Recently the ISRO GSLV launch was called off on account of a fuel leak. Other launches too have, on occasion, been called off for similar reasons.

Fuel used to launch a craft to orbit may be solid, or liquid.

Has solid fuel leakage ever been reported? Can solid fuel even leak?

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    $\begingroup$ A leak of the container of solid fuel could be very dangerous when the solid fuel is burning under high pressure. There is no solid or liquid leaking but very hot gases. Remember the Space Shuttle Challenger accident, it was a caused by a leaking O-ring seal of the solid fuel boosters. $\endgroup$
    – Uwe
    Oct 10, 2017 at 18:48

2 Answers 2


"Solid" fuels are not all completely solids.

Some are actually pastes — viscous liquids, often colloidal suspensions — these can (very slowly) ooze. Some are pastes until they are cured; if not properly cured, they can remain liquid.

Some are particulates with binder chemicals. If the binder ages, liquifies, or otherwise becomes less effective, the particles can fall out.

Some are themselves solids that can liquify at certain temperatures below ignition temperature; if heating happens, this can result in liquefaction.

Potassium Nitrate and Sugar fuels can be liquified by humidity and/or temperature, and is crystalline and thus fragile and frangible. Vibration can render it cracked or even powdered, and it's hygroscopic; in wet enough conditions, it dissolves in water, and can result in sticky flammable messes.

Zinc-Sulfur propellant and black powder propellant are pressed powders - vibration can cause particles to come loose and "leak". (corollary: Never store a black powder rocket next to your subwoofers...)

Ammonium-nitrate & Aluminum or Aluminium Perchlorate & aluminum fuels use a binder, typically Hydroxyl-terminated polybutadiene (HTPB); the binder can potentially degrade over time resulting in fuel particle losses.

Hydroxyl-terminated polybutadiene (HTPB) itself is used as a solid fuel itself in a hybrid design; it's oxidizer is Nitrous Oxide.

Gunpowder & wax is a rarely used colloidal solid propellant; thin layers of wax are used to bind together the powder and reduce the powder's reaction rate. The wax can melt at not too terribly high a temperature, and a hot summer day can result in such propellant slumping or even running. Parafin, while melting at 122°F or so, will slump at about 80°F, so if experimenting with wax and powder mixtures, use beeswax, and even then, don't leave it in the car on a hot day - beeswax melts around 145°F, and a closed car on a hot summer day can hit 160°F readily.

Any hybrid rocket can have leaks of the liquid component, while still having the solid.


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    $\begingroup$ What about auxilliary systems? The solid rocket boosters for the space shuttle were steerable; the steering system needs a power source to drive the hydraulic actuators, which came from hypergolic fuel - a liquid. So, although a solid fuel rocket, still contained/employed liquid fuel which, technically, could be vulnerable to leaking. $\endgroup$
    – Anthony X
    Aug 27, 2013 at 3:16
  • $\begingroup$ Thr question is about the solid fuels themselves not auxiliary systems, at least as currently written... "Has solid fuel leakage ever been reported? Can solid fuel even leak?" ... thus APU fuel is off topic. $\endgroup$
    – aramis
    Aug 27, 2013 at 17:12

Solid Fuel, per se, ought not to leak.

But there is hydraulic fluid for Thrust Vector Systems (TVC) that can leak.

Hybrids, like Virgin Galactic's Space Ship 2 will use have a solid fuel, but a liquid oxidizer so they can be started and stopped.

There may be an APU (Aux Power Unit) like system that burns some kind of fuel to provide electrical power needs beyond what a battery could provide.


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