ILS Proton M successfully launches Intelsat 31 despite underperformance
International Launch Services (ILS) has launched its Proton M rocket on Thursday from the Baikonur Cosmodrome in Kazakhstan. The Russian workhorse – successfully lofted the Intelsat-31 communications satellite on a multi-hour flight to its transfer orbit – despite an underperformance from the Proton-M booster than required the Briz-M upper stage to pick up the slack.
Proton M Mission:
ILS noted the launch was postponed from its initial launch target due to an issue associated with electrical ground system equipment at Launch Pad 24.
“The issue has been identified, equipment has been replaced and verification of all associated cabling and connectors is in work. The Proton launch vehicle and the Intelsat 31 satellite were unaffected and remain in a safe configuration at the launch site,” added the company.
Following a successful outcome of the cable and connector verifications, Khrunichev State Research and Production Space Center were ready to make another attempt at 07:10 UTC on Thursday.
ILS confirmed the issue was resolved during Wednesday, adding and clarifying: “following the additional verifications of the cables and connectors associated with last night’s issue which resulted in a delay to the Intelsat 31 launch, the problem has been isolated to a connector on the flight vehicle.
“The ground system was wrongly identified as the cause of the delay. The flight connector issue has been resolved and the vehicle cleared for flight.”
The Proton booster that launched Intelsat-31 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 three stages of the Proton booster is 42.3 m (138.8 ft).
The Proton vehicle has a heritage of over 400 launches since 1965 and is built by Khrunichev Research and State Production Center, one of the pillars of the global space industry and the majority owner of ILS.
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 first stage power. Total first stage vacuum-rated level thrust is 11.0 MN (2,500,000 lbf).
Of a conventional cylindrical design, the second stage is powered by three RD-0210 engines plus one RD-0211 engine and develops a vacuum thrust of 2.4 MN (540,000 lbf).
Powered by one RD-0213 engine, the third stage develops thrust of 583 kN (131,000 lbf), and a four-nozzle vernier engine that produces thrust of 31 kN (7,000 lbf).
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.
It has suffered its fair share of problems, but successfully conducted a Return To Flight (RTF) mission in 2015, following the May 16 failure that resulted in the loss of the MexSat-1 (Centenario) communications satellite on what was supposed to be a multi-hour flight to its transfer orbit.
This was ILS Proton’s second mission of the year, utilizing a 5-burn Breeze M Supersynchronous Transfer Orbit (SSTO) mission design.
The first three stages of the Proton used a standard ascent profile to place the orbital unit (Breeze M upper stage and the Intelsat 31 satellite) into a sub-orbital trajectory.
Due to an apparent underperformance by the Proton-M, the first burn of the Briz-M was longer than scheduled to make up for the shortfall. Roscosmos noted that one of the four second stage engines shut down nine seconds early, causing the lack of performance.
From this point in the mission, the Briz-M performed mission maneuvers to advance the orbital unit first 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 Intelsat 31 satellite occurred approximately 15 hours, 31 minutes after lift-off.
Intelsat 31, a flexible, powerful satellite built by SSL for Intelsat. It will be co-located with Intelsat 30 at 95 degrees West longitude, where it will augment and provide redundancy and reliability for direct-to-home broadcast services.
The 20-kilowatt satellite will be used by DIRECTV Latin America for high definition programming throughout Spanish-speaking South American and the Caribbean.
The SSL-1300 platform bird – sporting C-band and Ku-band transponders – has a separated spacecraft mass of 6,450 kg. It is expected to have a service life of 15 years.
“A launch is always a culmination of years of hard work and dedication that begin with the design and manufacture of the satellite up to its delivery to orbit,” noted said Executive Vice President and Chief Technology Officer, Thierry Guillemin.
“We appreciate all of the teams who worked with us to make this program another success, including ILS and Khrunichev for ensuring a successful launch.”
This mission was the 12th Intelsat satellite to be launched on the ILS Proton. Overall, it was the 28th SSL platform satellite involving an ILS Proton launch.
ILS made no reference to the issues suffered by the Proton-M during the launch.
“Our partnership with Intelsat spans 18 years with 12 of their satellites launched to date by Proton with the launch of Intelsat 31. We look forward to extending our partnership further with more launches over the coming years under our Multi Launch Agreement with Intelsat,” added ILS President Kirk Pysher.
“Each and every team member should be commended for their contributions to the success of the Intelsat 31 mission.”
(Images via ILS and SSL).