The Arecibo Observatory in Puerto Rico participated in the support of the U.S. International Cometary Explorer (ICE) mission when the ICE spacecraft passed through the tail of comet Giacobini-Zinner on September 11, 1985. The Arecibo Observatory is a research facility of the National Astronomy and Ionosphere Center (NAIC) operated by Cornell University under contract to the National Science Foundation (NSF). Coverage of the encounter involved the use of the observatory's 305-m (1000-ft) radio reflector antenna and RF and data system equipment fabricated or modified specifically for support of the ICE mission. The successful implementation, testing, and operation of this temporary receive, record, and data relay capability resulted from a cooperative effort by personnel at the Arecibo Observatory, the Goddard Space Flight Center, and the Jet Propulsion Laboratory

Gordon, D. D.

Ward, M. T.

English

NASA Technical Reports Server

N 8 6 - 2 2 8 0 4
TDA Progress Report 42-84 October-December 1985
Arecibo Observatory Support of the U.S. International
Cometary Explorer Mission Encounter at Comet
Giacobini-Zinner
D. D.Gordon
TDA Engineering Office
M.T.Ward
Flight Mission Support Office
Goddard Space Flight Center
The Arecibo Observatory in Puerto Rico participated in the support of the U.S.
International Cometary Explorer (ICE) mission when the ICE spacecraft passed through
the tail of comet Giacobini-Zinner on September 11, 1985 The Arecibo Observatory is
a research facility of the National Astronomy and Ionosphere Center (NAIC) operated by
Cornell University under contract to the National Science Foundation (NSF). Coverage of
the encounter involved the use of the observatory's 305-m (1000-ft) radio reflector
antenna and RF and data system equipment fabricated or modified specifically for sup-
port of the ICE mission. The successful implementation, testing, and operation of this
temporary receive, record, and data relay capability resulted from a cooperative effort by
personnel at the Arecibo Observatory, the Goddard Space Flight Center, and the Jet
Propulsion Laboratory.
I. Introduction
The Arecibo Observatory in Puerto Rico provided support
to the U.S. International Cometary Explorer (ICE) mission
when the ICE spacecraft passed through the tail of the comet
Giacobini-Zinner (G-Z) on September 11, 1985. The Arecibo
Observatory is a research facility of the National Astronomy
and Ionosphere Center (NAIC) operated by Cornell University
under contract to -the National Science Foundation (NSF).
The support involved the use of the observatory's spherical
radio reflector antenna (Fig. 1) having a diameter of 305 m
(1000 ft) and the installation of telemetry receiving and
recording equipment designed to handle the ICE spacecraft
telemetry signal. The Arecibo facility does not normally
receive modulated signals, and the frequency of the ICE
spacecraft signal is slightly below the observatory's S-band
receive capability. Observations of the comet at Kitt Peak
Observatory in April 1984 made it possible to target the
ICE spacecraft for the encounter coverage by the Arecibo
Observatory.
The ICE spacecraft, formerly designated the International
Sub-Earth Explorer-3 (ISEE-3) consistent with the objectives
of its earlier mission, was launched on August 12, 1978. For
that mission the NASA Ground Spaceflight Tracking and Data
197
https://ntrs.nasa.gov/search.jsp?R=19860013333 2020-03-20T15:03:48+00:00Z
Network (GSTDN), managed and operated by Goddard Space
Flight Center (GSFC), provided telecommunication and data
acquisition support for the spacecraft. After the spacecraft was
diverted from its earlier orbit and placed on an intercept path
with the comet Giacobini-Zinner (Ref. 1), it soon traveled
out of range of GSTDN stations and support responsibility was
transferred to the NASA Deep Space Network (DSN) operated
by the Jet Propulsion Laboratory (JPL).
Early DSN link margin calculations, which took into con-
sideration the 70 million-kilometer communication distance
and the desired 1024-bps telemetry data rate, indicated that
a signal-to-noise ratio margin of 1.0 ± 0.5 dB would be experi-
enced at encounter. However, it was recognized that there was
a potential for signal strength degradation and, therefore, a
loss in science data return due to the effects of cometary dust.
Use of the Arecibo facility to enhance the capability for data
recovery at encounter was deemed to be advisable in order to
increase the confidence in achieving a successful ICE mission.
Goddard Space Flight Center had responsibility for imple-
mentation and testing of the modified telemetry receiving and
recording system. GSFC also provided personnel to assist the
observatory staff in the operation of the NASA-supplied
equipment.
II. ICE Mission Support Requirement
