After over one and a half years worth of work, Orbital ATK is set to return their newly revamped and improved Antares rocket to flight, following the October 2014 mishap. Orbital ATK is currently targeting a May/June 2016 launch of the OA-5 flight for Antares’ Return To Flight mission.
Antares’ Return To Flight – Preparing for OA-5:
In what has been a major period of work for the company, Orbital ATK is nearing the finish line in terms of returning their Antares rocket to flight.
Currently headed toward a date of 31 May 2016 for the launch of the OA-5 Cygnus mission to the International Space Station (ISS), Antares Deputy Program Manager, Kurt Eberly, in an exclusive interview with NASASpaceflight.com, stated that NASA has indicated that the mission will likely move to the end of June due to ISS schedule constraints.
While the final considerations for the launch date occur in the coming weeks and months, Mr. Eberly stated that the company is continuing to process toward the 31 May launch date to be ready to go in case they are needed at that time.
Presently, all is going well with the conversion of Antares to its 230 variant — with RD-181 engines replacing the previous Aerojet AJ26 engines.
According to Mr. Eberly, “Things have been going very well. Anytime you have to put the hood up and change out the engines, that’s a major task”
Following the failure of Antares shortly after liftoff in October 2014 at the start of the Orb-3 mission, Orbital and soon-to-be-merged company ATK decided to introduce the Antares 230 version of the vehicle.
To this end, the company decided to replace the two AJ26 engines at the base of the Antares’ first stage with two RD-181 engines to provide increased reliability and thrust for the upgraded version of the rocket.
The RD-181s were chosen for a variety of reasons, as Mr. Eberly expanded on.
“For us, the RD-181s are ideal replacement engines because they use the same combustion cycle and same mixture ratio between propellants as the AJ26 engines did, and they’re the same size as the previous engines.”
This was especially important to Orbital ATK as it allowed engineers, during the Antares redesign, to keep the tanks of the first stage identical to the tanks used on the Antares 100 series.
Prior to acceptance for use on Antares 230, the RD-181 engines underwent an intensive certification process.
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That process, now complete according to Mr. Eberly, saw one engine fired seven times at its vendor before being disassembled to assess its post-fire configuration and condition.
Currently, there are four produced RD-181 engines, two flight sets, that have passed through acceptance, including a full-duration test firing.
During those full-duration firings, all four engines hit the power levels necessary for use on the first two Antares 230 flights, and all four engines have since been delivered to Wallops for integration to modified Antares 230 first stages.
At present, the first two of those engines have been mounted to an Antares first stage core that was modified at the Orbital ATK Antares integration site at the Mid-Atlantic Regional Spaceport (MARS).
This first stage has already passed its engine and feedline leak checks and is progressing through electrical engine testing as well as hydraulic, avionics, and commanding of the Thrust Vector Control system for the engines.
Once this is complete, the vehicle will be hooked up to flight avionics that will “trick the vehicle into flying and executing stage tests,” notes Mr. Eberly.
These tests will help verify the flight avionics performance packages prior to launch on the RTF mission.
After this, the first stage will be taken from the Horizontal Integration Facility (HIF) to Pad 0A at the MARS.
The stage will then be erected at the pad where a Wet Dress Rehearsal (WDR) will occur.
During this WDR, Antares’ first stage tanks will be completely loaded with propellant, the tanks pressurized to flight level, and the vehicle taken through all of the pre-launch countdown operations right up to but not including engine start.
“Once we do that, we’ll come back and do a hot fire test,” noted Mr. Eberly. “We’ll do the hot fire and look at all the information we’ve gathered from the lots of extra instrumentation we’ll have on this vehicle for the test.”
Once the hot fire – currently targeted for sometime in April – is complete, the first stage will be taken back to the HIF for post-hot fire examination.
Notably, this first stage will not be the one flown on the OA-5 mission.
That flight will use the second modified first stage which is currently at Wallops having just completed engine attachment operations.
Antares 230 – a more powerful vehicle:
All told, the Antares 230 series variant will provide a 25% net increase over the payload-to-orbit capability of the Antares 100 series.
This total increase comes specifically from a 13% higher thrust performance of the RD-181 engines over the AJ26 engines as well as a 10 second higher Specific Impulse (ISP) of the RD-181s over the AJ26s – which comes from higher pressure in the combustion chamber.
But this increased performance comes with a caveat.
“Our focus was to change as little as possible and get back flying,” noted Mr. Eberly. “Having these engines with higher thrust and a higher ISP is going to give us the higher performance, so we did not go after optimizing the core tanks or the structural capabilities of the core for the 230 series.
“Instead, we are going to fly a throttle notch at MaxQ.”
This means that when Antares 230 lifts off later this year, its two RD-181 engines will fire at 100% thrust at liftoff, throttle down at MaxQ – the region of higher dynamic loading – before throttling back to 100% until the rocket starts hitting its axial G force limit.
Impressively enough, the change from the AJ26 engines to the RD-181 engines did not require a huge modification effort at the launchpad itself.
“Fortunately, the Orb-3 mishap didn’t destroy structural elements at the pad. It was mainly the cross country piping that was destroyed,” states Mr. Eberly.
While all of the Orb-3 launch mishap pad damage has been repaired at this point, the modifications needed for the RD-181 engines focused on two specific areas, both of which were minor.
In all, the modifications revolved around the different services needed for the RD-181s, specifically the engine’s need for heated nitrogen to evacuate their combustion chambers of air prior to ignition.
For this modification, a heater panel was created to heat the nitrogen flow and feed it at the right pressure into the engines.
Likewise, the other main modification at the pad related to the RP-1 kerosene used as hydraulic fluid.
“For AJ26, we had accumulators that gave us the prelaunch pressures onboard the vehicle,” noted Mr. Eberly.
“The RD-181s do not have that. So we have to have a ground-pressurized RP source to serve the pressurized hydraulic fluid to provide pressure to the actuators pre-ignition.”
But perhaps most impressively, there was no need to modify any of the pad structures pertaining to the engines — flame deflector, water suppression systems, etc.
This was made possible by the fact that Orbital ATK was able to situate the RD-181s inside the core stage in just the right way to allow the nozzle exit plane to sit exactly where the nozzle exit plane of the AJ26 engines had been.
“The choice of these engines really allowed us to bypass a lot of issues with the interfaces at the pad,” noted Mr. Eberly.
Now, with the launchpad ready and Antares’ first stage ready for its slew of pad tests, Orbital ATK’s aim of returning their vehicle to flight this year is on track for accomplishment this summer.
(Images via NASA and Orbital ATK).