Mro-launch qxp

few seconds after that, the vehicle will shed the fairing that has shielded the payload to

this point. The Centaur engine's first burn will last 9 minutes and 35 seconds, deliver-

ing the spacecraft and upper stage into a parking orbit around Earth and cutting off at

about 13 minutes after liftoff. At this point the spacecraft will be about 3,200 kilometers

(approximately 1,990 miles) downrange at an altitude of 185 kilometers (115 miles). 

The shape of the planned parking orbit is an ellipse varying in altitude from 148 kilome-

ters (92 miles) to 185 kilometers (115 miles). However, the spacecraft will not complete

even one orbit. The Centaur engine will start its second burn anywhere from 33 to 55

minutes after its first cutoff, depending on launch date. This burn will last about 5 min-

utes and 29 seconds, lofting the spacecraft out of Earth orbit and on its way toward

Mars. Six minutes after the Centaur engine's second cutoff, the second stage releases

the clamp that attaches the Mars Reconnaissance Orbiter. By that point, not quite an

hour after liftoff, the two-stage Atlas V will have accelerated the spacecraft to about

11,000 meters per second (25,000 miles per hour). Shortly after that, the separated

Centaur performs its last maneuver, taking itself out of the orbiter's flight path to avoid

colliding with the orbiter or flying to Mars.

Once the orbiter has separated from the upper stage of the launch vehicle, it will unfold

its two solar-array panels from their stowed configuration. The spacecraft will be on the

night side of Earth when this happens, so it will still be running on batteries until it gets

back into sunlight, 20 to 30 minutes after separation. Deployment and pointing of the

high-gain antenna, a dish 3 meters (10 feet) in diameter, will follow deployment of the

solar arrays.

Interplanetary Cruise

The trip from Earth to Mars will take about seven months, with arrival on March 10,

2006. For planning purposes, project managers consider the cruise phase as begin-

ning about three days after launch and ending two months before Mars arrival. Main

activities during cruise include daily monitoring of orbiter subsystems, navigation activi-

ties to determine and correct the vehicle's flight path, as well as checkout and calibra-

tion of spacecraft subsystems and science instruments. 

During cruise, the spacecraft will keep its solar arrays facing the Sun and will periodi-

cally adjust its high-gain antenna to maintain communications with Earth.

Five trajectory correction maneuvers are planned during the trip. The first and largest

is scheduled 15 days after launch, and will use the orbiter's most powerful 170-newton

thrusters. Up until that point, the spacecraft's flight path will have been intentionally

biased slightly off-course to prevent the Centaur upper stage from following the space-

craft and hitting Mars. This is an extra precaution in addition to the Centaur's final colli-

sion-avoidance maneuver after separation from the orbiter.

The rest of the trajectory correction maneuvers will use the spacecraft's intermediate-

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power, 22-newton thrusters instead of the more powerful set. All the maneuvers,

including the first, will also use smaller, 0.9-newton thrusters to provide attitude control

during the change in velocity.

The second trajectory maneuver is scheduled Nov. 17, or 99 days after the opening of

the launch period. The third and fourth maneuvers are 40 days and 10 days before

arrival at Mars. The last scheduled maneuver is a contingency activity to be performed

only if needed. It can be conducted as early as 24 hours before orbit insertion and as

late as six hours before orbit insertion.

The calculations for trajectory corrections are based on very accurate determinations

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Flight path

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of the spacecraft's position, direction of movement and velocity. The Mars

Reconnaissance Orbiter mission will combine two traditional tracking techniques with a

newer triangulation method to improve navigational precision. One of the traditional

methods is ranging, which measures the distance to the spacecraft by timing precisely

how long it takes for a radio signal to travel to the spacecraft and back. The other is

Doppler, which measures the spacecraft's speed relative to Earth by the amount of

shift in the pitch of a radio signal from the craft. 

The newer method, called delta differential one-way range measurement, adds infor-

mation about the location of the spacecraft in directions perpendicular to the line of

sight. Pairs of antennas at Deep Space Network sites on two different continents simul-

taneously receive signals from the spacecraft, then the same antennas are used to

observe natural radio waves from a known celestial reference point, such as a quasar. 

Other important events during the cruise stage will put various systems and instru-

ments into final working order. Among these tasks are calibrations and alignments of

antennas, cameras and reaction-control thrusters. Camera checks will include imaging

of Earth's Moon and the star Omega Centauri. The Electra ultra-high-frequency com-

munications system will be tested in a link with a ground station at Stanford, Calif.

Other tests will assess electromagnetic interference among spacecraft systems and

instruments in the space environment, and for jitter disturbance in high-resolution cam-

era images. 

Approaching Mars and Entering Orbit

The mission's approach phase begins two months before arrival at Mars and extends

until the spacecraft gets a health check after it begins orbiting Mars. The most critical

event is the "Mars orbit insertion" thruster burn calculated to slow the spacecraft

enough for Mars' gravity to capture it into orbit.

One month before reaching Mars, the spacecraft will begin its optical navigation experi-

ment, which lasts until two days before Mars arrival. It will point the Optical Navigation

Camera at Mars' moons, Phobos and Deimos. By comparing the observed positions of

the moons to their predicted positions relative to background stars, navigators will cal-

culate the precise position of the orbiter. This optical navigation is a demonstration to

prepare for future missions that might use this technology. Mars Reconnaissance

Orbiter's own orbit insertion will not require use of position calculations from this exper-

iment. 

Navigators' aim point for Mars Reconnaissance Orbiter is 360 kilometers (223 miles)

above the planet's surface, with the spacecraft approaching from the south. The space-

craft will need to slow itself by about 1,000 meters per second (about 2,200 miles per

hour) in order to be captured into orbit. The six main engines will fire for about 25 min-

utes. About 15 minutes into the burn, the spacecraft will pass as close to the planet's

surface as it will get on this day, and at about that same time it will both enter into

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