Building a rocket that still works after 1000 years

Building a rocket to Mars is one thing. Building a rocket that is still functional after a thousand years is quite another. First, you have to freeze the crew. Otherwise, they'd be long dead before you got there. Second, it has to be as simple as possible. The fewer moving parts, the less likely something will break. Third, volatile propellants will dissipate over time. Magnetism is reliable. I had my characters use magnetic boots to grip the outer hull of the Ark. Magnetism lasts a long time.

The Ark used solid-state fuel for their retros and their SSTO booster. In theory, the fuel could last ten times that. Finally, the explosive "bolts" that were used to separate the various sections of the Ark weren't bolts at all. It was a continuous ring of thermite. This would be stable for the requisite time. To ignite it and separate the sections, a space walk is required. You can see the mechanics in the short story "Rei's Space Walk" to be published in 2014 but here is a synopsis:

Rei pulled the cover free, exposing a crank. He turned the crank which energized a magneto which rotates a permanent magnet around within a coil. The resultant EM force is stored within a capacitor. When the capacitor is fully charged, shorting it out causes a spark which ignites the thermite. Thermite is very stable. Rei had a little trouble but he was able to overcome it. Here's a brief excerpt:

“Stuck, duh,” Rei thought to himself. He pressed the ignition switch and stood up. A puff of smoke shot out of the rim of cargo section where the lattice-work attached. The smoke raced around the circumference of the ship until it was out of sight. Rei bent past the rear stabilizer and in a less than a minute, the circle of smoke came back around, ending where it began.

He was successful, in the end. He was able to jettison the propulsion section and MINIMCOM was able to tow the Ark at a 20% higher velocity thus getting them to Deucado in under a year.