Launch and trajectory The
MESSENGER probe was launched on August 3, 2004, at 06:15:56 UTC by
NASA from
Space Launch Complex 17B at the
Cape Canaveral Air Force Station in Florida, aboard a
Delta II 7925 launch vehicle. The complete burn sequence lasted 57 minutes bringing the spacecraft into a heliocentric orbit, with a final velocity of 10.68 km/s (6.64 miles/s) and sending the probe into a 7.9 billion-kilometer (4.9 billion mi) trajectory that took 6 years, 7 months and 16 days before its orbital insertion on March 18, 2011. To further minimize the amount of necessary propellant, the spacecraft orbital insertion targeted a highly
elliptical orbit around Mercury. The elongated orbit had two other benefits: It allowed the spacecraft time to cool after the times it was between the hot surface of Mercury and the Sun, and also it allowed the spacecraft to measure the effects of
solar wind and the magnetic fields of the planet at various distances while still allowing close-up measurements and photographs of the surface and exosphere. The spacecraft was originally scheduled to launch during a 12-day window that beginning May 11, 2004. On March 26, 2004, NASA announced the launch would be moved to a later, 15-day launch window beginning July 30, 2004, to allow for further testing of the spacecraft. This change significantly altered the trajectory of the mission and delayed the arrival at Mercury by two years. The original plan called for three fly-by maneuvers past Venus, with Mercury orbit insertion scheduled for 2009. The trajectory was changed to include one Earth flyby, two Venus flybys, and three Mercury flybys before
orbit insertion on March 18, 2011. File:MESSENGER - exploded launch vehicle diagram.png|alt=Exploded launch configuration diagram with MESSENGER and Delta 2 rocket|Exploded diagram of Delta II launch vehicle with
MESSENGER File:MESSENGER launch on Delta 7925 rocket.jpg|alt=The launch of MESSENGER on a Delta II launch vehicle|The launch of
MESSENGER on a Delta II launch vehicle. File:Animation of MESSENGER trajectory.gif|Animation of
MESSENGER trajectory from August 3, 2004, to May 1, 2015 File:MESSENGER trajectory.svg|alt=Interplanetary trajectory of
MESSENGER orbiter|Interplanetary trajectory of the
MESSENGER orbiter.
Earth flyby MESSENGER performed an Earth
flyby one year after launch, on August 2, 2005, with the closest approach at 19:13
UTC at an altitude of 2,347 kilometers (1,458 statute miles) over central
Mongolia. On December 12, 2005, a 524-second-long burn (Deep-Space Maneuver or DSM-1) of the large thruster adjusted the trajectory for the upcoming Venus flyby by 316 m/s. During the Earth flyby, the
MESSENGER team imaged the Earth and Moon using MDIS and checked the status of several other instruments observing the atmospheric and surface compositions and testing the magnetosphere and determining that all instruments tested were working as expected. This calibration period was intended to ensure accurate interpretation of data when the spacecraft entered orbit around Mercury. Ensuring that the instruments functioned correctly at such an early stage in the mission allowed opportunity for multiple minor errors to be dealt with. The Earth flyby was used to investigate the
flyby anomaly, where some spacecraft have been observed to have trajectories that differ slightly from those predicted. However no anomaly was observed in MESSENGER's flyby. File:MESSENGERearth.jpg|alt=A view of Earth from
MESSENGER during its Earth flyby|A view of Earth from
MESSENGER during its Earth flyby. File:View of Earth from MESSENGER.jpg|alt=Another view of Earth from
MESSENGER during its Earth flyby|A view of Earth from
MESSENGER during its Earth flyby. File:Earth and Moon seen from 183 million kilometers by MESSENGER.png|alt=The Earth and Moon captured by the MESSENGER Wide Angle Camera from a distance of 183 million kilometers|The
Earth and
Moon (lower left), captured by
MESSENGER from a distance of 183 million kilometers. File:Mdis depart anot.ogv|alt=Departure sequence captured as Messenger flew past Earth on August 3, 2005|Earth flyby sequence captured on August 3, 2005 (
Full-size video).
Two Venus flybys On October 24, 2006, at 08:34 UTC,
MESSENGER encountered Venus at an altitude of . During the encounter,
MESSENGER passed behind Venus and entered
superior conjunction, a period when Earth was on the exact opposite side of the Solar System, with the Sun inhibiting radio contact. For this reason, no scientific observations were conducted during the flyby. Communication with the spacecraft was reestablished in late November and performed a deep space maneuver on December 12, 2006, to correct the trajectory to encounter Venus in a second flyby. On June 5, 2007, at 23:08 UTC,
MESSENGER performed a second flyby of Venus at an altitude of , for the greatest velocity reduction of the mission. During the encounter, all instruments were used to observe Venus and prepare for the following Mercury encounters. The encounter provided visible and
near-infrared imaging data of the upper
atmosphere of Venus.
