POLLUTION PROBE

Science for the people!
The technology of model rocketry is being used to make accurate forecasts of pollution problems.

G. HARRY STINE

If you happen to be driving through a city or town and see a couple of people out in the middle of a school football field or a park looking as though they are getting ready to fly a rocket, don't immediately assume that they are model rocket hobbyists.
They could be meteorologists preparing to launch a LARS(R)*—Low Altitude Rocket Sonde—for air pollution forecasting. (*LARS is a registered trademark of Colspan Environmental Systems, Inc., Boulder, Colorado.)
If you stop, get out of your car, and go over to have a closer look, it will still appear that the meteorologists have one of those little solid-fuel model rockets that have made some thirty million flights in the United States over the past fifteen years. You'd be one hundred percent right if you thought it looked just like the model rockets you can buy down at the local hobby store.
Professional rocket engineers and meteorologists have put the safe, reliable inexpensive model rocket to work measuring air pollution over our cities and towns. It is important work for a little gadget, because if you can't measure something, you may have trouble doing something effective about it.
Nearly a hundred years ago, it was Lord Kelvin who said, "When you can measure what you are speaking about and express it in numbers, you know something about it; but when you cannot measure it, when you cannot express it in numbers, your knowledge is of a meager and unsatisfactory kind; it may be the beginning of knowledge, but you have scarcely, in your thoughts, advanced to the stage of science, whatever the matter may be."
Air pollution was a reality even in Lord Kelvin's time. It was an early consequence of the Industrial Revolution, and you could probably trace it back to even more ancient times. Air pollution probably occurred—as it does now—anywhere with a high population density, such as a city with a population of 25,000 or more, and with a high energy density created by combustion processes. For the purposes of this discussion, however, let's use Stine's Definition of Pollution: All living organisms produce waste (to them) products, but they pollute their immediate environment only when they produce these waste products in greater quantity and density than the immediate environment can absorb or dispose of.
Thus, air pollution as we know it probably didn't exist before the Industrial Revolution, and people put up with it because it was one of those consequences they were willing to live with. They were also probably ignorant of the ecological and physiological effects. I grew up in a house on a hill overlooking Colorado Springs, Colorado. Everyone believes that "out thar" the air is sweet and pure and clear. But I can well remember cold winter mornings when a pall of gray-brown smoke hung over the city for a couple of hours after sunrise. This pall was created by thousands of household furnaces burning bituminous coal. Nobody paid much attention to the smoke pall because it broke up and drifted down the valley toward Pueblo about 9:00 a.m., and then the mountains stood out bright and clear as always. The Chamber of Commerce kept telling us that it was a privilege to live in Colorado, but maybe they didn't get up until after 9:00 a.m. on winter mornings.
At any rate, even if the townspeople had complained about air pollution then, coal was the only thing available to heat homes; natural gas had not yet become available. And they could not have measured the air pollution. It was a go-no-go proposition; it was either there or it wasn't; like the oil pressure idiot light on an automobile. If you can't measure it, you can't determine time-rate and you can't establish any baseline data for comparison.
In order to do something about a physical condition such as air pollution, you must be able to measure it in accordance with Lord Kelvin's criteria. Once you can measure it, you can begin to establish baselines and perhaps link cause and effect. Then you can begin to forecast it and do something about it.
The act of measuring implies the possession of the correct, calibrated measuring instrument. Both a calendar and a stopwatch are accurate time-measuring tools, but they have widely different ranges, tolerances, and limits of accuracy. A calendar is useless at a track meet.
The pivotal science behind air pollution can be considered as macrofluid-dynamics or local meteorology. It was patently obvious to technical observers that urban air pollution seemed to be dependent upon the weather. But what weather conditions caused air pollution? The measurement tools of meteorology—the barometer, thermometer, hygrometer, and anemometer—could produce some Kelvinian numbers of current ambient surface conditions. But the readings were made at a single point on the ground; the air pollution existed over the entire city and extended several thousand feet upward as well. A synoptic weather map was useful in forecasting weather conditions, and this could give meteorologists and long-suffering townspeople some idea of when the winds might blow the smog away to somewhere else.
Other measurements were required to get a numerical handle on air pollution. Experts discovered that they needed (a) vertical temperature profiles, taken at least daily and preferably several times each day from at least one location and preferably, in a large industrial city, from several locations; and (b) air movement data to accompany the temperature profile data.
Instruments existed to measure these parameters, and vehicles were available to put the instruments where you wanted the measurements to be made. You could use a rawinsonde weather balloon, an off-the-shelf item, which would provide temperature readings at 1,000-foot intervals or so and wind velocity data from the surface to 60,000 feet or so. This would set you back about $100 per flight, mainly because it was rare to get the instrument package back. It was like using an expensive stopwatch as a substitute for a calendar. You could de-rate the balloon system, but it still had more performance and therefore greater cost than needed. Or you could go first-class, put the instruments in an airplane, and hire a pilot to fly around in an ascending spiral over the city—but this costs many dollars per hour and complicates the data reduction problem because the airplane doesn't go straight up over its takeoff point.
Be that as it may, early air pollution measurements were made using this existing instrumentation and these vehicles. In solving an engineering problem, one must always start somewhere with existing art. And one must learn what measurements are really necessary and then what to look for in those necessary measurements.
It was no surprise to learn that you didn't need to make measurements all the way up to the stratosphere; you only needed to know what was going on up to, say, 4,000 feet or so at the very most. Nearly all urban air pollution takes place in a thin layer next to the ground and ranges in thickness from about 1,000 to 4,000 feet. It is also quite localized.
Numbers were obtained. And the numbers were combined, synthesized, analyzed, massaged, plotted, graphed, and studied. It was learned that you did not need wall-to-wall data to do effective air pollution forecasting. If you had the regular U.S. Weather Service synoptic data, you only needed to obtain (a) the vertical temperature profile and (b) the average speed of horizontal air movement through the air pollution layer.

