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Producer: Mike McClare & Michael Starobin

Animation/Viz credit: Studio 13

Some elements of this video provided courtesy NHTSA

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March, 2003 - (date of web publication)

NASA Takes the Family Car Out for a Spin

TABLE OF CONTENTS

Introduction:

Space flight and advanced aeronautics require specialized engineering expertise and test equipment. Throughout its storied history NASA has acquired both. Yet as a civilian agency, NASA's mandate ultimately is to serve the public. When the National Highway Traffic Safety Administration wanted to test a particular characteristic of ordinary consumer cars and sport utility vehicles, it turned to NASA for the hardware and know-how to get the job done. By using a remarkable one-of-a-kind machine, the two agencies have begun a collaborative series of experiments that could help keep your family wheels turning safely.

Wheels in a Wheel -- Reporter Package

 

still from Reporter's Package showing an engineer
Click here or on image for the LONG version of the reporter's package
50 MB

Click here for TEXT of Reporter's Package - Long version

Click here for VIDEO of Reporter's Package - Long version

 

 

 

All Wheels Forward - VO

 

still image from movie of car in the centrifuge

Click here or on image for Reporter's Package video - SHORT version - 8.19 MB

 

Click here for TEXT of short Reporter's Package

Click here for VIDEO of the short Reporter's Package

 

 

 

New Kinds of Tests-NHTSA Turns to the Space Agency

Taking the family car out for a spin assumes a whole new meaning in NASA's one-of-a-kind High Capacity Centrifuge. Yet when officials with the National Highway Traffic Safety Administration wanted to test rollover limits of consumer cars and SUVs, they approached the one federal agency with an out-of-this-world record for vehicle performance tests.

As a result of investigations after the widely reported factory recall of Firestone tires, Congress mandated that NHTSA develop a dynamic rollover test for vehicles. Currently NHTSA employs a rating system called a Static Stability Factor. Experiments used to derive this number involve the placement of a test vehicle on a platform designed to determine the rollover susceptibility of a car or truck. According to NHTSA, a one star rating means a high likelihood of rolling over; a five star rating means a low likelihood of rolling over.

NHTSA still uses the Static Stability Factor for passenger vehicles. But critics assert that while laboratory numbers like the Static Stability Factor may provide some useful information, they cannot approach the accuracy or detail of a dynamic test-- that is, a test with a vehicle in motion.

In engineering terms, the experiments using NASA's High Capacity Centrifuge are not actually dynamic. In terms of structural dynamics the vehicles being tested are not really moving; a test instrument-in this case a centrifuge--on which the vehicles are placed, is doing the moving through space.

Additionally, these will be limited tests. As lateral forces increase, vehicles on the giant centrifuge will be prohibited from tipping beyond twenty degrees. But officials at NHTSA say this novel battery of experiments is a good intermediate step to the design of actual dynamic tests. Experts are counting on a variety of new and valuable data about vehicle safety by spinning them on the centrifuge. In fact, if these preliminary tests deliver strong results, NHTSA and NASA are likely to continue the collaboration several dozen vehicles getting a ride on the giant machine.

By leveraging the strengths of both agencies, officials at NASA and NHTSA expect this first-of-its-kind test will enable them to learn valuable safety information about vehicles that continue to move millions of Americans every day.

One Car, Several Trucks and SUVs, No Satellites Anywhere

 

prepping the car for the centrifuge test

Click here or on image for animation demonstrating the preparation of the vehicle for testing. - 31.7 MB

 

Experiments like this require careful procedures. Safety is always a concern, of course, but the efforts behind the experiments are wasted if the data collected isn't accurate. That's why engineers started their tests with a practice vehicle. Before placing the first actual test vehicle on the test platform, a 1993 Chevrolet Caprice went around the room. The Chevy simply allowed engineers to polish their procedures prior to placing other subject vehicles on the platform. After putting the sedan through its paces, the experimenters used the massive overhead crane to swap the Chevy for each SUV and light truck.

Typically the main platform on the centrifuge supports hardware that's being tested prior to being sent into space. These experiments replace spacecraft and flight hardware with the kinds of machines that might instead be found in a driveway or parking space.

