TRACK1 G STUDIES O F OLLO 7 AND INTELSAT I1

M. GRANDFIELD, D. HANLON, K. HEBB, E. JENTSCH, . YORKE, and MI. R. WOLF

Srnit hsoni strophysical ClAL REP0

https://ntrs.nasa.gov/search.jsp?R=19710005189 2020-05-19T15:30:13+00:00Z

Research in Space Science

SA0 Special Report No. 298

APOLLO 7 RETROFIRE AND REENTRY OF

SERVICE PROPULSION MODULE

Mary Grandfield, Daniel Hanlon, Karen Hebb, Edward Jentsch, and Robert Yorke

FURTHER STUDY OF INTELSAT I1 F - 2 APOGEE BURN

Michael R. Wolf

Apri l 4, 1969

Smithsonian Institution Astrophysical Observatory

Cambridge, Massachusetts 021 38

901-24

TABLE OF CONTENTS

Page

APOLLO 7 RETROFIRE AND REENTRY OF SERVICE PROPULSION MODULE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 APOLLO7RETROFIRE . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.1 Predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.3 Description of Photographs . . . . . . . . . . . . . . . . . . . . 6 2.4 Station-Satellite Range . . . . . . . . . . . . . . . . . . . . . . . 8

2.5 Pre l iminary Photometric Results . . . . . . . . . . . . . . . . 9 3 SERVICE-PROPULSION-MODULE REENTRY . . . . . . . . . . . 11

3 . 1 Predictions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.2 Observation Descriptions . . . . . . . . . . . . . . . . . . . . . . 11

4 ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . 18

5 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

FURTHER STUDY OF INTELSAT I1 F - 2 APOGEE BURN . . . . . . . . . . 21

ABSTRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

2 SATELLITE POSITION . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3 PROBABLE IGNITION TIME . . . . . . . . . . . . . . . . . . . . . . 25

4 CLOUDPHOTOMETRY . . . . . . . . . . . . . . . . . . . . . . . . . . 27

5 PHOTOGRAPHY AT GREATER DISTANCES . . . . . . . . . . . . 32 . 6 ACKNOWLEDGMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . 33

BIBLIOGRAPHY . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

APPENDIX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 7

iii

APOLLO 7 RETROFIRE AND REENTRY OF

SERVICE PROPULSION MODULE

Mary Grandfield, Daniel Hanlon, Karen Hebb, Edward Jentsch, and Robert Yorke

ABSTRACT

The retrofire of the Apollo 7 manned spacecraft was photographed by

the Smithsonian Astrophysical Observatory (SAO) Baker-Nunn camera at

Maui, Hawaii. Shortly thereafter, the service propulsion module was photo-

graphed by the SA0 Baker-Nunn camera in Arizona and visually observed by

several Moonwatch teams as it entered the earth's atmosphere.

This report presents the data from these observations and a preliminary

analysis of the retrofire photographs.

La m i s e A f e u d e s r g t r o f u s g e s d u v a i s s e a u s p a t i a l p i l o t 6

A p o l l o 7 a Gte' p h o t o g r a p h i 6 e p a r l a came'ra B a k e r - N u n n d u

S m i t h s o n i a n A s t r o p h y s i c a l O b s e r v a t o r y ( S A O ) , M a u i , H a w a i i .

P e u a p r g s , l e m o i e u r d u m o d u l e d e s e r v i c e a e'te' p h o t o g r a p h i ;

p a r l a came'ra B a k e r - N u n n d u S A 0 e n A r i z o n a , e t il a e'te' o b s e r v ; v i s u e l l e m e n t p a r p l u s i e u r s e ' q u i p e s " M o o n w a t c h " l o r s

d e s o n e n t r e ' e d a n s l ' a t m o s p h & r e t e r r e s t r e .

C e t t e p u b l i c a t i o n d o n n e l e s r L s u l t a t s d e c e s o b s e r v a t i o n s

e t p r g s e n t e u n e a n a l y s e p r L l i m i n a i r e d e s p h o t o g r a p h i e s d e l a

m i s e A f e u d e s r 6 t r o f u s ; e s .

2

APOLLO 7 RETROFIRE AND REENTRY O F

SERVICE PROPULSION MODULE

Mary Grandfield, Daniel Hanlon, Karen Hebb, Edward Jentsch, and Robert Yorke

1. INTRODUCTION

Apollo 7 (COSPAR designation 6808901), the first manned miss ion in the

series, was launched f rom Cape Kennedy, Florida, on October 11, 1968, at

15 03 UT. During the 10.8 days of the mission, the Apollo 7 spacecraft

was optically tracked by the worldwide network of Baker-Nunn cameras and

Moonwatch teams operated under the direction of the Smithsonian Astrophysical

Observatory (SAO).

h m

Among the major events during the mission were eight maneuvers of

the spacecraf t that were performed by using the engine of the service pro-

pulsion system. The last of these, the deorbit manuever (Event SPS-8), was

photographed by the Smithsonian astrophysical observing station at Maui,

Hawaii.

