Polaris Dawn in context: Where exactly is this mission going?

 The 870-mile peak altitude reached by the mission was high enough to plunge the Polaris Dawn crew into the inner band of Earth’s Van Allen radiation belts, which begin at around 600 miles (1,000 kilometers) in altitude. 

The belts are areas where concentrations of high-energy particles that come from the sun and interact with Earth’s atmosphere are trapped, creating two dangerous bands of radiation, according to NASA. Before the Apollo program, the global space community had no idea whether humans could survive passing through this area at all.

The International Space Station orbits about 250 miles (400 kilometers) above Earth. The Hubble Space Telescope, which NASA astronauts have conducted spacewalks to repair, orbits about 320 miles (515 kilometers) high. The innermost of two bands that make up the Van Allen radiation belts begins at about 600 miles (1,000 kilometers). The Polaris Dawn mission will reach a maximum altitude of 870 miles (1,400 kilometers) before lowering its apogee for the spacewalk.

Today’s spacewalk, however, will occur at a slightly lower altitude — traveling between 190 and 700 kilometers above Earth (118 to 435 miles).

For context, humans commonly visit the International Space Station at about 400 kilometers (250 miles), and astronauts have previously conducted spacewalks at about 515 kilometers (320 miles), where the Hubble Space Telescope orbits