Encyclopedia Astronautica

American Mercury probe. One launch, 2004.08.03. NASA probe, launched in 2004 with the challenging mission of comprehensively mapping Mercury from orbit between March 2011 and March 2012.

To achieve Mercury orbit using a conventional liquid rocket engine meant a seven year flight. During that time Messenger would make six flybys of Earth, Venus, and Mercury to lower the aphelion of its solar orbit and minimize the needed final engine burn to place the spacecraft into Mercury orbit. Even with these planetary gravitational assists, 55% of Messenger's launch mass was rocket propellant, and the scientific payload amounted to less than 5% of its launch mass.

Spacecraft description

To minimize empty mass, Messenger's structure was primarily composed of graphite epoxy material and its dual-mode, liquid chemical propulsion system was integrated into the spacecraft's structure. Two solar panels, charging a nickel-hydrogen battery, provided power. Due to the intense sunlight at Mercury, the panels were mirrored to reflect away 67% of the sunlight.

Redundant integrated electronics modules controlled the spacecraft, each with two processors -- a 25 MHz main processor and a 10-MHz fault-protection processor. Attitude was determined using star-tracking cameras and an Inertial Measurement Unit. Six Digital Solar Sensors provided a backup. Attitude control was accomplished using four reaction wheels. Messenger's 16 small thrusters were available if needed as a back-up or for coarse maneuvers. Communications was through circularly polarized X-band phased-array antennas. A conventional dish antenna could not be used due to the temperatures at Mercury.

For heat protection at Mercury, where the Sun was 11 times brighter than Earth, a sunshade made of heat-resistant ceramic cloth was used. At Mercury the sunshield would reach 370 deg C, while keeping the spacecraft below 20 deg C.

Scientific Payload - the demanding mission meant a net scientific payload of only 50 kg, less than 5% of the spacecraft mass. Nevertheless the miniaturized instrument suite included:

  • Mercury Dual Imaging System (MDIS): This instrument consisted of wide-angle and narrow-angle imagers. A pivot platform was used for pointing.

  • Gamma-Ray and Neutron Spectrometer (GRNS): This instrument was to detect gamma rays and neutrons emitted by Mercury's surface. It was to be used to map the relative abundances of different elements and was to determine if there was ice at Mercury's poles

  • X-Ray spectrometer (XRS): XRS was to detect these X-rays emitted by the surface and measure the abundances of various elements in Mercury's crust.

  • Magnetometer (MAG): This instrument was at the end of a 3.6 meter boom, and was to map Mercury's magnetic field and was to search for magnetized rocks in the crust.

  • Mercury Laser Altimeter (MLA): This instrument was to map Mercury's topography with high accuracy.

  • Mercury Atmospheric and Surface Composition Spectrometer (MASCS): This spectrometer was sensitive to light from the infrared to the ultraviolet and was to measure the abundances of atmospheric gases, as well as detect minerals on the surface.

  • Energetic Particle and Plasma Spectrometer (EPPS): EPPS measured the composition, distribution, and energy of charged particles in Mercury's magnetosphere.

  • Radio Science (RS): RS experiment used the Doppler effect to measure very slight changes in the spacecraft's velocity as it orbited Mercury. This was to allow scientists to study Mercury's mass distribution, including variations in the thickness of its crust.

Mission Profile

Messenger was to use gravity assists from Earth, Venus and Mercury to lower its speed relative to Mercury at orbit insertion. It would flyby Earth in August 2005, then Venus twice, in October 2006 and June 2007. Three Mercury flybys, in January 2008, October 2008 and September 2009, would each be followed two months later by a course correction maneuver by Messenger's engine. The flybys would be used to map most of the planet and measure the composition of the surface, atmosphere and magnetosphere.

In a final encounter with the planet in March 2011. 33% of the spacecraft's propellant would be used to make a maneuver of 0.83 km/sec, putting the spacecraft into a near-polar 200 kilometer x 15,193 kilometer 12-hour orbit inclined 80 to Mercury's equator. The perigee was over the northern hemisphere to allow Messenger to conduct a detailed investigation of Mercury's geology and composition of the Caloris impact basin. The orbit was to be maintained by small engine corrections every 88 days (Mercury year) until the one earth-year survey of the planet was completed in March 2012.


RCS Coarse No x Thrust: 16 thrusters. Spacecraft delta v: 2,300 m/s (7,500 ft/sec).

AKA: MErcury Surface, Space ENvironment, GEochemistry and Ranging mission.
Gross mass: 1,100 kg (2,400 lb).
Unfuelled mass: 500 kg (1,100 lb).
Payload: 50 kg (110 lb).
Thrust: 666 N (149 lbf).
Specific impulse: 290 s.
First Launch: 2004.08.03.
Number: 1 .

More... - Chronology...

Associated Countries
See also
  • Delta The Delta launch vehicle was America's longest-lived, most reliable, and lowest-cost space launch vehicle. Development began in 1955 and it continued in service in the 21st Century despite numerous candidate replacements. More...