The Arecibo Observatory was requested to provide cover-
age for approximately 2 h each day for the 8-day period
bracketing the ICE spacecraft encounter at the comet. This
support required the installation of RF and data system
equipment to provide a receive and record capability compati-
ble with the ICE spacecraft transponder A telemetry signal,
and activation of a real-time data quality circuit between the
observatory and GSFC.
The ICE spacecraft transponder A downlink characteristics
are as follows:
(1) Transponder A, link 2, 2270.4 MHz
(2) Convolutionally coded PCM
(3) 1024-bps telemetry rate
(4) Split phase modulation code
(5) PM modulation
(6) 1.08 modulation index
III. System Implementation
Studies at JPL and GSFC indicated that the most expedient
and cost effective approach to implementing a temporary
receive, record, and data relay capability at the Arecibo
facility included: (1) fabricate a circularly polarized antenna
feed and cryogemcally cooled low-noise amplifiers (LNAs) to
accommodate the 2270.4-MHz downlink signal from the ICE
spacecraft transponder A; (2) make use of existing RF and
data processing hardware borrowed from GSFC; and (3)
arrange through NASCOM for the lease of a data quality
circuit for transfer of data from the Arecibo Observatory to
GSFC.
A. Functional Description
The implemented operational configuration is represented
in Fig. 2. The functions depicted in Fig. 2 are as follows:
(1) LNAs receive and amplify ICE spacecraft signal at
2270.4 MHz.
(2) Down convert (D/C) the 2270.4-MHz signal to 260 MHz.
(3) Up convert (U/C) the 260-MHz signal to 670 MHz.
(4) Input the 420-MHz signal to the multi-function receivers
(MFRs, Rx).
(5) MFR video output to bit synchronizers.
(6) Hard decision output of bit synchronizers to frame
synchronizers.
(7) Soft decision output of frame synchronizers to sequen-
tial decoders.
(8) Output of decoders to tape recorders and communica-
tion data formatters (CDFs).
(9) Output of the CDFs through a modem to the NASCOM
line.
B. NSF/NAIC Fabricated Equipment
NAIC designed the circularly polarized antenna feed and
low-noise amplifier (LNA) to be compatible with the ICE
telemetry signal at 2270.4 MHz. These items were fabricated
at NAIC's engineering laboratory at Cornell University and
shipped to the observatory in May and June 1985 for installa-
tion in the carriage house suspended over the antenna (Fig. 3).
NAIC also provided down converters at the output of the LNA
for conversion of the received signal to a 260-MHz interme-
diate frequency.
The LNA was designed with two channels to accommodate
reception and amplification of both left-circular polarized and
right-circular polarized signals. This allowed some redundancy,
as one channel could substitute for the other in the event of a
failure. The right-circularly polarized channel was the prime
supporting channel, as that is the polarization of the ICE
downlink signal. There was no on-line operational redundancy
198
in the remaining components of the LNA; however, spare
parts had been procured and were on hand for replacement of
components considered to be candidates for failure.
NAIC development of these devices was funded by NASA
specifically for support of the ICE mission, but are to be
retained at the observatory for use by NAIC in future scien-
tific applications.
C. NASA/GSFC-Supplied Equipment
GSFC provided the additional RF and telemetry data
processing equipment required to complete the ICE spacecraft
compatible link at the Arecibo Observatory. In order to
increase the probability of successful data capture, redundant
equipment was installed for all operational functions:
(1) Multi-function receivers: 2
(2) Analog tape recorders: 2
(3) Up converters: 2
(4) Bit synchronizers: 2
(5) Frame synchronizers: 2
(6) Sequential decoders: 2
(7) Time code generators: 2
(8) Communication data formatters • 2
(9) Signal generator: 1
(10) Cables for the above equipment
All of the above equipment was assembled and tested at
GSFC prior to shipment. It was delivered to the observatory
pre-assembled m equipment racks for installation and integra-
tion at the observatory. This equipment was provided on loan
from GSFC specifically for support of the ICE mission and
was returned to GSFC following the comet encounter.
D. Communications Link
After the implementation task was underway, approval and
funding became available for a communications circuit to pro-
vide the real-time transfer of telemetry data from the Arecibo
Observatory to the Multi-Satellite Operations Control Center
(MSOCC) and the Telemetry Processing Facility (TPF) at
GSFC. NASCOM procured a commercial link for this purpose.
The link was composed of several segments, principally a satel-
lite link to an Earth station in Puerto Rico and microwave
links from there to the observatory. The operational employ-
