The activities of the Deep Space Network in support of radio and radar astronomy operations during July and August 1980 are reported. A brief update on the OSS-sponsored planetary radio astronomy experiment is provided. Also included are two updates, one each from Spain and Australia on current host country activities

Manchester, R. N.

Taylor, R. M.

English

NASA Technical Reports Server

TDA Progress Report 42-60 September and October 1980 
Radio Astronomy 
R. M. Taylor 
Deep Space Network Operations Section 
R. N. Manchester 
Division of Radiophysics, CSIRO, Sydney, Australia 
This article reports on the activities of the Deep Space Network in support of Radio 
and Radar Astronomy operations during July and August 1980. A brief update on the 
aSS-sponsored Planetary Radio Astronomy experiment is provided. Also included are 
two updates, one each from Spain and Australia,· on current Host Country activities. 
I. Introduction 
Deep Space Network (DSN) 26-, 34- and 64-meter-antenna 
stations are utilized in support of experiments in three cate-
gories: NASA Office of Space Science (OSS), Radio Astronomy 
Experiment Selection (RAES), and Host Country. 
II. Radio Astronomy Operations 
A. NASA OSS Category 
During this period support has increased for the series of 
ALSEP/Quasar VLBI observations to 56 hours of station 
time·. Support for Pulsar Rotation Constancy observations has 
continued at prior levels at the Goldstone and Madrid 26-meter 
antenna stations. Similarly, the Planetary Radio Astronomy 
experiment has enjoyed a consistent level of support. The 
following is a brief summary of the status of this activity. 
Planetary Radio Astronomy (OSSI96-41-73) 
1. Observational objectives. These objectives are twofold: 
first, to study the variations in synchrotron emissions from 
Jupiter's radiation belts and, second, to make precision mea-
surements, over a long period, of atmospheric stability in the 
outer planets. 
2. Observed results. 
(a) Synchrotron variations change on time scales of days 
or months or years. 
(b) Data must cover 11 years for solar wind and long-
term orbital parameters. 
(c) In collaboration with Professor E. Gerard of Nancay 
Observatory, France, a concentrated 6-hour-per-day 
observation effort (at the Madrid 26-meter station) for 
three months at 21 cm in early 1979 produced good 
Jovian short term variation data from which publica-
tion of the results is eagerly awaited. 
(d) Radio astronomy can make high precision, consistent 
measurements year after year and, thus, is very useful 
for studying atmospheric stability and seeking correla-
tion between atmospheric changes and other natural 
variations such as solar flux. These studies involve the 
https://ntrs.nasa.gov/search.jsp?R=19810004700 2020-03-21T14:39:26+00:00Z
outer planets and require long-term observations in 
order to detect large-scale time changes. 
3. Implications. 
(a) It is interesting to try to determine the correlation, if 
any, of the synchrotron variations with solar param-
eters, orbital parameters, solar wind parameters and 
other natural phenomena. 
(b) What mechanism causes this type (source function) of 
variations? 
(c) How deep in planetary atmospheres can we detect 
climatic changes? Certainly to 10 atmospheres in the 
outer planets. Long-term observations are required, 
over several years. For example, the equatorial-to-pole 
temperature variation of 30 to 35 percent in the planet 
Uranus changes in a 22-year cycle. Can we detect 
climatic changes in the troposphere? 
4. Future interest. In the Jupiter Patrol experiment the 
future looks toward millimeter or submillimeter observations 
but useful work could be done between 20 and 24 GHz in 
the molecular line area with a 64-meter single telescope. 
K-band interferometry looks like an exciting, realizable 
prospect in the near future. The question of why choose the 
DSN when the Very Large Array is available is answered by 
the Southern Hemisphere view not seen by the Very Large 
Array. It would be exciting to record the waterline spectra 
of planetary objects, including comets, in the Southern 
Hemisphere. 
5. Deep Space Network contribution. The DSN provides 
facilities which have a long-term base, consistently high 
quality, stable instrumentation with continuity and instru-
ment traceability and well-calibrated antennas. Planetary 
Radio Astronomy provides the DSN with a calibration base 
and a list of radio sources. The remaining problem with the 
facilities is that of blind pointing accuracy, a problem which 
is being resolved at this time. 
B. RAES Category 
1. RA 175. On June 13 and 14 and again on July 1 and 3, 
1980, for a total of 51 hours, the Goldstone 26-meter station 
supported VLBI observations of the source SS 433 (1909+04). 
These observations represent continuing efforts in support of 
the experimental objective of resolving this bizarre gala tic 
object to determine its angular radio structure and, if possible, 
its origin. These activities will continue in a similar fashion at 
regular intervals until the end of the year. 
2. RA 137 Quasar Patrol. Dual polarization Very Long 
Baseline Interferometry (VLBI) observations were made on 
2 
July 31 and August 1 at the Goldstone and- Madrid 64-meter 
antenna stations of the source 3C454.3. Other telescopes 
supporting this experiment were Onsala, Sweden (26-meter), 
Haystack, Massachusetts (26-meter), Owens Valley, Cali-
fornia (40-meter),Fort Davis, Texas (26-meter), Green Bank, 
West Virginia (40-meter). 
