The National Air and Space Museum's Steven F. Udvar-Hazy Center has welcomed more than a half million visitors since the Smithsonian facility in Chantilly, Va., opened to the public Dec. 15.

The attendance milestone was reached on the last day of February, putting the total number of visitors for the 11 weeks of operation at 510,658. The Udvar-Hazy (OOD-var HAH-zee) Center was an immediate hit with the public, attracting just under 220,000 visitors in its first two weeks of operation alone.

A companion facility to the museum's building on the National Mall in Washington, the Udvar-Hazy Center houses many rare aircraft and large space vehicles that had been in storage for years such as a Lockheed SR-71 Blackbird and the space shuttle Enterprise, as well as numerous collections of smaller artifacts.

Tremendous interest in the new center during the Christmas holiday season, combined with a heightened security alert nationwide, led to some delays for visitors at the parking and building entrances. Long waits have since been alleviated but the museum is taking steps to avoid future delays such as increasing the number of informational signs and, beginning this spring, providing guidance for arriving visitors through low-watt AM radio.

"We place the highest priority on making our visitors feel welcome," museum director Gen. J.R. "Jack" Dailey said. "An enjoyable and enlightening museum experience has to begin even before the visitor gets inside. We're trying to make the arrival process as quick and as easy as possible."

Visitors to the Udvar-Hazy Center are encouraged, if possible, to car pool or use the shuttle bus service from the museum's Mall building. Although admission to the center is free, there is a $12 fee for parking. A roundtrip ticket for the shuttle bus is $7, with discounts available for groups. As at the museum's Mall building, express security screening is available for visitors without bags. Comfortable rubber-soled shoes are recommended for walking in the Udvar-Hazy Center.

The museum's Mall building welcomed one million visitors in its first 25 days after opening on July 1, 1976. It marked two million visitors on its 50th day of operation. The Mall building is the most visited museum facility in the world, averaging more than 9 million people each year.

The museum has begun refurbishment, viewable by the public, of the Enterprise in the Udvar-Hazy Center's James S. McDonnell Space Hangar. After work is completed, staff will move other artifacts into the McDonnell hangar, which will be fully accessible to the public later this year and will ultimately house some 135 large space artifacts. Many can be seen now in the center's aviation hangar.

The aviation hangar opened in December with 82 aircraft installed. Several more will be added this year. The hangar, ten stories high and the length of three football fields, displays aircraft at two hanging levels as well as at floor level. It will ultimately house some 200 aircraft.

The National Air and Space Museum building on the National Mall in Washington, D.C., is located at Sixth Street and Independence Avenue S.W. The Steven F. Udvar-Hazy Center is located in Chantilly off Route 28 near Washington Dulles International Airport. Both facilities are open daily from 10 a.m. until 5:30 p.m. (Closed December 25.) and admission is free.