According to LiveScience, as of 2014, 18 astronauts have died during launches or re-entry from space, but none have been lost outside of the Earth's atmosphere. Additionally, three astronauts died in the Apollo 1 fire while testing the Apollo spacecraft on the ground.
The fatalities in human space travel include the shuttle crews of the Challenger in 1986 and the Columbia in 2003, as well as a single cosmonaut in Soyuz 1 and the three-man crew of Soyuz 11. The Challenger exploded during lift off, while the Columbia broke up before landing. Soyuz 1 crashed to Earth after a malfunction, and Soyuz 11 depressurized during re-entry, killing its crew.