Ion Propulsion (2011-05-29)

Ion Propulsion - Transport System to the Planets The efficiency of a rocket engine can be described by its specific impulse, which is the change of momentum gained from a 1 kilogram weight of propellent. The Space Shuttle main engines have a specific impulse of 453 seconds which is typical of a liquid fuelled rocket engine. An Ion thruster has a specific impulse of more than 3000 seconds and so requires less than a sixth of the fuel of a liquid fuelled engine. Gridded electrostatic ion thrusters commonly utilize Xenon gas. The gas is first ionized by bombarding it with electrons. The positively charged ions then diffuse through the positive grid and enter a potential difference between the positive and negative grids. The potential difference accelerates the ions to high velocities, which then leave the engine to create thrust. An electron emitter, on the exterior of the engine, neutralizes the ion beam to prevent charge build-up. The typical thrust of an ion engine is equivalent to a weight of 10 grams - about the weight of a sheet of paper. This means ion thrusters need to provide continuous thrust for a very long time in order to achieve a reasonable change in velocity. Electrostatic ion engines have been tested for 3.5 years of continuous thrust at full power. Collision of ions with the charged grids causes their erosion and will lead to eventual failure. Ion engines consume more than 2 kilowatts of electrical power, which may be generated by solar arrays or nuclear ...

The Phoenix Mars Lander (2011-06-03)

A new space explorer is waiting in the wings and ready to take center stage: the Mars lander called Phoenix. Phoenix's assignment is to dig through the Martian soil and ice in the arctic region and use its onboard scientific instruments to analyze the samples it retrieves. Mars is a cold desert planet with no liquid water on its surface. But in the Martian arctic, water ice lurks just below ground level. Discoveries made by the Mars Odyssey Orbiter in 2002 show large amounts of subsurface water ice in the northern arctic plain. The Phoenix lander targets this circumpolar region using a robotic arm to dig through the protective top soil layer to the water ice below and ultimately, to bring both soil and water ice to the lander platform for sophisticated scientific analysis. The complement of the Phoenix spacecraft and its scientific instruments are ideally suited to uncover clues to the geologic history and biological potential of the Martian arctic. Phoenix will be the first mission to return data from either polar region providing an important contribution to the overall Mars science strategy "Follow the Water" and will be instrumental in achieving the four science goals of NASA's long-term Mars Exploration Program. - Determine whether Life ever arose on Mars - Characterize the Climate of Mars - Characterize the Geology of Mars - Prepare for Human Exploration The Phoenix Mission has two bold objectives to support these goals, which are to (1) study the history of water ...

THEMIS Launch (2011-06-15)

NASA's THEMIS mission successfully launched, on board a Delta II rocket, Saturday, Feb. 17, at 6:01 pm EST from Pad 17-B at Cape Canaveral Air Force Station. THEMIS stands for the Time History of Events and Macroscale Interactions during Substorms. It is NASA's first five-satellite mission launched aboard a single rocket. The spacecraft separated from the launch vehicle approximately 73 minutes after liftoff. By 8:07 pm EST, mission operators at the University of California, Berkeley, commanded and received signals from all five spacecraft, confirming nominal separation status.