COMMUNICATIONSCOMMUNICATIONSRESEARCHRESEARCHLABORATORYLABORATORY

Serial No. 22

June

2003

CONTENTS
Technical Reports
Wide-band high-temperature superconductor ﬁlter on 2.2GHz RFI mitiga- . . . . . . 2
tion
Eiji Kawai, Junichi Nakajima, Hiroshi Takeuchi, Hiromitsu Kuboki, and Tetsuro
Kondo
First detection of 2-Gbps wide-band fringes between two PC-based VLBI . . . . . . 5
systems
Moritaka Kimura, Junichi Nakajima, Jouko Ritakari, and Ari Mujunen
Rapid UT1-UTC estimation from Westford-Kashima e-VLBI experiment...... 6

Yasuhiro Koyama, Tetsuro Kondo, and Hiro Osaki
VLBI application for spacecraft navigation (NOZOMI) Part I– Overview –Ryuichi Ichikawa, Mamoru Sekido, Hiro Osaki, Yasuhiro Koyama, Tetsuro Kondo,
and NOZOMI VLBI group. . . . . 10

VLBI application for spacecraft navigation (NOZOMI) Part II– Delay model and analysis –Mamoru Sekido, Ryuichi Ichikawa, Hiro Osaki, Tetsuro Kondo, and Yasuhiro
Koyama. . . . . 12

- Topics - Topics - Topics - Topics Kashima 34m radio-telescope 2003 annual maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

1

IVS CRL-TDC News No.22

2

Wide-band High-temperature
Superconductor Filter on 2.2GHz
RFI Mitigation
Eiji Kawai (kawa@crl.go.jp),
Junichi Nakajima, Hiroshi Takeuchi,
Hiromitsu Kuboki, and Tetsuro Kondo
Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

Introduction

To remove radio frequency interference (RFI),a new High-Temperature Superconductor (HTS)
band-pass ﬁlter is developed for radio-astronomy
geodesy and astrometry reception in S-band. The
ﬁlter has sharp frequency cut-oﬀ and wide bandpass characteristics. We have installed the ﬁlter
into the Kashima 34-m antenna interfered by local
mobile phone base station. As the result the telescope recovered its wide band-pass and the interferences were totally attenuated. We already reported
use of an Ambient Temperature Cavity (ATC) ﬁlter against the severe interference [Kawai et al.,2002]. In this report, the HTS ﬁlter produces very
good results in the S-band reception.
2.

RFI from IMT-2000 and other radio services

The Kashima 34-m antenna S-band receiver frequency is 2150-2350 MHz. From their historicalbackground most of the VLBI telescopes are receiving the bandwidth. Though, oﬃcially there is
no radio astronomical frequency allocation in thisrange by the ITU. Thus, without the authority, radio telescopes can not take strong stand point to
the other radio services. Recently IMT-2000 mobile phones are appears between 2110-2170 MHz
and 2.4-GHz radio LAN system started in many
areas. As a consequence, severe RFI in the S-bandreceiving system occurred in telescopes. Typicallythe strong RFI causes saturation of down converter
system in telescope and occasionally with heavyinter modulations (Figure 1). Still the spectrum
between 2110-2170MHz are clean, we have to develop techniques to live together these new radio
applications.

Figure 1. Saturated S-band receiver output just after IMT-2000 started. The base station signal andlocal frequency are inter modulated. Under thiscondition observations were impossible.

LNA
dewar

D/C

To
Obs. room

ATC
FilterHTS
Filtersubsystem

Figure 2. A schematic block diagram of S-band receiver. In this experiment the HTS filter is installedat the output of the LNA to compare ATC filter.

converter. The receiver output when using an ATC
ﬁlter is shown in Figure 3. By this ambient ﬁlter werealized suﬃcient -60dB attenuation at 2170 MHz,
where the upper end frequency assigned for IMT2000. For this case cut-oﬀ frequency of the ﬁlter
was set to 2250 MHz. Though the reception ranges
was narrowed between 2250-2350 MHz, receiving
spectrum was recovered. The signal of IMT-2000
is still obvious in the spectrum. The strength of
the IMT-2000 signal is varied by communication
traﬃc, enough margin up to 11dB should be considered. By the characteristic of the ATC ﬁlter
shape, the receiving range cannot be extended from
3. HTS ﬁlter
this range. With the ﬁlter range, we had problems in international VLBI experiment frequency
The experimental receiver installation diagram
assignment. In addition, there is a possibility ofof HTS and ATC ﬁlters is shown in Figure 2. They
saturation in the front-end LNA in the strong RFI
are currently installed between the LNA and downcase. ATC can not be installed ahead of the cooledJune 2003

3

Figure 5. HTS filter subsystem installed at LNA
Figure 3. Receiver spectrum with started from
output.
2250MHz when using ATC filter. IMT2000 signal
is remaining 2160MHz.

