Russia’s space agency yesterday called off all predictions of the likely crash site of its ill-fated Mars probe only hours before the 13.5-tonne spacecraft was due to begin its fatal descent.
Roscosmos said on its Web site that fragments of the stranded Phobos-Grunt voyager would probably fall to Earth yesterday between 1436 GMT and 2224 GMT.
However, it canceled its Saturday forecast of the debris splashing down in the Pacific off the western coast of Chile. Two earlier updates had the fragments falling into the Indian and Atlantic Oceans.
The ITAR-TASS news agency cited space agency sources as saying the descent was now likely to begin at 1751 GMT.
The unmanned US$165 million vessel — stuck in a low Earth orbit since its Nov. 9 launch — will be one of the largest objects to re-enter the atmosphere since Russia brought down the Soviet-era Mir space station in 2001.
It is loaded with enough toxic fuel to take it to the mysterious Mars moon Phobos and is weighed down further by a Chinese satellite it had been scheduled to put into orbit around the Red Planet.
Roscosmos predicts that only 20 or 30 segments weighing no more than 200kg combined will survive the fiery re-entry and actually hit the Earth’s surface.
Meanwhile, the chief NASA scientist on orbital space debris dismissed the threat posed by the craft’s toxic fuel.
Nicholas Johnson said the Russian craft’s fuel tanks are made of aluminum rather than the much tougher titanium metal preferred by US space officials.
“According to Mr Johnson, aluminum has a lower melting point than titanium and that significantly reduces the chances of the propellant reaching the surface of the Earth,” NASA reported on its Web site.
ITAR-TASS said Roscosmos expected the fuel to burn up at an altitude of 100km.
The inglorious ending provides a bitter reminder for Russia of the prowess it has lost in the half-century since Yuri Gagarin’s historic first space shot in 1961.
The ambitious project had initially aimed to revive Russia’s interplanetary program and prepare the way for a manned mission to Mars.
However, Russia lost sight of the probe almost immediately after its launch and then spent weeks trying to send commands that would either nudge it on its way to Mars or at least enable its controlled return to Earth.
Neither proved successful and Roscosmos now admits that the impact location will depend on varying circumstances such as atmospheric density and even solar activity.
“The change in the time and location of the fragments’ landing ... is based on the diminishing altitude of the vessel’s orbit, solar activity and atmospheric conditions,” Roscosmos said.
The November accident instantly came to represent one of the more high-profile mishaps in a year littered with unprecedented setbacks in the Russian space program.
It struck less than three months after an unmanned Progress supply ship bound for the International Space Station crashed into Siberia.
Russia has also lost three navigation satellites as well as an advanced military satellite and a telecommunications satellite over the past year.