In January 2016, the US Air Force awarded a US$33.6 million development contract to SpaceX develop a prototype version of its methane-fueled reusable Raptor engine for use on the upper stage of the Falcon 9 and Falcon Heavy launch vehicles, which required double-matching funding by SpaceX of at least US$67.3 million. Work under the contract is expected to be completed in 2018, and engine performance testing will be done at NASA's John C. Stennis Space Center in Mississippi.
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
The Raptor engine is designed to work using deep cryogenic methalox propellants—fluids cooled to near their freezing points rather than nearer their boiling points which is more typical for cryogenic rocket engines.
The turbopump and many of the critical parts of the injectors will be manufactured by using 3D printing, which also increases the speed of development and iterative testing.
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
Stated design size for the Raptor engine has varied widely as design continues, from a high target of 8,200 kN (1,800,000 lbf) of vacuum thrust to a more recent, much lower target of 2,300 kN (510,000 lbf). Estimates target a vacuum Isp of 363 seconds and a sea-level Isp of 321 seconds. Final thrust and Isp specifications for the as-built engines may continue to change dramatically as SpaceX moves the engine through the multi-year development cycle
SpaceX announced an ambitious plan to send its first uncrewed Dragon capsule to Mars as early as 2018. The Merlin engine — which uses kerosene and liquid oxygen as propellants — will power the Falcon 9 and future Falcon Heavy launch vehicles, the Raptor engine will power the next-gen rocket.
One audience member at the 30th Annual Conference on Small Satellites at Utah State University questioned SpaceX’s plans for human settlement of Mars, wondering why anyone would want to live there. “There are a lot of people on this planet that have a lot of very different ideas,” she said. “I’m sure there’s plenty of people who will want to go settle on Mars.”
To test this, Spacex President and COO Gwynne Shotwell asked a show of hands from the standing-room-only audience of those who would be willing to go to Mars on an early expedition. About five to ten percent of the audience raised their hands. “Five percent of the world’s population is a lot,” she said.
Shotwell also emphasized the company’s efforts to make the Falcon 9 first stage reusable as another key element in its efforts to provide affordable smallsat launch services, calling reusability “the single most important thing SpaceX is working on.”
As part of that work, SpaceX is test-firing one of the Falcon 9 stages it successfully landed, from the May launch of the JCSAT-14 satellite, at its McGregor, Texas, test site. That stage has already completed some full-duration static test firings. “We’re going to run as many tests on this stage as we can pull off,” she said. “Hopefully we’ll get more than four, and maybe eight to ten of these, before we go ahead and refly.”
Shotwell said there’s “a lot of interest” from customers interested in flying on a Falcon 9 with a reused first stage. “We may fly two of the previously-flown hardware this year,” she said.
Ride sharing with small satellite rings
SpaceX, which retired its Falcon 1 small launch vehicle several years ago, believes it can more effectively serve the growing small satellite market through rideshare accommodations on its larger vehicles, the company’s president said Aug. 9.
In a keynote speech at the 30th Annual Conference on Small Satellites at Utah State University here, Gwynne Shotwell said the company was working with companies that aggregate secondary payloads, such as Seattle-based Spaceflight, to fly on the Falcon 9 and future Falcon Heavy launch vehicles.
Spaceflight announced in September 2015 that it had purchased a Falcon 9 launch for what it called a “dedicated rideshare” mission planned for the second half of 2017. That mission will carry more than 20 spacecraft, including a lunar lander developed by SpaceIL, an Israeli team competing in the Google Lunar X Prize.
Spaceflight is also flying nearly 90 satellites as secondary payloads on its SHERPA payload adapter. SHERPA will fly with a Taiwanese satellite, Formosat-5, on a Falcon 9 later this year. Jason Andrews, president and chief executive of Spaceflight, said in an Aug. 8 presentation here that he expects that launch to take place in late October.
Shotwell said SpaceX also believes it can offer extensive secondary payload accommodations on its Falcon Heavy rocket. “There should be a lot of extra capacity on this rocket, and hopefully we will fly a lot of ESPA or ESPA-like rings underneath the primary payload to provide regular access for you all,” she said, referring to the EELV Secondary Payload Adapter, a common payload interface for small secondary payloads.
Development of the Falcon Heavy has been beset by delays, she acknowledged. “Sorry we’re late,” she said. “This is actually a harder problem than we thought.” Those delays have pushed back one early Falcon Heavy mission, carrying the Space Test Program 2 mission, with more than 30 satellites, to the third quarter of 2017.
SOURCES -Space News, Wikipedia, Spacex,