by Scott Prater
12/4/2014 - SCHRIEVER AIR FORCE BASE, Colo. -- The
Air Force launched four GPS satellites into orbit this year, the
highest number of GPS launches since 1993. But as the Air Force quickly
upgrades its most recognizable space constellation, a little known
group of Airmen works tirelessly behind the scenes.
Between the time a satellite is launched and the 50th Space Wing
receives satellite control authority for it, a small team is busy
testing and evaluating, ensuring that each spacecraft is ready to begin
its job of providing position, navigation, and timing to more than 3
billion worldwide users.
As part of the 2 SOPS Mission Analysis Flight, these analysts work
through a complex launch and early-orbit process, all while maintaining
each of the other 38 satellites in the GPS constellation.
"It can be a stressful time," said 1st Lt. Robert Heffner, 2 SOPS chief
of GPS subsystems analysis shop. "If there is a lag on anyone's part, it
can set the whole launch timeline off, which means more work for
Their work often begins more than 60 days out from launch.
Heffner, who concentrates on the GPS vehicle or "bus," first sets up
links with the satellite as it sits on the ground at Cape Canaveral,
"We start with compatibility tests," he said. "Our teammates at the Cape
plug it into our monitor-station network. We put the vehicle in a known
configuration, upload software and then ensure its components are
functioning properly. This is our last chance to test before launch. We
don't want any surprises when it's actually on orbit."
As Heffner evaluates the vehicle, Capt. Aaron Blain, 2 SOPS chief of GPS
navigation payload analysis shop, focuses on the spacecraft's payload -
it's position, navigation, and timing components. Like Heffner, he's
testing and ensuring functionality.
Much of the action occurs while the satellite is still waiting to be lifted on to a launch platform at the Cape.
Following the launch, their work kicks into an even higher gear.
Once the vehicle reaches its proper orbit, 2nd Lt. Christopher Phillips,
2 SOPS chief of NDS analysis and tactics shop, begins testing and
evaluating the secondary payload that resides on every GPS vehicle: the
Nuclear Detonation Detection System.
Though GPS is perhaps the most recognizable satellite constellation in
the world, it's safe to say most people don't know that each of its
satellites carries an NDS payload.
"NDS performs an important mission," Phillips said. "It helps verify the
Limited Test Ban Treaty of 1963. It makes sense. The whole reason the
GPS constellation has these nuclear detonation sensors is because it
provides global coverage. We can see every part of the planet."
While Phillips tests the satellite's NDS components, Heffner and Blain perform a second round of evaluations.
"We have to make sure the telemetry, tracking and control system works,
so that we can command the vehicle. That's our first concern," Heffner
said. "This occurs the same day as the launch, while the vehicle is in
sun safe mode and still spinning."
Meanwhile, Heffner performs a ground-antenna evaluation, loads programs
and commands, and evaluates the vehicle's computer processor and
electrical power system. Then he switches individual components on.
"We evaluate everything just like we did on the ground," he said. "Because...things behave differently in space."
Blain's first job once the vehicle reaches orbit, is to determine its
exact location. He uses a variety of ground antennas to narrow down,
then determine the precise orbit trajectory of the satellite. Once
complete, he begins turning on payload components as well.
"When we turn on the payload antennas, the vehicle heats up," he said.
"We do that partly to cook off all the excess particulate matter,
specifically air. The vacuum of space will pull air out of the the
vehicle. That step helps us avoid electrical shorts. It's one of our
lessons learned throughout the years from previous launches."
From there, Blain switches the navigation payload on, then attempts to
get all of the computers that generate the GPS signals to synchronize.
The process performed by each of the analysts is an important segment of
what's known in the Air Force as the on-orbit check out. All of a
satellite's systems must check out prior to the transfer of satellite
control authority, which typically occurs within a few weeks of launch.
Recently, the 50 SW received SCA of the GPS Block IIF-8 satellite, also
known as SVN-69, but it's not the final step for the vehicle. It must
be approved for operational acceptance, which is on pace to occur later
this month, in order to be an official active satellite in the GPS
The Air Force plans to continue upgrading the constellation in the next
few years, replacing aging Block IIA vehicles with more robust, modern,
and capable Block IIFs. Three Block IIF satellites are planned for
launch in 2015, with the first tentatively scheduled for March.