The uncrewed spacecraft re-entered the atmosphere over the Pacific Ocean east of New Zealand at about 2:15 p.m. EDT (1815 GMT), according to Orbital Sciences Corp., the prime contractor for Cygnus.
The re-entry ended 35 days in space for the first Cygnus spacecraft, which was named for G. David Low, a former NASA astronaut and Orbital executive who was instrumental in development of the company's cargo transport system.
The re-entry punctuated a successful demonstration for Orbital Sciences, in which the company tested the Cygnus spacecraft and Antares rocket on a complete mission profile mimicking eight operational space station logistics flights the company plans to begin in December.
Orbital conducted the test flight under the banner of NASA's Commercial Orbital Transportation Services program, which fostered a public-private partnership between the space agency and two companies - Orbital Sciences and SpaceX - to develop private cargo transportation systems to replace capability lost with the space shuttle's retirement.
Orbital's Cygnus and SpaceX's Dragon spacecraft are now part of the space station's fleet of cargo vehicles, joining Russia's Progress freighter, Europe's Automated Transfer Vehicle and Japan's H-2 Transfer Vehicle.
The Cygnus demo flight launched on an Antares rocket Sept. 18 from Wallops Island, Va., and the 16.8-foot-long spacecraft arrived at the space station Sept. 29 with more than 1,300 pounds of food, experiments and other supplies.
The space station's astronauts unpacked the cargo and replaced it with bags of unneeded equipment and trash, preparing Cygnus to leave the complex Tuesday.
Since the craft's departure, Cygnus fired its thrusters to fly a safe distance from the space station, then lowered its orbit in two major braking burns Wednesday to plunge back into the atmosphere.
Officials designed most of the spacecraft to burn up during re-entry, but a few fragments of the spaceship were expected to survive the fiery fall into the remote South Pacific Ocean.
"With the COTS development phase now successfully completed, we are now turning our full attention to the eight operational resupply missions covered by our Commercial Resupply Services contract with NASA," said Frank Culbertson, Orbital's executive vice president and general manager for advanced programs. "Each Cygnus is capable of delivering a large quantity of pressurized cargo, totaling up to 20,000 kilograms over the eight missions, including crew supplies, spare parts and equipment, and scientific experiments for the ISS. We are looking forward to starting these missions in December."
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Astronauts will loosen the robot arm's grasp on the craft's grapple fixture and back the arm about 1.5 meters, or about 5 feet, away from the vehicle. The space station crew will send an "abort" command to Cygnus using a control panel inside the cupola module to initiate a series of rocket burns to take the automated spaceship away from the space station.
The actual release time is scheduled specifically to coincide with favorable lighting conditions in orbit.
Four latches and 16 bolts held the vehicles together on the nadir, or Earth-facing common berthing mechanism on the space station's Harmony module.
Over the next 90 minutes, the Orbital Sciences ground team in Dulles, Va., will activate essential systems on-board the Cygnus spacecraft to prepare the vehicle for its automated departure from the space station.
In the meantime, the robot arm will maneuver Cygnus to a release point about 30 feet below the space station.
The Cygnus spacecraft spent nearly 23 days mated to the complex, delivering more than 1,300 pounds of cargo and taking away more than a metric ton of trash.
The automated cargo freighter, concluding its first visit to the space station, delivered more than 1,300 pounds of supplies to the complex Sept. 29. At the end of its mission, the Cygnus spacecraft is designed to carry trash and unneeded equipment and burn up during re-entry into the atmosphere.
Astronauts closed hatches between the spacious Cygnus pressurized module and the space station's Harmony module at 6:42 a.m. EDT (1042 GMT) Monday. Flight engineers Karen Nyberg, Luca Parmitano and Michael Hopkins prepared for the departure by configuring the vestibule connecting Harmony and Cygnus for depressurization, then the trio reviewed procedures for the unberthing and release of the robotic spaceship, according to an update posted on NASA's website.
