Optical laser satellite range measuring syste

Anderson, P. H.

Lehr, C. G.

Maestre, L. A.

English

NASA Technical Reports Server

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S M I T H S O N I A N  I N S T I T U T I O 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  
Research in Space  Science 
S P E C I A L  R E P O R T  
Number 190R 
USE O F  A LASER FOR SATELLITE-RANGE MEASUREMENTS 
P.H. Anderson, C. G. Lehr,  and L.A. Maestre  
October 21., 1965 
(Revised December 3, 1-965) - 
CAMBRIDGE, MASSACHUSETTS 021 38 
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https://ntrs.nasa.gov/search.jsp?R=19660010251 2020-03-16T22:44:54+00:00Z
SA0 Special Report No. 190 R 
USE O F  A LASER FOR SATELLITE-RANGE MEASUREMENTS 
by 
P.H. Anderson, C. G. Lehr, and L.A. Maestre  
. 
Smithsonian Institution 
Astrophysical Observatory 
Cambridge, Massachusetts 02138 
t Wh!le the Baker-Nunn c a m e r a  i s  capable of making highly accurate an- 
gular measurements  of satell i te positions, it cannot measu re  range directly 
f r o m  a single s i te ;  supplemented with a system capable of precise  range 
xxeasurements, it would completely define the position vector of a satellite 
at a given t ime. 
8 . 
USE OF A LASER FOR SATELLITE-RANGE MEASUREMENTS~ 
by 
4 P. H. Anderson, C. G. Lehr, and L.A. Maestre  
Abstract. --A L a s e r  Satellite-Ranging System i s  being devel- 
oped at a Smithsonian Observatory astrophysical 
observing station. Range measurements  have 
been obtained on re tr o r e  fle c to r -e quipped s ate llite s . 
Introduction 
The Smithsonian Astrophysical Observatory and the Re -entry Systems 
Department of the General Elec t r ic  Company a re  engaged in  a se r i e s  of 
experiments using l a s e r s  to measu re  ranges to satell i tes.  
will evaluate an optical ranging sys t em as a supplement to the 
c a m e r a  for  the purpose of increasing the accuracy with which satellite o r -  
bits can be determined. 
These experiments 
Baker-Nunn 
This work was supported by Grant KO. NsG 87-60 f rom the National 
Aeronautics and Space Administration. 
Elec t r ic  a1 Engineer, Smiths onian Astrophysical Obs e rvatory. 
1 
2 
3Staff Engineer,  Smithsonian Astrophysical Observatory. 
4 
Senior  Obs e rve r, Smiths onian As tr ophys i c  a1 Obs e rvato ry. 
A laser  sys tem appears to be the most  promising to f i l l  this need since 
I 
i t  has  several  advantages over other ranging systems.  Among these a re :  
( 1 )  lower equipment cost ,  
( 2 )  higher spec t ra l  radiant intensity, and 
( 3 )  lower ionospheric distortion. 
As the work in the evaluation study continues, various experiments a r e  
being carr ied out that  eventually w i l l  define a l a s e r  sys tem to be considered 
for use at SA0 stations. 
covered in a report  by General Electr ic  Co. (1965);  this repor t  deals with 
the recent progress  in obtaining range measurements .  
Our previous efforts leading to this experiment a r e  
System description 
The Re-entry Systems Department of General Elec t r ic  supplied the 
l a se r ,  with i ts  power supply, and the photoelectric receiving system. The 
Smithsonian Astrophysical Observatory supplied the Baker-Nunn camera ,  
the l a se r  tracking mount, and the satell i te predictions, as  well as the nec- 
e s s a r y  materiel ,  personnel, and facilities a t  the Organ Pass, New Mexico, 
astrophysical observing station. 
The significant character is t ics  of the G E  l a s e r  a r e  summar ized  in Table 1. 
A combination of rotating p r i s m  and RG8 Schot tglass  was used to obtain the 
single 50-nanosecond (ns) Q-switched pulse. The passive Q-switched pulse 
train was achieved by use of only the Schott glass .  Figure 1 shows the v a r -  
ious l a s e r  output pulses. 
