A NASA Discovery mission to conduct the first orbital study
of the innermost planet
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Frequently Asked Questions
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The Mission
Basic information about MESSENGER

1. What is MESSENGER?

MESSENGER is a scientific investigation – by spacecraft – of the planet Mercury. The name comes from “MErcury Surface, Space ENvironment, GEochemistry, and Ranging,” highlighting the project’s broad range of scientific goals.

Mercury itself is named after the mythological messenger of the gods.

2. What are MESSENGER's scientific goals?

MESSENGER is designed to answer six broad scientific questions:

  • Why is Mercury so dense?
  • What is the geologic history of Mercury?
  • What is the nature of Mercury's magnetic field?
  • What is the structure of Mercury's core?
  • What are the unusual materials at Mercury's poles?
  • What volatiles are important at Mercury?

The "Why Mercury?" section of this Web site explains the rationale for these six questions.

3. Who is on the MESSENGER Team?

Dr. Sean C. Solomon, of the Carnegie Institution of Washington, leads the MESSENGER mission as principal investigator. The Johns Hopkins University Applied Physics Laboratory (JHU/APL) manages the mission for NASA and designed and built the spacecraft, in collaboration with industry partners GenCorp Aerojet (propulsion system) and Composite Optics Inc., now ATK (spacecraft structure). JHU/APL, NASA’s Goddard Space Flight Center, the University of Colorado, and the University of Michigan supplied scientific instruments and related subsystems. JHU/APL also operates MESSENGER in flight, with Deep Space Network support from NASA’s Jet Propulsion Laboratory.

The MESSENGER science team includes investigators from

  • Carnegie Institution of Washington
  • Goddard Space Flight Center
  • University of Arizona
  • Arizona State University
  • Brown University
  • University of California, Santa Barbara
  • University of Colorado
  • Massachusetts Institute of Technology
  • University of Michigan
  • Planetary Science Institute
  • Southwest Research Institute

The science team was augmented in 2007 with the addition of 23 MESSENGER Participating Scientists from

  • Carnegie Institution of Washington
  • Goddard Space Flight Center
  • University of Arizona
  • University of California, Berkeley
  • University of California, Los Angeles
  • University of California, San Diego
  • Case Western Reserve University
  • The Catholic University of America
  • Computer Sciences Corporation
  • University of Hawaii
  • University of Maryland, College Park
  • Planetary Science Institute
  • Raytheon Technical Services
  • Smithsonian Institution
  • Deutsches Zentrum für Luft- und Raumfahrt in Germany

Visit our “Who We Are” pages for information on team members.

4. What are the basic components of the MESSENGER spacecraft?

  • The scientific payload includes the instruments that will gather MESSENGER's science data.
  • The sunshade protects the spacecraft from direct sunlight, allowing the spacecraft electronics and instruments to operate at room temperature even in the hot Mercury environment.
  • The solar array provides power to the spacecraft. MESSENGER also carries a battery that stores the power generated by the solar array and feeds it to other systems.
  • The thrusters perform fuel burns to change the spacecraft's trajectory and attitude.
  • The launch vehicle adapter was the spacecraft's connection point to the launch vehicle; it has not been used for anything after MESSENGER separated from the launch vehicle.

Click here to watch how MESSENGER came together!

5. What are MESSENGER's scientific instruments?

MESSENGER carries seven scientific instruments:

  • Mercury Dual Imaging System (MDIS), a camera with wide and narrow fields-of-view, for monochrome, color, and stereo imaging.
  • Gamma-Ray and Neutron Spectrometer (GRNS), which maps the elemental makeup of Mercury’s crust.
  • X-Ray Spectrometer (XRS), also used to map elemental abundances in crustal materials.
  • Magnetometer (MAG), which maps the detailed structure and dynamics of Mercury's magnetic field and magnetosphere and searches for regions of magnetized crustal rocks.
  • Mercury Laser Altimeter (MLA), which measures the planet’s topography.
  • Mercury Atmospheric and Surface Composition Spectrometer (MASCS), which measures the abundance of atmospheric gases and detects minerals in surface materials.
  • Energetic Particle and Plasma Spectrometer (EPPS), which measures the makeup and characteristics of charged particles within and around Mercury's magnetosphere.

