It is technically the oldest operational spacecraft[note 1], but it has no power supply or fuel; it is merely a passive metal sphere.

[3] The sphere was constructed from two hemispheres, made by spinning sheet metal over a mold.

These hemispheres were fastened to an internal, circumferential hoop by 440 countersunk screws, then milled and polished.

The initial finish had a surface roughness less than 10 micrometres and was expected to last for five years.

[5] Since its launch, I-band measurements have shown periodic deviations that likely correspond to one or more new surface irregularities.