With launch of British communications satellite, Proton-M rocket set to return to flight
The Russian Proton-M rocket is well on track to return to regular flights after the May 16 accident when it failed to deliver the Mexican Mexsat-1 communications satellite. On Friday, Aug. 28, the International Launch Services (ILS) company will use the booster to send the British Inmarsat 5-F3 satellite into a supersynchronous transfer orbit.
The launch is scheduled to take place at 7:44 a.m. EDT (11:44 GMT) from Launch Pad 39 at the Baikonur Cosmodrome in Kazakhstan. The Proton-M launch vehicle, utilizing a 5-burn Briz-M rocket stage, will be responsible for delivering the satellite into space.
The first three stages of the Proton-M rocket will use a standard ascent profile to place the orbital unit (Briz-M upper stage and the Inmarsat-5 F3 satellite) into a sub-orbital trajectory. From this point in the mission, the Briz-M will perform the planned mission maneuvers to advance the orbital unit. Firstly, to a circular parking orbit, then to an intermediate orbit, followed by a transfer orbit, and finally to a supersynchronous transfer orbit.
Separation of the Inmarsat-5 F3 satellite is scheduled to occur approximately 15 hours, 31 minutes after the lift-off.
The satellite is currently in the final phase of preparations for the flight.
“The team at the Baikonur Cosmodrome in Kazakhstan has completed the fueling [of] the spacecraft for flight and Inmarsat-5 F3 is now safely ‘latched’ on top of the rocket fourth stage or Briz-M upper stage as it is usually called,” Jonathan Sinnatt, the Director of Corporate Communications at Inmarsat, told SpaceFlight Insider.
“The Briz-M will release the spacecraft at 65,000 km from the Earth using pyrotechnic devices which will literally be exploded in flight and release the latches,” he added.
The Proton-M rocket was rolled out to the Launch Facility on Tuesday, Aug. 25. It was then erected vertically onto the launch pad. Ground processing for the upcoming launch is also proceeding on schedule.
Inmarsat 5-F3, built by Boeing Satellite Systems for the British satellite telecommunications company based on Boeing’s 702HP High-Power Satellite Platform that is capable of hosting powerful communications payloads. The satellite 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 needed. 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.
Once operational, the satellite will deliver Global Xpress services to the Pacific Ocean Region, complementing Inmarsat 5-F1 coverage in the Indian Ocean Region and Inmarsat 5-F2 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.
The mission on Friday, Aug. 28, will be the third Proton-M launch this year and the first since the May 16 accident. The failure has delayed the Inmarsat 5-F3 launch that was initially planned to be launched in June.
“This incident involving a failed Proton launch… is extremely unfortunate and will inevitably delay our launch plans for our third Global Xpress satellite,” Inmarsat Chief Executive Rupert Pearce said in May. “This is the third time our Global Xpress program has suffered launch delays because of Proton launch failures.”
The Proton failures in 2013 and 2014 forced the rescheduling of Inmarsat’s plans. The Proton-M failure 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 Proton-M booster that will be 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.
Friday’s flight will mark the fourth Inmarsat satellite to be launched on a Proton rocket and the 90th ILS Proton launch overall.
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.