Tapping into MESSENGER’s telecommunications system, a radio science investigation will monitor the Doppler effect – the shift in the frequency of the spacecraft's radio signal with changes in the spacecraft's velocity relative to Earth – to measure Mercury's mass distribution, including spatial variations in crustal thickness.

6. What are other key characteristics of the spacecraft?

While NASA Discovery missions offer lower costs, they must also be scientifically robust and technologically sound. MESSENGER met these goals by combining existing technologies with efficient engineering. For example:

  • All major spacecraft systems are redundant; if any one system fails, another system (or a backup of the original) can take over its tasks.
  • MESSENGER used mostly off-the-shelf components and standard data interfaces, reducing the need for unproven and potentially expensive new technologies.
  • The spacecraft inherited subsystem designs from missions such as NEAR (Near Earth Asteroid Rendezvous) and TIMED (Thermosphere, Ionosphere, Mesosphere, Energetics and Dynamics).
  • Antennas are fixed – rather than deployable – eliminating the chance of lost communications in case of antenna-deployment problems.
  • The “passive thermal design” of the ceramic-cloth sunshade removed the need for high-temperature electronics.

7. What type of propulsion system does MESSENGER use? How much propellant does it carry?

The MESSENGER spacecraft uses liquid chemical propulsion for cruising to Mercury and orbit insertion. MESSENGER's 16 small, monopropellant thrusters (used for main tank propellant settling and small orbit-correction maneuvers) use hydrazine. Its main, bipropellant engine - which MESSENGER uses for large trajectory-correction maneuvers on the way to Mercury and to inject into orbit around the planet - uses both hydrazine and nitrogen tetroxide.

MESSENGER carried about 600 kilograms (1,323 pounds) of propellant at launch - nearly 55 percent of its total launch weight of about 1,100 kilograms (2,442 pounds).

8. How do mission controllers communicate with the spacecraft?

MESSENGER has two lightweight phased antenna arrays for downlink communications and medium-gain and low-gain antennas for both uplink and downlink communications. The downlink sends scientific data and spacecraft status information to Earth; uplink communications are used to send commands to the spacecraft.

The mission operations team communicates with MESSENGER through NASA’s Deep Space Network (DSN) of antenna stations. The DSN consists of facilities in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia. Since these stations are spaced about 120° apart on the globe, the spacecraft can be observed at any time as Earth rotates.

9. How would the team know if MESSENGER has a problem during flight?

If the spacecraft encounters a problem, it can establish contact with controllers on Earth through the Deep Space Network. If the problem is minor, the spacecraft can turn off an affected component and resume normal operations even before contacting Earth.

If the problem is more serious and requires remedial action, the spacecraft goes into a "safe" mode. In safe mode, the sunshade is pointed at the Sun and the medium-gain antenna at Earth, and the spacecraft waits for further instructions from the operations team.

10. Can the team fix the spacecraft from Earth?

If a component on the spacecraft fails, controllers on Earth can instruct MESSENGER to bring a backup online. If the spacecraft points in the wrong direction, its attitude can be corrected. If the spacecraft deviates from the desired trajectory, a controlled burn (thruster firing) can be performed to put it back on track.

Most minor problems can be corrected from Earth with existing onboard instruction systems or by transmitting software “fixes” to the spacecraft.

11. How is the spacecraft powered?

MESSENGER is mainly powered by its solar array, which includes two solar panels covering a total area of 5 square meters. The panels are made of materials rated to withstand high temperatures – 250°C or 480°F – but the system is designed to keep the panels from facing the Sun directly, yielding a nominal operational temperature in the range 100° to 150°C.

