SpaceForest is located in the Pomeranian Science & Technology Park (PPNT) in Gdynia () SpaceForest...

SpaceForest is located in the Pomeranian Science & Technology Park (PPNT) in Gdynia (www.spaceforest.pl)

SpaceForest creates and actively explores innovative ideas. Our company specializes in Artificial Intelligence (AI) and Video Recognition (VR) solutions, which are used in optimization of industrial processes. SpaceForest works on diverse tasks in many different areas of engineering related to electronics, IT and space-tech.

the software for post-production computer aided tuning of microwave filters

TrimSolutions software is applicable in tuning ofvery high frequency telecommunication single and multimode satellite filters up to Ka band (40 GHz)

2013 SpaceForest Ltd. – All rights reserved.

Purpose of building a rocket

Call: ARTEMIS 2013; European Commission

Project: DEWI Dependable Embedded Wireless Infrastructure

(3rd place of 22 Artemis projects)

Business Needs: Reduction of aircraft weight by removing wires and using WSN (Wireless Sensor Network)

Domain: AERONAUTICS aeroplanes, helicopters, launchers

Example: the Ariane 5 telemetry system contains of 600 to 800 sensors. Telemetry system control unit is centralized. Thousands of cables are spread all over the 40 meter launcher. 70 % of Ariane 5 avionics mass are cables.


Purpose of building a rocket

Use Case: MTL (Multilink Telemetry Logger) in Space Test, supported by Spain

Demonstrator: TEST ROCKET SpaceForest as the lead partner

Demonstrator of outcomes of the project – a test rocket proposed by SpaceForest - was very well received. Large of the needed demonstrator propulsion:

100 [kNs] of engine total impulse,

1 [Ton] of thrust

~50 [kg] of burned propellant


Why hybrid propulsion?

Advantages (in comparison to solid rocket engines):- Fully legal regarding to the Polish law. This kind of engine is not a pyrotechnic or explosive material. R&D activities are not restricted.- Increased personnel safety.- Possibility of thrust control.- Possibility of emergency shut down.

figure made by Paweł Surmacz

Disadvantages:- More complicated.- Lower oxidizer and fuel density.- Bigger propulsion system volume.- Oxidizer losses during the rocket tank fueling.


Our choiceNitrous Oxide N2O as oxidizer

Advantages:- relatively inexpensive and available on the market,- easy storable in normal conditions,- auto-pressurized 51 [bar] @ 200

(extrusion system not needed),- non-toxic,- possibility to use typical materials like aluminum, stainless steel, Teflon.

Disadvantages:- pressure tank needed (large mass),- low density of the liquid phase 0,786 [kg/dm3] @ 200C only,- lowest specific impulse in comparison to other

oxidizers.- critical temperature 36,42 0C


Our choice

Paraffin wax as fuel

Advantages:- inexpensive and available,- non-toxic,- environmentally compatible,- high regression rate, possibility to use a single hole grain,- short combustion chamber with a single port grain,- reusable grain and easy to mix with additives.

Disadvantages:- engine excitation problems,- low density 0,92 [kg/dm3],- low mechanical strength. figure made by Paweł Surmacz


Proof of concept

1. Minimal construction material cost.2. Use of industry standard equipment.3. Easy to transport test platform.4. Use of safe uninhabited area for testing.


First cold test 3,2 [kg] of N2O in 8,0 [dm3]45 [bar] tank pressure90 [mm2] injector throat Liquid:2,54 [kg] & 0,82 [kg/dm3]Vapour:0,66 [kg] & 0,13 [kg/dm3]

1,7 [s] dicharge time; 1,49 [kg/s] flow rate; of N2O liquid phase

injector discharge coefficient Cd:

Cd = flow rate / injector throat * (2 * liquid density * Δpressure)^0,5

Cd = 0,194

Valve gear box and hydraulic system worked properly.


