Smithsonian

Contributions to Astrophysics

VOLUME 5, NUMBER 4

OBSERVATIONS OF

SIMULATED METEORS

by RICHARD E. MCCROSKY

SMITHSONIAN INSTITUTION

Washington, D.C.

1961
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Observations of Simulated Meteors

By RICHARD E. MCCROSKY *

On October 16, 1957, three shaped-charges

were fired simultaneously from an Aerobee

Rocket at an altitude of 80 kilometers over the

New Mexico range in an attempt to simulate

meteor phenomena. The charges were mounted

in such a way that there would be no ambiguity

in the angle between the axes of trajectory of

any two simulated meteors, or "meteoroids."

Hence, if all three charges were successfully

fired and observed, each meteoroid could be

related to the specific shaped-charge that

ejected it. Absolute aspect information could

not be predicted since the rocket and the

ejected nose cone, containing the charges, are

subject to spin and tumbling.

Shaped-charges are explosive devices designed

to focus the detonation front in such a way

that a cylindrical or conical metal liner, inserted

in the explosive, will collapse on itself and be

ejected along the axis of the charge. The

tangential forces, which collapse the liner, are

symmetrical about the axis and cause no

acceleration normal to the liner axis. Three

different types of liners were used in this

experiment.

Charge A was constructed at the Poulter

Laboratories of Stanford Research Institute.

The liner was a cylinder of aluminum, closed

at the bottom end, 3 inches long and 0.5 inch

in diameter. The thickness of the wall, from

which the high-speed particles originate, was

0.028 inch and the total liner mass was approximately 5.5 grams. Firings of similar charges

at the Poulter Laboratory show that the

maximum particle velocity obtainable, for other

than an extremely small amount of essentially

gaseous material, is 14 km/sec. The particles

ejected at this velocity are estimated to be less

than 5 microns in diameter. Larger particles

are produced but are ejected at lower velocities.

1

 Harvard College Observatory and Smithsonian Astrophysics] Ob-

•ervatory.

At most, only 2 percent of the liner is expelled

at velocities greater than 10 km/sec.

Charge B, also made at Poulter Laboratories,

was constructed with a conical aluminum liner,

0.375 inch thick, with an apex angle of 120°.

Similar charges have attained velocities of 5 to

7 km/sec. These charges eject a limited number

of large particles.

Charge C, with a coruscative liner, was

constructed by Dr. Fritz Zwicky, of the

California Institute of Technology. It produces

luminosity through self-contained chemical

energy. Velocities in excess of 10 km/sec are

thought to be obtainable.

Ground-based optical and radar equipment

was employed to observe the luminosity and

ionization produced by the ejected material.

This paper analyzes the optical observations of

two of the charges.

Observations

Five stations on or near the firing range were

equipped to make optical observations. Each

of the Harvard Meteor Stations—at Sacramento

Peak and at Organ Pass—has two SuperSchmidt meteor cameras. One at each station

had the usual rotating focal-plane shutter which

introduces a time scale on the meteor trail.

At Sacramento Peak, an f/0.8, 5-inch aperture

Schmidt with a transmission grating yielding

1250 A/mm was also used. The three other

stations, which were manned by observers

from the Physical Science Laboratories of the

New Mexico State University, used ballistic

tracking cameras (without rotating shutters)

with f/2.5, 3-inch lenses.

Each of these ballistic cameras obtained good

photographs of the brilliant explosion and two

meteors emanating from it. The Organ Pass

station failed to secure observations because

clouds obscured the region for the few minutes

surrounding the explosion time. The Sacra29
30 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

mento Peak Schmidts obtained successful

photographs, although the films show only one

meteor. Subsequent analysis has shown that

the two meteors and the Sacramento Peak station lay almost precisely in the same plane.

Also, the meteor motion was essentially in the

direction of dispersion of the grating camera.

The meteor spectrum was completely overridden by the spectrum of the explosion, as

well as smeared by its own motion.

