MESSENGER (Discovery 8)

Launch data: Designation  28391 / 04030A Launch date  03 Aug 2004 - 06:15:56 UT Launch site  CC, SLC-17B Launch vehicle  Delta 7925H (#D307) Mission  Mercury probe Heliocentric orbit Perihelion / Aphelion   Incl. to ecliptic   ° Period   min

Spacecraft data: Prime contractor   Operator  NASA Platform   Mass at launch  1066 kg Dry Mass   kg Basic shape   Dimension   Solar array   Stabilization   DC power   Decay: Descent date:  30 Apr 2015 (crashed into Mercury) Cause:  Running out of fuel Lifetime:  days

Description:

• After Mariner 10's visits to Mercury the space science and engineering communities yearned for a longer and more detailed look at the innermost planet - but that closer look, ideally from orbit, presented formidable technical obstacles. A Mercury orbiter would have to be tough, with enough protection to withstand searing sunlight and roasting heat bouncing back from the planet below. The spacecraft would need to be lightweight, since most of its mass would be fuel to fire its rockets and slow the spacecraft down enough for Mercury's gravity to capture it. And it would have to be compact enough to lift off on a conventional and cost-effective rocket.
• Designed and built by the Johns Hopkins University Applied Physics Laboratory - with contributions from organizations in 24 states and six countries - the MESSENGER spacecraft tackles each of these challenges. A ceramic-fabric sunshade, heat radiators and a mission design that limits time over the planet's hottest regions protect MESSENGER without expensive and impractical cooling systems. The spacecraft's graphite composite structure - strong, lightweight and heat tolerant - is integrated with a low-mass propulsion system that efficiently stores and distributes the approximately 600 kilograms (1,323 pounds) of propellant that accounts for 55 percent of MESSENGER's total launch weight.
• To fit behind the 8-foot by 6-foot sunshade MESSENGER's wiring, electronics, systems and instruments are packed into a small frame that could fit inside a large sport utility vehicle. And the entire spacecraft is light enough to launch on a Delta II rocket, the largest launch vehicle allowed under NASA's Discovery Program of lower-cost space science missions.
• The Mercury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) mission was designed to study the characteristics and environment of Mercury from orbit. Specifically, the scientific objectives of the mission are to characterize the chemical composition of Mercury's surface, the geologic history, the nature of the magnetic field, the size and state of the core, the volatile inventory at the poles, and the nature of Mercury's exosphere and magnetosphere over a nominal orbital mission of one Earth year.
• Science Payload & Systems

Mission details:

• The MESSENGER probe to Mercury was launched on Aug 3, 2004. The Boeing Delta 7925H went into parking orbit from Cape Canaveral; the second stage's second burn raised the orbit, and then the PAM-D solid motor burn put the probe on an escape trajectory. MESSENGER will pass lunar orbit at 0600 UTC on Aug 4 and leave the Earth's sphere of influence at around 1800 UTC on Aug 5, entering a 0.92 x 1.08 AU x 6.4 deg heliocentric orbit, with a perihelion about 0.0013 AU (200000 km) larger than planned, due to a 15 m/s underspeed on the third stage burn.
• It is the first spacecraft to be launched towards the planet Mercury since Mariner 10 in 1973. MESSENGER will use the gravity fields of Earth, Venur and Mercury during fly-bys to lower the velocity required to enter orbit around Mercury.
  
• The following is the schedule for the fly-bys:
  
  

  Planet	Date	Closest Approach
  Earth	02 Aug 2005 - 19:13 UT	2336 km
  Venus	24 Oct 2006 - 08:34 UT	2990 km
  Venus	06 Jun 2007	300 km
  Mercury	14 Jan 2008	200 km
  Mercury	6 Oct 2008	200 km
  Mercury	30 Sep 2009	200 km
  Mercury	18 Mar 2011	Mercury orbit injection

  
  
• Mercury orbit injection will require a delta-V of 867 m/s and the resulting 80 deg inclination orbit will be 200-15193 km (the high point may be greater than 15193 km); the low point will initially be located over 60°N on the planet. It is planned to counter the expected orbital perturbations with corrections every 88 days (one "Mercury year") to keep the low point below 500 km.
• The Messenger probe made its first Venus flyby on Oct 24, 2006. It passed 2990 km from the surface of Venus at 0834 UTC on a hyperbolic trajectory with an inclination of 116 deg to the Venus equator and an eccentricity of 3.27.
• Before the flyby Messenger's orbit around the Sun was 0.60 x 1.05 AU inclined 2.6 deg to the ecliptic. Now it is 0.55 x 0.90 AU with an increased inclination of 8.1 deg.
• NASA's Messenger probe flew past Mercury at 200 km altitude at 1904 UTC on Jan 14, 2008. This was the first Mercury encounter since Mariner 10 in 1975. The flyby hyperbola is inclined 5.0 deg to the Mercurian equator, and the encounter changes Messenger's orbit around the Sun from 0.33 x 0.75 AU to 0.32 x 0.70 AU.
• On October 6, 2008, the MESSENGER spacecraft passed a mere 200 kilometers (124 miles) above Mercury's surface for the mission's second flyby of its target planet. The flyby¹s primary purpose was to use Mercury for a gravity assist, a crucial encounter needed to enable MESSENGER, in 2011, to become the first spacecraft ever to enter into an orbit around Mercury. Though the gravity assist was the top priority for the flyby, MESSENGER's second flyby of Mercury also provided an opportunity to make significant and exciting science observations and measurements.
• On September 29, 2009, the MESSENGER spacecraft passed by Mercury for the third time, flying 141.7 miles above the planet’s rocky surface for a final gravity assist that will enable it to enter orbit about Mercury in 2011. During the encounter, the MESSENGER cameras imaged a portion of Mercury's never-before-seen surface and the Mercury Atmospheric and Surface Composition Spectrometer (MASCS) observed Mercury's exospheric "tail" during approach. With more than 90 percent of the planet’s surface already imaged, MESSENGER’s science team had drafted an ambitious observation campaign designed to tease out additional details from features uncovered during the first two flybys. But an unexpected signal loss prior to closest approach hampered those plans.
  After more flybys, Messenger will enter orbit around Mercury in 2011.
• On Jan 1, 2010 Messenger is in a 0.31 x 0.57 AU x 7.0 deg solar orbit setting up for Mercury arrival in Mar 2011.
• The Messenger probe is now in orbit around the planet Mercury. The orbit insertion burn began at 0045 UTC Mar 18, 2011 and was completed at 0100 UTC. The planned orbit is 200 x 15193 km with perigee over 60 deg N. According to SpaceflightNow, actual orbit is 207 x 15261 km, inclined 82.5 deg to Mercury's equator
• The Messenger probe, in orbit around Mercury, reached a record low orbit of 23 x 10610 km x 83.5 deg on Sep 12, 2014. An engine burn then raised periapsis, making the orbit 92 x 10610 km.
• The Messenger space probe crashed into Mercury on April 30, 2015 after running out of fuel, ending a nearly 11-year journey that provided valuable data and thousands of photos.