BY JUSTIN RAY

Follow the preparations and launch of the Orbital Sciences Pegasus rocket with NASA's HESSI solar flare research spacecraft. Reload this page for the very latest on the mission.

1901 GMT (2:01 p.m. EST)

The L-1011 carrier aircraft, called "Stargazer", is now taxing from the Hot Pad staging zone to the runway at Cape Canaveral Air Force Station for takeoff in at about 2:28 p.m. EST (1928 GMT). The countdown continues for the scheduled release of the Pegasus rocket over the Atlantic Ocean at 3:26 p.m. EST( 2026 GMT). The only issue being worked is higher than expected temperatures on the HESSI spacecraft's batteries. These temperatures are expected to fall back to normal after the L-1011 carrier aircraft takes flight, according to launch commentator George Diller

1:00 p.m. EST (1800 GMT)

NASA is not reporting any problems as the countdown continues to launch of the Pegasus rocket. Over the next hour the L-1011 carrier aircraft will taxi to end of the runway at Cape Canaveral in preparation for takeoff at 2:28 p.m. EST.

11:00 a.m. EST (1600 GMT)

Countdown operations are underway for today's planned launch of the Orbital Sciences Pegasus rocket with NASA's HESSI spacecraft. Release of the air-launched rocket from the L-1011 carrier jet is targeted to occur at 3:26 p.m. EST.

There are no technical problems being reported by the launch team and the weather remains favorable for today's flight.

Clocks are counting down to departure of the "Stargazer" carrier aircraft from Cape Canaveral, bound for the preset launch zone over the Atlantic Ocean. Takeoff is about 3 1/2 hours away, and the Launch Panel Operator will now board the jet at the "Hot Pad" staging area at the ramp. The LPO will power up the Pegasus rocket under direction from the Launch Conductor.

While that chore is underway, efforts to close out the Pegasus' access compartments will be finished and Range Safety engineers are scheduled to verify that the Flight Termination System is functioning by inhibited sending arm and fire commands to the FTS antennas.

Later, other tests will be conducted to ensure the readiness of Pegasus systems. The checks will include verifying the rocket can switch from aircraft-supplied power to its own internal batteries, the guidance computer, the Pegasus' flight computer and telemetry system are working normally and testing the control link from the LPO to the payload.

TUESDAY, FEBRUARY 5, 2002

An air-launch Pegasus rocket will be dropped from the belly of an L-1011 jetliner off the coast of Central Florida at 3:26 p.m. EST (2026 GMT) today to carry NASA's HESSI solar explorer spacecraft into Earth orbit.

Here is a preview of the countdown from NASA Launch Manager Omar Baez:

The launch team will open their checklists to begin countdown activities at 10:55 a.m. at Cape Canaveral Air Force Station where the flight is being controlled. Range and other facility set ups will start at that time, too.

At 11:15 a.m. the Orbital Sciences Pegasus XL rocket and the HESSI spacecraft will be powered up and the launcher's inertial navigation system and flight computer will undergo alignment. A "sweep" test to move the rocket's fin aerosurfaces also will be performed.

A half-hour later a power systems test and spacecraft closeouts will begin, followed by an open-loop test of the flight termination system.

A 20-minute built-in hold is scheduled into the countdown at 12:26 p.m. to give the launch team time to catch up on any work that could be running behind schedule.

Once the countdown resumes Launch Weather Officer Jim Sardonia will give mission managers a briefing on weather conditions for takeoff of the L-1011 and the flight path over the Atlantic Ocean.

At 1:16 p.m. the launch team will be polled to verify all is in readiness for engine start on the carrier aircraft. Engine No. 2 -- the engine on the tail -- then will be started.

Workers at the "hot pad" where the L-1011 has been parked since arriving at the Cape last Friday will then disconnect ground-provided air conditioning and nitrogen feeds to the aircraft and the vacuum pump for HESSI, remove the stairs to the plane and close its doors. Engines 1 and 3 are then started.

At 1:46 p.m. the L-1011 is scheduled to taxi from the "hot pad" on the ramp to the end of the runway.

A poll of the launch team will be performed at 2:23 p.m. to get a "go" for takeoff, which is slated to occur at 2:28 p.m.

Once the L-1011 is off the ground it will fly a preset course, called "the racetrack" to gain altitude and provide time to perform final work to ready Pegasus and HESSI for launch.

The drop is planned at 3:26 p.m. at 39,000 feet with a speed of Mach 0.8, some 75 miles east of Palm Bay, Florida.

This will mark the 31st flight of the winged Pegasus rocket and the 21st for the stretched "XL" version of the rocket.

Spaceflight Now will provide comprehensive live coverage of the countdown and launch on this page.

MONDAY, FEBRUARY 4, 2002
12:00 p.m. EST (1700 GMT)

The launch readiness reviewing meeting was held this morning at Kennedy Space Center and all systems remain "go" for the Pegasus rocket to loft NASA's HESSI spacecraft tomorrow.

NASA Launch Manager Omar Baez said there are no technical problems being addressed and the weather forecast is favorable.

Overall Launch Weather Officer Jim Sardonia is giving an 80 percent chance of acceptable conditions on Tuesday.

"Conditions continue to look promising for Tuesday's launch attempt as model guidance indicates a delay in the movement of a weather disturbance that is expected to impact the local area weather this week," Sardonia said in his morning forecast.

