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:
https://en.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.

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:

https://www.quora.com/What-is-density-impulse-and-why-do-propellants-with-higher-densities-have-higher-density-impulses

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.

ROCKET PROPELLANT PERFORMANCE
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.

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