First cold test


First burn test MDF tube saturated with paraffin wax

3,3 [s] of liquid phase burn time as expected6570 [kNs] of total impulse 1797 [Ns/kg] of specific impulse large excitation of thurst on the end of liquid phase

small port diameter 30 [mm] => large oxidizer mass flux 1100 [kg/s*m2]


First burn test MDF tube saturated with paraffin waxGrain advantages:good density 1,02 [g/cm3]

Grain disadvantages: - low strength -> grain damages (several cracks),

- small content of paraffin wax in the grain (36 % only),- low regression rate (@ L/D = 15,4)- too big Oxidizer-to-Fuel ratio (O/F) = 8,6 N2O share 89,7%,- graphite nozzle throat erosion,


Test no.2 and no.3 Wastepaper tube saturated with paraffin wax

Different tank pressure40 [bar] and 57 [bar]

Other conditions unchanged

No influence on O/F ratio

Visible influence on efficiency

40 [bar] - 1567 [Ns/kg]57 [bar] - 1719 [Ns/kg] (10% more than @ 40 [bar])

Big influence on average thrust in the liquid phase40 [bar] – 1400 [N]57 [bar] – 2600 [N] (86% more than @ 40 [bar])


Test no.2 and no.3 Wastepaper tube saturated with paraffin wax

Stable combustion: Ox Mass Flux 410 – 550 [kg/s*m2]

Grain advantages:- good grain density: 1,01 [g/cm3],- good ignition and test performance,- good strength of the fuel grain.

Grain disadvantages:- low paraffin saturation level - 35% only,- low availability of a thick-walled paper pipe, - low regression rate,- glue content (polyvinyl acetate + polyvinyl alcohol +

kaolin),- empty spaces in spirally wound tubes – gas channels,- graphite erosion.


Test no.5 Clean cellulose roll saturated with paraffin wax- no data, acquisition failure

- impressive flame

- too high regression rate

- very low O/F = 3,8 N2O share 79 %

- risk of setting the launch site on fire by scraps of cellulose

- lower grain density than MDF and wastepaper tube 0,86 [g/cm3] only

- saturation problem, air bubbles in the grain



Test no.6 Polypropylene fiber roll saturated with paraffin wax

- severed and burned injector plate- low Throat/Injector ratio T/I = 4,0- high liquid phase average thrust Lt = 3300 [N]

Grain advantages:- only 30% of the PP reinforcement- easy to saturate- fuel grain unbreakable - regular port surface after burning- no risk of throwing burning PP pieces

Grain disadvantages:- too low O/F = 3,8 ; N2O share 78 %, similar to cellulose fiber


Test no.7 and no.8 Polypropylene fiber roll saturated with paraffin wax

Repeatability verification of test results with the same test bed and engine

similar test conditions:

Tank pressure 50 – 51 [bar]

similar test result:

efficiency difference 1% only

liquid phase average thrust difference 3% only



Cold tests due to ignition failures

Tank pressure 51 [bar] and 52 [bar]Combustion chamber (CC) pressure 4 - 5 [bar] onlyLiquid phase thrust 380 [N] only

In comparison, hot tests in thesame conditions:

CC pressure 35 – 36 [bar]Liquid phase thrust 3300 [N]

Both parameters about 8x bigger than @ cold test



Comparison of the T/I ratio’s influence on test performance

Test no. 11 new injector 21x2,5 mmT/I = 6,2tank pressure 51 [bar]CC pressure 35 [bar]typical Isp = 1744 [Ns/kg]ideal shape of thrust characteristics

Test no. 12 injector extended to 21x2,8T/I = 4,9tank pressure 52 [bar]CC pressure 38 [bar]lower Isp = 1666 [Ns/kg]visible excitation of thrust


Test no.12 and no.13 Polypropylene fiber roll saturated with paraffin waxComparison of the L/D ratio influence on test

performance

Test no. 12port diameter 50 [mm]; L/D = 8,6tank pressure 52 [bar]efficiency 1666 [Ns/kg]Ox mass flux = 830 [kg/s*m2]excitations but stable flame

Test no. 13port diameter 38 [mm]; L/D = 15,4tank pressure 50 [bar]efficiency 1637 [Ns/kg]Ox mass flux = 1650 [kg/s*m2]excitations but extinguished flame on the end of liquide phase


Test no.13


Test no.14 Polypropylene fiber roll saturated with paraffin wax

Check of the influence of a low T/I value on test performance

Test no. 14 – injector extended to 21x3,0 mmT/I = 4,3port diameter 50 [mm]tank pressure 52 [bar]CC pressure 42 [bar]efficiency 1708 [Ns/kg]

large excitation of thrustin whole liquid phase


Test no.15 and no. 16 Polypropylene fiber roll saturated with paraffin waxTest of a new injector type

Test no. 15 new injector 36x1,5 mmT/I = 10,0port diameter 50 [mm]tank pressure 50,5 [bar]CC pressure 42 [bar]very low Isp. 1279 and [Ns/kg]

Test no. 16 injector 51x1,5 mmT/I = 7,1port diameter 38 [mm]tank pressure 51 [bar]CC pressure 38 [bar]very low Isp. 1394 [Ns/kg]

very large excitation of thrust


Test no.17 Polypropylene fiber roll saturated with paraffin waxTest bed changes: stable trolley, loose engine,

joint ball on S-cell

modified injector from test 14 15 x 3,0 mm T/I = 6,0port diameter 50 [mm]tank pressure 56 [bar]good Isp 1812 [Ns/kg]

100 Hz large excitation of thrust not eliminated

What to do ???