The experimental objective was to observe the source in 
dual polarization, that is, right circular polarization and left 
circular polarization, as part of a scheme to construct a radio 
map of the region surrounding the quasar. Recordings were 
made using the Mark II VLBI Data Recording System. One of 
the principal investigators, Dr. William Cotton, of NRAO was 
in attendance during the experiment at the Goldstone 64-
meter antenna station. Due to the failure of one of the S-band 
masers at Goldstone, it was not possible to record dual polari-
zation simultaneously, so a time sharing technique was adopted, 
observing primarily in left circular polarization. 
At this time, data reduction and analysis is in progress and 
the published results are anticipated in the near future. 
C. Host Country 
The primary host country activity in Spain is the Instituto 
Geografico Nacional Interferometric Survey (IGNIS) project. 
The objectives of this activity are: 
(1) To conduct VLBI measurements of the relative posi-
tion vectors between the 34- and 64-meter-antenna 
stations at Robledo de Chavela, the 26-meter-antenna 
station at Cebreros and comparison with other geo-
detic techniques. 
(2) In cooperation with other agencies involved in geo-
detic VLBI to exchange information on the following: 
(a) Scale and orientation of the European Geodetic 
Net. 
(b) UTI and polar motion. 
(c) Lithospheric plate motion. 
(3) Software development for post correlation data pro-
cessing. 
From time to time, when scheduled, observations are per-
formed using the bandwidth switching technique in order to 
obtain the synthesized delay and fringe rate observables. Early 
results, reduced and analyzed in an IBM 370/158 computer 
with JPL-generated software, show the following baseline 
components and length of the Cebreros 26-meter to Robledo 
64-meter baseline vectors in a right-handed coordinate system 
with the Z-axis directed to the Continental International 
Origin and the X-axis along the Greenwich Meridian: 
Bx = -2392.192 ± 0.028 m 
By = -10015.228 ± 0.011 m 
Bz = 1797.116 ± 0.019 m 
Totallength = 10452.607 ± 0.013 m 
In order to compare these results with those of classical 
methods, several previous surveys performed during the last 
10 years in this zone were reanalyzed. The analysis indicated 
that the compatibility between the different surveys is not 
assured due to various reoccupation problems of the common 
points and the existing uncertainty regarding the altitude of 
the geoid over the ellipsoid in this zone. Nevertheless, the 
difference between the VLBI and the classical results is 18 
centimeters. 
Planning for the future includes the following objectives: 
(I) Perform a new survey by tridimensional methods 
(laser, vertical deflection, etc.) for comparison pur-
poses. 
(2) Make VLBI measurements of the relative position 
vectors between the three antennas. 
(3) P~rticipate in European and transcontinental pro-
jects related to geodetic and geophysical applications 
ofVLBI. 
The only host country·activity being supported in Australia 
during this period has been the pulsar observations being con-
ducted for the Commonwealth Scientific and Industrial 
Research Organization (CSIRO) in Australia. The observations 
are conducted almost exclusively at the 26-meter-antenna 
facility at Honeysuckle Creek. The following is a brief sum-
mary of the status of this activity prepared and submitted by 
R. N. Manchester of the Division of Radiophysics of CSIRO, 
Sydney, Australia. 
III. Pulsar Observations Using DSN 
Facilities in Australia 
Since May 1975 a program of pulsar radio science observa-
tions has been carried out using the 26-meter-antenna station 
at Tidbinbilla, and more recently the similar facility at Honey-
suckle Creek. The objective of this program is to determine 
accurate positions and pulsational periods for a set of southern 
pulsars and to monitor variations in the observed period. To 
achieve this objective a regular series of observations of pulse 
arrival times is required with an antenna and receiver system 
which has stable characteristics over long time intervals (several 
years) and high sensitivity at a radio frequency in the L- or 
S-bands. An accurate time reference is also required. Since the 
Deep Space Network provides an S-band system with these 
characteristics it is ideal for this program. 
Pulsars were first discovered in late 1967 by Antony 
Hewish and Jocelyn Bell of the Mullard Radio Astronomy 
Observatory, Cambridge, England, using a large 80-MHz array 
designed to study interplanetary scintillations of compact 
radio sources. Several time-varying sources not attributable to 
scintillation were detected. After further investigation it was 
realized that the emission from these sources was unlike that 
from any other natural celestial radio source and consisted 
of a series of regularly spaced pulses. The pulse interval was 
typically about 1 s. Publication of this result triggered a large 
effort at many radio observatories to understand these sources 
and to detect new examples. The searches have been very 
successful, with over 300 pulsars now known. 
In 1968 the Molonglo radio telescope in Australia detected 
a relatively strong pulsar near the center of the Vela supernova 
remnant, which had the very short period of 89 ms. At about 
the same time a pulsar was detected by Green Bank, West 
Virginia, near the center of the Crab nebula (a well-known 
supernova remnant whose birth was observed by the Chinese 
in A.D. 1054), which had an even shorter period of 33 ms. The 
