Welcome Guest [Log In] [Register]

Forum rules [2009.07.18]    List of members    Contact
Welcome to Anatomia Universalis! This is a forum dedicated to discussion, learning and news concerning all things astronomy.

You're currently viewing Anatomia Universalis as a guest. This means your forum experience will be limited and you will not be able to enjoy all the features we offer. If you join our community, you'll have access to all the information and discussions in all the sections and to many member-only features: you'll be able to see posted images, post new threads, reply to existing ones, send private messages, create and edit your profile, participate in polls, and much more!

Registration is simple, fast and free. Register now! Your e-mail address will not be disclosed to anyone and will only be used to confirm that you are human and not a robot; we will never spam your inbox.

If you're already a member, please log into your account to access all of our features:

Username:   Password:
Reply
Mariner 7; 1969 // USA
Topic Started: Friday 31-07-2009, 00:26 (406 Views)
[Publisher] Magrathean
Member Avatar
point of ignition
Mars > Missions > Mariner 7 > Index
 
Posted Image

  1. Index
  2. [go2=missionoverview]Mission overview[/go2]
  3. [go2=spacecraftandinstruments]Spacecraft and instruments[/go2]
  4. [go2=results]Results[/go2]
Quote    ↑
 
[Publisher] Magrathean
Member Avatar
point of ignition
[anchor]missionoverview[/anchor]
Mars > Missions > Mariner 7 > Mission overview
 
Objectives
  1. perform a flyby of Mars and study its surface and atmosphere
  2. establish the basis for future investigations of the planet
  3. demonstrate and develop technology required for future missions to other planets




Summary

Launch date: 27 march 1969

Mars flyby & mission end: 05 august 1969

Mariners 6 and 7 were identical probes sent to Mars in early 1969. Since they were unable to orbit or land on the planet, they were designed to perform a single flyby and take photographs during it.

Both of them completed their mission successfully and returned many more pictures than their predecessor, Mariner 4.
Sources: Wikipedia / Mariner 6 and 7 | Absolute Astronomy / Mariner 6 and 7 | James H Wilson, Two over Mars
Quote    ↑
 
[Publisher] Magrathean
Member Avatar
point of ignition
[anchor]spacecraftandinstruments[/anchor]
Mars > Missions > Mariner 7 > Spacecraft and instruments
 
Mariner 7, like Mariner 4, consisted of an octagonal magnesium frame base. The base was 138.4 centimeters diagonally and 45.7 centimeters tall. On top of the frame were a high-gain parabolic antenna one meter in diameter and four 215-by-90-centimeter solar panels. Next to the high-gain antenna stood a 2.23-meter-tall mast with a low-gain antenna at the top. Under the frame was a scan platform with the scientific equipment.

Posted Image

Posted Image

Bottom image © NASA
The spacecraft propelled itself by means of a monopropellant hydrazine rocket motor within the frame. The motor nozzle protruded from one of the sides of the frame.

Attitude was controlled by a set of three gyroscopes, nitrogen jets at the ends of the solar panels, a Canopus tracker and six Sun sensors.

Power was provided by the 17,472 cells in the solar panels (4,368 cells per panel), which provided 800 watts at Earth and 449 watts at Mars. Power requirement reached 380 watts at Mars encounter but stayed below that throughout the mission, so power shortages were never a problem for Mariner 7. In any case, backup power was available via a 1,200-watt-hour rechargeable silver-zinc battery.

Temperature was controlled by adjustable louvers on the sides of the frame.

The science instruments were the camera used to image Mars, an infrared spectrometer, an ultraviolet spectrometer, a two-channel infrared radiometer for measuring Mars's surface temperature, a thermal control flux monitor, a celestial mechanics experiment and a general relativity experiment.

Posted Image

Posted Image

Both images © NASA
Three telemetry channels were available for communications: one for carrying engineering data at 8 1/3 or 33 1/3 bits per second, one for carrying scientific data at 66 2/3 or 270 bits per second, and one for carrying scientific data at 16,200 bits per second. The antennas achieved communication via dual S-band travelling-wave tube amplifiers and a receiver.