Keeping Four on the Floor

 

car on crane being prepped for centrifuge test

Getting ready to be spun.

Still Image

Any vehicle can roll over. The real questions is, How much force does it take? In the course of normal driving, most private cars and trucks are not subjected to the kinds of forces that might send them off their stable four-wheeled bases. But what happens when a driver makes a sudden sharp turn in an emergency? What happens to a vehicle on a curving road? In an effort to learn valuable information about sport utility vehicle rollover safety, the National Highway Traffic Safety Administration asked NASA to help them find out. Using the space agency's High Capacity Centrifuge at the Goddard Space Flight Center, Highway Administration officials spun ordinary cars, trucks, and SUVs on a test platform to study their rollover limits.

While immensely popular for their large cargo capacities and muscular driving characteristics, sport utility vehicles are more prone to tip over in a turn than ordinary sedans. With comparatively higher bodies and ground clearances, they tend to have high centers of gravity, a characteristic which makes rollovers more likely. These tests at NASA will help officials study the physical limits of several makes and models, providing valuable insights into automotive safety.

Center of Gravity-Why Rollovers Happen

 

still from animation demonstrating why cars roll over

Click here or on image for an animation demonstrating why cars roll over. - 2.5 MB

 

Picture a perfect, solid sphere that's uniformly dense. It's practically intuitive: the center of gravity for this object is the absolute center of the sphere.

But what about a geometric shape that's not uniformly dense? What about an irregular shape, like a table, or a boat…or a car? Finding the center of gravity for an object like that is more complicated. Generally speaking, the mathematics necessary to calculate the center of gravity for a particular vehicle is a function of how the mass of that vehicle is distributed, from engine block to upholstery. Additionally, the distribution of that mass is dependent on its spatial orientation. If, for example, the majority of the vehicle's mass if suspended high above its points that are in contact with the road-the tires-that vehicle is said to have a high center of gravity. The support structure of the vehicle matters. A drag racer with two small wheels extended way out in front of the engine, cockpit and big back wheels will have a much lower center of gravity than a boxy sport utility vehicle with a relatively short wheel base.

In stable conditions, a vehicle's typical center of gravity is usually found somewhere around the middle of the passenger cabin. But in a rollover situation, a vehicle's support structure changes. As the wheels of a car or truck begin to lift off the ground, the relationship of the vehicle to the Earth's gravitational pull shifts. At first, lateral forces begin to push the vehicle off its center. But as an SUV begins to tip and its geometric relationship to the ground begins to change, its center of gravity will begin to move closer to the edge of its support structure. The center of gravity for the vehicle by itself has not changed, but its relative center of gravity has. As forces shift across the shape of the frame, the tendency for additional disorientation increases. Rapidly these forces compound and the likelihood of a rollover increases.

Here's another way to look at it. A particular object's center of gravity-in this case an SUV-- will always be contained within the geometric confines of that vehicle as it's oriented in space relative to the pull of gravity. If there's a change in a vehicle's spatial orientation due to the imposition of some external force, the vehicle's center of gravity will shift from its original position as long as that external force persists. That means that the tires, which had supported a vehicle's center of gravity, begin to lose their usefulness as supporting structures relative to the pull of gravity. As a result, the vehicle seeks a new structural support relative to the pull of gravity, like its side or roof. If this change happens fast enough, the vehicle will not only fall over: it will roll.

The Centrifuge-How it Works, What it Does

 

another image of car on crane being prepped for centrifuge test

Prepping for a spin.

Still Image

NASA uses its High Capacity Centrifuge to test spacecraft before they're sent into space. By spinning flight hardware at high speeds, engineers can subject it to many times the force of Earth's gravity-forces that approximate similar effects that satellites will undergo during the rigors of a rocket launch. By testing hardware on a centrifuge, project managers and engineers can both validate a satellite's structural integrity prior to lift-off, as well as help refine potential problems.

But why does a high-speed spin put stress on an object?
Consider the last time this happened to you. On the way home from the grocery store you come around the last corner a little too fast, and the next instant you hear a container of orange juice crushing a bag of potato chips as your shopping sack spills out across the back seat. You've just experienced a real-world effect of centripetal force. Rollovers happen because the same physical principals that sent your groceries flying affect entire vehicles, only on a larger scale.

