Fuels for Space Flight

Handling Hypergolic_Fuel_for_MESSENGER spacecraftFuel for Thought.

by Robert Brand. Fools and Fuel. It is the one thing that you can’t avoid and possibly the biggest risk to spaceflight. Fuel.

ThunderStruck will start with the premise that we are going to use the safest fuels and the greenest where ever possible.

Since we are initially talking about booster capability, we are looking at solid fuels and for safety, we will also not use hypergolic fuels as they are very dangerous.

This excerpt from Wikipedia:

A hypergolic propellant combination used in a rocket engine is one whose components spontaneously ignite when they come into contact with each other.

The two propellant components usually consist of a fuel and an oxidizer. Although commonly used hypergolic propellants are difficult to handle because of their extreme toxicity and/or corrosiveness, they can be stored as liquids at room temperature and hypergolic engines are easy to ignite reliably and repeatedly.

In contemporary usage, the terms “hypergol” or “hypergolic propellant” usually mean the most common such propellant combination, dinitrogen tetroxide plus hydrazine and/or its relatives monomethylhydrazine and unsymmetrical dimethylhydrazine

Our booster will have a mass of about 2500Kg to 3,000Kg with fuel and the fuel will be about 2/3rds of the mass.

Below is a list of most common space fuels in use today. Please look up any words that you don’t understand.

We will discuss the Specific Impulse and Density Impulse more in a later post.

Specific Impulse:

Wikipedia:    https://en.wikipedia.org/wiki/Specific_impulse

Specific impulse (usually abbreviated Isp) is a measure of the efficiency of rocket and jet engines. By definition, it is the total impulse (or change in momentum) delivered per unit of propellant consumed and is dimensionally equivalent to the generated thrust divided by the propellant flow rate. If mass (kilogram or slug) is used as the unit of propellant, then specific impulse has units of velocity. If weight (newton or pound) is used instead, then specific impulse has units of time (seconds). Multiplying flow rate by the standard gravity (g0) before dividing it into the thrust, converts specific impulse from the mass basis to the weight basis.

A propulsion system with a higher specific impulse uses the mass of the propellant more efficiently in creating forward thrust, and in the case of a rocket, less propellant needed for a given delta-v, per the Tsiolkovsky rocket equation. In rockets, this means the engine is more efficient at gaining altitude, distance, and velocity. This is because if an engine burns the propellant faster, the rocket has less mass for a longer period of time, which makes better use of the total force times time that was acquired from the propellant. This is much less of a consideration in jet engines that employ wings and outside air for combustion to carry payloads that are much heavier than the propellant.

Density Impulse:


Impulse density is a way of measuring the performance of different propellants regardless of their density. It’s a measure of how much force per time (impulse) you’ll get from a given volume of propellant. Higher density fuels have a higher Impulse Density because Impulse density is basically the propellants Specific Impulse multiplied by it’s density.

As comparison Lox-Butane and Lox-Methane both have a specific impulse of 365s, but the average density of Lox-Butane (at 1000psi) is 890.62kg/m3 while Lox-Methane is 823.34kg/m3. So Lox-Butane’s Impulse Density = 890.62 * 365 = 325076.3Kg-f-s/m3 and Lox-Methane = 300519.1Kg-f-s/m3.

This basically means that per Kg of Lox-Methane you’ll get the same Isp as Lox-Butane, but Lox-Butane can be stored in a smaller tank.

Combustion chamber pressure, Pc = 68 atm (1000 PSI) … Nozzle exit pressure, Pe = 1 atm
Oxidizer Fuel Hypergolic Mixture Ratio Specific Impulse
(s, sea level)
Density Impulse
(kg-s/l, S.L.)
Liquid Oxygen Liquid Hydrogen No 5 381 124
Liquid Methane No 2.77 299 235
Ethanol + 25% water No 1.29 269 264
Kerosene No 2.29 289 294
Hydrazine No 0.74 303 321
MMH No 1.15 300 298
UDMH No 1.38 297 286
50-50 No 1.06 300 300
Liquid Fluorine Liquid Hydrogen Yes 6 400 155
Hydrazine Yes 1.82 338 432
FLOX-70 Kerosene Yes 3.8 320 385
Nitrogen Tetroxide Kerosene No 3.53 267 330
Hydrazine Yes 1.08 286 342
MMH Yes 1.73 280 325
UDMH Yes 2.1 277 316
50-50 Yes 1.59 280 326
Red-Fuming Nitric Acid (14% N2O4) Kerosene No 4.42 256 335
Hydrazine Yes 1.28 276 341
MMH Yes 2.13 269 328
UDMH Yes 2.6 266 321
50-50 Yes 1.94 270 329
Hydrogen Peroxide (85% concentration) Kerosene No 7.84 258 324
Hydrazine Yes 2.15 269 328
Nitrous Oxide HTPB (solid) No 6.48 248 290
Chlorine Pentafluoride Hydrazine Yes 2.12 297 439
Ammonium Perchlorate (solid) Aluminum + HTPB (a) No 2.12 277 474
Aluminum + PBAN (b) No 2.33 277 476