In the meantime, there were those of us who were working with small rockets for fun and profit. For many years, I have been interested personally in the nonmilitary applications of small rocket vehicles; one of the most urgent applications, then and now, was in the educational-recreational hobby area. Back in 1957, an alarming number of young people were being seriously injured or killed because it is a natural American trait for the amateur scientist-technologist to attempt to emulate the pros, usually without the expertise and equipment of the professionals. This provided the stimulus for us to launch the hobby of model rocketry (or "space modeling" as it is growing to be called). A model rocket is a space-age version of the model airplane; it is a small (less than 24 inches long), lightweight (less than 16 ounces), nonmetallic (paper, plastic, and balsawood), fin-stabilized aeromodel propelled by an expendable, factory-loaded solid-propellant rocket motor. It uses a parachute or other high-drag recovery device to return it slowly to the ground. It can be used over and over again by simply repacking the recovery device in the model and inserting a fresh model rocket motor.
At the present time, millions of model rockets have been flown allover the world by ordinary people. There has been nothing more serious in the way of accidents than a couple of minor burns caused by failure to follow instructions. This makes model rocketry the safest of all hobbies except, perhaps, stamp collecting. Because the models, motors, and other equipment were going to be used by young people and/or those who were not rocket experts, a lot of thoughtful development went into them. Their reliability is very high—the proverbial nine-nines. They are so simple that a grade-school child can assemble and fly one successfully. They are cheap; a ten-dollar bill will put you in the model rocket hobby with flying model kit, expendable model rocket motors, launch pad, electric ignition system, and firing battery.
Most important, these model rockets could carry small, light payloads.
One of the favorite payloads of the model rocket hobbyist is a single, Grade A, fresh (not hard-boiled) hen's egg; it is a supreme test of skill to be able to launch, fly, and recover a fresh egg without breaking it ... and thousands of model rocketeers do it regularly. But a hen's egg doesn't do anything except to teach you how to handle and cushion a very fragile payload, sort of a simulated miniature astronaut. Other model rocket payloads were developed, and most of these are inexpensive, off-the-shelf items today. For a ridiculously low price ($20), you can buy a 3-ounce movie camera that will take cine pictures in flight. Or there's the cheaper ($5) still camera that takes one picture per flight. In addition, you can buy a cheap ($14.95), lightweight (0.6 ounce) radio transmitter kit that operates with low power on the citizen's band and is capable of sending back data on air temperature.
With existing, factory-made, off-the-shelf rocket motors selling for less than $5 each, it is possible to loft these payloads to several thousand feet and get them back unharmed.
If cheap, reliable, safe model rockets could do this sort of thing on a fun-and-games basis for hobbyists, why couldn't they also do it seriously for scientific purposes?
Back in the late 1950's, several of us knew this was a possible market for small rockets. We designed and developed a small rocketsonde capable of carrying modified radiosonde equipment up to 100,000 feet. It was not the usual de-rated military rocket system, but an "up-rated model rocket" using the same technology with an increase in size and power. We hoped it would replace the slow and expensive weather balloon. This was all reported, incidentally, in George Willard's article, "The Complex Problem of the Simple Weather Rocket," in the June 1961 issue of Analog.
It didn't occur to us at that time to apply the model rocket to the measurement of air pollution. That was before air pollution was recognized as a serious environmental problem by anybody outside of Los Angeles. But times changed. And air pollution increased. And people got really concerned- about it.
And air pollution meteorologists began looking for cheap methods to obtain their needed temperature and wind speed data over cities.
And there was the model rocket system, ready and waiting, with over a decade of development already put into it.