Shortly after this event, the Smithsonian astrophysical observing station

at Mt. Hopkins, Arizona, as well as severa l Moonwatch teams, observed the

service propulsion module (which had been separated f rom the command

module after re t rof i re ) during its reentry into the atmosphere.

vations were made at the request of NASA's Goddard Space Flight Center.

These obser-

This repor t will present a prel iminary analysis of the photographs of

the deorbit maneuver and will list the observations of the service-propulsion-

module reentry.

This r e s e a r c h was supported in pa r t by grant NGR 09-015-002 f rom the National Aeronautics and Space Administration.

3

2. APOLLO 7 RETROFIRE

2. 1 Predictions

Before launch, nominal orbital parameters for the Apollo 7 miss ion

( see Table 1) were supplied to SA0 by the Mission Planning and Support

Office of NASA's Manned Spacecraft Center in Houston, Texas. As the

miss ion progressed, revisions to the planned t ra jector ies were provided

by telephone.

The parameters for Event SPS-8 ( re t rof i re ) were converted to c lassical

elements and used as input to SAO's general /ephemeris program (EPHEM), which generated look-angle predictions at 15-sec intervals on both sides of

the expected ignition time.

2. 2 Observations

Well i n advance of the expected time of ignition, the Baker-Nunn camera

(Henize, 1957) at Maui, Hawaii, was set up at the position predicted f o r ret-

rofire.

The observers (D. LeConte, W. Pe r ry , W. Phillips, and M. Salisbury)

selected a camera operating cycle of 16 sec, which provided a 1 .6 - sec

exposure (including chop time) per frame at intervals of 8 sec between exposures.

The sky a r e a was then searched both visually and photographically.

h m s Retrofire occurred on October 22 at 10 42 00. 94 U T o r 2 min and 28

s e c ea r l i e r than was anticipated f rom the nominal orbital parameters ;

however, the spacecraft was in the field of view of the camera, and the

camera shutter was open when ignition took place.

4

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5

At the t ime of re t rof i re , the spacecraft was in the ear th ' s shadow

approximately 10" above the observers ' horizon.

at a thrus t of 21,500 l b (Normyle, 1968).

The burn lasted fo r 1 0 s e c

2. 3 Description of Photographs

The first photograph (Figure la) was taken with the camera stationary.

The clamshell shutter was open fo r 1 .6 s e c with the midpoint of the exposure

occurring at 1 0h42m01.s245 U T (approximately 0. 3 sec af ter ignition).

During the exposure, the exhaust cloud was moving f r o m right to left

a c r o s s the photograph, thus creating a triangular- shaped image with the

apex representing the ignition point. The "break" in the image was caused

by the rotating chopping shutter, which interrupted the exposure five times

(the third interruption represents the center, o r time, of the exposure). In

this case, the only "break" visible is the third; the first two occurred before

ignition, and the last two are not evident, owing to the expansion of the cloud.

The apex of the image is located at right ascension 06 20m0 and declination

- 3 2 " 3 3 ' . to the motion of the spacecraft was approximately 6 arcmin.

of these measurements is f O . 7 arcmin.

h

At the end of the exposure, the dimension of the cloud perpendicular The uncertainty

During the second exposure (Figure 1 b), the camera was slewed while

the shutters were open.

parallel to the spacecraf t ' s motion, the dimension of the cloud image normal

to the path can still be measured. The image was scanned normal to the path

at 500-p intervals with a microdensitometer. At its widest point, it meas-

u res approximately 52 arcmin, with an uncertainty of f 2 arcmin. Burnout

occurred approximately 0. 9 s e c af ter the end of this exposure.

However, since the slewing was unidirectional and

The camera was slewed in a much m o r e complex pattern during the

third exposure. An analysis of this pho.tograph was not attempted.

6

Figure 1. Apollo 7 retrofire photographed at 8-sec intervals by the Smithsonian astrophysical observing station at Maui, Hawaii, October 22, 1968.

7

2. 4 Station-Satellite Range

The final, actual orbital elements before Event SPS-8 (see Table 2)

were input to the general ephemeris package to determine the right ascen-

sion, declination, and range of the spacecraft f rom the Maui station- at the

approximate time of retrofire.

d.

The computed values are the following:

d h m s Time 22 10 42 01

Right ascension 6 h Z O m l

Declination - 3 2 ? 8

Range 1188.9 km.

Table 2. Actual Apollo 7 orbital elements before re t rof i re (Event SPS- 8 ) t

259 h m s 38 15 elapsed time f rom Epoch T = 0

Semimajor axis 21897672 f t

Eccentricity 0. 0185488

Inc 1 inat ion 29?88417

Right ascension of ascending node 17; 58052

Argument of perigee 143?85149

Mean anomaly 242: 51662

Period 90m44355

JI - Geocentric coordinates of Maui Station: Z = 2.242170 Mm.

