The implementation of a satellite tracking and antenna control system is described. Due to the loss of inclination control for the symphonie satellites, it became necessary to equip the parabolic antennas of the mobile Symphonie ground station with tracking facilities. For the relatively low required tracking accuracy of 0.5 dB, a low cost, step track system was selected. The step track system developed for this purpose and tested over a long period of time in 7 ground stations is based on a search step method with subsequent parabola interpolation. As compared with the real search step method, the system has the advantage of a higher pointing angle resolution, and thus a higher tracking accuracy. When the pilot signal has been switched off for a long period of time, as for instance after the eclipse, the antenna is repointed towards the satellite by an automatically initiated spiral search scan. The function and design of the tracking system are detailed, while easy handling and tracking results

Ernsberger, K.

Lorch, G.

Waffenschmidt, E.

English

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https://ntrs.nasa.gov/search.jsp?R=19820019452 2020-03-21T07:16:52+00:00Z
NASA TECHNICAL MEMORANDUM 	 NASA TM-76649
AUTONOMOUS ANTENNA TFACKING SYSTEM FOR MOBILE SYMPHOivIE
GROUND STATIONS
K. Ernsberger, G. Lorch, E. Waffenschmidt
(biASA-T11-76649)	 AUZCNCM0L3 ANTENNA ZBACKIHG 	 N82-27328
SYSTES FOR d0bILE SYMEHCNIE GECUND STATIONS
(National Aeronautics and Space
Admiuistration)	 13 p eC A02/MF A01 C3CL 22D	 [tuc as
G3/14 282314
Translation of
"Autonomes Antennennachfiihrsystem Fur S;ymphoniebodenstationen,"
In: Symphonie Symposium, 1980, Centre National D'Etudes Spatiales,
Toulouse (France) and Deutsche Forschungs- and Versuchsanstalt Fiir
Luft- and Raumfahrt, Cologne (West Germany), (Symposium held in
Berlin, 4-7 Feb. 1980), pp. S41-SS2.
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, DC 20546
	 NINRCI1 198 2
ORIGINAL PAGE IS
OF POOR QUALITY
STANDARD TITLE PACE
an
ti
eq
1.	 Report No.
..NASA TM-76649
2. Government Accession No.
--
)t	 Recipient's Catalog No.
4.	 Title and Sub itle S. M511982, DoteAutonomous Antenna Tracking System for !
A.	 Performing Organisation CodeMobile Symphonie Ground Stations
7.	 Autherls) !.	 Performing Organisation Report No.
K. Ernsberger, G. Lorch, E. Waffen-
10.	 work unit No.schmidt
9 •	 Perlormtng Organisation Name and Address 11.	 Contract or Grant No.
NASw-3541 
Leb Kanner Assoc., Redwood City, CA.
94063 ls.	 Type of Report and Period Coverert
Translation
12.	 Sponsoring Agency Name oral Address
National Aeronautics and Space Administration 14
	
Sponsoring Agency Code
Washington, DC	 20S40
15. SvpplementaryNotes	 Translation of
"Autonomes Antennennachfuhrsystem Fur Symphoniebodenstationen," In:
Symphonie Symposium, 1980, Centre National D'Etudes Spatiales, Toulouse
(France) and Deutsche Forschung,s-und Versuchsanstalt Fur Luft-und
Raumfahrt, Cologne (West Germany), (Symposium held in Berlin, 4-7 February
1980), pp.	 S41-5S2.
(s^.^ N ^/
	
1 yZ_
16. Abstract	 The implementation of a satellite tracking and
enna gontrol system is described.	 Due to the loss of inclina-
n control for the symphonie satellites, it became nedessary to
ip the parabolic antennas of the • mobile Symphonie ground statio
with tracking facilities.	 For the relatively low required
tracking accuracy of 0.5'dB, a low cost, 	 step track system
was selected.	 The step track system.developed for this
purpose and tested over a long period of time in 7 ground
stations is based on a search step method with subsequent
parabola interpolation.- 	 As compared with the real search ste
method, the system has the advantage of a higher pointing•
angle resulution,'and thus a higher tracking accuracy. When
the pilot signal has been switched off for a long period of
time, as for instance after the eclipse, the antenna is re-
-pointed towards the satellite by an automatically initiated
spiral search scan.	 The,,function and design of the tracking
system are detailed, while easy handling and tracking result.
17.	 Key Words (Selected by Author(o) 18.	 Distribution Stotement
Unclassified--Unlimited
19.	 Seturtry Ciassil, (of this report) 20.	 Security ClostiO. (of this page) 	 i 21• No. of Pages 22.
Unclassified Unclassified
.uct% 110
Posing the Problem 	 /542*
Switching off the inclination stabilization in a geostatiotiary
satellite causes initially a time-proportional increase in inclina-
tion. This is caused primarily by the modulated gravitation forces
of the sun and moon. In the [illeg.] model 2 of the Symphonie
satellite, the inclination stabilization was shut off in 1977.
Since then, the inclination has increased annually by ca. 0.8 degrees.
The maximum rate of change in line of bearing (LOB) is time-
dependent and changes proportionally with the increase in inclina-
tion.
Table 1.1 shows the values up to 1982:
Time	 Inclination
1978
	
