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The Mission

Rocket: Delta 2 (7920)
Payload: Gravity Probe-B
Date: April 19, 2004
Time: 1701 GMT (1:01 p.m. EDT)
Site: SLC-2W, Vandenberg Air Force Base, California
Satellite feed: AMC 9, Transponder 9, C-band

GP-B mission overview

Launch events timeline

Ground track map time

Mission Status

The Payload

NASA's Gravity Probe-B is an exotic satellite mission to test aspects from Albert Einstein's general theory of relativity.

GP-B spacecraft overview

Learn about the experiment

An intro to general relativity

The Launcher

Boeing's workhorse Delta 2 rocket has flown more than 100 times, launching military, scientific and commercial satellites.

Delta 2 fact sheet

Learn about launch site

Archived Delta coverage


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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

After 40 years of development, the Gravity Probe-B spacecraft will spend one more day on Earth because high-altitude winds over the California launch site caused trouble during today's countdown to launch.

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)

The official reason for the countdown being halted was engineers could not determine if the proper wind profile data had been loaded into the Delta 2 rocket's guidance system based on the latest weather balloon. With no time to address the situation, officials had no choice but to call a scrub.

Liftoff is rescheduled for 1657:24 GMT (12:57:24 p.m. EDT; 9:57:24 a.m. local time) Tuesday.

1658 GMT (12:58 p.m. EDT)

HOLD! Countdown has been stopped. This effectively scrubs today's launch attempt since there was just one second in which to get the Delta 2 rocket off the pad.

1657 GMT (12:57 p.m. EDT)

T-minus 4 minutes and counting. The final phase of the countdown is now underway for the launch of the Delta 2 rocket and the GP-B satellite. The final weather balloon is still being examined.

1656 GMT (12:56 p.m. EDT)

Standing by for final word on the upper level winds.

1653 GMT (12:53 p.m. EDT)

The launch team has been polled by the Boeing launch conductor for a "go" to proceed with the countdown. The team is now receiving final instructions on countdown procedures.

1651 GMT (12:51 p.m. EDT)

NASA launch manager Chuck Dovale has polled his agency team. There are no technical issues -- just upper level winds standing in the way of liftoff.

1651 GMT (12:51 p.m. EDT)

The latest weather balloon shows upper level winds remain "no go" for launch. Officials are awaiting for data from an additional balloon before launch time.

1647 GMT (12:47 p.m. EDT)

T-minus 4 minutes and holding. The countdown has entered the final planned hold point for today's launch attempt. This planned 10-minute hold.

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).

1647 GMT (12:47 p.m. EDT)

The Gravity Probe-B is now confirmed to be on internal battery power for flight, NASA says.

1643 GMT (12:43 p.m. EDT)

Inhibited checks are now beginning for the Range Safety command destruct receivers that would be used in destroying the Delta rocket should the vehicle veer off course and malfunction during the launch.

1641 GMT (12:41 p.m. EDT)

The Range has resolved its glitch, clearing the way for the safety checks to be performed.

1640 GMT (12:40 p.m. EDT)

The next weather balloon data on upper level winds is expected once the countdown enters the T-minus 4 minute hold.

"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.

1637 GMT (12:37 p.m. EDT)

The Range has experienced a problem, which will delay the command destruct receiver checks that are scheduled at this point in the countdown.

1631 GMT (12:31 p.m. EDT)

T-minus 20 minutes and counting. The planned hold in the countdown has been released. Clocks will now tick down to T-minus 4 minutes where the final hold is planned.

1628 GMT (12:28 p.m. EDT)

Boeing and NASA officials have conducted readiness polls in preparation for continuing the countdown. No technical problems were reported. Clocks will resume counting at 1631 GMT as planned.

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)

NASA launch manager Chuck Dovale reports that upper level winds are out of limits in the transonic region of flight. Winds aloft are currently too strong for the rocket to safely fly through. Weather balloons are continuing to be released to measure the speed and direction of the winds.

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.

1623 GMT (12:23 p.m. EDT)

A P-3 aircraft is now stationed over the Pacific Ocean, more than 1,000 miles downrange, to receive live telemetry from the Delta rocket's second stage during ascent today. The data relay plane will transmit the information back to Vandenberg.

1621 GMT (12:21 p.m. EDT)

Now half-way through this built-in hold at T-minus 20 minutes.

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.

1612 GMT (12:12 p.m. EDT)

Data link tests between the Range and rocket are beginning.

1611 GMT (12:11 p.m. EDT)

T-minus 20 minutes and holding. The countdown has entered the 20-minute built-in hold. This pause is designed to give the launch team a chance to work any problems or catch up on activities that might be running behind schedule. Engineers will also have time to examine all the data from the just-completed steering tests.

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.

1608 GMT (12:08 p.m. EDT)

The first stage steering checks are complete.

1606 GMT (12:06 p.m. EDT)

T-minus 25 minutes and counting. The countdown is nearing a planned 20-minute built-in hold at the T-minus 20 minute mark. Another hold is scheduled at T-minus 4 minutes.

1604 GMT (12:04 p.m. EDT)

Second stage engine slews are complete. First stage tests have started.

1601 GMT (12:01 p.m. EDT)

There is 60 minutes remaining until launch.

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.

1555 GMT (11:55 a.m. EDT)

The Delta's onboard guidance computer -- called the Redundant Inertial Flight Control Assembly, or RIFCA -- has been turned on for launch.

1551 GMT (11:51 a.m. EDT)

The countdown is being controlled from the "soft blockhouse" located about 8 miles from the Space Launch Complex-2 West pad. Senior launch officials are stationed in the Mission Directors Center located on South Base of Vandenberg.