The space station's 57.7-foot-long robot arm will pull the Cygnus spacecraft away from Harmony at about 6 a.m. EDT (1000 GMT) Tuesday, once bolts fastening the cargo carrier to the space station are driven open.
The robot arm will maneuver the Cygnus spacecraft to a point about 30 feet beneath the space station, then release the vehicle at about 7:30 a.m. EDT (1130 GMT).
The Cygnus spacecraft will pulse its rocket jets several times to put itself on a safe trajectory away from the space station and prepare for two de-orbit burns Wednesday to guide the expendable spacecraft to a safe re-entry over the South Pacific Ocean between New Zealand and South America.
The first de-orbit burn is scheduled for 9:06 a.m. EDT (1306 GMT) Wednesday, followed by a final rocket firing at 1:41 p.m. EDT (1741 GMT) to slow the craft's velocity enough to drop from orbit and fall into the atmosphere.
Re-entry is expected at about 2:18 p.m. EDT (1818 GMT). The bulk of the spacecraft will disintegrate and burn up in the atmosphere, and surviving fragments will splash down in the remote South Pacific.
The commercial Cygnus spacecraft launched Sept. 18 aboard an Orbital Sciences Antares rocket. After overcoming a data discrepancy in its GPS navigation link with the space station, the Cygnus completed a near-flawless rendezvous with the outpost Sept. 29.
Nyberg, Parmitano and Hopkins oversaw the unpacking of the freighter's pressurized cargo module, removing bags of food, computer gear, crew care kits and student-built experiments. The astronauts replaced the supplies with trash and other items no longer needed aboard the space station.
The first Cygnus mission is a demonstration flight under NASA's Commercial Orbital Transportation Services program, a public-private partnership between the space agency and Orbital Sciences conceived to develop a private rocket and spacecraft to restore a domestic U.S. capability to deliver cargo to the space station after the retirement of the space shuttle.
NASA selected Orbital Sciences and SpaceX for the job. SpaceX accomplished its demonstration flight to the station in May 2012 and has since begun operational resupply missions.
Orbital's first operational Cygnus flight is set for launch in a window from Dec. 15 to Dec. 21.
Orbital Sciences says the Cygnus spacecraft has performed well during its 23-day stay at the space station.
"The near flawless in-orbit performance was a great testament to the work of the Orbital/NASA team that designed, built, tested and operated the spacecraft, and also a clear indication of how capable and versatile an in-space logistics vehicle we now have for both space station cargo delivery and other advanced space missions," said David Thompson, Orbital's chairman and CEO.
Orbital Sciences Corp., owner and operator of the Cygnus spacecraft, announced Tuesday the six-person Expedition 37 crew has finished unloading the food, computer equipment, supplies and student experiments delivered to the space station when the commercial resupply freighter reached the outpost Sept. 29.
Space station flight engineers Karen Nyberg, Luca Parmitano and Michael Hopkins did most of the work, and the astronauts have started packing trash back inside the Cygnus spacecraft's pressurized compartment for disposal at the end of its mission.
The first layer of trash has been placed inside the Cygnus cargo module, with the second layer being added this week. A third layer of equipment and bags for disposal will be installed next week, followed by closeouts of the spaceship's pressurized section.
The Cygnus cargo module, built by Thales Alenia Space in Italy, has an internal volume of about 667 cubic feet, about the size of a mid-sized moving truck.
The Cygnus should get rid of about 2,400 pounds of trash from the space station.
Work on the space station continues despite the partial shutdown of the federal government due to a funding impasse in Congress. About 97 percent of NASA's civil servant workforce was furloughed by the shutdown, but the space agency granted exemptions for space station flight controllers.
The Cygnus spacecraft is set to leave the space station is scheduled for Oct. 22, and its departure is not affected by the government shutdown. Orbital Sciences oversees the operations of its Cygnus spacecraft from a control center at the company's headquarters in Dulles, Va.
