Exotic?

The structure of the satellite is mostly aluminum, and the solar panels are mostly silicon. Burning them in reentry forms compounds with oxygen.

Those are the three most common elements on the planet. Aluminum-Silicon-Oxygen compounds make up more than 60% of the Earth's crust. Add water and you basically have common clay.

There isn't a single combination of elements that's less exotic.

Redshifting slows down the frequency of light. But the total amount of oscillations of the light signal isn't affected.

Suppose a far away galaxy sends a 1 second long burst at 1 GHz, 1 billion cycles. At Earth it arrives redshifted to twice the wavelength, and a frequency of 0.5 GHz. We still receive 1 billion cycles, they're just spread over 2 seconds of time now. So we effectively see the signal - and everything else from that distant galaxy - at 0.5 speed.