Technicians complete connections between the LRO and LCROSS spacecraft and the Atlas V rocket at Cape Canaveral Air Force Station, in Florida. Credit: NASA/Dimitri Gerondidakis

Update 6:18 p.m. EDT: the orbiters have launched! Follow their mission progress.

At approximately 5:12 P.M. EDT today, a pair of robotic lunar "scouts" will hopefully be launched aboard an Atlas V rocket. Their mission is to map the moon's surface, search for ice, and assess levels of radiation in the environment. The flight is the first U.S. mission to the moon in more than a decade, and the first step toward returning humans by 2020.

The first of the two lunar probes is a spacecraft called the Lunar Reconnaissance Orbiter (LRO), and it is part of NASA's Vision for Space Exploration. Richard Vondrak, a project scientist for LRO, told me during an interview last year that "LRO is the most advanced lunar satellite NASA has built. It will provide information that would have been impossible to collect a few decades ago."

LRO will carry seven instruments, including a cosmic-ray telescope, to measure the effects that lunar radiation could have on humans, and a laser altimeter, to map the surface of the moon. It will also take high-resolution images and temperature measurements.

The second lunar probe is a smaller spacecraft called the Lunar CRater Observation and Sensing Satellite (LCROSS), and it has a simpler mission: to crash into the surface of the moon where experts believe that ice may be present. Unlike LRO's four-day cruise to the moon, it will take LCROSS months to get there. It will ride on the Atlas V upper stage and will first observe the upper stage's smackdown before flying through the plume and crashing into the moon's surface minutes later. LRO and the Hubble Space Telescope will observe the collisions, hopefully viewing and sensing any water ice that gets thrown up.

Engineers are anxious to get the probes into space--the $583 million mission has been delayed since October 2008, and has endured more setbacks this week due to Space Shuttle launch delays. In addition, China, Japan, and India have launched lunar probes within the past three years. (China's Chang'e 1 and Japan's Kaguya both launched in 2007 and crashed into the moon this year.) Russia and Europe have more recently joined in, announcing their own lunar ambitions but not fully disclosing their plans. The race to return humans to the moon is well under way.

The probes have three chances to launch this evening, and a few opportunities on Friday. But the flight window closes on Saturday, and then it will be another two weeks before the spacecrafts get another shot at liftoff.

Atlas V launches from Florida carrying LRO and LCROSS. Credit: NASA

Sea-surface temperatures from NASA's Jason-1 satellite. Credit: NASA

While the start of summer mostly brings warm weather and sunny skies, it also marks the start of the Atlantic hurricane season, which officially begins June 1 and lasts until November 30. (For the Pacific Ocean, hurricane season starts on May 15.) This year, NASA is using, as it has in the past, its orbiting satellites to study and research tropical cyclones, and it will provide the data that the National Oceanic and Atmospheric Administration (NOAA) National Hurricane Center uses in advanced models and hurricane predictions.

So far, the news is good. The satellites, which measure such things as storm and surface winds, sea-surface heights and temperatures, rainfall intensity, lightning, water vapor, humidity, cloud development, and atmospheric pressure, indicate that sea-surface temperatures in the tropical Atlantic are below normal. Such lower-than-normal temperatures could "starve" developing hurricanes of their driving force--waters warmer than 80 °F--meaning fewer hurricanes.

Despite the good news, peak hurricane season is not until late summer and early fall, and NASA's William Patzert says that oceanic and atmospheric conditions can change dramatically. "You can be clobbered no matter what the expert outlook is today," he says. People need to remain prepared.

Hurricane Gustav moves along the southern side of Jamaica on August 29, 2008. The image was taken by the MODIS instrument on NASA's Aqua satellite. Credit: NASA

Hurricane Fay's wind speeds on August 19, 2008, taken using NASA's QuickSCAT satellite. Highest wind speeds, in purple, are over 46 miles per hour. Credit: NASA

A map of Hurricane Dolly's rainfall over the Gulf of Mexico and Texas from July 25 to 28, 2009, created using NASA's TRMM satellite. Red and orange are highest rainfall totals: over six inches. Credit: NASA

Damage to the shuttle's heat shield. The white pockmarks in the black tiles were caused by a piece of debris that struck the shuttle during liftoff. The debris made multiple hits on four heat-resistant tiles lining the forward right side of the shuttle, just ahead of where its body and its starboard wing meet. Credit: NASA

During a 10-hour-long inspection of Space Shuttle Atlantis's heat shield on Tuesday, astronauts found a trail of damage on its starboard wing. This was caused by launch debris that fell from the shuttle's external tank during liftoff. NASA says that the dings are minor but is taking no chances, and it will investigate the damaged wing further.

Ever since the 2003 Columbia disaster, when damage to the shuttle's wing went undetected and the shuttle broke apart during reentry, killing seven astronauts, NASA has developed new technology to better inspect the shuttle, and has equipped astronauts with the necessary tools should a repair need to be conducted. In the worst case, if the shuttle is damaged beyond repair, NASA has a second shuttle, Endeavour, on the launch pad ready to depart on a rescue mission.

New policies put in place after the Columbia disaster require astronauts to inspect the shuttle twice: once after liftoff, and once again before descent. Atlantis astronauts spotted the damage during their routine post-liftoff check, in which they scan the heat shield using a pole mounted with a camera and laser sensors. Sensors on the shuttle's wings also recorded an impact 106 seconds after liftoff, and cameras on the external fuel tank showed debris falling at the same time.

The images from the astronauts' inspection were then beamed to Earth, where they were analyzed by a team of image experts. "This is not something that we're very concerned about, but we want the team to do our normal assessment and evaluation of it. And we will do that overnight tonight," LeRoy Cain, deputy shuttle-program manager at NASA, said during a press briefing yesterday.

The dings could compromise the shuttle's thermal protection system, which is a combination of reinforced carbon-carbon (RCC) on the wing leading edge, thermal blankets on the fuselage, and thermal protective tiles covering the underside of the vehicle and the nose cap. This system protects the spacecraft and its human occupants from the extreme heat of reentry into Earth's atmosphere.

Space Shuttle Atlantis lifted off from Cape Canaveral, FL, on May 11 for a final servicing mission to the Hubble Space Telescope.

Space Shuttle Endeavour on Launch Pad 39B. Credit: Brittany Sauser