Two days later, on Oct. 24, Orbital engineers will command the spacecraft to fire its rocket thrusters for a de-orbit burn, guiding Cygnus to a re-entry over the remote South Pacific Ocean. Like Russian Progress supply ship, Japan's H-2 Transfer Vehicle and Europe's Automated Transfer Vehicle, the Cygnus spacecraft is designed to burn up in the atmosphere.
The official time of capture of Cygnus with the Harmony module's common berthing mechanism was 8:44 a.m. EDT (1244 GMT) as the space station flew over the Indian Ocean southwest of Indonesia.
Teams are inspecting the Cygnus hatch and berthing mechanism are debris and obstructions, but no signs of any problems are reported.
Over the next 90 minutes or so, the astronauts will guide the robot arm to move the Cygnus spacecraft through a choreographed set of maneuvers to line up the pressurized compartment's hatch with the Earth-facing port on the Harmony module.
Once in position there, a series of latches and bolts will drive closed to create a sturdy connection between Harmony and Cygnus.
The astronauts plan to open hatches into the Cygnus spacecraft's cargo module Monday around 5:55 a.m. EDT (0955 GMT).
We're really proud to have the G. David Low aboard the ISS today," said CAPCOM Cady Coleman from Houston.
Orbital Sciences christened the first Cygnus spacecraft the "G. David Low" after the late astronaut and Orbital executive. Low was a three-time space shuttle astronaut and spearheaded Orbital's efforts to develop a commercial resupply system for the space station.
"I would like to say, first of all, I was honored to be allowed to be part of this today," said Luca Parmitano, who controlled the robot arm during the manual capture sequence. "It was really a pleasure and it was a privilege to work today with all the teams on the ground, both the teams from Houston, of course, from Orbital and from here on the station."
"It was great to see you in action," Coleman replied. "It was really everything we could have wished for today."
"We see a good capture down here," said astronaut Cady Coleman, CAPCOM in mission control Houston. "That's a long time coming. Looks great."
Teams will be polled in the next few minutes to verify all systems are ready for Luca Parmitano to take manual control of the station's Canadian robot arm to grapple Cygnus.
Its destination is a capture box about 32 feet below the space station.
Final approval for grapple still depends on NASA's concurrence with the results of the demo data.
Range is now 133 meters, or 436 feet.
Along the way, at a range of about 55 meters, Cygnus will do its final rendezvous demo, firing its laser sensors toward a single reflector mounted on the space station's Japanese Kibo lab module to test its precision.
Mission control sees the spacecraft slowing its approach.
The spacecraft will hold at the 220-meter point for about 30 minutes while engineers at space station mission control in Houston and Cygnus mission control in Dulles, Va., look over data coming down from the cargo vehicle.
The space station flight director will soon. poll controllers for a "go" to move Cygnus inside the space station's keep-out sphere. The departure of Cygnus from its current position is expected around 6:17 a.m. EDT (1017 GMT) if things proceed on schedule.
The spacecraft's next destination is a 30-meter, or 98-foot, hold point. The spacecraft's LIDAR laser sensors will zero in on one reflector on the space station's Kibo lab module to demonstrate precision guidance.
After another check of the status of Cygnus, ground teams should approve the vehicle to continue its laser-guided rendezvous up to a point about 30 feet from the space station, close enough for astronaut Luca Parmitano to snag the spacecraft with the space station's robot arm.
Coming up in a few minutes, Cygnus will resume moving toward the space station, and the astronauts aboard the outpost will use a command panel to order Cygnus to retreat, demonstrating the crew can send emergency commands to the visiting vehicle in case it runs into trouble.
After retreating back to the 250-meter hold point, Cygnus will again start moving toward the space station before a hold command is issued at 220 meters, or 722 feet.
Once those demos are completed, and if all systems are healthy, mission control centers in Houston and Dulles, Va., will give the "go" to press on inside the space station's keep-out sphere, an imaginary zone 200 meters, or 656 feet, around the complex.