ment of this circuit routed data through JPL's Network Opera-
tions Control Center, which maintained overall operations
control of communications circuits in support of the ICE
mission.
IV. Test and Training
The test and training for the Arecibo support (NASA/GSFC
document1) was composed of two basic parts: (1) a series of
engineering tests, and (2) a series of operations tests, with the
latter including operations training.
Initial testing began with the completion of the equipment
link implementation at GSFC prior to its shipment to the
observatory. A series of tests were conducted at GSFC to
verify the functional integrity of the link and its interface with
the MSOCC and TPF facilities. The results of these tests were
satisfactory except for a timing interface problem between
the link and the TPF. This problem was discovered early in the
testing and survived through several tests until isolated in the
Communications Data Formatter firmware. Upon its discovery
the problem was promptly corrected, and the system was
declared ready for shipment to the observatory.
Prior to shipment of the GSFC equipment to Arecibo,
NAIC personnel installed the feed and LNA in the carriage
house suspended over the antenna and performed preliminary
tests of these units. After arrival of the GSFC equipment, an
engineering test of the entire link was possible for the first
time.
A. Engineering Tests
The engineering test series at Arecibo tested the link's
capability to process ICE telemetry signals. During the first
tests, simulated and pre-recorded signals were injected into the
system. After successful conclusion of these tests, the link
successfully tracked the ICE spacecraft, and the recorded data
was shipped to the GSFC for verification by the TPF. At this
point the link was declared operational and operations tests
began, although the communications circuit remained to be
tested since it was not yet available from the vendor.
B. Operations Tests
The operations tests consisted of a series of simulations to
exercise equipment and procedures under conditions simulat-
ing those of the encounter support. These tests were conducted
using both live spacecraft and recorded data sources with the
participation of Arecibo, JPL, and GSFC. The tests concluded
with an Operational Readiness Test conducted on September 6
after the communications circuit was available.
'"Space Tracking and Data Network ICE Network Test Plan," STDN
No. 403/ICE, NASA/GSFC document, June 1985.
199
V. Operations
Encounter operations support at the observatory (Refs. 2
and 3) began on September 8, 1985, and continued through
September 14, three days following the transit through the
comet tail on September 11. The daily support consisted of an
approximately 2-h period, the maximum coverage time avail-
able at the observatory during which telemetry data was received,
transmitted to the MSOCC and TPF at GSFC, and recorded on
station for possible playback. Operations at the observatory
were supported by a team of NAIC personnel and GSFC per-
sonnel who operated the GSFC equipment. The overall opera-
tions control, integrating the Arecibo support operations with
that of the DSN complexes at Madrid and Goldstone, was
carried out by the JPL Network Operations Control Center.
The Arecibo Observatory performance profile is repre-
sented in Fig. 4. The telemetry equipment performed very well
during the encounter, achieving solid lock with good data
delivered at 72 deg of elevation. The effective threshold corre-
sponds to an AGC reading of -154 dBm. At higher elevations,
and for at least one-half hour of the time of comet tail crossing,
the SNR was about 3.5 dB above this threshold value.
References
1. Farquhar, R., Muhonen, D., and Church, L. C., "Trajectories and Orbital Maneuvers
for the ISEE-3/ICE Comet Mission," Journal of Astronautical Sciences, Vol. 33, No. 3,
pp. 235-254, July-Sept. 1985.
2. Fanelli, N. A., and Morris, D. G., "ICE Encounter Operations," TDA Progress Report
42-84, this issue.
3. Layland, J. W., "ICE Telemetry Performance," TDA Progress Report 42-84, this issue.
200
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OF POOR QUALITY
Fig. 1. Arecibo Observatory 305-m (1000-ft) diam radio reflector antenna
2270
Fig. 2. ICE Arecibo support capability functional block diagram
201
ORIGINAL PAGE IS
OF POOR QUALITY
Fig. 3. Close-up view of the structure suspended above the reflector antenna supporting
two carriage houses and the antenna feeds
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Fig. 4. Arecibo Observatory performance at ICE mission encounter on
September 11, 1985 (OOY 254)
202


Arecibo Observatory support of the US international cometary Explorer mission encounter at comet Giacobini-Zinner

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