BY JUSTIN RAY
Follow the countdown and launch of the Boeing Delta 2 rocket with NASA's Gravity Probe-B spacecraft. Reload this page for the very latest on the mission.
MONDAY, APRIL 19, 2004
A series of weather balloons were dispatched to gather data on winds aloft, giving engineers the information they needed to generate a flight profile for the Boeing Delta 2 rocket to safely ascend through the atmosphere.
With just one second to launch today -- 1701:20 GMT -- there was no time to spare. The countdown resumed from a planned hold at T-minus 4 minutes. But less than a minute later, officials were forced to stop the clock and postpone the launch until Tuesday.
"It just became too close on the upper level winds. That last balloon, which appeared to be green ('go' for launch), probably would have allowed us to go. But there wasn't time to load the data onboard (the rocket) and confirm we actually had the right flight profile based on those wind conditions on the vehicle," NASA spokesman George Diller said.
"Once you are inside T-minus 4 minutes and counting you really shouldn't be working that kind of thing and Boeing mission director Rich Murphy decided we weren't. So he called a hold and the NASA launch director, NASA management and NASA engineering have agreed with that and said that was a good call to make."
The winds were the only significant problem experienced today.
"We didn't work any issues on the launch vehicle or the spacecraft at all, which is very encouraging," Diller said.
Tuesday's instantaneous liftoff time is 1657:24 GMT (12:57:24 p.m. EDT; 9:57:24 a.m. local time). The launch opportunity is constrained to one-second to place the Gravity Probe-B spacecraft into its desired polar orbit.
There is a 90 percent chance of favorable ground weather conditions. Upper level winds are not factored into that percentage, however, since the conditions aloft is a rocket flight dynamics issue and not a weather rule.
1659 GMT (12:59 p.m. EDT)
Liftoff is rescheduled for 1657:24 GMT (12:57:24 p.m. EDT; 9:57:24 a.m. local time) Tuesday.
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Although there are no technical issues being addressed, the upper level wind conditions are currently too strong for the rocket to ascend through. If winds do not improve, launch cannot occur today.
The one-second launch opportunity today is 1701:20 GMT (1:01:20 p.m. EDT; 10:01:20 a.m. local time).
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"The concern is a level of wind shear that the vehicle would fly through and not fully be able to correct for," NASA spokesman George Diller says.
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But high-altitude winds are presently unacceptable for the Delta 2 rocket's launch. Winds are currently computed at 147 percent on the vehicle's control system. That has to be 100 percent or less to ensure a successful flight through the atmosphere.
1625 GMT (12:25 p.m. EDT)
Ground weather conditions are perfect this morning with a 100 percent chance of meeting the launch rules. However, not factored into the weather forecast are upper level wind conditions since they a vehicle issue not weather.
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Once the countdown resumes, clocks will tick down to the T-minus 4 minute mark where a 10-minute hold is planned.
There is a single instant in time for the Gravity Probe-B spacecraft to be launched today -- 1701:20 GMT. This restrictive requirement means the launch team has just one shot at getting the Delta 2 rocket airborne today.
"With NASA launching unique scientific spacecraft, we very frequently have to deal with instantaneous or short windows. We wished they were a little bit longer, NASA launch manager Chuck Dovale says. "The built-in holds are good for catch up. But as we get further down toward T-0, it just leaves you with little or no flexibility to recover from any kind of hiccup."
Indeed, if there is a problem inside the final four minutes of the countdown and the clocks are halted, the launch will have to be scrubbed for today. Another attempt is available on Tuesday at 1657:24 GMT.
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The launch weather officer has removed any concerns about cumulus clouds at launch time. Therefore, there is now a 100 percent chance of weather conditions being acceptable today.
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The launch team is beginning the "slew" or steering checks of the first and second stage engines. These are gimbal tests of the nozzles on the first stage main engine and twin vernier engines and second stage engine to ensure the rocket will be able to steer itself during launch.
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At this point, the countdown is progressing extremely smoothly this morning. Liftoff is set for 1701:20 GMT.
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The rocket is now fully fueled for launch. The vehicle's first stage was successfully loaded with RP-1 kerosene fuel along with the liquid oxygen over the past hour. The second stage was filled with its storable nitrogen tetroxide and Aerozine 50 fuels last Friday. The nine strap-on booster rockets are solid-propellant.
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A large crowd is expected at Vandenberg to see Gravity Probe-B embark on its trek to orbit aboard the Boeing Delta 2 rocket at 1701 GMT.
"We have about a thousand guests all together," said Rex Geveden, Gravity Probe-B program manager. "So the interest in this mission is extraordinarily high -- not only because of the number of people that have worked on the mission over the years but the interest in Einstein and general relativity. We are really excited to be at this stage."
1527 GMT (11:27 a.m. EDT)
Meanwhile, the Rafety Safety beacon checks have been completed.
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The liquid oxygen is flowing from a storage tank at the launch pad, through plumbing and into the bottom of the rocket. The LOX and the RP-1 kerosene fuel -- loaded aboard the vehicle less than an hour ago -- will be consumed by the first stage main engine.
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Skies over the launch pad are clear, winds are light and the countdown is on schedule for today's launch. You can see the latest weather satellite image here.
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The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage.
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The propellant will be guzzled along with liquid oxygen -- to be pumped into the rocket a little later -- by the first stage Rocketdyne RS-27A main engine and twin vernier steering thrusters during the initial four-and-a-half minutes of flight.
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The countdown currently stands at T-minus 150 minutes. However, there are a pair of holds -- totaling 30 minutes in duration -- planned at T-minus 20 minutes and T-minus 4 minutes.
