Fittingly for a veteran rocket and a veteran spacecraft, traveling to visit a group of veteran astronauts and cosmonauts aboard a veteran space station—including the first Marine Corps skipper of the multi-national orbiting outpost—it was hoped that the OA-8 Cygnus cargo mission would coincide with Veterans Day, by launching on Saturday, 11 November. As well as honoring the fallen from World War I, and marking 99 years to the date since the official end of hostilities on 11 November 1918, Veterans Day reminds us of the respect owed to our military service personnel.
Alas, it was not to be. In spite of a near-perfect countdown, yesterday’s opening launch attempt was scrubbed in the final minutes, when an aircraft strayed into the launch danger zone. Liftoff was correspondingly rescheduled for 7:14 a.m. EST on Sunday, 12 November, and proceeded without incident. Orbital ATK’s 133-foot-tall (40.5-meter) Antares 230 booster rose from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., delivering Cygnus perfectly into low-Earth orbit. Rendezvous and berthing with the International Space Station (ISS) is currently scheduled for Monday morning.
“Today’s successful launch of the OA-8 Cygnus on our Antares launch vehicle once again demonstrates the reliability of Orbital ATK’s hardware along with our commitment to deliver critical cargo to astronauts on the International Space Station,” said Frank Culbertson, President of Orbital ATK’s Space Systems Group. “Soon, Cygnus will rendezvous with the space station to deliver valuable scientific experiments, hardware and crew supplies to the orbiting platform. On this mission, Cygnus will again display its flexibility as an in-orbit science platform by supporting experiments to be performed inside the cargo module while attached to the space station. We are proud to dedicate this mission to Apollo astronaut Gene Cernan and his family and look forward to celebrating the OA-8 contributions to science in his name.”
It was the seventh outing and sixth successful launch for Antares, which represents Orbital ATK’s first large, homegrown liquid-fueled rocket. Originally developed under the nomenclature of “Taurus”, the vehicle underwent a lengthy and tortured development, before flying its maiden voyage in April 2013. Antares 100-series boosters went on to deliver three Cygnuses to successive ISS crews between September 2013 and July 2014, but suffered a catastrophic explosion, seconds after liftoff, on 28 October 2014. By that time, problems with its Soviet-era AJ-26 engines were already well known and efforts to upgrade them were underway. In December 2014, it was announced that the enhanced Antares 230 booster would utilize a pair of RD-181 engines at the base of its first stage.
A lengthy campaign of repairs to the heavily damaged Pad 0A and Antares upgrades pushed the booster’s return to flight well in 2016. In order to limit the impact on Orbital ATK’s $1.9 billion Commercial Resupply Services (CRS) commitment to NASA, United Launch Alliance (ULA) was contracted to fly at least several Cygnuses atop its Atlas V rocket. In the meantime, the upgraded Antares 230—which includes new RD-181 first-stage engines and an enhanced Castor-30XL upper-stage engine—drew nearer to a return to flight. In May 2016, the RD-181 engines were static-fired at Pad 0A without incident and on 17 October an Antares 230 delivered the OA-5 Cygnus safely into orbit.
The OA-8 mission was originally targeted to fly as early as September 2017, but was moved at NASA’s request, as the visiting-vehicle manifest morphed throughout the year. The Cygnus Pressurized Cargo Module (PCM) was delivered to Wallops in late June, followed by its Service Module in early October. The two components were mated to form a spacecraft which stands 15.9 feet (4.86 meters) tall and 10.1 feet (3.07 meters) in diameter. Both were subsequently loaded aboard the Antares 230, which rolled horizontally out to Pad 0A last week. Early Saturday, engineers set to work fueling the booster with a combination of liquid oxygen and a highly refined form of rocket-grade kerosene, known as “RP-1”.
Weather conditions were expected to be chilly for Saturday’s opening launch attempt. “Our air temperature constraint for #Antares is 20 degrees F, so we do not anticipate any issues,” Orbital ATK tweeted Friday. “We currently have a less than 5% Probability of Violation (POV) for Saturday’s launch.” As the weekend dawned, this had improved to 100% favorable.
