Spaceflight Insider

Ariane 5 launches GSAT-18, Sky Muster II commsats

Ariane 5 lifts off on flight VA231 with Sky Muster II and GSAT-18.

Ariane 5 lifts off on flight VA231 with Sky Muster II and GSAT-18. Photo Credit: ESA/CNES/Arianespace

An Ariane 5 booster has successfully lifted off from Kourou, French Guiana, at 5:30 p.m. local time (4:30 p.m. EDT; 20:30 GMT) on Wednesday, Oct. 5, carrying a duo of communications satellites. The mission, designated VA231 in Arianespaces numbering system, was launched from the Ariane Launch Complex № 3 (ELA-3).

The Ariane 5 rocket, with India’s GSAT-18 and Australia’s Sky Muster II (also known as NBN-Co 1B) commsats, was tasked with delivering both spacecraft into geostationary orbits. The deployment of the satellites was conducted some 30 minutes after launch. Liftoff of the mission was initially planned for Oct. 4; however, it was postponed due to unsettled weather. The mission campaign started on May 18, 2016, with the unpacking of the rocket’s cryogenic main stage, called EPC.

Ariane 5 approaches the ELA-3 launch zone in Kourou, French Guiana.

Ariane 5 approaches the ELA-3 launch zone in Kourou, French Guiana. Photo Credit: Arianespace

The countdown campaign for liftoff began some 11 hours and 43 minutes before the scheduled launch. During this final phase of preparations, engineers performed final checks of electrical systems and filled the Ariane 5’s two stages with liquid oxygen and hydrogen.

About one hour and 15 minutes ahead of rocket ignition, the teams carried out pre-launch checks of telemetry, tracking, and command systems. Some seven minutes before the start of the mission, all the systems were reported as ready for launch, commencing a synchronized sequence leading to ignition of the rocket’s engines.

The fully automated countdown conducted the final procedures on the launch vehicle prior to its liftoff. It was performed by the launcher’s onboard computer and two redundant computers at the ELA-3 complex that carried out electrical operations like the startup of the flight program and switching from the ground power supply to batteries on the vehicle. Finally, some four seconds before the ignition, onboard systems were cleared to immediately take control over the mission.

The EPC’s engine was ignited first, which was followed by the ignition of the launcher’s solid boosters (EAP) seven seconds later. The launch vehicle began its short six-second vertical climb until the beginning of the pitch motion and roll maneuver.

The solid boosters powered the launch vehicle during the initial phase of the flight until they were jettisoned at two minutes and 23 seconds after launch. Nearly one minute later, the payload fairing was detached, uncovering the mission’s two satellites. The rocket continued the flight while being accelerated by its main stage alone for the next five minutes and 44 seconds. Then, at T+9 minutes, EPC separation occurred.

Afterward, the rocket’s upper stage, known as ESC-A, took control over the flight. Tasked with injecting the duo of spacecraft into orbit, this stage burned its engine for about 16 minutes until it reached the targeted geostationary orbit. Sky Muster II was released first, at 28 minutes and 26 seconds into the flight, while GSAT-18 separated four minutes and seven seconds later.

After the deployment of both satellites, the upper stage conducted its secondary task that included completing a series of engineering tests. Finally, this stage was shut down at T+1 hour and 22 minutes, ending the VA231 mission.

Manufactured by Space Systems Loral (SSL), Sky Muster II is based on the SSL 1300 bus. The satellite has a mass of about 6.4 metric tons, and its dimensions are 27.9 by 9.84 by 11.5 feet (8.5 m × 3.0 m × 3.5 m). The spacecraft’s two deployable solar arrays and batteries will generate up to 16.4 kW of onboard power for more than 15 years of its operational lifetime.

