Two Stage Autonomous Self-Landing Rocket

MISSION AIMS

The MANSEDS Rocketry Group have designed and prototyped a second stage rocket, powered by a solid fuel motor, which will be entered into the national rocketry competition organised by UKSEDS.

In a bid to surpass ourselves, it was decided to create a first stage booster, with the added requirement that it must be self-landing. This will enable the second stage rocket to achieve a higher apogee, as well as develop the technical expertise of the team. And also because we love a tough challenge.

In order to make a successful self-landing booster, the design of this first stage includes a hybrid rocket. This type of rocket provides greater thrust than any solid rocket motors we can procure, thus further elevating the apogee. It also allows for controlled thrust and multiple ignitions, crucial for a safe return to Terra Firma.

Download Technical Document

rocket-schematic

Hybrid Rocket Motor

Fuel

The fuel of choice for the hybrid rocket is paraffin wax doped with a binding agent and aluminium powder. Original, HTBP and Paraffin wax were considered, however HTBP was hard to procure and provides a lower regression rate so paraffin wax was chosen.

Oxidiser Tank

The tank used for the N2O oxidiser will be pressurised between 100 bar and 200 bar. Any higher pressures could damage the vessel, due to the tendency of N2O to drastically increase in pressure for small changes in temperature.. It will also be fitted with a gas regulator that reduces output pressures to a more manageable pressure.

Control Valve

The control valve of choice is actuated needle valves as they provide fine control of the gas flow, allowing for the ability of a soft landing. The control valve will have a working pressure in the 10 Bar range as gas
from the regulator would reduce the output pressure to manageable pressures.

oxidiser_canister

Hybrid Rocket Motor

Combustion Chamber

This will be both the combustion chamber and the solid fuel container. A metal cylinder will encapsulate the fuel with a central bore, allowing the flow of the oxidiser and the exit of the exhaust gases, hence producing thrust. To ensure maximal efficiency, a screw-like apparatus will be fitted at the top of the chamber to create a flowing, turbulent motion of the oxidising gas, thus inducing a higher reaction rate. The whole tube is conveniently removable to permit easy refuelling.

Nozzle

The nozzle will be a converging diverging nozzle to increase thrust in comparison to simply releasing the expanding gas from the combustion chamber directly to the atmosphere, the nozzle will be designed to operate in the ~1km altitude pressure range and will be over pressured at first and reach max efficiency mid flight. The nozzle will be made with graphite or Titanium for their heat resistance
properties

combustion_chamber

Stage 2 Rocket

Internal Structure/Layout

The 2nd stage rocket will be about 600mm long including fins with an outer diameter of 40mm. It will be 3D printed using ABS or PLA polymers.

Solid Rocket Motor

The rocket used in this stage will be the CESARONI-P29-2G Solid Motor. It has a total impulse of 116 Ns for a maximum thrust of 167.4 N. Its total mass is 145.0 g, 52.1 g of which are the propellant. According to computer simulations of the
design with this motor, stage-2 will reach a maximum speed of 331 ms-1 within the 0.9 s of burn time of the motor. An ejection charge will be released 13 s after the engine cuts out, hence deploying the recovery parachute (see Recovery below).

Stage 2 Rocket

Rocket Electronics & Software

The brain of the second stage will be a ‘Raspberry Pi Zero’ controller. This will be powered by lithium ion polymer battery, or LiPo. This battery was chosen due to its high specific energy and its low weight. A DC-DC converter shall be used to convert between the different voltage levels.

In a competition setup (ie. the launch takes place without the first stage booster), the electronics on board have a passive role during the flight: they will not contribute to the control or recovery of the vehicle. They are responsible, however, for the science and telemetry payloads on board.

When mounted atop the booster, it will be the first stage electronics payload that shall trigger the launch of the upper stage.

Internal Structure/Layout

The 2nd stage rocket will be about 600mm long including fins with an outer diameter of 40mm. It will be 3D printed using ABS or PLA polymers.

