Ecological Water-Based, Electric Rocket

LAS is an ecological rocket. Regardless of its version (expendable or reusable), a LAS vehicle is made of a composite materials propellant tank, a feed system, an engine, the electric heating system and avionics. The water from the tank is electrically heated to up to 250 deg.C. At engine start, the water is injected into the engine’s chamber through the feed system where transforms partially from liquid to vapors. A further heating phase takes place in the engine (only for the reusable LAS version), using the power generated by the high discharge LiPo batteries. These water vapors are accelerated through the engine’s nozzle to supersonic speeds creating thrust.
The expendable LAS will be used mostly as strap-on boosters for third party vehicles upon request, while the reusable version of LAS will be used exclusively by ARCA and third parties in conjunction with their own vehicles.




Aerospike Rocket Engine

The expendable LAS uses a bell-shaped nozzle engine, while the reusable LAS uses a toroidal aerospike engine. The expendable LAS needs to be simple to fabricate in large volumes and at a lowest possible cost, while the reusable version is focused more on higher performance.

An aerospike engine offers a higher specific impulse, but at the same time is made of more parts and the associated cost is higher. Also, the aerospike engine will have a second phase heating system for the water, a system not present on the expendable version of LAS. Both engine versions are made of lightweight composite materials. For the ground tests the bell-shaped nozzle engine of expendable LAS is also fully reusable, requiring virtually no maintenance due to propellant benign nature.
ARCA tested initially the classic engine and then the aerospike engine on the same stand, using the same tank, same feed system, same pressures, same sensors, allowing us to further find unprecedented answers regarding the direct comparison between the two engine configurations.

For the first aerospike test, we were able to draw an initial conclusion that the aerospikes are indeed better than the bell shaped nozzle engines at sea level, and not by a little, but by a large margin, as follows:

For the first test we didn’t want to push the test installation too far, and for the following tests we will increase the work parameters until we will reach a specific impulse in the range of 60s. We can see that the aerospike had a 15% higher specific impulse but a question arises: From where this increase of specific impulse? ARCA have some hypothesis, but until we are not going to perform further tests and be sure, we don’t want to publicly conclude at this point. We expect that this percentage to get even higher as the test pressure increases as the push effect of engine exhaust on the central plug will increase.



Fully Composites

The whole LAS vehicle is made of composite materials, including the propellant tank. ARCA has extensive experience with composite materials tanks fabrication. All our previous rockets used composite tanks never recording a single fail.
For LAS however a special challenge arose from the fact that the propellant needs to be heated at around 250 deg.C and the regular composites are susceptible to ruptures at these temperatures. Since the fibers are not posing special challenges of usage at these temperatures, the only challenge was to select the proper resin. Tests were performed on various tanks to find the right type of resin able to withstand the relatively high temperatures required for the stored propellant.
The tanks are made of two separate layers. An internal thermal liner over wrapped in glass fiber fabric/filament and epoxy resin. The thermal liner’s acts as a thermal insulator that is protecting the outer mechanical layers from overheating, keeping the external temperature below 140 deg.C. While it features the same fabrication technology, the tanks for the expendable version of LAS has a high length to diameter ratio, while the tanks for the reusable version has a smaller length to diameter ratio.
This is due to the fact that the reusable version needs to accommodate a large diameter aerospike engine, while keeping the center of gravity as low as possible and a wide base for increased stability during the landing phase.

Differently than the classic rockets, the LAS tank doesn’t need a dedicated pressurization system. So, the high-pressure bottles, pumps, conduits and valves are completely eliminated. The pressurization is achieved when the water is heated. It generates vapors that are keeping the tank’s internal pressure at a value corresponding to the boiling temperature, preventing the water to boil. As an example, when the temperature is reaching 200 deg.C the tank pressure is 16 bars.





In February 2019 ARCA started the study of a reusable LAS vehicle using an aerospike engine, with VTOL capability, that will serve as a fast turnaround shuttle. Considering the propellant’s benign nature, the reusability was seen as a very tempting option.
After the launch the vehicle will climb and accelerate to altitudes of around 3,000m and speeds of Mach 1.5, and this performance will be achieved during of around 23 seconds of engine run.
After the LAS main tank depletion and engine stop, the upper stage will continue the flight to reach orbit.
LAS, it will start the powered descent to the ground under 8 chambers out of 32 from the aerospike engine. The vehicle will land and be prepared for the upper stage integration and batteries recharge.
The team aims to a very fast return to flight of the vehicle, of around 24 hours, since the recovery takes place from altitudes that pose no thermal and mechanical challenges and the LAS engine run at low pressures and temperatures. In April 2020 ARCA scheduled the first test flight of LAS 25DA (DA-Demonstrator Aerospike).











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