Following today's scrub, engineers were developing the troubleshooting plan that will be implemented beginning Friday morning. If all goes well, the team believes the hardware will be ready to support a successful launch attempt on Friday afternoon at 2:42 p.m. EDT.
Engineers initially considered potentially sending a crew to the pad to investigate that valve during the countdown today. However, it was determined a viable solution to the issue could not achieved during the day's launch window.
The Atlas 5 will fly a 51-minute mission to supersynchronous transfer orbit for deployment of the second Advanced Extremely High Frequency satellite, AEHF 2.
Priced at $1.7 billion and weighing 13,567 pounds at launch, the craft will provide the president and military leaders with a secure and survivable communications link in wartime.
Built in a collaboration between Lockheed Martin and Northrop Grumman, a series of AEHF spacecraft will replace the aging Milstar satellite fleet. They feature the highest levels of encryption, low probability of intercept and detection, jammer resistance and the ability to penetrate the electro-magnetic interference caused by nuclear weapons.
AEHF was envisioned to keep communications flowing between the military and civilian leadership in a nuclear war, giving the U.S. information superiority.
"The launch of an Atlas 5 carrying the United States Air Force's Advanced Extremely High Frequency 2 (AEHF 2) payload was scrubbed today due to lack of helium flow from the ground support equipment to the Interstage Adapter compartment on the launch vehicle. The Atlas 5 vehicle and AEHF 2 are safe and secure at this time. The launch is rescheduled for Friday, May 4 from Space Launch Complex 41 at Cape Canaveral Air Force Station, Fla. The opening of the launch window is 2:42 p.m. EDT and extends until 4:42 p.m. The forecast for May 4 shows an 80 percent chance of favorable weather conditions for the launch tomorrow.
The outlook calls for scattered clouds at 3,000 feet, scattered high clouds at 25,000 feet, a chance isolated showers, good visibility, southeasterly winds of 12 to 16 knots and a temperature around 79 degrees F.
In the end, officials decided against sending a crew into the launch platform, beneath the million-pound rocket, to check a manually-operated valve in the purge system that feeds the Centaur interstage adapter.
The United Launch Alliance and Air Force launch team plans will try again tomorrow at 2:42 p.m. EDT (1842 GMT).
The weather is fine and no other technical issues have been noted throughout the countdown.
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Topped with the high-energy Centaur upper stage, Atlas rockets have been used since the 1960s to dispatch ground-breaking missions for NASA, including the Surveyors to the Moon, Mariner flights to Mars, Venus and Mercury, and the Pioneers that were the first to visit Jupiter and beyond.
In its newest era, the Atlas 5 rocket sent the Mars Reconnaissance Orbiter to the red planet in 2005, propelled the New Horizons probe toward Pluto and the solar system's outer fringes in 2006, doubled up with the dual Lunar Reconnaissance Orbiter and LCROSS impactor to the Moon in 2009, hurled Juno to Jupiter last August and dispatched the car-sized Curiosity rover on the Mars Science Lab mission in November.
Today marks the 30th flight for Atlas 5, born of the Air Force's competition to develop next-generation Evolved Expendable Launch Vehicles. In its previous 29 missions since debuting in August 2002, the tally shows nine commercial flights with communications spacecraft, nine dedicated to the Defense Department, five missions with spy satellites for the National Reconnaissance Office and six for NASA.
Still calling for scattered clouds at 3,000 feet, scattered high clouds at 25,000 feet, a chance of isolated coastal showers, good visibility, southeasterly winds of 16 to 20 knots and a temperature around 79 degrees F.
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And if you are need tips on picking a good viewing spot, check out this authoritative guide on where to go.
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The Common Core Booster stage's liquid oxygen tank is the largest tank to be filled today. It holds 48,745 gallons of cryogenic oxidizer for the RD-180 main engine.
The liquid oxygen -- chilled to Minus-298 degrees F -- will be consumed during the launch by the Centaur's single RL10 engine along with liquid hydrogen to be pumped into the stage a little later in the countdown. The Centaur will perform two firings to propel the payload -- initially into a parking orbit, then into a highly elliptical supersynchronous transfer orbit.
Clocks have one more built-in hold planned at T-minus 4 minutes. That pause will last 10 minutes during which time the final "go" for launch will be given. All remains targeted for liftoff at 2:46 p.m. EDT from Cape Canaveral's Complex 41.