detection of these two pulsars and the subsequent observation 
that the pulsation period was increasing at a slow but regular 
rate established that pulsars are born in supernova events and 
consist of rapidly rotating neutron stars. By some means not 
yet fully understood the neutron star emits a narrow beam of 
intense radiation and we observe a pulse each revolution of the 
star as the beam sweeps across the earth. A neutron star, which 
is one of the possible end points of the evolution of normal 
stars, is an extremely compact star with a mass about equal to 
that of our sun but a radius of only 10 km or so. Only a star 
as compact as this could survive rotation at speeds up to 30 
revolutions per second (1800 rpm!). 
In general, pulsar periods are very stable and predictable. 
Typical rates of change are less than one part per billion per 
day and many are predictable to better than one part in 1012 • 
However, some pulsars are subject to unpredictable changes in 
period. In the Vela pulsar these changes are more dramatic 
than for any other known pulsar. On four occasions since its 
discovery the Vela pulsar period suddenly decreased by about 
200 ns (two parts in a million) and then, after some perturba-
tions, resumed its normal rate of increase of about 11 ns per 
day. These peridd jumps are thought to be caused by a change 
in the moment of inertia of the neutron star and correspond to 
a shrinking of the stellar radius by about 1 cm. Observations 
3 
limit the time taken for the change to less than a week or so, 
but theoretical models suggest that it occurs within minutes. 
Since observations began at Tidbinbilla, two of these jumps 
have been observed, one in October 1975 and the other in 
July 1978. Figure 1 shows these two discontinuities in the 
otherwise regular increase of period. 
Closer examination of the data shows that the rate of period 
increase is greater after the jump than before by about I per-
cent and that this excess rate decays away on a time scale of 
a few years. In fact, the Tidbinbilla observations show that 
decay after the 1976 jump was still occurring at the time of 
the 1978 jump. This increase in period derivative followed by 
an approximately exponential decay suggested a model in 
which the neutron star consists of two main parts, a solid 
outer crust (probably a lattice of iron atoms) and an inner 
superfluid consisting largely of neutrons. Figure 2 shows the 
result of fitting this model to the Tidbinbilla and Honey-
suckle Creek data. The parameters for the two jumps obtained 
from this fit are important constraints on the model. In par-
ticular, there are important differences in the post-jump 
recovery for the two events which cannot be accounted for 
in the simple version of the model. 
Figure 2 shows that, while the model provides a close fit 
to the observed variations, the fit is not perfect. On top of 
the other variations the period appears to wander in random 
fashion. These fluctuations are very small (about one part in 
4 
a billion per year) and quite unpredictable, but nevertheless 
they are significant and are present to a greater or lesser extent 
in all pulsars. Several of the pulsars monitored at Tidbinbilla 
and Honeysuckle Creek show relatively strong period fluctua-
tions. Analysis of these results is giving further information on 
the interior structure of neutron stars. 
Besides the Vela pulsar the only other large period discon-
tinuity observed was also detected at Tidbinbilla. In November 
1977 it was discovered that the period of the pulsar PSR 
1641-45 had decreased by about 90 ns or two parts in 107 . 
The post-jump recovery seems to be well fitted by the expo-
nential decay model in this case also. Two similar events have 
been observed in the Crab pulsar, but both were much smaller, 
about one part in 108 . 
The Vela events occur on average approximately once 
every three years, so we are about due for another one. Regular 
observations of this and the other pulsars are continuing at 
Tidbinbilla and Honeysuckle Creek with the cooperation of 
the Director of the Canberra Deep Space Communications 
Complex and the staffs of the stations. Along with similar 
programs at Goldstone and Madrid operated by G. S. Downs 
(JPL) these observations form the only long-term monitoring 
of pulsar periods and their variations currently being under-
taken. The Deep Space Network is therefore fulfilling a unique 
and valuable role for radio science which we hope will con-
tinue and expand in the future. 
• 
1980 
0.089250 
45 
0.089235 
3000 
JULIAN DAY - 2440000 
Fig. 1. Observed variations in the intrinsic period (i.e., after cor-
rection for doppler shifts resulting from the Earth's motion) of the 
Vela pulsar, PSR 0833-45, over the five-year interval, 1975-1980. 
The two period jumps are indicated by the arrows on the lower axis 
o 
-1 
w 
~3000 
:I: 
"-
~ 
~ 2000 
::l 
"-
1000 
o 
/ -. . .. ~ . , 
- ..... _--' 
RESIDUAL PHASE 
" '..... ,.-- - .. --." 
JULIAN DAY - 240000 
4500 
Fig. 2. Results of a fit of an exponential post-jump decay model to 
two period discontinuities observed in the Vela pulsar, PSR 0833-45. 
The lower part of the figure shows the model contribution to the 
observed pulse phase; the upper part of the figure shows the phase 
residuals after the fit. The two period discontinuities, indicated by 
arrows on the lower axis, each result in a discontinuous change in 
the gradient of the model phase. 
5 


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