MESSENGER - WikiHQ

MESSENGER was a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field. The name is a backronym for Mercury Surface, Space Environment, Geochemistry, and Ranging, and a reference to the messenger god Mercury from Roman mythology.

MESSENGER was launched aboard a Delta II rocket in August 2004. Its path involved a complex series of flybys – the spacecraft flew by Earth once, Venus twice, and Mercury itself three times, allowing it to decelerate relative to Mercury using minimal fuel. During its first flyby of Mercury in January 2008, MESSENGER became the second mission, after Mariner 10 in 1975, to reach Mercury.

MESSENGER entered orbit around Mercury on March 18, 2011, becoming the first spacecraft to do so.

Mission overview

MESSENGERs formal data collection mission began on April 4, 2011. The primary mission was completed on March 17, 2012, having collected close to 100,000 images. MESSENGER achieved 100% mapping of Mercury on March 6, 2013, and completed its first year-long extended mission on March 17, 2013. The probe's second extended mission lasted for over two years, but as its low orbit degraded, it required reboosts to avoid impact. It conducted its final reboost burns on October 24, 2014, and January 21, 2015, before crashing into Mercury on April 30, 2015.

During its stay in Mercury orbit, the probe's instruments yielded significant data, including a characterization of Mercury's magnetic field which had long been suspected on the basis of Earth-based radar data.

Mission background

Previous missions

In 1973, Mariner 10 was launched by NASA to make multiple flyby encounters of Venus and Mercury. Mariner 10 provided the first detailed data of Mercury, mapping 40–45% of the surface. Mariner 10's final flyby of Mercury occurred on March 16, 1975. No subsequent close-range observations of the planet would take place for more than 30 years.

Proposals for the mission

In 1998, a study detailed a proposed mission to send an orbiting spacecraft to Mercury, as the planet was at that point the least-explored of the inner planets. In the years following the Mariner 10 mission, subsequent mission proposals to revisit Mercury had appeared too costly, requiring large quantities of propellant and a heavy lift launch vehicle. Moreover, inserting a spacecraft into orbit around Mercury is difficult, because a probe approaching on a direct path from Earth would be accelerated by the Sun's gravity and pass Mercury far too quickly to orbit it. However, using a trajectory designed by Chen-wan Yen in 1985, the study showed it was possible to execute a Discovery-class mission by using multiple, consecutive gravity assist, 'swingby' maneuvers around Venus and Mercury, in combination with minor propulsive trajectory corrections, to gradually slow the spacecraft and thereby minimize propellant needs.

Objectives

The MESSENGER mission was designed to study the characteristics and environment of Mercury from orbit. The scientific objectives of the mission were:

to characterize the chemical composition of Mercury's surface.
to study the planet's geologic history.
to elucidate the nature of the global magnetic field (magnetosphere).
to determine the size and state of the core.
to determine the volatile inventory at the poles.
to study the nature of Mercury's exosphere.

Spacecraft design

alt=Interactive 3D model of MESSENGER|thumb|298x298px|Interactive 3D model of MESSENGER

The MESSENGER spacecraft was designed and built at the Johns Hopkins University Applied Physics Laboratory. Science operations were managed by Sean Solomon as principal investigator, and mission operations were also conducted at JHU/APL. At launch, the spacecraft weighed approximately with its full load of propellant. MESSENGER<nowiki>'</nowiki>s total mission cost, including the cost of the spacecraft's construction, was estimated at under US$450 million.

Attitude control and propulsion

Main propulsion was provided by the 645 N, 317 sec. Isp bipropellant (hydrazine and nitrogen tetroxide) large velocity assist (LVA) thruster. The model used was the LEROS 1b, developed and manufactured at AMPAC‐ISP's Westcott works, in the United Kingdom. The spacecraft was designed to carry of propellant and helium pressurizer for the LVA.

Power

The space probe was powered by a two-panel gallium arsenide/germanium solar array providing an average of 450 watts while in Mercury orbit. Each panel was rotatable and included optical solar reflectors to balance the temperature of the array. Power was stored in a common-pressure-vessel, 23-ampere-hour nickel–hydrogen battery, with 11 vessels and two cells per vessel.

Objectives:

{|style="text-align:center"

! colspan="4" scope="col" style="width:350px;"| Wide Angle Camera Filters

! scope="col" style="background:#e5e5e5; width:90px;"| Name (pos)

! style="background: #e5e5e5" | Wavelength

! style="background: #e5e5e5" | Sensitivity

| Clear (2, B)

| center|400–1000 nm

| Violet (6, F)

| 420–440 nm

| style="background: #2e00ff" |

| Blue (3, C)

| 465–485 nm

| style="background: #00d5ff" |

| Green (4, D)

| 555–565 nm

| style="background: #c0ff00" |

| Far Red (1, A)

| 695–705 nm

| style="background:#f00;"|

| N-IR (7, G)

| 745–755 nm

| style="background: #a30000" |

| N-IR (12, L)

| 825–835 nm