Satellite laser ranging (SLR) ground station at the University of Hawaii. Photo courtesy of NASA

Satellite laser ranging (SLR) ground station at the University of Hawaii. Photo courtesy of NASA

When you think of a time capsule, you imagine something that stays in the same place until it is ready to be opened. What M-BARC is creating is no typical time capsule, however. It will be hurtling through space in an orbit around Earth for 100 years. That orbit will change over time, which creates a new challenge: finding the spacecraft when the time comes to retrieve it in 2117.

The M-BARC team is addressing this challenge by developing an active tracking scheme using satellite laser ranging (SLR).

SLR is a technique that uses laser pulses to measure the distance to a satellite equipped with retroreflectors. A retroreflector is a device that is designed to reflect incoming light to its origin, regardless of the light’s angle of entry. To determine the range, the SLR system uses a time-of-flight method to measure the delay in sending a laser pulse to the retroreflectors on a spacecraft. This range is then used in an orbit determination model to estimate the spacecraft’s orbit and instantaneous position. By taking regular SLR measurements, the spacecraft can be tracked with high accuracy for future retrieval.

The M-BARC team is currently designing the retroreflectors that will be placed on the external faces of the spacecraft. The results of preliminary analyses have shown sufficient probability of detection by a SLR system. Soon, the retroreflectors will begin to be tested to confirm our predicted results.