Geometrical Reductions

Measurements of the ballistic camera plates

and of the Super-Schmidt films have permitted

a determination of the trajectory of both

meteors (see table 1). The ballistic cameras

are designated as B18, B50, and B55. The

letter s or I denotes the short or the long meteor

trails visible on each plate. The poles of the

apparent great circle motions of the s-trails

lie approximately on the same great circle, and

therefore the trails are due to the same meteor.

This is also true for the /-trails. Because of

the unfortunate geometric configuration relating the Sacramento Peak Station and the

meteor trails, either great circle passing through

the poles of the trails fits the Super-Schmidt

pole equally well. However, a preliminary

radiant for each meteor, determined from two

pairs of the ballistic camera photographs, indicated that the /-trail as seen from Sacramento

Peak was nearly perpendicular to the line of

sight (84°), whereas the s-trail departed from

the line of sight by only 23°.

One may roughly estimate the length of the

s-trail, as it would have appeared on the SuperSchmidt film, by comparing the length of the

/-trails on the photographs from the SuperSchmidt and the ballistic cameras. The end of

the s-trail will probably not extend beyond the

first quarter of the Super-Schmidt meteor and

certainly most of the light of the s-trail will fall

within the explosion image. I have therefore

included the Super-Schmidt data in a leastsquares solution for the /-trail radiant. This

result, and a similar solution for the s-trails, are

represented in table 1. The rms deviations

given in the table are derived from the minimum distance between the great circle of meteor

motion and the least-squares radiant.

The probable error for a radiant determined

from two photographs is given (Hawkins, 1957)

by the equation,

5#=cosec Q12 (sin Ex 5&,)2+ (sin E% 8ba)

2

, (1)

where Q is the angle of intersection of the trails

at the radiant, E is the distance from the radiant to the trail, and 8b is the error in the angle

of the trail. The subscripts distinguish between the quantities at each of two stations.

Q and E are known from the measures but

8b must be estimated. In extreme cases, such

as the l-to-2-millimeter trails produced by the

simulated meteors, 8b is given by the expression

8y/x where x is the length of the trail and 8y is

the probable error of measurement perpendicular to the trail. A value of 10 microns is

certainly a generous estimate for 8y. Probable

errors not exceeding 0.7° could be expected

for radiants determined from most pairs of the

present trails, and radiants determined from

TABLE 1.—Data for trajectories of two artificial meteors

Meteor

I

II

Film

B18

B50

B55

SS

B18

B50

B55

Trail

8

8

8

I

I

I

Radiant position

t

153?3 E

40?4 W

5

-66? 2

-66? 2

rms error

±0?01

±0?43

Zenith angle of

radiant

143?9

103?0
OBSERVATIONS OF SIMULATED METEORS 31

four trails should yield rms errors of the same

order as given for the Z-meteor in table 1. The

small rms error given for the s-meteor is

certainly fictitious.

The weight to be given a single meteor in

determining the radiant is proportional to the

length of the visible trail, and inversely proportional to the angular distance of the trail

from the radiant. Weights tend to be equalized

because the meteor trail appears to be longer

when it is at a greater distance from the radiant.

Weighting factors for the ballistic camera trails

vary from one another by only 20 percent. The

weight of the Super-Schmidt trail was one and

a half times that of the ballistic camera trails.

The Super-Schmidt trail was not given the extra

weight, however, because a possibility existed

that some asymmetry of the trail could have

been caused by a blending of the two meteors

at a point just outside the explosion image. The

small difference in weights among the various

ballistic camera trails was also ignored and a

weight of unity was used throughout the radiant

calculations. The angle between the two meteors as derived from these measures is 52 ?2,

with an estimated probable error of less than 1°.

