Immediately after the touchdown, Phobos-Grunt will load a soil sample into a return rocket. In case of a breakdown of communications with mission control, it can enter an emergency mode to collect samples and still send them home in the return rocket. Normal collection could last from two days to a week.
“There are a number of complications in taking that soil,” Zakharov says. “We are working in near-weightlessness, and to test this on Earth is practically impossible. Therefore, we go into all kinds of tricks.”
Scientists hope that Phobos-Grunt will beam to Earth a panoramic view of Phobos’ surface to help scientists select targets. For collection, engineers had hoped to use a variation of a drill the Soviet Luna probes employed to return samples of Earth’s moon in the 1970s. But in the low gravity on Phobos, which has an average diameter of less than 14 miles, the spacecraft will weigh less than a pound. The action of a drill might overturn the lander, depending on how hard a surface it encounters. So IKI developed a small robotic arm to scoop spots around the craft.
“Obviously, [the scoop] loses the ability to drill deep into the surface, as Luna did,” Zakharov says. “However—and I was personally involved in the analysis of it—the drills by Luna to the depths of more than one meter showed that there is not much difference in the chemical composition of the soil with increased depth. Therefore, it seems [drilling] is not really necessary.”
The scoop can penetrate about an inch below the surface. “What’s really critical here is to take rocks,” says Zakharov. “Because the surface regolith was reprocessed many times, it is very possible it reflects the history of something other than Phobos itself.”
The robotic arm can collect rocks up to about half an inch in diameter. It ends in a pipe-shaped tool that splits to form a claw. This encloses a piston that will push the soil sample into an artillery-shell-shaped container. A light-sensitive photo-diode in the claw will help scientists confirm that the device did scoop material. They hope also to see images of trenches the claw leaves on the surface. The manipulator should perform 15 to 20 scoops yielding a total of three to five and a half ounces of soil.
“Nobody knows what Phobos’ soil is going to be like,” Zakharov says. “It might be perfect beach sand. But we hope—and something is whispering to us—that it will be a combination of sandy soil and small rocks.” IKI scientists studied images from the NEAR probe, which NASA landed on the asteroid 433 Eros in 2001, and concluded that the soil on Phobos may be similar. The team also created a model of Phobos’ soil, based on samples of Earth’s moon, and found that it likely sticks together well enough to stay inside the claw during the transfer to the return container. “We hope that in the lack of gravity, this sticking effect will be even stronger,” says Zakharov.
The return rocket will sit atop the spacecraft, and will need to rise at 22 mph to escape Phobos’ gravity. To protect experiments remaining on the lander, springs will vault the rocket to a safe height, at which its engines will fire and begin maneuvers for the eventual trip to Earth.
The lander’s experiments will continue in-situ on Phobos’ surface for a year. To conserve power, mission control will turn these on and off in a precise sequence. The robotic arm will place more samples in a chamber that will heat it and analyze its spectrum. This analysis might determine the presence of easily vaporized substances, such as water.
In addition to its promised scientific harvest, Phobos-Grunt is rejuvenating old alliances between Russian scientists and their colleagues abroad. Such cooperation reached its finest hour in 1984, when the Soviet Union launched the Vega 1 and 2 probes to Venus. By releasing balloons into that planet’s atmosphere and a flyby of Halley’s Comet, Vega returned volumes of scientific data, forging worldwide scientific cooperation. The spacecraft carried science payloads produced in more than half a dozen countries, and the comet approach included a flotilla of probes from Japan and Europe.