With the countdown underway, the activities planned over the next hour include verifying the hazard danger area is cleared, activating the rocket's Redundant Inertial Flight Control Assembly guidance computer, pressurizing the first and second stage helium and nitrogen systems and second stage fuel tanks and checking the C-band tracking beacon on the rocket.
The loading of RP-1 kerosene fuel into the rocket's first stage will begin in about 20 minutes. This operation will be followed by loading of super-cold liquid oxygen in about 75 minutes.
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Over the next hour, the entire launch team and management will be seated at their consoles. A series of polls will be conducted to verify all is in readiness for entering Terminal Count at end of the built-in hold.
The mobile service tower has been rolled back and liftoff remains set for 1701:20 GMT from Vandenberg Air Force Base, California.
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"1964: The Beatles play Shea Stadium, yours truly is born and, more importantly, NASA funds the Gravity Probe-B spacecraft," said NASA launch manager Chuck Dovale. "So 40 years in the making, you can just imagine the excitement here. People's lives, professional careers dedicated to one program. It is certainly great to be part of that."
Liftoff is scheduled for 1701:20 GMT (1:01:20 p.m. EDT; 10:01:20 a.m. local time) today from California's Vandenberg Air Force Base atop a two-stage Boeing Delta 2 rocket.
"We are through the readiness review process. We have conducted all of our reviews," Dovale said Sunday. "Everything is proceeding well."
Countdown activities were scheduled to get underway at 0300 GMT (8 p.m. local time) Sunday night with a team briefing, followed by a weather briefing an hour later.
Retraction of the mobile service tower is expected at 0700 GMT (midnight local) as the fully assembled Delta 2 rocket is exposed for the first time. Workers will spend several hours getting the Space Launch Complex-2 West pad configured for liftoff.
Launch managers will take their positions in the control room at 1300 GMT (6 a.m. local) in support of the Terminal Countdown, which commences at 1401 GMT (7:01 a.m. local).
The weather forecast now calls for a 60 percent chance of acceptable conditions. Winds at mobile service tower rollback time and unfavorable cumulus clouds during launch are the two concerns.
"The latest model run has increased the amount of moisture at the lower levels and decreased temperatures at 5,000 ft. This leads us to an increase in (probability of violating weather constraints) from yesterday with greater chance for cumulus in the area and over the pad," weather officer Lt. Breea Lemm said Sunday.
We will post live updates on this page during the final hours of the countdown.
SATURDAY, APRIL 17, 2004
Liftoff of the Gravity Probe-B spacecraft atop a Boeing Delta 2 rocket from Vandenberg Air Force Base, located 140 miles northwest of Los Angeles, is scheduled for 1701:20 GMT (1:01:20 p.m. EDT; 10:01:20 a.m. local time). There will be just one second to get the rocket off its Space Launch Complex-2 West pad or else wait until Tuesday.
The rocket's 10-foot diameter nose cone was attached earlier this week, encapsulating the Gravity Probe-B satellite. Loading of the storable propellants into the Delta's second stage was successfully completed on Friday.
On Saturday workers were installing the ordnance used to separate the rocket's nose cone during launch, performing Range Safety radio beacon checks, filling the pad's water deluge system and closing out parts of the rocket. On Sunday, the final touches will be made on Gravity Probe-B and the nose cone shrouding the satellite will be sealed for flight.
The mobile service tower enclosing the rocket is scheduled to be rolled back early Monday. The Terminal Countdown will commence three hours before liftoff.
The weather forecast calls for a 70 percent chance of favorable conditions for the launch attempt. Gusty winds at tower rollback time preventing the structure to be moved safely and cumulus clouds in the rocket's flight path are the two worries.
"A trough moving in off the Pacific will pass over Vandenberg AFB late Sunday night, but lingering moisture in the upper levels will not pose a threat to launch," Air Force launch weather officer Lt. Breea Lemm reported Saturday.
"The main concern with this trough will be the cold air moving in behind it. This cold air, combined with lower level moisture, will spawn the development of cumulus clouds. It is the placement of these clouds at T-0 that is the primary forecast challenge.
"As a strong Pacific high develops off the coast, SLC-2W will be under the influence of northwest winds at launch. Upper level winds on launch day will be from the west-northwest, reaching a maximum of 50 knots near 35,000 feet.
"The model is still under scrutiny at this point, but a similar trend tomorrow will enhance its reliability."
The launch time forecast calls for clouds at 2,500 and 30,000 feet, visibility of 7 miles, northerly winds from 340 to 020 degrees at 12 to 15 knots and a temperature of 54 to 59 degrees F.
Should liftoff slip to Tuesday, the instantaneous launch time is 1657:24 GMT (12:57:24 p.m. EDT; 9:57:24 a.m. local time). Meteorologists are predicting a 70 percent chance of good weather for the backup launch opportunity.
"With a strong upper level ridge building to the west, scrub day conditions remain favorable aloft. Surface winds are still forecasted from the northwest with a tightening of the gradient leading to stronger winds. Upper level winds will be from the west-northwest, reaching a maximum of 65 knots near 35,000 feet," Lemm reported.
Gravity Probe-B is a $700 million NASA mission that has a history dating back four decades, nearly as long as the space agency itself.
The satellite is equipped with four gyroscopes that serve as the heart of its experiment. Over the course of several months in space, scientists will look for very precise changes in the direction of spin of the four gyros as they provide an almost perfect space-time reference system.
The mission will test two predictions of Einstein's general theory of relativity: the "geodetic effect" of how space and time are warped by the presence of the Earth and "frame dragging" of how Earth's rotation drags space and time around with it.
Watch this page for live play-by-play updates throughout Monday's countdown and launch.