Viewing the Transit of Venus From Space

Observations of the Transit of Venus during the 17th, 18th, and 19th centuries allowed scientists to calculate the distance between the Earth and the Sun, while revealing the existence of an atmosphere around Venus. Since the previous pair of transits of Venus in 1874 and 1882, humans have developed the ability to view the phenomena from space -- both directly from low-Earth orbit and remotely from sensors on spacecraft collecting data about the Sun.

Astronaut Don Pettit, flight engineer for International Space Station (ISS) Expedition 31, was particularly keen to take photos of the event from orbit -- even bringing a solar camera filter aboard for the event. This top image, from the first half of the 2012 transit, is one of hundreds taken from the ISS Cupola, a windowed module that provides the crew with unparalleled views of both Earth and astronomical phenomena.

In fact, history will record the ISS as the first orbital, crewed spacecraft from which the Transit of Venus has been observed. In addition to the dark circle of Venus visible at image upper left, several smaller sunspots are visible at image center.

For more info, visit:
http://www.nasa.gov/mission_pages/station/research/news/transit_from_space.html

Spacecraft Design

MESSENGER's dual-mode, liquid chemical propulsion system is integrated into the spacecraft's structure to make economical use of mass. The structure is primarily composed of a graphite epoxy material. This composite structure provides the strength necessary to survive launch while offering lower mass. Two large solar panels, supplemented with a nickel-hydrogen battery, provide MESSENGER's power.

The "brains" of the spacecraft are redundant integrated electronics modules (IEMs) that house two processors each -- a 25-megahertz (MHz) main processor and a 10-MHz fault-protection processor.

Mercury Dual Imaging System (MDIS): This instrument consists of wide-angle and narrow-angle imagers that will map landforms, track variations in surface spectra and gather topographic information. A pivot platform will help point it in whatever direction the scientists choose. The two instruments will enable MESSENGER to "see" much like our two eyes do.

Gamma-Ray and Neutron Spectrometer (GRNS): This instrument will detect gamma rays and neutrons that are emitted by radioactive elements on Mercury's surface or by surface elements that have been stimulated by cosmic rays. It will be used to map the relative abundances of different elements and will help to determine if there is ice at Mercury's poles, which are never exposed to direct sunlight.

Gamma rays and high-energy X-rays from the Sun, striking Mercury's surface, can cause the surface elements to emit low-energy X-rays. XRS will detect these emitted X-rays to measure the abundances of various elements in the materials of Mercury's crust.

Magnetometer (MAG): This instrument is at the end of a 3.6 meter (nearly 12-foot) boom, and will map Mercury's magnetic field and will search for regions of magnetized rocks in the crust.

Mercury Laser Altimeter (MLA): This instrument contains a laser that will send light to the planet's surface and a sensor that will gather the light after it has been reflected from the surface. Together they will measure the amount of time for light to make a round-trip to the surface and back. Recording variations in this distance will produce highly accurate descriptions of Mercury's topography.

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

Energetic Particle and Plasma Spectrometer (EPPS): EPPS measures the composition, distribution, and energy of charged particles (electrons and various ions) in Mercury's magnetosphere.

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