Press Release

Protecting America’s Spacecraft

By SpaceRef Editor
August 21, 2003
Filed under , ,

KIRTLAND AIR FORCE BASE, NM. — Since Sputnik first circled the earth nearly
half a century ago, aerospace engineers have searched for better ways to protect
spacecraft from the violent engine vibrations transmitted through the rocket
body during launch. In some cases, satellites have actually been shaken apart
inside their payload shroud before reaching orbit and their mission. Not only
costly, but also ruined payloads can be potentially disastrous to national
defense in wartime when rapid response to orbit has to be done right the first
time — every time.

Scientists here at the Air Force Research Laboratory (AFRL), working with their
CSA Engineering, Boeing, and Delta Velocity Corporation partners, may have found
a way to save those payloads.

Launched today (Wednesday, 20 August 2003) on a sounding rocket off the coast of
Virginia from Wallops Island Flight Facility, AFRL’s Vibro-Acoustic Launch
Protection Experiment (VALPE-2) carried new "active isolation and acoustic
mitigation" technology that counteracts vibrations produced by the rocket motor
and sound waves during launch. And it uses something much like a home stereo
speaker to do it.

"Much of our work here in the Space Vehicles Directorate over the past few years
has dealt with controlling unwanted launch vibrations that damage sensitive
spacecraft components," said Dr. Kyle Henderson, manager of AFRL’s Advanced
Spacecraft Mechanisms Program.

"In the past, we developed what was called the SoftRide passive isolation system
for launch vehicles with CSA Engineering, which reduced vibrational disturbances
at a ratio of 5 to 1. Softride, which has flown on Taurus and Minotaur launch
vehicles, performs very much like the shock absorbers on your car, using the
same principle that soaks up the jarring shocks annoying to passengers when
driving on a bumpy road," Henderson said.

But hybrid active-passive vibration isolation is a more advanced process. Such
systems may reduce vibrations at a ratio of 10 to 1.

Henderson put it this way: "An active isolation system, like today’s experiment,
improves upon Softride’s passive technology by actively pushing and pulling to
provide better isolation performance."

To do this, the hybrid isolation system on VALPE-2 uses a "voice-coil actuator"
similar to that found in a speaker in your home stereo system. For example, if
you watch a sub-woofer when sound is being produced, you will see that the
speaker cone itself actually moves in and out, keeping time, so to speak, with
the base tones heard. This is that foot-tapping "beat."

Driven by a magnet, the speaker cone "pumps" in and out to alternately compress
and decompress the air, the actions required to ‘spread’ the sound throughout
the room. VALPE-2 uses the same principle to move the payload actively. A
similar device developed with Boeing — called the adaptive Vibro-Acoustic
Device — pushes against the air inside the payload shroud and compensates for
harmful oncoming sound waves created at launch. In effect, VALPE-2 dampens the
harsh environment considerably by counteracting ambient vibration and "noise"
and prevents payload damage.

Another type of coil-based isolation system aboard VALPE-2, and developed by
Boeing, is an experimental power source called regenerative electronics. This
converts motion to the energy (launch vibrations into the electricity) needed to
provide active isolation during the violent shock of separating rocket stages
during the flight to orbit.

VALPE-2 is also the first flight of a new AFRL composite fairing (protective
payload shroud) called ChamberCore. Built by Delta Velocity, this technology,
because of its unique construction characteristics, may also reduce unwanted sound.

In the 1971, some researchers estimated that nearly half of all payloads that
failed in the first 24 hours came from vibro-acoustic stresses during launch.
Consequently, spacecraft designers had to beef up their work, and in some cases
added nearly forty percent worth of structural bulk to a spacecraft just to
survive launch.

AFRL has spent about $1 million on VALPE-2, an investment that may help put an
end to payload losses by using technology that also reduces the mass and weight
of a spacecraft. And weight saving is a key contributor to lowering the cost of
access to space, especially when you figure that it runs about $10,000 to put
one pound of payload into orbit. Reduce the weight, and you can use smaller
launch rockets.

"I suppose what we are really doing is "quieting" the air all around our
payload," Henderson summarized. "And it is this protective cushion that has the
potential to save our industry millions of dollars every year by getting
payloads into orbit safety and cheaply."

IMAGE CAPTIONS:

[Image 1:
http://www.vs.afrl.af.mil/News/images/03-23A.jpg (60KB)]
VALPE-1 On Rail

[Image 2:
http://www.vs.afrl.af.mil/News/images/03-23B.jpg (166KB)]
VALPE-2 Experiments and Assembly

SpaceRef staff editor.