SpaceX shows mach diamonds are a rocket’s best friend with Raptor sneak peek
While much of the Western Hemisphere was still sound asleep on Sept. 26, SpaceX CEO Elon Musk conducted the first firing of the company’s Raptor engine. On the eve of what is expected to be a defining announcement from Musk as he outlines the NewSpace firm’s goals for Mars at the International Astronautical Congress (IAC), the CEO shared a couple photos and provided a few insights into the engine’s capabilities.
Although short on deep details of the engine’s performance numbers, Musk did provide enough to whet observers’ appetite.
“Production Raptor goal is specific impulse of 382 seconds and thrust of 3 MN (∼310 metric tons) at 300 bar”, Musk tweeted. “Chamber pressure is almost 3X Merlin, so engine is about the same size for a given ratio”.
That indicated the engine would be more powerful than the RS-25 powerplant on NASA’s Space Launch System (SLS), although not as efficient. However, with the SpaceX design being a methalox-fueled (liquid methane and liquid oxygen) engine, as opposed to the hydrolox-fueled (liquid hydrogen and liquid oxygen) RS-25, the efficiency difference is to be expected.
If a hydrolox engine is more efficient, why would SpaceX elect to use a methalox-based design? One of the overriding reasons is being able to produce the propellant – both liquid oxygen and liquid methane – from resources relatively readily accessible on Mars. Having the ability to manufacture propellant on the Martian surface rather than bring it along greatly reduces the logistical requirements of the mission. This process is called In-Situ Resource Utilization (ISRU) and is a critical capability to employ if human travel to the Red Planet is to become more than a rare occurrence.
Musk noted he would provide more details in the course of his talk during his Tuesday, Sept. 27, session at the IAC. However, that didn’t stop those on the Internet from attempting to extract a bit more information from Musk, and to some degree, he obliged.
Responding to questions posted on Twitter, Musk further elaborated on some of the engine’s characteristics. Noting that the numbers he tweeted were for conditions expected on the Martian surface, Musk also confirmed the engine’s nozzle would be approximately 14 feet (4.26 meters) in diameter. Additionally, he alluded to a booster-optimized version of Raptor, though again deferred to his IAC talk when asked for details.
Musk’s session is scheduled to begin at 2:30 p.m. EDT (6:30 pm GMT) Sept. 27, 2016, and is expected to be a highlight of the conference as he’s expected to give details on the company’s plan to send humans to Mars. It will be broadcast live.
Curt Godwin has been a fan of space exploration for as long as he can remember, keeping his eyes to the skies from an early age. Initially majoring in Nuclear Engineering, Curt later decided that computers would be a more interesting - and safer - career field. He's worked in education technology for more than 20 years, and has been published in industry and peer journals, and is a respected authority on wireless network engineering. Throughout this period of his life, he maintained his love for all things space and has written about his experiences at a variety of NASA events, both on his personal blog and as a freelance media representative.
I don’t think it is well appreciated what Mister Musk has announced. The SpaceX team has developed a two staged combustion Methane fueled engine that has greater ISP than the Russian RD-180, with a significant higher chamber pressure (4350 psig) than that of the RD-180 or the RS-25 that is reusable. That is just astonishing.
From what we know the Raptor differs from Blue Origin’s BE-4 Methane engine in that the BE-4, like the RD-180, is an oxygen rich single staged combustion engine. The BE-4 is reported to have a chamber pressure of 1950 psig which is lower than the RS-25 or the RD-180 and more in line what one might expect out of a reusable engine.
Having the extraordinary high Raptor chamber pressure implies some real leaps in metallurgy technology or some other technological advancement heretofore unknown. The Raptor is also the first two staged combustion engine ever built.