When the Apollo astronauts first landed on the moon some twenty
years ago, they were thoroughly prepared for that first step because they had
rehearsed the mission hundreds of times in simulators back on earth.
Mission rehearsal was the key to the success of the Apollo
program. Now it is becoming critical to success—and survival—in the increasingly
demanding world of tactical warfare. Fortunately for the US Air Force,
supporting technologies are keeping pace with the challenge.
Apollo astronauts trained rigorously for two years in a
mission simulator that would be considered primitive by today's standards.
They "landed" a replica of their lunar module, using actual flight
controls, on a simulated area of the Sea of Tranquillity known as a model
board. They viewed this subscale world out the window via closed-circuit
television. As the astronauts manipulated their controls, the TV camera moved
correspondingly to give them a realistic sense of motion.
Until the computer revolution hit the simulation business
with gale force within the past decade, that's all mission-rehearsal simulators
were: TV cameras, model boards, and replicas of flight vehicles. Now the
outside world is being reproduced digitally in the bowels of computers and
displayed to the trainees in a way that allows them to interact with a broad
range of stress-inducing situations.
This new technology is called computer-generated imagery
(CGI), and it is the foundation for new training methods with sufficient realism
to prepare today's warriors for tomorrow's challenges.
A Broad Geographic
Unlike TV model boards, CGI simulators can provide trainees
with pictures of large geographic areas (including the routes to and from
targets as well as the targets themselves) in which all the threats are
accurately located with the aid of timely intelligence data. The astronauts
could be reasonably confident that there wouldn't be anybody on the moon
shooting at them, but that would not be the case for Special Operations Forces
on missions to such areas as the Middle East.
Furthermore, in the increasingly threatening environment of
electronic warfare, mission success will depend on sensor data from outside
the narrow visual portion of the spectrum. These data can also be
computer-generated during mission rehearsals. So can fog, smoke, and haze. Just
as the new sensor suites are intended to give fighter aircraft all-weather,
day/night capabilities, their supporting mission-rehearsal simulators must do
George H. Branch III, manager of military marketing at
General Electric's Simulation and Control Systems Department in Daytona
Beach, Fla., sees a trend toward greater reliance on nonvisual data in both
training and actual missions. Ten years ago, the out-the-window view amounted
to 100 percent of tactical-warfare simulation, he says. Today it's seventy-five
percent and dropping. He sums up the situation succinctly: "There's more
avionics to simulate."
These nonvisual data, which occupy much larger portions of
the electromagnetic spectrum, include forward-looking infrared (FLIR) and
narrow-field infrared, synthetic aperture radar, night-vision goggles, and
low-light-level TV (LLLTV). This increased data flow requires sensor fusion
techniques to funnel vital information to the pilot [see "Sensors Across
the Spectrum," November '87 issue] in both the operational vehicles and
the mission-rehearsal simulators.
That, in turn, increases the need for computer power to run
today's state-of-the-art CGI simulators. For example, the MH-53J helicopter
weapon system trainer, which GE is developing for the Air Force's Special
Operations Forces, uses a combination of general- and special-purpose
computers with processing speeds ranging from ten to fifty billion
instructions per second, according to Mr. Branch. That is much faster than
even the most powerful supercomputers of today, although the two classes of
machines aren't quite comparable because of the specialized nature of
The data-storage requirements are equally demanding. To
simulate a 300,000-square-mile area of the United States used for Air Force
training exercises (essentially from Arkansas to Kentucky and parts of
California), GE used four 300-million-byte disk storage devices. To simulate
the 3.6 million square miles of the fifty states would require twelve times
that amount. Of course, for mission rehearsals the areas to be simulated would
be mostly in the Eastern Hemisphere, and the database for that is available
from the Defense Mapping Agency and from what are known in the trade as
"national technical means."