The hobbyist's little model rocket was converted into a genuine piece of Kelvinian instrumentation by Robert Strieby, Dr. Bill Womack, and their colleagues at Colspan Environmental Systems, Inc., of Boulder, Colorado.
Their system is called LARS—Low Altitude Rocket Sonde. It uses a plastic rocket vehicle with a miniaturized radio transmitter in its nose, a bead thermistor to measure air temperature, and a modularized factory-loaded solid-propellant rocket motor made by Flight Systems, Inc.
The launch pad is also the carrying case for the rocket vehicles and other equipment. It fits easily into the trunk of a car, and one man can set it up in minutes. The launcher is a simple aluminum rail, and launching lugs on the vehicle slide up and down the rail.
Launch control and the telemetry ground station is built into a suitcase 19" x 14" x 7". The suitcase contains the entire electrical launch system, adipole antenna, FM radio receiver, and a strip-chart recorder. If you wish, you can plug in a portable tape recorder as well.
The whole LARS system is a one-man portable operations station. And it is not labeled portable just because there are handles on the equipment boxes. The rocket launcher weighs 25 pounds; the ground station suitcase weighs 20 pounds.
LARS flights should be made at least once each day about one hour after sunrise. Making a LARS sounding is somewhat anticlimactic if you are expecting something as complex, heart-stopping, or world-shaking as a Saturn-V launch. It's about as exciting and difficult as pouring water out of a boot with instructions written on the heel. LARS can be launched from any clear area about 20 feet in diameter with no overhead obstructions. But if you want to get the LARS vehicle back again, you will have to have some additional ground area for the vehicle to land in. You will also need to be able to measure some ground distances, as we shall see. (Naturally, if there are any trees around, the LARS parachutes have a high probability of ending up snagged in the branches, as any model rocketeer will quickly tell you.)
Out of the car trunk comes the launch pad, a long plywood box that opens into two hinged parts. It opens again to reveal two storage volumes and an extruded aluminum launchrail about 3 feet long. By tightening a few thumb screws, the launcher is all set up and ready to go.