60 mm
Figure 4. Receiver spectrum with started from
2193MHz when using HTS filter. It is remarkablethat the filter increased the bandwidth and the interference is disappeared.

LNA due to its insertion loss. For these reason
we developed HTS ﬁlter and installed to the system. The receiver output when using the HTS ﬁlter
subsystem is shown in Figure 4. It is remarkablethat the signal of IMT-2000 in 2160MHz is completely attenuated and reception range is lowered
to 2193MHz. The receiving frequency band was
expanded 57MHz. In this experiment both higher
end of receiving range is limited by a ﬁlter in thedown converter. In future it is possible to locate
the HTS ﬁlter ahead of the LNA. The HTS ﬁlter
subsystem is shown in Figure 5. A small cryostat isused and the ﬁlter unit is cooled at 70K to sustain
superconductivity. The compact HTS ﬁlter unit isshown in Figure 6.
The characteristics of the ATC ﬁlter and the
HTS ﬁlter unit are summarized in Table 1. As seen

Figure 6. HTS filter unit.

in the Figure 4, the HTS ﬁlter can set the cut-oﬀ
frequency of 23 MHz separation from the interference. In addition by its low insertion loss, this is a
hopeful device for front-end. If an ambient temperature ﬁlter of 1dB attenuation inserted in front of
the LNA, increase system temperature (Tsys) 62K,
but if the cooled HTS ﬁlter of insertion loss 0.5dB
is used, the Tsys increase is remained 8K. Tsys is
aﬀected by slightly.
4.

Conclusions

Severe radio frequency interference occurred at
S-band receiver of Kashima 34-m antenna by the
IMT-2000 mobile phone and other radio service
were solved by the HTS ﬁlter installation. Compared to ATC ﬁlter, the HTS ﬁlter can extend receiver range 57MHz (57%). Since IMT-2000 andother radio services are increasing year by year.
This will be a remedy against the severe interfer-

IVS CRL-TDC News No.22

4

Table 1. The characteristics of filter.
Passband
Attenuation
Insertion Loss
Dimension (mm)ence in other telescope sites.

ATC ﬁlter (19 section)
2250–2450 MHz>60 dB at 2170 MHz<1dB
260 × 42 × 27

HTS ﬁlter (32 section)
2193–2473 MHz>80 dB at 2170 MHz<0.5dBφ 60 × 14

Reference

Acknowledgement:
We wish to thank Dr. Kawai,E, H. Ohkubo, J. Nakajima, and J. Amagai, Sband RFI problems at Kashima 34-m antenna andNobuyoshi Sakakibara, Mr. Akito Torii, and Mr.
a passive filter for mitigation, IVS CRL-TDC News,
Shunji Okemoto of DENSO CORPORATION ReNo.21, pp.9–11, 2002.
search Laboratories for their contribution to develop an HTS ﬁlter adapted for an S-band radio
astronomical receiver.

- Topics - Topics - Topics - Topics - Topics - Topics -Kashima 34m Radio-telescope 2003 Annual Maintenance
34m radio-telescope maintenance group
Annual maintenance of the Kashima 34-m radio telescope started 1st July. Every year, themaintenance is carried out during July thorough August, the ﬁst half of the period is usedby regular maintenance and then additional repair continues. The operation of the improved
34m telescope will start in September again. To cut a huge summer maintenance work short,followings are main headings to keep the telescope in good condition.
The mechanical maintenance includes six motors overhaul, back structure rust removals,
main-reﬂector support ﬁxture replacement, and azimuth wear-strip clean up. Most of thesafety related components are replaced. Electronics components including antenna controller,
DC power amps and high precision encoder units are re-checked and part of instruments are
replaced to prevent failures in future. Receiver cooling cryogenics are stopped and send backto factory to replace wearing components. They are re-installed as completely new. This year,
especially we disassemble sub-reﬂector unit. The huge complex 5-axies unit located in severe
weather environment is removed by dual crane tucks from top of the antenna. It needs special
consideration to work properly.
In recent year, observations in higher frequency on 22/32/43 GHz are increasing. In addition
special demands like spacecraft monitoring are frequently programmed. To accomplish thesetasks successful, the telescope maintenance becomes important year by year.
Though its maintenence budget is limited, local companies which consider the symbolic
telescope in this area provide us their best eﬀort. Occasionally aﬀected by weather conditions,
often these contractors had to give up their summer vacation. But still they are zeal forjob completion before the ﬁrst observation deadline. In the CRL side, two staﬀs are newly
joined the telescope maintenance group. Hiromitsu Kuboki is a specialist of 34m operationand maintenance. Hiroshi Takeuchi is a researcher and he also take a part of engineering
issue. Since they joined the 34m group, numerous part of the telescope are already modiﬁed
or improved. The details of these will be reported in a separate issue of TDC news.
(see page 15 for a picture)June 2003

5

First Detection of 2-Gbps Wideband Fringes between two PCbased VLBI Systems
Moritaka Kimura1 (mkimura@crl.go.jp),
Junichi Nakajima1 , Jouko Ritakari2 , andAri Mujunen2
1

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
Metsähovi Radio Observatory, Finland
1.

