The world oldest and functional satellite is the Lincoln calibration sphere, it’s a huge, aluminum sphere possessing a cross section that has been existing on the Earth orbit since 1965.

It is said to be the oldest satellite without having power, is has a 3 feet 8 inch diameter metal sphere and also provides ground based radars with the aim to calibrate their instruments.

During calibration, one needs to posses a reference data at which the radar output can be juxtaposed. It as well helps in fine running of the radar to make sure it’s output is same as the expected result.

Ready full blog article
https://link.medium.com/ODju97NkOAb