The LARS vehicle is made from plastic and is a simple fin-stabilized, free-ballistic airframe 1.25 inches in diameter and about 24 inches long with four clipped-delta fins epoxied on the rear end. The propulsion assembly contains the expendable solid-propellant rocket motor and two parachutes—one for the LARS vehicle and the other for the propulsion assembly. The unit slides into the aft end of the LARS body and is held in place by a pin inserted through the vehicle. This can be pre-assembled ahead of time. All together with loaded rocket motor and transmitter, LARS weighs a maximum of 14 ounces.
That's why there is no problem with air traffic clearances when flying LARS. Back in 1961, the model rocketeers of the National Association of Rocketry convinced the Federal Aviation Agency that there was no real hazard involved with nonmetallic rocket vehicles weighing less than a pound and carrying less than 4 ounces of rocket propellant. Their efforts appear to be justified because there haven't even been any near misses between aircraft and small rockets. After all, the Department of Defense spends millions of dollars in order to have rocket-powered guided missiles designed to deliberately hit an airplane. It's an incredibly difficult task. The chances of an unguided rocket hitting an airplane are pretty slim—as the U.S. Army learned twenty years ago with a little unguided antiaircraft rocket called Loki. Thanks, therefore, to C.A.R. Part 101.1(c), you can fly a LARS anytime without having to fill out two pages of F.A.A. clearance forms in advance for each launch.
The LARS radio telemetry transmitter is completely enclosed in the nose section of the vehicle with only the thermistor bead sticking out into the airstream from the nose tip. The transmitter is completely transistorized, of course, and uses a rechargeable 9-volt battery. The battery will permit the transmitter to blare forth with 35 milliwatts of r-f power on 403 mHz. for 25 minutes. The first thing you must do is calibrate the thermistor and system. The transmitter is turned on by pulling the "umbilical plug" on the side of the nose section. The signal as received and recorded at the suitcase ground station is calibrated against an ordinary thermometer which measures the ambient ground temperature.
The electric igniter is stuffed up the nozzle of the rocket motor, the vehicle is placed on the launch rail, and the electric ignition system is hooked up. You are now ready to launch a rocketsonde.
If there is some wind blowing, you may wish to tilt the launcher rail slightly. LARS is a fin-stabilized vehicle and will therefore weathercock slightly into the surface wind as it comes off the launch rail after ignition. By tilting the launch rail, you can put the vehicle into that part of the sky you desire. And if you're really good at it, you can put in the right tilt to get the parachutes to land close by.
Big countdown. Push the firing button. Firing current comes from the 12-volt lantern battery that's also operating the ground station. Or you can use the auto's battery.
And LARS is on its way up.

Three different rocket motors are available for LARS. They are all the same size. But they produce different total impulses and therefore different peak altitudes. All three produce about 35 pounds of thrust. The MARK II unit has a thrust duration of about 0.5 seconds and will loft LARS to 1,800 feet. The MARK III has a longer duration and gives a peak of 3,000 feet. The MARK IV will boost LARS to 4,000 feet.
As you can imagine, the 14-ounce LARS scats with that sort of thrust behind it.
The rocket motor contains an integral pyrotechnic time delay to permit LARS to coast up to peak altitude. For the MARK II 1,800-foot motor, this is 8 seconds of delay. Then a gas generator charge in the motor casing is activated, ejecting the propulsion unit from the tail of the vehicle. This is all quite straightforward to any model rocketeer because it works just like a rear-ejection model rocket. The ejecting propulsion assembly also extracts two parachutes, one for the vehicle itself and the other for the propulsion unit.
Although the LARS telemetry transmitter has been operating on the ascent, the system response times are far too long to permit any sort of accurate temperature data during the 8 seconds or so it takes to get to peak altitude. But there is plenty of time available as the vehicle drifts down under its little red parachute. The nose thermistor busily converts temperature to an electrical voltage which modulates the transmitter which squirts the signal back to the suitcase ground system on the 403 mHz. carrier. Back on the ground, the receiver decodes this signal and drives the recording pen of the strip chart recorder. It takes several minutes for the LARS parachute to lower the vehicle back to the ground.
Now you've got your vertical temperature profile.
Obtaining the average horizontal wind velocity through the sounding layer is even simpler and is the result of some brilliant thinking.
The LARS vehicle and its propulsion unit are recovered on separate parachutes. Both objects have different weights and different parachute sizes. Therefore, they have different but known descent rates. The average wind through the sounding layer will cause the two different parachute-load systems to have different horizontal drifts. The higher the average wind, the greater the differential drift. All you have to do is measure the ground distance between the landing points of the LARS vehicle and the propulsion unit. After you bring the two items back to the launch site (and insert the umbilical plug to turn off the telemetry transmitter), the average wind speed through the sounding layer is determined directly from a chart. For example, if you shot to 1,800 feet and had a ground distance of 250 feet between the two units, the graph would tell you that you had an average wind velocity of 13 mph.

Armed with these two pieces of data, you can now compute air pollution dispersal data and forecast the air pollution index for the remainder of the day.
If there is a poor air pollution situation, LARS will probably find and measure a temperature inversion. Normally, the air temperature decreases approximately 3° F. per thousand feet of altitude increase. As you go up, it usually gets colder. This is known as the "normal adiabatic lapse rate." But, with a temperature inversion, as the altitude increases, the air temperature also increases. This is a situation that can easily exist in a large urban area where considerable energy is being dumped into the atmosphere. A "lid" of warmer air overlies the area. Therefore, the air near the ground cannot rise by convection and is trapped on or near the surface. LARS would see a temperature inversion by virtue of its vertical temperature profile. If you've put in a rocket motor of great enough total impulse, it may have gone through the top of the inversion into the region of normal lapse rate above.

