Bryan Butler, age 15, of Barre, Vt., for his question:

JUST WHAT IS TELEMETRY?

Telemetry means "measuring at a distance."

Scientists and engineers use telemetry in many ways. Scientists send weather balloons as high as 30 miles into the air to measure the air temperature, pressure and humidity above the earth. Radios attached to the balloons relay this information back to the ground.

Telemetry also helps man explore outer space.

In temperature measurement, the measuring instrument is an electrical thermometer. The second part is the transmission link. In most systems, this part consists of signals sent along wires or through space by radio. The third part is an indicator that changes the signals into readings at the receiving station. These readings are usually recorded on strips of paper or magnetic tape.

On manned space flights, telemetry systems provide data on astronauts' physical conditions by reporting pulse rate, blood pressure and temperature. To save space and weight, special miniature telemetry equipment is used in spacecraft.