X = -5.466055 Mm, Y = -2.404275 Mm,

tProvided by NASA's Manned Spacecraft Center, Mission Planning and Analysis Division, Houston, Texas.

8

sections we

The width of the image 1(1) is 0.6 m the film. The Baker-Nunn plate scale is 1 m m = 418". The image I(1), then, min in actual

size. If we follow the same calculation 0 .95 m m on

the film, and 6.61 a rcmin in actual size.

The densitometer scan of Figure l b is shown in par t in F igure 2b. In this instance, the cloud was scanned at intervals of 500 p.

the image on film is 7 . 50 rnm.

the cloud a total brightness of a 4th-magnitude s ta r .

The actual s ize of

Integrating the multiple scans renders for

9

2.70 rnm FILM SCALE

I I

1.6 rnrn FILM SCALE

l+--+l 0.95 rnrn FILM SCALE

(a)

Figure 2. Graphic representation of microdensi tometer scans of F igures l a and 1b.

10

3 . SERVICE- PROPULSION-MODULE REENTRY

3 . 1 Predictions

An ephemeris giving subsatellite points was run with the nominal

orbital parameters for the spacecraft following retrof i re (Event SPS-8,

Table 1).

then derived f rom the subsatellite path on the assumption of a 100-krn

altitude (the height at which reentering objects become incandescent) for

the service propulsion module.

Culmination look-angles for each potential observing s i te were

A le t ter was sent to each potential observing site, notifying them that they should be able to witness the reentry.

giving the predicted culmination look-angles.

This was followed by a telegram

3 . 2 Observation Descriptions

Relevant portions of reports received f rom sites that witnessed the

reentry a r e quoted below, in order of their position along the reentry path.

The time of the Dallas observation does not correlate with those of the

others.

station is reproduced in Figure 3 .

A photograph of the reentry taken at the Mt. Hopkins observing

Figure 3. Service-propulsion-module reentry photographed by the Baker-Nunn Camera at Mt. Hopkins, October 22, 1968.

11

3.2. 1 Smithsonian astrophysical observing station, Mt. Hopkins, Arizona (observed by Jeffrey Bosel)

At approximately 10302 I went up to watch for the reentry that was

predicted for 10442;. The camera was at the predicted settings of az. 175",

alt. 15", which placed the controls in an inconvenient position. Therefore,

I reset to az. 355" and alt. 165".

At approximately 10512 a relatively la rge glowing and fluctuating object

was sighted traveling W to E at about 3000 a r c s e c sec-l.

slightly higher than predicted, being about 20" above the horizon.

camera was started before the object came into the field.

motor was switched on and the velocity adjusted in a n attempt to follow the

object , . . .

The altitude was

The

The tracking

The object did not fluctuate as a n entity but ra ther as if different par t s

of it were tumbling. The

appearance of the object did not change noticeably f rom when it was first

sighted until it disappeared into the haze.

The overall color of the object was a dull red.

3. 2 .2 Moonwatch Team, Phoenix, Arizona (reported by R. K. Reynolds)

At 13" altitude our field is limited to about 35" in azimuth between two

t rees , i. e . , f r o m about 145" to 180". Rhoda watched the a r e a with naked

eye, while I scanned it with an M-17 mounted piggy-back on one of the apogee

scopes. I caught it at about 180" and tracked for 2 or 3 sec before switching

to the apogee, with which I tracked it fo r 8 o r 9 sec before taking a t ime at a

good star field.

edge much brighter than the rest , which had a comet-like glow (see sketch

below).

The satell i te appeared like a fat sausage with the leading

A-

/ 5 4 h MAG POINT

12

F r o m the reticule divisions in the apogee telescope, I estimated the

bright portion to be 0: 10 and the trail ing portion to be 0: 25.

in the leading edge I estimated at 5 mag, compared with the 5-mag star under

which I t imed the satellite.

limited field.

The brightest spot

At no time was it visible to the naked eye i n our

3 .2 . 3 Moonwatch Team, Dallas, Texas (observed by H. W. Rose)

At . . . about 5:53 o r 5:54 A. M . , although it was still dark, I noticed that

the dull gray of the clouds seemed to have a few breaks toward the SSE close

to the designated look-angle, s o I continued to watch, hoping to s e e some-

thing. I was looking SSE at approximately 5:58 A. M. when I became aware

of a faint but definitely noticeable brightening behind the cloud layer to m y S

and SSW, at a n altitude of about 20" to 25".

slightly f o r severa l seconds, although it never did get very bright; it remained

The brightening increased

at a relatively constant intensity for the next 10 to 15 sec and then gradually

diminished back to the fo rmer dull gray during the next 1 0 to 15 sec. The

brightening made the clouds change f r o m a very dull gray to a faint golden

pink.

