PROJECT BLUE BOOK

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PROJECT 10073 RECORD CARD

1. DATE 2. LOCATION E CONCLUSIONS
D Was Balloon
\ : UEFEUO. TOXSs D Probably Balloon
3. DATE-TIME GROUP 4. TYPE OF OBSERVATION ——|0 Possibly Balloon
: O Was Aircraft
—e OSaeenae eeprom Roger Q Probobly Aircraft
GMT = Fees 0 Air Visual DO Air-Intercept Rodar 0 Possibly Aircraft
+ SHOTCS | & SOURCE O Was Astronomical Meteor
‘D:Yes OX Probably Astronomical
D No O Possibly Astronomical

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"J. LENGTH OF OBSERVATION

8. NUMBER OF OBJECTS | 9. COURSE

23 seconds two not siven
10. BRIEF SUMMARY OF SIGHTING 11. COMMENTS

A radar
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Insufficient Data for Evaluation

Unknown

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INTERIM LETTER REPORT

CONTRACT NOt AF30(602)=17L2

UNIDENTIFIED TARGET OF AN/FPS-17(XW-2) RADAR MISSION 16)

I. INTRODUCTION

The AN/FPS-17(XWe2) radar at the Laredo Test Site, Laredo, Texas

was in operation on 11 October 1958. The expected target was 1958
O 2, the instrumented portion of the third Russian satellite, Sputnik
III, <A target was observed, but the characteristics of the intercept

would make one believe that the object observed was not the one expected,

Other possible explanations are discussed below,

II, CONCLUSIONS

The object observed was most probably:

(a) a meteor showing both a head echo type reflection
and a specular type reflection from the trail, or

(b) two meteors occurring in the same portion of space
at very nearly the same time.

III. ANALYSIS
A. FACTS RELATED TO THE UNIDENTIFIED TARGET
The known facts related to the intercept of this unidentified

target are?
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(a) the target was observed on 11 October 1958 beginning
at .O7h 21m h.0s Universal time and lasting until
O7h 22m 12.0s, an overall duration of 28.0 seconds.
Se nal

(b) the target as displayed on film recordings of the radar
Signal consisted of two unusually distinct sections.

: The first of these lasted for approximately 0.75 seconds,
showing a range change from 54 to 473 nmi, The second
portion began where the first left off and lasted for
27.3 seconds. The range of this target changed from
462 to h67 nmi-in that time. Absolute range as indicated
here 4s accurate to within 5 nmi, but relative to each
other they are accurate to within 2 nmi,

(c) the target was observed in three of four beams being
energized as follows:

Beam 1 Low No target

Beam 2 Low 0721:h4.3 to 0722:03.0
Beam 1 High O721:45* to 0721255.5
Beam 2 High 0721:4.0 to 07:22:12.0

# May have entered prior to this time, but beam was
not energized because of Beam Switching.

(d) No doppler frequency information was available be-
cause the range gate was set so that only targets
between 50) and 1178 nmi would alarm the Lincoln
Coded Pulse doppler system.

(e) An intercept of the Russian satellite, 1958 42 had
been expected at about 07332 at a range of 700 to 900
nmi,

(f) No other targets were observed by the radar between

B, POSSIBLE TARGETS
A signal such as that received by the radar could, at first

glance, have been reflected from any one of the followings ;

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,

(a) <A rocket launched from the vicinity of the
White Sands Proving Grounds,

(b) A satellite passing through the beams in a northe
easterly direction.

(c) <A meteor or meteors,

(a) Some unknown and unexpected object.

