Solar Sentinels

The Solar Sentinels was a proposed space mission to Sun. Solar Sentinels was proposed in 2006 in conjunction with other Sun missions, and a Solar Sentinels lite was proposed in 2008.

It might have studied the Sun during its solar maximum, the last before the beginning of the Orion program. Six spacecraft will be launched, which will separate into three groups. The Solar Sentinels are part of the NASA program Living With a Star.

Goals
The goals of the Solar Sentinels are: This mission's driving energy is that the solar maximum of solar cycle 24 will be the final one before the first upcoming manned missions to the Moon and Mars. This means that this will be the last chance to understand the solar storms and the deadly radiation of a solar maximum.
 * 1) Understand the acceleration and transit of solar energetic particles
 * 2) Understand the initiation and evolution of coronal mass ejections (CMEs) and interplanetary shocks in the inner heliosphere

Spacecraft
There will be six spacecraft: four identical spacecraft which will explore the inner heliosphere, one spacecraft which will take its post near Earth, and the final sentinel to trail slowly behind Earth. They are discussed in greater detail below.

Inner Heliospheric Sentinels
The majority of the sentinels are the Inner Heliospheric Sentinels (IHS), which will observe the Sun at distances of 0.25 AU. This will be a challenge to scientists and engineers working on these probes, as this is one-fourth the distance between the Earth and the Sun. These probes will make in-situ measurements of energetic particles and plasma. Instruments to measure X-ray, radio, and neutron emissions will be included. Part of the mission plan includes Venus flybys.

Near Earth Sentinel
The Near Earth Sentinel (NES) will study the corona in UV and visible light.

Farside Sentinel
The Farside Sentinel (FSS) will study the photospheric magnetic field. As three spacecraft are needed to completely monitor this magnetic field, partnerships with two other spacecraft will be made: NASA's Solar Dynamics Observatory and the European Space Agency's Solar Orbiter.

Launch
It is likely the three Inner Heliospheric Sentinels will be launched together. The proposed launch dates are 2014, 2015, or 2017. The nominal mission lasts three years, with an extension to five years if possible.

Cooperation
Several other solar spacecraft will help with this mission, such as STEREO, Japan's Hinode, the Solar Dynamics Observatory, and ESA's Solar Orbiter. Ground-based telescopes will also assist the mission. It will be part of a group of four missions, including the Solar Dynamics Observatory and the Geospace missions (Radiation Belt Storm Probes and Ionosphere-Thermosphere Storm Probes), from the Living With a Star program.