In the f i r s t  phase of the experiment,  the l a s e r  was mounted on the Baker-  
Nunn camera,  as  shown in Figure 2(a). 
plate allowed the operator to make ve rn ie r  adjustments in along-track and 
cross - t rack  position while sighting through a modified M-  17 apogee telescope 
and tracking with the Baker-Nunn c a m e r a  drive.  Figure 2(b) shows the l a s e r  
The special ly  designed mounting 
- 2  - 
mounted on the surplus 3-inch gun mount used for  the second phase of the 
experiment. 
cranks while viewing through apogee telescopes: 
elevation; the other, azimuth. 
To use this mount, two operators were  required to turn hand- 
one operator  controlled 
A 60-inch searchlight modified with an RCA 7265 (S-20 surface)  photo- 
0 
multiplier and two 70 A bandpass interference f i l ters  se rved  as the receiving 
system. 
sighting through 6 -inch telescopes. 
allowed them to follow the satell i te and keep i t  within the 1 / 3 "  receiver  beam 
width. 
Figure 2 ( c )  shows how two operators pointed the searchlight while 
Azimuth and elevation velocity controls 
Figure 3 shows the physical configuration of the experimental  equipment. 
The relative placement of the 3-inch gun mount and searchlight receiver  was 
selected to account for  possible velocity aberration effects with the BE-C 
satellite. 
square,  placed on a hill visible f rom both the l a s e r  (3-inch gun mount) and 
the searchlight locations. A survey of the combined optical distance f rom 
l a s e r  to ta rge t  to searchlight yielded a figure of 5038 feet. 
The calibration ta rge t  consisted of a white matte surface,  6-foot 
I 
A block diagram showing the electr ical  connection of the equipment is 
given in  Figure 4. 
an EECo Prec is ion  Time Standard. In the normal,  free-running o r  passive 
Q-switch modes, the l a s e r  f i red approximately 0 . 4  ms af ter  receipt of this 
signal. 
p r i s m  was i n  proper  alignment after the firing signal was received. 
in te rva l  can be up to 4 m s  af te r  the clock signal. T'he relationship between 
the clock signal and l a s e r  fir ing was, i n  all cases ,  recorded f rom an oscil-  
loscope that displayed a phototube sampling of the l a s e r  output on a sweep 
t r iggered  by the clock signal. 
graphs of this presentation. 
The l a se r  received its firing signal f rom the station clock, 
In the Q-switch mode, the l a s e r  fired the next t ime the rotating 
This 
Figure 1 represents  sample Polaroid photo- 
- 3 -  
The searchlight received the l a se r  reflection f rom the satell i te,  and , 
the output of i ts  photomultiplier was presented on an oscilloscope. 
sweep fo r  this t race  was expanded and triggered through a delay circui t  s o  
as  effectively t o  place a rough range gate around the expected time of the 
re turn  pulse. 
The 
The sampled l a s e r  output and the re turn  pulse were each amplified by 
the oscilloscope preamplifiers and fed into threshold gates for the 10-Mc 
counter, 
10-Mc pulses to accumulate until a stop signal was received f rom the sea rch -  
light receiver. 
so  that it  took a second o r  more  before a noise pulse of sufficient strength 
came along to stop the counter. 
ous check on the counter ' s  crystal-clock frequency. 
then computed f rom the relation 
The "s tar t"  gate was t r iggered by the l a se r  pulse allowing the 
The "stop" gate threshold was var iable;  it was normally s e t  
The frequency monitor provided a continu- 
The satell i te range was 
where 
P =  
N =  
F =  
c =  
C 
C 
tabulated range (megameters )  (Mm), 
cycles counted, 
counter frequency (cps),  
299.7928 (Mm/sec) .  
The only correction contained in the above expression represents  the 
total equipment delays. 
a t  the calibration target  and the counter reading of 5. 0 p s  being noted. 
represents a distance of 4918 feet, a s  opposed to the surveyed distance of 
5038 feet. 
mised for equipment delays. 
be shown to be smal l  compared to * 1 5  m, the resolution of the counter p r e s -  
ently in use (see Appendix). 
pheric correction will have to be made. 
