It was a crowded field on Monday, with commenters weighing in on everything from zombie-cakes to the first families of science fiction to the hidden motivations of flesh-eating plants, but only one comment can be comment of the day and today that comment comes from Rod Brock.

He shared this bit of trivia, responding to "The Union Jack on the Moon," about what rocket fuel is made of and it's surprisingly pencil eraser-like consistency:

If memory serves me, the solid fuel boosters on the Shuttle were comprised of a mixture of powdered aluminum, ammonium perchlorate (oxidizer), iron oxide, and an epoxy binder. The final result was a product about the consistency of a pencil eraser; this semi-soft quality is important because the way solids work, with a hollow core, it is potentially disastrous if any cracks should develop in the grain, because the fuel will burn along the length of the crack, quite likey burning through the outer shell of the rocket and causing a catastrophic failure.


You learn something new everyday, and today that thing is what rocket fuel feels like.

Image: Celso Diniz / SHUTTERSTOCK