| http://www.spaceflightnow.com/atlas/ac160/status.html
THURSDAY, SEPTEMBER 6, 2001 As we reported yesterday, the planned launch time for the Atlas rocket on a classified mission for the National Reconnaissance Office is 1524 GMT (11:24 a.m. EDT; 8:24 a.m. PDT) on Saturday. The Air Force officially announced the time today as preparations entered the final 48 hours to blastoff. The veil of secrecy shrouding this launch continues, however, as the duration of the launch window was not disclosed. However, sources say it will extend for 12 minutes to 1536 GMT (11:36 a.m. EDT; 8:36 a.m. PDT). The weather forecast is excellent with a 100 percent chance of conditions being acceptable for liftoff on Saturday, as well as backup launch opportunities on Sunday and Monday. "For launch Saturday morning expect an offshore flow with light and variable winds, five to eight knots, visibility three to five nautical miles with patchy fog and temperatures in the mid 50's," Launch Weather Officer Dr. Christy Crosiar says. "Maximum upper level winds will be 15 to 20 knots from the northwest at 45,000 feet." The Launch Readiness Review is planned for Friday morning at Vandenberg when senior officials will gather to discuss preparations for liftoff and any technical concerns. At this point, there are no issues being reported. At the Space Launch Complex-3 East pad, the rocket's Atlas stage fuel tank has been loaded with approximately 15,000 gallons of RP-1 fuel -- a highly refined kerosene. Slightly more fuel was pumped into the rocket than originally envisioned, a change that forced a two-week delay in the launch from August 25 to September 8. During a mission review one month ago, the amount of fuel being carried on this launch was called into question. Engineers were looking at the pre-flight predictions and data for this mission and then compared that information to the historical experience gained in over 50 launches of Atlas 2 and 2AS rockets, Mike Gass, Lockheed Martin's vice president of Atlas and EELV programs, explained in a recent interview. "Everything in our predictions and calculations in mission design were well within spec, well within our capability. But now we were asked the question 'where is it against that experience?'" One parameter of over 1,500 examined was not in the middle of the target as officials wanted. The issue was the amount of RP-1 fuel onboard since this launch will carry the heaviest payload ever lofted by an Atlas rocket. "When we have (Booster Engine Cutoff on the Atlas stage) we are at a 5-g acceleration. If you start with a heavy payload, the time to get to (Booster Engine Cutoff) is going to be slightly longer. We would like to have the fuel level at the (Booster Engine Cutoff) to be right there at the experience point where we have always been. And we can do that by adding more fuel." The Atlas will deliver a critical national security payload into Earth orbit, and Lockheed Martin obviously wants to cut out any threats against mission success. Added Gass: "Why on this mission be at a new experience point?" By loading more propellant, the daily launch window in which to get the rocket airborne had to be shortened from about 24 minutes down to roughly 12 minutes. "There is an optimal point in time that you launch, and on either side of that optimal point in time you are doing more steering and using more propellant," Gass said. "Instead of reserving capability for window time, we put the margin on the vehicle. You can never use margin in the window after you lift off, you would rather have the margin on the vehicle." The time needed to validate and double-check the changes made with adding more fuel and adjusting the vehicle's propellant utilization system required the two-week launch postponement. Spaceflight Now will provide complete live coverage of Saturday's countdown and launch. Watch this page for continuing updates! |