In the absence of any horizontal wind flow, the only way that air pollution can be dispersed is by mixing throughout the trapped volume of air in the inversion. Once all of the trapped volume is mixed, there is nowhere else for the pollution to go, and it just sits there and builds up.
The maximum vertical dimension available for the mixing of polluted air in any one day is known as the "maximum mixing depth." This is not necessarily the top of the inversion layer. Using the LARS vertical temperature profile data and dry adiabatic lapse rate charts, it is a simple matter to determine the mixing depth by graphical means.
There is enough baseline data available now in the air pollution discipline to permit forecasting of afternoon conditions from the results of an early morning sounding. If your friendly local weather bureau tells you that they don't expect any frontal activity, thunderstorms, or other rapid weather changes for the remainder or the day, you know that you've got the possibility of an air pollution problem. The LARS data will tell you how bad the pollution situation will be. It is just a matter of comparing the early morning data against baseline factors to produce highly probable p.m. conditions.

We've been working with numbers here—or at least, our hypothetical LARS meteorologists have been. We're getting more Kelvinian all the time. Now comes the piece de resistance, an empirical factor known as the Air Pollution Dispersal Index. This is the product of the mixing depth in feet and the average wind speed through the mixing layer in miles per hour—multiplied in turn by a Finagle Constant of 1.3 and divided by 1.000:
APD INDEX = Mixing Depth X Avg. Wind Speed X 1.3 = 1,000
Aha! Now we have a number! Now we can compare the APD Index against how bad the air pollution is and come up with something that will stop Lord Kelvin from spinning in his mausoleum:
APD			AIR POLLUTION
INDEX			DISPERSAL
NUMBER		CONDITION
0-19			Poor
20-39			Fair
40-59			Good
60 and up		Excellent

If the APD Index is less than 20 and the condition persists for more than 36 hours, you've got troubles. Better start shutting down furnaces, restricting auto travel, and otherwise eliminating sources of air pollution.
If the air pollution begins to get bad, it is always possible to go out and keep tabs on it with additional LARS flights. You'll then get some trend data that could be even more valuable than the spot data.
If you make regular daily LARS soundings, you will begin to build a library of baseline data for various months and seasons of the year. After a time, you will be able to compare the current APD Index data against a baseline. You will be able to tell if air pollution campaigns are effectual. You will be able to forecast with greater accuracy what the air pollution situation is likely to be. Voila! You are beginning to talk as a scientist!
The cost of doing this with the LARS is sort of ridiculous—ridiculously low, that is—when compared to the cost in terms of human lives, human suffering from respiratory ailments, and possible ecological damage. Colspan's price for a complete LARS system—three vehicles, propulsion units, launcher, and ground station—is about $3,000. The cost per flight is only the cost for the expendable Flight Systems, Inc., solid-propellant rocket engines: it's about $5.
LARS is being used by several government and private agencies interested in air pollution—the states of California, New York, and Colorado; the TVA; Colorado State University, Montana State University, and the Chattanooga Institute of Technology; Martin-Marietta Corporation; and NASA-Lewis Research Center in Cleveland. The city of Pueblo, Colorado has the big steel mills of Colorado Fuel and Iron Corp. to complicate their air pollution situation, and they are running a LARS program there for $3,000 per year.
Obviously, we are well past the first phase of solving the air pollution problem: recognizing that there is a problem. We are well into the second phase: doing something about it, because we are starting to measure, to get numbers, to advance air pollution control to a science instead of an empirical rule-of-thumb art. And we are doing it with technology being used to solve the problems caused by technology. We are doing it by clever synthesis, by bringing together two previously unrelated fields of interest.
Whoever would have believed that air pollution would be measured and controlled because of those silly, unimportant little toy rockets you could buy down at the hobby store?
I did, for one. And I am simply delighted. Now, let's see: I wonder what other problems could be solved by using the techniques we've developed for small, safe, light, reliable, inexpensive rocket propulsion systems . . .?