Introduction

2-Gbps (1-Gsps/2-bit/1-ch) wide-band e-VLBI
observations between Communications ResearchLaboratory (CRL) and Metsähovi Radio Observatory succeeded 17th June 2003. First 2-Gbps
fringes were detected by high-speed CRL multibaseline software correlation system [Kimura andNakajima, 2002]. This 2-Gbps observation isplaced as ﬁnal goal of a series of observations in
October 16, 2002 and February 7, 2003 reported in
the previous issue [Koyama et al., 2002].
2.

2Gbps e-VLBI observation

Two diﬀerent PC systems adapted to VSI-H(VLBI Standard Interface Hardware) were used tocarry out the 2Gbps e-VLBI. These are named
as ‘PC-VSIB’ in Finland [Ritakari and Mujunen,
2002] and ‘PC-VSI’ in Japan. Though these systems are developed independently, raw data of the
VLBI bit stream stored to PC standard ﬁle format has a compatibility. CRL G-bps AD sampler,ADS-1000 [Nakajima, 2000] had been installed at
Metsähovi Radio Observatory and the unit is connected to the PC-VSIB. Wide-band IF of telescope,
converted from 22.020GHz to 22.532GHz are connected.
The wide-band IF signals were sampled at baseband is now extended to 2bit quantization (MSB
and LSB: Most and Least Signiﬁcant Bit) fully utilizes ADS-1000 performance and 2048- Mbps VSI
data is recorded to RAID disks. Two continuum
sources and a maser source were observed automatically during 2 hours session. All observation dataﬁles recorded at Metsähovi station were transferredto Kashima site by using multi-thread FTP.
After obtained the ﬁrst requested ﬁle, cross correlation were carried out by software correlator immediately. Using the popular high performance
personal computers which has some CPUs. The
ﬁrst 2Gbps fringe of NRAO150 integrated 16 seconds presented in Figure 1. SNR of the 2-bit cor-Figure 1. The first 2-Gbps e-VLBI fringe between
Metsähovi and Kashima. The fringe is projected inrate and delay windows.

Table 1. Improvement of the SNR in 2-bit correlation of NRAO150. SNR were measured with same
integration time (16 sec).

Kashima 1bit
Kashima 2bit

Metsähovi 1bit
22.8
27.2

Metsähovi 2bit
27.4
31.8

relation is 39.5% higher than that of 1-bit (onlyMSB) correlation (Table 1)
From this SNR increase, expanded lower bit acquisition in both 2-Gbps systems worked perfect.
Further K-band wide-band G-bps observation willcontinues between the Finnish-Japanese 7400-km
baseline.
References
Kimura, M. and J. Nakajima, The implementation of
the PC based giga bit VLBI system, CRL-TDC News
No.21, pp.31, November 2002.
Koyama, Y., T. Kondo, J. Nakajima, M. Kimura, H.
Uose, and S. Iwamura, International e-VLBI experiments, CRL-TDC News No.21, pp.23, November
2002.
Nakajima, J., Another giga-bit sampler prototype,nearly completion – ADS-1000 development status(October, 2000) –, CRL-TDC News No.17, pp.18,
November 2000.
Ritakari, J. and A. Mujunen, The Metsähovi solution
for gigabit VLBI, CRL-TDC News No.20, pp.2, June
2002.

