PARIS — Satellite fleet operator Satmex has again revised upward its estimate of how long the Satmex 5 satellite can remain in orbit as the company awaits a return to flight of the Proton rocket to launch Satmex 5’s replacement.

According to a fresh estimate of the fuel remaining on Satmex 5, made by Comsat Technical Services, Satmex said Satmex 5 will be able to remain operational at least until Oct. 5, 2013, five months longer than a previous estimate made this year, which was already an extension of previous end-of-life predictions.

Industry officials have said precisely estimating a satellite’s remaining fuel, and thus the amount of time it can remain fully stabilized in orbit before either being placed in inclined orbit or retired, remains as much an art as a science.

The Satmex 5 lifetime has taken on added drama in recent months because of two failures — one in August and a second on Dec. 9 — that have pushed back the launch date of Satmex 8.

The satellite, built by Space Systems/Loral of Palo Alto, Calif., had already arrived at the Baikonur Cosmodrome in Kazakhstan to prepare for a Dec. 28 launch when the Proton rocket’s Breeze M upper stage shut down early.

The failure left the Yamal 402 telecommunications satellite, owned by Gazprom Space Systems of Moscow, in a useless orbit. Yamal 402, built by Thales Alenia Space of France and Italy, has since been raised to geostationary orbit. It remains unclear how many years of life it expended making the climb from where the Breeze-M stage left it.

Industry officials have said it is likely that Yamal 402 will have at least a decade’s life in orbit remaining, perhaps a bit more, as it was fueled to the brim in preparation for a service life well beyond its contracted 15 years.

Satmex said it had completed its analysis of the Comsat fuel assessment Dec. 12. The company said it hired Comsat to perform a “propellant gauging system” study, which Satmex said yielded a worst-case scenario that put Satmex 5 out of service in early October.

Satmex and the other customers of International Launch Services (ILS) of Reston, Va., which markets the Proton vehicle, are now awaiting parallel investigations into the Dec. 9 failure and an indication of when Proton will return to service.

Satmex said the new October end-of-life assessment should give Proton’s builders and the investigation teams “adequate time to reach resolution and execute the corrective actions necessary to ensure the reliable launch of Satmex 8.”

Peter B. de Selding was the Paris Bureau Chief for SpaceNews.