Orbital Sciences’ new Antares booster must remained shackled to Earth for at least another 24 hours, having succumbed to its second launch delay in three days. On Wednesday, a data umbilical cable linking the Transporter Erector Launcher (TEL) to the rocket’s second stage prematurely disconnected and prompted a scrub, just 12 minutes ahead of the scheduled liftoff. Today’s second attempt to despatch Antares on its long-awaited “A-ONE” maiden voyage from Pad 0A at the Mid-Atlantic Regional Spaceport (MARS) on Wallops Island, Va., was frustrated, not by a technical issue, but by unacceptable high-altitude winds. Following evaluations last Thursday, the launch team is ready for two back-to-back launch attempts this weekend and another try to get Antares into space will be made tomorrow (Sunday), with the window opening at 4:30 p.m. EDT.
Following the disappointing weather outlook on Wednesday, whose conditions remained iffy for much of the countdown and never peaked much above a 45-percent probability of being acceptable at T-zero, it seemed that the prospects would improve on Saturday. When the launch team received their ‘call to stations’ at approximately 9:00 a.m. EDT, it was hoped that the chance of weather violating today’s attempt would be as low as 10 percent. However, it was noted that an unusually strong jetstream was responsible for problematic upper-level winds at 35,000-40,000 feet. By late morning, these winds were classified as “marginal”, based on meteorological balloon data, although clouds in the Wallops area were expected to clear by the start of the two-hour launch window at 5:00 p.m.
Within the span of the window, managers refined the launch time at 5:10 p.m., to allow for additional balloon data to be received. According to AmericaSpace’s Launch Tracker, the decision to begin fueling Antares’ first stage with a refined form of rocket-grade kerosene (known as “RP-1”) and liquid oxygen was scheduled to begin 90 minutes ahead of the scheduled launch time, due to the time-limits associated with the boil-off of the propellants. “A delay in the fueling,” noted the Tracker, “will probably mean a retimed T-zero.”
With all eyes keenly focused on the weather, that is exactly what happened. At 3:40 p.m., just before fueling would have needed to begin in order to achieve a 5:10 p.m. liftoff, the launch time was postponed an additional hour into the window, to 6:10 p.m. At the same time, efforts to extend the range debris area to take into account the strong south-westerly winds were not approved by the Federal Aviation Administration. Ironically, all systems aboard the 133-foot-tall Antares – which represents Orbital’s first cryogenically-propelled rocket – continued to operate smoothly during this time. A minor glitch with a connection between the payload S-band transmitter and range tracking telemetry was quickly resolved and all systems were ready to go.
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.
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 Sunday, 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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