6

IVS CRL-TDC News No.22

Rapid UT1-UTC estimation IVS Technology Development Centers including
Observatory and Communications Refrom Westford-Kashima e-VLBI Haystacksearch Laboratory have been concentrating theirexperimenteﬀorts to realize the e-VLBI in the global geodetic VLBI observations. At Communications Research Laboratory, the K5 VLBI system (Figure 1)
Yasuhiro Koyama (koyama@crl.go.jp),
has been developed based on the UNIX PC sysTetsuro Kondo, and Hiro Osaki
tems. The K5 VLBI system, or also called as Versatile Scientiﬁc Sampling Processor, is consist of
Kashima Space Research Center
four UNIX PC systems. Each UNIX PC system
Communications Research Laboratory
has one IP-VLBI data sampling board on its PCI
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan interfacing bus. The board can sample 4 channelsof baseband signals at various sampling rates rang1. Introduction
ing from 40kHz to 16MHz. Quantization bits canCurrently, minimum delay time to obtain results be set from 1, 2, 4, and 8. The maximum datafrom IVS global sessions is about two weeks for rate from one IP-VLBI board is 512Mbps, but the
IVS-R sessions and about one week for intensive actual usage is limited by the data transfer speed
sessions. As it is pointed out by the report of the of the PCI bus of the UNIX PC system. The curIVS Working Group 2 for Product Speciﬁcation rent prototype system has achieved data recording
and Observing Program (Schuh, et al., 2002), it is at the data rate of 128Mbps by one PC system. Asvery important to shorten this processing time de- the results, the K5 VLBI system (VSSP) can belay to improve the products of the IVS. The report used up to the data rate of 512Mbps as the whole.
set the goal of the IVS observing program to make The sampled data can be recorded to internal hard
the time delay from observing to product less than disks as ordinary data ﬁles and softwares to transone day by the year 2005. To achieve this goal, it is fer and receive observation data in real-time arenecessary to transfer observation data electrically under developments.
In this report, the results of the test observations
over the high speed global communication network
performed
between Kashima and Westford VLBI
by replacing the current magnetic tape recording
stationson
March 25 will be presented.
system at the observing sites and correlator sites
with the e-VLBI systems.
2. Experiment

Figure 1. K5 VLBI system (Versatile Scientific
Sampling Processor)

The test e-VLBI session was performed for twohours from 16:00 UT on March 25, 2003 with
the Kashima-Westford baseline. The 34m antenna
VLBI station at Kashima and 18m antenna station at Westford were used for the observations(Figure 2). This was the fourth test in the seriesof e-VLBI test observations. During the previous
tests, successful detections of the fringes from thee-VLBI observations were demonstrated and thesoftware developments have been continued withthe obtained data sets.
At the Kashima station, K5 VLBI system wasused to record observed data. At the Westford station, Mark5 VLBI system developed by HaystackObservatory was used to record observed data.
The observed data were recorded to internal harddisks at each site and transferred to Kashima andHeystack Observatory after the observations by using FTP. For this purpose, a program was executed
to extract the data from the Mark5 and to generate data ﬁles. At Haystack Observatory, K5 dataﬁles were converted their format and recorded toMark5 system. After the conversion, both data
recorded at Kashima and at Westford were processed for cross correlation processing using theJune 2003

7

Figure 2. 34m antenna VLBI station at Kashima (left) and 18m antenna VLBI station at Westford(right).

Mark-4 correlator. At Kashima, Mark5 data ﬁleswere converted to K5 ﬁle format and then bothdata recorded at Kashima and at Westford were
processed for cross correlation processing by using
the software correlator on the K5 VLBI system.
After the cross correlation processing, bandwidth
synthesis processing was done and database ﬁles(one for X-band and another for S-band) for data
analysis. Table 1 lists the observed radio sources
and the sizes of the data ﬁles. The total data volume was hence 56Mbps. The observations were
performed with 14 channels (8 for X-band and 6
for S-band) and 2MHz for each channel. The ﬁlesize of the Mark5 system was checked from the extracted ﬁles from the Mark5 disks. The extracted
ﬁle contains 36 channels for data space and theparity bits and therefore the ﬁle size is larger than
the actual data volume. File size of the K5 VLBI
system is the total of the four data ﬁles recorded
at four UNIX PC system of the K5 VLBI system.
In this case, data space for the two channels wereredundant.
Firue 3 and Figure 4 show the schematic route of
the high speed network used in the e-VLBI tests.
Kashima is connected to the Galaxy network under the collaboration with NTT cooperations at the
maximum bandwidth of 2.4Gbps. The Galaxy network is then connected to Abilene network in the
United States by Super-SINET route (622Mbps)
and GEMnet route (20Mbps) for trans-Paciﬁc connection. The maximum bandwidth of the GEMnet
trans-Paciﬁc connection was upgraded to 150Mbps,
but there is still a bottleneck between Galaxy network and connecting point in Tokyo which limits
the eﬀective bandwidth to 20Mbps. During the test
session on March 25, the route of Super-SINET wasused. The Haystack Observatory is connected to

Abilene network via BOSSNET and GLOWNET
at the maximum bandwidth of 1Gbps.
3.

