Heliophysics Sentinels 2024

There have been some changes since the 2022 Heliophysics Fleet. AIM and ICON have been decommissioned while two other instruments have been added. AWE is an instrument mounted on the ISS, and RAD is a particle detector on the Curiosity Mars rover.

As of Winter 2024, here's a tour of the NASA Heliophysics fleet from the near-Earth satellites out to the Voyagers beyond the heliopause.

Excepting the Voyager missions, the satellite orbits are color coded for their observing program:

• Magenta: TIM (Thermosphere, Ionosphere, Mesosphere) observations
• Yellow-Orange: 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
• TIMED: Studies the upper layers (40-110 miles up) of Earth's atmosphere. SVS page
• AWE (on the ISS) studies atmospheric gravity waves
• 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
• GOLD: Global-scale Observations of the Limb and Disk is a spectroscopic imager for studying the ionosphere. 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 THEMIS-ARTEMIS. (SVS page)
• IBEX: The Interstellar Boundary Explorer measures the flux of neutral atoms from the heliopause. SVS page

Lunar Orbiting Fleet:

• THEMIS-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 (L1) 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: The remaining STEREO spaceraft orbits the Sun in roughly the same orbit as Earth. SVS page
• Parker Solar Probe: On an orbit that takes it closer to the Sun than any other mission. SVS page
• Solar Orbiter: On an orbit that takes it to high solar latitudes. SVS page
• RAD is an instrument aboard the Mars rover, Curiosity, to measure the solar and cosmic ray flux on the surface of the planet, important for the safety of future astronauts.

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. At the time of this visualization, Voyager 2 has just crossed the heliopause.SVS page