| The Voodoo Crew
It wasn't too long after I agreed to be the Thermal Integration
Manager for the Space Shuttle Advanced Solid Rocket Motor
(ASRM) program that I gained an appreciation for why the
thermal community was always viewed by the Shuttle Program
Office as a group of "out-there" voodoo practitioners.
Because it was, well, true.
Despite a technical background that included aerothermodynamics,
I was still surprised by the degree (no pun intended)
to which cutting-edge predictions of Shuttle ascent aerodynamic
and plume heating depended on educated guesses and extremely
murky empirical formulae. My new team, comprised of highly
seasoned experts from two NASA Centers and a half-dozen
contractor companies, apparently based its products on
equations laden with fudge-factors, the values of which
were argued strenuously at each meeting of the governing
Thermal Panel -- which I now chaired. To each prediction,
a margin of safety was attached, the magnitude of which
also depended on the much-argued consensus of the Thermal
Panel. With this being the state of the art, no wonder
our craft was viewed by outsiders as black magic.
| With this
being the state of the art, no wonder our craft
was viewed by outsiders as black magic.
One of the major components of ascent heating, the
radiation produced by the Shuttle's two solid rocket
booster plumes, was known to depend on the size and
distribution of individual aluminum-bearing particles
throughout each plume. Estimates of this crucial variable
were crude at best, and were based on extrapolations
of data collected from firings of much smaller motors
with different propellant mixtures than that of the
ASRM. As a result of this uncertainty, the factor of
safety applied to radiation predictions was typically
on the order of 100%. Such large uncertainty margins
presented a significant impact to the design of the
Shuttle launch vehicle's thermal protection system,
as well as to the vehicle's ascent profile. The effect
on the Shuttle system's payload-to-orbit capacity was
But how to improve the accuracy of the prediction?
Conventional means of collecting particles would have
required a significant test equipment design effort;
even if we could piggyback on already-planned tests,
we'd have to design and build instrumented test stands
able to withstand the harsh plume environments. And
we had no budget for such an endeavor.
Fortunately, we had our share of out-of-the-box thinkers
on our voodoo team, and the thought du jour was... Lawn
Seeds of Our Magic
|QM-6 test firing
at Wasatch Operations, Morton Thiokol, Utah.
One of the analysts had spent his early career with the
Coast Guard, and he was familiar with the harpoon-like
guns used to hurl hawsers from Coast Guard ships to other
boats, to allow the two vessels to be lashed together
for boarding. He assumed, and was correct, that such surplus
equipment could be acquired via inter-agency requisition.
His boss, a member of our Thermal Panel, proposed to me
that he get a couple of these guns and have one of his
co-operative education students design a particle-catching
projectile for them to hurl through the plume. The scheme
quickly drew the moniker "lawn dart."
Several upcoming subscale solid rocket motor tests
would provide excellent opportunity to test and fine-tune
the system and collect preliminary data. The major payoff
would come later, if we could collect particles from
the plumes of two full-scale test firings. The guns
were free, the co-op needed a meaningful project to
work on, and this organization's discretionary budget
could handle the minor materials costs associated with
fabricating whatever lawn dart design the co-op came
Vital data at no cost to the program? How could I
The co-op proved to be especially inventive, and he devised
a blunted aluminum dart, the bulbous head of which was
covered with double-sided tape. The time to transit the
plume was calculated short enough not to allow the contraption
to melt. We secured the use of an electron microscope
to allow an admittedly arduous counting of particles of
various sizes per unit area of tape. The machine shop
quickly produced several specimens, and the initial non-plume
test firings initiated by remote control were successful.
lawn dart team learned to shoot straight, we were
set for a test with a real plume as target.
Once the lawn dart team learned to shoot straight,
we were set for a test with a real plume as target.
The first subscale motor test firing of the lawn dart
was nearly its last. The motor sat in its vertical test
stand with the exhaust end pointed skyward. Once the
motor was fired and its plume was well established,
the lawn dart team did its thing, whereupon the dart
was promptly carried several hundreds of feet into the
air with the plume, only to fall back to strike the
test stand. Suddenly, the test director wasn't so sure
he wanted to let our bunch near his equipment. After
much cajoling, and once we reduced the dart's fin surface
area, he gave us the OK for a second attempt. This one
sent the dart through the plume, but not without another
surprise: an unanticipated, plume-assisted journey several
hundred yards out the other side -- which required a
determined search to find the darn thing. Nonetheless,
the team was jubilant. The darts were surviving their
journeys with only minor scorching, and the materials
lab analysis showed we were indeed capturing excellent
particle samples! After a second refinement of the dart's
design, the lawn dart crew was ready for the full-scale
As it turned out, the crew did an expert job; the
darts launched during the two critical tests flew beautifully,
intersected the plumes at the points of interest, and
collected particle samples that allowed the analysis
team to develop a repeatable particle-size distribution
model. Along with the concurrent radiometer measurements
our team took, and the factoring in of some computational
fluid dynamics predictions of the plume flow's structure,
the particle data allowed us to refine our radiation
models to the point that the prediction uncertainty
level could be reduced from 100% to 10-15%. This represented
a major leap forward in the state of the art, all made
possible by some out-of-the-box thinking.
Gotta love that voodoo engineering!
- In a problem-solving situation, all ideas (no matter
how "out-there") should be considered.
- We shouldn't be so focused within our professional
specialties that we forget we are the sum total of
our life experiences; the solution to a work-related
problem may well lie within the memory of some totally
How often do project managers use "alternative" resources
to solve technical problems?
Search by lesson to find more on:
Jansen is the Manager for Launch On-need at
Johnson Space Center, External Carrier's Office,
International Space Station Program Office. He also
serves as ASK Magazine's Associate Editor