5:59 A. M. CDT.

W t o E, nor did I s ee anything in any of the few openings in the clouds to the

SSE, not even any stars.

under the cloudy conditions, I did not have m y binoculars with me.

observations were made with naked eye, and altitudes were estimated.

The whole phenomenon lasted less than a minute, between 5:58 and

I could detect no apparent motion of the bright a r e a f rom

Because I did not really expect to see anything

The

3 .2 .4 Moonwatch Team, Panama City, Flor ida (observed by Dr. M. A. Elliot)

On the morning of October 22, 1968, three objects, all traveling h m s

together, were observed to pass near the zenith (est. * l o 0 ) at . . . 4 57 49

CST. The zenith crossing was t imed by naked eye and stopwatch (the stop-

watch was checked 2 h r la te r against WWV), with a n estimated accuracy of

f 2 sec. The objects were traveling f r o m W to E o r possibly f rom slightly

S of W t o slightly N of E.

13

The following figure shows the objects plotted in their relative positions

as seen overhead. They a r e numbered 1, 2, and 3. I est imate that all of

them would fall within a circle of 15" diarneter.

about 2 o r 3 sec before reaching the zenith, and observation continued until

they passed behind the clouds at a n angle of altitude of about 45".

were observed par t 02 this t ime through 8 X 30 binoculars.

They were first observed

They

N

I ** DIRECTION OF TRAVEL

I

S

The sky overhead was dark and clear. There was no noticeable wind,

No noise was heard to come f rom the

Total t ime of observation was estimated to be l e s s than 6 0 sec.

and the background noise was low.

objects.

The objects were traveling at a higher angular ra te of speed than normally

observed for satell i tes in orbi t o r fo r high-flying planes.

Object no. 1 was brighter than a 1-mag star (possibly -1) and was

yellow orange. Object no. 2 was much dimmer than no. 1 and varied in

brightness as if tumbling o r flashing.

of no. 1 but possibly more red and of estimated +2 or +3 mag. Object no. 3

was dimmer ye t than no. 2 (estimated t 3 to t 4 mag) and consisted of a trail

of sparks or f i r e of about 1" angular length.

dull red and could have been f rom a burning object; t he re was no noticeable

head.

The color of no. 2 was similar to that

This trail (object no. 3 ) was

These objects a r e thought to have been the Apollo 7 craf t and associated

par ts , but they were considerably off the predicted path.

14

[Mr. and Mrs . Suber descr ibe three separate objects, tify as I, 11, and 111 (see figure below).]

Object I:

Object 4:

Object 111: magnitude +2; white.

appeared flaming on trail ing (W) s

small and bright, with comet-like magnitude 0; red.

The colors a r e thought to have been due to burning, not to reflected

sunlight.

Objects I1 and I11 disappeared about the zenith.

Object I disappeared 40 O (approx. ) E of the zenith, its color changing

to light orange at disappearance; it grew fainter toward disappearance.

E stimated separation:

I - I1 0:25 to 0: 5

I - I11 0: 75

I1 - I11 0: 2 5 . Total duration of visibility was something l e s s than 1 min.

Speed of t rave l appeared to be too slow for meteors .

E

DISAPPEARANCE OF I

0 ZENITH N I-

S

45*1: UP FROM WESTERN

ABOUT IOh 57m 00' UT, OCTOBER 22, 1968 Et HORIZON WHEN FIRST SEEN

(OBSERVER FACING WEST 1

W

15

A few minutes before 6 A.M. CDT [t estimated the time], they saw three obje

path. The brightest o

s e c ond b r ighte s t ob j e c t blinke d . c t led the others and gave off a s

They interpreted this second object as a craf t with a red light blinking

i n it. The third object was observed to be fainter and l e s s well defined.

the objects appeared to be traveling together and were yellow orange to

reddish.

All

All observations were by naked eye,

The objects were seen fairly soon af ter coming over the horizon in the

W sky and followed until they disappeared at a n elevation of about 40" to 45"

i n the E. 6 0 sec.

The objects were visible for a total t ime estimated as l e s s than

No sound of a i rc raf t was heard at the time. Another reason why

a i rc raf t can be ruled out is that observers at all th ree local s i tes saw these

objects as passing near the zenith.

near ly 8 mi.

they could not have appeared to be nearly overhead at both the northernmost

and the southernmost s i tes unless they were much higher than conventional

planes can fly.

The spread f r o m N to S of these s i tes is

Since the objects were moving on an approximately W to E line,

A s w n m a r y of these observations is given in Table 3.

16

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17

4. ACKNOWLEDGMENTS

We thamk Dr. Charles A. Lundquist, Assis tant Director f o r Science at SAO, for his guidance in preparing this report , and John R. Gurley and

Ben McCreary of NASA's Manned Spacecraft Center f o r their ass i s tance in

obtaining information on the Apollo 7 mission.

