... The first person to orbit the Earth was the Russian Yuri Gagarin, on April 12, 1961. The first American to do so was John Glenn, who completed three orbits on February 20, 1962; more than 26 years later, at age 77, Glenn returned to space aboard the space shuttle. ... Any manned mission faces the problem of safe return to Earth, which requires getting rid of the huge amount of energy associated with orbital motion. A spacecraft in low Earth orbit moves at about 24 times the velocity of sound. ...

Mariner 10 . ... Mariner 10 was the seventh successful launch in the Mariner spacecraft series, and the first to use the gravitational pull of one planet ( Venus ) to reach another ( Mercury ). ... It measured 1.39 meters (4.56 feet) diagonally and 0.457 meters (1.5 feet) in depth. ... Views of Mariner 10 . ... Venus/Mercury Mission . ... Launched in November 1973, this mission provided new information about Mercury and Venus in the Mariner program's first dual-planet mission. ...

... Galileo Probe . The Galileo spacecraft was designed to study Jupiter's atmosphere, satellites, and surrounding magnetosphere for two years. ... From there, Galileo will spend more than five years traveling to Jupiter, where it will become the first spacecraft to make direct measurements from an instrumented probe within Jupiter's atmosphere. ... This image, taken by the Hubble Space Telescope, shows the predicted site at which the Galileo Probe will enter Jupiter's atmosphere on December 7, 1995. ...

Cosmic Research, Vol. 42, No. 5, 2004, pp. 435­488. Translated from Kosmicheskie Issledovaniya, Vol. 42, No. 5, 2004, pp. 453­508. Original Russian Text Copyright © 2004 by Veselovsky, Panasyuk, Avdyushin, Bazilevskaya, Belov, Bogachev, Bogod, Bogomolov, Bothmer, Boyarchuk, Vashenyuk, Vlasov, Gnezdilov, Gorgutsa, Grechnev, Denisov, Dmitriev, Dryer, Yermolaev, Eroshenko, Zherebtsov, Zhitnik, Zhukov, Zastenker, Zelenyi, Zeldovich, Ivanov-Kholodnyi, Ignat'ev, Ishkov, Kolomiytsev, Krasheninnikov, Kudela,