The Super-Schmidt trail, lasting about 0.07

second, exhibits four shutter breaks. This trail,

in conjunction with the B18 /-trail, was analyzed

for velocities, ranges and heights by the standard meteor reduction methods (Whipple and

Jacchia, 1957). The wide separation between

the stations, 52.0 kilometers, is more than sufficient for the determination of accurate distances. The length, from the center of the

explosion to the end, is 0.95 kilometer with the

midpoint occurring at an altitude of 79.2 kilometers above sea level. The velocity, as determined from the spatial distances between the

three adjacent pairs of shutter breaks, shows a

marked, although not exceptionally well-determined, deceleration. These velocities are

plotted in figure 1 as a function of time. If the

deceleration was constant, the meteoroid had

an initial velocity of 14.4 km/sec at a point in

the center of the explosive burst.

Measurements of the angle between the

charge axes were made by Dr. Milton C. Kells

of Poulter Laboratories after the charges were

mounted in the rocket. A comparison of these

angles with the observed angle, corrected for

the aberration introduced by the moving

rocket, can supply the only reliable method of

determining which pair of charges was observed.

The correction for aberration requires a knowledge of the vector velocities of both meteors

and the rocket. The present measures provide

the necessary data for the /-meteor. The

vertical component of the rocket velocity (0.81

km/sec) is accurately determined by the observed maximum altitude. The horizontal

components may be estimated from the launching position, the rocket position at the time of

the explosion as determined from the photographs, and the time elapsed between launching

and explosion. This simplified technique assumes a constant horizontal velocity, a condition not met before rocket burn-out. However, this component is in reality small enough

(0.078 km/sec) to neglect entirely. The direction of motion of the s-meteor is welldetermined.

Thus, of the nine quantities needed to

correct for the angular aberration, only the

speed of the second meteor is unknown. A

one-parameter solution has been made to determine the angular separation of the two

meteors with respect to the rocket as a function

of the unknown space velocity of the s-meteor.

Figure 2 shows the results. Table 2 gives the

actual separation angles along with the velocity

that must pertain to the s-meteor for each of

the three separation angles as read from

figure 2. The last column of this table summarizes the arguments, given below, for rejecting or accepting each of the six possible

associations.

All three shaped-charges were expected to

eject their liners with velocities of 5 km/sec

or more. Such a velocity would seem to

eliminate pairs B-C and A-C but since there

may be some chance of a substandard ejection,

these possibilities are included.

If the B-C pair produced the two meteoroids,

and charge B produced the s-meteor (first row

of table 1), the luminosity must have been

produced by aluminum particles travelling at

a velocity comparable to that of the rocket

itself. Certainly no meteoric luminosity can

be expected at such low velocities; indeed, this

is demonstrated by the absence of ablation from

the rocket. If charge C (coruscative) were
32 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

TABLE 2.—Separation angles and velocities for s-meteors

Charge Pairs

B-C

A-C

A-B

Separation angle

in rocket (±1°)

36°

48°

53.5°

If s-trail is

produced by

charge:

B

C

A

C

A

B

Velocity of

s-meteor must

be:

1 km/sec

2 km/sec

5-9 km/sec

Then: intensity (/) or velocity (V) of

meteor is:

7B: too small

FB: too large

I A', too small

possible, but Vc substandard

FB: too large

Consistent with expected values of velocity

substandard but produced luminosity by burning, then charge B must have had a velocity of

14 km/sec, twice its expected value. The

possibility of a superstandard charge is too

remote for consideration.

The same arguments apply to the hypothetical pair A-C; luminosity cannot be produced by the meteoric process at 2 km/sec.

The velocity of the Z-meteor is perfectly consistent with results obtained in ground tests

of charge A. It is therefore at least a possibility that the two meteors were produced by

a successful charge A and a substandard coruscative charge with a velocity of about 2

km/sec.

For a separation angle of 53?5, the s-meteor

must have attained a velocity between 5 and

9 km/sec. The velocity with respect to the

rocket, for this range of spatial velocities, is

approximately 0.65 km/sec less, and is consistent with that expected for charge B; the

14.5

14.0

135

13.0

U S

-

-

-

1

— Center of explosion

t Visible beginning

1 '

1 IPMMSIIWld

iwtociBes

-

1 1

Z-meteor is consistent with charge A. The

reverse identity is not acceptable because of

the excessive velocity that must be attributed

to charge B.