Up to 195,000,000 bits of imaging data could be stored in an analog tape recorder for later transmission, and scientific data was stored in a digital recorder.

The command system consisted of a computer and a sequencer. This executed specific commands at specific times, making the probe automated, but ground instructions overriding the preset mission and backup mission could be sent at any time.

Mariner 7's total height was 3.35 meters. With its solar panels deployed, the spacecraft's span was 5.79 meters.
Source: Wikipedia / Mariner 6 and 7
Quote    ↑
 
[Publisher] Magrathean
Member Avatar
point of ignition
[anchor]results[/anchor]
Mars > Missions > Mariner 7 > Results
 
As was the case with its sister probe, Mariner 7's liftoff phase went completely as planned; however, this craft too would spell trouble early on.

Mariner 7's radio receiver dropped to 20% of its usual power due to excessively low temperatures. The problem was solved by setting the radio transmitter to high power, which heated the radio compartment back to its normal operating temperature.

Afterwards, as Mariner 6 finished its far-encounter imaging phase, Mariner 7's signal disappeared completely. At least one of the spacecraft's batteries had exploded due to an electrical breakdown; the explosion had released the internal liquids in the battery or batteries, which then vaporized and, together with the high voltages in the spacecraft's electrical equipment, caused lightning bolts in the craft's interior. This damaged some of the craft's circuits. Mariner 7 tumbled through space, its orientation lost, and the ground team was unable to reestablish contact for a while. They eventually switched transmission to the probe's low-gain antenna, which could receive data regardless of orientation or direction, and in this way regained contact. A few engineering measurements, however, had been damaged and therefore lost. Other damages included part of the telemetry system and some of the telemetry data. The scientific equipment had taken no damage. The engineers corrected the probe's orientation using pictures taken by its cameras, since they couldn't use any of the sensors which had been designed for such a purpose.

From then on, all of Mariner 7's instruments operated perfectly.





Pictures of Mars

Some of the data collected by Mariner 6, such as the irregularity of the icecap at the south pole and the atmospheric haze, encouraged scientists to instruct Mariner 7 to further explore the poles. Thus, during the three days of the far-encounter imaging session Mariner 7 returned 93 pictures of the red planet.

The near-encounter pictures of Hellas Planitia were surprising because they showed an unexpected absence of craters.

Combined, the images taken by Mariners 6 and 7 cover about 20% of the planet's surface.

The closest approach to the planet was 3,430 kilometers from the surface.

Phobos can be seen in a few of the pictures returned by Mariner 7. It was concluded to be one of the darkest objects in the Solar System discovered thus far.

Far-encounter pictures taken by Mariner 7

Color photograph

Near-encounter pictures taken by Mariner 7

Mosaics created with the pictures taken by Mariner 7

Mariner 7's trajectory

Mariner 6-7 map of Mars





The martian atmosphere

Readings of Mars's atmosphere at the tropics returned warmer temperatures than predicted by theory. In other places, however, the temperature readings were consistent with theory. Data indicated that carbon dioxide clouds could form at any altitude near the north pole. Atmospherical composition turned out to be dominated by carbon dioxide (CO2) and its chemical derivatives, especially carbon monoxide (CO). It was surprising at the time that no nitrogen or ozone was detected.

Clouds on Mars are formed by CO2 ice, water ice and dust particles. Although it was determined to be impossible for rain to fall on Mars, frost was detected and snow was predicted (the snow was confirmed almost four decades later by Phoenix).

Temperature readings indicated highs of about 16°C near the equator during summer and lows of about -151°C near the south pole.
Sources: James H Wilson, Two over Mars | Stewart A Collins, The Mariner 6 and 7 pictures of Mars | Wikipedia / Mariner 6 and 7
Quote    ↑
 
1 user reading this topic (1 Guest and 0 Anonymous)
« Previous Topic · Past missions · Next Topic »
Reply


[This theme is Magrathean's variation on a theme created by Wanboa of AnimeBoxCafe.]