US, Soviet space programs have faced great risks

July 21, 1961 -- Mercury spacecraft Liberty Bell 7 America's first space scare came on its second manned space flight, when the spacecraft and its sole occupant -- Air Force Lt. Col. Virgil (Gus) Grissom -- parachuted into the Atlantic and sank. Grissom had to swim for his life. February 20, 1962 -- Mercury spacecraft Friendship 7

In the first American orbital flight by John H. Glenn Jr., Mission Control got an indication that a heat shield was loose and possibly would not work. Without it, the capsule would have burned up during reentry. March 16, 1966 -- Gemini 8

Two American astronauts -- Neil Armstrong and David Scott -- barely escaped death on Gemini 8. Minutes after their craft had linked up in space with an unmanned rocket, their capsule began to spin out of control. Armstrong stopped the spin by firing a re-entry rocket and the ship came safely home. January 27, 1967 -- Apollo 1

Three American astronauts -- Virgil (Gus) Grissom, Edward Higgins White II, and Roger B. Chaffee -- died in a launch pad fire during a simulated launch. The tragedy caused NASA to bolster its on-board safety procedures. April 24, 1967 -- Soyuz 1

Soviet astronaut Vladimir Komarov was killed during reentry due to a parachute failure. April 13, 1970 -- Apollo 13

An oxygen tank exploded in the moon-bound module 200,000 miles away, leaving three American astronauts without power and heat. The astronauts crawled into the attached lunar lander and huddled there while gravity carried them around the moon and back to Earth. June 30, 1971 -- Soyuz 11

Three Soviet cosmonauts died aboard their capsule when it depressurized during re-entry into the Earth's atmosphere. 1981 to 1985 -- US Space shuttle program

Since its first flight in April 1981, the space shuttle has had its share of scares, but none before in a life-threatening category. There have been a number of launch pad aborts, and last July there was an ``abort to orbit,'' which meant that one of the ship's three engines had to be shut down during ascent.