Several years ago, mission
scientist Aleksandr Selivanov explained the cigar-shaped shadow in the
Fobos-2 images this way.
The imaging system is a
"scanning radiometer," not a camera, Selivanov pointed out. A
rotating mirror moves perpendicular to the line of the probe's motion
over Mars. As a result, "a picture is generated by the motion of
the spacecraft in its orbit." The probe did NOT gather an entire
image in one snap, but accumulated it over a period of time, line by
line.
Fobos-2 was staring straight
back along the Sun-to-Mars line, to get the best infrared readings. In
contrast, visible light imagers prefer to look for shadows cast by
surface features, so they are aligned at large angles to the Sun's rays.
This made the visible-light images from Fobos-2 look washed out.
Now, Fobos-2 was quite near
the moon Phobos in the last days of its flight, both circling Mars along
the same path. So the roundish shadow of Phobos was on Mars's surface,
within the field of view of the scanner, when the scanner was looking
"down sun" at Mars.
Selivanov explained that if
the probe had been rock steady, the Phobos shadow would have left a dark
streak right through the entire center of each image, as the image was
assembled line-by-line over the course of each orbit. Because of a
slight rocking of the probe, however, the scanning beam
"sliced" the Phobos shadow at different points, from back to
front, over the course of each imaging session.
The resulting elongated shadow
is thus an artifact of the imaging technology, and of the probe's motion
through space and around its own axis. Selivanov argued that since these
shadows are all precisely aligned along the probe's flight path over
Mars, they are unquestionably not shadows of other objects near Mars.
They show the shadow of Phobos.
One supposed photograph, the
"last one before the attack," shows Phobos and a bright
vertical line below it. Since the line runs right along the telemetry
scan lines, space experts are confident it is some sort of transmission
flaw, not a real object in space. Besides, the date on the image is
March 25, two days before the probe's loss.
Hurry and other human
errors
The breakdown of Fobos-2 was
disappointing to experts associated with the program, but not
surprising. They had seen human error doom its sister craft, Fobos-1,
before it even got to Mars, and they had seen signs that Fobos-2 wasn't
in much better shape.
Dr. Larry Soderblom was one of
the American scientists who had instruments aboard the probe.
"There is a feeling in the American space science community the
Russians were in too much of a hurry," he later told a reporter.
"The two satellites lost were launched without much thought to a
system of checks and balances that might have prevented such
problems."
And even the design was
questionable. "Soviet scientists at the Space Research Institute in
Moscow complained that the new, sophisticated spacecraft actually was
designed for purposes other than those for which it was being used on
the missions to Phobos," wrote a British space expert.
"Engineers adapted it for the mission in order to flight-test it
for future missions to which it was considered better suited."
These problems were recognized
even as the missions were launched. I remember telling another reporter:
"I'd be surprised if both make it -- and I wouldn't be surprised if
neither do."
Everything returns
But space is full of
surprises, and 11 years later, Fobos-2 has suddenly been reborn. A
rocket stage based on its design was launched into orbit on February 9
and performed perfectly.
A second and more ambitious test on March 20 also
went perfectly.
The stage is called "Fregat,"
Russian for "Frigate" -- and in fact, on many Fobos-2
photographs from 1989, one can read the designation "Phobos-Fregat."
In 1995, project manager Vladimir Ashushkin described to me his hopes
for a commercial deal to carry paying customers into space by adapting
and improving the interplanetary module.
That deal has now been signed
with a number of European customers and Fregat spacecraft will soon be
heading off into space again, into high Earth orbits, out to the moon,
and even back to Mars -- a Fregat is slated to carry the European Space
Agency's Mars Express
probe in 2003.
With a better design, and
better luck, the curse of Fobos-2 may be dispelled. But Mars may have
its own ideas about that!