NASA has set its sights on the moon, aiming to send astronauts back to the lunar surface by 2026 and establish a long-term presence there by the 2030s. But the moon isn't exactly a habitable place for people.

Cosmic rays from distant stars and galaxies and solar energetic particles from the sun bombard the surface, and exposure to these particles can pose a risk to human health.

Both galactic cosmic rays and solar energetic particles, are high-energy particles that travel close to the speed of light.

While galactic cosmic radiation trickles toward the moon in a relatively steady stream, energetic particles can come from the sun in big bursts. These particles can penetrate human flesh and increase the risk of cancer.

Earth has a magnetic field that provides a shield against high-energy particles from space. But the moon doesn't have a magnetic field, leaving its surface vulnerable to bombardment by these particles.

A pair of NASA astronauts are scheduled to do a 6.5 hour spacewalk on the morning of June 13 outside the International Space Station.

At 8 a.m. Eastern time, astronauts Tracy C. Dyson and Matthew Dominick are expected to enter the vacuum of space to perform station maintenance and science work.

NASA said the two will remove some communications equipment from one of the ISS' laboratory modules, getting help from a robotic arm on the station. Astronauts Mike Barratt and Jeanette Epps will be maneuvering the Canadarm2 to assist Dyson and Dominick in their work.

Then, Dyson and Dominick will move on to a science experiment involving microorganisms. They will swab surfaces on the ISS to "determine if microorganisms released through station vents can survive the external microgravity environment," NASA said in a statement.

NASA TV will begin its spacewalk broadcast at 6:30 a.m. Thursday. Live coverage will air on NASA+, NASA Television, the NASA app, YouTube, and the agency's website.

Among those watching the spacewalk up close will be Butch Whitmore and Suni Williams, the crew of the Boeing Starliner which launched from the Kennedy Space Center on June 5 en route to the ISS.