Rocket Control Systems

The stability of the rocket is provided by four fins about 50 mm long, 3d printed as one component along with the body of the rocket. This ensures that they will be robust enough to resists the stresses of near Mach-speed flight.

Stage 2 Rocket

Rocket Science & Telemetry

Stage-2 will be fitted with a lightweight camera and altimeter, operated by the Pi Zero controller.

A suitable scientific payload is being actively researched and is to be confirmed.

Concerning telemetry and data transmission, the second stage will be fitted with a bluetooth transmitter to be able to communicate with first stage electronics

Rocket Recovery

Taken the mass after the engine has burned out and the desired terminal velocity of 5 ms-1, the parachute will need an area of 0.105 m2. The 18’ hexagonal printed nylon parachute from Apogee Rockets was chosen for its lightness and robustness.

The deployment of the parachute will occur via the ejection charge of the solid rocket. The nose cone will detach allowing the exit of the canopy. The delay after the engine cuts out is to allow the rocket to reach its maximum apogee before releasing the parachute.

Stage 2 Rocket

Competition Guidelines

The UKSEDS competition has strict requirements for the design and construction of the rocket.

First of all, the motor size is limited to a 29 mm wide Cesaroni solid rocket motor of G impulse, which must be securely mounted in the body of the rocket. The rocket may only travel at subsonic speeds, while leaving the launch stand with a minimum speed of 20 m/s.

For the structure, the ratio between length and diameter must be between 10 and 35. The static margin, defined as the distance between the centre of mass and the centre of pressure, has to lie between 1.5 and 2.5 diameter lengths. Finally, the coefficient of normal force must sit between 15 and 35. This is all to ensure the stability of the rocket.

The fuselage must resist various stress loads on the fins and on the body. These stresses will generally be twice as big as the expected values during
motorised flight.

However, stress due to parachute deployment greatly exceed that experienced during ascent. The recovery system must thus be securely fixed to the fuselage.

Another requirement for recovery is a maximal drift of up to a kilometre.

Finally, the electronics system must have enough autonomy to last 15 minutes on the launch pad before take-off. They must also exhibit a capacity to withstand the rigours of flight and ideally be housed in a tidy manner.

Stage 1 Booster

Internal Structure / Layout

The 1st stage booster will be approximately 1.2m long with an outer diameter of 76mm and will be made of carbon composite materials.

Control Systems

The 1st stage booster will not be actively controlled on ascent, the only passive control applied are the fins. However, on descent, control surfaces will deploy

Telemetry

In flight computers will collect data from accelerometers, cameras and GPS receiver. The
data from the accelerometer and GPS receiver will
then be sent to the Raspberry Pi controller, which
will be converted into signals sent to the control
surfaces.

Stage 1 Booster

Electronics & Software

The booster will need to take real-time data and act upon the information it receives as fast as possible, whether it be a required correction to the thrust, or contracting a sudden increase in wind. As such, a controller with high processing power will be needed. The most likely candidate is the Raspberry Pi. The software will be coded in C++, because it will allow us to work in real-time at high speeds and efficiency.

Recovery

The hybrid rocket will be reignited during descent to slow down the first stage. The valves coupled with the on-board hardware will allow the rocket to be actively throttled, allowing it in essence to make a soft, upright landing. As per the mission goals, a parachute will thus not be required. However, one may be fitted during the test phases as part of an abort system.

To ensure stability on the ground at touch-down, spring-loaded legs will be fitted on the bottom of the rocket, flush to the fuselage. During descent, the legs will be allowed to spring open and hence lock into place. When possible, damping will be integrated into the legs.

Launches

The video below is from our launch on the 11th of march 2018 of our prototype competition rocket that will become the second stage of the final rocket. The launch was largely successful, minus the parachute deployment failure. The motor used in for the launch was a Cesaroni Bluestreak with 116 Ns of total impulse.