0.350
After
1 year 1.150
After
2 years 1.950
After
3 years 2.750
After
4 years 3.660
After
4.5 years 40
Max. rate of change of LOB
0.087 degrees/h
0.29
0.49
0.69
0.80
1.0
From the table we see that at the end of 1978, a deviation from
stationary alignment of ca. 0.35 degrees had set in. For a 4.5 m
antenna, this corresponds to a signal loss of ca. 3.5 dB at 4 GHz
downlink. On additicn of losses in the Up- and Downlink, the
signal loss was max. ca . 10 dB. The antenna must thus track the 	 /543
satellite.
Since the earth radio stations were already completed, the
tracking system to be develcped will require only slight modifications
to existing equipment. The interfaces, like motor control, ACC-signal,
mains power supply, had to be adapted to the existing equipment.
*Numbers  in the margin indicate pagination in the foreign text.
1
2.	 Concept Alternatives
In order to track a satellite, there are basically two possible
ways:
-a system, time-controlled by stored path data
-a tracking circuit closed over the AGC-signal.
The time-controlled method requires considerable software effort
for coordinate transformations in the different axis arrangements
of antenna rotation states. The memory size is very large and in
addition, the data practically has to be input new, each day.
For reasons of cost and operations, this alternative is rejec-
ted.
The second possibility, the AGC-signal tracking system, can be
built in two versions:
-Step tracking with fixed search or correction increments (antenna-
dependent), or
-Step tracking with fixed measuring increments, but adaptive correc-
tion step.
If we proceed from a deviation value	 from the LOB, then the
search-correction step method needs
steps to reach the maximum in one axis, i.e. the existing asynchron-
ous motors are triggered n-times.
The adaptive method is derived mathematically below:
The antenna characteristic of the used antenna has the following
standardized function:
^z
2 I• • *^ S;n^ ,
G s	 i
Go	 I	 .Sing
L 
Legend:	 /544
i,t'^^ ► - Bessel function, 1s*_ order
2
ORIGINAL PAC;,,.- 13
	d = an+.enna diameter	 OF POOR QUALITY
a = wavelength
r = deviation angle
The Bessel function 1,10 can be expanded into the following series:
4X 1 10 - -1 0- a +102-...1
For small deviation angles, we have:
G
	 !o2)2=r2
Go	 8	 4
This parabola can be uniquely det-tnined by 3 measured points, so
that the AGC-maximum, i.e. the c- imal alignment, is known.
The equation of a normal parabola has the form:
y = ax  + bx + c.
With the measured AGC values, we obtain the equations
	
Y, - sx 1 2 + bx l + c	 111
	
Y2-u22+b%2+e
	 121
	
Y3 - lx32 + bx3 + c	 131
The values y i
 are the measured AGC values, the xi are the attendent
angles.
The apex point xo of the parabola y - ax  + bx + c is defined
by the first derivative
	
Y'-2sxo +b=o
	 (4)
from (4)	 b
xo = _
ISI
Solving the equations gives:
xj Y,
x Y2
	
x	 Y3	 i
	
V,
	
x,
2 I Y2 x2
:	 Y3	 x 3 1,
3
-1
►0
'_	 For reasons of system complexity, an angle reply is not used. /545
The offset angle o+► , values between 0.1 degrees and 0.2 degrees,
were specified via the motor run times of the speed-redaction spindle
drives ( a = 1 degree/minute).
In order to reduce measuring errors by scintillation effects
k	 and transponder switching, during the measurement phase, the AGC
value is determined. The response time is 80 sec.
t
The advantages of the method are summarized:
-only 3 triggerings per axis and track cycle
-knowledge of lobe curvature is unnecessary
-no angle reply of the antenna rotation position.
3. Requirements
The requirements of the tracking unit are defined by the inter-
faces with the existing ground stations, and by the operating modes
of the satellite.
3.1 Functional Requirements
The Symphonie ground stations can be classed in two groups:
-mobile facilities:
	
