PYTHOMSPACE
The Asterex Rocket Engine
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The mission in 20 seconds
Pythom is building an interplanetary space system, with a human mission to Mars as first target.

Alpine style: Lightweight hardware, efficient software, agile design and rapid manufacturing.

We build as we go, step by step, for quick development and radical cost cuts.

Our dev team is strong on applied STEM, with added experience from extreme, unguided expeditions around the world.

Keep it real.
Engine 5kN
Injector Servo
Asterex is a throtteable engine designed for all aspects of ascent and descent.

"Deep-throttle" capacity down to 20% is hard to achieve and requires a unique combination of propellant choices and injection construction.

The high torque small servo is wirelessly controlled by Pythom software and will regulate injection openings in steps of only 0.05 mm (0.002 inch).
Oxidizer Inlet
The oxidizer (nictric acid) inlet will be welded to the top of the pintle casing.

The fitting is a flare fitting, using 37° flared tubing to form a metal-metal seal. The cost includes material and welding.
Pintle Casing
The pintle casing gives support and enclosure to the injector package.

Asterex feed system will use 100 times the fuel/second rate of a Formula One car. The oxidizer moves at 2.5 MPa pressure and 1.6 liters per second flow rate.

What an 18 wheeler truck uses in one hour of driving, Asterex will burn in one second!
Pintle Tip
The oxidizer (nictric acid) is forced through a tiny gap (1.2 mm) between the pintle tip and the moveable sleeve, the "pintle gap", creating a fine high pressure spray into the engine chamber.

Pintle type injector was first used on the Apollo Lunar lander, and is a great choice for a rocket engine that needs to be throtteable. After Simon Ramo invented the rocket engine pintle it quickly became classified due to higher target accuracy of ICBM's. The Apollo lander injection system was classified by the same reason.

Contrary to the engine shell, the tip can not be fuel cooled so it will have an ablative layer to withstand the temperatures of 2800 C (5000 F).
Moveable Sleeve
As the servo moves the sleeve downwards it will simultaneously open the fuel and oxidizer gap and increase the propellant flow. This is what makes Asterex throtteable.

The sleeve must be 100% leak proof. Custom teflon seals prevent the oxidizer and fuel to mix before entering the engine chamber.
Engine Body
Asterex double walled engine would not have been possible without 3D printing.

Print material is Inconel, a metal nickel alloy, with great strength and heat properties.

When the oxidizer and fuel react in the chamber they create gases at a temperature of 2800 C (5000 F), twice the melting temperature of steel, or half the surface temperature of the sun.

To prevent catastrophic meltdown the engine is cooled by fuel passing through the engine walls ("regenerative" cooling), before injected into the chamber. The inner wall is only 1 mm thick and holds a pressure of 2.5 MPa. The gas is forced through the throat and nozzle at 1500 m/s speed.

9 of these engines will power the Mars lander.
Fuel Inlet
The fuel (furfuryl alcohol) inlet is welded to a manifold. The fuel is dispersed into 24 channels running between the inner and outer shell of the engine to cool the walls (regenerative cooling).

The fitting is a flare fitting, using 37° flared tubing to form a metal-metal seal. The cost includes material and welding.
Electronics
Electronics for remote control of injector and solenoids. Includes RF, microcontrollers and sensors. Software not included.
Oxidizer, Nitric Acid
Asterex propellant mix of nitric acid and furfuryl alcohol is "hypergolic" or self-igniting. Medium high ISP compensated by high density and less weight of tanks and structures.

Nitric acid (HNO3) or "white fuming nitric acid" is environmentaly friendly and common ingredient in fertilizers.
Fuel, Furfuryl Alcohol
Asterex propellant mix of nitric acid and furfuryl alcohol is "hypergolic" or self-igniting. Medium high ISP compensated by high density and less weight of tanks and structures.
Pressure Gas, Helium
An inert gas, Helium is injected into the propellant tanks to keep pressure at 2.8 MPa.
Feed System
Dome Regulator
The dome regulator reduces the high pressure in the Helium tank, from 14 MPa to 3 MPa. The gas enters the propellant tanks and keeps them under constant pressure during operation. Helium is an inert gas and will not mix with the propellants.
Helium Tank
The first link in a rocket engine pressure feed system, the Helium tank is machined of spun aluminum. The gas will be contained at 14 MPa pressure and fed into the propellant tanks via the dome regulator at 3 MPa.
Helium Pipes
Stainless steel pipes transport Helium gas to the propellant tanks.

The inside of all pipes, valves and tanks must be compatible with Nitric acid, a very strong oxidizer. Stainless steel, Inconel (nickel alloy), aluminum and teflon all work, while copper, for instance, doesn't.

An interesting feature is that concentrated nitric acid reacts with aluminum to form a protective thin layer of aluminum oxide. This process is called passivation and also occurs with nickel.
Fuel Shut-off Valves
Before operation the fuel tank is opened/closed manually with the shut-off valves. The shut-off valves are also used for drain and fill.
Oxidizer Shut-off Valves
Before operation the fuel tank is opened/closed manually with the shut-off valves. The shut-off valves will aso be used for drain and fill. As with all other parts of the plumbing system, the shut-off valves must be able to withstand the intense corrosion effect of the nitric acid. Consequently all inner parts must be of stainless steel or other compatible materials.
Fuel Tank
Precision made of spun aluminum. the fuel tank holds furfuryl alcohol for up to 20 sec of max injection flow. Pressure will be kept constant in the tank at 2.8 MPa by the helium gas.

A CNC lathe machine forms a block of aluminum into a perfect hemisphere which is welded to a second hemisphere to form a sphere. The sphere is the most effective (minimum material) shape to achieve a desired volume.

Oxidizer Tank
The oxidizer tank is also made of spun aluminum. It will hold nitric acid (aqua fortis) for up to 20 sec of full force testing. The pressure will be kept constant in the tank at 2.8 MPa by the helium gas.

The helium will not mix with the nitric acid, but it must be kept from entering the chamber inlet, or the engine will become unstable. For testing purposes this is achieved by keeping the tanks in a vertical position with the helium entering at the top. For a later low-gravity situation the tanks will be fitted with an expandable separation material (diaphragm) to keep the gas away from the outlet.
Fuel Safety Valve
The safety valve dumps the fuel if pressure reaches dangerous level. The risk is small but possible if the dome pressure regulator malfunctions.
Oxidizer Safety Valve
The safety valve dumps the oxidizer if pressure reaches dangerous level. It's unlikely to be ever activated, but valve malfunctions are common origins of catastrophic rocket engine failures.
Fuel solenoid Valve
The fuel solenoid valve is operated wirelessly at a distance. It's opened within milli seconds of the oxidizer solenoid at countdown. The short delay is due to the fuel having to travel to cool the engine, before mixing with the oxidizer.
Oxidizer Solenoid Valve
The oxidizer solenoid valve is operated wirelessly at a distance. The solenoid is an all-or-nothing valve, contrary to Asterex moveable sleeve which can meter the propellants.

The software (not included) controlling the solenoids is written in-house and part of the overall propulsion control system.
Fuel and Oxidizer Pipes
Braided stainless steel propellant pipes. The pipes are lined with teflon (PTFE) to withstand corrosion from the nitric acid.
Asterex Full Propellant System
Engine and Feed System


Showing the full system with cooling channel ridges.