Putting the heat to Helios — Science News, July 6, 1974 Helios, a space probe scheduled to go closer to the sun than any other manmade object ever launched, has successfully survived a ground test that exposed it to temperatures believed to be as high as any it will face during its mission…. During the test, parts of the spacecraft reached — and survived — temperatures up to 700 degrees F. Helios, to be launched in [December], will pass within 28 million miles of the sun.