ARCA Space Corporation has announced its linear aerospike engine is ready to start ground tests as the company moves towards installing the engine in its Demonstrator 3 rocket. Designed to power the world's first operational Single-Stage-To-Orbit (SSTO) satellite launcher, the engine took only 60 days to complete from when fabrication began.
Over the past 60 years, space launches have become pretty routine. The first stage ignites, the rocket lifts slowly and majestically from the launch pad before picking up speed and vanishing into the blue. Minutes later, the first stage shuts down and separates from the upper stages, which ignite and burn in turn until the payload is delivered into orbit.
This approach was adopted not only because it provides enough fuel to lift the payload while conserving weight, but also because the first-stage engines, which work best at sea level, are very inefficient at higher altitudes or in space, so different engines need to be employed for each stage of flight.
The aerospike engine is different because it basically works by cutting a rocket engine's bell, which directs the exhaust of a rocket engine in one direction, in half, then placing the two halves back to back to form a tapering spike. This means the air itself acts as the missing half of the rocket bell, containing the hot gases as they leave the combustion chamber.
As the rocket flies higher, the thinner air holds the gases less tightly and they spread out more, as if the rocket bell has gradually grown larger. This allows the aerospike engine to automatically adjust itself in flight, turning itself from a sea-level engine into a high-altitude one with virtually unlimited expansion ratios.
According to ACRA, the new test engine uses a monopropellant of 70 percent hydrogen peroxide mixed with RP-1 – a highly refined form of kerosene – and has a sea-level thrust of 4.2 tons. Despite using a low-energy propellant, the aerospike's increased efficiency and a special lightweight composite propellant tank will make the Demonstrator 3 ballistic suborbital rocket capable of reaching space.
The engine is slated to undergo a series of ground tests to certify it as flight ready before being integrated into the Demonstrator 3 rocket. This will be followed by a suborbital test launched from Spaceport America in New Mexico to an altitude of 120 km (75 mi), which will be the first spaceflight ever of a linear aerospike engine.
The ultimate goal of the tests will be to develop a practical working engine for ACRA's Haas 2CA SSTO rocket slated to make its first flight from NASA's Wallops Flight Facility next year. The Haas 2CA is aimed at the small satellites market with a projected cost of US$1 million per launch.
The video below introduces the ACRA linear aerospike engine.