Orbital ATK’s Antares and Cygnus flight controllers came to their stations in the small hours to commence the power-up of the vehicle and chilling of the liquid oxygen loading systems with liquid nitrogen. The rocket’s Flight Termination System (FTS)—tasked with destroying Antares in the event of a major malfunction during ascent—completed its final checkout and the countdown entered a 20-minute-long built-in hold. Emerging from the hold, the launch team received a “Go” to begin cryogenic tanking.
Tanking was critically timed to commence about 90 minutes before T-0, a little after 6 a.m. EST, due to temporal limits associated with the rapid boil-off of the cryogens. A final poll of flight controllers occurred in two phases and liquid oxygen fueling concluded at T-15 minutes, by which time all of Antares’ propellant tanks had attained “Flight Ready” levels. Shortly afterwards, the vehicle transferred to Internal Power and at T-11 minutes the Transporter-Erector-Launcher (TEL) “strongback” was armed to permit it to execute a rapid retraction at T-0.
Unlike several previous Cygnus missions launched atop ULA’s Atlas V, which were able to benefit from a longer, 30-minute “window”, the more restricted operational flexibility of Antares tied it to a standard five-minute opportunity between 7:37 and 7:42 a.m. EST. However, in the final minutes, an unauthorized aircraft strayed into the launch danger area, forcing a scrub for the day. “We were working no issues until an aircraft flew into restricted airspace,” Orbital ATK tweeted at 7:54 a.m. “We are currently de-tanking and will be ready to go tomorrow morning.” It was later revealed that the small aircraft was flying at an altitude of about 500 feet (150 meters), approximately six miles (9.6 km) offshore.
Sunday’s revised attempt proceeded with similar smoothness, tracking a T-0 at 7:14 a.m. EST. With three minutes and 30 seconds remaining on the countdown clock, the “Terminal Count” was initiated and Antares’ autosequencer assumed primary control of vehicle critical functions, commanding all events up until the ignition of the twin RD-181 engines at T-0. During this period, the OA-8 Cygnus spacecraft transitioned from ground-support utilities onto internal battery power, until such time as its solar arrays were deployed in orbit.
Antares’ engines roared to life in the early morning gloom, ramping up to a combined thrust of 937,000 pounds (425,000 kg). This represents a 12.5-percent performance hike over the old AJ-26 engine suite. The booster rose swiftly, clearing Pad 0A and commencing its combined pitch and roll program maneuver to establish itself onto the proper flight azimuth to insert the OA-8 Cygnus into low-Earth orbit. Maximum aerodynamic turbulence on the vehicle’s airframe was encountered about 80 seconds into the ascent. All told, the first stage and the RD-181 engines boosted Antares for 3.5 minutes, burning around 527,500 pounds (239,280 kg) of liquid oxygen and RP-1.
Following shutdown of the engines, the 90.5-foot-long (27.6-meter) first stage was jettisoned, exposing the spacecraft and its attached Castor-30XL upper stage to continue the journey into low-Earth orbit. Tonight’s launch was the second outing of the Castor-30XL, a solid-fueled motor, which measures 19.7 feet (6 meters) long and 7.7 feet (2.3 meters) in diameter and weighs 58,000 pounds (26,300 kg). This burned for the next 2.5 minutes to deliver Cygnus to an orbital “slot” at an altitude of 121 miles (195 km), inclined 51.6 degrees to the equator. The Castor-30XL was then shut down and Cygnus separated into free flight, exactly 546 seconds after departing Wallops.
The spacecraft will now spend two days in transit to reach the space station. Early Tuesday, European Space Agency (ESA) astronaut Paolo Nespoli, backed-up by Expedition 53 Commander Randy Bresnik, will grapple the OA-8 Cygnus with the 57.7-foot-long (17.6-meter) Canadarm2 and berth it at the Earth-facing (or “nadir”) port of the Unity node. All told, Cygnus is carrying an estimated 7,385 pounds (3,350 kg) of payloads, supplies and equipment into orbit.
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