18

5. REFERENCES

HENIZE, K. G. 1957. The Baker-Nunn satell i te-tracking camera. Sky and Tel.

V O ~ . 16, pp. 108-111.

NORMYLE, W. J.

1968. Apollo 7 miss ion focuses on operations. Aviation Week &

Space Technology, vol. 89, no. 12, pp. 36-37.

19

FURTHER STUDY O F INTELSAT II F-2 APOGEE BURN

Michael R. Wolf

ABSTRACT

The Intelsat 11 F-2 communications satellite was placed in a synchronous

earth orbit on January 14, 1967. thrust apogee motor for 16 sec at the seventh apogee after launch.

B ake r -N unn satellite - t racking cameras re cor de d the event simultaneously.

From these films, the position during f i r ing, probable ignition time, cloud

brightness, and total magnitude are calculated. The possibility of photo-

graphing such events at even greater distances is discussed.

This was accomplished by firing its 3000-lb-

Three

Le s a t e l l i t e d e c c m m u n i c a t i o n I n t e l s a t I 1 F - 2 fu^t p l a c g e n o r -

b i t e s y n c h r o n e a u t o u r d e l a t e r r e l e 1 4 j a n v i e r 1 9 6 7 . C e c i f i t

a c c o m p l i p a r l a m i s e f e u d e s o n m o t e u r d ' a p o g g e d e p o u s s g e d e

3 0 0 0 l b s . , p e n d a n t 1 6 s e c o n d e s , A l a s e p t i g m e a p o g g e a p r e s le

l a n c e m e n t . T r o i s cam6ras B a k e r - N u n n p o u r l e d 6 p i s t a g e d e s s a t e l -

l i t e s o n t s i m u l t a n g m e n t e n r e g i s t r ; l ' g v g n e r n e n t . o n a c a l c u l e '

p a r t i r d e c e s f i l m s l a p o s i t i o n p e n d a n t l a m i s e f e u , le m o m e n t

p r o b a b l e d e l ' i g n i t i o n , l a b r i l l a n c e d u n u a g e e t l a m a g n i t u d e t o -

t a l e . On d i s c u t e d e l a p o s s i b i l i t ; d e p h o t o g r a p h i e r d e t e l s e ' ~ ; - n e m e n t s : d e s d i s t a n c e s e n c o r e p l u s g r a n d e s .

s.

KOHCI'IEKT

22

FURTHER STUDY OF INTELSAT I1 F-2 APOGEE BURN*

Michael R. Wolf

1 . INTRODUCTION

On January 14, 1967, th ree Baker-Nunn cameras photographed the f i r ing

These cameras of the apogee motor of the Intelsat communications satellite.

were located at Tokyo Astronomical Observatory (TAO), Mitaka, Japan;

Johnston Island, Pacific Ocean; and Rosamund, California. The photography

was requested by NASA Goddard Space Flight Center fo r optical confirmation

of the event.

The resulting films were as follows: Mitaka - 36 frames fo r lm43s;

Rosamund - 39 frames for 5m37s; Johnston - 9 frames for 4 m s 55 . raphy at Mitaka was curtailed because of a bright sky low toward Tokyo.

Photog-

The data were analyzed with the following questions in mind:

1) What was the position of the satell i te during burn?

2) Wha t was the probable t ime of ignition?

3) How did the brightness decrease with time after burnout?

4) W h a t was the total magnitude of the cloud af ter burnout, and did it

change with time?

5) How far away could one expect to observe such events?

The answers to these questions are discussed below.

This work was supported in par t by grant NGR 09-015-002 f rom the National Aeronautics and Space Administration.

T Presented at the Astronomical Society of Japan Conference at Mizusawa, Japan, October 18, 1967.

23

2. SATELLITE POSITION

The Mitaka and Rosamund films were analyzed at the Smithsonian

Astrophysical Observatory (SAO) headquarters in Cambridge, Massachusetts,

to determine the satell i te position during burn.

f r o m each station were chosen, and right ascension and declination fo r each

image on each frame were determined.

and declination to time were obtained by a least-squares process.

common time fo r both stations (January 14, 1967, 10 11 h m s 42.997 UT1) was chosen, and corresponding a, 6 pairs were determined fo r each station for that

time.

sys tem (x, y, z ) was obtained by a triangulation. follow.

Several contiguous frames

Parameters relating right ascension

A

From these two positions, the satell i te position in the earth's coordinate

The resu l t s of this analysis

Satellite position:

x = -42,879 km, S

= -5047 km, YS

z = 3 9 k m , S

Distance f r o m geocenter: 43, 175 km,

Range f r o m Mitaka: 39,999 km,

Range f r o m Edwards: 40,590 km.