Results

After the data processing, CALC and SOLVE
softwares were used to perform data analysis. In
the estimation process, positions of both Kashima
and Westford stations were ﬁxed to the ITRF2000
values and the UT1-UTC was estimated along withthe clock oﬀset, clock rate, and the atmosphericzenith delay. The estimated UT1-UTC value isshown in the Table 2 as well as the values published in the Bulletin B of the IERS (IERS Bulletin
B 183, May 2, 2003).
Table 3 shows the required time for various processing steps. As shown in the table, the ﬁle transfer and the correlation processing are dominating
the time. But it is also shown that the time delay from the observations to obtain results can beshorten to less than two days. At the time of
the test, the ﬁle transmission speed was not as
fast as expected from the network capacity. The
speed was only about 2.4 Mbps while the overall
network capacity was 100Mbps which was limitedby the network interface card of the K5 system.
The reason of the slow traﬃc was found to be thesmall transmission buﬀer for the TCP/IP connection (64kBytes) and the large transmission time delay (more than 200 milli-seconds). By adjusting the
buﬀer size larger, the ﬁle transmission speed is expected to be improved and hence the time required
for the ﬁle transmission will become much shorter.
The correlation processing also can be shorten byusing more CPUs to process the data. By combining these eﬀorts, it will become feasible to estimate
UT1-UTC within one day after the observations.

IVS CRL-TDC News No.22

8

Table 1. List of observed radio sources and the sizes of the data files.
No.

Source Name

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
Total

4C39.25
1736+455
1357+769
0059+581
2234+282
1300+580
0955+476
2113+293
1739+522
1357+769
0059+581
2234+282
1044+719
1128+385
1300+580
0955+476
2113+293
1739+522
1357+769

Duration
(sec)
90
200
90
250
310
140
90
300
500
90
270
510
784
180
130
90
390
530
90
5,034

NTT
Musashino

Usuda

File Size
K5 (MB)
720
1,600
720
2,000
2,480
1,120
720
2,400
4,000
720
2,160
4,080
6,272
1,440
1,040
720
3,120
4,240
720
40,272

GEMnet (20Mbps)
Kashima

Galaxy Network (2.4Gbps)
Koganei

File Size
Mark5 (MB)
1,620
3,600
1,620
4,500
5,580
2,520
1,620
5,400
9,000
1,620
4,860
9,180
14,112
3,240
2,340
1,620
7,020
9,540
1,620
90,612NII

Super-SINET (622Mbps)

Figure 3. The logical configuration of the high speed network in Japan. The location of the NTT
Musashino R&D center and National Institute for Informatics (NII) are not accurate.

Table 2. Estimated results of UT1-UTC from the test e-VLBI session and values from IERS Bulletin
B.
UT1-UTC (epoch)
Estimated Value (at 20:00 UT on March 25, 2003)
Bulletin B (at 00:00 UT on March 25, 2003)
Bulletin B (at 00:00 UT on March 26, 2003)

microseconds-338727.0 ± 23.9
-337951-338610

June 2003

9

Super-SINET(622Mbps)
BOSSNET+GLOWNET(GigE)

GEMnet(20Mbps)

Haystack Observatory(Westford Station)

Abilene Network(10Gbps)

Figure 4. The logical configuration of the high speed network in the United States.

Table 3. Evaluation of required time for various
processing steps.
Processing
File Transfer
File Conversion
Bandwidth Synthesis
Correlation
Data Analysis
Total

Required Time
20 hours
1 hour
1 hour20 hours
1 hour< 2 daysAcknowledgement: The authors would like to appreciate many members of the Haystack Observatory for observations and data processing, Internet2 for the Abilene network, NTT corporations
for GALAXY network, and National Institute forInformatics for Super-SINET network.

Reference
Schuh, H., C. Patrick, H. Hase, E. Himwich, K. Kingham, C. Klatt, C. Ma, Z. Malkin, A. Niell, A. Nothnagel, W. Schlüter, K. Takashima, and N. Vandenberg, ”Final Report, IVS Working Group 2 for Product Specification and Observing Program”, in International VLBI Service for Geodesy and Astrometry2001 Annual Report, by N. Vandenberg and K.
Baver (eds.), NASA/TP-2002-00817-0, pp. 13-45,
2002.

IVS CRL-TDC News No.22

10

VLBI Application for Spacecraft Navigation (NOZOMI)Part I – Overview –ICHIKAWA, R.1 (richi@crl.go.jp),
SEKIDO, M.1 , OSAKI, H.1 ,KOYAMA, Y.1 , KONDO, T.1 , andNOZOMI VLBI group2
1

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
2
ISAS, NAO, GSI, NASDA, Gifu Univ.,
Yamaguchi Univ., Hokkaido Univ., and
SGL/CRESTech
Precise spacecraft positions can be obtained with
diﬀerential spacecraft-quasar VLBI observations
that directly measure the angular position of thespacecraft relative to nearby quasars. We performed more than 30 VLBI experiments for the
NOZOMI spacecraft navigation from September
2002 until June 2003. NOZOMI, which means“Hope” in Japanese, is the Japan’s ﬁrst Mars probe
developed and launched by the Institute of Spaceand Astronautical Science (ISAS) (see Figure 1).
NOZOMI was originally scheduled to reach its destination in October 1998, but an earlier Earthswingby failed to give it suﬃcient speed, forcing
a drastic rescheduling of its ﬂight plan. According
to the new trajectory strategy, NOZOMI’s arrivalat Mars is scheduled early in 2004 through two additional earth swingbys in December 2002 and June
2003 as shown in Figure 2 [ISAS web site, 2002].

