NASA said it is developing a car-sized satellite that by "no later than 2018" will plunge into the sun's outer atmosphere for an up-close study of its super-hot corona, solar wind and lethal radiation.

The ambitious project, first recommended at the dawn of the space age in 1958, will help "characterize and forecast the radiation environment in which future space explorers will work and live," the US space agency said Saturday on its website.

The sun probe is also part of President Barack Obama's long-term space policy announced in April calling for a "robotic exploration of the solar system" before sending US astronauts to orbit Mars by the mid-2030s.

NASA's Solar Probe Plus mission aims "to solve two key questions of solar physics: why is the sun's outer atmosphere so much hotter than the sun's visible surface and what propels the solar wind that affects Earth and our solar system?" said Dick Fisher, director of NASA's Heliophysics Division in Washington.

After a 144-million-kilometer (90-million-miles) journey to the sun including seven gravity-assists from planets including Venus, the Solar Probe Plus spacecraft will plunge directly into the sun's atmosphere some 6.4 million kilometers (4.0 million miles) from the star's surface.

It will tuck its two solar panels behind a revolutionary carbon-composite heat shield designed to withstand temperatures in excess of 1,400 degrees Celsius (2550 Fahrenheit) and take measurements with its sophisticated array of instruments.

The probe will also carry out several other experiments including studies of the particles that compose the solar wind, of the sun's electric and electromagnetic fields, of high-energy electrons, protons and ions, and 3D images of the corona.

The probe "is slated to launch no later than 2018," the National Aeronautics and Space Administration said.

"This project allows humanity's ingenuity to go where no spacecraft has ever gone before," said Lika Guhathakurta, Solar Probe Plus program scientist at NASA Headquarters, in Washington.