BY JUSTIN RAY

Follow the countdown and launch of the Boeing Delta 2 rocket with the U.S. Air Force's latest GPS navigation spacecraft. Reload this page for the very latest on the mission.

THURSDAY, NOVEMBER 16, 2006
1640 GMT (11:40 a.m. EST)

The weather forecast for Friday's launch opportunity projects an 80 percent chance of acceptable conditions. Thick clouds will be the main concern.

"The cold frontal system will continue to push through this morning. Most of the main thunderstorm and rain shower activity, as well as associated gusty winds, will subside by 11:00 a.m.," the launch weather officer reported in this morning's post-scrub forecast update.

"The actual front will push through by 1:00 p.m. with decreasing probabilities of precipitation throughout the afternoon. Partly to mostly cloudy conditions will remain throughout the rest of the day with gradual clearing by tomorrow morning. Main concern for the launch window (Friday) will be thick clouds remaining in the area.

Saturday's outlook, should the launch be delayed further for some reason, shows a 90 percent chance of favorable weather.

1412 GMT (9:12 a.m. EST)

SCRUB! Today's launch attempt has been stopped. Officials were forced to call a scrub due to the unfavorable launch weather conditions at Cape Canaveral. Liftoff is being rescheduled for Friday at 2:12 p.m. EST, when much improved weather is expected. The window will extend to 2:26 p.m. EST, Boeing officials said.

1300 GMT (8:00 a.m. EST)

The Delta rocket remains enclosed within its service tower at pad 17A. Officials continue to watch the weather and the progression of a cold front that has brought rain and gloomy conditions to the Cape today. A decision whether to move the tower and press forward with the countdown to launch is expected later this hour.

1030 GMT (5:30 a.m. EST)

It is a wet morning across Central Florida as a cold front pushes through the state. Interesting GOES satellite imagery showing the weather system draped across the region is available here.

Rollback of the mobile service gantry to reveal the Delta 2 rocket is scheduled for this morning, weather permitting. Liftoff remains targeted for 2:17 p.m. EST.

WEDNESDAY, NOVEMBER 15, 2006
2230 GMT (5:30 p.m. EST)

Preparations continue for tomorrow's launch of the Boeing Delta 2 rocket carrying a replacement satellite for the Global Positioning System, but bad weather at Cape Canaveral is threatening to delay the liftoff. Launch will be possible between 2:17 and 2:30 p.m. EST (1917-1930 GMT).

A cold front will be sliding through Central Florida on Thursday, and Air Force forecasters expect the Cape to feel the brunt of the stormy weather between 3 and 11 a.m. A severe weather watch has been issued.

Gradual clearing is predicted later in the day, but rain, lingering thunderstorms and thick clouds still pose a high concern for the mid-afternoon launch. There is a 70 percent chance that conditions will be unacceptable at liftoff time.

Mission managers will meet before dawn to assess the latest weather outlook and determine if it's safe to retract the mobile service tower from around the rocket at pad 17A. Winds cannot exceed 39 knots for the move, plus officials must be confident of no hazardous weather looming on the horizon that could harm the rocket while it stands exposed on the pad for the final hours of the countdown.

Tower rollback is targeted to occur around 6 a.m. The retraction could be postponed a couple of hours without impacting the launch time.

Air Force officials say their strategy, assuming weather is safe enough to retract the tower, will be pressing forward with the launch opportunity. An early decision to scrub is unlikely unless the launch time forecast gives absolutely no hope of allowable conditions, they said. As of right now, there is that 30 percent chance the storms will clear in time.

The outlook for Friday is beautiful, forecasters say.

Watch this page for live updates throughout the day. It will be the 45th Delta rocket launch Spaceflight Now has covered over the past seven years.

WEDNESDAY, NOVEMBER 15, 2006

Air Force meteorologists say the weather forecast for Thursday has worsened further. They now report a 70 percent chance of "no go" conditions at launch time because of predicted rain, thunderstorms and thick clouds over the Cape.

"Clear skies today, but increasing clouds tonight in advance of the approaching cold front. Rain showers and isolated thunderstorms will move into the area after 2 a.m. local. Expect these conditions to impact Cape Canaveral throughout the morning and into midday. As the front approaches, there will be potential for gusty winds near 35 knots. Behind the front cloudy conditions with isolated rain showers will persist for several hours," the latest forecast says.

