Two days after a disappointing scrub, late in the countdown for its “A-ONE” maiden voyage, the Antares booster stands ready for a second launch attempt from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., at the weekend. On Wednesday afternoon, at 4:48 p.m. EDT – a mere 12 minutes ahead of the scheduled liftoff time – Orbital Sciences Corp. flight controllers scrubbed the attempt after a data umbilical linking the Transporter Erector Launcher (TEL) to the rocket’s second stage had prematurely disconnected. Orbital’s Executive Vice President Frank Culbertson, who serves as Mission Director for the A-ONE flight, described the issue as “fairly straightforward” to resolve and engineers are presently pushing towards Saturday 20 April at 5:00 p.m. for the next attempt.
Investigations after the scrub indicated that two factors were to blame for the premature disconnect: a slight hydraulic movement in the TEL and insufficient slack in the umbilical itself to allow for this movement. “Neither issue alone would have caused the umbilical disconnect,” Orbital explained on its website, but added that “the combination resulted in the anomaly.” Yesterday afternoon (Thursday), the Mission Management Team – led by Culbertson, a former astronaut – met to evaluate predicted poor weather forecasts on 19 April and optimum schedules to provide for a sufficiently rested workforce in time for two back-to-back launch attempts on Saturday and, if necessary, Sunday 21 April. Weather conditions at Wallops, which remained at less than 50-percent-acceptable for most of Wednesday’s countdown, are expected to improve by the weekend.
“The good news is that this is a simple adjustment to the external support systems,” said Culbertson. “Given that this is a first run for the rocket and the first-time use of a new launch facility, the fact that all systems were performing as planned while the team proceeded through the pre-launch checklists is very encouraging. It speaks volumes about the quality of the work done by this team and our partners.”
As described in AmericaSpace’s A-ONE preview article, the first flight of this new rocket will come at the end of a long and difficult road for Orbital Sciences, the Dulles, Va.-based aerospace company, which in December 2008 won a $1.9 billion slice of NASA’s Commercial Resupply Services (CRS) pie. The provisions of this contract require Orbital to transport upwards of 44,000 pounds of equipment, payloads and supplies to the International Space Station aboard eight missions of its Antares-boosted Cygnus cargo craft by 2016. However, efforts to configure the MARS site on Wallops Island for Antares operations have been mired with technical difficulty. As part of the redevelopment of the site, Pad 0A was completely demolished and a new complex was assembled with kerosene and liquid oxygen tankage for Antares, which is Orbital’s first cryogenically-powered rocket. Problems with the cryogenic handling equipment and the completion of MARS have already conspired to delay the A-ONE mission by over a year.
Orbital remains upbeat about the situation, however, and a successful launch of A-ONE on Saturday may still place the company in a strong position to attempt an inaugural demo mission of the Cygnus craft to the space station “around mid-year”, with June apparently the preferred month. That flight will follow a rendezvous profile not dissimilar to the one followed by CRS competitor SpaceX’s Dragon ships: completing a series of incremental steps, over a two-day period, to bring it within range of the station’s 57-foot-long Canadarm2 robotic arm for grappling and berthing onto the Harmony node. Orbital’s current manifest shows an ambitious 2013 schedule for Antares: following the A-ONE launch, the Commercial Orbital Transportation Services (COTS) demo to the space station will occur in the summer, with the first dedicated CRS mission tentatively slated for September and, perhaps, CRS-2 in December.
Despite its difficulties, Antares has stepped smartly through its pre-launch checks. A successful hot-fire test of the twin AJ-26 first-stage engines was completed on 22 February and the 133-foot-tall booster was rolled from its assembly building to Pad 0A – a one-mile journey – and raised to the vertical position by the TEL on 6 April. Wednesday’s launch attempt dawned smoothly, culminating in a ‘call to stations’ of all personnel at 8:45 a.m. EDT, but the weather remained iffy throughout the morning and afternoon, with low and broken cloud ceilings causing the likelihood of acceptable conditions at T-0 to be placed at a mere 45 percent.
As Wednesday morning wore into the afternoon, the situation remained balanced on a knife-edge, although Orbital managers elected to proceed and vehicle and payload avionics were powered-up and transferred to internal power. At 3:30 p.m. final polling led to a decision to press on with fueling Antares’ first stage with a rocket-grade form of kerosene (known as ‘RP-1’), followed shortly afterwards by the loading of liquid oxygen. The launch window, which had already been adjusted to 5:00-7:00 p.m., was shortened to occur within a 10-minute block at the start of this period. By 4:00 p.m., the propellant tanks for Antares’ twin AJ-26 first-stage engines were fully-fueled and weather conditions had improved slightly. The premature separation of an umbilical from the rocket occurred at 4:44:20 p.m., at which point the final ‘chilldown’ of the vehicle’s first-stage engines with super-cold helium was underway and all other systems were classified as normal. The scrub was confirmed at 4:48 p.m.
Aboard Antares for the A-ONE mission is a full-size Cygnus ‘mass simulator’, weighing 8,400 pounds, which will be instrumented to gather data on the launch, ascent and orbital flight environments, preparatory to the first flight of the cargo ship to the ISS. The mass simulator – which measures 16.5 feet long and 9.5 feet wide – carries 22 accelerometers, 12 digital thermometers, 24 thermacouples, 12 strain gauges and two microphones. Additionally, four tiny ‘picosatellites’ will be deployed from a dispenser. Three of these have been provided by NASA’s Ames Research Center in Moffett Field, Calif., and are designed to demonstrate the use of smartphones as CubeSat avionics. (They are named Alexander, Graham and Bell, in honor of the Scottish-born inventor of the world’s first practical telephone.) The fourth payload, called Dove-1, is an amateur-radio satellite.
Assuming A-ONE proceeds to a successful launch on Saturday, the countdown will follow an almost-identical pattern to that followed for Wednesday’s scrubbed attempt. At T-3 minutes and 30 seconds, the terminal count will get underway, with the transfer of command to the vehicle’s autosequencer. Ignition of Antares’ twin AJ-26 first-stage engines will commence at T-2 seconds, with computer-controlled health checks conducted as they ramp up to full power. Each of these Aerojet-built powerplants produces a total sea-level thrust of 338,000 pounds. The engines were developed by the Soviet Union, as part of the ill-fated N-1 lunar rocket, and Aerojet purchased 36 of them from Russia in the mid-1990s and added modern electronics and instrumentation. Despite a kerosene fire in June 2011, caused by stress-corrosion cracks in the 40-year-old metal, the performance of the engines on the test stand has been encouraging so far.
Six seconds after liftoff, Antares will clear the TEL tower and establish itself onto a launch azimuth of 107.8 degrees. The AJ-26s will burn for almost four minutes, shutting down at an altitude of 66 miles. Five seconds will elapse before the separation of the first stage, after which the vehicle will coast for almost two minutes, before the jettisoning of the bullet-like payload fairing and ignition of the Castor-30A second-stage engine at T+328 seconds. By this point, Antares will have reached an altitude of 117 miles. The Castor-30A – a solid-fueled engine, built by Alliant TechSystems, with a maximum thrust of 89,000 pounds – will burn for more than two and a half minutes, providing the final impulse to achieve a low-Earth orbit of 155-186 miles, inclined 51.6 degrees to the equator. Finally, at T+603 seconds, the Cygnus mass simulator will separate from the vehicle. Unlike SpaceX’s Dragon, the Cygnus is not designed to survive re-entry and the simulator will burn up in the atmosphere.
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