The MESSENGER Spacecraft

Abstract

The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MES-SENGER) spacecraft was designed and constructed to withstand the harsh environments associated with achieving and operating in Mercury orbit. The system can be divided into eight subsystems: structures and mechanisms (e.g., the composite core structure, aluminum launch vehicle adapter, and deployables), propulsion (e.g., the state-of-the-art titanium fuel tanks, thruster modules, and associated plumbing), thermal (e.g., the ceramic-cloth sunshade, heaters, and radiators), power (e.g., solar arrays, battery, and controlling electronics), avionics (e.g., the processors, solid-state recorder, and data handling electronics), software (e.g., processor-supported code that performs commanding, data handling, and spacecraft control), guidance and control (e.g., attitude sensors including star cameras and Sun sensors integrated with controllers including reaction wheels), radio frequency telecommunications (e.g., the spacecraft antenna suites and supporting electronics), and payload (e.g., the science instruments and supporting processors). This system architecture went through an extensive (nearly four-year) development and testing effort that provided the team with confidence that all mission goals will be achieved.

Identification and measurement of neutron-absorbing elements on Mercury’s surface

“…The center block, a borated plastic (BP) scintillator, is sensitive to epithermal (0.4 eV to 500 keV) and fast neutrons (500 keV to few MeV), and the two planar lithium glass (LG) scintillators are sensitive to thermal (<0.4 eV) and epithermal neutrons. The NS is attached to the MESSENGER spacecraft on the side opposite the sunshade and is located close to one of three coaligned spacecraft fuel tanks (Leary et al, 2007). The NS is positioned on the spacecraft so that the normal to the LG1 sensor points in the direction of the spacecraft +x-axis and the normal to the LG2 sensor points in the direction of the spacecraft Àx-axis.…”

The Mercury Dual Imaging System on the MESSENGER Spacecraft

“…A large sunshade protects MESSENGER from this intense solar illumination but constrains the spacecraft pointing ability (Leary et al 2007). To support optical navigation during the flybys, Mercury will be imaged against the star background; MDIS thus had to be designed to image at phase angles as high as 140°.…”

“…The right column shows the ratio of the decompressed image to the original; the standard deviation of the ratio is a measure of the artifacts for typical illumination To increase the reliability of the payload, redundant DPUs were created to buffer all data interfaces between the payload elements and the spacecraft; one DPU is powered whenever a payload element is active, while the other DPU is maintained unpowered as a cold spare. The DPUs communicate with the spacecraft processors via the spacecraft MIL-STD-1553 busses (Leary et al 2007), but they communicate with the instruments via separate dedicated RS-422 Universal Asynchronous Receiver Transmitter (UART) interfaces. The DPUs greatly simplified the spacecraft-to-payload interface issues, allowing payload development and testing separate from the rest of the spacecraft.…”

“…The DPUs greatly simplified the spacecraft-to-payload interface issues, allowing payload development and testing separate from the rest of the spacecraft. Figure 7 provides a high-level flow diagram showing the relationship between the MDIS DPUs, the spacecraft Integrated Electronics Modules or IEMs (Leary et al 2007), and the other science payload instruments.…”

“…The bracket assembly, made of the same advanced composite material (graphite/cyanate ester fabric prepreg) as the MESSENGER spacecraft structure (Leary et al 2007), was chosen to minimize mechanical stresses due to mismatches in coefficients of thermal expansion. The composite bracket assembly, being a very poor thermal conductor, isolates the pivot platform and thereby the cameras from the payload instrument deck.…”