To summarize, then, it appears almost certain

that charges A and B produced the I and s

meteors, respectively. There remains a possibility that A and C produced I and s, respectively. In either case, the Z-meteor, for which

a velocity is known, must have resulted from

a successful ejection of the liner of charge A.

It is interesting to compare the characteristics of charge A, as determined from laboratory tests, with the meteor it produced.

Velocity.—If the rocket velocities are subtracted from the observed meteor velocity, one

finds that the meteor velocity, extrapolated to

the center of the explosion, was 14.2 km/sec.

The agreement with the laboratory measures

of maximum velocity is excellent.

Deceleration.—A second comparison between

the observations and the ejected particles can

be made by determining a characteristic

particle size from the deceleration. The drag

equation is given as

TApV2

m

(2)

1 2

n - Shutter breaks (.01669 sees/break)

FIGURE 1.—Velocity-time plot of /-meteor determined from

Super-Schmidt photograph.

where r=drag coefficient, A=cross-sectional

area, m=mass, p=atmospheric density, and

V=velocity. With the deceleration as determined approximately from figure 1, a drag

coefficient of 1.0, a spherical aluminum body,
OBSERVATIONS OF SIMULATED METEORS 33

V (km/sec)

FIGURE 2.—Space velocity of /-meteor as function of angle

between trajectory axes with respect to rocket.

and atmospheric density as given by the ARDC

Atmosphere of 1956 (Minzner and Ripley,

1956), computation yields a particle radius of

30 microns. Too much emphasis should not

be placed on this number since the deceleration

is not well determined, and the larger particles,

which are capable of lasting until the end of

the meteor, are probably ejected from the

charge with lower velocities. However, the

computation indicates that the general size

range is comparable to the expected particle

size.

Light curve.—Another estimate of a characteristic particle size may be determined by

the lifetime of the meteor or, more exactly, by

the shape of the light curve. Although the

quantity of light produced by a given body

cannot yet be specified, the form of the equations predicting meteor luminosity are undoubtedly valid over a far greater range of

velocities and atmospheric densities than

that experienced by this particular meteor.

The observed light curve is given in figure 3.

It is not possible to reproduce this light curve

with a cluster of particles of the same size,

but a characteristic size can be chosen which

will approximate the slope of the curve.2 The

instantaneous intensity of a meteor is given

by an equation of the form:

(3)

* The shape of the curve, exponential In intensity with time, strikingly

resembles the light corves observed in abrupt meteors for which

a catastrophic disruption is believed to take place at or near the point

of beginning (McCrosky, 1065). One is tempted to presume that the

disruption by explosion produced the same distribution of particle sizes

as in the pressure-fractured meteoroids.

where m is the rate of mass loss by vaporization.

The luminosity coefficient, specified by the

factor T0, is assumed to be constant. The

velocity exponent, n, is found to lie between

2 and 3. Since the present discussion attempts

to determine only the shape of the light curve,

the precise values of T0 and n are of little

importance.

The production rate of vaporized material

is given by the expression,

m

AApV* (4)

For aluminum the heat of vaporization, f, is

l'10u ergs/gram. The heat transfer coefficient,

X, measures the efficiency with which the

colliding air particles transfer energy to the

meteoroid. For small bodies this is probably

of the order of unity. The derived particle

size will vary approximately directly with the

value of A. Then for A=l (used here), one

obtains a maximum size. If the particles are

assumed to be spherical and of density 2.7,

one can replace the cross-sectional area by

0.624 m2/3. The instantaneous intensity is

then given by the expression,

/«3.2.10-12pF3+nm

2/s

. (5)

The time variations of /may be stated explicitly

if the trajectory and atmospheric parameters

are known. A considerable simplification

results when the velocity and atmospheric

density remain constant throughout the trajectory, as essentially occurs here.

