NASA’s twin spacecraft is nearing its entrance into the lunar orbit on New Year’s Eve and New Year’s Day to study the moon from crust to core.

The first probe is set to arrive in lunar orbit on Saturday December 31 at 4:21 p.m. EST and the second will enter orbit 24 hours later at 5:05 p.m. EST on Sunday during the New Year’s weekend.

"Our team may not get to partake in a traditional New Year's celebration, but I expect seeing our two spacecraft safely in lunar orbit should give us all the excitement and feeling of euphoria anyone in this line of work would ever need," said David Lehman, project manager for GRAIL at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, Calif.

The twin Gravity Recovery and Interior Laboratory, GRAIL probes were launched from Cape Canaveral Air Force Station on Sept. 10, 2011.

The distance from Earth to the moon is approximately 250,000 miles.

Scientists explained that NASA's Apollo crews took about three days to travel to the moon and it will take about 30 times that long for the twin probes to get there. The probes are covering more than 2.5 million miles to get there.

GRAIL-A was reported on Wednesday to be 65,860 miles from the moon and closing in at a speed of 745 mph while GRAIL-B was 79,540 miles from the moon and closing at a speed of 763 mph.

"This mission will rewrite the textbooks on the evolution of the moon," said Maria Zuber, GRAIL principal investigator from the Massachusetts Institute of Technology (MIT) in Cambridge.

The lunar orbit insertion burn for GRAIL-A will take approximately 40 minutes and change the spacecraft's velocity by about 427 mph. GRAIL-B's insertion burn 25 hours later will last about 39 minutes and is expected to change the probe's velocity by 430 mph, explained NASA.

But data collection won’t begin until March 2012 when the two probes will be in a near-polar, near-circular orbit with an altitude of about 34 miles.

An instrument aboard each spacecraft will measure the changes in their relative velocity.

The data will allow mission scientists to understand what goes on below the surface and educate them on how Earth and its rocky neighbors in the inner solar system developed into the diverse worlds today.

"Our two spacecraft are operating so well during their journey that we have performed a full test of our science instrument and confirmed the performance required to meet our science objectives," said Zuber.