The landing of the shuttle Atlantis July 21 marked the end of an era of space exploration. Behind the scenes, thousands of people have helped the U.S. space program make history while only a few faces have been recognized.

Several of the 21st Space Wing's geographically separated units have been critical in ensuring the safety and success of the shuttle program. The 6th Space Warning Squadron at Cape Cod Air Force Station, Mass., 7th SWS at Beale Air Force Base, Calif., and 20th Space Control Squadron at Eglin Air Force Base, Fla., track more than 22,000 near-earth and deep space objects, shuttle missions and the International Space Station.

From launch to landing these GSUs are tracking the shuttle and any objects that could potentially collide with the shuttle.

"The 6th Space Warning Squadron at Cape Cod Air Force Station supported NASA's space shuttle missions by tracking shuttle launches from Cape Canaveral into orbit, and then by tracking the shuttles, the International Space Station, and other low-earth orbiting objects," said 1st Lt. Stefan Wladyka, 6th SWS Operations Support Flight assistant commander.

"The 6th Space Warning Squadron frequently updates the Joint Functional Component Command for Space 'space catalog' to help maintain space situational awareness and facilitate safe and responsible orbital operations," Wladyka said. "The predictability and accuracy of the 6th Space Warning Squadron's space track observations contributed to the protection of the space shuttle and its astronauts, and will continue to help protect vital national resources into the future."

On the opposite coast, another of the 21st Space Wing's geographically separated units kept its eyes on the skies as well.

According to Capt. Chris Leininger, 7th SWS Operations Support Flight commander, the space surveillance mission provides data on the trajectories of low-earth orbiting objects, objects within 2,000 kilometers of earth's surface. This data is used to help improve collision avoidance and safety for objects currently in orbit and new ones being launched.

"(The) 7th SWS tracked the orbiter while it was on orbit, and during docking and undocking maneuvers with the International Space Station as part of our space surveillance mission," Leininger said.

The 20th SPCS, 6th SWS and 7th SWS have similar space surveillance missions and with manned space missions, surveillance becomes increasingly important.

"Much of the satellite tracking is done automatically by the radar," Leininger said. "But because these are manned missions, they are actively monitored by the radar operations crews."

Capt. Aaron Lynch, 20th SPCS Operations Flight commander , said, "In 2009, observations collected by the 20th SPCS led NASA to evacuate astronauts from the International Space Station into the Russian Soyuz manned spacecraft after identifying objects with a close trajectory to the space station."

Most of the space debris are less than one millimeter in diameter and cause no damage. However, according to the NASA website, the shuttle occasionally had to dodge objects if it was determined there was a one in 10,000 chance of a collision.

The shuttles are back on earth now, but the mission of the 6th SWS, 7th SWS and 20th SPCS continues with only a few minor changes.

"We continue to perform the space surveillance mission since there are still many objects up there (that) we want our functioning satellites to be able to avoid," Leininger said.

Additionally, the United States will continue to send astronauts to space using the Russian Soyuz capsule and the 6th SWS, 7th SWS and 20th SPCS will continue to closely monitor manned missions to the International Space Station.

When the United States once again sends astronauts into space, the crews will be ready to support the program safely and effectively, Lynch said.