24

3. PROBABLE IGNITION TIME

In order to calculate probable ignition time, we decided to scan the best

sequential frames with a microdensitometer and, from cloud dimensions

versus t h e , extrapolate backward to find the time when the cloud dimension

was zero. This was assumed to be ignition time. Frame nos. 1 through 15

f o r both Mitaka and Rosarnund were chosen for the scans.

was therefore 30 sec, since the exposure interval was 2 sec for both stations.

The time span

The cloud dimension versus midexposure epoch was submitted to a linear

least-squares program to obtain the parameters of the relationship between

cloud dimension and time. From the constant term, the x intercept or igni-

tion time can be calculated. Residuals of this fit were small and randomly

distributed in sign, indicating good fit.

corrected f o r finite densitometer slit width, finite image diameter, the

velocity of light, and the fact that the image size really relates t o the time

at the end of the exposure and not to the time presented on the film. With

all these steps completed and the ordinate converted to kilometers, the

results are those shown in Figures 1 and 2. (Cloud dimension is to be con-

sidered approximate because foreshortening effects have not been taken into

account. ) Table 1, which gives the results of these calculations, shows that

the mean of the two determinations agrees to about 0. 2 sec with the telemetry-

confirmed ignition time.

results from a completely photographic method.

The resulting ignition time must be

We consider these to be rather good quantitative

Table 1. Plume-expansion rates and ignition times

Mitaka Ros amund

Projected plume- expans ion rate

= 3.52 km/sec = 3.31 km/sec

Calculated ignition 0.347 f 0.481 sec 0 .216 f 0.867 sec time (compared to earlier later telemetry-confirmed ignition time)

25

904 - 180

TIME --c ( s e c )

Figure 1 . Intelsat cloud expansion (Mitaka data).

904 - 180

0

I 0 4 8 12 16 20 24 28 32

TIME -m- (sec)

Figure 2. Intelsat cloud expansion (Rosamund data).

26

4. CLOUD PHOTOMETRY

Two basic features of the cloud photometry will be considered. The first

is the "brightness, I ' o r lumens per unit area per steradian.

relates to an extended source only and consequently is independent of the dis-

tance of the source f r o m the observer .

irnage of a diffuse extended source on a plate is independent of that distance.

As the distance changes, only the size of the image on the plate changes, not the density.

g ra te the light f rom the irnage and calculate the total lux, o r lumens per

square meter , that falls on the collecting lens.

calculate the magnitude f r o m the relation m = - 2 . 5 log (lux) - 13.94 .

magnitude, unlike the brightness, obviously depends on the source-observer

distance

This quantity

This means that the density of the

The second feature is the total magnitude of the cloud. We inte-

F r o m this quantity we can

This

In the following analysis, extinction will be ignored because we decided

that to apply it a pr ior i t o the observations would be unjustified and no data

were taken during the observations that would allow its calculation. A sen-

s i tometer s t r ip exposed on the Mitaka film was crucial to its analysis. The

actual intensity that fell through each s tep of the wedge was accurately known.

By scanning the wedge with a densitometer, we could plot D vs. log (E), the

familiar Herter-Driffield (H-D) curve.

the film not exposed t o the sky, it could be used to calculate the average

magnitude per square degree of the sky l'background" light.

of interest, the H-D curve was quite linear.

be gained by assuming a nonlinear shape for the H-D curve.

used to reduce the data assumed the linear relationship log E = D/y + i, where E is the exposure in meter-candle-seconds, D is the "instrumental

Since the wedge was on an area of

Within the range

N o increase in accuracy could

The programs

27

* density,lt y is the contrast, and i is the inertia.

determined H-D curve (from the sensitometer strip), the density measure-

ments on incrementally small areas of the image of the Intelsat burn can be

made and the instrumental density can be converted to meter- candle- seconds.

If the effective meter-candle-seconds that came from the sky background

light are subtracted from this, what is left is the light from the object within

the scanned area. Figure 3 shows exactly this kind of analysis applied to an

area of 45 X 45 p. on each of seven Mitaka frames.

density readings on each image was the center of the brightest spot.

resulting values were converted to brightness by means of the formula

Given the empirically

The area chosen f o r the

The

B = lux/solid angle .

The brightness of the cloud decreases with time.

log and semilog scales, the data appear to follow a rule more of the form

B = k T-n than B = B e The value of n seems to be 0 approximately 4, but "noise" in the data makes probably fruitless any

further speculation, such as an attempt to derive an analytical expre,ssion

for the brightness versus time and compare it with the data.

When plotted on both log-

-at (see Figure 3 ) .

* -4-

The term "instrumental density'' is used to avoid any reference to absolute density, which is difficult to define. Here, "instrumental density" means the density as measured on the actual densitometer, with rather accurate scale and arbitrary zero. This definition introduces no problems, as the sensitometer wedge was measured in the same run as the film of the Intelsat burn, with the same slit and other parameters. standard of density is unnecessary. the instrument be accurate, i. e . , that density differences be accurately measurable. T o test this, the density wedge from the Kodak sensitometer was read on the machine. This wedge has 21 steps, from nominal density of 0. 05 to 3 . 05 in steps of 0.15. When read on the machine with the same scan parameters used to read the films, the density differences were as close to 0. 15 as the width of the ink line on the chart, i. e . , as accurate as could be read from the instrument.