C. INTERPRETATION OF THE FACTS
A knowledge of the location and path of the bbaerved cb test
is desirable if one is to distinguish between the above possibilities.
The range of about 70 nmi would position the observed object somewhere
in the vicinity of the White Sands Proving Grounds, The observation
of ths object simultaneously by three of the four beams energized allows

us to estimate the angular coordinates more exactly than if reflections

were seen in only one beam. If the possibility of side lobe reflections
are neglected, the object observed must have been at an elevation angle
between 3.5 and |.5 degrees and an azimuth angle from the radar between
312.5 and 313.5 degrees,

Conversion of these radar coordinates to a more meaningful
form Places the observed target probably within 5 nmi of a point in

space defined as follows: P

Origin: at the Air Force Missile Development Center,
Holloman Air Force Base, New Mexico

Coordinates: West 10 nmi
South 2 mni
Height 6) nm4

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uNcL CSIFIED

The path (direction and speed) of the target cannot be
resolved to any great degree of accuracy. The sudden appearance of
the signal in three beams indicates that the object suddenly appeared
at this position in space and didn't gradually move into one beam and

then another, The target Should be considered as two separate parts,

“that which lasted for 0.75 seconds and the other, which had a duration

of 28 seconds in Beam 2 High, The first target had a range rate of change
of about + 25 mmi per second. The second target had an average range rate
of change of 0.2 nmi per second,

The accompanying photographs show that the signal died out of
Beam 1 Hi before it died out of Beam 2 Hi. This could be explained by the
passage of the target from one beam into the other, or by a decrease in
the strength of the reflected signal, If the target were closer to the
center of Beam 2 Hi, we would expect to get the stronger signal in that

bean,

D. ELIMINATION OF POSSIBLE TARGETS
Consideration of the facts available indicates that several
of those objects listed as possible targets would not give rise to a

signal such as that received,

(a) A rocket launched from the White Sands Proving Ground
would have been picked up in a low beam about 30 to 0
seconds before it was seen in the high beams, and it
normally is seen for longer than 28 seconds. No
such phenomena as that demonstrated by the early portion
of the target kas been observed on previous rockets
launched at White Sands,

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(b) Only one satellite was known to have been in the
vicinity at the time of observation. This one
Bhould have passed through the beans over 200 nmi
to the northwest about 12 minutes later, The pre
diction bulleting, are subject to some error, but
they are seldom fur enough off in either position
of the orbit or time of passage for this observed
object to have been the satellite,

All previous observations of satellites on southe
toenorth passes have snown similar range rate
characteristics. But they have also gradually moved
into Beam 1 and then Beam 2, which is not the case
here. No satellites in orbit come so close to the
earth as the indicated 6) nmi, If they did, they
would soon fall out of orbit or burn up in the ate

- mosphere,

One should note that there may be several pieces

of satellites in orbit which nobody is keeping

track of, These pieces could, at times, be observed,
but the sudden appearance in three beams and a rate
of change of range of 25 nmi per second are not
characteristics of satellite intercepts.

(c) The observed target height, 6 nmi, is in the meteor
band. <A very sudden appearance of a strong signal is
characteristic of meteors. The appearance of the signal
Suddenly in three beams ig quite possible in the case
of a meteor. Although there is mich yet to be learned
about meteors, it is known that not all meteors in a
beam are detected by a radar, There are requirements
regarding the orientation of the meteor trail with
respect to the radar beam waich mst be met.

Then, too, the exact height at which a meteor trail

becomes defectable varies. Either one or both the
orientation of the trail and the ionization formation,

could explain why the meteor was not seen until such
a time as it reached a position within the beams.

The first portion of the observed trail might well
have been an echo from the soecalled meteor head, thus

giving us the very high rate of change of range (the meteor
head moves with the speed of the meteor itself). Meteor

velocities vary over a wide range, but they may be as high
as twice that range rate of change observed.

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The second portion of the trail. is characteristic

of meteor trail echoes, where the echo actually comes
from the ionized trail left behind the meteor, This
type of echo has a very little change in range, since
once the trail exists its only movement is caused by
expansion of the trail or movements of the air in which
the trail lies,

RECOMMENDATIONS

Two possible sources of information vertaining to this target have
not been approached as yet. The first of these is the White Sands
Proving Ground. They ordinarily notify the Laredo Test Site of any
rockets they plan to fire, which may pass through the radar beams,

The absence of any firings on 11 October 1958 should be verified by

contacting the authorities of the White Sands Proving Ground,

The Harvard College Observatory has two cameras recording pictures of
meteors which occur in the vicinity of the White Sands Proving Ground,
There is a possibility that they would have observed any meteor, or

other phenomena which created visible light, at the time and location

of this unidentified target,

r 1958