NASA's Mars Reconnaissance Orbiter (acronym: MRO) is a planned multipurpose spacecraft scheduled to launch August 10, 2005 to advance human understanding of Mars through detailed observation, to examine potential landing sites for future surface missions and to provide a high-data-rate communications relay for those missions. It will replace the aging Mars Global Surveyor as a Mars observation platform. Following launch, MRO will traverse interplanetary space for 7 months. After arrival and insertion the plans call for controlled use of atmospheric friction in a process called aerobraking for about six months to change the initial, very elongated orbit into a rounder shape optimal for science operations. MRO will conduct its science mission for a nominal 2 year period after aerobraking is completed (November 2006), after that extended science and communications relay missions are planned.

"We're reaching an important stage in developing the spacecraft," said James Graf, project manager for Mars Reconnaissance Orbiter at Jet Propulsion Laboratory, Pasadena, California, in September 2003. "The primary structure will be completed next month." The structure weighs 220 kilograms (484 lb) and stands 3 meters (10 ft) tall. At launch, after gear and fuel are added, it will support over 2 tons.

The Mars Reconnaissance Orbiter will lay the groundwork for later Mars surface missions in NASA's plans: a lander called Phoenix selected in a competition for a 2007 launch opportunity, and a highly capable rover called Mars Science Laboratory being developed for a 2009 launch opportunity. The MRO's high-resolution instruments will help planners evaluate possible landing sites for these missions both in terms of science potential for further discoveries and in terms of landing risks. The MRO's communications capabilities will provide a critical transmission relay for the surface missions, MRO will even be able to provide critical navigation data to these probes during their landing.

Mission timeline

Mars Reconnaissance Orbiter will launch in August 2005, most likely between August 10–August 30, with 30-minute launch windows available every day through this period. It will be launched from Space Launch Complex 41 at Cape Canaveral Air Force Station, aboard an Atlas V-401 rocket. At 56 minutes after launch the rocket will have completed its use and place MRO in an interplanetary Hohmann transfer orbit towards Mars.

MRO will cruise in interplanetary space for 7½ months before reaching Mars. At least 3 trajectory correction maneuvers are planned for any need to correct the trajectory for proper orbital insertion upon reaching Mars.

Orbital insertion will occur as MRO approaches Mars for the first time in March of 2006, passes below Martian southern hemisphere, at an altitude of about 300 km (190 mi). All 6 of the orbiter’s main engines will burn for 25 minutes reducing the speed of the probe (relative to Mars at closest approach) from 6500 mph (2900 m/s) to 4250 mph (1900 m/s).

Orbital insertion will place the orbiter in a highly elliptical polar orbit. The periapsis, the closest point in the orbit to Mars will be 300 km (180 mi). The apoapsis, farthest away from Mars will be 45,000 km (28,000 mi). The orbital period will be 35 h.

Aerobraking will be conducted soon after orbital insertion to bring the orbiter to a lower, quicker orbit. Aerobraking cuts the need for fuel by roughly one half. Aerobraking will consist of three steps:

1. MRO will drop the periapsis of its orbit to aerobraking altitude using its thrusters. Aerobraking altitude will be determined at that time depending on the thickness of the Martian atmosphere at the time (Martian atmospheric pressure changes over the seasons on Mars). This step will take about 5 orbits or 1 Earth week.

2. MRO will remain in aerobraking altitude for 5½ Earth months, or less than 500 orbits. Correct aerobraking altitude will have to be maintain with occasional corrections in periapsis altitude using its thrusters. Through aerobraking the apoapsis of the orbit will be reduced to 450 km (280 mi).

3. To end aerobraking, the MRO will uses it thrusters to move its periapsis out of the edge of the Martian atmosphere. This will take 5 Earth days or 64 orbits.

After aerobreaking another week or two will be spent to make minor adjustments in the orbit with thrusters. These corrections will not be until after solar conjunction when Mars will appear to pass behind the Sun from Earth perspective, between October 7 and November 8, 2006. After this science operations will begin. Final or science operations orbit will be roughly circularized at 450 km above the Martian surface.

Science operations will be conducted for a nominal period of two Earth years. After this extended mission operations will include communication and navigation for Lander and rover probes.

Science instrumentation

The broad goals of the Mars Reconnaissance Orbiter are to search for evidence of water, and characterise the atmosphere and geology of Mars.

Six science instruments are included on the mission along with two 'science-facility instruments', which use data from engineering subsystems to collect science data [1].

• Cameras
  • HiRISE (High Resolution Imaging Science Experiment)
  • CTX (Context Camera)
  • MARCI (Mars Color Imager)
• Spectrometer
  • CRISM (Compact Reconnaissance Imaging Spectrometer for Mars)
• Radiometer
  • MCS (Mars Climate Sounder)
• Radar
  • SHARAD (Shallow Radar)
• Science-Facility
  • Gravity Field Investigation Package
  • Atmospheric Structure Investigation Accelerometers

HiRISE

The HiRISE camera will consist of a 0.5 metre reflecting telescope, the largest of any deep space mission, and has a resolution of 0.3 metre at a height of 300 km. It will image in three colour bands, blue-green, red and near infrared.

To facilitate the mapping of potential landing sites, HiRISE can produce stereo pairs of images from which the topography can be measured to an accuracy of 0.25 metre.

CRISM

The CRISM instrument is an infrared/visible light spectrometer, to produce detailed maps of the mineralogy of the surface of Mars. It has a resolution of 18 metres at a 300 km orbit. It will operate from 400 nm to 4050 nm, measuring the spectrum in 560 channels, each 6.55 nm wide.

