New Year’s Day at NASA means prepping for a return to the moon.
Officials at NASA say they are now entering a new stage of a mission intended to place a pair of probes around Earth’s nearest neighbor and only satellite. In a statement issued earlier this week, NASA mission controllers say they are preparing for the twin spaceships, named Grail-A and Grail-B, to enter the moon’s orbit over the weekend, the space agency’s latest attempt to send probes to the moon.
NASA’s twin lunar Gravity Recovery and Interior Laboratory probes were launched from Cape Canaveral Air Force Station in September. The first moon probe is slated to arrive in lunar orbit beginning on Saturday, December 31. The second prove will enter the moon’s orbit on Sunday, January 1. On New Year’s Eve, the pair of probes will fire their engine to slow down so that it could be captured into orbit. This move will be repeated by the other the following day.
Once in orbit, the pair will spend two months following each other around the moon. Scientists back on Earth will measure the varying distance between the pair of spaceships to calculate the lunar gravity field. NASA officials said the pair of probes are specifically tasked with measuring the uneven gravity field of the moon and determine what lies beneath — straight down to the core. The pair of probes will reportedly spend upwards of 90 days gathering data to create the first complete high-resolution map of the Moon’s gravitational field.
Speaking Monday, the team expressed confidence that the mission will continue to perform flawlessly, adding that they expect to gather an unprecedented amount of data from the mission.
“Both spacecraft have performed essentially flawlessly since launch, but one can never take anything for granted in this business,” said mission chief scientist Maria Zuber of the Massachusetts Institute of Technology.
Engineers said the chances of the probes overshooting are remote, noting that since their launch in September their trajectories have been precise. The U.S. space agency, which is facing serious budget cuts, said the pair of probes are taking 30 times longer than the Apollo space program to reach the moon. The team said they were relying on a low-energy, high-cruise time trajectory to reach the moon. The low-energy, high-cruise time trajectory is beneficial for mission planners and controllers, as it allows more time for preparing the pair of spacecrafts, and NASA said the path would allow the program to save money and increase the chances of a successful mission.
Once at the moon, the probes will spend the next two months tweaking their positions before they start collecting data in March. The pair will fly in formation at an altitude of 34 miles above the surface, with an average separation of 124 miles.
The latest mission to the moon will allow scientists to focus on the moon’s gravitation field. As the probes circle the moon, changes in the lunar gravity field will cause them to speed up or slow down. This in turn will change the distance between them, allowing scientists to observe how the moon’s gravitation field interacts with smaller bodies. NASA officials said that the observation and data gathered from the mission would allow them to better understand the moon’s composition, and possibly reveal answers related to how the moon formed billion of years ago.
The Moon orbits the Earth from an average distance of about 385,000 kilometers. It has a diameter of nearly 3,500 kilometers. By contrast, the Earth’s is 12,756 kilometers wide. Because the Moon is smaller and has less weight, the force of gravity on the lunar surface is only 17 percent of that on the Earth. That means the same object that weighs 100 kilograms here on Earth will weigh only 17 kilograms on the Moon.
NASA officials say the mission could reveal how the moon formed nearly 4.5 billion years ago, some 30 to 50 million years after the origin of the Solar System. The prevailing hypothesis today is that the Earth–Moon system formed as a result of a giant impact: a Mars-sized body that impacted the newly formed earth, blasting material into orbit which later became the moon. However, the theory is far from consensus within the scientific community and astronomers have long sought a mission that would provide data that could provide scientists with an answer.
The mission comes as NASA has sought to scale back its program in recent months. The space agency retired the last of its shuttle fleet earlier this year, leaving it reliant on private space ventures. The Constellation program was canceled last year by President Barack Obama, who favors landing on an asteroid rather than returning to the moon.
The mission is currently slated to end in June, however, NASA officials said they remain confident that they will receive an additional grant for a mission extension through next December. Officials working on the project say they will likely use the additional time to send the probe closer to the moon. Should the probes fail to align correctly, the mission would likely have to be scrubbed, said officials. However, if just one probe fails to align, the space agency said it would attempt the mission again in April.
Speaking over the weekend, NASA officials said they remain unsure if the orbiters would make it through eclipses that happen at the moon every six months, since their technology depends on lithium-ion batteries and solar panels. A lunar eclipse occurred in early December, and the next one is in June. Based on the current performance, scientists think GRAIL can continue through the June eclipse.
Researchers also want GRAIL to raise public awareness about the moon, and to help engage kids in math and science. To this end, special cameras aboard the probes will be used to encourage middle-school students to participate in lunar research and follow along with Grail, during both its nominal mission and any extended campaign.
The study technique GRAIL will use was pioneered by the joint U.S.-German Earth observing Gravity Recovery and Climate Experiment, or Grace, mission launched in 2002. The Grace satellites measure gravity changes related to the movement of mass within Earth, such as the melting of ice at the poles and changes in ocean circulation. As with Grace, both GRAIL spacecraft will be launched on a single launch vehicle.
GRAIL’s principal investigator is Maria Zuber of the Massachusetts Institute of Technology in Cambridge. Zuber’s team of expert scientists and engineers includes former NASA astronaut Sally Ride, who will lead the mission’s public outreach efforts. A camera aboard each spacecraft will allow students and the public to interact with observations from the satellites. Each Grail spacecraft will carry the cameras to document their views from lunar orbits.
GRAIL will support NASA’s exploration goals as the agency returns humans to the moon by 2020. In 2008, the agency launched the Lunar Reconnaissance Orbiter to circle the moon for at least a year and take measurements to identify future robotic and human landing sites. The orbiter also will look for potential lunar resources and document aspects of the lunar radiation environment. After a 30-year hiatus, the Lunar Reconnaissance Orbiter represents NASA’s first step toward returning humans to the moon. The orbiter is accompanied by another spacecraft, called the Lunar Crater Observation and Sensing Satellite mission, which will impact the lunar south pole to search for evidence of polar water frost.
Created in 1992, NASA’s Discovery Program sponsors a series of scientist-led, cost-capped solar system exploration missions with highly focused scientific goals. The GRAIL proposal was selected from 24 submissions in response to a 2006 Announcement of Opportunity for the program.
