Mro-launch qxp

The Gravity Investigation will track variations in the orbiter's movement during the

primary science phase of the mission in order to map the effects of variations in Mars'

gravity on the spacecraft. Gravity provides information on the distribution of mass on

and below the surface. Previous orbiters have identified variations in the planet's gravi-

ty that result from regional differences in crustal thickness, seasonal changes in polar

caps and other factors. This spacecraft will yield higher-resolution data because it will

be orbiting at a lower altitude, about 30 percent closer to the planet than Mars Global

Surveyor or Mars Odyssey. This will allow smaller features on the surface to be

resolved in gravity maps. 

Researchers will use the gravity measurements to study the processes that led to for-

mation of surface features. They expect to study the thinning of the crust beneath the

Valles Marineris rift zone, to map how volcanic material accumulated beneath the

largest volcanoes and to see how impact structures modified the early Martian crust.

They also anticipate that the data will reveal tiny changes in mass distribution as car-

bon dioxide moves from the surface to the atmosphere and back again. (In its frozen

form, carbon dioxide is known as dry ice.) From changes in mass revealed by the

gravitational effect on the spacecraft, scientists expect to measure how much dry-ice

snow falls at high latitudes in the winter. These measurements will contribute to under-

standing the weather and climate on Mars.

Team leader for this investigation is Dr. Maria Zuber of the Massachusetts Institute of

Technology, Cambridge, and NASA's Goddard Space Flight Center, Greenbelt, Md.

The Atmospheric Structure Investigation will measure the vertical structure of

Mars' upper atmosphere using sensitive accelerometers throughout the aerobraking

phase of the mission. The rate at which the spacecraft is slowed by atmospheric fric-

tion (or drag) is proportional to the density of the air encountered. Thus, the upper

atmosphere's effect on the spacecraft's velocity will be analyzed for information about

changes in the density of the atmosphere on each of more than 500 orbits, at altitudes

sometimes as low as 95 kilometers (59 miles) and possibly as high as 200 kilometers

(124 miles). The information will guide safe aerobraking because knowledge of the

changing upper atmosphere is critical for avoiding excessive friction that would over-

heat the spacecraft. This investigation will also contribute directly to the mission's sci-

ence results, particularly regarding the major question of where Mars' ancient water

has gone. 

From the vertical structure of atmospheric density, scientists can determine atmospher-

ic temperature and pressure. These may be clues to the fate of the water that was

clearly on the Mars surface billions of years ago. One possibility is that water mole-

cules are broken up by solar radiation into atomic hydrogen and oxygen, with the

hydrogen escaping into outer space; another possibility is that some of the water is

underground. The Atmospheric Structure Investigation will address the first possibility,

loss of water via the escape of hydrogen to outer space. If the upper atmosphere is

warm enough, some of the hydrogen atoms would have enough energy to escape the

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planet. Determining the density and temperature of the atmosphere will improve esti-

mates of this loss process. 

Other information about Mars atmosphere could also come from this investigation, just

as discoveries resulted from the team's similar accelerometer measurements during

aerobraking phases of the earlier Mars Global Surveyor and Mars Odyssey missions.

The Global Surveyor investigation determined that even intermediate-size dust storms

in the southern hemisphere immediately produced threefold increases of density in the

northern hemisphere at aerobraking altitudes. These increases could have put the mis-

sion at risk if the spacecraft had not been raised to a higher altitude. The team also

discovered enormous planetary-scale waves in density, which could also put the

spacecraft at risk. Investigators developed techniques to predict when the spacecraft

would fly through the peaks and valleys of these waves to establish safe aerobraking

altitudes. During Odyssey's aerobraking, the team discovered "winter polar warming"

near the north pole of Mars at high altitudes. North polar Martian winter atmospheric

temperatures were warmer than expected by about 100 degrees Kelvin (180 degrees

Fahrenheit). Mars Reconnaissance Orbiter's Atmospheric Structure investigators will

search for similar winter warming near the south pole. 

A new electronics design by Honeywell is expected to improve the signal-to-noise ratio

of the Mars Reconnaissance Orbiter's accelerometers by more than a factor of 100

over the accelerometers on Mars Odyssey. This should allow measurements to be

made at much higher altitudes than in the past, substantially improving estimates of

the environment where hydrogen may escape. The investigation should also establish

the nature of atmospheric changes due to variations in altitude, latitude, season, 

time-of-day, Mars-Sun distance, meteorological activity, dust storm activity, and solar

activity. 

Dr. Gerald Keating of George Washington University, Washington, is the team leader

for this investigation. 

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Technology Objectives

The mission objectives for Mars Reconnaissance Orbiter do not end with the space-

craft's scientific discoveries. It also has important work to do in relaying communica-

tions from robots on Mars' surface and in demonstrating communication and navigation

technologies for use by future missions. Three instruments in the payload serve these

purposes:

Electra is a technology package enabling Mars Reconnaissance Orbiter to act as a

navigational and communications aid for other spacecraft as they approach Mars and

operate on the surface of Mars. It will use ultra-high frequency radio for relaying com-

mands from Earth to stationary and mobile robots on the surface and for receiving sci-

ence and engineering data to be relayed back to Earth via the orbiter's main antenna.

As spacecraft with compatible systems approach Mars, signals from the

Reconnaissance Orbiter's Electra will provide information about the arriving space-

craft's speed and distance relative to Mars, allowing improved precision in landing.

Similarly, Doppler data from Electra communications, coupled with information about

the orbiter's position, can accurately indicate the position of a stationary lander or a

rover on the surface.

If either or both of the Mars Exploration Rovers Spirit and Opportunity are still operat-

ing in the late 2006, they could be the first surface robots to use Mars Reconnaissance

Orbiter as a communications relay. The navigation and communications strategies for

the Phoenix Mars Scout mission, scheduled for launch in 2007, are being developed to

take advantages of the capabilities of Electra. Phoenix is slated to arrive at Mars in

May 2008 and land at a site in the arctic plains.

The Optical Navigation Camera is part of a technology demonstration of a naviga-

tion technique. The demonstration will compare the predicted positions of Mars' two

moons, Phobos and Deimos, with this camera's observations of the moons as the

spacecraft approaches Mars. While this technique is not necessary for Mars

Reconnaissance Orbiter's own navigation, the demonstration will prepare the way for

relying on it for navigating precise arrivals for future missions that land on Mars. The

camera has an aperture of 6 centimeters (2.3 inches) and a narrow field of view of 1.4

degrees. 

The Ka Band Telecommunications Demonstration will allow comparison of the

shorter-wavelength Ka radio band with the X band that is the standard for interplane-

tary spacecraft communication with Earth and the primary band for this mission. The

Ka band equipment uses less power than its X-band counterpart to send the same

amount of data. However, Ka band transmissions are more susceptible to being dis-

rupted by water in Earth's atmosphere. Mars Reconnaissance Orbiter will use both

bands for sending data to Earth, providing a comparison that will aid planning of com-

munication systems for future interplanetary missions. 

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