SHARAD

The orbiter's shallow radar experiment "SHARAD" is designed to probe the internal structure of Mars' polar ice caps, as well as to gather information planet-wide about underground layers of ice, rock and, perhaps, liquid water that might be accessible from the surface.

Engineering data

Structure

Workers at Lockheed Martin Space Systems in Denver, assembled the spacecraft structure and attached instruments. The instruments were built for it at the University of Arizona, Tucson; at Johns Hopkins University Applied Physics Laboratory, Laurel, Md.; at the Italian Space Agency, Rome; at Malin Space Science Systems , San Diego, Calif.; and at JPL.

The structure is made of mostly carbon composites, as well as aluminium honeycombed plates. The titanium fuel tank takes up most of the volume of the structure and provides a large percentage of structural load and integrity.

• Total weight is less than 2,180 kg (4,806 lb)
• Dry mass (without fuel) is less than 1,031 kg (2,273 lb)

Power systems

Mars Reconnaissance Orbiter gets all of its electrical power from two solar panels. Each panel can move independently around two axes of movement (up-down, or left-right rotation). Each solar panel has an area of approximately 10 metres square (100 m² or 1100 ft²), and contains 3,744 individual solar cells. The very high efficiency triple junction solar cells are able to convert more than 26% of the Sun's energy directly into electricity, and are connected together so that the power they produce is at 32 V, which is the voltage that most devices on the spacecraft need in order to operate properly. At Mars, the two panels together produce 1,000 watts of power.

Mars Reconnaissance Orbiter uses two nickel metal hydride rechargeable batteries. The batteries are used as a power source when the solar panels are not facing the Sun (such as during launch, orbital insertion and aerobraking)or when Mars blocks out the Sun during a period in each orbit. Each battery has an energy storage capacity of 50 ampere-hours. The spacecraft can't use this total capacity, because as the batteries discharge their voltage drops. If the voltage drops below about 20 volts the computer will stop functioning. So only about 40% of the battery capacity is planned to be used.

Electronic systems

Mars Reconnaissance Orbiter’s main computer is a 133 MHz, 10.4 million transistors, 32-bit, RAD750 processor. The processor is basically a space/radiation hardened version of a PowerPC750 or G3 processor, with specialized built on motherboard. The RAD750 is a successor to the RAD6000. This processor may seem underpowered in comparison to a modern PC or Mac processor but it is extremely reliable and resilient, and can function in solar flare ravaged deep space.

Data is stored in a 160 Gb (20 GB) flash memory module consisting of over 700 memory chips, each with 256 Mb capacities. This memory capacity is not actually large in considering how much data is going to be acquired; for example, a single image from HiRISE camera can be as big as 28 Gb.

The operating system software is VxWorks and has extensive fault protection protocols and monitoring.

Navigation systems

Navigation systems and sensor will provide data on position, course and attitude throughout the mission.

• Sixteen Sun sensors (eight are backups) are placed around the spacecraft to measure what direction the Sun is at in accordance with spacecraft position.
• Two star trackers are used to provide full knowledge of the spacecraft orientation and attitude. Star trackers are simple digital cameras used to map the position of catalogued stars autonomously.
• Two inertial measurement units are onboard (the second for backup purposes) provide data for any spacecraft movement. Each inertial measurement unit is a combination of three accelerometers and three ring-laser gyroscopes.

The Optical Navigation Camera will image Phobos and Deimos against background stars, to precisely determine MRO's orbit. This isn't mission critical, and has been included to test the system for future orbiting spacecraft. ([2]).

Telecommunications system

The Telecom Subsystem uses a large antenna to transmit at the normal Deep Space communications frequency (X-band, 8 GHz), as well as demonstrating the use of the Ka-band, at 32 GHz, for high data rates. Maximum transmission speed from Mars is projected to be as high as 6 Mbit/s, a rate ten times higher than previous Mars orbiters. Two amplifiers for the X-band radio frequency transmits at 100 watts, the second is a backup. One amplifier Ka-band radio frequency transmits at 35 W. Two transponders are carried in total.

Two smaller low-gain antennas are present for lower-rate communication during emergencies and special events, such as launch and Mars Orbit Insertion. These antennas do not have focusing dishes and can transmit and receive from any direction.

Propulsion system

A 1175 L (310 US gallon) fuel tank filled with 1187 kg (2617 lb) of hydrazine monopropellant. Fuel pressure is regulated by adding pressurized helium gas from an external tank of helium. Seventy percent of the fuel will be used for orbital insertion alone.

A total of 20 rocket engine thrusters.

6 large thrusters, mainly meant for orbital insertion. Each producing 170 N (38 lbf) of thrust; total 1,020 N (230 lbf) of thrust.

6 medium thrusters, for performing trajectory correction maneuvers and attitude control during orbit insertion, each producing 22 N (5 lbf) of thrust.

8 small thrusters, for attitude control during normal and all operations, each producing 0.9 N (0.2 lbf)

Four momentum wheels are also used for precise attitude control, such has during high-resolution imaging where the slightest unwanted motion could case blurring of the image. Each wheel is used for one axis of motion, the spar wheel is for backup, in case one of the other 3 wheels fails. Each wheel weighs 10 kg (22 lb), and can be spun as fast as 6000 rpm.

Extended mission equipment

The Electra , an UHF antenna, is designed to communicate with spacecraft as it lands on Mars, aiding pinpoint landings ([3]).

See also

• Exploration of Mars

External links & references

• NASA's Mars Reconnaissance Orbiter website
• HiRISE Instrument website
• "CRISM Instrument Overview." CRISM Instrument Website. Accessed on April 2, 2005.