Mars '73: Learning from Mistakes

?? Serge Pod #14.02.2000 20:03

Serge Pod


Mars '73: Learning from Mistakes
by Ted Stryk

The recent failure of NASA's Mars Surveyor '98 missions was a
painful blow to space exploration. However, it was not the first time
a major Mars mission composed of multiple spacecraft has ended in
disaster. It is instructive to look at another failure to learn from
its mistakes and look for parallels with the Mars '98 program.

The year was 1973. The Soviets were coming off their
disappointing Mars 2 and 3 missions two years earlier which had been
largely thwarted by a dust storm (the same dust storm which the
American orbiter Mariner 9 had to wait out before it could begin to
photograph Mars). The 1973 launch window was a particularly
unfavorable one, severely restricting the weight a rocket could send.
However, with America planning to launch its Viking missions in 1975
to land on the Red Planet, the Soviets could not wait. Consequently,
the orbiter/lander combinations they had intended to send were
separated into four launches. Two, Mars 4 and 5, were orbiters that
were to serve as radio relays for the landers, as well as conduct
extensive scientific investigations themselves. They carried numerous
instruments, including multiple spectrometers and cameras. The other
two, Mars 6 and 7, were to deploy landers from a bus that would merely
fly by the planet rather than enter orbit, greatly reducing the
spacecraft weight. The landers were also well-equipped, carrying
television cameras, experiments to measure the composition of the soil
and atmosphere, and instruments to measure temperature, wind speed,
and atmospheric pressure. The flyby bus also carried a few
instruments to study the planet.

It was during launch preparations that engineers made a
horrific discovery: the computer chips that had been integrated into
all four spacecraft contained serious flaws leaving them highly
susceptible to corrosion in space, dooming each spacecraft to suffer
equipment malfunctions and eventually total failure. The chips were
so thoroughly integrated into the spacecraft that replacing them
before the launch was not an option. It became obvious that if the
mission was to succeed, it must be delayed until 1975 at least.
However, despite the elaborate instrumentation of the spacecraft, the
true goal of the mission was not to study Mars. Rather, it was to put
an operational lander on the planet before the Americans did. Thus,
the mission must proceed in the 1973 launch window. They hoped that
at least one of the landers would get lucky and touch down before it
became inoperable.

In late July, Mars 4 was launched, and Mars 5, 6, and 7 soon
followed. As the flight progressed, problems began to crop up. Mars
4 began to leak its fuel into space, and its onboard computer was
impotent to take measures to stop it. Realizing that Mars 4 would be
unable to enter Martian orbit, it was reprogrammed to photograph the
planet as it flew by in February of 1974, allowing one swath of
pictures to be salvaged, along with some ionospheric data obtained
from analyzing the radio signal as the spacecraft was occulted by the
planet with respect to earth.

A few days later Mars 5 arrived at the planet and successfully
swung into orbit, where it began to take data and images. It also was
the task of Mars 5 to serve as a relay for the Mars 7 lander, which
had passed Mars 6 on the way to Mars. However, the computer chips
struck again: Mars 7 lost the ability to maneuver, as Mars 4 had, and
rather than landing, it flew by the planet and headed off uselessly
into interplanetary space, a complete failure.

This left the burden of beating the Americans to Mars 6. In
the meantime, a computer failure aboard Mars 5 led to the
depressurization of its instrument compartment containing the radio
transmitter, causing the orbiter to fail after only twenty two
circuits of the planet. This meant that Mars 6 would have to
accomplish its mission on the surface quickly: with no orbiter
remaining to relay its radio signal back, it would have to rely on its
flyby module as a relay, which would be in a position to do so only
briefly. Having traveled for 219 days, Mars 6 entered the Martian
atmosphere on March 12, 1974, over Pyrrhae Regio (24 deg. latitude, 19
deg. longitude.). However, computer problems caught up with it as
well. Its signal became largely unreadable and often blacked out as
it headed through the atmosphere. As it approached the surface, its
retrorockets did not fire, and it crashed. Such was the inglorious
end of the Mars '73 missions.

Science Results and Lessons Learned

The results gleaned from the Mars '73 spacecraft were meager,
though interesting. Mars 5 provided the first basic characterization
of the plasma and magnetic environment of Mars, giving hints that Mars
might possess a slight intrinsic magnetic field. Occultation data
from Mars 4,5, and 6 yielded the first detection of the Martian
ionosphere on the night side. The Mars 5 gamma-ray data indicated
that the composition of Martian rocks was similar to low silica rocks
found on Earth, while other instruments discovered that Mars was
losing water vapor to space. Mars 5 also provided the first high
resolution color imagery over a small portion of the southern
hemisphere. In all these areas, however, the data were too sparse for
the results to be well understood.

The Mars 6 decent module data from the atmosphere was mostly
uninterpretable, but what was gleaned from the telemetry caused quite
a stir. The craft carried a mass spectrometer that was to measure the
composition of the atmosphere during descent. Due to the volume of
the data, it stored the results on board, and was to transmit its
measurements from the surface. The results were, of course, never
sent, but engineering data from the pump which supplied the instrument
air to analyze did reach Earth. It indicated that the pump was taking
in much more air than expected, indicating that there was a large
amount of some inert substance in the atmosphere, presumably argon.
This caused much concern to the planners of the Viking mission, as a
large amount of argon would wreak havoc on the American landers.
Engineers, however, later found that it was a bad gauge on the pump
that caused the reading, and not Martian argon.

Other than the bogus pump reading, the only other data that
was pulled from the garbled signal were a few measurements from the
accelerometer and Doppler analysis of the radio signal. This yielded
good atmospheric density, pressure, temperature, and wind speed
estimates to about 12 km, with poorer data all the way to the surface
(after 12 km, the signal quality greatly degraded). Analysis of the
signal to the surface yielded a pressure of 5.45 ± 0.3 millibars, a
temperature of -27 ± 8 degrees Celsius, and wind blowing at 8-12
meters per second. This was the first direct weather report from the
Martian surface.

These results, while interesting, provided no great surprises,
other than the erroneous argon measurement. The Soviets worked
frantically to design an improved Mars lander for the 1975 launch
opportunity, but were unsuccessful in doing so on time, and after the
spectacular success of the American Viking mission, the Soviets ceased
their Mars activity for the next 14 years. They operated under the
idea that if they could not do something first, it was not worth
doing. They had by that time successfully landed on Venus several
times, and would concentrate their future planetary exploration
missions there.

Despite the very different origins of Mars '73 and Mars '98,
there are some parallels. Although in one case it was politically
motivated, and in the other case motivated by budget, both missions
were rushed to launch with inadequate testing. Also, that rush caused
problems to be ignored or accepted rather than solved because of lack
of time and resources.

The Soviet Mars program is now a thing of the past, but the
American program continues. Hopefully, unlike the Soviets in '73,
America will not use its recent failure as a reason to give up, but
instead look into the factors that caused Mars '98 to fail, and look
to safeguard future missions against suffering the same fate. If its
failure leads to no longer sending out missions without adequate staff
and resources, and rushing under-tested spacecraft to the launch pad,
some good might yet come out of the ill-fated mission.

Ted Stryk is a senior philosophy major at Carson-Newman College in
Jefferson City, Tennessee. He has spent three years as a planetarium
intern and has been active in the Association of Lunar and Planetary
Observers, publishing several articles in its journal.

This has been the February 14, 2000, issue of SpaceViews.
In knowledge we trust!  

в начало страницы | новое
Твиттер сайта