Heliophysics Sentinels 2017

There have been few changes since the 2015 Earth-Orbiting Heliophysics Fleet. As of summer 2017, here's a tour of the NASA Heliophysics fleet from the near-Earth satellites out to the Voyagers beyond the heliopause.

The satellite orbits are color coded for their observing program:

• Magenta: TIM (Thermosphere, Ionosphere, Mesosphere) observations
• Yellow: solar observations and imagery

• Cyan: Geospace and magnetosphere

• Violet: Heliospheric observations

Near-Earth Fleet:

• Hinode: Observes the Sun in multiple wavelengths up to x-rays. SVS page
• RHESSI : Observes the Sun in x-rays and gamma-rays. SVS page
• TIMED: Studies the upper layers (40-110 miles up) of Earth's atmosphere. SVS page
• SORCE: Monitors solar intensity across a broad range of the electromagnetic spectrum.
• AIM: Images and measures noctilucent clouds. SVS page
• Van Allen Probes: Two probes moving along the same orbit designed to study the impact of space weather on Earth's radiation belts. SVS page
• TWINS: Two Wide-Angle Imaging Neutral-Atom Spectrometers are two probes observing the Earth with neutral atom imagers.
• IRIS: Interface Region Imaging Spectrograph is designed to take high-resolution spectra and images of the region between the solar photosphere and solar atmosphere. SVS page

Geosynchronous Fleet:

• SDO: Solar Dynamics Observatory keeps the Sun under continuous observation at 16 megapixel resolution. SVS page

Geospace Fleet:

• Geotail: Conducts measurements of electrons and ions in the Earth's magnetotail. SVS page
• Magnetospheric Multi-scale (MMS): This is a group of four satellites which fly in formation to measure how particles and fields in the magnetosphere vary in space and time. SVS page
• THEMIS: This is a fleet of three satellites to study how magnetospheric instabilities produce substorms. Two of the original five satellites were moved into lunar orbit to become ARTEMIS.SVS page
• IBEX: The Interstellar Boundary Explorer measures the flux of neutral atoms from the heliopause. SVS page

Lunar Orbiting Fleet:

• ARTEMIS: Two of the THEMIS satellites were moved into lunar orbit to study the interaction of the Earth's magnetosphere with the Moon. SVS page

Sun-Earth Lagrange Point One Fleet:

The L1 point is a Lagrange Point between the Sun and the Earth. Spacecraft can orbit this location for continuous coverage of the Sun.

• SOHO: Studies the Sun with cameras and a multitude of other instruments. SVS page
• ACE: Measures the composition and characteristics of the solar wind. SVS page
• Wind: Measures particle flows and fields in the solar wind. SVS page

Solar Orbiting Fleet:

• STEREO-A & STEREO-B: The two STEREO spaceraft orbit the Sun in roughly the same orbit as Earth. There have been some communications problems with STEREO-B since 2014. SVS page

Interstellar Fleet:

• Voyager 1 & Voyager 2: The two Voyager spaceraft orbit originally performed flybys of the outer planets of the solar system but continued to operate. They are now the most distant monitors of the plasma in the space between the stars. SVS page

Major changes with earlier versions:

• L1 fleet, STEREOs and Voyagers added
• CINDI de-orbited and removed
• Camera move extended to out beyond the heliopause