3.3 m container antenna
-stationary facilities: 	 4.5 m and 8.8 m systems.
The tracking system must take into account the following elec-
trical interfaces of existing ground stations:
1. Motor type of the linear adjuster
2. AGC Interface of the various receiver types.
The table below shows the various motor types
Motor Overview
Antenna type	 Motor Power Motor type
Output
8.8 CGTI	 0.8 KW-1.9 KW Asynchronous, 3-phase
4.5 m	 0.18 KW	 Asynchronous, 3-phase, operated as
1-prase motor with operating capacitor
4
uRiGi► AL PAG2 IS
OF POOR QUALITY
3.3m	 0.18 KW Asynchronous, 3-phase, operated as 1-phase motor
with operating capacitor
Table 3.1
The tracking algorithm requires an AGC signal proportional to /546
the antenna characteristic, i.e. the AGC reference voltage must
be a linear function of the receiver damping in the working range.
The function is specified as 1vAcc f 1 d6, uAcc,,,,, _ 10v.
Since the receivers of the stations are different, the norming
must be adjustable.
3.2 Operational Requirements
The operational requirements of the tracking unit result from
the operating modes of the Symphonie satellite.
The various channel popula-
tions of the transponder and the
shut-off of the transponder due to
earth shadow (eclipse phase) have a
marked influence on the AGC signal.
The shut-down time is 90 minutes.
^^;..
Figure 4.1
In order to assure reliable, continuous operation of the 	 /547
tracking system, it is important to cover the "Eclipse" operating
mode by a special program mode.
The software is organized into the following segments:
-initializing
-eclipse wait-phase
-search mode
-tracking mode
As branching criteria for the individual program segments, the
level of the AGC signal is used.
5
We have:
uAGC <o,3v = eclipse waiting-phase
o,av	 search mode
ssv	 tracking mode.
This specifies the main parts of the software.
4.	 System Description
In this section, the equipment developed as per the require-
ments in section 3 and the attendant software are described in
detail. Figure 4.1 shows a front view of the control plug-in unit.
4.1 Hardware
4.1.1 Mechanical Design
The control unit is housed in a standard 19 inch plug-in
housing with 7 height units. The front side of the unit is also
the control panel and the reverse is a plug terminal plate. In
the plug-in unit there is d card rack as carrier of the electronic
boards and an assembly plate for the circuit elements.
4.1.2 Control Panel
All operating elements needed for normal operation are placed
on the control panel.
These are:
-switch for on/off, run/stop, auto/manual
-input switch for waiting time adjustment
-key for manual motor control
-display and potentiometer for the AGC signal smoothing
-alarm tone, alarm indicators and alarm reset switch
/548
All other input parameters which are programmed only once
during installation, are adjusted on a special input circuitboard
inside the unit.
4.1.3 Tracking Computer
The prescribed taskz of the tracking computer are:
6
ORMINAIL r-ML:: IS
OF POOR QUALITY
-query measured data and input parameters
-process data according to specific algorithms
-verification of final control elements,
these tasks are performed in the present case, by an 8-bit micro-
processor system. The block diagram of the processor system and
the attendant periphery are presented in fig. 4.2.
The processor system is of standardized, modular design with
modules linked via a normed bus. Besides the actual processor
module, a memory module and an interface module are provided.
1
'	 The memory module has the following compgnents:
-volatile memory for variable data (RAM): 1 K-words (byte)
f	 -nonvolatile memory for program and invariable data (PROM):
4 K-words (byte)
S1-0.11•w14Y•.G 1
– — - ---	 -- °--	 ---	
x741. 12P ^.lEO.
26
r. t r	 I .ti' r a	 .4 .	 ( aaY	 l.ruol	 ( L ftt ^Eaa^.l w^ 11!,•l•1..,. ^. ^	 ^, ,,,.1	 i 1• .. '
	 ' 
^ ^'.. ^^. ^ ^..1,.5.^ ^ •11..1.•..! 	 ^	 T_....
1	 1
1	
^;... . t tlw -18
^	 h	 I	 t	 f	 "
3	 I
,.9	 10 I	 10
.	 I	 1	 I .i.:•Y	 y^l.	 .	 uYip•	 )t[UIM}^	 .'1 '11. .	 1	 11	 "	 •^^ 12
a4r. S
. ^^..	 I^	 1'.1•t..0
13t	 J " t``	 --	 1
15 K t 1 oX^a t! n 	 MQl ryf .tl rOt 1112tY
Fig. 4.2 Block Diagram of Symphonie Antenna Tracking Plug-In Unit
Key: 1-power supply 1 0 or 3 0; 2-test plug; 3-end and limit switch
4-mains filter 5-memory 6-interrupt control 7-fuses 8-on/off
switch 9-output 10-manual control 11-motor control R/L
12-motor control, up/down 13-interface bar 14-param. setting,
OP switch 15-emergency end switch. Others illegible.
/549
7
6
f-
p	 ORIGINAL PAGE 15
OF POOR QUALITY
The interface module permits query of 40 input signals and 	 /550
output of 32 control signals.
Adaptation of the AGC signal (level) to the interface module
is via an analog electronic circuit and an 8-bit A/D converter.
Due to the limited number of input lines to the interface module,
the digital parameters are fed via a multiplexer. The addressing
needed for this is via the processor over 3 output lines.
The GO/NO GO signal generated by a self-monitoring routine of
the processor, is fed over a booster to the alarm tone and alarm
indicator lamps. Thus, any incorrect operation of the system can
be recognized by the operator at once.
4.1.4 Parameter Input
To adapt the control plug-in unit to the characteristics of
the particular ground station, as mentioned, a special program
card is present. Seven circuits with 8 contacts each are provided.
The programming is by setting these contacts into a binary coded
form. The meaning and weighting of the 7 circuits are given in
the table below:
Circuit Function	 No. of bits
sz	 h
Ut
	rf
I
51
Sb	 2.	 ,t .	 .7Lt .•I
I S6	 l^^
1
	
