Applicants must, among other things, submit some basic information and upload a private-pilot medical examination certificate from an aviation medical examiner.

The short-listed candidates will then go through a series of additional selection procedures, including psychological and aptitude evaluations and a formal interview. At the end of the process, four candidates will be invited to become members of the European Astronaut Corps and begin basic training at the European Astronaut Center in Cologne, Germany. The final appointments will be announced next year.

The ESA says candidates should be competent in scientific disciplines, such as physics, chemistry and medicine and/or be an engineer or experimental test pilot.

Applicants should be fluent in English, with Russian being an asset.

The space agency said candidates from all 17 European Union states -- Austria, Belgium, Denmark, Finland, France, Germany, Greece, Ireland, Italy, Luxembourg, the Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and the United Kingdom -- are welcome to apply.

Prospective candidates can file their initial application online at www.esa.int/astronautselection.