A Level Chemistry pupil, Fraser, has produced a fascinating article on rocket fuels and propellants

Fraser H (L6^th Form, Blackford House) has undertaken some extensive research into rocket fuels and propellants to produce a presentation for the Chemistry Symposium at Sherborne School for Girls. In the article below he has summarised his findings and it makes for a fascinating read.

Hannah Seal - Head of Chemistry

Rocket propellants are, broadly, substances combusted in an engine to produce thrust. This thrust provides the kinetic energy a rocket needs to transport its payload, be that astronauts or intercontinental ballistic missiles, from point A to point B.

When these propellants (a combination of energy-dense fuel and oxidiser) are ignited they release hot, high-pressure gasses which exit a rocket as exhaust. This departure of the propellant mass causes a rocket to accelerate forward, as Newton’s 3^rd law of motion dictates that when propellant mass is ejected from the back of a rocket, it pushes the rocket with an equal but opposite force.

An example of one of the most long-established fuels is Kerosene, made of Carbons and Hydrogens. Although you can purchase it in almost every petrol station across the UK, it was powerful enough to transport the first humans to the moon!

A more recent innovation in rocket locomotion was shown in 2021 when the company bluShift Aerospace launched the first rocket using a proprietary biofuel hybrid-propellant engine. The fuel contains ethanol derived from corn, a nearly carbon-neutral source of alcohol.

However, it’s not all smooth sailing for interstellar satellites; rocket propellants are incredibly dangerous substances. Ammonium Perchlorate Composite Propellant was used on the U.S. Titan rockets in addition to the UK’s submarine launched ballistic missiles, and is a combination of Ammonium Perchlorate (AP) and a metal (normally aluminium) fuel. On the 4^th of May 1988, a fire followed by several explosions occurred at the PEPCON chemical plant, causing two fatalities, 372 injuries, and $100 million dollars worth of damage. It occurred when sparks from a welder’s torch spread into a fiberglass material. While fiberglass is normally used in insulation and is non-flammable, some AP residue nearby caused the sparks to turn into a fire, spreading to nearby barrels of chemicals. This caused a chain reaction, and the first explosion alone was the equivalent of 17 to 41 kg of TNT.

From information hailing from research done before the space race, my final tale of danger and caution is about Chlorine Trifluoride, a high-performance oxidiser investigated by Germany in WW2 as a potential oxidiser for self-igniting flamethrowers before being researched by rocket scientist John D. Clark. ClF₃’s danger comes from, at most*, its extraordinary property of hypergolicity; spontaneously igniting when coming into direct contact with a number of substances, including but not limited to:

• Wood
• Cloth
• Sand
• Asbestos fireproofing
• Water

It also reacts explosively with the last three items listed. When dealing with spillages of this chemical, Dr Clark personally recommends “a good pair of running shoes”.

*ClF₃ is also highly toxic and corrosive.

Fraser H - L6^th Form, Blackford House

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