In the next couple of minutes, chilldown thermal conditioning of the mobile launch platform upon which the rocket stands will begin. This is meant to ease the shock on equipment when supercold cryogenic propellants start flowing into the rocket.
Loading of cryogenic liquid oxygen and liquid hydrogen into the Atlas 5 rocket will be getting underway a short time from now.
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There is just a slight concern for cumulus clouds or a detached anvil cloud coming within the restricted area around the launch site this afternoon.
For launch time, Air Force meteorologists are calling for some scattered low clouds at 3,000 feet, scattered high clouds at 25,000 feet, potentially an isolated shower in the vicinity, good visibility, southeasterly winds of 16 gusting to 20 knots and a temperature around 78 degrees F.
What's more, the craft are nuclear-hardened to survive the effects of hellish warfare and possess built-in autonomy to resolve onboard problems while enduring hostile conditions.
They are built to follow the military's aging Milstar satellite series that provide the preeminent communications with top-level protection.
While all five Milstars remain in use, the emerging AEHF fleet will fly alongside to offer their faster data speeds and expand the capacity for secure communications across the world.
"This system is integral to our national security space architecture. It provides significantly improved protected communications capabilities for both tactical and strategic users. With the addition of a second AEHF satellite in the constellation, the nation will have a robust and resilient seven-satellite combined Milstar-AEHF constellation that will add significant protected communications capabilities for the warfighter," said John Miyamoto, Lockheed Martin's vice president for advanced programs in Global Communications Systems.
If you are in the local Cape Canaveral area and would like to watch today's Atlas 5 rocket launch in person, check out this authoritative viewing guide on where to go.
We're now streaming live views of the launch pad. And join us for a live broadcast of the launch, complete with ULA's commentary, starting at 2:26 p.m.
The countdown clocks are starting to tick right now, beginning a seven-hour sequence of work that will prepare the rocket, payload and ground systems for today's blastoff at 2:46 p.m. EDT (1846 GMT).
Soon the launch team will begin powering up the rocket to commence standard pre-flight tests. Over the subsequent few hours, final preps for the Centaur's liquid oxygen and liquid hydrogen systems will be performed, along with a test of the rocket's guidance system and the first stage propulsion and hydraulic preps, internal battery checks and testing of the C-band system used to track the rocket as it flies downrange, plus a test of the S-band telemetry relay system. The Complex 41 site will be cleared of all personnel at 11:51 a.m.
A planned half-hour hold begins at 12:06 p.m. when the count reaches T-minus 120 minutes. Near the end of the hold, the team will be polled at 12:33 p.m. to verify all is in readiness to start fueling the rocket for launch.
Supercold liquid oxygen begins flowing into the Centaur upper stage around 12:53 p.m., followed by the first stage filling around 1:06 p.m. Liquid hydrogen fuel loading for Centaur will be completed a short time later.
A final hold is scheduled at the T-minus 4 minute mark starting at 2:32 p.m. That 10-minute pause will give everyone a chance to finish any late work and assess the status of the rocket, payload, Range and weather before proceeding into the last moments of the countdown.
Today's launch window extends from 2:46 to 4:46 p.m. EDT (1846-2046 GMT).
"The Advanced EHF satellite is really our secure satellite communications system. It will provide survivable, global, secure and protected, jam-resistant communications to our national command authority as well as military forces in the field. It is the follow-on to the Milstar system, augmenting, improving and expanding the Department of Defense's MILSATCOM architecture," said Dave Madden, director of the Military Satellite Communications Systems Directorate at the Air Force's Space and Missile Systems Center.
"The satellite is ready and waiting for our buddies over in ULA and our mission director to get us off the ground and get us into space so we can start executing the mission. It is a critical part of our national defense strategy."
The two mobile trailers connected to the launching platform, which were part of the convoy during this morning's rollout, soon will be hooked up to power and communications systems at the pad. These trailers provide conditioned air to the payload and communications with the rocket during the rollout and the countdown. They are protected from the blast of launch by a concrete structure on the north-side of the platform.
Within the next hour, the auto couplers between the pad and platform will be engaged to route umbilical connections from the ground to the rocket for tomorrow's fueling of the booster with cryogenic propellants.