"This disturbance is now expected to form late Tuesday in the western Gulf of Mexico and move into the Florida peninsula on Wednesday. High pressure will dominate central Florida on launch day (Tuesday) bringing northeasterly winds and a slight chance of some isolated rainshowers along the coast and within the flight path of the L-1011.

"Weather is expected to deteriorate on Wednesday in the event of a 24 hour delay as the weather system in the Gulf moves into central Florida.

"The main concern for launch day will be the slight chance of coastal rainshowers prohibiting take-off, and isolated rainshowers in the flight path."

SUNDAY, FEBRUARY 3, 2002

Its launch has been delayed 19 months by six different concerns, but finally all appears ready for NASA's HESSI satellite to soar into space Tuesday to study the most powerful explosions in the solar system. Read our full story about the saga of HESSI.

FRIDAY, FEBRUARY 1, 2002
6:50 p.m. EST (2350 GMT)

An Orbital Sciences Pegasus rocket, with a NASA solar flare research satellite onboard, made a transcontinental ferry flight Friday from the booster's home base in California to its launch site at Cape Canaveral, Florida.

The air-launch Pegasus will be flown off the coast of Central Florida on Tuesday and dropped at 3:26 p.m. EST (2026 GMT) to propel into orbit NASA's High Energy Solar Spectroscopic Imager satellite, nicknamed HESSI.

Attached to the belly of an L-1011 jet, the air-launched rocket departed Vandenberg Air Force Base in California at about 10 a.m. local time (1 p.m. EST) Friday for the 3,000 mile trek across the southern U.S.

Called "Stargazer", the carrier aircraft touched down on the Skid Strip runway at Cape Canaveral Air Force Station just after sunset at 6:39 p.m. EST.

A plan to have the L-1011 fly the same course over the Atlantic Ocean that will be used on launch day, allowing ground antennas and other equipment to be aligned and checked out, was scrubbed Friday due to bad weather.

Chase aircraft from Langley did intercept the rocket-carrying jet, providing spectacular video of the L-1011 as it neared Florida's Space Coast with a setting sun as backdrop. The chase aircraft will be in the sky on Tuesday to provide live video of the Pegasus' launch.

Now at the Cape, "Stargazer" will be positioned in a corner of the air station's ramp, in a zone called "the hot pad." Workers will immediately begin unloading the ground support equipment packed aboard the L-1011, setting up a lightning protection mast and connecting a vacuum pump to the HESSI spacecraft's cryo cooler.

On Saturday the launch team will hold a mission dress rehearsal to practice the countdown and flight of the Pegasus rocket.

The Combined Systems Test will be performed Sunday to verify the readiness of the L-1011, rocket and satellite. A similar test was conducted at Vandenberg earlier this week after the rocket was bolted to the jet, but it is re-performed to ensure all is well after the cross-country ferry.

Senior mission officials will gather for the Launch Readiness Review meeting on Monday to give final approval to proceed with the flight. At the hot pad, meanwhile, the rocket's nose cone will be closed out and ordnance checked.

On Tuesday the L-1011 will take off about one-hour prior to the scheduled release of Pegasus, heading over the Atlantic and flying a race track-like pattern to give time to perform final checks on the rocket and HESSI. The rocket will be released 39,000 feet above the ocean at a point about 75 miles east of Palm Bay, a community south of the Cape.

The weather forecast for Tuesday calls for a 70 percent chance of acceptable conditions for launch. The concerns will be thick layered clouds in the flight path preventing L-1011 from taking off and proximity to rainshowers within 10 miles of the flight path.

Meteorologists say a disturbance is expected to form in the Gulf of Mexico on Tuesday, spreading thick cloud layers, numerous rainshowers and some embedded thunderstorms into the western part of Florida.

Some of these cloud layers and showers may move within 10 nautical miles of the Skid Strip prior to take-off and there may be scattered pockets of thick cloud layers and rainshowers within 10 nautical miles of the flight path and drop point.

At the aircraft take-off time, conditions at the runway are predicted to include scattered cumulus clouds at 3,000 feet, broken altostratus clouds at 8,000 feet and broken cirrus clouds at 25,000 feet, visibility of five miles, southeasterly winds at 8 gusting to 16 knots and a temperature of 74 to 76 degrees F.

At the 39,000-foot flight level for launch, there will be seven miles visibility, west-southwesterly winds at 105 knots, temperature of -48 degrees C and chance of light to moderate turbulence and isolated rainshowers in the flight path.

The weather worsens on Wednesday, should the launch be delayed for some reason. There is only a 40 percent chance of meeting the launch weather rules as that system is expected to move over central Florida, bringing the chance of heavy cloud cover and moderate to heavy rainfall.

Once released from "Stargazer", the three-stage Pegasus rocket will fly a nine-and-a-half minute flight to deliver HESSI into a 373-mile high orbit inclined 38 degrees to the equator. HESSI is supposed to operate for two-to-three years, taking color X-ray images of solar flares. Scientists hope the $85 million mission will yield clues about what triggers the flares, which are the most intense explosions in our solar system.

Watch this page for updates on mission preparations and complete live coverage of Tuesday's countdown and launch. We'll post a full story on the saga of the HESSI mission this weekend, detailing the year-and-a-half delay in launching the satellite due to a variety of problems.