Engineers at SpaceX’s Rocket Development and Test Facility in McGregor, Texas are continuing to conduct a series of firings of the company’s upgraded Falcon 9 v.1.1 launch vehicle – which is scheduled to debut this summer. Testing on the core stage – with its new Merlin 1D engines – has proven to be challenging, due to a number of aborted firings.

Falcon 9 v1.1:

SpaceX have successfully flown the Falcon 9 v1.0 – powered by nine SpaceX Merlin 1C engines arranged in a “tic-tac-toe” pattern – via the first five F9 launches, including four launches of the Dragon spacecraft – three of which resulted in a successful mission to the International Space Station (ISS).

The upgraded Falcon 9 v1.1 will utilize a longer first stage, powered by nine Merlin 1D engines arranged in an “octagonal” pattern. The additional performance from the Merlin 1D’s will increase the payload capability to over 29,000 pounds to Low Earth Orbit (LEO).

(*Falcon 9 V1.0 vs. V1.1 image left is Photoshopped as to what the change in configuration may look like*)

The plan to upgrade the Merlin engine related not only to the vast improvement in performance, but also – according to SpaceX – the reliability and manufacturability, with the engines also enabling the company’s aspirations with the fully reusable Falcon 9 (F9-R) and their Falcon Heavy.

Essentially, the Falcon 9 v1.1 is the same vehicle as the F9-R, minus the landing legs – currently being tested via the Grasshopper program – and other modifications that will eventually be installed on the vehicle. UPDATE: The Grasshopper enjoyed a huge 325 meter leap into the air on Friday, before successfully landing after nearly 70 seconds in the air.

SpaceX began live testing of the Merlin 1D powerpack in 2011, achieving a full mission duration firing and multiple restarts at target thrust and specific impulse (Isp). During the 2012 series of testing, the engine fired for 185 seconds with 147,000 pounds of thrust, the full duration and power required for a Falcon 9 rocket launch.

By March of this year, SpaceX announced the completion of a 28-test qualification program, with the Merlin 1D accumulating 1,970 seconds of total test time, the equivalent run time of over 10 full mission durations.

However, test firings of all nine Merlin 1D’s together on the test stand at McGregor have yet to result in a full first stage burn duration, for various reasons.

According to L2 information, a May 31 attempt to fire the first stage on the test stand was aborted at just after the first-stage ignitor – a pyrophoric mixture of triethylaluminum-triethylborane (TEA-TEB) – was initiated. The reason for the abort was due to one of the Merlin 1D’s Gas Generator’s exceeding a conservatively-set limit.

Following a recalibration of the limitations, another attempt took place the following day (June 1), this time resulting in all nine engines coming to life, before aborting 10 seconds into the test due to an issue with a Gas Generator inlet temperature.

SpaceX engineers then spent a few days changing out and repairing components damaged in the aborted firing, including three chamber walls. However, it was also noted that eight of the engines are classed as non-flight hardware, and as a result are less robust than the flight version of the Merlin 1D.

The next test firing resulted in the longest duration burn so far, with the stage firing for a total duration of 112 seconds out of a planned 180 seconds. This time the abort was caused by an over-temperature alarm at the top LOX dome, after the stage – which is filled with hot helium taken from the engines’ heat exchangers – was evidently exceeding temperature limitations.

Surprisingly, a video was published by SpaceX CEO and Chief Designer Elon Musk, showed the test firing taking place, along with the abort – mixed in with some choice words from observers within ear shot of the camera, before an edited version of the video was reuploaded.

While sparks were observed to be coming from the aft during the abort, L2 source information noted they did not originate from the engines, but from the heat shields around the engines and the octaweb structure.

This was in part related to the thermal environment at the base of the stage, which is more intense during ground testing than it would be during an actual ascent – the former resulting in a larger recirculation zone.

Another test firing then took place on June 13. However, the firing was again aborted, this time at the T+70 second mark, due to a “fire” in engine bay 9. The engine – which is located in the center position of the new arrangement – will be replaced, allowing for inspections ahead of another test fire attempt in the coming days. SpaceX did not immedaitely respond to requests for further information.

A successful test will be key for several of SpaceX’s future ambitions, not least their upcoming increase in launch frequency, with the next Falcon 9 – the debut of the v1.1 – set to loft Canada’s space weather satellite, CASSIOPE, out of Vandenberg Air Force Base. This mission has officially slipped to August, with the likelihood it will be re-targeted to September.

Focus will then switch to Cape Canaveral, with two satellite missions, the first carrying SES-8, to be followed by the Thaicom 6 launch.

In order to be in a launch stance, the SpaceX team have been working several issues, ranging from the Second Stage Merlin VacD engine nozzle, to the new 43×17 foot diameter fairing that will debut during the CASSIOPE mission.

It was noted (L2) that during testing at NASA Plum Brook Station test facility, the qualification fairing unit failed at 99 percent of maximum load, due to a small amount of debonding between separate components at the interface between the fairing and payload adapter.

However, once all the issues are resolved, SpaceX should be able to hit the ground running, with L2 information noting a large amount of completed – or almost-completed – Merlin 1Ds and Merlin VacD engines ready, along with enough tanks, fairings, interstages, and octawebs for numerous upcoming launches.

Ironing out the issues on the ground is always the best solution for any rocket, the very reason the motto “this is why we test” having been cited by engineers ever since the early days of the rocket business.

(Images: via SpaceX)