Mro-launch qxp

Mission Overview

NASA's Mars Reconnaissance Orbiter will put a large, capable spacecraft into a low-

altitude orbit around Mars for two years dedicated to examining the planet in unprece-

dented detail and, at least, an additional two years of providing communications-relay

support for other missions. Before the primary science phase and the relay phase, the

mission must execute four challenging phases to get where it needs to be to do its job:

the launch phase of a few hours, the cruise phase of about five months, the approach

and orbit insertion phase of about two months, and the aerobraking phase of four to six

months. 

Launch Vehicle

A two-stage Atlas V-401 launch vehicle will lift Mars Reconnaissance Orbiter from

Space Launch Complex 41 at Cape Canaveral Air Force Station, Fla., and put the

spacecraft on a course toward Mars. The spacecraft's large payload of science instru-

ments and, even more, the high-capacity telecommunications system needed to han-

dle the huge flow of data from high-resolution instruments, add up to a heavy space-

craft and the need for a powerful launch vehicle. The Atlas V-401, provided by

Lockheed Martin Space Systems, Denver, was selected through a competitive procure-

ment process.

The first stage, or booster, of the Atlas V-401 will combust 284,089 kilograms (313

tons) of fuel and oxidizer in just over four minutes within a single, throttlable engine --

model RD-180, supplied by Russia -- with two thrust chambers. The kerosene-like fuel

(type RP-1) and liquid oxygen will be loaded shortly before launch into cylindrical tanks

that make up most of the vehicle's height. The booster engine will provide thrust total-

ing about 4 million newtons (900,000 pounds).

The second stage, connected with two interstage adaptors, is a Centaur upper stage.

Its single, restartable engine -- model RL-10, from Pratt & Whitney Space Propulsion,

West Palm Beach, Fla. -- uses liquid hydrogen and liquid oxygen and can provide up

to 99,200 newtons (22,300 pounds) of thrust. The Centaur can control its orientation

precisely. This ability is important both to control the direction of thrust during the

engine burns and also to prevent sunlight from shining directly into the spacecraft cam-

eras and sensors that would be damaged by such intense light.

A payload adaptor connects the orbiter to the Centaur. This structure is about 1.2

meters (47 inches) in diameter. It provides an electrical interface through which the

orbiter communicates with the launch vehicle, and thus to ground crews, before and

during the launch. A releasable clamp band attaches the orbiter to the Centaur. When it

is released, push-off springs separate the two.

The spacecraft will ride aloft inside a protective fairing atop the Centaur stage. The fair-

22

---

ing, or nose cone, is 4 meters (13 feet) in diameter. With the fairing on top, the vehicle

ready for launch will stand 57.4 meters (188 feet) tall.

The first Atlas V was launched in August 2002. Mars Reconnaissance Orbiter will be

the first interplanetary spacecraft launched on an Atlas V, and the first on any of the

Atlas series since Pioneer Venus in May 1978. However, the Atlas series, with more

than 580 launches since the first in 1957, served frequently in the lunar and interplane-

tary missions of the 1960s and '70s. An Atlas launched the very first successful mis-

sion to Mars, NASA's Mariner 4, on Nov. 28, 1964. 

Launch Timing

As Earth and Mars race in circles around the Sun, with Earth on the inside track, Earth

laps Mars about every 26 months. The two planets come relatively close together at

that point, which is called an opposition because Mars is temporarily on the opposite

side of Earth from the Sun. The best time to launch a mission to Mars, in terms of how

much energy is required for the trip, is a few months before that happens. NASA has

used every one of these Mars launch opportunities since 1996 and plans to use future

ones indefinitely. The next Mars opposition will be Nov. 7, 2005. Not all Mars opposi-

tions are the same, because the two planets' orbits are elliptical, not circular. 

During the 2005 opposition period, the closest approach of the two planets will be on

Oct. 30, when they will be 69.42 million kilometers (43.1 million miles), about 24 per-

cent farther than during the 2003 opposition. That distance, the launch vehicle's power,

the spacecraft's weight, and the desired geometry of approach to Mars are all factors

in determining the range of possible launch dates. The period begins on Aug. 10,

2005, and lasts 21 days, through Aug. 30, 2005. 

The window of possible launch times on the first day of the launch period will begin at

7:54 a.m. Eastern Daylight Time and last for two hours. The length of the window on

the other 20 days ranges from 30 minutes to two hours. 

Launch Sequences

Between ignition and liftoff, the booster engine will ramp quickly to an initial throttle set-

ting of 75 percent. Before the vehicle clears its own height, the engine will throttle up to

92 percent. The throttle settings vary by launch date for most of the remaining burn

until the booster engine shuts off four minutes after liftoff. Ten seconds before cutoff,

engine will throttle back to about 50 percent. By the time of booster-engine cutoff, the

launch vehicle will be about 300 kilometers (186 miles) downrange at an altitude of

101 kilometers (63 miles).

Ten seconds after booster-engine cutoff, the Centaur upper stage, with payload

attached, will separate from the depleted first stage. The first stage will fall into the

Atlantic Ocean. Nine seconds after separation, the Centaur's engine will ignite, and a

23

---