S 1.0

• t Extrapobtco to

N . _

c M n

\

-i

\

-

)— otiim (S«P»SUIWMU

- 20. |Mda IconputKl)

-

^ \ -

n . Shutter tvwks (.01669 Mcs/tmk)

FIGURE 3.—Light curve of /-meteor determined from SuperSchmidt photograph.
34 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

A spherical particle of radius 20 microns,

with trajectory and velocity determined for

the /-meteor, would produce a light curve

of the shape shown by the dotted curve in

figure 3. The ordinate has been adjusted to

permit an easy comparison with the observed

curve. The agreement between the particle

size and the upper limit expected from charge

A is excellent. However, as with the deceleration analysis, this size should be interpreted

as representing only an order-of-magnitude

measure of the pertinent particles.

A determination of the number-size-velocity

distribution of the ejected particles is an extensive laboratory problem that has not been attempted for charges of this design. Were these

data available, one could predict the wake—the

luminosity that occurs in the shutter breaks—

or the elongation of the dash images resulting

from the velocity dispersion of the particles.

In fact these two effects are small, indicating

(a) that the velocity dispersion of the luminous

particles is small («2 km/sec), or (b) that the

velocity-size relationship is such that much of

the light in any one dash is produced by particles of similar characteristics; or (c) that the

meteor was not produced by charge A but

rather by charges B or C, either of which may

produce a very limited number of larger particles. However, the reproduction of the observed separation angle, velocity, deceleration

and light curve by another charge seems most

improbable. One is forced to accept explanation (a), or (b), or a combination of both. The

conditions in (b) are not as artificial as they

may first appear. The smaller particles are

known to attain higher velocities. Their lifetime would be short, but spectacular. A smaller

number of larger particles, at lower velocities,

would contribute relatively little to the initial

luminosity but would persist to the end and

become the major light producers.

Luminous efficiency

An integration of equation (3) gives the equation

2 f* / To=mj0 VdL (6)

The luminosity coefficient, T0, is determinable

if the total mass, velocity, and integrated intensity are known. The integrated intensity

of a meteor is independent of the distribution

of the particle size, except as the velocity varies

with size either through differential deceleration or a distribution of initial velocities.

Of the two present estimates of T0, one results from a theoretical investigation of this

difficult problem by Opik (1933, 1955). The

other is a semi-empirical result by Cook and

Whipple (Cook, 1955) in which the observed

forward momentum of a meteor train was related to the mass of the meteor and this, in turn,

through the observed luminosity, was related to

the luminosity coefficient. Cook and Whipple

found a value 220 (±150) times smaller than

that of Opik.

The experiment described here offers the

first example of a measure of meteoric luminosity produced by a known material. For

a lower limit on the luminosity coefficient, I

have assumed that 2 percent (0.11 grams) of

the mass was ejected at the observed velocity.

I have also assumed that n=3 in equation (6).

The luminous efficiency, or the effectiveness

with which the kinetic energy is transformed to

visible radiation, is then

T=T0V.

The spectral distribution of the light required

to determine the relationship between the

intensity (in ergs/sec) and the photographic

image is generally unknown. In meteor investigations one commonly adopts Opik's (1937)

expression,

Mvl8=24.6-2.5 log / (ergs/sec), (7)

and applies a "color index" correction derived

from visual and photographic observations of

the same meteors (Jacchia, 1957). For bright

meteors of Mpg<C —1.0, this color index is —1.8

magnitudes.

From these relationships and the integrated

photographic intensity, one finds the luminosity

coefficient of aluminum in the meteoric process

to be TO(AD=9X1O~10 sec/cm, and for a velocity

of 14.4 km/sec rA1=0.0013. Opik's (1933)

value3 for natural meteoric material may be

'This value and the n =» 3 velocity exponent have been used extensively

by the Harvard Meteor Project and elsewhere to determine masses.