Later today, the undercarriages used to move the mobile platform will be disconnected and the "trackmobiles" pulled free.
Ground crews will secure the rocket for a quiet evening leading into tomorrow's launch opportunity. Countdown clocks will start ticking seven hours before liftoff time.
Thursday's two-hour launch window opens at 2:46 p.m. and closes at 4:46 p.m. EDT.
Here's a timeline of the countdown's key events:
HR:MM..Eastern...Event T-6:20...7:46am...Countdown begins with rocket power up T-5:30...8:36am...Weather briefing T-4:55...9:11am...Start clearing assembly building area T-4:20...9:46am...C-band tracking beacon testing T-3:40..10:26am...S-band telemetry link checks T-2:55..11:11am...Establish blast danger area roadblocks T-2:20..11:46am...Weather briefing T-2:15..11:51am...Clear the pad T-2:00..12:06pm...T-120 minutes and holding (for 30min) T-2:00..12:31pm...Launch conductor briefing to team T-2:00..12:33pm...Readiness poll for fueling T-2:00..12:36pm...Resume countdown T-1:50..12:46pm...Centaur LOX transfer line chilldown T-1:43..12:53pm...Begin Centaur liquid oxygen loading T-1:30...1:06pm...Begin Atlas first stage LOX loading T-1:25...1:11pm...Centaur LH2 transfer line chilldown T-1:10...1:26pm...Centaur RL10 engine chilldown T-1:02...1:34pm...Begin Centaur liquid hydrogen loading T-0:40...1:56pm...FLight termination system final test T-0:16...2:20pm...RD-180 engine fuel fill sequence T-0:10...2:26pm...Weather briefing T-0:04...2:32pm...T-4 minutes and holding (for 10min) T-0:04...2:39pm...Readiness poll for launch T-0:04...2:42pm...Resume countdown T-0:00...2:46pm...LAUNCH
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The outlook at launch time includes scattered low-level clouds at 3,000 feet, some broken high cirrus at 25,000 feet, a chance of isolated showers in the area, good visibility of 7 miles, southeasterly winds of 14 to 18 knots and a temperature around 77 degrees F.
"A broad area of low pressure and disturbed weather is in the Eastern Gulf of Mexico and expected to remain well south and west of the area through launch day and into Friday. Isolated thunderstorms associated with this system will favor the western peninsula and Gulf of Mexico with a small threat of anvil cloud reaching the wast coast on launch day. High pressure off the southeast coast will result in on-shore east winds with a coastal shower threat," Air Force meteorologists report.
"On launch day, the disturbed weather pattern persists over the Eastern Gulf. Easterly winds in the low to mid-levels of the atmosphere will result in a coastal shower threat. Upper level northwesterly winds will act to transport any anvil cloud from the disturbance in the Gulf of Mexico back toward the East Coast. Surface winds expected to persist from the east-southeast with gusts in the mid to upper teens. The primary concerns for launch are Cumulus Clouds and Anvil Clouds," the latest forecast says.
Riding atop a mobile launching platform, the 196-foot-tall satellite booster is moving to Cape Canaveral's Complex 41 for the second launch to deploy the U.S. Air Force's Advanced Extremely High Frequency constellation.
"On behalf of our 3,600 employees, United Launch Alliance is honored to be supporting the United States Air Force in the launch of the Advanced EHF 2 satellite. The ULA team is focused on attaining perfect product delivery Advanced EHF 2 mission, which includes a relentless focus on mission success and also excellence in meeting all of the needs of our customers. The focus is paramount as we singularly launch critical capabilities for the thousands of men and women protecting our freedoms around the world," said Jim Sponnick, United Launch Alliance vice president for mission operations.
This slow half-hour drive from the 30-story Vertical Integration Facility to Cape Canaveral's Complex 41 pad uses a pair of specially-made "trackmobiles" to carry the rocket's 1.4-million pound mobile launching platform along rail tracks for the 1,800-foot trip.
The two-stage rocket and the AEHF 2 spacecraft were put together inside the assembly building over the past seven weeks preparation for this rollout event. The Atlas 5 is designed to spend minimal time at the launch pad, which does not include a service gantry like other sites.
First motion for the rollout is targeted for 10 a.m. EDT (1400 GMT). Watch this page for updates and photos!
