The Navy & Satellites - SOHO

The Solar and Heliospheric Observatory (SOHO) satellite is a joint project of NASA and the European Space Agency (ESA). Through ONR and the Naval Research Laboratory, the Navy supported the design and construction of 3 of SOHO's instruments, which are helping scientists understand how the Sun works.

Purpose: To study the internal structure of the Sun, its extensive outer atmosphere and the origin of the solar wind, the stream of highly ionized gas that blows continuously outward through the solar system.

Artist's rendering of SOHO (courtesy of ESA & NASA).

Launch vehicle: Atlas IIAS (Atlas/Centaur)

Deployed: SOHO was launched on December 2, 1995

Orbit: Halo orbit around the L1 Lagrange point. The satellite does not orbit the Earth, but orbits the Sun while maintaining a distance of 930,000 miles (1.5 million km) from the Earth, held there by the gravitational pulls of the Earth and Sun. Just like the Earth, SOHO takes a full year to orbit the Sun. Its orbit affords SOHO an uninterrupted view of the Sun, unlike satellites that orbit the Earth and periodically see the Sun "eclipsed" by the Earth.

Size: 12 by 12 feet (3.65 x 3.65m), 31 feet (9.5m) with solar panels deployed, approximately two tons.

Navy-supported instruments:

• The Large Angle Spectrometric Coronagraph (LASCO): takes white light and spectral images of the corona by blocking light from the Sun with an occulting disk, mimicking an eclipse.
• The Extreme Ultraviolet Imaging Telescope (EIT): images the solar atmosphere at several different wavelengths, and therefore different temperatures.
• The Michelson Doppler Imager (MDI): monitors magnetic fields and sound-generated ripples on the Sun's surface.

Program Participants: Naval Research Lab, Stanford University, NASA, ESA, and several European scientific organizations.

Mission duration: Planned for a minimum of two years continuous observing with enough fuel for six years, the satellite surpassed that goal in 2002.

The SOHO satellite is being used to study the solar interior, atmosphere, and wind. Scientists hope to better understand the mechanisms that produce the Sun's activity and to predict when this activity will occur. Storms on the Sun that send powerful disturbances to the Earth can affect our atmosphere and damage communication and power systems. With advance warning, we can protect these and other sensitive systems by temporarily turning them off, as you might protect your computer by turning it off during an electrical storm.