftoff – five minutes and 11 seconds after SECO-2 – the SES-18 satellite separated from the top of the payload stack. Five minutes and 10 seconds later, SES-19 separated from the bottom position, concluding Falcon 9’s mission.

With the satellites deployed from Falcon 9, they will now conduct a series of orbit-raising maneuvers under their own power to reach their final home in geostationary orbit. Both satellites will be positioned over the Americas, with SES-18 expected to be stationed at a longitude of 103.05 degrees West, and SES-19 at 134.9 degrees West.

During their first month in space, SES-18 and 19 will also undergo on-orbit checkout and deploy various appendages such as antennae and solar panels, as they are prepared to enter service.

Friday’s launches continued another busy year for SpaceX, which – as of the CRS-27 launch on Tuesday – has already flown 17 missions since the start of January. On the current schedule, the company will only have a week to turn around before another Falcon 9 is due to lift off from SLC-40 with more Starlink satellites.

(Lead image: Falcon 9 lifts off from SLC-40 on the SES-18 & 19 mission. Credit: Stephen Marr for NSF)

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