Maintaining a universal, although avowedly relative, mass scale has

obvious merit in the present situation. For this reason the comparisons

have not been made with Opli's (1955) more recent value which is 60

percent of the earlier estimate.
OBSERVATIONS OF SIMULATED METEORS 35

expressed (Whipple, 1943) asT0=8.5X10~10 sec/

cm. However, aluminum is not a major constituent of meteors and these two values can

not be compared directly. Corrections are

required for the difference in composition

between natural and simulated meteoroids

and for any extraneous luminosity produced by

oxidation of the aluminum. Neither correction

can be reliably computed, but upper limits for

these effects can be estimated and may be

useful in the design for future experiments of

this nature.

Correction for oxidation. The oxidation of

aluminum provides a particularly efficient

visual light source (White, Rinehart, and Allen,

1952). Photoflash lamps yield about 7X105

lumen-sec/gram aluminum in the conversion of

the metal to AI2O3 (Forsythe and Easley, 1931).

If we assume a constant energy per unit wavelength from 3800 to 6000 angstroms, the total

luminous energy of the flash lamps is 3X1010

ergs/gram. The blue-sensitive emulsions used

for meteor photography would be sensitive to

perhaps one-half of this. The luminous efficiency for oxidation alone could then be as high

as

TAIO=3.0-101 0 /V2=0.015,

or more than an order of magnitude larger than

the minimum value of TAI derived from the

observations. Oxidation, then, can conceivably

be an overwhelming factor and must be considered. However, the conditions under which

oxidation takes place in the flash bulb differ

substantially from those in the meteor. Appreciable differences in the luminous efficiency of

the two processes would not be unexpected.

To set an upper limit on the luminous efficiency of the aluminum molecule in the meteoric

process, I will utilize evidence derived from

spectra of natural meteors. The band radiation has never been observed in these spectra.

This is certainly due to the low abundance of

aluminum in meteors and does not imply a

zero luminous efficiency of oxidation in the

meteoric process. But nevertheless, the mere

absence of sensible band radiation is sufficient

to specify a significant limit on the efficiency.

To determine this limit, suppose the total

instantaneous intensity of a meteor is derived

from two sources:

(8)

where IQ is the usual line radiation observed in

meteors and /Aio is the molecular band radiation. It is reasonable to assume that the oxidation is proportional only to the mass of the

aluminum and, unlike the atomic radiation,

is not a direct function of the meteor velocity.

Collisional energies exceed the dissociation

energy of AIO for even the slowest meteors,

and some deceleration of the aluminum atoms is

always required before appreciable oxidation

will occur. An increase in velocity will, at

most, delay the oxidation. (An inverse velocity dependence may exist because of the increased oxygen-aluminum ratio for slow—and

therefore low altitude—meteors. The form of

this function is unknown and will be neglected;

the upper limit obtained (below) for the

luminous efficiency of oxidation is thus increased.) Then,

(9)

where AM is the abundance of aluminum by

weight, taken to be 1.5 percent for natural

meteoroids (Opik, 1955) and E is the luminous

efficiency of the oxidation process expressed as

luminous energy/gram.

The absence of AIO radiation in any meteor

spectra can, in principle, be used to set a limit

on the ratio, k=IAK)f^o- Certainly k=0.5 is

a conservative upper limit. We have then,

E--. Ho t

~AAlm

and, from equation (3),

2A,

(10)

(ID

Note that since the last term of equation (8)

is independent of the velocity, one cannot

rigorously apply an intensity law of the form

of equation (3), to both /and 70. Although the

final results are not significantly affected if /,

rather than 70, is used in equation (3) a choice

must be made, and the one made here reflects
36 SMITHSONIAN CONTRIBUTIONS TO ASTROPHYSICS

the writer's opinion that oxidation is negligible

in the natural meteor phenomena and that the

actual value of k is very much less than 0.5.

The lowest velocity for which a meteor

spectrum has been obtained is 8 km/sec. As

in all other cases, no A1O radiation was detected

(Millman and Cook, 1959); E, then, cannot

exceed 8.5-1018T0.

