SpaceX joy at Merlin 1D test – Orbital fire up their AJ-26 engine

by Chris Bergin

Two loud rumbles in the south of the United States marked two milestones for the country’s drive to regain its space flight independence, as SpaceX and Orbital both fired their new engines. SpaceX’s Merlin 1D rumbled for a full mission duration firing, while Orbital’s AJ-26 continued its testing ahead of its debut on their Antares launch vehicle.

SpaceX Merlin 1D:

SpaceX’s Falcon 9 currently employs nine “SpaceX designed and built” Merlin main engines on the First Stage – sporting a single shaft. propellent fed, dual impeller turbo-pump, operating on a gas generator cycle which also provides the high pressure kerosene for the hydraulic actuators, which then recycles into the low pressure inlet.

The turbo-pump also provides roll control by actuating the turbine exhaust nozzle on the single second stage MVac engine.

With three successful Falcon 9 launches now in the bag, SpaceX are looking to work into their upgraded engine into the Falcon 9 manifest – with F9 Flight 6 in 2013 the likely debut – providing a vast improvement in performance, reliability and manufacturability, all of which could provide a timely boost to aiding the potential for success for the fully reusable Falcon 9 and their Falcon Heavy.

“Increased reliability: Simplified design by eliminating components and sub-assemblies. Increased fatigue life. Increased chamber and nozzle thermal margins,” noted SpaceX in listing the improvements in work for the Merlin 1D, during an interview with

“Improved Performance: Thrust increased from 95,000 lbf (sea level) to 140,000 lbf (sea level). Added throttle capability for range from 70-100 percent. Currently, it is necessary to shut off two engines during ascent. The Merlin 1D will make it possible to throttle all engines. Structure was removed from the engine to make it lighter.

“Improved Manufacturability: Simplified design to use lower cost manufacturing techniques. Reduced touch labor and parts count. Increased in-house production at SpaceX.”

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During the testing of the Merlin 1D at SpaceX’s rocket development facility in McGregor, Texas, the engine achieved a full mission duration firing and multiple restarts at target thrust and specific impulse (Isp).

The engine firing was for 185 seconds with 147,000 pounds of thrust, the full duration and power required for a Falcon 9 rocket launch.

The extra power and multiple restart elements are major steps towards achieving the highly complex task of making Falcon 9 reusable, a vehicle known as F9r or Grasshopper.

Realizing the goal of returning the Falcon 9 to the launch site for reuse would involve the entire first stage rotating 180 degrees via Reaction Control System (RCS) thrusters – following staging – before reigniting three of its nine engines to “boost back” the near-empty stage back to the launch site.

Descending back to the launch pad, a video simulation shows the First Stage firing one engine to decelerate to a pinpoint landing on its specially made landing legs – hardware that is already under construction – in an area depicted in the video as the Cape Canaveral Air Force Station (CCAFS) Skid Strip runway complex.

The video also shows the Upper Stage completing its orbital insertion burn, prior to spacecraft separation, with thrusters once again rotating the stage 180 degrees, aft forward, ahead of engine restart for another burn to deorbit the Upper Stage.

Protected by what appears to be a version of the PICA-X (a proprietary variant of NASA’s phenolic impregnated carbon ablator (PICA) material) heat shield used by the Dragon spacecraft, the Upper Stage dives back to Earth, protected against the heat and force of re-entry, prior to using what is depicted as four thrusters to decelerate and land on its landing legs.

With Dragon already designed to return home for a splashdown in the Pacific Ocean – as it has achieved twice already – the stack could then be reused, vastly reducing costs.

The monster of SpaceX’s near term fleet will be the Falcon Heavy, with its first stage will be made up of three nine-engine cores. In total, 27 of SpaceX’s upgraded Merlin engines will generate the 3.8 million pounds of thrust at liftoff for the new vehicle.

The Falcon Heavy’s performance stats are impressive, with a Mass to Orbit (200 km, 28.5 deg) of 53 metric tons (117,000 lbs), with its 3.8 million lbs of thrust lifting the 1,400 metric tons of vehicle off the pad. The FH will be 69.2 meters (227 ft) in length, a total width of 11.6 meters (38 ft), with a fairing width of 5.2 m (17 ft).

Falcon Heavy will debut at Space Launch Complex 4 (SLC-4) at the Vandenberg Air Force Base (VAFB) in California, before eventually setting up its primary home at Cape Canaveral in Florida. This plan will allow the new vehicle to play tag team with the Falcon 9, with both vehicles sharing the launch manifest for their larger passengers.

“This is another important milestone in our efforts to push the boundaries of space technology,” said SpaceX CEO and Chief Designer Elon Musk in reference to the test firing. “With the Merlin 1D powering the Falcon 9 and Falcon Heavy rockets, SpaceX will be capable of carrying a full range of payloads to orbit.”

SpaceX added that the enhanced design makes the Merlin 1D the most efficient booster engine ever built, with a vacuum thrust-to-weight ratio exceeding 150, while still maintaining the structural and thermal safety margins needed to carry astronauts.

Additionally, as SpaceX continues to fulfil an extensive manifest of launches, the new engine is designed for improved manufacturability by using higher efficiency processes, increased robotic construction and reduced parts count.

SpaceX are expected to be next in action on October 5 of this year, a slightly slipped launch date, pending the approval of SpX-1 – the first Commercial Resupply Services (CRS) mission to the International Space Station (ISS). NASA and SpaceX teams are deep into their review of the COTS 2+ mission, with a view to approve the SpX-1 mission.

Orbital AJ-26 Test:

SpaceX are one of two CRS partners for NASA, with Orbital’s Antares set to launch the Cygnus spacecraft on resupply missions from next year.

Orbital have to successfully complete two major milestones prior to their CRS runs, the first being the launch of their new Antares launch vehicle.

The Antares – formerly known as Taurus II – will then be followed by a one-off full COTS level demonstration mission, not unlike SpaceX’s C2+ mission, tasking Cygnus with a single flight to prove its ability, prior to starting CRS operations proper.

The Antares launch vehicle is powered by two Aerojet produced AJ26-62 main engines, running LOX/RP, producing 3,265kN of thrust at Sea Level. This engine is a rebuilt version of Soviet NK-33, originally intended for the massive N-1 launch vehicle that was intended to send the Soviets to the Moon.

Aerojet originally purchased approximately 40 NK-33 engines in the mid-1990s and, under contract with Orbital, the company has modified the engines specifically for its Antares rocket.

Throughout the years, more than 200 NK-33 engines were built and 575 engine tests conducted, totaling more than 100,000 seconds of test time. Aerojet has been developing design modifications to the NK-33 since that time to ensure that the AJ26 is suitable for commercial launchers.

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In preparation for the debut of Antares, the AJ-26 has been undergoing testing at NASA’s Stennis Space Center (SSC), with the latest test taking place on Monday.

The upcoming milestones for Antares include what documentation describes as the 7K hot fire test on the launch pad at Wallops. Antares’ testing had placed the hardware into a stance to be ready to conduct this hot fire by the first half of 2012.

However, the delays to the schedule, caused by ongoing construction of the new pad by the Mid-Atlantic Regional Spaceport (MARS) teams, caused a slip to at least the third quarter of 2012.

(Images via SpaceX, NASA and Orbital).

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