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2001 Mars Odyssey
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MISSION

Sequence of Events

Mars Orbit Insertion in story form

All times p.m., PDT:


4:56 About two-and-a-half hours before the engine firing, commands are sent to fire small onboard thrusters to "desaturate" or unload the momentum of the spinning reaction wheels. These devices are similar to gyroscopes and are used to control the spacecraft's orientation - its positioning in three axes - so that it is facing the desired direction. The desaturation readies the reaction wheels for the task of turning Odyssey into the proper pointing position for the orbit insertion engine firing.

7:06 Catalyst bed heaters, called "catbed" heaters, are turned on to warm the "catbeds" to an operational temperature for more efficient operation of the reaction control thrusters. These small jets control the spacecraft's position in three axes: pitch, yaw and roll. They will fire intermittently during the main engine firing to keep the spacecraft on an even keel.

7:12

The lines from the fuel and oxidizer tanks to the main engine (which were vented of any residual gas before launch) are now filled by opening pyrotechnic valves. Five minutes later, the fuel and oxidizer tanks are pressurized by opening additional pyrotechnic valves to ensure an even and steady flow of fuel and oxidizer during the engine operation. This is important to provide smooth combustion within the engine for stable thrust and steady deceleration of Odyssey.

(Propulsion system valves for filling the lines and pressurizing the tanks are activated when small pyrotechnic charges are electrically ignited to open valves in tubing about the diameter of a pencil. Each charge breaks open a seal and creates a clear line to allow the pressurant - helium gas - to flow into the tanks. gasses to flow freely into the empty tubes.)

7:18 Telecommunications channels are switched from the spacecraft's high-gain antenna to the medium gain antenna for transmission of a carrier signal to the Earth, and to the low-gain antenna for receipt of commands from the Earth. These antennas are less powerful, but they can receive and send signals from through a wider arc than the high-gain antenna. Only the carrier signal -- which includes no telemetry -- will be transmitted from now until the spacecraft has emerged from behind Mars into full view of the Earth. At that time, the spacecraft will have completed its engine firing and been captured by the Martian gravity into a large elliptical orbit around Mars.

7:19

The 70-meter (230-foot) diameter antenna of the Deep Space Network complex in Goldstone, Calif., locks on to Odyssey's carrier signal. Receipt of this signal will allow ground controllers to gauge the spacecraft's motion by the changes in the carrier frequency. These changes, called Doppler shift, will occur as the spacecraft's velocity changes during the main engine firing. Reaction wheels now turn the spacecraft to face the proper direction in preparation for the engine firing.

7:26 Ignition of the main engine starts for the Mars orbit insertion.

7:36 The Deep Space Network loses the spacecraft signal as Odyssey passes behind Mars.

7:36 Still behind Mars and incommunicado, the spacecraft enters Mars' shadow and darkness for two minutes.

7:39 Odyssey reaches periapsis - the lowest point in its first orbit of Mars, at an altitude of about 328 kilometers (203 miles). It is still out of reach of Earth ground stations.

7:45 The main engine firing is now complete.

7:49 Still out of touch with the Deep Space Network, Odyssey's reaction wheels turn the spacecraft to point the high-gain antenna toward Earth. Fault protection software that was turned off during the important orbit insertion phase orbit insertion firing is turned on again. (Fault protection software overrides normal spacecraft operations when an unexpected event occurs on the spacecraft, and directs the spacecraft to stop what it's doing, place itself in a safe state and orient itself to await further commands from Earth. Fault protection software is turned off during important single-opportunity events to prevent such an override from interfering with accomplishing these events.)

7:56 From Earth's point of view, Odyssey emerges from behind Mars, and the Deep Space Network antennas seek to lock on to the spacecraft's carrier signal.

8:00 Odyssey's propellant, oxidizer and pressurant tanks are mechanically isolated with pyrotechnically activated valves so the propellant tanks will not be overpressurized.

8:01 Odyssey turns on its telemetry and begins transmitting data at 40 bits per second. The Deep Space Network will take several minutes to synchronize their equipment with the pattern in the telemetry because of the slow rate at which the data is being received. Once the Deep Space Stations' equipment has locked on to the signal, the messages from Odyssey will be forwarded to JPL.


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