The visual fidelity of CGI simulators is good and getting
better, to the point where further improvements may not be necessary. As a
rough measure of the capability of the human eye, if the normal field of view
is digitized, it amounts to about a million pixels (picture elements) of
direct vision and roughly another million pixels of peripheral vision.
Today's CGI simulators update the scene sixty times a second
to give the illusion of reality. The human eye cannot sense individual pictures
at rates greater than twenty-four a minute; therefore, that is the rate used in
motion pictures (although each frame is projected twice to eliminate the
jerky motion of the early silent films).
This rate, providing a further smoothness of motion, is
essential in interactive mission simulations because conflicting visual cues
can cause motion sickness among the trainees.
Thus the computational requirement for CGI is dictated by
the need both to provide at least a million digitized picture elements per
scene and to do it sixty times a second. That's where today's computers built
out of very-large-scale integration (VLSI) components have taken over,
muscling out TV model boards in the process. "The picture quality is
there," says Mr. Branch. "No more pixels are needed."
This approach of high fidelity, relatively high costs, and
limited interaction for simulators based on powerful stand-alone central computers
can be thought of as the antithesis of the Defense Advanced Research Projects
Agency's Simnet (simulator network) approach. Simnet uses low-cost distributed
computers to produce maximum interaction among participants in training
exercises, but at this point it is capable of only relatively crude graphics
[see "Planet Simnet," August '89 issue, p. 60]. It is reasonable to
expect that, in the future, these approaches could converge to create even more
According to Michael R. Willmore, a staff scientist at Link
Flight Simulation, Binghamton, N. Y., a division of Toronto-based CAE
Industries, effective mission rehearsal depends on countering three kinds of
uncertainty: situational uncertainty, probabilistic uncertainty, and
Situational uncertainty applies to the purely physical
nature of a region where the conflict is to be modeled, essentially terrain
and weather. Probabilistic uncertainty includes the capabilities of the weapons
that all the participants bring to the battlefield: system performance,
reliability, probabilities of hit and kill, even electronic signatures. Both
of these are well within the realm of current simulation technology, Dr. Willmore
The outlook is not so bright for operational uncertainty.
Dr. Willmore calls it the most difficult aspect of warfare to simulate or even
account for in reality. It is the result of how cohesively the command
structure is organized, how efficient the control processes are in directing
force responses on the battlefield, and the connectivity strength of
communications systems in passing essential information among the entire
command control and communications (C3) architecture.
"It is pointless to design a static threat simulation
for mission rehearsal that can only record and play back one presupposed set
of conclusions about the mission environment or what the conflict should look
like during mission rehearsal," Dr. Willmore states. "Such
'tactical' simulations, created by writing scripts from a set choreography,
cannot possibly respond to the dynamics generated by a single participant, let
alone several others who may be operating together as a mission unit.
"Instead, mission rehearsal should serve as an adjunct
to the final mission planning activity that occurs just prior to executing
tactical missions in reality," he continues. "Participants explore the
planned missions by asking themselves, 'What if we did this?' and 'What if the
enemy does that?' and 'What if this happens?' and the entire litany of other
questions designed to better prepare themselves for the uncertainty at
High Costs—For Now
Then there's the issue of costs. Simulators aren't cheap.
GE's MH-53J system, for example, is projected to cost more than $30 million.
But they are getting cheaper, at least on a cost-per-function basis. Through
the use of VLSI components (and soon, it is hoped, transportable software),
simulators are getting smaller, cheaper, and easier to support. Mr. Branch
estimates this price decline at about ten percent a year, but he cautions that
simulator prices are likely to remain steady because the military customers
are likely to opt for increased performance instead of lowered system costs.
A rule of thumb in the industry is that the customer will
pay about ninety percent of the unit cost of the aircraft for its simulator. In
the case of the Air Force's Advanced Tactical Fighter (ATF), which has a projected
$35 million program unit cost, that means a likely ceiling price of close to
$32 million for the simulator.