This delay was determined by the l a s e r  being f i r e d  
This 
A correct ion of to. 1 ps,  o r  1 cycle count a t  1 0  Mc, i s  thus s u r -  
The e r r o r  due to a tmospheric  re f rac t ion  can 
When a m o r e  p rec i se  counter i s  used, the a tmos-  
-4 - 
b 
Results 
A compilation of the important information pertaining to the observa-  
tions, including the measured ranges,  i s  found in Table 2. Oscilloscope 
presentations of the transmitted and received pulses a r e  displayed in Figures  
5 through 15. The transmitted pulses for the rotating p r i s m  Q-switch mode 
I were always identical in amplitude, t ime scale, and s t ructure .  Therefore,  
I only a single representative photograph is shown. 
I No oscilloscope pictures a r e  available for success  numbers 6, 7,  and 8, 
as  l isted in Table 2. In these cases ,  the oscilloscopes did not t r igger  properly. 
The returns  obtained can be divided into four separate  groups according 
to the type of Q-switch used for the output pulse and the recording device 
froin which the range measurement  w a s  made. 
Group I. 
of 1-ms duration. 
range counter, the pulse length and i t s  varying amplitude made it impossible 
to determine which pa r t  of the pulse stopped the counter. More reasonable 
range values were obtained through a visual correlat ion of the output and the 
received pulses. 
Successes  1 through 5 resulted f rom non-Q-switched output pulses 
Although the returns  had sufficient amplitude to stop the 
I 
Group 11. 
which includes successes  6 through 8. 
0. 5-ms t ime duration. 
Only range-counter measurements were  obtained for this group, 
The output pulse was reduced to 
Group 111. 
threshold was se t  high to avoid stopping the counter with noise pulses. 
fortunately, the received signals had insufficient strength to stop the counter. 
Consequently, only oscilloscope presentations of the return signals were  pos - 
sible. 
horizontal  oscilloscope scale of 0. 5 m s / c m  for  the transmitted pulse presen-  
tation. 
F o r  this group (successes  9 through l l ) ,  the counter amplitude 
Un- 
The random delay of up to 4 m s  in the Q-switched mode required a 
-5-  
Group IV. 
were  made with the range-counter and a Q-switched pulse. 
presentations of the returns  were also acquired. 
Altogether, 8 range determinations ( successes  12 through 19) 
Oscilloscope 
The 10-Mc range counter was monitored by a Hewlett Packard  frequency 
counter during the returns  in  this group. 
t imes were then cor rec ted  for the frequency offset of the counter oscil lator.  
In addition, the delays arising f r o m  the circui t ry  were  identified through use 
of our system's  calibration target,  and suitable correct ions were made to the 
measured ranges of the satellite. 
All of the measured  propagation 
The accuracies of the ranges l isted in Table 2 for  successes  12  
through 19 a r e  limited to f 15 m by the par t icular  range counter which was 
used for  these initial experiments.  
The eight re turns  of Group IV  were  made during seven passes  of 6532A 
over the New Mexico tracking station. 
conditions prevented additional measurements  f r o m  being secured. 
Bright sky/poor satell i te visibility 
The Baker-Nunn c a m e r a  was synchronized with the l a s e r  firing t imes for 
re turns  9 through 19, s o  that the l a s e r  beam would appear on the film while 
the sunlit satellite was being photographed. 
eous laser  Baker-Nunn observations to be effected,  with t imes recorded on 
the Baker-Nunn fi lm to 0. 1 -ms  accuracy. 
This expedient allowed simultan- 
A noteworthy accomplishment was that f o r  success  numbers  1 3  through 
doppler range-rate measurements  on 6532A were  made simultaneously 19, 
with Baker-Nunn photography of the sunlit sa te l l i te  and l a se r - r ange  de ter -  
minations. This constitutes what is probably the first s e t  of simultaneous 
measurements  made on a satell i te by three  accura te  tracking sys tems.  (The 
doppler range-rate measuring system, owned by the Navy, i s  co-llocated 
at the New Mexico station for the purpose of a sys t ems  comparison with the 
Baker-Nunn camera.  ) 
~ 
~~ 
-6 - 
Acknowledgments 
We thank Mr. J. T. Williams and his staff a t  the Organ Pass ,  New Mexico 
tracking station for  the assistance they provided i n  acquiring the measu re -  
ments l isted in this paper. 
ful in  supplying the required satell i te predictions. 