The spacecraft has completed a course-correction maneuver and is on track to arrive at a point 820 feet below the space station at about 5:10 a.m. EDT (0910 GMT).
The space freighter just completed a major rendezvous maneuver to guide Cygnus toward a point on the "R-bar" about 820 feet directly below the space station.
NASA reports the automated spacecraft, making its first flight to the station, has completed six of 10 milestones required to prove out Cygnus propulsion, guidance and navigation systems before mission control gives the green light to move in to an approach corridor just 30 feet below the complex.
Engineers uploaded a software fix a few days ago to overcome a data discrepancy in GPS navigation data. The computer on the Cygnus spacecraft, packed with 1,543 pounds of supplies and experiments, compares position data from Cygnus and the space station to guide itself toward the complex, ultimately reaching a point about 820 feet below the outpost.
The Cygnus will then switch to a LIDAR sensor, which fires light pulses at reflectors mounted on the space station to measure the range and closing rate between the two vehicles.
The laser-guided navigation system will feed data into the Cygnus guidance computer, telling the spacecraft when and where to fire its rocket jets to maneuver the unmanned freighter to a point 30 feet below the space station.
Once Cygnus arrives at a hold point just below the complex, astronaut Luca Parmitano will take control of the lab's robot arm to reach out and grapple the free-floating 16.8-foot-long spacecraft at about 1115 GMT (7:15 a.m. EDT) and move it to a berthing port on the space station a few hours later.
NASA requires Cygnus complete several key demonstrations during Sunday's rendezvous, including an on-board targeting demo, a test of a control panel inside the space station to prove the astronauts can send emergency commands, and the activation and checkout of the LIDAR navigation sensor.
Orbital Sciences Corp. engineers have overcome the problem that cut short the spacecraft's first rendezvous Sept. 22, uplinking a software patch to Cygnus to resolve a roll-over discrepancy in GPS navigation data between the cargo craft and the space station.
The Cygnus approached within a few miles of the complex Sept. 22 and established two-day communications with the space station, but officials aborted the rendezvous when the data glitch appeared.
Managers earlier this week pushed back the Cygnus arrival until after the Wednesday docking of a Soyuz capsule with two cosmonauts and and a NASA astronaut.
Barry Beneski, an Orbital spokesperson, said ground controllers have uploaded and fully tested the software fix and expect no problems with the GPS system Sunday.
You can view live coverage of the Cygnus rendezvous here beginning at 4:30 a.m. EDT (0830 GMT) Sunday, with capture by Parmitano scheduled for 7:15 a.m. EDT (1115 GMT). A few hours later, the robot arm will put the Cygnus spacecraft on a berthing port on the space station's Harmony module.
"The Cygnus spacecraft remains healthy in-orbit, with all major onboard systems performing as expected," Orbital said in a statement today. "Over the past several days, the Cygnus engineering team has developed, validated and uploaded the one-line software 'patch' that resolved the GPS data roll-over discrepancy that was identified during the initial approach to the ISS last Saturday."
Officials are discussing the best time to attempt the rendezvous, with the earliest opportunity now Sunday, pending final approvals from Orbital and NASA.
The spacecraft's first approach was aborted Saturday, and managers decided to put off another rendezvous until after the arrival of three fresh crew members aboard a Russian Soyuz spacecraft. Two Russian cosmonauts and a NASA astronaut successful blasted off from Kazakhstan yesterday and reached the complex overnight after a fast-track six-hour rendezvous.
Orbital says the Cygnus spacecraft is currently about 2,400 kilometers, or about 1,500 miles, behind the space station. The automated spacecraft will fire thrusters this evening to begin setting up for a second rendezvous opportunity Sunday.
The Cygnus spacecraft, on its first test flight, launched Sept. 18 from Virginia and was supposed to rendezvous with the outpost Sunday, but the approach was aborted after a technical snafu involving incompatible navigation data between Cygnus and the space station.
