Three weeks later than originally planned, and after a 24-hour delay due to extreme solar activity, Orbital Sciences Corp. stands ready again to launch its first dedicated Cygnus mission to resupply the International Space Station. Liftoff from the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., from which Cygnus’ Antares rocket will begin its journey, is scheduled for 1:07 p.m. EST.
The launch will kick off a month-long mission to the ISS, which will deliver around 2,800 pounds (1,300 kg) of supplies to the station’s Expedition 38 crew. Thursday’s scheduled flight, designated “ORB-1,” has been a long time in the planning. As part of its Commercial Orbital Transportation Services (COTS) commitment to NASA, Orbital Sciences was required to conduct a full-up Cygnus Demonstration mission (ORB-D) to the ISS, which it triumphantly completed last September-October. The success of this mission cleared the way for the company to set its feet firmly on the road to stage eight dedicated Cygnus cargo flights (ORB-1 through 8) by 2016, under the provisions of a $1.9 billion contract signed with NASA back in December 2008.
Antares’ twin AJ-26 first stage engines, developed by Aerojet, can trace their heritage back to the Soviet era, having been purchased from Russia in the mid-1990s as part of a consignment of 36 powerplants originally conceived for the ill-fated N-1 lunar rocket. Powered by liquid oxygen and rocket-grade kerosene (known as “RP-1″), they have been extensively upgraded, and at the instant of liftoff each engine produces a sea-level thrust of 338,000 pounds (153,300 kg). Despite a handful of problems, including stress corrosion of the 40-year-old metal, the engines performed generally well on the test stand, but Orbital also struggled with the development of the new MARS launch site and experienced difficulties with the construction of new kerosene and liquid oxygen tankage. These conspired to delay the inaugural test launch of Antares from early 2012 until April 2013.
The last 12 months have proven a banner year for Orbital. Despite many engineering challenges, the company’s Antares rocket completed its maiden test flight on 21 April 2013, successfully lofting a mass simulator of Cygnus into orbit and providing a close analog for the opening minutes of a “real” ISS mission. Five months later, on 18 September, the Demonstration mission, ORB-D, was launched into orbit. Although technical difficulties were encountered during the early rendezvous phase, Cygnus was berthed perfectly at the “nadir” (or Earth-facing) port of the space station’s Harmony node on 29 September. The cargo ship spent three weeks attached to the ISS, before being unberthed on 22 October and commanded to perform a destructive re-entry into the upper atmosphere.
Fittingly, on the very day that ORB-D departed the ISS, the service module for the ORB-1 mission arrived at the MARS launch site on Wallops Island, Va., to begin processing for its mid-December liftoff. Originally scheduled to launch on 18 December, preparations proceeded without incident, and on 9 December the Antares booster was lifted onto its support structure, known as the Transporter/Erector/Launcher (TEL), ahead of rollout from the Horizontal Integration Facility (HIF) to Pad 0A. Over the next two days, Cygnus was mated with the booster and a complete launch sequence, known as “Flight Sim 2,” was conducted to ensure that the combined stack operated as expected.
Then, on 11 December, the starboard pump module on one of the space station’s external ammonia coolant loops automatically shut down when it reached pre-set temperature limits. In spite of the looming likelihood of contingency EVAs to replace the failed pump, Orbital pressed on with its launch preparations, whilst “awaiting word from NASA on whether there will be a schedule impact on the ORB-1 mission.” To preserve its options, NASA directed Orbital to postpone by 24 hours its “late loading” of time-sensitive cargo aboard Cygnus until 15 December, thereby shifting the opening launch date to the 19th. This proceeded without incident, and on 17 December the 133-foot-tall (40-meter) Antares rocket, with Cygnus aboard, was transferred from the Horizontal Integration Facility (HIF) to Pad 0A.
However, with ISS program managers acutely aware of the need to have the station in the best possible position to support the arrival of a Visiting Vehicle, it was ultimately decided to press on with a series of contingency EVAs by Expedition 38 astronauts Rick Mastracchio and Mike Hopkins during Christmas week and postpone ORB-1 until January. “There are some issues with redundancy right now,” said ISS Mission Operations Integration Manager Kenny Todd, “that when you get into a situation where you need to bring up another visiting vehicle, you want to make sure you’re in the best possible position. For that reason, we have Launch Commit Criteria and that criteria is in place to ensure that the systems are at the right level of redundancy and operating properly. Based on that criteria, there are a few of those commit criteria that we cannot meet.”
