Antares launch scrubbed due to boat in restricted zone. How did that happen?

[Update: On Tuesday night, the Antares rocket exploded during launch. Story to follow.]

For Orbital Sciences Corp., expectations are running high that the third time will be a charm.

At 6:22 EDT Tuesday night, the company is slated to launch cargo to the International Space Station after Monday evening's launch was scrubbed at the last minute. The rocket was ready, and weather at the launch site was perfect. But a sailboat had wandered into restricted waters off Wallops Island, Va., where the launch site is.

The boat's presence some 40 to 50 miles offshore – well over the horizon but within a 1,400-square-mile restricted area for the launch – violated the range-safety requirements for the mission, explains Keith Koehler, a spokesman at the National Aeronautics and Space Administration's Wallops Flight Facility.

The incident highlights the challenge that range-safety officers face in keeping boats and aircraft out of restricted airspace or offshore waters during a launch. On one level, only one boat in the danger zone suggests that “everyone else got the word,” Mr. Koehler says.

At the same time, one boat can ruin a great launch opportunity.

“It's a fairly large area that we need to try and clear,” Koehler says. The goal is straightforward: to ensure that if a rocket has to be destroyed early in its ascent, the debris will fall harmlessly into a patch of ocean where no people or their boats risk getting struck.

On occasion, launches from the Kennedy Space Center and the US Air Force's launch facilities at Vandenberg Air Force Base on the central California coast have been either delayed or scrubbed because of errant boats in restricted waters. If a rocket is merely launching a satellite, mission controllers often can wait until a vessel sails out of restricted space. But if the mission is to rendezvous with another craft on orbit, such as the space station, launch windows are just a few minutes long.

The window for Tuesday evening's launch is a scant 10 minutes long. To miss it means at least a 24-hour delay and the extra costs associated with it.

“We eat the cost; so does NASA. It's part of doing business,” says Orbital Sciences spokesman Barron Beneski. “But it's not something we want to see happen.”

Prior to Monday evening's launch attempt, the mission had endured another launch delay imposed by hurricane Gonzalo as it bore down on Bermuda. The island hosts a key tracking site that had to be taken offline until the storm had passed.

In setting up restricted zones above a launch site or offshore, their sizes and orientations vary by the type of rocket and path it follows as it rises.

To restrict aircraft overflights, launch operators apply to the Federal Aviation Administration's Office of Commercial Space Transportation for a launch permit. Working with local air-traffic control centers, an operator identifies the boundaries needed. Air-traffic controllers steer aircraft clear of the area until after the launch. In addition, pilots receive advance warning through the FAA's notices to airmen.

For mariners, the US Coast Guard issues similar warnings through weekly notices. NASA also issues such notices. The launch facility's danger zone is marked on navigation charts. And the Coast Guard has a recording identifying such zones that it broadcasts over a special channel on marine VHF radio.

As for enforcement, the Coast Guard and, in this case, the Virginia Marine Police have the authority to arrest violators and fine them.

On Monday, radar on patrol aircraft picked up the errant vessel and sent the information back to Wallops at least two hours before launch time, Koehler says. Range-safety officials tried to reach the craft by radio, but it didn't respond. The aircraft flew close enough to identify the boat and also tried to hail it.

Whoever was aboard could have turned off the marine radio, if the vessel had one. Pleasure boats shorter than 65 feet aren't required to have such radios or to keep them tuned to the right channel to pick up the Coast Guard's broadcast. Moreover, the winds were light at the launch site, Mr. Beneski says – suggesting that, given the large size of the restricted zone and the small engines on many sailboats, the boat might not have been able to sail out of the zone in time for the launch.

Whatever the explanation, in the end, the system worked, Koehler says. During the day, several boats were turned away from the launch site's restricted waters. And when an interloper appeared that evidently wasn't going to clear the danger zone in time, controllers scrubbed the launch.

Weather permitting and a successful launch, the Antares rocket and its Cygnus cargo capsule should be visible along the Eastern Seaboard during its ascent.