Development of the simulators for ATF, as well as those for
the X-30 National Aerospace Plane, the aircrew training system for the Special
Operations Forces, and the upgrade of the F-16 simulators, are all managed now
out of the System Program Office for Training Devices (still referred to as SIM/SPO)
under Col. Wayne Lobbestael at Aeronautical Systems Division, Wright-Patterson
This is a departure from past Air Force practice, in which
the simulator efforts had been under the SPO managing the weapon system development.
The Army and Navy have centralized their simulator development and procurement
under the Program Manager for Training Devices (PM-TRADE) and the Naval
Training Systems Center, respectively, both located in Orlando, Fla.
Centralizing the simulator effort removes it by at least one step from the
budgetary pressures that normally afflict weapons development programs—a
Navy, USAF Take
Because of the differing natures of their tactical air
missions, the Air Force and Navy have taken different approaches to flight
simulation. Since Navy fighters customarily operate off the decks of aircraft
carriers, the Navy early on recognized the benefits of simulation to reduce
the number of risky carrier operations. A classic example is an engine
flameout during a carrier landing, something no pilot wants to practice in a
The Air Force has not felt such a need for flight simulators
and did not introduce visual simulation until the recent F- 16 upgrade program
recently won by Evans & Sutherland of Salt Lake City, Utah. Dave Eccles,
manager of strategic planning at E&S, describes the new F-16 simulators as
relatively small field-of-view devices capable of simulating takeoffs and
landings and some missions—but not traditional full-mission simulators. These
are also relatively low-cost, estimated at about $1.5 million apiece.
But Mr. Eccles sees other forces at work that may win
further customer acceptance of flight simulators. His company recently received
a contract to supply at least six low-level flight trainers for the West German
Tornado fighter, and this may be a bellwether for future procurements. Just as
one of the purposes of DARPA's Simnet is to prevent tanks from tearing up farmland
and causing intolerable traffic jams in West Germany, simulators for tactical
aircraft in the NATO environment can be a force for better relations among
Looking beyond these current applications of flight
simulators, Mr. Branch of GE traces the impact of size reduction made possible
by new electronic components. GE's original Compu-Scene II system, introduced
in 1980, consisted of twenty-six cabinets, each standing about six feet high
and weighing 900 pounds. Compu-Scene V, introduced at this year's Paris Air
Show, dropped that to six cabinets, and Mr. Branch says the next goal is to get
an entire simulator into a single cabinet.
At 900 pounds per cabinet, the simulator could easily be
installed on board an aircraft the size of a USAF C-5 transport to permit embedded
training during normal flight operations. Another order of magnitude
reduction, down to ninety pounds, would put that capability within reach of the
The Totally Enclosed
Given the increasing importance of nonvisual sensor data,
future derivatives of today's flight simulators might entirely replace the
out-the-window view. Submarine commanders have been doing this for years.
They rarely peer through periscope eyepieces anymore; the sensor data are
funneled to them through a variety of mast-mounted devices and displayed in the
submarine control center on television screens. This enables submarines to
reduce their visibility to enemy forces.
In the case of high-performance fighters, it might be more
efficient for the pilot to be in a supine position monitoring the sensor data
over CCTV during periods of high G-forces. This approach could eliminate the
traditional cockpit entirely, which would be valuable in reducing the
aircraft's radar cross section. Pilots are already overly task-loaded with
through-the-window data, and the use of sensor fusion could eliminate
extraneous information. The value of sealing off the aircraft in a nuclear
environment is obvious.
Taken together, these potential capabilities of CGI give
this technology the edge for a variety of future applications. TV model boards
put Americans on the moon and performed many other valuable functions, but
today their importance has shrunk to what Mr. Eccles of E&S calls the
equivalent of HO-scale railroad models.
John Rhea is a
free-lance writer living in Woodstock, Va., who specializes in military
technology issues. His most recent article for AIR FORCE Magazine,
"Silicon's Speedier Cousins," appeared in the November '89 issue.
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