The distinct blue flame in recent tests is produced by the thruster’s methane fuel. Data gathered from testing will be used to develop optimized components that could support engine designs for NASA’s next generation of exploration landers. (Image courtesy of NASA/MSFC.)
Methane, a fuel which has not previously been used to power any NASA spacecraft, is being used in a series of tests for components of a new engine design.
The goal is to develop methane engines that can be used to propel landers, as well as other space exploration vehicles, for the journey to Mars.
The blue flame in the video below, atypical of most engine tests, is the signature of the thruster’s methane fuel.
The current thruster being tested is part of a pressure-fed design and produces 4,000 pounds of thrust.
However, 25,000 pounds of thrust would be needed for larger descent/ascent landers on Mars. To accomplish this, a pump-fed engine design is in development. This design will also enable the engines to be throttled as needed.
In the pump-fed design, a turbopump will use a turbine capable of 95,000 revolutions per minute to deliver methane to the thruster. This will allow for higher thrust levels.
Thrusters are comprised of two main components, a combined injector and a combustion chamber.
Thrusters fueled by methane using liquid oxygen as an oxidizer have been under development at NASA’s Marshall Space Flight Center for the last decade.
“With the current configuration, these methane thrusters could propel a small lander,” said Steve Hanna of NASA’s Advanced Exploration Systems at Marshall. “With the data gained from these tests, the technology is scalable for even larger applications for in-space engines and larger landers.”
Why Travel to Mars with Methane
Methane is considered a promising fuel for future Mars missions. It is more stable than liquid hydrogen and can be stored at temperatures that are easier to manage. The tanks can also be smaller, as methane is denser than liquid hydrogen.
Because the storage temperature of methane is similar to that of liquid oxygen, the storage tanks will need less insulation and might be able to share a single cooling system. This could help make the tanks more affordable.
Perhaps the most appealing benefit to methane-fueled engines is that methane can be recovered or created from local resources using in-situ resource utilization (ISRU).
With the Mars 2020 mission, NASA plans to demonstrate ISRU technologies that could enable propellant and consumable oxygen production from the Martian atmosphere.
If the technologies prove successful, it could mean astronauts can create both the fuel and the oxidizer needed to propel an ascent vehicle into Martian orbit.
3D Printing, Thermocouple Ports and a Regenerative Engine System
The 3-D printed, methane-powered thruster consists of an injector, left, and combustion chamber, right. The 3-D printing techniques allow Marshall engineers to incorporate thermocouple ports into the chamber’s design, which collect discrete data during testing. (Image courtesy of NASA/MSFC.)
Both the thruster components and the turbopump were manufactured with additive manufacturing, or 3-D printing.
Using 3-D printing allows for 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 previously unavailable discrete temperature data.
“This data will help critical thermal modeling,” said Sandra Greene, an engineer in Marshall’s Propulsion Systems department. “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.”
Marshall engineers recently performed preliminary “chill” tests on a 3-D printed turbopump to be used with a methane-powered engine. The tests, a precursor to full-scale testing, verified hardware and test instrumentation for the temperatures required during the firing of a methane engine. (Image courtesy of NASA/MSFC.)
This thermal data will be used to anchor thermal models to optimize the design of the thruster into a full regenerative methane fuel engine system.
A regenerative engine system cycles fuel through channels within the chamber to cool the chamber before and during ignition. This will improve the overall efficiency of the system.
In previous methane thruster development efforts at Marshall, chamber designs were primarily uncooled -- using ablative or high-temperature refractory materials to prevent the chamber from overheating.
So far, Marshall engineers have successfully conducted preliminary testing and facility checkout of the methane engine turbopump.
A series of tests planned for later this year will verify that the turbopump, previously tested with liquid hydrogen, can be used with either fuel and that it will be capable of delivering enough fuel to power a large methane engine.
With this type of methane engine, are we another step closer to sending astronauts to Mars?
If the technology proves to be scalable and capable of providing enough thrust, will we see return missions to and from Mars in the near future?
For more information, visit NASA’s website.