Mr. Gordon Snyder of the Re-entry Systems Department, General  Electr ic  
Company, without whose equipment and serv ices  this work could not have 
been performed. 
Mrs.  Bea Miller of SA0 Data Division was help- 
Gratitude is also due 
- 7 -  
APPENDIX 
The Correction for Atmospheric Refraction 
Veis (1960) gives the following expression for the refractive index of 
the atmosphere as a function of altitude: 
ah n - 1 = K e  , 
-6 where K = 292 X 10 , a = -0.1385 km-', and h is the altitude in km. 
F o r  an atmospheric correction to laser - range  measurements ,  the dif- 
ference between the optical path in the atmosphere and the optical path in the 
vacuum is desired. This difference is the following: 
d =  r(n - ') J (A2) 
0 
where R is the slant range to the satellite. 
le t  h = p 
this expression and equation (Al)  into (AZ), we obtain 
Assuming a flat ear th ,  we may 
Substituting sin 8, where 8 is the elevation angle of the satell i te.  
R 
sin 8 
d = KeaP dp J 
0 
~ 
- 8 -  
which yields 
aR sin 9 
[ e  -11 , K a s in  9 d =  
K - 
a sin 8 
The lowest elevation for which range was measured in this experiment 
Using this value of 8, and the constants given above, the co r rec -  was 41 '. 
tion to the range measurement  would be 
i 
= 3 . 2 m  2.1 s in  41 O d =  
References 
GENERAL ELECTRIC COMPANY 
1965. Lase r  experiments with a Baker-Nunn camera.  Final Report on 
Contracts SI-7 15 and SI-71 8 with the Smithsonian Astrophysical 
Observatory, Cambridge, Massachusetts. 
VEIS, G. 
1960. Geodetic uses  of art if icial  satellites. Smithsonian Contr. Astrophys. , 
V O ~ .  3 ,  pp. 95-161. 
- 9 -  
E 
0 
\ + 
d 
4 
E 
V 
\ + 
N 
0 
E 
0 
\ + 
N 
0 
Figure 
0 .  5 m s / c m  
1. --Laser output pulses: (a) Normal,  free-running mode; (b) Passive 
Q-switched mode; ( c )  Single-pulse Q-switched mode. 
-1 0- 
Figure 2. --Polaroid photos of (a) Laser mounted on Baker-Nunn camera;  
(b) Lase r  mounted on 3-inch gun mount; and (c)Searchlight __ 
receiver.  
-11- 
Cali brat ion 
Target 
Sear 
Camera 
Figure 3 .  --Physical configuration of experimental  equipment. The distances 
a r e  not to scale. 
- 1 2 -  
E E C o  T i m e .  
S tanda rd  
I 
I 
- 
LASER 
F r e q u e n c y  
Moni to r  
C r y s t a l  
C lock  and 
P e r i o d  Counter  
4 
S e a r c h l i g h t  
and  Phototube 
Rece ive  r 
V 
F i g u r e  4. - -B lock  d i a g r a m  of l a s e r - r a n g i n g  s y s t e m .  
Sampl ing  
Ph o totube 
- 
-13-  
C i r c u i t  
, 
0.2 m s / c m  
T r ansmitted Pulse 
for Success #1 
1. 0 m s l c m  
Success #1  
Received Pulse  
Figure 5 
-14- 
0.2 m s / c m  
Transmitted Pulse 
for Success #2 
0 . 2  m s / c m  
Success #2 
Received Pulse 
Figure  6 
-1 5- 
0 .2  m s / c m  
Transmitted Pulse 
for Success # 3  
0 . 2  m s / c m  
Success # 3  
Received Pulse  
Figure 7 
- 1 6 -  
4 . 
0.2 m s / c m  
T ransmitte d Pulse 
fo r  Success #4 
0. 2 m s / c m  
Success #4 
Received Pulse 
Figure 8 
-1 7- 
. 