Working swiftly, on 21 December Mastracchio and Hopkins removed the failed pump during a 5.5-hour EVA and successfully installed a replacement on a mammoth 7.5-hour excursion on Christmas Eve. By this time, NASA and Orbital had agreed to launch ORB-1 no earlier than 7 January, with rendezvous and grappling by the space station’s 57.7-foot (17.6-meter) Canadarm2 robotic arm anticipated on 10 January. Antares was removed from Pad 0A and returned to the HIF, where its time-sensitive payloads were removed to be “refreshed” by their provider. On Friday, 3 January, Orbital announced that it would reschedule the launch until the 8th, or more likely the 9th, “due to the extreme cold temperatures that are forecasted … coupled with likely precipitation events predicted for Sunday night and Monday morning.” Antares and Cygnus were returned to the pad on Sunday, 5 January.
About three hours ahead of launch, all personnel will be cleared from Pad 0A and the process of chilling down the Ground Support Equipment will get underway. Shortly afterward, Antares’ ordnance—including pyrotechnics to separate various components of the vehicle during flight—will be enabled, and at about T-2 hours the cooling of the liquid oxygen transfer lines will commence, ahead of loading propellants into the first stage tanks. Forty-five minutes before launch, the avionics system will be loaded with the flight software to guide its ascent. Propellant loading aboard Antares is timed to begin at about T-90 minutes, due to time limits associated with the rapid boil-off of the cryogenics. This should produce a state with all propellant levels declared to be “Flight Ready,” and the liquid oxygen will remain in a “topping off” mode, being continuously replenished until just before liftoff. Following a final “Go/No-Go” poll of the launch team, Antares and Cygnus systems will be transferred to internal power and the TEL will be armed to execute a rapid retraction at the moment of launch.
At T-5 minutes, the Flight Termination System will be armed, and at T-3 minutes and 30 seconds the Terminal Count will get underway, with Antares’ on-board autosequencer now in primary control of all vehicle critical functions. These will include the final pressurization of the first-stage fuel tanks and the gimbaling of the two AJ-26 engines. Under computer command, the engines will ignite at T-2 seconds, ramping up to full power, with liftoff at 1:32 p.m. EST Wednesday. Seconds after clearing the tower, Antares will execute a pitch and roll program maneuver to establish itself onto the proper flight azimuth for insertion into a low-Earth orbit, inclined 51.6 degrees to the equator.
Maximum aerodynamic turbulence (known as “Max Q”) will be encountered about 80 seconds into the flight, and the AJ-26 engines will continue to burn hot and hard until they finally shut down about 4 minutes after launch. At an altitude of about 70 miles (110 km), and traveling in excess of 10,000 mph (16,000 km/h), the first stage will separate at 1:35 p.m. EST. This will leave the second stage and Cygnus to coast for two minutes, prior to jettisoning the bullet-like payload shroud. Ignition of the second stage’s solid-fueled Castor-30B engine—making its first flight on this launch—will occur soon afterward to inject Cygnus into low-Earth orbit. The cargo ship will separate from the second stage about 10 minutes after launch.
Cygnus will then embark on a four-day rendezvous profile, which requires several orbit-raising and “phasing” maneuvers to bring it into the neighborhood of the ISS on Sunday, 12 January. In a manner not dissimilar to September’s ORB-D mission, the ORB-1 profile will see Cygnus showcasing its ability to “hold” position at various distances, before entering the Keep-Out Sphere—a virtual exclusion zone, extending about 660 feet (200 meters) around the space station to prevent a collision—and being grappled by Canadarm2. Under the control of Expedition 38 crewmen Mike Hopkins, Koichi Wakata, and Rick Mastracchio, it will be berthed onto the “nadir” port of the Harmony node. Current plans call for Cygnus to remain berthed at the ISS until 30/31 January, at which time it will be robotically detached and later commanded to execute a destructive re-entry into the upper atmosphere. In so doing, it will dispose of about 2,200 pounds (1,000 kg) of waste material.
Like September’s ORB-D mission, which was named for former Orbital executive G. David Low, the upcoming flight of ORB-1 pays tribute to another shining light in the company’s fortunes. It will bear the name “Spaceship C. Gordon Fullerton” to honor the former shuttle astronaut and research pilot who died last year. Assuming a successful ORB-1 mission, Orbital plans two further Cygnus flights in 2014, with ORB-2 scheduled for May and ORB-3 for October.
This article was authored by AmericaSpace writers Ben Evans and Mike Killian.
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