Orbital Sciences developed a software fix for the commercial resupply vehicle, but officials opted to delay the Cygnus rendezvous until after the Soyuz launch and docking to give engineers more time to work on the problem and ensure control teams are fully rested.
Officials said Monday the earliest the Cygnus spacecraft could arrive at the space station was Saturday morning, U.S. time, but managers planned to meet again Thursday and Friday to formally settle on the date for a second rendezvous attempt.
Joel Montalbano, NASA's deputy space station program manager, said Wednesday the next rendezvous would occur no earlier than Sunday. Montalbano make the remarks in an interview from the Baikonur Cosmodrome aired on NASA TV following the Soyuz launch.
But meetings Thursday and Friday will officially determine the next course of action for Cygnus, including its arrival date at the space station, a NASA spokesperson said.
The delay gives ground crews more time to prepare for a second rendezvous attempt after officials called off an approach early Sunday due to a data mismatch in the navigation data link between Cygnus and the space station.
A rendezvous Saturday comes after the scheduled launch and docking of three new space station residents aboard a Russian Soyuz capsule Wednesday. Space station managers do not schedule vehicle arrivals and departures too close to each other to allow time for technical reconfigurations and crew rest between major operations.
In an update posted on its website, Orbital said an exact schedule for the arrival of the Cygnus spacecraft will be determined following the Soyuz docking.
"Over the past 24 hours, the Orbital team developed and tested a software fix for the data format mismatch that necessitated a postponement of the first rendezvous operation that was scheduled for the early morning of September 22," Orbital said in a statement on its website. "However, that process, together with the impending Soyuz crew operations, resulted in a tight schedule to the point that both Orbital and NASA felt it was the right decision to postpone the Cygnus approach and rendezvous until after Soyuz operations."
The Cygnus spacecraft is on a demonstration mission to prove the cargo ship can safely approach and berth with the space station. Orbital Sciences has a $1.9 billion contract for eight further Cygnus missions to deliver supplies to the complex through 2016.
"This new schedule will allow the Orbital operations team to carefully plan and be well-rested before restarting the critical final approach to the space station. Meanwhile, Cygnus has all the resources needed to remain in orbit for an extended period of time," said Frank Culbertson, Orbital's vice president of advanced programs.
Orbital says a software update to resolve the glitch in the Cygnus freighter's communications and navigation link with the space station will be installed and tested on a ground simulator today. If the testing goes well, the software patch will be uploaded to the Cygnus spacecraft overnight tonight.
"Once this has been accomplished and verified, the current plan is for Cygnus to begin a second rendezvous and approach late Monday night, with final approach to the ISS and grapple taking place early Tuesday morning," Orbital said in a statement.
The spacecraft, making its first flight in orbit, remains otherwise healthy, Orbital said.
"Orbital Sciences has confirmed that this morning, around 1:30 a.m. EDT, its Cygnus spacecraft established direct data contact with the International Space Station (ISS) and found that some of the data received had values that it did not expect, causing Cygnus to reject the data. This mandated an interruption of the approach sequence.
"Orbital has subsequently found the causes of this discrepancy and is developing a software fix. The minimum turnaround time to resume the approach to the ISS following an interruption such as this is approximately 48 hours due to orbital mechanics of the approach trajectory."
The approach was aborted a few minutes ago due to an issue with the unmanned spacecraft's GPS navigation system. Mission control in Houston informed the crew of the postponement at about 3:30 a.m. EDT (0730 GMT).
The GPS navigation system is used for the freighter's "far-field" rendezvous until the Cygnus spacecraft switches to a laser-guided rendezvous sensor for the final approach within 820 feet of the complex.
The Cygnus spacecraft's guidance system uses relative GPS navigation by comparing its location with navigation data beamed to the Cygnus from the space station using a Japanese communications system.
The craft will soon pass about 2.5 miles below the space station and set up for another rendezvous attempt no earlier than Tuesday, mission control radioed the crew.