Calibration to an absolute The important thing is that the scale of

28

8 x IO-"

7 x

6 X IC4

t 2 5 X I d 4

a 0 n W + v) , 4 x

N I

w z w 3x1d4 5: 3 _J

\

e x

I x

904-180 -

-

-

-

-

-

-

-

0 I I I I I I I 0 2 4 6 8 10 12

TIME - (secl Figure 3 . Cloud brightness versus t ime af ter burnout.

The total magnitude of frames no. 9 and no. 13 f rom Mitaka was calcu-

lated in a way similar to the brightness scheme already outlined, except that

more than one intensity was involved per image. Actually, the images were

digitized in density, and a total of about 150 incremental areas per irnage

resulted. Each of these density values was converted to lux and the value

for the sky background, calculated in a s imi la r way f rom the density of the

sky near the image, was subtracted.

give the total light intensity f rom the source.

to magnitude via the familiar formula

Then a l l the values were summed to

The intensity was converted

m = -2. 5 log (lux) - 13. 94.

The value t8. 77 resulted for frame no. 9, and t 9 . 12 for frame no. 13.

Hence, the total .magnitude increased 0. 35 m in 8 sec.

perhaps a slight increase due t o condensation o r clumping of the grains

after burnout.

One might expect

29

The program used to determine total magnitude a l so calculated total

magnitude p e r square degree fo r sky background.

value of tl. 9 compared to t1. 3 derived photoelectrically a t Mitaka some

y e a r s ago at the same azimuth and elevation.

F o r Mitaka it yielded a

Since the Rosamund f i l m had no sensitometer strip, the parameters y

and i had t o be determined in a different way.

was on the film. Also, since the f i l m appears to have been taken under

perfect sky conditions, a sky background of t4 magnitude per square degree

was assumed. These two facts enabled u s to calculate y and i in the follow-

ing way.

preceding analysis, except that f o r the Orion nebula, m o r e than 700 points

resulted instead of 150.

calculated magnitude per square degree for the sky f rom the background

density above developer fog.

came out t4.

did not agree with the published value, a new pair of y, i was chosen and the

process repeated.

as t o maintain a constant sky brightness makes the process much speedier.

A pair y , i can always be chosen so that the background magnitude comes out t 4 . In fact, this rest raint establishes a single-valued relationship between

y and i. Thus, all that had to be

done was t o choose successive values of y until the magnitude of the Orion

nebula agreed with the published value. Then the values that the computer

used for y and i were printed out.

physically meaningful for the film.

Intelsat image was digitized in density and the same process that was used

f o r the Mitaka film was employed t o calculate the total magnitude, which

was t8. 04 for frame no. 9 f r o m Rosarnund.

ment fo r such a crude method.

Fortunately, the Orion nebula

The image of the Orion nebula was digitized in density as in the

The program used to calculate total magnitude also

The y and i were chosen s o that this calculation

Then the total magnitude for the nebula was calculated. If it

The fact that it is possible to covary y and i in such a way

A choice of y determines i automatically.

These values were assumed to be

Once y and i were determined, the

This is rather remarkable agree-

Ignoring the extinction would affect the resul ts in the following manner.

The Edwards data were calibrated on the light f rom the Orion Nebula

diminished by extinction, while the value used for the nebula's magnitude

30

was that f o r outside the atmosphere.

Intelsat magnitude too small (8. 04).

sensitometric data and yielded a magnitude f

the lens (i. e . , diminished by extinction) that is too large (8.77).

know the values were affected in op by the same amount by extinction,

value, i. e . , m = +8. 34.

This procedure tends to make the

The Mitaka data were calibrated on

iately in front of

Since we

s and, at least

ake the logarithmic mean

31

5. PHOTOGRAPHY AT GREATER DISTANC

One rather interesting and useful feature of photo

sources" such as Intelsat is that the density of the i m

distance f r o m source to camera .

is appreciably l a rge r than the s te l la r image s ize f o r the camera involved.