At this point, the countdown is progressing extremely smoothly this morning. Liftoff is set for 1701:20 GMT.

1542 GMT (11:42 a.m. EDT)

The launch team reports the loading of the Delta 2 rocket's first stage liquid oxygen tank was completed at 1541:52 GMT. The operation took 24 minutes and 11 seconds today. The tank will be replenished through the countdown to replace the super-cold liquid oxygen that naturally boils away.

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.

1537 GMT (11:37 a.m. EDT)

No problems have occurred during liquid oxygen loading this morning. Once the first stage tank is 95 percent full, the "rapid load" valve will be closed and the slower "fine load" phase will continue to fill the rocket.

1531 GMT (11:31 a.m. EDT)

The countdown is entering the final 90 minutes to launch from Space Launch Complex-2 West at Vandenberg Air Force Base in California. The site is on the Pacific Coast, about 140 miles northwest of Los Angeles.

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)

The normal layer of ice is beginning to form on the rocket's skin. And a plume of white vapor is streaming from the vent port of the first stage as the cryogenic tanking passes the 10-minute mark.

Meanwhile, the Rafety Safety beacon checks have been completed.

1522 GMT (11:22 a.m. EDT)

It will take approximately 25 minutes to fill the first stage liquid oxygen tank. The operation has been underway for five minutes.

1517 GMT (11:17 a.m. EDT)

Super-cold liquid oxygen, chilled to Minus-298 degrees F, is being pumped into the first stage of the Boeing Delta 2 rocket as the countdown continues for today's 1701 GMT launch.

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.

1514 GMT (11:14 a.m. EDT)

The launch team members have begun preparations to load the rocket's first stage liquid oxygen tank.

1512 GMT (11:12 a.m. EDT)

Boeing officials have confirmed their approval for liquid oxygen tanking.

1507 GMT (11:07 a.m. EDT)

There are no technical issues being addressed on the Delta 2 rocket or Gravity Probe-B spacecraft with just under two hours remaining until liftoff time today.

1505 GMT (11:05 a.m. EDT)

NASA launch manager Chuck Dovale has polled his management team and the space agency is "go" for loading liquid oxygen into the first stage starting at approximately 1516 GMT.

1459 GMT (10:59 a.m. EDT)

The launch weather officer just provided a detailed briefing to the management team in advance of loading liquid oxygen into the Delta 2 rocket's first stage. All weather rules are currently "go." The forecast is now calling for a 80 percent chance of favorable weather at launch time -- with cumulus clouds the only concern.

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.

1444 GMT (10:44 a.m. EDT)

The first stage fuel tank of the Boeing Delta 2 rocket has been fully loaded for today's liftoff of Gravity Probe-B. The tank was filled with a highly refined kerosene, called RP-1, during a 19-minute, 4-second process that concluded at 1444:30 GMT.

The next major task in the count will be loading super-cold cryogenic liquid oxygen into the first stage.

1441 GMT (10:41 a.m. EDT)

Once the tank is filled to 98 percent, the "rapid load" valve will be closed and the slower "fine load" phase will continue top off the tank.

1438 GMT (10:38 a.m. EDT)

The launch team has computed that the full load for the first stage fuel tank is 9,950 gallons. Over 7,000 gallons are already aboard.

1430 GMT (10:30 a.m. EDT)

RP-1 has been flowing for five minutes with no problems reported. Over 2,000 gallons have been loaded into the rocket.

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.

1425 GMT (10:25 a.m. EDT)

Fueling of the Delta 2 rocket's first stage has begun for today's launch. About 10,000 gallons of a highly refined kerosene propellant, called RP-1, are being pumped into the rocket from a 15,000-gallon storage tank at the Space Launch Complex-2 West pad.

1421 GMT (10:21 a.m. EDT)

Boeing technicians are starting preparations for loading the Delta 2 rocket's first stage RP-1 fuel tank. After verifying valves, sensors, flow meters and equipment are ready, the highly-refined kerosene fuel will start flowing into the vehicle.

1401:20 GMT (10:01:20 a.m. EDT)

T-minus 150 minutes and counting! The Terminal Countdown has commenced for today's launch of the Boeing Delta 2 rocket carrying the Gravity Probe-B satellite for NASA. Over the next three hours, the launch team will prep the rocket, payload and ground support systems for the planned 1701:20 GMT liftoff from the SLC-2W pad at Vandenberg Air Force Base, California.

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.

1354 GMT (9:54 a.m. EDT)

The team has been polled for a "ready" status to pick up the countdown. No issues were reported. Clocks will start ticking again at 1401:20 GMT as the Terminal Countdown begins.

1346 GMT (9:46 a.m. EDT)

The launch team members have been instructed to man their stations for Terminal Count. A readiness poll will be performed in a few minutes to verify everyone is prepared to resume the countdown at the end of this scheduled hold.

1331 GMT (9:31 a.m. EDT)

Now half-way through this scheduled hold. The hazardous area around the Delta 2 rocket's launch pad has been cleared of all workers with the departure of the last personnel a few minutes ago.

1301 GMT (9:01 a.m. EDT)

T-minus 150 minutes and holding. The countdown has entered a planned 60-minute built-in hold. This is the first of three holds scheduled into the count to give workers a chance to catch up on any activities that may be running behind.

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.

0401 GMT (12:01 a.m. EDT)

Launch day has finally arrived for the Gravity Probe-B spacecraft!

"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.


Forty years in the making, NASA's exotic satellite mission to test Albert Einstein's theories of space and time is finally ready for launch Monday from California.

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.