First rocket motors were made from gun powder tamped inside a
tube. Tamped gun powder had several disadvantages:
Nowadays gun powder is no more used inside rocket motors.
Solid rocket fuel is made of a mixture of a high yield oxidizer
(ammonium perchlorate for example) instead of potassium nitrate
and a high yield fuel (a plastic or rubber) instead of charcoal
- It was very fragile. Cracks could appear inside the powder
the motor was lit. The flame would then penetrate inside the cracks,
the powder inside the cracks was lit and the rocket motor explodes.
- Tamping the gunpowder with a hammer was dangerous work.
- Two different rocket motors would work differently. One
could not trust the thrust of a rocket motor.
- Gun powder does not contain a lot of energy.
The plastic allows to mold the fuel block any shape and makes
it be very strong. The boosters of the Space Shuttle and the
Ariane 5 space rocket are powered that way.
A lot of receipts exist and additives are most often added to
regulate the burning speed versus pressure and to increase the
yield. Part of the plastic can be replaced by aluminum powder
which is a better fuel. A very satisfactory solid fuel is a
mixture of nitroglycerin and nitrocotton, two high explosives.
During my experimentation with solid fuels, I used mixtures of
an oxidizer powder and viscous fuels like glycerin or paraffin.
The result is a more or less fluid paste. Maybe paste fuel can be used
for big high yield rocket
motors. One way would be to mix an oxidizer powder with an excess of
in order to get a rather fluid paste and a high yield. The paste would
inside a burning chamber. The paste reservoir would be a long silo
above the burning
It is possible to let the reservoir be under low
pressure and let a pump inject the paste inside the motor
chamber at huge pressure. Yet I'm not quite sure this would be
very effective. Probably the best solution will be to let the
reservoir be at the same pressure as the motor chamber or
higher. That can be achieved through a tube going from the
motor chamber towards the top of the reservoir or by using gas
generators. The reservoir must be able to resist that pressure,
just like a common solid fuel rocket motor envelope does.
The paste will flow inside the motor chamber through one or
more holes at the bottom of the silo. It is essential electric
motors are used to crumble the paste in very small pieces. Those
pieces will light easily and power the motor.
Such a rocket motor would have several advantages:
- The reservoir can be made of materials that do not
withstand high temperatures. This allows to use staunch high
technology materials. The reservoir weight saving can be
- It is rather easy to control the flow of paste inside the
chamber. High pressure peaks can thus be avoided. So a lower
construction security factor can be used.
- Because less or no additives will be necessary to
stabilize the burning speed and because
paraffin is one of the best rocket fuels, the specific impulse
will be higher than that of a standard solid fuel rocket.
- The rocket will be more compact than an equivalent solid
fuel rocket because there is no need for the huge central
chimney inside the solid fuel block.
- Unless it is crumbled, a paste containing a lot of paraffin
is impossible to light. Should an accident occur the paste will
fall on the ground and will not burn.
- Fuel transport and storage is made considerably safer and
cheaper because the oxidizer powder and the paraffin can be
apart. They can be mixed only to be put inside the rocket
reservoir. Even if the reservoir must be emptied because of
launch delays the fuel will remain safe to handle inside
reservoirs situated close to the rocket.
- Dropable reservoirs can be used with a single motor.
Please do not experiment with rocket fuel
if you are not part of an authorized laboratory.
accidents is not possible. Every person I know who did
private experiments got a severe accident and was awfully hurt. One
person lost his brother. Another person got a friend's hand exploded.
Yet another got several months in hospital and bad sequels. Although
having a very good
understanding of whatever I was doing, I got accidents too.
Luckily, because I followed strictly a lot of tight security
rules and never made any exception, I did not get injured severely
the cost of the destruction was not too high. Most effective rules are
to keep cans always closed, store oxidizers and fuels far apart, use
only very little quantities at a time and make very little rocket
motors, use no metal or glass parts and only cardboard, glue and soft
plastic, be patient, have a bucket of water at hand, always use an
electric ignition system with a very long wire, stop working when tired
and especially avoid unresponsible people. Authorized
laboratories have insurances, own different kinds of security
and protection equipment and every experiment is checked
beforehand by trained people. At least ask a Chemistry teacher.
I wish to thank Bob Russell for reading and correcting the text.
October 28 1998
till February 18 2003