The test of the relative GPS system was one of eight demonstrations in the Cygnus flight plan for today, all of which must be satisfied before NASA gives the green light for the 17-foot-long, 10-foot-diameter spacecraft to move to a capture point about 30 feet from the outpost to be grabbed the lab's robotic arm.
No problems were reported with the Cygnus spacecraft since its Wednesday launch from Wallops Island, Va.
Officials said before launch the cargo transporter carries enough propellant to loiter in orbit for several weeks before arriving at the space station, giving ground teams at Orbital Sciences Corp.'s headquarters in Dulles, Va., time to resolve any problems.
The Cygnus spacecraft is on a demonstration mission under NASA's Commercial Orbital Transportation Services program, a public-private partnership in which Orbital Sciences and NASA jointly funded development of the cargo craft and its Antares rocket booster.
Orbital has signed up for eight operational missions beyond the current flight under a $1.9 billion contract through 2016.
Two orbit-raising "Delta-V" burns have been conducted using the Cygnus main engine since launch, and the freighter accomplished the first of 10 demonstration milestones on its way to the International Space Station.
"The team is packaging data from the test for NASA's review and approval, which is expected to be received today," Orbital said in a statement.
Another orbit-raising burn is scheduled later today.
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This maneuver changed the freighter's velocity by nearly 100 mph and sets up the spacecraft for the first of 10 demonstration maneuvers this evening, in which the Cygnus will prove its ability to transition to free drift and abort an approach to the International Space Station.
NASA and Orbital Sciences planned 10 demo objectives on the Cygnus mission before it is approved to move toward the imaginary capture box underneath the space station, where European astronaut will grab it with the lab's Canadian robotic arm.
The Cygnus spacecraft extended its two solar array wings shortly after deployment from the Antares solid-fueled second stage, and the freighter's propulsion system pressurized as planned to prepare the vehicle for the first in a series of engine firings to reach the International Space Station.
"The solar arrays have deployed, and we're getting good power from them," Culbertson said. "The propulsion system has activated, and we're getting good stable control of the spacecraft, pointing at the sun, and getting ready to execute the maneuvers to get to the International Space Station in four days."
The first engine burn is scheduled for approximately 4 p.m. EDT (2000 GMT) to adjust the Cygnus spacecraft's orbit and set it up for its chase of the space station. "This was hard," Culbertson said. "It's difficult to get a rocket off the launch pad. There are a lot of things that have to come together no matter how many times you do it."
The flight is now entering a coast phase lasting approximately 98 seconds, in which the rocket will ascend to an altitude of 189 kilometers, or 117 miles. In the last few seconds of the ballistic coast, the Antares rocket will jettison its 12.8-foot-diameter payload fairing and an interstage adaptor around the second stage motor.
At T-minus 15 seconds, the two AJ26 first stage engines will swivel at the base of the rocket to ensure they can steer the launch vehicle in flight.
At T-minus 5 seconds, the transporter-erector-launcher will retract away from the rocket, leading to ignition of the AJ26 engines as clocks hit zero.
Liftoff will occur 2 seconds later after computers verify the engines are running normally.
At T-minus 3 minutes, 30 seconds, the automatic countdown sequence will begin. The first stage's propellant tanks will begin pressurizing at T-minus 2 minutes.
An Orbital Sciences spokesperson says the launch delay earlier this morning from 10:50 a.m. to 10:58 a.m. EDT was due to a regulator issue on the first stage fuel system.
Check out a timeline of key events during the launch.
Engineers will soon do final checks of the rocket's flight termination system and configuring that device for launch.
Here are some statistics on today's launch:
The tower will retract a few degrees away from the rocket in the final seconds of the countdown.
Officials are still optimistic the concern will be lifted in time for launch, and there are backup procedures in place to evacuate nearby public buildings to remove the threat of a blast damaging a building with occupants.
The tower will retract a few degrees away from the rocket in the final seconds of the countdown.
