For a long time, Rocket Propellant-1, or RP-1, reigned supreme as the fuel of choice for the first stage of rocketry. This highly refined form of kerosene, which was derived from jet fuel, propelled the Saturn, Delta, Atlas and Soyuz rockets throughout the 20th century. It even served as fuel for modern rockets like the Falcon 9.
RP-1 has the advantage of being compact, which means that a lot of fuel can be packed into a relatively small tank. However, RP-1 is not the most efficient fuel, a measurement known as specific impulse. Liquid hydrogen, on the other hand, has a very high specific impulse. But because it is not dense at all, it cannot be used efficiently as fuel for the first stage.
This is one of the reasons why a number of major new rocket engines developed over the past decade, including SpaceX’s Raptor engines and Blue Origin’s BE-4 engines, are designed to use methane as a fuel. It represents a compromise between RP-1 and hydrogen – not as close as the former, and with a not as high specific impulse as the latter. Methane is also useful if you want to go to Mars, as it is relatively abundant in the thin atmosphere of the Red Planet and can be used to fuel an ascending vehicle.
However, an old rocket scientist named John Garvey believes that there is another viable rocket fuel, propylene, and he has been working with it for over a decade. After co-founding Vector with Jim Cantrell and Eric Besnard in late 2015, Garvey had the opportunity to use his propylene fuel for a true orbital rocket.
And now, he says, propylene has proven itself. Vector has received a patent for its liquid oxygen propylene rocket engine and is approaching the maiden flight of its orbital Vector-R rocket, powered by three of these engines.
In an interview, Garvey said the company has been able to scale up from experimental engines to the LP-1 engines in the Vector-R rocket, each of which produces about 6,000 pounds of thrust. “The biggest challenge was optimizing the boot mode,” he said. Essentially, Garvey and the other engineers had to do a lot of tinkering to make sure that during the final seconds of the countdown, the igniter works properly and the engine quickly reaches full thrust without the engine running. to damage yourself.
For a small rocket like the Vector-R, designed to take payloads of 26 kg or less to low Earth orbit for less than $3 million, a fuel like propylene is essential, Garvey said. With the optimum density and performance values of propylene, the Vector-R can keep its first stage diameter to just over one meter, with smaller fuel tanks. The propylene fuel also allows the engine design to avoid the use of turbopumps, which are used to increase the fuel pressure in most rocket engines.
Without turbopumps, engine design can be simpler and designers don’t have to worry about air bubbles or cavitation in the propellant. “For us, every bit of extra performance we can get matters,” said Garvey.
The company is still working on a first launch of its Vector-R rocket this year, from a launch site in Alaska. Every day, Garvey said, engineers at Vector evaluate risk and performance. How hard do they have to push the Vector-R on its first flight? How much risk do they have to accept that something could go wrong?
“We’re coming,” he said. “Part of the trade that we evaluate all the time is risk. Now that we’re getting into bigger vehicles, we’re still pretty risk-aggressive, but we’re not like we used to be.”