Helios A and Helios B

German and American

Helios A launched on December 10, 1974, and Helios B launched on January 15, 1976, both joint missions of the Federal Republic of Germany and NASA.The instruments were launched from American Titan rockets at Cape Canaveral and went into orbit around the Sun about one-third the distance from the Sun to the Earth. Helios A and B survived the high temperatures and sent back data for more than 10

years.They both measured the content of the solar wind, the strength and direction of the Sun's magnetic and electric fields, and they measured high-energy gamma rays and X-rays emitted from the Sun. Though the instruments can no longer transit data, they remain in their orbits around the Sun. (Oddly, they are also called Helios 1 and Helios 2, names similar to the top secret French satellites Helios 1A and 1B of the late 1990s, advanced surveillance imaging satellites which are widely believed to have 1 meter resolution capability.)

American

Voyager 2 actually launched on August 20, 1977, several days before Voyager 1, which launched on September 5, 1977. They were both launched from Cape Canaveral, Florida, aboard Titan-Centaur rockets. Although these spacecraft were designed to visit planets, which they did between 1977 and 1989, they have continued to transmit data back to Earth as they travel out of the solar system. In December 2004, Voyager 1 crossed the termination shock, where the solar wind collides with the interstellar medium, and became the first man-made object to leave the solar system.Though the program was almost canceled in 2005, the $4.5 million annual budget for Voyagers 1 and 2 was continued and the craft are still in contact with the Earth. By 2008, scientists should detect the bow shock, where the supersonic solar wind strikes the interstellar gas. For more on these missions, see the section on the heliopause (page 46).

American

Launched on February 14, 1980, by NASA, this satellite examined ultraviolet, X-ray, and gamma ray emissions from solar flares. The launch was set to coincide with a period of high solar activity. In 1984, the instrument was rescued and repaired by the space shuttle Challenger, and as a result, the Solar Maximum Mission (SMM) spacecraft was able to continue taking data.This mission was the first to demonstrate that the Sun is actually brighter during periods of high sunspot activity. Though the spots themselves are dark, the regions around the spots are far brighter and make up more than the deficit of the spots themselves. SMM observations showed that energetic X-rays are emitted from the bases of solar flare magnetic loops, and that large coronal

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