Proton-M returns to flight with launch of Inmarsat 5-F3

Tomasz Nowakowski

Proton-M lifting off with the Inmarsat 5-F3 satellite. (Click to enlarge.) Photo Credit: Roscosmos

The Russian Proton-M launch vehicle, grounded since the May 16 accident when it failed to send the Mexican Mexsat-1 communications satellite to orbit, has returned to regular flights by successfully launching the British Inmarsat 5-F3 comsat into a supersynchronous orbit. The flawless launch took place on Friday, Aug 28, at 7:44 a.m. EDT (11:44 GMT) from Launch Pad 39 at the Baikonur Cosmodrome in Kazakhstan.

The countdown for the launch, conducted by International Launch Services (ILS), started on Thursday, some 11 and a half hours before the planned liftoff. After the launch, the Proton-M, utilizing a 5-burn Briz-M rocket stage, commenced a standard ascent profile, burning its six RD-275M engines for two minutes, until first stage separation occurred. Three minutes and 27 seconds later, the second stage separated from the launcher and, shortly after that, payload fairing separation occurred. The launch vehicle flew for an additional four minutes until the third stage was detached from the Briz-M.

The Briz-M upper stage, during its trip to the targeted supersynchronous orbit, completed five engine burns to increase its orbital altitude. After completing all these burns, the satellite was deployed, approximately 15 hours and 31 minutes after lift-off.

Inmarsat 5-F3 is planned to operate from a position of 180 degrees west, joining the F1 satellite that is located at 63 degrees east and F2 at 55 degrees west. It will deliver Global Xpress services to the Pacific Ocean Region, complementing Inmarsat 5-F1’s coverage in the Indian Ocean Region and Inmarsat 5-F2’s coverage in the Americas and Atlantic Ocean Region. Global Xpress will be the first globally available high-speed mobile broadband network delivered by a single operator. It will be provided via an initial fleet of three Inmarsat 5 satellites.

Inmarsat 5-F3, built by Boeing Satellite Systems for the British satellite telecommunications company, is based on Boeing’s 702HP High-Power Satellite Platform that is capable of hosting powerful communications payloads. The spacecraft will have a launch mass of 6.1 metric tons.

The spacecraft has the height of a double-decker bus – about 22.9 ft. (6.98 m). It includes 89 Ka-band beams generated by two transmit and two receive apertures and six steerable spot beams to direct additional capacity where it is required. The satellite features a xenon ion propulsion system (XIPS) that will handle in-orbit maneuvering. Using ion thrusters is more efficient in terms of fuel consumption and could extend a satellite’s lifetime. Inmarsat 5-F3 is expected to be operational for 15 years.

The launch campaign was resumed in early August after the satellite had to remain in storage for three months, being kept safe as it waited for liftoff. The Proton failures in 2013 and 2014 forced the rescheduling of Inmarsat’s plans. The Proton-M accident in May came exactly a year after the same model of the booster carrying Russia’s most advanced communications satellite fell back to Earth just minutes after lift-off.

The satellite underwent a set of stand-alone testing to ensure it was functioning well after its long wait inside the processing facility. The propellant loading on the satellite was completed by Aug. 12 as it received propellants for the climb to orbit and stationkeeping once reaching its destination.

Next was the integration of the Upper Composite of the vehicle that was completed by Aug. 17 as the satellite was installed atop its payload adapter and then joined to the Briz-M upper stage. Afterward, the stack was encapsulated in the protective payload fairing and transferred to the Launcher Integration Building where the assembled three-stage Proton rocket was awaiting the installation of the payload stack.

The rocket was rolled to the Briz-M fueling station on Sunday, Aug. 23. At the fueling station, the upper stage received nearly 20 metric tons of Unsymmetrical Dimethylhydrazine and Nitrogen Tetroxide.

Proton-M made its way to the launch pad on Tuesday, Aug. 25. After arriving at the launch pad, the rocket was placed in its vertical launch position. Teams moved the Service Structure into position around the vehicle to provide access platforms for the final preparatory steps performed prior to the initiation of the countdown. These measures include detailed testing of the Proton-M and Briz-M systems to ensure all subsystems are ready to support the mission.

The Proton-M booster used for the Friday launch is 4.1 m (13.5 ft) in diameter along its second and third stages, with a first stage diameter of 7.4 m (24.3 ft). The overall height of the Proton booster’s three stages is 42.3 m (138.8 ft).

The first stage consists of a central tank containing the oxidizer surrounded by six outboard fuel tanks. Each fuel tank also carries one of the six RD‑276 engines that provide power for the first stage. The cylindrical second stage is powered by three RD-0210 engines plus one RD‑0211 engine. The third stage is powered by one RD-0213 engine and a four-nozzle vernier engine. Guidance, navigation, and control of the Proton-M during operation of the first three stages is carried out by a triple redundant closed-loop digital avionics system mounted in the Proton’s third stage.

The Briz-M is powered by one pump-fed gimbaled main engine. This stage is composed of a central core and an auxiliary propellant tank that is jettisoned in flight following depletion. The Briz-M control system includes an on-board computer, a three-axis gyro stabilized platform, and a navigation system. The quantity of propellant carried is dependent on specific mission requirements and is varied to maximize mission performance.

Today’s mission is the third Proton-M launch this year and the first since the May 16 accident. That failure had delayed the Inmarsat 5-F3 launch that was initially planned to be launched in June.

For the next Inmarsat 5-F4 satellite launch, the company has chosen SpaceX’s Falcon 9 rocket, but given Falcon’s recent launch accident, this satellite will likely also encounter delays.

“We believe that SpaceX has demonstrated tremendous successful progress in its launch capabilities and is now a fully-credible provider of vehicles to support geostationary missions. In view of capacity constraints in the satellite launch market, Inmarsat believes that securing optionality today is an important business safeguard to mitigate future launch schedule risk,” Jonathan Sinnatt, the Director of Corporate Communications at Inmarsat, told SpaceFlight Insider.

Friday’s flight marks the fourth Inmarsat satellite launched on a Proton rocket and the 90th ILS Proton launch overall.

Video Courtesy of RT News