| MISSION_DESCRIPTION |
Mission Overview
================
On November 14, 1971, Mariner 9 became the first spacecraft to
orbit another planet. Six experiments were carried as part of
the science payload: television, ultraviolet spectrometer,
infrared spectroscopy, infrared radiometry, S-band occultation
and celestial mechanics. Two experiments (S-band occultation
and celestial mechanics) utilized the radio telemetry subsystem
to derive data; the other required specially developed
instruments, mounted, and boresighted to each other, on the
spacecraft's scan platform. Pre-launch mission planning
encompassed two separate, but complementary, missions. The
orbit of each spacecraft was optimized to match the
corresponding objective. The mapping mission was designed with
an Earth-synchronous orbit (about a 12-hr periods) to maximize
antenna utilization, or communications efficiency. For maximum
surveillance of an area, it was designed with a steep
inclination (80 degrees) to the equatorial plane of Mars. The
dynamic objective dictated a Mars-synchronous (or
sub-synchronous) orbit and a lower (50 degree) inclination for
closer observations of specific areas. The plans for the two
missions were in detailed stages of development on May 9, 1971
when Mariner 8 was lost because of guidance difficulties in the
second stage of the launch vehicle. It was determined that an
orbit for a single-spacecraft mission could be developed to meet
all basic mission and specific science objectives. A
single-spacecraft plan, involving an inclination of 65 degrees,
a period of about 12 hours, a periapsis altitude of 1350 Km, and
an arrival date of November 14, 1971, was evaluated and
formalized in 2 weeks.
Mariner 9 Statistics
--------------------
Total mission 516 days
Required minimum useful orbital lifetime - 90 days
Actual useful orbital lifetime - 349 days
Distance from Earth to Mars on 10/27/72 - 383,675,000Km
Commands received by Mariner 9 - 45,960
TV pictures received of Mars and its satellites - 7329
TV shutter actuations - 14,004
Required minimum mapping coverage - 70% of planet
Actual mapping coverage obtained - 100% of planet
Science data received from Mariner 9 - 54 billion bits
Mariner 9 'firsts'
------------------
1. Orbit another planet,
2. Detail observation of Martian Atmospheric Changes,
3. Complete mapping of another planet,
4. Detail observations of satellites of another planet,
5. Observation by spacecraft of receding polar cap.
Mariner 9 'Discoveries'
-----------------------
1. Tectonic action on Mars (Crust movement),
2. Existence of volcanoes and lava flows,
3. Evidence of past fluid flow,
4. Eolian activity (wind erosion and deposition),
5. Rough gravity field,
6. Triaxiality of Mars,
7. Evidence of process of differentiation of Mars similar to
that of Earth,
8. Permanent residual polar cap.
On October 28, 1972, Mariner 9 ran out of attitude control gas
and was commanded to be silent for the final time. It is
estimated that Mariner 9 will remain in Mars orbit for more
than 50 years.
Mission Phases
==============
CRUISE
------
On June 5th, a planned trajectory correction was made.
Martian ephemeris data and spacecraft tracking calculations
were determined with such accuracy that no other midcourse
corrections were necessary during the 167 day flight to Mars.
Other events during cruise were scan calibration no. 1 on
October 1, scan calibration no. 2 on October 8, Mars TV
calibration on November 8 and November 9.
Spacecraft Id : MR9
Target Name : MARS
Mission Phase Start Time : 1971-05-30
Mission Phase Stop Time : 1971-11-14
Spacecraft Operations Type : ORBITER
LAUNCH
------
Mariner 9 was successfully launched from Cape Kennedy, Florida
at 6:23 PM EDT. The Centaur-Mariner 9 separation occurred at
6:36 PM EDT.
Spacecraft Id : MR9
Target Name : MARS
Mission Phase Start Time : 1971-05-30
Mission Phase Stop Time : 1971-05-30
Spacecraft Operations Type : ORBITER
ORBITAL
-------
The 1398 Km periapsis altitude of the insertion orbit was
accurate to with 50 Km from the aiming point, and the initial
period of 12 hr and 34 min was within seconds of the time
desired for the insertion orbit. The non-synchronization with
Earth provided the timing slip until coincidence of the
Goldstone 64-m antenna zenith position and orbit periapsis was
obtained and a trim maneuver 'locked' the two into
synchronization. On November 16, the spacecrafts' orbital
period was changed by more than 30 min by a 6-sec firing of
the rocket engines. However, because of the previously
unknown gravity-field variation of the planet the average
orbital period was found to be slightly shorter that the
11:58:52 planned, gradually changing the time relationship of
periapsis to the view period of the 64-m antenna at Goldstone,
California, which would eventually affect data playbacks. On
December 30 (revolution 94), a second trim maneuver adjusted
the orbital period, correcting periapsis-passage timing with
the view period of the 64-m antenna. This new orbit
established a higher periapsis altitude, which provided a
broader area coverage for each television picture, thus
requiring fewer picture to complete the desired mapping of 70%
of the surface during the standard 90 day mission. The
broader area coverage for each pictured resulted in a
corresponding loss of surface resolution. About 122 days
after orbit insertion, the pointing direction of the
spacecraft's high-gain antenna drifted off of Earth, and
communications became more difficult. A high-gain antenna
maneuver (HGAM) of the spacecraft became necessary to point
the antenna to Earth. On October 27, 1972, telemetry data
indicated that the spacecraft was no longer capable of holding
the fixed attitude and, as the last battery power was being
used, a final command was sent to stop transmitting. The
slowly tumbling Mariner 9 will remain in orbit for a minimum
of 50 years before it enters the atmosphere of Mars,
disintegrates, and falls to the surface.
Spacecraft Id : MR9
Target Name : MARS
Mission Phase Start Time : 1971-11-14
Mission Phase Stop Time : 1979-10-27
Spacecraft Operations Type : ORBITER
|
.png)
.png)