The review culminated with a consensus to press ahead with countdown operations starting with Wednesday's rocket rollout to the Complex 41 pad starting at 10 a.m. EDT.
Thursday's liftoff of the Atlas rocket from Cape Canaveral is targeted for 2:46 p.m. EDT, the opening of a 120-minute launch opportunity extending to 4:46 p.m. EDT.
The launch weather outlook has improved a bit, prompting an increase in odds of acceptable conditions to 70 percent.
"A broad area of low pressure and disturbed weather in the Florida Straits and Eastern Gulf of Mexico continues to slowly migrate West. The bulk of the moisture and precipitation associated with this system is expected to remain in the southern portion of the peninsula and transition to the Eastern Gulf of Mexico by mid-week," meteorologists reported this morning.
"On launch day, the disturbed weather pattern persists over the Eastern Gulf. Easterly winds in the low to mid-levels of the atmosphere will result in a coastal shower threat. Upper level westerly winds will act to transport any anvil cloud from the disturbance in the Gulf of Mexico back toward the East Coast. Surface winds expected to persist from the east with gusts in the mid to upper teens. The primary concerns for launch are cumulus clouds and anvil clouds."
The latest prediction for launch time includes scattered low-level clouds, a broken deck of high cirrus, a chance of isolated showers in the area, good visibility, southeasterly winds of 14 to 18 knots and a temperature around 77 degrees F.
This will be the second flight of the Atlas vehicle's 531 configuration, which is distinguished by the combination of a five-meter payload fairing, three solid rocket boosters and a single-engine Centaur upper stage.
Depending on a payload's weight and desired orbit, mission planners add strap-on solid boosters to the United Launch Alliance-made rocket to incrementally increase the vehicle's performance.
Atlas 5 vehicles are capable of flying with as many as five boosters, an option that was employed to generate as much power as possible to launch NASA's New Horizons space probe bound for Pluto, the Juno mission to Jupiter and the Navy's hefty MUOS 1 mobile communications satellite.
Thursday's flight heads to supersynchronous orbit around Earth to dispatch the new AEHF 2 craft for secure and dependable war-time communications to the U.S. military.
The Russian RD-180 first stage main engine will ignite at T-minus 2.7 seconds, shooting a giant cloud of steam from the pad's main exhaust duct while undergoing a check to ensure its vital signs are healthy. The three strap-on solid rocket boosters are lit at T+plus 0.8 seconds, leading to liftoff at T+plus 1.1 seconds.
The combined power will send the 19-story Atlas vehicle thundering into the afternoon sky in a hurry. Its fast speed off the launch pad will be remarkably different than other Atlas 5 missions without solid boosters that appear majestically slow.
The Aerojet-made solid boosters will burn for about 90 seconds to assist the RD-180 in propelling the rocket. The SRB casings remain attached to the first stage for a short time after burnout, waiting to be jettisoned until the rocket reaches a suitable region of flight for separation.
Once out of the discernible atmosphere, the bulbous nose cone encapsulating the AEHF payload can be shed at T+plus 3 minutes, 34 seconds. The fairing was made by RUAG Space of Zurich, Switzerland.
The kerosene-fueled first stage will continue to fire until T+plus 4 minutes, 18 seconds. The bronze stage separates about six seconds later, leaving the hydrogen-fueled Centaur upper stage to ignite for a burn lasting just under 10 minutes that will inject itself into a preliminary orbit.
Centaur completes its first burn over the central Atlantic Ocean and enters an 8-minute coast to the equator. The Pratt & Whitney Rocketdyne RL10 cryogenic engine then restarts for a five-and-a-half-minute firing to propel the spacecraft into the targeted supersynchronous transfer orbit stretching from 140 statute miles at its lowest point to 31,070 statute miles at its highest and inclined 21 degrees to the equator.
Although the Centaur finishes firing by T+plus 27 minutes, 48 seconds, the rocket won't immediately deploy the payload. That milestone moment will wait about 23 minutes as the rocket crosses Africa and Madagascar, eventually flying within communications range of the Diego Garcia tracking station on an island in the Indian Ocean.
Release of the payload from the rocket to complete the launch is expected at T+plus 51 minutes, 11 seconds.
Built by Lockheed Martin with help from Northrop Grumman, the AEHF 2 satellite continues the next generation of geosynchronous spacecraft that relay secure communications amongst the national leadership and battlefield commanders. Advancements in the spacecraft will offer faster connectivity to a greater number of warfighters for assured and protected communications.