Assuming this efficiency applies also to the

simulated meteor, for which AAi=l, we obtain

from equations (8) and (9)

or, dividing by

/=/0+8.5-1018r0m

mV3

2 /

we obtain

1.7-1019

V

3

(12)

(13)

But the left-hand side is equivalent to the

apparent value of the luminosity coefficient

TO(AI), determined from the observations. The

maximum correction to be applied for oxidation

is then

TO=0.17T0(A1,. (14)

Correction for composition.—Estimates for the

corrections necessary because of the difference

in composition between natural meteors and the

simulated meteoroid can also be based on

observations of meteor spectra. The strong

aluminum pair at X3944/3962 (2P°—aS) is sometimes visible in meteor spectra. In low dispersion spectra the pair cannot be resolved from

the H and K lines of Ca+. Although the Ca

and Al abundances are comparable in stony

meteorites (and presumably also in photographic meteoroids),the Al lines are weak compared to H and K. Even in low-velocity

meteors, where H and K are not observed and

where it might be expected that conditions

would favor the excitation of the neutral

aluminum, such aluminum is generally absent

in the spectra.

The luminosity of low-velocity meteors observed on blue-sensitive emulsion results almost

entirely from the iron line emission, particularly

from the

 6D—6Ui

 and

 6D—s

/"°multiplets;and a

determination of the efficiency of iron is tantamount to determination of the efficiency for

natural meteors. Both the Fe and Al lines

have upper levels of about 3 volts. The number abundance of Fe in stony meteorites is

about 10 times that of Al, but since luminosity

arising from the latter is concentrated in two

lines, one would expect to observe these lines if

the rate of population of the upper levels were

comparable for the Fe and Al. Apparently

then, the luminous efficiency of aluminum is

less than that of iron in the meteoric process.

Therefore a lower limit for the luminous efficiency

of natural meteors is obtained by assuming

equal efficiencies, per atom, of iron and aluminum. For the number of iron atoms in a

natural meteoroid to equal the number of

aluminum atoms in the simulated meteor, the

mass of the former must be /iFo/MAi-4pe=13.8

times the latter where y. is the atomic weight

and AVt is the abundance by mass of iron,

taken to be 15 percent (Opik 1958).

Applying the corrections for both oxidation

and composition to the observed luminous

efficiency for the simulated meteor, one finds

a lower limit to the luminous efficiency of

natural meteors,

=l.lO~" sec/cm,

13.8

or about 3 times larger than the mean value

given by Cook and Whipple, but within their

probable error.

The value given here is thought to be an

extreme lower limit. An equally safe upper

limit cannot be obtained from the available

data, and a value for as much as 100 times as

large has not been precluded by this experiment.

Acknowledgment

The experiment to simulate meteor phenomena

was designed and executed by Dr. Maurice A.

Dubin of Air Force Cambridge Research

Center, Dr. Milton C. Kells of Poulter

Laboratories, Dr. John S. Rinehart of Colorado

School of Mines, and Dr. Fritz Zwicky of

California Institute of Technology.

The analysis was supported by Contract

AFl9(604)-5l96 with the Geophysics Research

Directorate of the Air Force Cambridge Research Center.
OBSERVATIONS OF SIMULATED METEORS 37

References

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Abstract

An attempt has been made to simulate meteor phenomena by the high-speed ejection of shaped-charge liners

at an altitude of 80 kilometers. Photographs of two of the three charges flown in an Aerobee rocket have supplied

sufficient information to specify, with a high degree of probability, which charges were responsible for the observed

meteors.

Laboratory tests of one charge give an upper limit to the mass ejected at significant velocities. This limit,

together with the observed velocity and integrated intensity, is used to compute a lower limit on the luminous efficiency of aluminum in the meteoric process. The relative efficiencies of aluminum and natural meteoric materials are

estimated and a lower limit is derived for the luminous efficiency of this latter material, assumed to have the composition of stony meteorites. This lower limit is comparable to an upper limit determined by Cook and Whipple

from meteor train data. An upper limit on the luminous efficiency has not been well defined by this experiment, and

a value 102 times larger, as has been suggested by Opik, cannot be excluded.