Figure 2. NOZOMI mission sequence toward Mars.

swingby. ISAS scientists were afraid that the range
and range rate (R&RR) orbit determination might
not be available because it was diﬃcult to point thehigh-gain antenna mounted the spacecraft toward
the earth during the period between two swingby
events. So we started to support the orbit determination of the NOZOMI using VLBI techniquesince September 2002. These experiments are also
aimed to establish the positioning technology forthe interplanetary spacecrafts in realtime.

Figure 1. NOZOMI image.
Figure 3. VLBI stations participating to NOZOMI
experiments.
Our main concern was to determine the NOZOMI orbit just before the second earth swingby on
June 19, 2003. It was signiﬁcantly important to get
the timing to maneuver the NOZOMI before the

We use nine VLBI antennas in Japan to carryout the NOZOMI VLBI experiments at X-band.

June 2003
Algonquin 46-m antenna operated by Natural Resource Canada and the Space Geodynamics Laboratory (SGL) of the CRESTech also participatedin the several experiments. The VLBI stations areshown in Figure 3. In each experiment, several
quasar VLBI obsevables are obtained in conjunction with NOZOMI VLBI observations in orderto determine the clock oﬀset. We equipped thestate of the art “K5 VLBI system” to these stations. The K5 system is the multiple PC-based
VLBI system equipped with a PCI-bus Versatile
Scientiﬁc Sampling Processor (VSSP) board on the
FreeBSD and Linux operating system [Osaki, 2002;
Kondo et al., 2002]. The K5 system includes theoriginal software packages which are data sampling
and acquisition, real-time IP data transmission,and correlation analysis. For the purpose of analyzing the VLBI observables we are developing thespeciﬁc VLBI delay model for ﬁnite distance radiosource [Sekido and Fukushima, 2003; Sekido et al.,2003]. The model is already implemented in the
VLBI software package. The package will include
the VLBI observation scheduling to take account of
the passage of the spacecraft near the quasar lineof sight and the propagation delay estimating forthe ionosphere and the neutral atmosphere.

11

termine the NOZOMI orbit using R&RR observables at the end of May 2003. Preliminary results
demonstrate that the VLBI delay residuals are consistent with R&RR observables. However, the rms
scatter between them are relatively large up to several tens nanoseconds. We are now evaluating our
VLBI data sets in more detail by comparing with
the R&RR results.
References
ISAS web site, http://www.isas.ac.jp/e/enterp/missions/index.html, 2002
Kondo, T., R. Ichikawa, Y. Koyama, M. Sekido, and
H. Osaki, VLBI observations using IP-VLBI systemfor orbit determination of deep space spacecraft –Group delay measurements of GEOTAIL and NOZOMI telemetry signals–, TDC News No.21, pp18–
22, 2002.
Osaki, H., Advancement of versatile scientific sampling processor (VSSP), TDC News No.21, pp.16–
17, 2003.
Sekido, M., R. Ichikawa, H. Osaki, T. Kondo, andY. Koyama, VLBI application for spacecraft navigation (NOZOMI) part II –Delay model and analysis–,
TDC News No.22 (this issue), pp12–15, 2003.
Sekido, M. and T. Fukushima, Relativistic VLBI Delay
Model for Finite Distance Radio Source, 2003 (to besubmitted to J. Geodesy.)

Figure 4. Detected fringe of NOZOMI range signal.

We could successfully detect fringes of NOZOMI
range signal for several baselines using software correlation in spite of weak and narrow-bandwidth
signal. An example of NOZOMI fringe is shownin Figure 4. We provided 15 VLBI group delay
data sets to ISAS to support the orbit determination at the end of May 2003. On the other hand,
ISAS scientists have fortunately succeeded to de-IVS CRL-TDC News No.22

12

VLBI Application for Spacecraft Navigation (NOZOMI)Part II– Delay Model and Analysis –

0

R20
R10

Mamoru Sekido (sekido@crl.go.jp),
Ryuichi Ichikawa, Hiro Osaki,
Tetsuro Kondo, and Yasuhiro Koyama

2

Kashima Space Research Center
Communications Research Laboratory
893-1 Hirai, Kashima, Ibaraki 314-8501, Japan
1.