Sky Muster II will be operated by NBN Co Limited – an Australian government-owned corporation that manages the country’s National Broadband Network (NBN). Carrying 202 Ka-band transponders, the satellite will occupy a geostationary position between 135 and 150 degrees East. It is expected to extend high-speed internet to Australia, including the Norfolk, Christmas, Macquarie, and Cocos islands, in conjunction with the services already delivered by Sky Muster I spacecraft that was launched on Oct. 1, 2015.

“The Sky Muster service is intended to be a game changer for the way people work, learn and live in regional and remote Australia,” said Bill Morrow, chief executive officer of NBN.

Ariane 5 lifts off on flight VA231 with Sky Muster II and GSAT-18

Photo Credit: ESA/CNES/Arianespace

The company hopes that Sky Muster satellites will bring them closer to their goal of connecting all Australians to the NBN network. The firm aims to provide everyone in the country with access to fast broadband by 2020.

GSAT-18 is India’s latest communications satellite. It was built by the Indian Space Research Organization (ISRO) and will be operated by the Indian National Satellite System (INSAT). The spacecraft weighs about 3.4 metric tons, and its dimensions are 10.17 by 5.57 by 6.56 feet (3.1 m × 1.7 m × 2.0 m). The satellite is based on ISRO’s I-3K platform and is fitted with two solar arrays and batteries that will generate up to 5.600 kW of power for a designed lifetime of about 15 years.

GSAT-18 will carry 24 C-band, 12 extended C-band, and 12 Ku-band transponders to provide telecommunications services for India. The satellite will be positioned at 74 degrees East longitude and co-located with other operational INSAT satellites.

Commissioned in 1983, INSAT is the largest domestic communication system in the Asia Pacific Region. The system consists of a series of multipurpose geostationary satellites launched by ISRO to satisfy the telecommunications, broadcasting, meteorology, and search and rescue operations. Eleven out of 24 INSAT satellites launched to date are still operational.

“GSAT-18 carries 48 communication transponders to provide services in normal C-band, upper extended C-band and Ku-bands of the frequency spectrum,” ISRO said on its website.

The Ariane 5 in ECA configuration, which was employed for Wednesday’s launch, is the heavy-lift rocket Arianespace uses for missions to geostationary transfer orbit (GTO) and usually carries two telecommunications satellite payloads.

The flight is powered during the initial flight phase by a cryogenic core stage and two solid rocket boosters, followed by the use of a cryogenic upper stage for orbital injection of the payload.

The 180-foot (54.8-meter) tall ECA is an improved version of the Ariane 5 launcher and is designed to deliver payloads, mainly communications satellites, weighing up to 10 metric tons.

Although it has the same general architecture, some significant changes were made to the basic structure of the generic version to increase thrust and enable it to carry heavier payloads. ECA is also used by institutional customers for non-GTO missions; for example, launching ESA’s Herschel and Planck scientific missions in 2008.

Wednesday’s mission was the 233rd liftoff of an Ariane vehicle from the Kourou Spaceport. It was the fifth Ariane 5 launch of 2016 (the 88th Ariane 5 launch overall) and the eighth of 12 flights planned this year by Arianespace, utilizing its family of the heavy-lift Ariane 5, the medium-lift Soyuz, and the lightweight Vega. GSAT-18 and Sky Muster II are the 542nd and 543rd satellites launched by Arianespace.

Arianespace’s next launch is scheduled for Nov. 17 when it is expected to deliver into space four Galileo navigation satellites for the European Space Agency (ESA). That mission will also be performed by the Ariane 5 launcher, lifting off from Kourou.

Video Courtesy of



Tomasz Nowakowski is the owner of Astro Watch, one of the premier astronomy and science-related blogs on the internet. Nowakowski reached out to SpaceFlight Insider in an effort to have the two space-related websites collaborate. Nowakowski's generous offer was gratefully received with the two organizations now working to better relay important developments as they pertain to space exploration.

Reader Comments

Interesting differences in Count Down philosophies. 0 indicates ingnition sequence start as opposed to actual lift off.

⚠ Commenting Rules

Post Comment

Your email address will not be published. Required fields are marked *