The Delta launch team is resting today after three consecutive countdowns were thwarted by Florida's summertime thunderstorms while engineers perform some routine testing of the rocket's safety system that is necessary after several launch attempts.

Rain falls on the Delta 2 rocket during Sunday's countdown attempt. Photo: Carleton Bailie/Boeing

"The weather really has not cooperated. We've tried three times now and the weather has got us every time. We are in that pattern with afternoon thunderstorms and with the GPS launch time being around 7'ish in the evening it is tough," Rich Murphy, Boeing's mission director, said in an interview today.

The Boeing Delta 2 rocket will try again Wednesday to launch the Global Positioning System 2R-12 military navigation satellite for the Air Force. Liftoff from Cape Canaveral's pad 17B will be possible between 6:54 and 7:21 p.m. EDT (2254-2321 GMT). The launch window is dictated by the satellite's targeted orbit.

"We are hoping the pattern will shift later this week and at least shift the thunderstorms to a different time period so that we've got a shot," Murphy said.

"We are taking today off. We give the crew some rest and we do some Range Safety work. (The Range) wants us to retest the flight termination system after three days of attempts. So we are doing that. And the weather forecast for today was the same. We still had an 80 percent chance of 'no go.'"

Air Force meteorologists say the the chance of bad weather decreases over the next few days.

"Later in the week looks like it might be the start of a transition back to little better weather. We will probably attempt Wednesday, Thursday and Friday, if needed," Murphy said.

Another launch attempt is scheduled for Wednesday. Photo: Carleton Bailie/Boeing

The forecast for Wednesday still calls for an 80 percent chance that lightning, anvil and cumulus clouds and rain in the rocket's fight path will prevent launch.

"Weak shear line oriented east to west across Jacksonville aiding in early formation of thunderstorms to the north and pushing south along the east coast sea breeze through the afternoon and evening," today's updated forecast said.

"The surface and upper level ridge remains to the south resulting in west-southwesterly flow at all levels. With this type of pattern expect formation of east coast sea breeze thunderstorms between 2:00-3:00 p.m. EDT.

"The Cape will see showers and thunderstorms forming overhead and west of the Indian river with the onset of the sea breeze, throughout the afternoon hours. The primary concern will be showers and thunderstorms over launch pad 17B through the launch countdown."

Thursday's outlook is a 70 percent chance of "no go" weather. Friday improves slightly to 60 percent.

NASA is anxious to see this GPS mission get off the ground because the agency's MESSENGER space probe, which is destined to orbit the planet Mercury, must use this same launch pad for liftoff aboard another Delta 2 rocket at the end of July. Once the GPS rocket is launched, workers will need several days to refurbish the pad before MESSENGER's rocket can be erected.

Artist's impression of the MESSENGER spacecraft in orbit at Mercury. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

MESSENGER has a 15-day launch window beginning July 30 that would send the spacecraft on its 7-year, looping trajectory to the solar system's innermost planet before becoming the first probe to orbit Mercury in March 2011. If the orbiter misses its planetary launch opportunity that closes August 13, the mission must wait until the next launch window in July 2005.

But calling quits on the GPS launch and removing that Delta 2 rocket from pad 17B is not an easy option because the vehicle's second stage is filled with its supply of fuel -- a hydrazine propellant mixture and nitrogen tetroxide oxidizer. The storable fuels are loaded into the rocket a few days prior to launch. Draining the unfriendly hypergolics from the vehicle and handling the rocket stage would use up even more time.

"Obviously we want to get the (GPS) launch off as soon as practical, as soon as possible. We are committed to this launch. There is no chance of destacking or anything to do MESSENGER (first) -- not once we committed and loaded propellants," Murphy said.

This file photo shows a Delta 2 rocket second stage being lifted into the launch pad tower during pre-flight assembly. Photo: NASA-KSC

"The second stage propellants pretty much commit us to launching. Detanking the hypergolic propellants is a very time consuming and difficult process. That is why we pay so much attention to putting them on...because detanking does not only consist of taking the stuff out but you've got to purge and get safety (officials) to buy into all of this before you can take the stage down (from the pad)."

The GPS launch was originally scheduled for June 4, with on-pad stacking of the MESSENGER vehicle expected to start June 18. But technical problems and then the weather scrubs have kept GPS 2R-12 grounded. Despite the slips, officials still believe a July 30 launch of MESSENGER is doable.

"We've been looking at the schedule. We're still capable of making the beginning of their window, even through the end of this week. The guys are looking at the schedule by putting more people on it and taking some of the contingency days out. Obviously if we get ourselves into a situation where we can't (make the 30th), we will just slip slightly into the window," Murphy said.

"The best thing we can do it concentrate on this (GPS) launch and get it launched successfully," Murphy said. "We're hopeful but there is not much I can do about the weather. We'll just keep trying until we get this launched. Following that, we will get into the pad conversion and setting up for MESSENGER."