CAPE CANAVERAL AIR FORCE STATION, Fla. --
NASA's newest Mars mission is scheduled to launch from Cape Canaveral today at 1:28 p.m. For weeks leading up to today, an Air Force officer has been monitoring weather reports to ensure it's safe for the probe-carrying rocket to take off.
"Everything is looking good so far," Launch Weather Officer Mike McAllenan, a member of the Air Force's 45th Weather Squadron, which oversees the launches at Cape Canaveral, told weather.com. "The main weather threat is towards the end of the launch window, closer to 3:30 p.m. We'll be watching the area near the 'big bend' of Florida, which currently has lightning."
The mission, called MAVEN, is packed inside of a 46,000-pound Atlas V rocket, an unmanned craft that will hoist the probe into space to begin its 10-month journey to Mars. The Federal Aviation Administration sets launch-weather requirements, which apply to launches all over the country. But each location brings its own weather concerns. In Florida, where MAVEN will take off, lightning is one of the biggest.
"You would think launching a rocket in the Sunshine State would pose no problem, weather-wise," Weather Channel meteorologist Jonathan Erdman said. "However, Florida averages over 1.4 million lightning strikes each year, the most of any state. That figure doesn't count lightning flashes occurring within the clouds, but not striking ground."
Regulations require that lightning strikes must be at least 10 nautical miles (11.5 miles) away. Any strike closer than that could hold up launch for at least 30 minutes, the mandated time to wait after last observed strike.
But it's not just existing lightning that causes concerns, according to McAllenan. Storm clouds contain electricity, he said, and if there's enough of it, a rocket launching through the clouds can generate its own lightning strike, damaging the rocket and creating danger on the ground.
There's always a risk of a rocket going off course after launch, in which case a flight control officer would employ the rocket's mechanism to destroy itself. A lightning strike could impair this mechanism. "The worst case is we launch through an electrified cloud and generate our own lightning strike and damage the capability to destruct the vehicle," McAllenan told Weather.com. "So you have something that doesn't know where it's going and there's no way to stop it."
Weather officers for an Atlas launch also have to consider wind, temperature and space weather -- the amount of electrified particles coming from the sun, which can damage on-board computers. If a long-range wind blows through during the first 10 to 15 seconds of the launch, it can push the rocket into its launch tower, causing destruction to both the rocket and the tower.
"Some vehicles have constraints for flying through precipitation, because of ice build up and those kind of things," McAllenan said. "Atlas is pretty robust. The liftoff wind criteria is between 25 and 35 knots (29 to 40 mph), so that's fairly high. It can fly through rain as long as it's not violating lightning criteria."
The launch window for MAVEN is two hours, meaning that if conditions aren't right at 1:28 p.m., the team will continue to evaluate the weather and hope it improves. For a deep-space mission like MAVEN, as opposed to something like a GPS satellite being launched into Earth orbit, launch opportunities don't last long. If MAVEN doesn't launch sometime during the next three weeks, the orbits of Earth and Mars won't line up properly again for a launch for another 26 months.
As of yesterday morning, the Air Force listed a 40 percent chance that weather would impede the launch, with a 60 percent chance that launch would be delayed by 24 or 48 hours. Clouds and ground winds are the biggest current concerns.
"Good weather is always good weather," McAllenan said. "It's just that our weather goes a little bit bad earlier than typical bad weather."
MAVEN will enter the Red Planet's orbit in September 2014. The $671 million mission will study Mars' upper atmosphere to help scientists understand how Mars went from a warm planet with flowing, liquid water to the cold, dry desert it is today.
For the full article please go to: http://www.weather.com/news/science/space/maven-launch-mars-20131118