Lockheed Martin technicians are replacing one of the solid-fuel boosters attached to the Atlas 5 rocket that will launch NASA's New Horizons spacecraft to Pluto because of damage the motor sustained during Hurricane Wilma.

This file image shows an Atlas 5 solid rocket booster being raised into the Vertical Integration Facility. Credit: Lockheed Martin

The Atlas 5 is being assembled inside the 30-story Vertical Integration Facility at Cape Canaveral's Complex 41 in advance of the targeted January 11 liftoff that will send the five-ton New Horizons probe on its decade-long cosmic cruise to encounter the unexplored planet Pluto.

Although the center of Wilma remained well south of the Cape, the large storm delivered heavy rain and hurricane-force winds to the Space Coast on October 24 as it sliced across Florida.

A third of the 41-by-275-foot reinforced fabric "MegaDoor" on the assembly building's opening that faces the launch pad tore in the storm, causing some debris to fall inside the facility.

The Atlas 5's bronze first stage and Centaur upper stage were erected atop a mobile launch platform, and the first of five strap-on solid rocket boosters was attached to the first stage when Wilma blew through. Atlas 5 rockets are put together within the VIF, then moved to the pad in the final 12 hours of the countdown.

Post-storm inspections revealed a ding on the solid motor casing, prompting officials to order the booster's removal and replacement. The motor could have been safe to fly, engineers believed, but officials ruled that exchanging it would be quicker than the time required to analyze the damage and re-certify the booster.

The Atlas 5 rocket to launch New Horizons will appear similar to the vehicle pictured in this image. It will feature a large nose cone, as depicted here, and strap-on solid motors. Photo: Lockheed Martin

The launch campaign resumed this week following the Wilma cleanup and vehicle assessments. A second booster was added to the Atlas 5 on Tuesday, and the remaining three boosters earmarked for the mission will be installed through next week.

The damaged motor was detached Wednesday. Its replacement is expected to arrive in early December.

The slender white boosters are 67 feet long. They are ignited at liftoff to provide a powerful kick in combination with the rocket's RD-180 kerosene-fueled main engine. This launch will mark the first time an Atlas 5 has flown with five strap-on boosters; earlier flights have featured pairs, and one mission used three.

Exactly what caused the damage or even what punctured the MegaDoor remains unclear, officials say, since the event wasn't witnessed.

A re-planning of the pre-launch schedule is being conducted to recover from the unanticipated booster replacement.

The original plans allowed time off during the Thanksgiving and year-end holiday seasons. But New Horizons must depart Earth within a narrow launch window dictated by alignment of the planets, making it appear inevitable that some holiday time will have to be spent readying for the launch.

New Horizons could reach Pluto as early as 2015, depending on the exact launch date. Credit: Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute

The overall launch opportunity extends from January 11 to February 14. However, the first 23 days of the window are most desirable because a launch during that period enables the spacecraft to swing past Jupiter for a gravity sling-shot that speeds the travel to Pluto. The final 12 days of the window would miss Jupiter, significantly delaying the Pluto arrival.

Lockheed Martin is looking at a temporary repair to the torn MegaDoor, while hoping tropical weather systems stay clear of the Cape during the waning month of hurricane season. A long-term fix to the door is being studied.