till b	 i
Weighting ILSB
Key: 1-axis
r 2 7 ht„ l'opi. y Achsc l
0►.)
^l Y., 111.E
The abbreviations mean:
^l	angular velocity of up/down motions
angular velocity of left/right motions
up down measarement increment trigger time
left/right measurement increment trigger time
8
1,,	 run-up time
t o,	 ' braking time
The x- and y-multipliers (S5) are used for setting the first
	
/551
spiral steps of the search-Scan increment width.
The input of waiting time--which only has to be adapted to the
satellite inclination--is via the input switch on the control panel,
using decimals in minutes.
4.1.5 Power Interface
The power region of the triggered stepping motors in the various
ground stations extends from 0.18 KW to 1.9 KW, either single or 3-
phase. In order to cover all possible interfaces, a universal
power interface was developed. This interface is based on special
semiconductor relays with minimum interference sensitivity by
galvanic decoupled triggering. In addition, switching processes
occur on voltage or current zero-passage, so that a favorable elec-
tromagnetic system compatibility results.
All motors are secured by motor protection switches in the
control plug-in unit. In addition, the stepping motors are protected
by appropriate end switches which define the permitted range of action.
4.2 Software
The entire software of the control plug-in unit, including
the self-monitoring routines, has a size of 4 K words.
4.2.1 Initializing
In this program section, the antenna-specific parameters and
the tracking wait-time are read in. The values are checked and
prepared for further processing. If the inputs are outside the
specified range, an input alarm message is generated.
Branching into the "Search-scan" program section or into
"Ma:t-Tracking" is via a comparison of the AGC level with the spec-
ified, programmed bounds.
9
Note here that the named threshold values relate to the normed
AGC voltage.
4.2.2 Search Mode
This program section permits finding of satellites after a
longer shut-down of the transponder (eclipse etc.).
The subprogram is called up by the branching described above,
and controls the stepping motors so that the antenna moves in an
opening spiral. If the AGC signal exceeds the 5 V threshold,
then the "Max-Tracking" subprogram is called up automatically and
the search mode is ended.
For the case where the satellite is not found, the opening 	 /552
spiral is limited by 4 magnetically operated region switches.
If all 4 switches have been addressed, the program triggers
the motors so that a closing spiral antenna motion occurs. This
increases the probability of finding the satellite.
If the antenna makes no contact with the satellite in the
closing spiral, then the processor generates a NO-GO alarm.
4.2.3 Maximum Tracking
The program section permits continual contact with the satellite.
The drive of the one axis lasts initially 1 second in order
to determine the direction of an ascending AGC signal. The trigger
time of the following 2 measuring increments is programmed antenna-
specitic. We thus obtain 3 AGC measured values as a function of
the 3 step angles.
With the tracking algorithm, the program computes the value of
the parabola inflection point and triggers the motor as pev the
position difference = "vertex - last measured point". The trigger
time is determined from this difference and the programmed, antenna-
10
specific adjusting speed.
Incorrect measurements which can occur through noise or
jump changes in the field strength during a tracking cycle, are
determined by comparison of measured values and suppressed.
The tracking cycle runs as follows:
Elevation to maximum, azimuth to maximum, waiting time, azimuth
to maximum, elevation to ma):imum, waiting time, etc.
The waiting time depends on the size of the inclination.
In order not to incriyase motor wear unnecessarily, this value
is adjusted at longer time intervals cf ca. 1 year.


Autonomous antenna tracking system for mobile symphonie ground stations

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