medium earth orbit search and rescue satellites locate people or craft in distress through beacon signals and transmit their location to first respondersmedium earth orbit search and rescue satellites locate people or craft in distress through beacon signals and transmit their location to first responders
The MEOSAR architecture helps first responders locate people in distress. Credit: NASA
SAR, global navigation satellite system, GPS, GNSS, emergency position-indicating radio beacon, emergency locator transmitter, global positioning, aircraft beacon, maritime beacon, personal locator beacon, data relay 

NASA’s SAR Office Plays Critical Role in Life-Saving Upgrades to Search and Rescue Infrastructure

By Matthew D. Peters

November 21, 2019

NASA’s Search and Rescue (SAR) office at Goddard Space Flight Center (GSFC) in Greenbelt, Maryland is helping to transform the way people in distress receive assistance from first responders around the globe. SAR is even helping astronauts who are part of NASA’s upcoming Artemis missions to the Moon!

SAR is NASA’s contribution to technology research and development as part of both national search and rescue efforts and the international satellite-aided search and rescue community known as Cospas-Sarsat. Founded in 1979, Cospas-Sarsat began as an agreement between Canada, France, the former Soviet Union and the U.S. The community now consists of 45 member countries and organizations working together to provide accurate, timely and reliable distress alert and location data.

Currently, the Cospas-Sarsat system infrastructure is undergoing enhancements known as Medium Earth Orbit Search and Rescue (MEOSAR). These upgrades work together to deliver quicker response times and more accurate location data than the system could previously provide.

The system works through the use of locator beacons for planes, ships or individuals. When someone is in distress, they activate their beacon to transmit a radio frequency signal which is then picked up by satellites in orbit. The satellites transmit that signal back down to ground stations on Earth called local user terminals (LUT). From there, the location data makes its way to first responders who mobilize to assist the people in distress.

SAR developed a second generation beacon (SGB) with a signal that is more robust, reduces interference and increases location accuracy. This translates to reduction in the time it takes to rescue people in distress.

The first people to use the SGB technology will be astronauts of the Artemis missions. The Advanced Next-Generation Emergency Locator (ANGEL) beacon, a beacon attached to astronauts’ life preserver units may be used when astronauts splash back down to Earth, after their historic return to the Moon. These beacons will allow Artemis crew to be located in case of separation in the water.

Another critical element of the upgrades are the satellite payloads called SAR/GPS repeaters. These relay the beacon signal back to Earth. As a proof of concept for the MEOSAR upgrades, repeaters were initially integrated into 19 GPS satellites. These satellites are in Medium-Earth-orbit (MEO) at an altitude of over 12,000 miles. They have a much wider field of view than the Low-Earth-orbit (LEO) search and rescue satellites used in the older system architecture. The MEO satellites can provide continuous full Earth coverage and detect beacon signals almost instantaneously. In contrast, the LEO satellites could take up to 90 minutes to detect a signal.

“The advantages of MEOSAR’s near instantaneous reception of beacon signals directly contributes to saving lives,” said David Watson, a radio frequency engineer at the SAR office.

Now that the MEOSAR architecture has proven itself, the SAR office is collaborating with multiple agencies to design, develop and integrate more of these repeaters on the new generation of GPS satellites. Watson’s role is to ensure the integrated SAR/GPS system meets its performance requirements.

“The SAR/GPS repeater development and integration is an international effort involving the governments of the United States and Canada,” Watson said. “The Canadian Department of National Defense is providing the repeater hardware. The SAR Mission Office is providing engineering oversight and safety and mission assurance support for the repeater development and integration. The U.S. Air Force is hosting the repeater on the new GPS satellites.”

The first of the new GPS satellites is scheduled to launch in 2026. The total number of SAR payloads will approach 80 as additional payloads are deployed into the Global Navigation Satellite System.

In addition to their work on the repeaters in orbit, the SAR office implemented upgrades to the ground segment of the Cospas-Sarsat system. These upgrades include the very first LUT for use with the MEOSAR satellites, which is located at GSFC. SAR is also building a phased array antenna which will replace six parabolic dishes that are currently used to track MEOSAR satellites. The phased array has no moving parts. This, coupled with the need for many fewer antennas means a huge savings in maintenance costs.

All signal processing for MEOSAR is completed at the LUT ground stations, rather than onboard the satellites. This means any future changes will be easier to complete and will not impact the satellites.

If you are in trouble, whether you are splashing down from the Moon, traveling the skies, sailing the oceans or hiking in the mountains, thanks in part to NASA’s SAR office, help can find you!

The SAR office is located at NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Goddard’s Exploration and Space Communications projects division manages the office and NASA’s Space Communications and Navigation (SCaN) program office provides programmatic oversight. To learn more about NASA’s SAR office, visit

By Matthew D. Peters
NASA’s Goddard Space Flight Center, Greenbelt, Md.

The advantages of MEOSAR’s near instantaneous reception of beacon signals directly contributes to saving lives.

— David Watson

SAR Radio Frequency Engineer