Fifteen Spacex Raptor Engines, Five engines per core on a three core rocket could launch 536 tons of payload

Exoscientist Robert Clark has calculated a two stage three core Spacex rocket with the proposed Spacex methane fueled Rocket Engine would enable 536 tons of payload in a single launch. Each core has 5 raptor engines for a total of 15 raptor engines.

A June 2014 talk by Tom Mueller, the head of rocket engine development at SpaceX, provided more specific engine performance target specifications indicating 6,900 kN (705 tonnes-force) of sea-level thrust, 8,200 kN (840 tonnes-force) of vacuum thrust, and a specific impulse of 380 seconds.

The Spacex Falcon heavy has three cores and has nine engines on each core as seen in this picture from the site. Having five engines per core would show about three engines in profile on each core.

Pictures of the Falcon Heavy engines from Spacex.

In April 2014, SpaceX completed the requisite upgrades and maintenance to the Stennis test stand to prepare for testing of Raptor components, and expected to begin tests at the facility prior to the end of May 2014.

The Raptor engine will be powered by liquid methane and liquid oxygen using a more efficient staged combustion cycle, a departure from the ‘open cycle’ gas generator system and lox/kerosene propellants that current Merlin engines use. The Space Shuttle Main Engines (SSME) also used a staged combustion process, as do several Russian rocket engines.

More specifically, Raptor will utilize a “full-flow” staged combustion cycle, where 100 percent of the oxidizer—with a low-fuel ratio—will power the oxygen turbine pump, and 100 percent of the fuel—with a low-oxygen ratio—will power the methane turbine pump. Both streams—oxidizer and fuel—will be completely in the gas phase before they enter the combustion chamber. Prior to 2014, only two full-flow staged combustion rocket engines have ever progressed sufficiently to be tested on test stands: the Soviet RD-270 project in the 1960s and the Aerojet Rocketdyne Integrated powerhead demonstration project in the mid-2000s.

Raptor is being designed to produce 8,200 kN (1,800,000 lbf) of vacuum thrust—6,900 kN (1,600,000 lbf) thrust at lift-off—with a vacuum Isp of 380 seconds and a sea-level Isp of 321 seconds. Final thrust and Isp specifications for the as-built engines are expected to be refined as SpaceX moves the engine through the multi-year development cycle.

Additional characteristics of the full-flow design that are projected to further increase performance or reliability include:

* eliminating the fuel-oxidizer turbine interseal, which is a potential point of failure in more traditional engine designs
* lower pressures are required through the pumping system, increasing life span and further reducing risk of catastrophic failure
* ability to increase the combustion chamber pressure, thereby either increasing overall performance, or “by using cooler gases, providing the same performance as a standard staged combustion engine but with much less stress on materials, thus significantly reducing material fatigue or [engine] weight.”