It's difficult to give an exact number of astronauts who have died because the definition of "astronaut" can vary and there are different ways to categorize deaths related to space travel.

Here's a breakdown of the key figures:

* 14 astronauts have died during spaceflight: This includes the crew of the Apollo 1 mission, the Challenger crew, and the Columbia crew.

* 5 astronauts have died during training or testing: These are accidents unrelated to actual spaceflight but related to the astronaut program.

* 4 cosmonauts have died during spaceflight: This includes the Soyuz 11 crew.

Important Considerations:

* Definition of "astronaut": The definition of an astronaut can be broad or narrow. Do we include those who were selected for spaceflight but died before launch? Do we include test pilots who were involved in spaceflight-related activities?

* Cause of death: Some deaths are directly related to spaceflight, while others are accidents or illnesses that occur during training or other activities related to the space program.

It's important to remember that every loss of life related to space exploration is a tragedy. These individuals were pioneers who dedicated their lives to pushing the boundaries of human knowledge and exploration.