Sandia National Laboratories has extended a contract with National Technical Systems Inc. to assist in developing a drone program to monitor nuclear emissions. The $1.6 million contract covers the second phase of the multiphase Harvester project. The Calabasas company also worked on the first phase. Harvester is being developed to measure radiation in the atmosphere as a means of monitoring the use of nuclear devices. National Technical will develop and test airborne collection and sampling systems, as well as the payload pods that carry the systems aboard the unmanned aerial vehicles. The contract extension from the Albuquerque, N.M. national laboratory demonstrates the National Technical’s capabilities in engineering, design, fast prototyping and testing capabilities with unmanned aerial vehicles, said Chief Executive William McGinnis. “This is an important focus for us, and we are committed to expanding our presence in this growing international market,” said McGinnis, in a prepared statement. Shares of National Technical fell 24 cents, or 2.5 percent, to close at $9.65 on the Nasdaq.