1
Baseline B

Introduction

VLBI is one of the most precise technology tomeasure angular distance in the celestial sphere.
It is not only tool for astronomy but also is quite
useful in engineering application such as spacecraft
navigation. VLBI is good at measurement in coordinates perpendicular to the line of sight. It hascomplementary sensitivity with that of range andrange rate (R&RR) measurement, which is commonly used for spacecraft navigation in deep space.
Thus a combined analysis is expected to increase
accuracy of orbit determination of spacecraft.
Pioneering work in spacecraft navigation withVLBI has been performed by JPL [Border et al.,1982] with group delay (Delta Diﬀerential One way
Range). Institute of Space and Astronautical Science (ISAS) in Japan and CRL is collaborating touse VLBI for Japanese space mission. A spacecraft NOZOMI launched by ISAS was going to do
two earth swingbys in the period of December 2002
and June 2003 [Yoshikawa et al., 2001]. And arequest for support the orbit determination withVLBI data arose. Orbit determination of NOZOMI
has been performed by the ISAS and we provided
VLBI data delay for supporting their work. On theother hand, our group is planning to develop a tool
for spacecraft navigation with VLBI independently
from the ISAS. Here we introduce some points indata reduction and analysis procedure of spacecraft
coordinates estimation.
2.

K

VLBI Delay Model for Finite DistanceRadio Source

The standard VLBI delay model so called ‘consensus model’ [Eubanks, 1991] uses plane wave approximation based on a assumption that a radiosource is at inﬁnite distance from observer. Whenthe distance is less than 30 light years, however,curvature of wavefront of the signal from radiosource is not negligible as pointed out by Sovers

Figure 1. Schematic diagram of pseudo source vec The vector K is on the diagonal line of
tor K.
 20 .
 10 and R
parallelogram composed from vector R
and Jcobs [Sovers and Jacobs, 1996]. They andFukushima [Fukushima, 1994] argued about ﬁnite
distance VLBI model, but an expression including coordinates transformation of general relativity have not been given. Sekido and Fukushima[Sekido and Fukushima, 2003] have derived a expression of VLBI delay for ﬁnite distance radiosource corresponding to the ’consensus model’ bytaking into account relativistic eﬀects. That formis
τ2 − τ1−1=
 (1 + β02 ) 

e ·w
 ·
2
V 2 + 2VKb∆tg −1 − (1 + γ)U − e
2c2
c


e ·b
 · (V e + 2w
 2)VK−
1 + β02 −
,
c2
2c

(1)

where valuable in large capital indicates quantity
in barycentric reference frame and that in small
 i−X
j ij = X
capital is that of geocentric frame. R
and Xi is position vector in barycentric reference
frame. Suﬃx 0,1, and 2 respectively indicate radio source, station 1, and 2. b is baseline vector
 e and w
 2 are barycentric velocity
on the geoid, Vof geocenter and geocentric velocity of station 2,
 and parespectively. And pseudo source vector K
rameter β20 are deﬁned as :
β02
 02
R

K


 02 · V2
= R
c

R02
=
R02
 02 (T1 ) + R
 01 (T1 )R=.
R02 (T1 ) + R01 (T1 )

(2)
(3)
(4)

June 2003

13

1e-06

Amplitude of pseudo source vector(1-|K|)

Angular difference
between K and K0 (rad.)0.001

KashimaUsuda
0.00050-0.0005

KashimaAlgonquin-0.001-0.0015-0.0015-0.001-0.0005

Kashima-Algonquin

1e-07

KashimaTomakomai

00.0005

0.001

1e-08

Kashima-Tomakomai

1e-09

Kashima-Usuda

1e-10
06/04
00:00

0.0015

Angular differene between K and K0 (rad.)

06/04
03:00

06/04
06:00

06/04
09:00

06/04
12:00

06/04
15:00

06/04
18:00

06/04
21:00

06/05
00:00

Time (UT) in comparison with geocentric source unit vector K 0 . Left
Figure 2. Behavior of pseudo source vector Kpanel shows changes of the direction of K vector during 24 hours. The origin of the plot is the direction
 vector. Three lines on both two panels
 0 vector. Right panel shows change of the magnitude of K
of K
correspond to Kashima-Algonquin, Kashima-Tomakomai, and Kashima-Usuda baselines. Predicted orbitof NOZOMI on 4th-5th June 2003 was used for computation of the vectors here. Distance to the
NOZOMI was 4. × 109 m from the geocenter in this period.
The formula of (1) is very similar with that of’consensus model’ and both formulae become identical when the radio source is at inﬁnite distancefrom observer. In this sense, our formula (1) will be
regarded as expansion of ’consensus model’. The
main diﬀerence between them comes from deﬁni Actually, that vector musttion of source vector K.
be called as pseudo source vector, and is neither
unit vector nor constant vector as deﬁned in equation (4). The schematic view of pseudo source vec is displayed in Figure 1. It changes the magtor K
nitude and direction with baselines and with time.
 vector durFigure 2 demonstrate the behavior of K
ing 24 hours in comparison with geocentric source
vector to the spacecraft (NOZOMI) on KashimaAlgonquin (9109 km), Kashima-Tomakomai (750km), and Kashima-Usuda (208 km ) baselines. The vector was computed with based on predicted
K
coordinates of NOZOMI in 4th-5th June 2003. Leftpanel in the ﬁgure shows deviation of the pseudo
source vector from the direction to the source fromgeocenter. The deviation is larger as baseline isshorter. It is because parallax aﬀect more directly
 vector on shorter baseline. Since the NOto K
ZOMI is moving, the track of the vectors are notclosed curves in 24 hours. Right panel indicate
 In contrast to the dimagnitude of the vector K.

