Mars Climate Orbiter

The Mars Climate Orbiter (formerly the Mars Surveyor '98 Orbiter) was a robotic space probe launched by NASA on December 11, 1998, to study the Martian climate, Martian atmosphere, and surface changes and to act as the communications relay in the Mars Surveyor '98 program for Mars Polar Lander. However, on September 23, 1999, communication with the spacecraft was permanently lost as it went into orbital insertion. The spacecraft encountered Mars on a trajectory that brought it too close to the planet, and it was destroyed in the atmosphere. An investigation attributed the failure to a measurement mismatch between two measurement systems: SI units (metric) by NASA and US customary units by spacecraft builder Lockheed Martin.

Mission background

History

After the loss of Mars Observer and the onset of the rising costs associated with the future International Space Station, NASA began seeking less expensive, smaller probes for scientific interplanetary missions. In 1994, the Panel on Small Spacecraft Technology was established to set guidelines for future miniature spacecraft. The panel determined that the new line of miniature spacecraft should be under with highly focused instrumentation. In 1995, a new Mars Surveyor program began as a set of missions designed with limited objectives, low costs, and frequent launches. The first mission in the new program was Mars Global Surveyor, launched in 1996 to map Mars and provide geologic data using instruments intended for Mars Observer. Following Mars Global Surveyor, Mars Climate Orbiter carried two instruments, one originally intended for Mars Observer, to study the climate and weather of Mars.

The primary science objectives of the mission included:

Determine the distribution of water on Mars
Monitor the daily weather and atmospheric conditions
Record changes on the Martian surface due to wind and other atmospheric effects
Determine temperature profiles of the atmosphere
Monitor the water vapor and dust content of the atmosphere
Look for evidence of past climate change.

Spacecraft design

The Mars Climate Orbiter bus measured tall, wide and deep. The internal structure was largely constructed with graphite composite/aluminum honeycomb supports, a design found in many commercial airplanes. With the exception of the scientific instruments, battery and main engine, the spacecraft included dual redundancy on the most important systems. The spacecraft weighed .

The spacecraft was three-axis stabilized and included eight hydrazine monopropellant thrusters: four thrusters to perform trajectory corrections and four thrusters to control attitude. Orientation of the spacecraft was determined by a star tracker, two Sun sensors and two inertial measurement units. Orientation was controlled by firing the thrusters or using three reaction wheels. To perform the Mars orbital insertion maneuver, the spacecraft also included a LEROS 1B main engine rocket, providing of thrust by burning hydrazine fuel with nitrogen tetroxide (NTO) oxidizer.

The spacecraft included a high-gain antenna to transceive data with the Deep Space Network over the x band. The radio transponder designed for the Cassini–Huygens mission was used as a cost-saving measure. It also included a two-way UHF radio frequency system to relay communications with Mars Polar Lander upon an expected landing on December 3, 1999.

The space probe was powered with a three-panel solar array, providing an average of 500 W at Mars. Deployed, the solar array measured in length. Power was stored in 12-cell, 16-amp-hour nickel-hydrogen batteries. The batteries were intended to be recharged when the solar array received sunlight and power the spacecraft as it passed into the shadow of Mars. When entering into orbit around Mars, the solar array was to be utilized in the aerobraking maneuver, to slow the spacecraft until a circular orbit was achieved. The design was largely adapted from guidelines from the Small Spacecraft Technology Initiative outlined in the book, Technology for Small Spacecraft.

In an effort to simplify previous implementations of computers on spacecraft, Mars Climate Orbiter featured a single computer using an IBM RAD6000 processor implementing the POWER1 ISA, capable of 5, 10 or 20 MHz operation. Data storage was to be maintained on 128 MB of random-access memory (RAM) and 18 MB of flash memory. The flash memory was intended to be used for highly important data, including triplicate copies of the flight system software.

Scientific instruments

Pressure Modulated Infrared Radiometer (PMIRR)

thumb|PMIRR diagram

The Pressure Modulated Infrared Radiometer (PMIRR) uses narrow-band radiometric channels and two pressure modulation cells to measure atmospheric and surface emissions in the thermal infrared and a visible channel to measure dust particles and condensates in the atmosphere and on the surface at varying longitudes and seasons. Its principal investigator was Daniel McCleese at JPL/CALTECH. Similar objectives were later achieved with Mars Climate Sounder on board Mars Reconnaissance Orbiter. Its objectives:

Map the three-dimensional and time-varying thermal structure of the atmosphere from the surface to 80 km altitude.
Map the atmospheric dust loading and its global, vertical and temporal variation.
Map the seasonal and spatial variation of the vertical distribution of atmospheric water vapor to an altitude of at least 35 km.
Distinguish between atmospheric condensates and map their spatial and temporal variation.
Map the seasonal and spatial variability of atmospheric pressure.
Monitor the polar radiation balance.

Mars Color Imager (MARCI)

thumb|MARCI camera

The Mars Color Imager (MARCI) is a two-camera (medium-angle/wide-angle) imaging system designed to obtain pictures of the Martian surface and atmosphere. Under proper conditions, resolutions up to are possible. The principal investigator on this project was Michael Malin at Malin Space Science Systems and the project was reincorporated on Mars Reconnaissance Orbiter.

Its objectives:

Observe Martian atmospheric processes at global scale and synoptically.
Study details of the interaction of the atmosphere with the surface at a variety of scales in both space and time.
Examine surface features characteristic of the evolution of the Martian climate over time.

File:Mars Climate Orbiter - spacecraft diagram.png|Diagram of Mars Climate Orbiter

File:Mars Climate Orbiter 1.jpg|Mars Climate Orbiter during assembly

File:Mars Climate Orbiter during tests.jpg|Mars Climate Orbiter undergoing acoustic testing

File:Mars Climate orbiter - awaiting spin test - mco9811165.jpg|Mars Climate Orbiter awaiting a spin test in November 1998

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Mission profile

{| class="wikitable"

|+ Timeline of travel

! scope="col" | Date !! scope="col" | Time<br>(UTC) !! scope="col" style="width: 20em;" | Event

| align="center" | Dec 11<br>1998 || 18:45:51 || Spacecraft launched

| rowspan="7" align="center" | Sep 23<br>1999 || 08:41:00 || Insertion begins. Orbiter stows solar array.

| 08:50:00 || Orbiter turns to correct orientation to begin main engine burn.

| 08:56:00 || Orbiter fires pyrotechnic devices which open valves to begin pressurizing the fuel and oxidizer tanks.

| 09:00:46 || Main engine burn starts; expected to fire for 16 minutes 23 seconds.

| 09:04:52 || Communication with spacecraft lost

| 09:06:00 || Orbiter expected to enter Mars occultation, out of radio contact with Earth.

| 09:27:00 || Expected to exit Mars occultation.

External links

Mars Surveyor '98 launch press kit
Mars Climate Orbiter arrival at Mars press kit
Mars Climate Orbiter Mission Profile by NASA's Solar System Exploration
NASA Space Science Data Coordinated Archive
Mars Climate Orbiter Mishap Investigation Board Phase I Report - November 10, 1999