Ultraviolet and X-ray
spectrometry of the upper atmosphere were also recorded, to characterize the composition. The
ESA's
Venus Express was also orbiting during the encounter, providing the first opportunity for simultaneous measurement of particle-and-field characteristics of the planet. File:MESSENGERvenus1approach.jpg|alt=Venus Imaged by MESSENGER on the first flyby of the planet|Venus imaged by
MESSENGER on its first flyby of the planet in 2006. File:Venus 2 Approach Image.jpg|alt=Venus imaged by MESSENGER on the second flyby of the planet|Venus imaged by
MESSENGER on its second flyby of the planet in 2007. File:MESSENGER - Venus 630 nm stretch.jpg|alt=A more detailed image of Venus by MESSENGER on the second flyby of the planet|A more detailed image of Venus
MESSENGER on the second flyby of the planet. File:MESSENGER - Venus2 departure seq.jpg|alt=Sequence of images as MESSENGER departs after the second flyby of the planet|Sequence of images as
MESSENGER departs after the second flyby of the planet.
Three Mercury flybys MESSENGER made a flyby of Mercury on January 14, 2008 (making its closest approach of 200 km above the surface of Mercury at 19:04:39
UTC), followed by a second flyby on October 6, 2008. One last deep space maneuver, DSM-5, was executed on November 24, 2009, at 22:45 UTC to provide the required velocity change for the scheduled Mercury orbit insertion on March 18, 2011, marking the beginning of the orbital mission. File:Mercury in color c1000 700 430.png|alt=The first high-resolution color Wide Angle Camera image of Mercury acquired by MESSENGER|The first high-resolution color Wide Angle Camera image of Mercury acquired by
MESSENGER. File:MESSENGER first photo of unseen side of mercury.jpg|alt=Mercury from later in the first flyby|Mercury from later in the first flyby, showing many previously unknown features File:MESSENGER's first view of Mercury with name labels.jpg|Labeled version of the previous image File:CW0131775256F Kuiper Crater.png|alt=View from the second flyby in October 2008|View from the second flyby in October 2008, with Kuiper crater near center File:MESSENGER - CN0162744010M RA 3 web.png|alt=Smooth plains on Mercury imaged by MESSENGER during the third flyby of the planet.|Smooth plains of
Borealis Planitia imaged by
MESSENGER during the third flyby of the planet. File:MESSENGER EN0108828359M.png|alt=An image of part of the previously unseen side of the planet|An image of part of the previously unseen side of the planet, including what is now called
Manley crater. File:MESSENGER - BV Microsymposium49.jpg|alt=Lava-flooded craters and large expanses of smooth volcanic plains on Mercury.|Lava-flooded craters and large expanses of smooth volcanic plains on Mercury. File:Rachmaninoff crater.png|alt=A photo of Mercury with Rachmaninoff crater centered|View with
Rachmaninoff crater, from third flyby
Orbital insertion The thruster maneuver to insert the probe into Mercury's orbit began at 00:45 UTC on March 18, 2011. The 0.9 km/s (0.5 mi./sec.) braking maneuver lasted about 15 minutes, with confirmation that the craft was in Mercury orbit received at 01:10 UTC on March 18 (9:10 PM, March 17 EDT). Mission lead engineer Eric Finnegan indicated that the spacecraft had achieved a near-perfect orbit.
MESSENGER's orbit was highly elliptical, taking it within of Mercury's surface and then away from it every twelve hours. This orbit was chosen to shield the probe from the heat radiated by Mercury's hot surface. Only a small portion of each orbit was at a low altitude, where the spacecraft was subjected to radiative heating from the hot side of the planet. File:Animation of MESSENGER trajectory around Mercury.gif|Animation of
MESSENGER trajectory around
Mercury File:MESSENGERannouncement.jpg|alt=Charles Bolden and colleagues wait for news from MESSENGER.|
Charles Bolden and colleagues wait for news from the
MESSENGER probe. File:Celebrating Mercury Orbit.jpg|alt=Charles Bolden congratulates Eric Finnegan as the spacecraft successfully inserted itself in Mercury's orbit.|Charles Bolden congratulates Eric Finnegan following the successful orbital insertion. File:First ever photograph from Mercury orbit.jpg|alt=The first-ever photograph from Mercury orbit, taken by MESSENGER on March 29, 2011.|The first-ever photograph from Mercury orbit, taken by
MESSENGER on March 29, 2011. File:MercuryOrbitInsertionDirectionofSunFull.jpg|alt=A Chart of MESSENGER's Orbital Insertion|A simplified chart showing the path of
MESSENGERs orbital insertion. ==Primary science==