The power produced by the solar array is stored in a nickel-hydrogen (NiH2) battery, then distributed from the battery to the spacecraft subsystems.

12. Have other spacecraft visited Mercury?

Only one: Mariner 10 flew by the planet three times in 1974 and 1975. Much of what we know about Mercury is based on data from these flybys, even though they provided pictures of only about 45% of the planet and at roughly 1-kilometer (0.6-mile) resolution.

13. Does MESSENGER incorporate any new developments that make it unique from Mariner 10 or other spacecraft?

To keep costs down the MESSENGER program limited the number of "new" developments, but a few key technologies have enabled the mission. MESSENGER is the first deep-space mission to use a circularly polarized phased-array antenna - the antenna "points" electronically, which allows MESSENGER to return a large amount of data without using a deployable, gimbaled antenna (such as the one that failed to deploy on the Galileo mission).

MESSENGER's all-composite structure keeps the spacecraft relatively lightweight. Composites are routinely used on spacecraft, but usually not for the entire structure.

As an orbiter, MESSENGER must be able to withstand a much more severe thermal environment at Mercury than Mariner 10, which was a flyby mission. MESSENGER's sunshade and blanketing are based on materials similar to Mariner 10's, but MESSENGER carries thicker and additional blanketing.

MESSENGER's solar arrays are about one-third solar cells and two-thirds mirrors. The panels will face intense solar energy, but the small mirrors placed between the power-generating solar cells reflect nearly 70 percent of that energy and keep the panels cooler. This technique has been used on other missions, but not this extensively.

Because the sunshade so effectively eliminates the Sun's input, everything else on MESSENGER is typical for other spacecraft.

14. What other missions are scheduled to study Mercury?

After MESSENGER, the next mission planned to Mercury is the BepiColombo project of the European Space Agency and the Japan Aerospace Exploration Agency. BepiColombo involves the launch in 2016 of two spacecraft to orbit Mercury, one to map the planet and one to examine the magnetosphere.

15. How will the MESSENGER and BepiColombo missions complement each other?

MESSENGER and BepiColombo scientists have held several discussions, both in the U.S. and in Europe, on opportunities for cooperation between the mission teams. These discussions are leading to a variety of cooperative efforts involving data exchange, targeting of observations during the missions, and potentially the sharing of ground resources and collaborative scientific analysis of joint data sets.

16. What is the NASA Discovery Program?

MESSENGER was the seventh mission selected for NASA's Discovery Program, the agency's innovative approach to low-cost, scientifically focused planetary missions. Discovery grew from the science community's calls for a space exploration program that balances scientific return and mission costs in an era of tight budgets.

Visit the NASA Discovery Web page for more information on the program.

17. What are other Discovery Program missions?

The completed Mars Pathfinder and Lunar Prospector missions collected valuable information on the surfaces of Mars and the Moon. The Near Earth Asteroid Rendezvous (NEAR) mission conducted the first orbital study of and landing on an asteroid.

Stardust, launched in February 1999, collected samples of comet dust and returned them to Earth. Genesis, launched in August 2001, collected particles from the Sun known as solar wind and returned those samples to Earth.

Deep Impact launched in January 2005 and sent a projectile into comet Tempel 1, creating an explosion that has helped scientists analyze the comet's interior. Dawn launched in September 2007 and will orbit Vesta and Ceres, the two largest main-belt asteroids in our solar system. Kepler, planned for a 2009 launch, will monitor 100,000 stars similar to our Sun in search of Earth-size (or even smaller) planets. The Gravity Recovery and Interior Laboratory (GRAIL) mission, to launch in 2011, will measure the lunar gravity field in unprecedented detail.

If you have a question that has not been answered here, we invite you to submit it to us.
We also welcome questions and comments on the MESSENGER Website. Send a note to the Webmaster or check our Contacts page.


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