- 
E 
U 
0 
0.2 m s / c m  
Transmitted Pulse 
for Success #5 
E 
V 
0 . 2  m s / c m  
Success  # 5  
Received Pulse 
Figure 9 
-1 8 -  
0 
E 
V 
0.1 p / c m  
Typical Transmitted Pulse 
for Rotating Prism Q-Switch 
0 . 1  m s / c m  
Success # 9  
Received Pulse 
Figure 1 0  
-1 9 -  
t 
0.1  m s / c m  
Success #10  
Received Pulse 
0.1 m s / c m  
Success # I 1  
Received Pulse  
Figure 11 
-20- 
E" 
0.1 m s / c m  
Success #12 
Received Pulse 
E u 
0.1 ms/cm 
Success # 1 3  
Received Pulse 
Figure 12  
-21 - 
0.1 m s l c m  
Success #14 
Received Pulse 
0.1 m s l c m  
Success  #15 
Received Pulse 
Figure 1 3  
-22 - 
0 
N 
0.1 m s / c m  
Success #16 
Received Pulse 
0 .1  m s l c m  
Success #17 
Received Pulse 
Figure 14 
-23 - 
0 
cu 
0.1 m s / c m  
Success #18 
Received Pulse 
E 
0 
0 
N 
0.1 m s / c m  
Success #19 
Received Pulse. 
Figure 15  
. . 
-24- 
Table 1. - -Lase r  character is t ics  
Wavelength 
Beam Divergence (at  output optics) 
Repetition Rate 
Normal 
Energy 
Pu l se  Width 
36 joules 
1 m s  
0 
6943  A 
1 m r a d  
One pulse per  minute 
Passive Q-Sw. Q- Sw itc he d 
11 joules 0. 5 joule 
1 ms 
(total) 
50 ns 
- 2 5 -  
m 
c, 
i 
E 
a, 
k 
3 
m 
Id 
a, 
M 
d 
Id 
k 
I 
k 
a, 
il) 
Id 
0 
P 
rd 
B 
i 
d 0
2 
m 
m 
d 
0 
0 VI 
0 
0 
0 
d 
c 
d d 4  
0 0 0  
, , I  
N N N  
0 0 0  m m m  
4 d d  d d 4 d  
0 0 0  0 0 0 0  
I , ,  , , I ,  
N N N  N N N N  
m m m  m m m m  
0 0 0  0 0 0 0  
m m m  m m m m  
m m  m m m m m m m  
m m m  0 0  0 0 0 0 0 0 0 ~ ! 4  
m m  m m m m m m m  
9 9  \ 0 9 9 9 9 9 9 d c  a 9 9  .o .O\o .o  a 9 1 0  V 
m m m  m m m m  m m m  
9 9 9  9 9 9 9  9 9 9  ....... ...
. + m m  t - m m  m m o -  ....... .. N N N  N N N O  
0 0 0  m o o  m o m 0  
0 0 :  
0 0  0 0 0 0 0 0 0 0  
d d  4 4 4 d d - 4 -  - 4 -  d 
. 
- 2 6 -  
NOTICE 
This s e r i e s  of Special Reports was instituted under the supervision of 
Dr. F. L. Whipple , Director of the Astrophysical .Observatory of the 
Smithsonian Institution, shortly after the launching of the f i r s t  art if icial  
ea r th  satell i te on October 4, 1957. 
the Observatory. 
Contributions came from the Staff of 
- 
F i r s t  issued to ensure the immediate aissemination of data for  satell i te 
tracking, the Reports have continued to provide a rapid distribution of cata- 
logs of satell i te observations , orbital  information, and prel iminary resul ts  
of data analyses p r io r  to formal  publication in the appropriate journals. The 
Reports a r e  a lso used extensively for  the rapid publication of preliminary o r  
special  resu l t s  in other fields of astrophysics. 
The Reports a r e  regularly distributed to all institutions participating in  
the U. S. space r e sea rch  program and to individual scient is ts  who request 
them f rom the Publications Division, Distribution Section, Smithsonian 
Astrophysical Observatory, Cambridge, Massachusetts 021 38. 


Use of a laser for satellite-range measurement

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