After chilldown begins at T-minus 30 minutes, the window will be limited to 10 minutes. After passing the T-minus 10 minute point, the launch window is again shortened to just 5 minutes.
The unmanned cargo hauler is comprised of two modules - a service and propulsion module built by Orbital Sciences and a pressurized logistics module built by Thales Alenia Space in Italy.
The spacecraft features 32 thrusters built by Aerojet Rocketdyne and solar panels provided by Dutch Space, a subsidiary of EADS Astrium based in the Netherlands.
Cygnus will extend its solar panels moments after deploying from the Antares second stage about 10 minutes after liftoff. Engineers expect get a signal from the spacecraft about a half-hour after launch that the panels have deployed.
Wallops regularly launches suborbital sounding rockets for scientific and engineering research purposes, and the facility has occasionally launched small satellites with Orbital Sciences Minotaur rockets.
The Virginia Commercial Space Flight Authority owns the Mid-Atlantic Regional Spaceport, which oversaw development of the launch pad used by Antares. The Commonwealth of Virginia paid for about $80 million of the $120 million cost of the launch pad, with most of the rest of the funding coming from the federal government.
Combined with the cost of the Antares hangar and a Minotaur rocket launch pad just south of the Antares facility, the MARS complex cost about $150 million.
The kerosene is stored at roughly room temperature and the liquid oxygen is chilled to minus 298 degrees Fahrenheit. The oxygen will slowly boil off during the countdown, and liquid oxygen continue flowing into the rocket until shortly before liftoff.
The first stage tanks are designed by Yuzhnoye and built by Yuzhmash in Ukraine based on heritage from the Zenit rocket. The liquid oxygen tank is positioned in the upper part of the 12.8-foot-diameter stage and the RP-1 tank is in the lower part of the stage.
The first stage's two AJ26 engines will consume the liquid propellant during a 3-minute, 50-second burn.
The Antares second stage, a Castor 30 motor built by ATK, is propelled by solid fuel already loaded into the rocket.
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The distance field overpressure rule addresses concerns that the blast of launch could damage nearby structures.
Chilldown of the liquid oxygen loading system is continuing as engineers prepare to power up the flight termination system for testing.
Coming in a few minutes will be testing of the rocket's telemetry links and flight termination system, which would be used to destroy the launcher if it flew off course.
Officials report no issues are being worked in the countdown at this point.
The Antares rocket was powered up early this morning and the launch team is going through a checklist of testing to ensure all systems are in good shape. The launch pad is also evacuated of all personnel at this time.
The launch team will soon begin the process of priming the plumbing on the launch facility for loading of super-cold liquid oxygen, which begins at about 9:20 a.m. EDT (1320 GMT).
Follow activities with this countdown timeline.
The mission will be the second launch of the Orbital Sciences Antares rocket after a successful test launch in April proved the two-stage rocket could deliver payloads into low Earth orbit.
Mike Pinkston, the Antares program director at Orbital, said engineers made very few changes to the design of the launch vehicle after the April mission.
The rocket's solid-fueled upper stage, provided by ATK, provided a bit less performance than anticipated, Pinkston said, adding it is difficult for engineers to predict how a solid rocket motor will perform in flight before testing it in the environment.
Pinkston said software engineers tweaked code in the Antares guidance computer to account for the performance data obtained in the April test flight.
Technicians also modified some of the umbilical connections between the Antares rocket and its Transporter/Erector/Launcher system, which services as a support tower during the countdown.
The call-to-stations for the engineers on the launch team is scheduled for 2:35 a.m. EDT (0635 GMT), with voice checks and opening of the prelaunch checklist scheduled for 3:05 a.m. EDT (0705 GMT).
Workers will clear the launch pad at about 4:20 a.m. EDT (0820 GMT), followed by vehicle power-up at 4:55 a.m. EDT (0855 GMT).
Chilldown of the Antares liquid oxygen loading system begins at 7:35 a.m. EDT (1135 GMT) in preparation for propellant loading at 9:20 a.m. EDT (1320 GMT).
