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On Mars:
Exploration of the Red Planet. 1958-1978
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- PLANNING SITE
CERTIFICATION
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- Certification Team
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- [317] In August 1973, Jim Martin selected
Hal Masursky to lead the landing site certification team, with
Norman L. Crabill from Langley as his deputy. This group, which
functioned as an operational organization rather than a planning
body, included members from orbiter imaging, infrared thermal
mapping, Mars atmospheric-water detection, and mission planning
and analysis teams, as well as radio astronomers.
1 Together they designed a strategy for landing site
certification, which R. C. Blanchard of the Viking Project Office
presented at the February 1974 meeting of the Science Steering
Group. Blanchard broke the certification process down into four
periods: l. Pre-Mars orbit insertion (MOI) for Viking 1 . 2.
Post-MOI and prelanding for Viking 1
. 3. Postlanding for
Viking 1 ; pre-MOI for Viking 2
. 4. Post-MOI and prelanding for
Viking 2 . Blanchard noted that before the first Viking
spacecraft orbited Mars, new sources of data that might possibly
affect the landing sites could include Earth-based radar studies
of the planet, Soviet missions flown before June 1976, and
scientific observations made by Viking as it approached Mars.
Analyzing all new information would help them make a "go/no-go"
decision concerning the desirability of landing at the prime site
latitude and, they hoped, would contribute to ``A-1" site (first
choice for first lander) certification.
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- [318] Viking
1 would make extensive
observations of the prime site, with special emphasis on the
low-altitude photographs obtained during the close approach
(periapsis). In addition, two or three picture pentads (groups of
five photos) would be taken on each revolution to permit
comparison of images taken at different exposures (due to the
elevation angle of the sun). The A-1 site would also be studied by
the orbiter water-vapor detector and infrared thermal-mapping
instrument to determine if the scientists' preconceived notions
about the target were valid. Viking
1 would also observe the second
lander's primary target (E- l) from low altitude with two picture
swaths and one high-altitude pentad. Should the A-1 site be found
acceptable (certified), then the lander would be targeted for that
site. If it was not acceptable, then the backup site (A-2) would
be examined. Once a landing area was chosen, orbiter trim
maneuvers would fix the spacecraft's periapsis near that
site.
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- During the third period, postlanding for
Viking1 and preorbit insertion for Viking 2, information sources
available to Earth control would include B-1 site data from the
first orbiter, entry and landed science data from the first
lander, evaluation of the first site certification procedure, and
approach observations made by Viking
2 . The team would then make its
commitment to the B mission target. Once the second craft was in
orbit, the men would confirm a B- l site using additional data
from the second orbiter and the further assessment of Viking 1
science results. Blanchard assured the Science Steering Group that
the A-1 and B-l targets chosen by the landing site working group
definitely would be used, unless compelling arguments materialized
to require a change. Further, the scientists were reminded that
the certification team would continue to be influenced strongly by
considerations of safety during the first landing, but hoped that
during the second landing it could look for a more scientifically
interesting site even if less safe than the first.
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- The first new data the Viking team
received came from the Soviet missions.
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- Soviet Attempts to Investigate
Mars
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- Much to the dismay of everyone working on
Viking, the four flights the Soviets sent to Mars in 1973 raised
as many issues as they settled. Mars
4 and 5 were launched on
22 and 25 July, followed by Mars 6
and 7 on 5 and 9 August.
Mars 4 came within 2100 kilometers of the Red Planet on 10
February 1974 but failed to go into orbit when the braking engine
did not fire. On 12 February, Mars 5
went into orbit. As no effort was
made to detach landers, Western observers assumed that these two
Soviet craft were designed to operate as orbiting radio links
between landers aboard Mars 6
and 7 and tracking
stations on Earth. Mars 7
approached its target on 9 March,
but the descent module missed the planet by 1300 kilometers when
some onboard system malfunctioned. On 12 March, the remaining
vehicle separated from its carrier ship, which then went into
orbit around the sun. [319] Mars 6
descended directly to the surface
and provided telemetry for 120 seconds before it crashed.
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- Soviet scientists reporting on the descent
and crash-landing of Mars 6
calculated that it landed at
23°54' south latitude and 19°25' longitude in the region
called Mare Erythraeum. The landing site was "situated in the
central part of an extensive lowland region," part of the global
zone of depression extending for several thousand kilometers north
and south of the Martian equator. Most of the landing zone (about
75 percent) was heavily cratered. Part of this terrain analysis
was based on Mariner 9
data, but the characteristics of
the actual landing zone were determined by the radar-altimeter
readings obtained during the parachute descent of the Soviet
craft. Additionally, Mars 6
instruments indicated "several
times'" more water vapor in the atmosphere than previously
estimated, news over which Viking scientists were cautiously
optimistic, since it enhanced the possibility of discovering some
kind of life forms. Mars 5
photographs provided additional
data on the planet's surface features, and while most of the
Soviet findings correlated with previous knowledge and predictions
there was one major anomaly. 4
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- One of the experiments carried on the
Mars 6 lander was a mass spectrometer designed to
determine the gaseous composition of the Red Planet's atmosphere.
Although the recorded mass spectrum data were not recovered,
engineering data on the operation of the vacuum pump appeared to
indicate unexpected quantities of noncondensable gases. Soviet
scientists interpreted the data as an indication that the
atmosphere might contain as much as 15 to 30 percent argon
(contrasting with l percent in Earth's atmosphere). The Americans
had been operating on the assumption that the thin Martian
atmosphere contained less than 3 percent argon. A concentration
approaching 15 to 30 percent would force some rethinking about
Mars and about Klaus Biemann's mass spectrometer experiment. It
would mean that the Martian atmosphere had been much denser in the
past than the specialists had believed. That would have made the
existence of liquid water possible, but it posed a question what
had happened to those atmospheric gases? That was the puzzler. A
great concentration of argon would also require some changes in
the use of the gas chromatograph-mass spectrometer, since inert
gases like argon tended to impede its operation. Obviously, the
Soviet Mars missions had not answered many of the U.S. questions,
but they had added another element of excitement to the first
Viking landing. Everyone would watch closely the results of the
entry science team's experiment to see just how much argon it
detected as the A lander made its way to the surface.
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