The backup launch opportunity on Friday still looks good with only a 10 percent chance of thick cloud cover violating the weather rules.

"Expect greatly improved conditions for Friday with mostly clear skies. Main concerns during the launch window will be showers and thunderstorms within 10 nautical miles of the launch pad as well as thick clouds remaining behind the front."

The final launch readiness review meetings will be held today, then the pre-launch news conference follows at 3:30 p.m. We'll post a countdown preview here later tonight.

TUESDAY, NOVEMBER 14, 2006

The odds of acceptable weather conditions during Thursday's launch window have worsened in the latest forecast.

"Today will be mostly clear, but expect increasing clouds late tomorrow. The frontal system that will be moving into the central Gulf of Mexico has slowed down and will push into Florida early Thursday," the Air Force weather team wrote in the new forecast this morning.

"Ahead of this system will be overcast conditions with rain showers and isolated thunderstorms. As the front approaches, there will be potential for gusty winds."

There is a 60 percent chance of violating the launch rules due to the rain showers, thunderstorms and thick cloud cover.

"Expect greatly improved conditions for Friday with mostly clear skies," the forecasters said. "Main concerns during the launch window will be showers or thunderstorms within 10 (nautical miles) of the launch pad as well as thick clouds remaining behind the front."

There is only a 10 percent chance of "no go" weather on Friday.

MONDAY, NOVEMBER 13, 2006
1855 GMT (1:55 p.m. EST)

Weather forecasters are predicting a 40 percent chance that rain or thunderstorms will prevent launch on Thursday. See the outlook here.

MONDAY, NOVEMBER 13, 2006

The latest Global Positioning System satellite awaits launch Thursday from Cape Canaveral to fill the role currently held by one of the older spacecraft operating in the orbiting navigation network.

Liftoff of the GPS 2R-16 satellite aboard a Boeing Delta 2 rocket is scheduled for 2:17 p.m. EST (1917 GMT). The day's launch window extends to 2:30 p.m.

Troubles with actuators on the rocket's second stage caused the mission to be delayed twice, cancelling Tuesday and Wednesday target launch dates. The Air Force announced this morning that new hardware had been installed on the booster and certified for flight.

The spaceborne GPS network features 24 primary satellites, plus several backups, flying in six orbital groupings. The Air Force began launching the fleet in 1989 and continues to send up new satellites to keep the navigation system in good health.

The $75 million craft lifting off Thursday is bound for the Plane B, Slot 4 position to replace the GPS 2A-22 satellite launched in August 1993. But the aging craft, which has lived nearly twice its design life, won't be retired quite yet. It is expected to be partnered with the GPS 2A-27 satellite at Slot 2 within Plane B to serve as backup, the Global Positioning Systems Wing at the Space and Missile Systems Center told Spaceflight Now.

GPS 2R-16 is the third in a new breed of updated craft built by Lockheed Martin. The modernized satellites transmit additional signals and feature improvements aimed at greater accuracy, tougher resistance to interference and enhanced performance for users around the world.

The advancements will provide the military with a more robust jam-resistant signal and enable better targeting of GPS-guided weapons in hostile environments. The new civilian signal removes navigation errors caused by the Earth's ionosphere.

"The Air Force is making steady progress to deliver modernized satellites, ground control systems and military user equipment to support our military and civilian users around the globe. The position, navigation and timing signals that GPS satellites provide not only support the warfighter, but also play an essential part in our nation's economic well being," said Col. Allan Ballenger, commander of the Global Positioning Systems Wing.

Thursday's launch follows the successful deployment of GPS 2R-15 in September and continues a hectic schedule for Boeing's Delta rocket fleet, which has flown seven times since April.

"We're ready for our second Delta 2/GPS launch in the last two months. The launch team has been working incredibly hard on this campaign during an especially busy stretch of Delta launches on both coasts," said Col. James Planeaux, the mission director and commander of the Space and Missile Systems Center's Delta Launch Systems Group.

"I'm proud of this tremendous team effort between our GPS customer, the Boeing Company, the 45th Space Wing, the Aerospace Corporation and the Launch and Range Systems Wing, keeping a sharp focus on mission success despite the demanding pace and a lot of overtime and weekend hours. We are looking forward to a terrific launch."