Press Release

Space traffic controllers keep satellites safe

By SpaceRef Editor
June 2, 2001
Filed under ,

By Lynn Gonzales, Air Force Space Command Public Affairs

A bullet fired on Earth travels 2,700
miles per hour and can do damage for up to 1,000 yards before it stops.
A loose bolt in space hits at 17,000 miles per hour, goes through a
spacecraft and keeps going.

It’s one office’s job to make sure such a catastrophe doesn’t happen.

One of the Air Force Space Command Space Safety Office’s missions is to
keep satellites away from the more than 9,000 pieces of space debris and
dead satellites flying around the Earth. If they fail, space assets worth
millions join the belt of worthless debris that surround the Earth.

“Some areas of concern are collision avoidance, radio frequency interference,
solar flares, Leonids [meteors], space debris and end-of-life ‘safing’
[making sure the satellite has a safe and passive afterlife in space],” said
Lt. Col. Ed Browne, chief of space safety for Air Force Space Command. “Each
one presents a huge risk to our space assets.”

Collision avoidance, also called COLA, is one of orbital safety’s primary
concerns. A collision can disrupt or destroy communications, navigation and
weather information.

While air traffic controllers must keep in radio contact with pilots to
maintain safe separation, orbital safety officers must monitor the satellites,
planning maneuvers through space riddled with thousands of objects.

Satellites are not only a target for visible debris but also for invisible
intruders. Radio frequency interference can block commands used to adjust a
satellite’s path from the ground. If it can’t get commands telling it to
get out of some debris’ way, there could be a collision. The number of
frequencies used is limited. Satellites at that distance from Earth’s
perspective are grouped closely together such as on the geostationary belt,
which increases the need to maintain RFI-free communications.

Space weather, such as an intense flurry of solar flares erupting on a cycle
of every 11 years (known as Solar Max), can also damage satellites orbiting
the Earth. Browne said satellite operations have statistically seen greater
losses of satellites during that time.

Another cyclic threat to orbiting space assets is meteor showers, such as
the Leonids that occur every year in mid-November.

“The risk associated with each threat seems to go in cycles,” said Browne.
“Each one becomes widely known at different times. When Leonids was in the
news, it was a great exercise for satellite operations and orbital safety
because everyone in satellite ops looked at this, planned for it and
started doing risk assessments as to what should be done and what could
happen to our satellites. They really started to think ahead and think
how to prevent a loss. Today, people are doing the same thing with solar
flares.”

Satellites aren’t the only space travelers protected. COLA also keeps
manned spacecraft safe. NASA’s Debris Quarterly magazine tracks the
maneuvers made by the new International Space Station and space shuttle
to avoid space debris, said Browne.

Orbital safety officers also make sure that once a satellite dies, it’s
safely placed in a graveyard that doesn’t interfere with live satellites.

Once the useful life of a satellite has come to an end, which is usually due
to running out of station-keeping or attitude control propellant or due to
degraded components, the satellite can become a hazard to other operational
satellites. This hazard can be minimized by moving the satellite to a
seldom-used orbit, referred to as a “graveyard” orbit, or re-entered and
burned up in the atmosphere if it is in a low orbit, as was done with Mir,
the aging Russian space station that re-entered the atmosphere in March.
Orbital safety can minimize the potential hazards of a satellite at the end
of its life by venting any pressurized tanks, to make safe any remaining
pyrotechnic devices and to turn off transmitters.

Orbital safety begins its work in the satellite’s cradle and ends with the
graveyard. They are there during the design phase to minimize the generation
of debris during the satellite’s life and minimize its vulnerabilities to
natural and manmade hazards.

Air Force space operations squadrons, which operate satellites, are required
to have an orbital safety program headed by an orbital safety officer. In
AFSPC, squadrons in the 21st and 50th Space Wings at Peterson and Schriever
AFBs, Colo., maintain programs that oversee collision avoidance, review
safety procedures and limit space debris.

At a recent orbital safety summit, more than 40 safety members from AFSPC
and Headquarters U.S. Air Force discussed orbital safety, its mission and
how the program is evolving.

“Due to the importance of current and future military operations and
on-orbit assets, operations crews, maintainers and monitors must have an
active and engaging safety program to protect space assets,” said Maj. Paul
Mejasich, the chief of orbital safety for the Air Force Safety Center at
the Pentagon. “A robust Air Force space program requires a proactive safety
program which can identify and mitigate space hazards; prevent mishaps
during development, testing, evaluation, and space operations; and enhance
the growing safe use of space products and tools by the joint warfighter.”

In addition to battling space debris and solar flares, orbital safety
experts maintain an engineering database of lessons learned from previous
situations, track the laser clearing house to ensure a clear path for
any radiated lasers, and conduct launch and early orbit rehearsals to
anticipate possible mishaps.

If there is a mishap, an investigation is conducted to determine the cause
so future mishaps are prevented. This is a challenging task, since hardware
typically can’t be recovered once in orbit. Preserving telemetry and other
data such as factory build and test data is a critical component in
determining the cause of an on-orbit mishap.

In the time it took to read this article, thousands of objects orbiting up
to 22,000 miles above the Earth passed overhead. Orbital safety officers
made sure they flew by each other without incident.

IMAGE CAPTION: [http://www.peterson.af.mil/hqafspc/news.asp?storyid=01-112]
More than 9,000 pieces of space debris and dead satellites orbit up to
22,000 miles above the Earth. Orbital safety officers ensure that Air Force
satellites pass by this debris without a scratch. (Courtesy of NASA/JSC
Space Sciences Branch)

SpaceRef staff editor.