The Mars Reconnaissance Orbiter, shown here in an artist's rendition, was launched in August 2005 to learn about the history of water on Mars. (NASA)

A spacecraft studying Mars that suddenly rebooted and went into "safe" mode early this week is expected to be fully operational again next week.

Jim Erickson, project manager for NASA's Mars Reconnaissance Orbiter, said Friday that researchers are doing final checks to find out as much as possible about what caused the incident before going through the long, involved process needed to bring the spacecraft out of safe mode.

"I'm actually hoping for somewhere in the middle of the week," he told CBCNews.ca.

The orbiter, which is trying to find out about the history of water on Mars, has been in a precautionary, low-activity mode since Monday around 4:25 a.m. PST, when it passed behind the side of Mars facing away from Earth.

At that time, the power supply for the main computer measured an abnormally high power load, and automatically shut off its instruments, pointed its solar panels toward the sun, and switched from its high gain antenna to a low gain antenna — a normal process designed to help it weather a problem while ground staff try to fix it.

Erickson said the spacecraft does not seem to have suffered any damage. However, either it did detect an abnormally high load, or a momentary glitch caused it to think there was an abnormally high load when in fact there wasn't. The latter may have been caused by a charged particle such as a cosmic ray or similar particle from the sun hitting the circuit that measures the load on the power source.

"That actually appears to be the most likely, but we have to look at all the options," Erickson said.

The cause, however, might never be known for certain.

"It's very difficult to definitively say something is one thing or another when you're doing the, so to speak, medical diagnosis from 20 light minutes away."

Twenty light minutes are equivalent to about 360 million kilometres, or a little less than 1,000 times the distance between been the Earth and the Moon.

Charged particles do hit susceptible parts of the spacecraft every few months, Erickson added.

The orbiter, launched in August 2005, has instruments that do close-up photography of the Martian surface, analyze minerals, look for subsurface water, trace how much dust and water are distributed in the atmosphere, and monitor daily global weather on the planet. The mission is to end on Dec. 31, 2010.