Designers say one AEHF spacecraft has more capacity than the earlier five-satellite Milstar constellation combined and its high data rates will benefit tactical military communications, enabling higher quality maps, targeting data and live video to be transmitted without being detected by the enemy.
"A broad area of low pressure and disturbed weather presently in the Florida Straits gradually lifts north over the peninsula through mid-week and expected to persist over Central and South Florida through early in the weekend," Air Force forecasters report.
"Adequate moisture coupled with the surface trough and upper level disturbance results in a rainshower and isolated thunderstorm threat as the disturbance lifts north into the Central peninsula and Eastern Gulf of Mexico."
The Atlas 5 will be transported by rail from its assembly building to the launch pad on Wednesday, and meteorologists expect an isolated coastal shower threat with breezy on-shore winds. Afternoon and evening isolated thunderstorms should say inland.
Liftoff of the United Launch Alliance Atlas 5 with the Advanced Extremely High Frequency 2 satellite from the Cape's Complex 41 is targeted for Thursday during a window of 2:46 to 4:46 p.m. EDT.
"On launch day, the disturbed weather pattern persists over the peninsula with a threat of showers and isolated thunderstorms. Easterly winds in the low to mid-levels of the atmosphere will favor the interior for afternoon and evening thunderstorms. Upper level westerly winds will act to transport any anvil cloud from interior thunderstorms back toward the east coast. Winds remain breezy from the east-southeast with gusts in the low to mid-20s expected," the forecasters say.
"The primary concerns for launch are cumulus clouds and anvil clouds."
The specifics predicted at launch time include scattered clouds at 3,000 and 10,000 feet, a broken deck of high cirrus at 24,000 feet, isolated showers in the area, good visibility, southeasterly winds of 20 to 24 knots and a temperature around 77 degrees F.
If the launch should slip to the backup opportunity on Friday, the same 60 percent chance of favorable conditions due to clouds will remain in place.
"In the event of a 24-hour delay, the surface trough persists over the peninsula and Gulf of Mexico with showers and isolated thunderstorms. Winds persist from the southeast with gusts in the upper teens. The primary concerns for a 24-hour delay are cumulus clouds and anvil clouds," the weather team said.
An initial run at the final 4-minute phase of the countdown was halted mid-way through to simulate a hold and recycle prior to the pretend launch time.
After demonstrating problem resolution and turning around the countdown for another attempt, clocks were reset and the second run resulted in a successful mock launch.
Activities remain on track for launching the Atlas 5 rocket with AEHF 2 next Thursday from Cape Canaveral at 2:46 p.m. EDT (1846 GMT).
Liftoff of the United Launch Alliance Atlas 5 with the Advanced Extremely High Frequency 2 satellite has officially been rescheduled for May 3 at 2:46 p.m. EDT.
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The Wet Dress Rehearsal culminated with the vehicle fully fueled to rehearse the real launch day coming in early May to deliver the U.S. Air Force's second Advanced Extremely High Frequency spacecraft into orbit.
The simulation ended in the countdown's final seconds before a pretend liftoff time around 3:20 p.m. EDT.
Once the clocks were halted just before the T-0 time, the launch team began exercising its hold and recycle steps to safe the rocket.
The cryogenic fuels will be offloaded this afternoon and the vehicle allowed to warm up before it is transported back to the assembly building tomorrow.
Next up in the pre-flight campaign is mounting the AEHF 2 payload atop the rocket.
The fully assembled Atlas-Centaur vehicle with the satellite aboard will be rolled out to the Complex 41 pad the day before launch.
The giant booster consisting of its bronze-colored first stage, Centaur upper stage and three strap-on solid-fuel rockets was recently assembled together atop the mobile launching platform at the Vertical Integration Facility.
Today's rollout is part of the Wet Dress Rehearsal activities that each Atlas undergoes prior to launch. The rocket will be fully fueled tomorrow for a realistic countdown simulation.
The event is designed to iron out any problems with the hardware and exercise the launch team.
Once the simulated launch day is completed, the rocket will be rolled back to the assembly building for final pre-flight work, including attachment of the AEHF 2 satellite payload.
Liftoff is targeted for early May, pending Range availability.
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