  Coronal mass ejections (CMEs) and corotating interaction regions (CIRs) as
well as their source regions are important because of their space weather
consequences. The current understanding of CMEs primarily comes from the Solar
and Heliospheric Observatory (SOHO) and the Solar Terrestrial Relations
Observatory (STEREO) missions, but these missions lacked some key measurements:
STEREO did not have a magnetograph; SOHO did not have in-situ magnetometer.
SOHO and other imagers such as the Solar Mass Ejection Imager (SMEI) located on
the Sun-Earth line are also not well-suited to measure Earth-directed CMEs. The
Earth-Affecting Solar Causes Observatory (EASCO) is a proposed mission to be
located at the Sun-Earth L5 that overcomes these deficiencies. The mission
concept was recently studied at the Mission Design Laboratory (MDL), NASA
Goddard Space Flight Center, to see how the mission can be implemented. The
study found that the scientific payload (seven remote-sensing and three in-situ
instruments) can be readily accommodated and can be launched using an
intermediate size vehicle; a hybrid propulsion system consisting of a Xenon ion
thruster and hydrazine has been found to be adequate to place the payload at
L5. Following a 2-year transfer time, a 4-year operation is considered around
the next solar maximum in 2025.
