Mro-launch qxp

through a northern hemisphere summer in November 2006. 

Throughout the science phase, the orbiter will generally keep its instruments pointed at

Mars to collect data and its high-gain antenna pointed at Earth to send the data home.

With daily support by NASA's Deep Space Network for receiving the data on Earth,

Mars Reconnaissance Orbiter will return more than five times as much data as all pre-

vious missions to Mars combined. 

The primary science orbit is designed to serve the mission's research goals. The

spacecraft will pass almost directly over the poles on each orbit. The orbit will remain

at a fixed angle to the Sun; every time the spacecraft passes northbound over the

equator, it will see mid-afternoon lighting on the ground. A complete orbit will take

about 1 hour and 52 minutes. By the next time the orbiter comes around and crosses

the equator again, the planet underneath will have rotated just enough that the orbiter

sees the same time-of-day on the ground beneath it. 

In altitude, the slightly elliptical orbit will range from 255 kilometers (158 miles) at the

low point, or periapsis, to 320 kilometers (199 miles) at the highest point, or apoapsis.

The periapsis will be over the south pole, the apoapsis over the north pole. This shape

reflects the slightly asymmetrical shape of Mars and so it deviates from a circular orbit.

For comparison with the orbiters currently at Mars, Mars Global Surveyor flies a nearly

circular orbit at about 378 kilometers (235 miles), Mars Odyssey flies one at 400 kilo-

meters (250 miles), and Mars Express flies an elliptical, 7.5-hour orbit ranging from

259 to 11,560 kilometers (161 to 7,183 miles). 

The primary science orbit for Mars Reconnaissance Orbiter will have two cycles of

repeating its ground track to allow researchers to go back for a closer look at features

seen in regional surveys. That is, 359 days after any given orbit, the spacecraft will

repeat essentially the same path as the earlier orbit. However, there is a much shorter

cycle of 17 days in which any place on the planet can be viewed by rolling the space-

craft up to 20 degrees to the left or right of straight-downward (nadir) pointing of the

instrument deck. Thus, a given target can be viewed in any 17-day cycle or can be

viewed from different direction (e.g., as need for stereo images) in two successive

cycles.

Relay Phase

A two-year phase when the top priority for Mars Reconnaissance Orbiter will be com-

munications support for other missions is scheduled to begin when the primary science

phase ends in December 2008 and run for two years. Important relay support will

begin before that, however.

The Electra communications package on Mars Reconnaissance Orbiter will enable the

orbiter to assist with navigation and communication for spacecraft arriving at Mars. It

will be able to communicate with spacecraft on the surface of Mars at data rates from 1

kilobit per second to 2 megabits per second. The relay can work only when the orbiter

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is about 20 degrees or more above the horizon from the perspective of a lander or

rover on the surface. Due to the orbiter's relatively low altitude, that will limit each relay

session to about five minutes or less. Communications between the orbiter and a lan-

der or rover will take advantage of the development of an international standard, called

the Proximity-1 protocol, for the data transfer. The Consultative Committee for Space

Data Systems, an international partnership for standardizing techniques used for han-

dling space data, developed Proximity-1.

NASA's Phoenix Mars Scout mission is in development for launch in August 2007 and

landing in May 2008. Phoenix would land in icy soils near the north polar ice cap of

Mars and spend up to three months examining the history of the water in these soils,

checking for organic chemicals and monitoring polar climate. Plans for the Phoenix

mission envision support from Mars Reconnaissance Orbiter for navigation and com-

munication during the approach to Mars, then two to three relay contacts daily at rates

of up to 128 kilobits per second during Phoenix' surface operations. 

The surprisingly long lives of NASA's Mars Exploration Rovers have raised the possi-

bility that either Spirit or Opportunity will be the first user of Mars Reconnaissance

Orbiter's relay capabilities. Those rovers have relied on NASA's Mars Odyssey for

relaying more than 90 percent of the data they have returned, and have also used

NASA's Mars Global Surveyor and the European Space Agency's Mars Express to

relay data. 

NASA's Jet Propulsion Laboratory is developing the next-generation Mars rover, with a

science payload about 10 times as massive as the current rovers'. This rover, called

Mars Science Laboratory, is slated for launch in October 2009 and landing on Mars in

October 2010. Mars Reconnaissance Orbiter will have an important role as communi-

cations relay for Mars Science laboratory. 

End of Mission

The Mars Reconnaissance Orbiter's prime mission will end Dec. 31, 2010, after the

two-year-long relay phase. If left at the low-altitude orbit used during the prime mission,

the spacecraft could be expected to gradually lose altitude due to friction with the

upper reaches of the atmosphere, and might fall to the planet's surface within a few

years. Instead, at the end of the prime mission, the orbiter's thrusters will take the

spacecraft to a higher orbit so that it will remain in orbit for decades. The end-of-mis-

sion orbit will be an ellipse ranging in altitude from about 350 to 410 kilometers (217 to

255 miles).

The initial launch mass of the orbiter will includes more than enough propellant for the

prime mission. Even after the end-of-mission maneuver, the orbiter is expected to have

enough extra propellant for about five additional years of operation. Unless that propel-

lant is needed for contingencies during the prime mission, NASA would have the option

of assigning the orbiter an extended mission to continue support for future Mars mis-

sions. From the end-of-mission orbit, Mars Reconnaissance Orbiter could supplement

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