It's finally happened ...
Since Robert Zubrin released his book 'The Case for Mars', where he outlined how methane could be fairly easily and economically produced on Mars, rocket scientists have considered using a methane rocket engine for powering Mars Lander and Ascent vehicles.
But no one has actually produced models that have ever gone into production.
A methane rocket engine has several drawbacks. The main problem is that they have a much lower performance, known as 'specific impulse' or ISP, than other rocket engine types, like hydrogen-oxygen powered systems.
For example, in vacuum, a H2/LOx engine has a theoretical ISP of about 456 seconds, while methane/oxygen rockets have an ISP of only 368 seconds (ISP is basically how long an engine will burn for a known amount of fuel, like one kilogram - the higher the ISP, the more efficient the engine).
But what's good about a methane rocket engine for Mars is that:
- the fuel can be easily produced
- methane much easier to handle and store than hydrogen, and
- the density of methane is much greater than hydrogen, which means fuel tanks are much smaller.
In other words, the performance drawbacks are offset by the positives when you consider the design of a Mars Lander or ascent vehicle.
Note: other hydrocarbon-based fuels can also be manufactured on Mars, but they all have lower ISPs than methane, so a methane rocket engine is typically the engine most discussed. Here's a quick chart if you are interested.
NASA Tests Methane Rocket Engine
Engineers at NASA's Marshall Space Flight Center have finally tested components for a methane rocket engine that could be used for Mars landers -- and released a video to prove it.
As Steve Hanna, the project lead for NASA's Advanced Exploration Systems at Marshall, said:
With the current configuration, these methane thrusters could propel a small lander. With the data gained from these tests, the technology is scalable for even larger applications for in-space engines and larger landers.
The current thruster being tested, a pressure-fed methane rocket engine design, produces 4,000 pounds of thrust. To achieve the 25,000 pounds of thrust needed for larger descent/ascent landers on Mars, and enable engines to be throttled as needed, Marshall engineers are also developing a pump-fed engine design.
In that design, a turbopump will use a turbine capable of up to 95,000 revolutions per minute to deliver methane to the thruster, allowing for higher thrust levels.
After a recent, and successful, test and facility checkout of a turbopump for a methane engine, Engineers at Marshall now plan to perform a series of tests later this year to verify that a turbopump previously tested with liquid hydrogen can also be used with methane and can deliver enough fuel to power a large methane rocket engine.
In addition to the turbopump, Marshall engineers have been testing methane thrusters for the last decade. Combine those thrusters with a methane-capable pump feed system, and a next generation lander may be closer than we think.
And to make the whole system even more enticing, the engineers have been maufacturing them using 3D printing processes.
Not only does 3-D printing allow for quicker production times and a reduction in the machining and brazing required with traditional fabrication processes, it also allows for the addition of thermocouple ports along the length of the chamber. These ports communicate with the chamber's coolant channels, providing discrete temperature data never before available.
As Sandra Greene, an engineer in Marshall's Propulsion Systems Department, said:
This data will help critical thermal modeling. That's why the thermocouple ports are so exciting - we not only get the inlet and exit temperature of the methane, but we also get data to help us verify what is happening inside the chamber's coolant system.
This thermal data will be used to optimize the design of the thruster and create what the engineers call a 'full regenerative engine system' that uses methane as fuel.
Note: A regenerative engine system cycles fuel through channels within the rocket chamber to cool it during ignition. In previous methane thruster development efforts at Marshall, chamber designs were primarily uncooled and used ablative or high-temperature materials to prevent the chamber from overheating.
As Greene said:
To maximize performance, a regeneratively cooled chamber is desired. This chamber is Marshall's first attempt at such a design in a methane-powered system.
NASA is not the only one looking at a methane rocket engine. Earlier this year, SpaceX hinted that they were also experimenting with the technology with their 'Raptor' engine. But with NASA closer to sending astronauts to Mars than ever before, the tests at Marshall and the technology they inspire could enable the first steps on the Martian surface to come from astronauts exiting a lander driven by a methane rocket engine.
Take a look at this video to see the methane rocket engine test in action.