Test no.18 Paraffin wax + PE wax + EVA

Test of a paraffin grain without reinforcement , with additives

the same injector as in the previous test,pre-combustion chamber used for the first time (20% shorter grain),still too low O/F ratio = 3,86 typical Isp = 1734 [Ns/kg],good grain state after burn,

excitation eliminated

100Hz character of fluctuation but on an acceptable level


Test no.19 Paraffin wax + PE wax + EVA

Using post-combustion chamber mixing plates

two mixing plates added into the post-ccthe same injector and pre-cc10% shorter grainideal O/F ratio = 5,6 (85% N2O)flame with a visible standing wave first mixing plate damaged

no excitation !no tones into characteristic spectrum(noise character of thrust fluctuation)


Test no.20 Paraffin wax + PE wax + EVASpaceForest’s invention to stabilize combustion and to

eliminate excitations: geometric configuration of the injector in a conical shape.

new cone-shaped injectormodified first mixing plate (bigger ablative thickness)the same pre-combustion chambersimilar grain without reinforcement

grain damaged due to defect of the casttoo low O/F ratio = 3,11 (76% N2O)

very good thrust characteristicsdespite the big paraffin consumption


Know-How conclusionsN2O tank pressure has the main influence on average thrust

and on resulting specific impulse.N2O flow rate has no influence on O/F ratio.

T/I ratio reduction increase CC pressure and thrust (the same T).

The most useful type of reinforcement was polypropylene fiber.

~30% share of PP does not attenuate the paraffin regression rate.

Enhancement of the paraffin wax grain with various additives gave good results, for example for hardness with PE wax and for flexibility with EVA - ethylene copolymer and vinyl acetate.

Used PP fiber and additives do not prevent motor excitation.

The main causes of the thrust excitation is a too big fuel share due to the high regression rate of the paraffin wax.


Know-How conclusionsOther causes of excitation during the test campaign:

- injector construction based on vertically and axially located holes,

- too low T/I ratio,- too large Oxidizer Mass Flux,- too large fuel share,- lack of pre-combustion chamber.

Ways to eliminate excitation are:

- injector with holes located away from the motor axis,- injector geometry based on cone shape as proposed by

SpaceForest,- proper nozzle throat diameter ensuring T/I ratio above 6,- proper port diameter ensuring Ox Mass Flux below 1000

[kg/s*m2]- proper L/D ratio ensuring 85% share of N2O,- using a pre-combustion chamber,- using mixing plates inside the post-combustion chamber.


Flight experimentAdaptation of the test engine to a rocket model RTP7the same engine (like in test 20) with added finsaluminum tank filled with 3 [kg] of N2O rocket height 3,3 [m], start mass 18 [kg]Flight organized and supported by PTR Polish Rocketry Society

Engine damage due to poor sealing near injector.


Flight experimentRegistered data of the engine thrust during the flight

two onboard ARECORDER flight computers

acquisition frequency 100 Hz

0,3 [s] of start thrust on expected level ~ 2,5 kN good start acceleration >10g


Flight experiment 2Launch experiment by Cracov Team of PTR

K1X rocket tested in several flights, equipped first time with hybrid engine based on N2O & PE, undependent own technology,

ideal ignition, impressive launch performance,



Flight experiment 2Launch experiment by Cracov Team of PTR

thrust based on flight acceleration data - above 1 [kN]

possible flight altitude of 11 km with fully filled tank

SpaceForest Ltd.Pomeranian Science & Technology Park

Al.Zwyciestwa 96/9881-451 Gdynia Poland

www.spaceforest.pl, www.ppnt.pl

[email protected];

phone: +48 58 698 21 86 ;

fax: +48 58 698 21 88;

R&D Department:

[email protected]; mob: +48 608 666 164;

Contacts


Thank you for your attention


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