Sir Isaac Newton determined with his first law of motion that a moving body will continue to travel along a straight path at a constant speed unless another force acts upon it. This is called inertia. But for an object to take a circular path, a separate force must push it towards the center of its arc. This center-seeking force is centripetal.

Newton also defined a different law of motion. It says that for any action there is an equal and opposite reaction. Therefore, in terms of a mass traveling a circular path, the center seeking centripetal force must be balanced by a "center phobic" force-a force that seeks to leave the center point of an arc. This is centrifugal force. It's important to realize, however, that centrifugal force is not what causes a mass to zoom away from its orbit when that mass is released. The real cause of orbital escape is either a new imbalance or removal of centripetal force-the center-seeking one. Orbital escape-the tendency for something traveling in a circle to fly off into space-is really a function of inertia, the force that keeps a particular object in motion. When the center-seeking force gets overwhelmed or disappears, a spinning pail of water, a satellite, or a planet will careen off into space. Remember, it's centripetal force that's acting on an already moving body, pulling it towards the center of an arc. Without it, Newton's first law of motion demands that the body move along a straight line, which in this case is a tangent to the arc of the original curved path.

So it turns out that the G forces created by NASA's centrifuge are actually the result of centripetal forces acting on test vehicles, in this case ordinary SUVs. As the machine's arm turns, the test platform at the end of the arm wants to continue in a straight line. But at every point along its path, it's pulled in towards the center of its arc due by the very structure of the arm. The centrifugal force described by the machine's name is actually a description of the force exerted on the center point where the testing arm is attached to its central axis.

The Nature of the Spinning Beast

 

car being spun in the centrifuge

Click here or on image for movie of the car in the centrifuge. - 7.34 MB

 

t's a big machine. With its two powerful motors running at full tilt, the outer edge of the test arm can reach speeds of two hundred miles an hour. But it's also a finely tuned machine. At rest, the giant multi-ton arm sits on bearings so smooth that just two or three people can push it around the room.

How about electricity? Again, NASA's huge centrifuge offers something of a surprise. While the machine's initial start-up power demands are rather gigantic, they drop off dramatically as soon as the arm gets running. Engineers associated with the centrifuge calculate that power costs little more than a few dollars per hour of operation.

In theory, the massive spinning arm could return energy to the electrical grid as it slows down. But in practice, NASA's engineering branch opts for a different deceleration strategy. Instead of letting test hardware slow down by simply allowing the arm to coast to a stop, project managers "drive the centrifuge down", analogous to a down-shift in a manual transmission car.

The reasons for this are two fold. First, the time necessary for the arm to coast to a stop would dramatically cut into available project time; it would take many minutes for the arm to slow down by itself. But the more pressing reason is that as long as the centrifuge continues to spin, even though it may be gradually slowing down, its test payloads are still being subjected to heightened G forces. And while those artificial stresses are initially the reason for the tests at all, engineers do not want to prolong those stresses beyond the length of time that they're necessary. Increased time under stress means increased chances for damage, so the centrifuge operators take active steps to slow the great arm down.

Full Tank, Fake Driver, Going in Circles

 

   
centrifuge door image   siren

Click on image for .WAV audio file of the centrifuge door closing.

  Click on image for .WAV audio file for the warning horn.
     

 

 

 

 

 

 

It's not enough to simply spin sport utility vehicles on a gigantic centrifuge. To test the vehicles properly, details count. That's why engineers have filled each vehicle's gas tank with a comparatively inert liquid called Stoddard fluid, a solvent with similar physical properties to gasoline. As the vehicle spins, the liquid sloshes to one side of the gas tank just like real gasoline will do in a real-world situation.

A crash test dummy will also go along for the ride. Sitting in the driver's seat, the dummy becomes part of the physical environment that describes the vehicle. Without the shape and weight of a person, the test cannot be run as accurately as it otherwise might.

A variety of sensors and instruments will record a number of parameters about the orientation of the vehicle as it makes its endless loops of the centrifuge rotunda. Engineers expect that they will only have to push the vehicles little more than one G laterally to collect all the useful information they need.

