The Oldest Functioning Satellite

The Lincoln Calibration Sphere 1, or LCS-1, is a large, hollow, aluminum sphere with a precisely defined cross-section that has been on Earth orbit since 1965. It is considered to be the oldest functioning satellite even though it has no power and no electronics. This is because, this 3 feet 8 inch diameter metal sphere is still true to its original purpose—provide ground based radars with a target to calibrate their instruments.

To calibrate radar, it's necessary to have a reference point of known data against which the radar output can be compared. This enables fine-tuning of the radar to ensure that its output matches the expected results. Calibration spheres are designed to have a consistent Radar Cross Section (RCS) value, making them an effective tool for calibrating. However, if more accurate tracking tools, such as lasers, are available for satellite tracking, the same satellites could also be used to calibrate radar position data.

Lincoln Calibration Sphere 1 was launched in 1965. Attempts to launch two more calibration spheres, designated LCS 2 and LCS 3, resulted in launch failures. LCS 4 was successfully launched in 1971 and is expected to have a life time of about 75 years. LCS 1, on the other hand, will probably outlast humanity with a predicted life time of 30,000 years.

The Lincoln Calibration Sphere 1

Apart from passive satellites such as the Lincoln Calibration Spheres, active calibration satellites equipped with transponders that emit a signal on command are also used. To determine the satellite's location, a ground radar station sends a transmission command and records the resulting measurement. The transponder's signal is received by a radar receiver and, along with the satellite's ephemeris data, used to compute the satellite's precise position. This position is then compared with the location obtained from the radar measurement to evaluate the accuracy of the radar. Examples include the Surveillance Calibration (or SURCAL) launched in the 1960s, and the RADCAL (short for RADar CALibration Satellite) that remained active from 1993 to 2013.