Ariane 5 lofts two satellites in important lead-up to James Webb launch

by Justin Davenport

Close to one year after its last flight, the Ariane 5 ECA has returned to service with its first launch of 2021, lifting off at 21:00 UTC on Friday, July 30. The sixth overall mission for Arianespace this year follows a rework of the payload fairing due to vibration issues that could have endangered payloads.

On board the mission, named VA254, were two communications satellites bound for geostationary transfer orbit. This flight is the first of two that precede the launch of the James Webb Space Telescope as early as this November.

The JWST program found that residual air in the telescope’s sunshield could cause an over-stress condition at the time of fairing separation, so the payload fairing was redesigned for a smoother de-pressurization process with new passive vents and sealant to trap air inside the fairing’s honeycomb material, in order to help ensure mission success for this most important payload. RUAG of Switzerland delivered these fairings for flights starting in early 2020.

However, during the Ariane flights in February and August 2020, the separation process with these redesigned fairings induced unacceptable vibrations into the payload stack. While these vibrations did not result in any sort of mission failure, Arianespace stopped flights of the Ariane 5 to investigate the issue.

The investigation also affected certain United Launch Alliance Atlas V flights that use similar fairings.

Ariane 5 launches the VA253 mission in August 2020, the final flight before a stand-down to investigate and resolve a payload fairing vibration issue – via ESA

Although no damage was done to the payloads on board the two flights where these vibrations were observed, they could have damaged the JWST and other future payloads, so a further redesign of the fairing was needed. The reworked fairings were delivered by RUAG to Arianespace and must now prove themselves on two flights before the James Webb Space Telescope can proceed on its long-awaited launch.

Flight VA254 launched two satellites into geostationary transfer orbit from Arianespace’s launch facility in Kourou, French Guiana. The Ariane 5 lifted off at 21:00 UTC on Friday, July 30 with the Star One D2 and Eutelsat Quantum communications satellites.

The Star One D2 satellite, massing 6190 kilograms and based on the Maxar 1300 bus, is intended to support telecommunications in South America, Central America, and the Atlantic, and was built for Brazilian operator Embratel by Maxar Technologies at its factory in Palo Alto, California. This satellite, which will occupy the 70 degrees West longitude slot in geostationary orbit, features Ku, Ka, C, and X-band transponders, which enables it to support communications using different wavelengths for multiple purposes.

For example, the X-band transponder will support government communications traffic over the Atlantic Ocean, while the other bands will be used to offer broadband services in South and Central America, though not with the speeds that low Earth orbit constellations like Starlink would offer due to the distance signals travel between Earth’s surface and geostationary orbit at 35,786 kilometers altitude. Underserved populations would be the primary users of this service.

The Star One D2 satellite undergoing testing at Maxar prior to shipping for launch – via Maxar

The Eutelsat Quantum satellite has a launch mass of 3461 kilograms and is built by Airbus Defence and Space based on the SSTL GMP-T bus. It is the first European commercial-sector communications satellite with programmable frequencies and power usage so that customers can shape the coverage to their specific needs. The satellite features an electronically steerable Ku-band antenna with eight independent, configurable beams to enable this capability.

Eutelsat Quantum will use a slot at 48 degrees East longitude to cover the Middle East and North Africa, with possibilities to cover a region from West Africa to further east in Asia. The spacecraft is equipped with the ability to support encrypted traffic, as its services are being offered to government users in the Middle East.

The Ariane 5 was rolled out to the launch pad on Thursday, July 29, and is fueled with liquid hydrogen and liquid oxygen starting just under five hours before the launch. The Vulcain 2 engine on the core stage ignites at T-0 and builds up its thrust.

At T+7 seconds, the solid rocket boosters ignite and the vehicle leaps off the pad with its satellite passengers. The SRB’s were jettisoned around T+2:20, and the all-important fairing separation occurred around T+3:10.

The core stage’s Vulcain 2 engine shut down around the T+9 minute mark, and the ESC-D upper stage separated and ignited shortly afterward to place the stage and the satellites in a 250 by 35,726 kilometer geostationary transfer orbit inclined three degrees to the Equator.

After the ESC-D stage did its work, the Star One D2 satellite separated first, from the top of the SYLDA structure (a “fairing within a fairing”) that contains the Eutelsat Quantum satellite.

The SYLDA structure separated after Star One, exposing Eutelsat Quantum for its deployment. The Eutelsat Quantum satellite’s deployment at the T+36:24 mark completed the VA254 mission, and both satellites will now continue coasting on their own to geostationary altitude.

Once at the apogee of 35,726 kilometers, they will use their own propulsion systems to circularize the orbit and change their orbital inclinations to zero degrees to occupy their operational slots, where they are expected to stay in service for the next fifteen years.

The launch vehicle’s performance, particularly the performance of its reworked payload fairing, will be closely scrutinized by NASA as well as ESA and RUAG in the run-up to flight VA255 no earlier than September with the SES-17 and Syracuse-4A satellites, to be followed by the VA256 flight of the James Webb Space Telescope, which promises to make significant discoveries in astronomy.

(Lead photo via ESA)

Related Articles