What are G Forces?

Gravity is one of the four fundamental physical forces. It's a function of an object's mass; it's the force that draws bodies together through space. But in terms of engineering, the force of gravity is one of many factors that must be taken into account. Machinery designed for operation in space-in ostensibly zero gravity--does not have to conform to the same structural specifications as systems designed for use on the Earth's surface. However, a machine designed for space flight must obviously leave the Earth's surface by overcoming the force of gravity. To do this, it must endure forces greater than it encounters on the surface. Every time that force increases by the equivalent of one unit of Earth's gravity, it's said to increase by one "G".

For obvious reasons, engineers prefer to know if their designs will endure potential rigors prior to encountering them in real life situations. That's why they run tests in facilities like NASA's High Capacity Centrifuge. By spinning subjects on the test platform, engineers can simulate the stresses of launch by exerting a force on their subjects. As rotational speed increases, force builds up against the test subject secured to the platform. Generally speaking, test items are pushed beyond the minimum levels of stress they're expected to encounter in a real situation, a launch for example. More specifically, some satellites are subjected to centrifuge tests that apply as much as twenty Gs, while actual launch conditions rarely apply as much as 8 or 9.

TRMMing the Sails before Launch

Prior to launch aboard a Japanese H-2 rocket, the joint U.S./Japanese research satellite called TRMM (Tropical Rainfall Measuring Mission) made the rounds of NASA's engineering division--many rounds, in fact. During its preflight validation, engineers spun TRMM on the High Capacity Centrifuge at the Goddard Space Flight Center. These tests helped insure that the complex research vehicle could withstand the rigors of launch. On November 27, 1997, the rocket tasked to put TRMM into space lifted of from the Tanegashima Space Center in Japan. Since then, the satellite has performed like a champ, delivering state of the art data about various aspects of the Earth's climate.

Applied Research: Partnerships and Innovation

NASA is not normally known for its work on Earth-bound vehicles. But owing to the potential public safety benefit and its unique engineering capabilities, the space agency teamed up with the National Highway Traffic Safety Administration. In many ways this partnership helps describe a new trend inside NASA. As the nation's premier engineering and scientific research agency, the space agency has accumulated valuable expertise that has the potential for many uses far beyond initial design intentions. In fact, history has shown that the United States space program finds its biggest dividend in the ancillary uses of the technologies that were developed in order for humans and their machines to leave the planet. By applying some of those technologies and skills to research pursuits that affect everyday life, ordinary citizens can reap the benefits of programs that on the surface might only seem like the stuff of stargazing.

What Should You Do to Prevent Rollovers?

Perhaps most important, don¹t speed. The force tending to tip a vehicle over on a curved path increases substantially as the speed around the curve increases. Further, the sharper the turn, the higher the tipping force. That's why increases in speed can dramatically increase the possibility of tipping over on a curved road. A typical SUV has a high center of gravity, which provides more leverage to tip over when the tipping force is high.

Avoid sudden lateral shifts. Lane changes should happen smoothly, with plenty of clearance in front and behind your vehicle. Take turns at angles that facilitate good connections between your tires and the road.

Maintain your full attention on the task of driving. Alcohol, sleep deprivation, distractions from passengers, and distraction from other activities like cell phones and car stereos can all contribute to unexpected changes in the orientation of a vehicle.


Special Thanks to:

Carmine Mattiello
and the NASA GSFC Code 750 engineering team

Pat Boyd
and the NHTSA engineering team
----------------------

The Official Reproduction Guidelines
for use of NASA images and emblems

This multimedia project is the work of a dedicated team of researchers, animators, and media specialists. A detailed companion video to this web site is available from NASA-TV. Below are a list of agencies, departments, and researchers who provided expertise and data for this production:

NASA Goddard Space Flight Center, Code 750
Television Production NASA-TV/GSFC
Animation by GSFC Studio 13

Content Preparation & Project Production:
Michael Starobin
Mike McClare

GSFC Public Affairs Contact:
Wade Sisler

Web Content Manager: Lynn Jenner

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