Despite ongoing engineering analysis with regard to the ammonia coolant loop malfunction aboard the International Space Station (ISS), Orbital Sciences Corp. continues to make steady progress toward its first dedicated Cygnus cargo mission (ORB-1), tracking an opening launch attempt at 9:19 p.m. EST on Thursday, 19 December. The launch window lasts just 5 minutes. Earlier today (Tuesday), the company—one of NASA’s two Commercial Resupply Services (CRS) partners—announced that it had rolled Cygnus’ giant Antares launch vehicle out to Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., but stressed that “We do not yet have a ‘Go/No Go’ decision for the launch” and added that “The rollout operation preserves that option for NASA in the event they are able to develop a plan that will allow the Cygnus spacecraft to rendezvous and berth with the ISS on 22 December.”
As noted in a recent AmericaSpace article, last Wednesday’s malfunction of one of two external ammonia coolant loops—whose pump module automatically shut down when it reached a pre-set temperature limit—has raised the likelihood of perhaps three EVAs by Expedition 38 astronauts Rick Mastracchio and Mike Hopkins, the first of which may occur as soon as Thursday, 19 December. Last week, ISS Mission Operations Integration Manager Kenny Todd deferred a firm “Go/No-Go” decision on the ORB-1 launch, until further information about the coolant loop issue was forthcoming. “There are some issues with redundancy right now,” he said, “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.”
Suspicion centered on the improper functionality of a regulating flow control valve inside the pump module as a possible root cause. Over the last few days, ground controllers have been attempting to position the valve in such a manner as to help maintain proper temperatures in the coolant loop, which could allow it to be re-integrated into the space station’s internal electronics network. In the station’s Quest airlock, Mastracchio, Hopkins, and fellow Expedition 38 crewmates Oleg Kotov and Koichi Wakata worked through the weekend on checks of their space suits and tools and reviewed procedures.
Should the ORB-1 mission be launched, as planned, on Thursday, it will cap a truly triumphant year for Orbital Sciences, which in December 2008 won a $1.9 billion contract from NASA to stage eight Cygnus cargo delivery missions and deliver 44,000 pounds (20,000 kg) of payloads and supplies to the ISS by 2016. Despite many engineering challenges, the company’s Antares rocket completed its maiden test flight on 21 April 2013, successfully lofting a mass simulator of the Cygnus spacecraft 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 to the station—designated “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. Cygnus 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 Cygnus spacecraft arrived at the MARS launch site on Wallops Island, Va., to begin processing for its mid-December liftoff. Originally scheduled to launch at 9:42 p.m. EST Wednesday, 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.
On Wednesday, 11 December, the coolant loop problem arose and Orbital announced that evening that it was “awaiting word from NASA on whether there will be a schedule impact on the ORB-1 mission.” It was anticipated the “late load” cargo would be placed aboard Cygnus on Saturday, 14 December, but at NASA’s direction this plan was moved 24 hours to the right. This correspondingly pushed the earliest available opportunity to launch ORB-1 back to no earlier than Thursday night. At length, on Sunday, 15 December, Orbital announced that it had received authorization from NASA to begin the late loading of about 210 pounds (95 kg) of time-sensitive cargo aboard Cygnus’ Pressurized Cargo Module (PCM). These items include 33 CubeSats, whose objectives range from enzyme behavior in microgravity to DNA mutation rates and from oil bubble formation to the behavior of groups of ants. This was followed by about 12 hours of payload closeouts, air purging in the PCM, final hatch closure, and leak checks. The Antares payload fairing was installed yesterday (Monday), ahead of today’s rollout to Pad 0A.
Antares’ twin Aerojet-developed AJ-26 first stage engines 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 had to struggle 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.
Assuming NASA remains happy to proceed with an on-time liftoff Thursday night, a Launch Readiness Review will occur Wednesday and this will enable Orbital managers and engineers to begin final preparations for the flight. About 3 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. “Cooling down of the equipment used to store and transfer the liquid oxygen is important,” noted AmericaSpace’s Launch Tracker in the build-up to the ORB-D launch campaign in September, “as the propellant boils at a temperature of -297F and the shock of the supercooled liquid hitting warm valves and lines could cause severe thermal shock and fracture.”
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 chilling down 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 anticipated at 9:19 p.m. EST Thursday, 19 December. 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 9:22 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 three-day rendezvous profile, which requires several orbit-raising and “phasing” maneuvers to bring it into the neighborhood of the ISS on Sunday, 22 December. 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 the 57.7-foot-long (17.6-meter) Canadarm2 mechanical arm. It will then be berthed onto the “nadir” port of the Harmony node. Current plans call for Cygnus to remain berthed at the ISS until mid-January 2014, at which time it will be robotically detached and later commanded to execute a destructive re-entry into the upper atmosphere.
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 earlier this year. As part of AmericaSpace’s coverage of the important ORB-1 mission, tomorrow’s article will focus on Fullerton’s life and career and how the voyage bearing his name will contribute to the future of space exploration.Missions » ISS » COTS » CYGNUS » ORB-1 »