Associated Launch Vehicles
  • Delta American orbital launch vehicle. The Delta launch vehicle was America's longest-lived, most reliable, and lowest-cost space launch vehicle. Delta began as Thor, a crash December 1955 program to produce an intermediate range ballistic missile using existing components, which flew thirteen months after go-ahead. Fifteen months after that, a space launch version flew, using an existing upper stage. The addition of solid rocket boosters allowed the Thor core and Able/Delta upper stages to be stretched. Costs were kept down by using first and second-stage rocket engines surplus to the Apollo program in the 1970's. Continuous introduction of new 'existing' technology over the years resulted in an incredible evolution - the payload into a geosynchronous transfer orbit increasing from 68 kg in 1962 to 3810 kg by 2002. Delta survived innumerable attempts to kill the program and replace it with 'more rationale' alternatives. By 2008 nearly 1,000 boosters had flown over a fifty-year career, and cancellation was again announced. More...
  • Delta 7925 American orbital launch vehicle. Four stage vehicle consisting of 9 x GEM-40 + 1 x EELT Thor/RS-27A + 1 x Delta K + 1 x Star 48B More...

Associated Manufacturers and Agencies
  • NASA American agency overseeing development of rockets and spacecraft. National Aeronautics and Space Administration, USA, USA. More...
  • APL American manufacturer of rockets and spacecraft. Applied Physics Laboratory, Johns Hopkins University, Laurel, MD, Laurel, Maryland, USA. More...

Associated Programs
  • Discovery The Discovery program was begun by NASA in the early 1990s as the planetary counterpart to the Explorer program. More...

Associated Propellants
  • N2O4/MMH Nitrogen tetroxide became the storable liquid propellant of choice from the late 1950's. Monomethylhydrazine (CH3NHNH2) is a storable liquid fuel that found favour in the United States for use in orbital spacecraft engines. Its advantages in comparison to UDMH are higher density and slightly higher performance. More...

  • McDowell, Jonathan, Jonathan's Space Home Page (launch records), Harvard University, 1997-present. Web Address when accessed: here.
  • NASA Report, Messenger Launch Presskit, Web Address when accessed: here.
  • NASA Report, Messenger Fact Sheet, Web Address when accessed: here.

Associated Launch Sites
  • Cape Canaveral America's largest launch center, used for all manned launches. Today only six of the 40 launch complexes built here remain in use. Located at or near Cape Canaveral are the Kennedy Space Center on Merritt Island, used by NASA for Saturn V and Space Shuttle launches; Patrick AFB on Cape Canaveral itself, operated the US Department of Defense and handling most other launches; the commercial Spaceport Florida; the air-launched launch vehicle and missile Drop Zone off Mayport, Florida, located at 29.00 N 79.00 W, and an offshore submarine-launched ballistic missile launch area. All of these take advantage of the extensive down-range tracking facilities that once extended from the Cape, through the Caribbean, South Atlantic, and to South Africa and the Indian Ocean. More...
  • Cape Canaveral LC17B Delta launch complex. Part of a dual launch pad complex built for the Thor ballistic missile program in 1956. Upgraded over the decades for use with Thor, Delta, Delta II, and Delta III launch vehicles, it remained in use for over half a century. More...

Messenger Chronology

2004 August 3 - . 06:15 GMT - . Launch Site: Cape Canaveral. Launch Complex: Cape Canaveral LC17B. Launch Pad: SLC17B. LV Family: Delta. Launch Vehicle: Delta 7925. LV Configuration: Delta 7925H D307.
  • Messenger - . Payload: Discovery 8. Mass: 1,066 kg (2,350 lb). Nation: USA. Agency: NASA. Manufacturer: APL. Program: Discovery. Class: Mercury. Type: Mercury probe. Spacecraft: Messenger. USAF Sat Cat: 28391 . COSPAR: 2004-030A. The NASA Messenger probe to Mercury was was first placed into a parking orbit. The Delta booster second stage's second burn raised the orbit, then the PAM-D solid motor burned to put the probe on an escape trajectory into a 0.92 x 1.08 AU x 6.4 deg heliocentric orbit. Messenger (Mercury Surface, Space Environment, Geochemistry and Ranging) was to make an Earth flyby on August 1, 2005; Venus flybys in 2006 and 2007; and Mercury encounters in January and October 2008 , September 2009 and March 2011 . On this last encounter the Aerojet 660N engine was to fire to put Messenger into a 200 x 15,193 km x 80 deg orbit around Mercury. Launch delayed from March 10, May 11, August 2

2005 March 8 - .
  • Messenger, Magnetometer Deployment, Successful - . Nation: USA. Spacecraft: Messenger.

2005 August 2 - .
  • Messenger, Earth Flyby, Successful - . Nation: USA. Spacecraft: Messenger.

2006 October 24 - .
  • Messenger, first Venus Flyby - . Nation: USA. Spacecraft: Messenger.

2008 January 14 - .
  • First Messenger flyby of Mercury - . Nation: USA. Spacecraft: Messenger. Summary: The Messenger spacecraft flew by Mercury at 200 kilometers altitude at 19:04 GMT. This changed the craft's solar orbit to to 0.32 x 0.70 AU leading to further flybys and a final orbital capture in 2011..

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