Last week, the European Space Agency released its report on the crash of Russia’s ill-fated Phobos-Grunt probe on Jan. 15. In it, the ESA came to the same conclusion as the other major space players: all pieces of the probe, which was bound for one of Mars’s moons, fell safely into the Pacific Ocean.
But this consensus isn’t reasonable at all.
Instead, a sound analysis of the data by space debris experts suggests that although most of the debris did plunge into the Pacific Ocean, other debris may have fallen onto regions of Chile and possibly Argentina.
This debris on land likely included the heaviest pieces, possibly even the heat-shielded return capsule carrying three bio-canisters – one from the U.S. Planetary Society and two others from the Russians, that organisms that were to test the “transpermia” hypothesis. Slowed by air drag, they would have hit the ground with speeds of only a few hundred miles per hour.
Some hazardous materials, such as 11 tons of rocket propellants, probably did disperse on the way down. But some of the smaller tanks, including a few likely made of titanium, could have survived. No pieces of the satellite have turned up yet, and actually searching for space debris is rarely successful. But once in a while, somebody stumbles across a genuine “space fall.”
Yet instead of alerting these nations to warn their citizens to watch out for any such debris, so far, the official response has been to deny the possibility of debris reaching dry land. Officials insist that the probe has “fallen into the Pacific.”
Confusion over the “entry point”
To explain how debris from Phobos-Grunt could have made landfall, it’s important to understand the terms “entry point” and “impact point.”
The US Strategic Command defines ‘entry point’ as the location where the descending probe falls below an altitude of 80 kilometers (about 50 miles), where air drag has built up into a destructive force. At this point the vehicle is beginning to “demise,” or disintegrate.
What is not always obvious is that such objects entering the atmosphere from orbit are not falling straight down. They have an enormous horizontal velocity. An entering object starts out at about 8 kilometers (25,000 feet) per second, but drops off rapidly as it enters thicker layers of the atmosphere. Nonetheless, a satellite that has passed its ‘entry point’ is still carried far downrange by its remaining inertia. In other words, it is falling “down” but also a lot “sideways.”
Heavier materials would fly farther, and lighter objects – such as emptied fuel tanks or scraps of engine nozzles – would fall sooner. All would fall within a narrow band to either side of the ground track, influenced mainly by any crosswinds.
The Russian location was frequently described in the news media (particularly in Russia) as the observed impact point, but Colonel Aleksey Zolotukhin, the Aerospace Defense Forces official who released it, made it clear it was an estimation based on calculations from the earlier orbital path. No actual observations – radar, visual, telemetry – existed. It was described as the place where the spacecraft entered the atmosphere. The Russian Federal Space Agency, Roscosmos, however, turned this modest and reasonable announcement into “the exact observed impact point.”
Moscow newspapers called it the spot “where the satellite dropped off their screens.”
Another look at Phobos-Grunt’s trajectory
The entry point identified by the U.S., also based on calculations, is very likely consistent with top secret observations by US missile-warning infra-red telescopes in space. So it is probably the most reliable candidate for location of where entry began – that is, where the satellite fell below 80 km.
The track of Phobos-Grunt. © Robert Christy, www.zarya.info
Projected forward, the probe’s final ground track crosses the Chilean coast between Concepcion and Valdivia in a northeastwards direction, crosses Argentina over the neighborhood of Cordoba and Resistencia, and clips southern Paraguay before entering Brazilian airspace along the Paraná River. Posting on a discussion at Universetoday.com, Luciano Anselmo of Italy’s “Space Flight Dynamics Laboratory” in Pisa described his team’s analysis of the path of debris after it entered.
Anselmo wrote: “We found that the small capsule with the LIFE experiment (the only element of Phobos-Grunt designed to survive reentry) should have impacted the ground approximately 820 km eastward along the trajectory and 15 minutes later…”
The US STRATCOM “entry position” was for Jan 15 17:46 GMT ± 1 minute, and the “Predicted Decay Location” was 46°S, 273°E. Using Google Earth’s ruler function, this places the entry 930 km off the South American coast, and about 1100 km from landfall along the probe’s north-east inclined ground track.
But each minute of error in the predicted moment of entry is equivalent to about 450 kilometers of orbital motion along its horizontal track. So using Anselmo’s calculated downtrack for the capsule, it would have fallen short of the coast by about half a minute, at the midpoint of the predicted interval. But that interval had a plus/minus uncertainty of an extra minute either way. And it easily could have been more.
Furthermore, the return capsule was designed to be passively stable through an entry and descent that deliberately was “draggy” — that is, it tried to slow down as quickly as possible. But other fragments, such as heavy metallic trusses, would have been slowed proportionately less and thus flown further.
Jonathan McDowell, one of the world’s foremost amateur satellite trackers, looked at the same issue and wrote, “the most probable debris area is still in the Pacific off the coast of Chile, but there’s a very slight chance some heavy debris might have made it all the way to Chile or northern Argentina.” Data from earlier satellite re-entries, such as NASA’s Upper Atmosphere Research Satellite, on the contrary, shows that it is very likely that some of the heavier pieces did cross the Chile coast, and that well within the margins for error of the predicted entry time, even the high-value landing capsule could have.
Adding to the suspicion of the official version out of Moscow is a well-documented history of deception over falling satellites. In 1977, pieces of the nuclear satellite Kosmos-954 survived reentry and left radioactive debris across northern parts of Canada.
In 1999, Russia’s Mars-96 probe also got stuck in parking orbit. It fell into the atmosphere only hours after launch, carrying a number of plutonium batteries that could present a substantial health hazard to any finders. After some confusion created by a jettisoned propulsion module that was assumed to be the probe itself, Russian officials assured everyone that the probe had fallen into the Pacific, even though it eyewitnesses spotted it heading toward Bolivia on a clear night,
Then, as now, Russia did not seem interested in knowing what actually happened to its probe.
Top image: Model of Phobos Grunt’s base section by Roscosmos at the 2007 Paris Air Show. Courtesy Wikipedia user Wikibob
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James Oberg is the author of ten books on space flight, including Red Star in Orbit: The Inside Story of Soviet Failures and Triumphs in Space. He served as a space engineer at NASA’s Johnson Space Center in Houston as a contractor for 22 years. His opinions do not necessarily reflect the views of Txchnologist.