A Cygnus spacecraft is mounted on top of the 131-foot-tall rocket, packed with more than 1,500 pounds of supplies destined for the orbiting space station.
It is a crucial demonstration flight for Orbital Sciences, which developed the Antares and Cygnus under a public-private partnership with NASA. After the completion of the demonstration mission, Orbital will begin a series of eight operational resupply flights under a $1.9 billion contract with the space agency.
Bill Wrobel, director of NASA's Wallops Flight Facility, gave formal approval to proceed with the launch earlier today.
The weather forecast calls for a 75 percent chance of favorable conditions, with scattered clouds at 2,500 feet, a temperature around 70 degrees Fahrenheit, and winds out of the east at 9 to 14 knots. The only concern with weather is the possibility of low clouds violating launch rules, according to Sarah Daugherty, Wallops test director.
Another meeting Tuesday of the Wallops Range Authority at NASA's Wallops Flight Facility will give final clearance to begin the countdown.
Liftoff of the 131-foot-tall rocket from launch pad 0A at the Mid-Atlantic Regional Spaceport is scheduled for precisely 10:50:12 a.m. EDT (1450:12 GMT), the opening of a 15-minute window timed for when the space station's flight path crosses over the launch pad on Virginia's Eastern Shore.
The preliminary weather forecast for Wednesday looks favorable.
"There is a 75 percent chance of favorable weather at the time of launch. Low clouds below 6,000 feet are the primary concern for a weather violation. If needed, multiple back-up launch opportunities are available through the end of September.
The 13-story rocket was rolled one mile Friday from its horizontal integration facility to launch pad 0A at the Mid-Atlantic Regional Spaceport, a complex leased and operated by the Virginia Commercial Space Flight Authority. The launch pad is located at NASA's Wallops Flight Facility on Virginia's Eastern Shore.
The launch was previously scheduled for Tuesday.
"The combination of yesterday's poor weather that delayed rollout of the rocket to the launch pad and a technical issue that was identified during a combined systems test held last night involving communications between ground equipment and the rocket's flight computer drove the decision to delay the launch," Orbital Sciences posted in an update on its website.
"After comprehensive inspection and testing this morning, the problem was found and turned out to be an inoperative cable, which is being replaced," Orbital posted on its website Saturday. "Orbital will repeat the combined systems test later today."
If the test goes well, the officials said they will press on toward a target launch date Wednesday.
The 15-minute launch window Wednesday opens at 10:50 a.m. EDT (1450 GMT), timed for when the ground track of the space station's orbit crosses over the launch pad in Virginia.
Affixed to a Transporter/Erector/Launcher system mounted to a wheeled Self Propelled Modular Transporter, the two-stage rocket left its processing hangar in the predawn hours Friday and rolled about a mile to the seaside launch pad.
Designed, manufactured and installed by Martinez & Turek Inc. and ATA Engineering, the Transporter/Erector/Launcher, or TEL, provides mechanical connections between the Antares rocket and ground systems. It also serves as an integration platform for the launcher inside the horizontal integration facility.
Once at the launch pad, the Antares rocket and its transporter were hoisted vertical by a hydraulic system and placed on the launch mount.
Orbital Sciences plans a launch readiness review Monday to discuss the status of launch preparations.
The one-day launch delay will not affect the arrival of the Cygnus resupply ship at the space station, which remains set for Sept. 22, according to NASA.
The flight is a demonstration mission under NASA's Commercial Orbital Transportation Services, or COTS, program. The COTS program is a public-private cost-sharing partnership between NASA and Orbital Sciences to develop the Antares rocket and Cygnus spacecraft.
NASA's other COTS partner, SpaceX, completed its demo flight to the space station in 2012 and is now executing a dozen operational logistics missions with its Falcon 9 rocket and Dragon cargo craft.
Once Orbital clears its test hurdles, the company will begin a series of eight operational missions under contract to NASA through 2017.
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