More discussion on fuels in a future post and we will explain our initial choice of booster propellant. The results of an explosion can ruin a flight or kill people. Safety is the big issue. More on that too in a later post.

aptopix india rocket fuel explosion

BOR-4 breakdown

ThunderStruck Spacecraft Development Begins

BOR-4 breakdownWinged Spacecraft Takes Form

Our Australian ThunderStruck team has commenced design of the ThunderStruck Spacecraft. This graphic (right), courtesy of Project Thunderstruck team member David Galea, is just a doodle to break down the benefits of the USSR BOR-4 design. Yes, we started with a 50 year old design and have worked our way forward as the basic air frame is a solid design that has a good flight track record. We then looked at Dream Chaser which looks surprisingly similar, but with a modern interior. We too will have a similar design to both of these but with some big differences. Our starting length will be 3m (10 feet); our unfueled mass is expected to be 400Kg and optimum payload return will be 50Kg. It will have hypergolic fuel for the space flight – main thrust and hypergolic thrusters. If our air-frame can’t support the mass, then we will increase the lift or size. The fuels under consideration are not like the very dangerous Hydrazine used extensively for most NASA missions, but much safer fuels that are pretty safe for humans. They often don’t pack the punch of Hydrazine, but safety is our biggest goal so long as the thrust is powerful enough to do the job.

This from Wikipedia: https://en.m.wikipedia.org/wiki/Hypergolic_propellant

A hypergolic propellant combination used in a rocket engine is one whose components spontaneously ignite when they come into contact with each other.

The two propellant components usually consist of a fuel and an oxidizer. Although commonly used hypergolic propellants are difficult to handle because of their extreme toxicity and/or corrosiveness, they can be stored as liquids at room temperature and hypergolic engines are easy to ignite reliably and repeatedly.

We are now go for liftoff in eerrhhhh …in 6 years… But we have started. We are choosing a suitable fuel at this time – one that is relatively safe for humans and still able to provide the thrust needed to de-orbit and maneuver. There are new fuels – not as powerfully as many of the well known thruster fuels, but sacrificing power for safety could be a really good thing if the numbers stack up.

Our Invasion of Space has Begun.

Let’s rewind a bit. ThunderStruck is a Spacecraft under development. This story is about our spacecraft that we are building for actual flight many years from now. We also have a transonic test vehicle that has yet to fly, but we hope early next year we will get permission to fly the craft in northern Queensland (QLD) – probably a little North East of Longreach, QLD. There may be more test vehicles and even the design of our spacecraft may end up radically different from our

At this time, the Thunderstruck transonic test vehicle has been on hold, but it too will benefit from the spacecraft design kicking off since they may share common components. The Spacecraft will be slow to design and build compared to the transonic testing flier, but we have to start this if we are to finish it in a timely fashion. So back to our spacecraft design.

It is expected that we will partner with a university that will assist with the build. At this time we are closest to Sydney University and we know that they have similar goals of working with a winged re-entry flier.

It is clear that we are not relying on using the Russian BOR-4 as a blueprint, but it is a starting point. It is also clear that the BOR-4 and the Sierra Nevada Corporation’s Dream Chaser share a lot of common air frame characteristics. So Dream Chaser was the next craft to go under the microscope.

Critical to the design and thus one of the first components to understand is the type of fuel that will be needed. This may determine that we need a bigger craft to carry the tanks or that the shape must be different to handle the large tanks.

Dream Chaser Graphic on top of a Rocket for LaunchDream Chaser (pictured right) is large and has a crew. Our craft does not have a crew and the ThunderStruck spacecraft is small in comparison.

Dream Chaser can launch on top of a rocket and we expect ThunderStruck to do the same. ThunderStruck is way smaller and potentially has folding wings and thus could sit inside a fairing making the ride more comfortable.

ThunderStruck will have a docking ring and the ability to swap old and new payload canisters. ie to provide a new empty canister to , say, an asteroid service craft and bring back a full set of samples.

ThunderStruck will evolve and its capabilities will change as we grow. Our aim is to make the smallest rocket launched spacecraft with wings for re-entry and an exchangeable payload.