LAUNCH ASSIST SYSTEM - LAS
The Launch Assist System - LAS is the the technology behind EcoRocket's first stage.
Current rockets are using polluting, explosive, corrosive, toxic, carcinogenic propellants. At launch, a rocket releases polluting chemicals into the atmosphere as much as 1 million cars running simultaneously.
ARCA created an electric, water-based rocket that works as first stage, or booster for launch vehicles, allowing the reduction of polluting propellant with 25-50%, or boost the payload capability with around 30% pollution free. LAS was built in two versions, using a classic bell shaped nozzle engine and a higher efficiency aerospike engine.
HOW DOES IT WORK
Extensive tests were done at ARCA since July 2018 to develop a water-based rocket engine, and here is how the system works: the rocket tank is filled with 98% water and benign phase destabilisers. In the tank, the water is electrically heated to 250 deg.C. When the water is injected into the engine, part of it evaporates. A second heating phase occurs in the engine powered by high discharge LiPo batteries. The same type of batteries used by ARCA to power the cutting edge, 700kW ArcaBoard. At 21MW for LAS 25R, the amount of electric energy released during engine run is more than what a small nuclear reactor generates. Solar and wind power can recharge the rocket’s batteries after each launch.
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 vapours. 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 vapours 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.
Even for our team an inherent question arose: how can we use a rocket that offers only around 50 - 60 seconds of specific impulse? Because this by itself can’t give the necessary performance for an orbital flight, and not even for a suborbital flight. We were literally struggling to find an option to work with a rocket with such low performance. Because when you look at current rockets and see specific impulses that are around four times higher, the first instinctual reaction is to quit the idea thinking: this isn’t going to work. But the tremendous advantages offered by the water in terms of cost, safety and lack of pollution was what kept us pushing and come back to it over and over again, to find an option to work with this system.
But then we looked at the Space Shuttle and Ariane 5’s SRBs that are indeed low performance rockets by themselves compared with the vehicle’s main engines from the core stages.
Their impulse is lower than their main engines and the propellant mass to empty mass ratio is very low, but the thrust to weight ratio is very high.
It was clear that what matters for boosters is the thrust/weight ratio, while the specific impulse is of secondary importance. As long as the thrust to weight ratio is higher than the first stages’, the booster will fulfill its duty to contribute to the vehicle’s acceleration during ascent, regardless of the booster’s impulse. Also, the higher the acceleration at start, the better the flight performance of the orbital vehicle and LAS was designed with this feature in mind.
With this conclusion well structured, the team started to perform simulations to see what is the impact of the use of a water booster having a low impulse on orbital vehicle’s performance.
We named it the Launch Assist System (LAS).
At impulses in the range of 50-60 sec, the engine’s performance is lower compared with the ones using classic propellants, but we found it ideal from many points of view to assist the launch of current rockets.
The Launch Assist System (LAS) is a lifting vehicle, designed to boost the orbital vehicle’s performance, using hot water as propellant, safe and clean, allowing a major cost reduction of orbital launches. Built in the corresponding size for the lifted payload, it can transport any orbital rocket to altitudes of around 3,000m and speeds of around Mach 2.
It was concluded that LAS can be used both as booster as well as a first stage for an orbital rocket, providing a boost of their payload weight with up to 30%, or make the current rockets use 25% less polluting propellant.
For more details about the Launch Assist System, check the: White Paper.
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 aerospike using this propellant provided a 15% higher specific impulse compared with the bell shaped nozzle engine. 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.
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 pressurisation system. So, the high-pressure bottles, pumps, conduits and valves are completely eliminated. The pressurisation is achieved when the water is heated. It generates vapours 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).
The initial concept of LAS 25R + Haas 2CA Mini vehicle
that led to the EcoRocket design..