Orbital ATK’s continuing preparations to return its Antares rocket to flight operations has resulted in an updated preliminary launch date in the August timeframe. The launch – involving the OA-5 Cygnus spacecraft to the International Space Station (ISS) – requires static fire test data analysis to be completed, along with final trajectory shaping work.
It’s been 20 months since the loss of the Antares that was attempting to launch the CRS-3 Cygnus to the ISS. The vehicle exploded seconds into its launch from the Wallops Flight Facility in Virginia.
The two RD-181 engines replaced Aerojet AJ-26 engines that were used in the first Antares launches in 2013 and 2014.
The new vehicle configuration is designated as the Antares 200 series.
Cygnus flights to the ISS will use the new first stage coupled with Orbital ATK’s CASTOR 30XL solid motor as a second stage in the Antares 230 configuration.
The new Antares first stage was rolled out on May 12 to Pad-0A at the Mid-Atlantic Regional Spaceport in Virginia for a series of key tests towards its return.
This included a Static Fire test that was conducted at the end of May, notably on the core destined to launch on the OA-7 Cygnus mission. The goal is to shake out the new stage, allowing for any issues to be implemented on the OA-5 first stage ahead of its launch.
According to Orbital ATK, in response to questions from NASASpaceFlight.com – the data review into the Static Fire is currently ongoing.
“We are continuing to prepare for the upcoming launch of the Antares rocket and Cygnus spacecraft for the OA-5 cargo logistics mission to the International Space Station from NASA’s Wallops Flight Facility. Our Antares team recently completed a successful stage test and is wrapping up the test data analysis,” noted the company.
The question put to Orbital ATK was in relation to source information (L2) the launch was set to be delayed.
Additional information pointed to data on “vibrations” during the Static Fire test that could be deemed as a problem for the vehicle’s avionics. A “fix” was already understood to have been approved.
Orbital ATK, while admitting the launch is slipping from its early July launch date estimate to a date likely to be in the August timeframe, pointed to trajectory evaluations as a specific relation to the launch date deliberations.
“Final trajectory shaping work is also currently underway, which is likely to result in an updated launch schedule in the August timeframe,” added Orbital ATK.
A final launch date decision won’t be taken for a few weeks, which is understandable based on the need to negotiate a slot for Cygnus’ arrival in the Station’s busy Visiting Vehicle (VV) schedule.
“A final decision on the mission schedule, which takes into account the space station traffic schedule and cargo requirements, will be made in conjunction with NASA in the next several weeks.”
UPDATE: A launch NET date of August 22 has been selected.
As preparations continue for the OA-5 mission, the OA-6 Cygnus is enjoying her final days on orbit following the conclusion of her successful flight to the orbital outpost.
Cygnus was less impacted by the CRS-3 failure as she’s designed to be compatible with multiple launch vehicles, allowing Orbital ATK to contract with United Launch Alliance to launch two Cygnus missions – OA-4 and OA-6 – aboard the veteran Atlas V rocket from the Cape Canaveral Air Force Station in Florida in December 2015 and March 2016, respectively.
Following several months berthed to the Station, the OA-6 Cygnus was released this week. However, she still had several objectives to complete before what will be her fiery demise via a destructive re-entry.
That included Tuesday’s Spacecraft Fire Experiment, or Saffire-I experiment, which saw Cygnus controllers deliberately ignite a fire inside a specially-designed 3x3x5 foot tall module mounted inside Cygnus’ pressurized cargo volume. The test was deemed a success.
“Our Cygnus spacecraft for the OA-6 mission successfully undocked from the space station and hosted the Spacecraft Fire Experiment-I (Saffire),” added Orbital ATK. “The team is now performing the final OA-6 mission milestones.”
The successful mission is partly in thanks to ULA’s Centaur upper stage, which came to the rescue during the OA-6 Cygnus launch back in March.
The Atlas V booster shutdown several seconds ahead of schedule due to what has since been classed as a fault with the RD-180 Mixture Ratio Control Valve (MRCV) assembly.
The first stage was set to burn for four minutes and 15.5 seconds before its engine shut down.
However, the timing of engine shutdown was shown to be six seconds earlier than planned.
Following staging, the Centaur’s RL10C-1 engine entered its prestart phase. Ten seconds after stage separation, the Centaur engine ignited to begin a single burn that was pre-planned for a duration of thirteen minutes and 38 seconds.
However, this burn lasted over a minute longer, as Centaur worked to overcome the shortfall of the Atlas V’s first stage performance.
Centaur ably delivered Cygnus into the correct 230km orbit and into its correct RAAN (Right Ascension of the Ascending Node), which ultimately classed the mission as a success.
The Upper Stage’s extra push resulted in Cygnus being 300 km further downrange than expected at spacecraft separation.
On Wednesday, ULA updated the status of its investigation into the Atlas V’s underperformance, caused by “an anomalous propellant mixture ratio resulting in an early booster shutdown and degradation of first stage performance.”
Citing a robust system design, flight software, vehicle margins and propellant reserves, the underperformance did not impact on the successful deployment of the Cygnus into her correct orbit.
This was thanks to the Centaur upper stage “identifying the first stage performance shortfall and compensated with an extended burn to deliver Cygnus to the precise orbit, well within the required accuracy,” as noted by ULA.
The ULA engineering team, along with our engine supplier and several government customers, formed a review team that assessed all flight and operational data to determine direct and root causes and implemented the appropriate corrective actions for future flights.
“Thanks to the robust vehicle system design of Atlas V, the OA-6 mission was delivered successfully to its intended orbit and Cygnus completed its mission to the ISS,” noted Gary Wentz, ULA’s vice president of Human and Commercial Systems.
“ULA applied a rigorous anomaly review process to identify and implement all necessary corrective actions to ensure we continue to reliably deliver critical capabilities for our customers with 100 percent mission success.”
The review determined that at approximately T+222 seconds, an unexpected shift in fuel pressure differential across the RD-180 Mixture Ratio Control Valve (MRCV) and a reduction in fuel flow to the combustion chamber caused an oxidizer-rich mixture of propellants and a reduction in first stage performance.
The imbalanced propellant consumption rate resulted in depletion of the first stage oxidizer with significant fuel remaining at booster engine shutdown.
In mitigation of this becoming an issue in the future, ULA noted that the engine supplier has implemented a minor change to the MRCV assembly. This change has been validated via “engine hot-fire testing, extensive component and assembly level testing and analyses.”
The final and corrective action reviews, as well as flight clearance for the Atlas V MUOS-5 mission occurred on June 2. The Atlas V MUOS-5 launch is scheduled for June 24 from Space Launch Complex-41 at Cape Canaveral.
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