This means that the event would have had the same apparent brightness no

mat te r how f a r away, except fo r the above limit.

change with distance would be l inear image dimension, which would vary

inversely.

s ize equal to s te l la r image size, then the same rules apply that apply to

s te l la r sources; i. e . , we need consider only the total magnitude of the source

in relation to the magnitude l imit of the camera .

which the cloud length of 50 k m (size a t burnout) would have yielded a point

image is roughly 1. 8 t imes the earth-moon distance.

place at about 0. 1 t imes the earth-moon distance. ) If the total magnitude of

the cloud is taken as t 8 . 3 at the actual distance of 4 X 1 0

apparent magnitude at 1. 8 t imes ear th-moon distance is t14 . 7.

tude limit of the New Mexico Baker-Nunn under perfect sky conditions has

been determined to be t15 . 5, although mos t Baker-Nunn cameras a r e per-

haps closer to i-14. 5. The cloud, then, could have been photographed by

Baker-Nunns in good optical ''tune" under perfect sky conditions at distances

up to 2. 5 . t imes the earth-moon distance.

assuming a shutter speed of 0 . 4 sec.

graph a t longer exposure t imes:

special purposes, although longer intervals between exposures would make

the data on the cloud l e s s meaningful.

This i s t rue a s long as the image dimension

The only thing that would

When the source is appreciably fa r ther than would yield an image

The distance to Intelsat f o r

(Actual firing took

4 krn, then the

The magni-

We must remember that we a r e

The Baker-Nunn can and does photo-

routinely up to 3.2 sec and up to 2 min f o r

32

6 . ACKNOWLEDGMENTS

I would like to thank the many people at Tokyo Astronomical Observatory

and at Smithsonian Astrophysical Observatory who helped me gather data fo r

this report. My special thanks go to Mr. K. Tomita and Mr. Hirayama of

TAO and to Mr . L. McGrath and Mr. P. Brovarone of SA0 fo r their valuable

assistance.

33

7. BIBLIOGRAPHY

HENIZE, K. G. 1957. The Baker-Nunn satell i te-tracking camera. Sky and T

vol. 16, pp. 108-111.

SOLOMON, L. H. 1967. Limiting magnitude of the Baker-Nunn camera. 2 Some Results

at Baker-Nunn Tracking Stations, Smithsonian Astrophys. Obs.

Spec. Rep. No. 244, 13 pp.

34

APPENDIX *

Intelsat I1 F - 2 Motor Plume Composition

(mole percent)

24. 94%

20 .61

18. 75

16.41

8. 40

7. 40

2. 64

0. 51

0. 24

0. 06

0. 02

0. 01

0. 01

9; Data courtesy of Comsat Corp .

35

BIOGRAPHICAL NOTES

MARY GRANDFIELD received the A. B. degree in 1964 f r o m Trinity

College in Washington, D. C .

Miss Grandfield worked at Smithsonian Astrophysical Observatory f rom

1964 to 1969.

supervised the Data Division's orbit evaluation unit.

F r o m 1967 to 1969 she served as chief mathematician and

DANIEL HANLON received the B. B. A. degree in 1959 f r o m the University

of Massachusetts at Amherst .

Mr. Hanlon has been with the Smithsonian Astrophysical Observatory

since 1959 and is currently working in the Moonwatch Division.

Mr. Hanlon is now involved in the gathering of information about satellite

observations.

MISS KAREN HEBB received a B. S. in astrophysics f rom Marlboro

College in 1965.

Miss Hebb joined SA0 in 1964 and completed her thesis work on s te l la r

and comet photometry.

and satell i te geophysics programs.

She is currently an astronomer with the Celescope

EDWARD H. JENTSCH was graduated with a B. S. in mechanical engineer-

ing f r o m Newark College of Engineering in 1963.

worked as an observer at Florida, Cold Lake, Canada, and Spain. He was

t ransfer red to headquarters as a mechanical engineer in 1967 and is now

Operations Officer fo r the Satellite-Tracking Program.

He joined SA0 in 1963 and

ROBERT YORKE expects t o receive the B.S. degree f rom Boston

University in 1970.

Mr. Yorke has beep with the Smithsonian Astrophysical Observatory since

1959 and is current ly assistant manager of the Mount Hopkins Department.

MICHAEL R. W O L F received his Bachelor of Science degree f rom the

Massachusetts Institute of Technology in 1964 and joined the Smithsonian

Astrophysical Observatory as an observer in the same year.

Mr . Wolf is currently working in Cambridge, in the satellite geophysics

group.

when he wrote this Special Report.

He was the SA0 representative at the Tokyo Astronomical Observatory

NO TIC E

This s e r i e s of Special Reports was instituted under the supervision of D r . F. L. Whipple, Director of the Astrophysical Observatory of the Smithsonian Institution, shortly after the launching of the first art if icial ear th satell i te on October 4, 1957. Contributions come f rom the Staff of the Observatory.

First issued to ensure the immediate dissemination of data for satel- l i te tracking, the reports have continued to provide a rapid distribution of catalogs of satellite observations, orbital information, and prelimi- nary results of data analyses pr ior to formal publication in the appro- priate journals. The Reports are also used extensively for the rapid publication of preliminary o r special results in other fields of as t ro- physics.

The Reports a r e regularly distributed to all institutions partici- pating in the U. S. space research program and to individual scientists who request them from the Publications Division, Distribution Section, Smithsonian Astrophysical Observatory, Cambridge, Massachusetts 021 38.