rection of K vector, the magnitude deviates fromunity more signiﬁcantly as baseline becomes longer.
Since the (pseudo) source vector aﬀects directly to
VLBI delay, change of its direction and magnitudecause change of delay in the same order. We implemented this model in our software by modiﬁcationof CALC ver.9. Apriori delay, delay rate, and par-tial derivatives computed by this software was usedin correlation processing and astrometric analysisof the spacecraft.
3.

Correlation Processing and Diﬀerence
from Normal VLBI

Observation and correlation processing of the
VLBI data has been performed with PC-based system [Osaki, 2002; Kondo et al., 2002]. We are seeking for better approach in both group delay andphase delay. In case of group delay, we used range
signal to measure group delay for NOZOMI. Since
the bandwidth of signal from the spacecraft is inorder of 1 MHz when it is modulated, the delay
resolution of group delay is in order of one nanosecond. To increase the spatial resolution of VLBI
observation, we have asked to Algonquin observatory to join NOZOMI observations sometimes besides Japanese domestic VLBI stations [Ichikawa
et al., 2003]. The delay model for spacecraft isdiﬀerent from normal VLBI observation even on
domestic baseline in Japan, since the radio sourcechanges its position in the celestial sphere duringobservation. Moreover curvature of wave front affect signiﬁcantly to the delay especially in intercontinental baseline. Figure 3 shows the delay rate
derived from observation data and that of VLBI delay model of equation (1). We used following way
to get continuous fringe rate for comparison here.
We observed NOZOMI for almost 24 hours in theexperiment of 4 June. Frequency of tone signal
from NOZOMI was extracted every 2 seconds with
1 Hz resolution from observed 2bit-4MHz sampling
VLBI data of each station via Fast-Fourier Trans-

IVS CRL-TDC News No.22

14

1e-06

8e-10

8e-07

Kashima-Algonqin
6e-10Rate (sec./sec.)

Rate (sec./sec.)

6e-07
4e-07
2e-07
0

4e-10

Finite VLBI
Model

Derived fromobserved freq. data

2e-10

-2e-07-4e-070-2e-10-6e-07-8e-07-4e-10Kashima-Algonquin-1e-0606/04 06/04
06:00 09:00

06/04 06/04
12:00 15:00

06/04 06/04 06/05
18:00 21:00 00:00

06/05 06/05
03:00 06:00

06/05 06/05
09:00 12:00

Time (UT)-6e-10
06/04
06:00

06/04
09:00

06/04
12:00

06/04
15:00

06/04
18:00

06/04
21:00

Time (UT)

06/05
00:00

06/05
03:00

06/05
06:00

06/05
09:00

Figure 3. Delay rate derived from Doppler frequency (left) and Residual of delay rate(right) on KashimaAlgonquin baseline. In the left panel, × mark indicates derived delay rates and broken line indicate VLBI
delay model of finite distance radio source. Plot in the right panel indicates residual of (observed) - (delay
rate model).
form (FFT). Then delay rate including clock rates 4.
of VLBI stations was derived by a relation
fx − fy
dτ
=
,
dt
fx

(5)

where fx , and fy is frequency of tone signal of NOZOMI observed at x and y station. Plot in Figure 3 scattered in range of ±10−10 (sec/sec) because precision of frequency measurement was 1
Hz, then resolution of delay rate measurement here
was 1(Hz)/8.4 (GHz) ∼ 1.2 × 10−10 . This order ofdelay rate resolution was not enough to compare
rate residual precisely, but increasing the frequency
resolution was limited due to some technical reasons (Number of FFT points, drifting frequency
with time, and etc...). Delay rate resolution is low
though number of data points is huge, so we canclearly recognize large systematic change of residual in Figure 3. It indicates apriori delay rate is notaccurate enough, and consequently fringe rotates
more than 1 turn in integration period (1 second
was normal integration time in correlation processhere). We think main reason of the rate residual
may comes from diﬀerence between predicted coordinates and true ones of NOZOMI. Generally,
this sort of error in predicted coordinates is supposed to be usual in also other spacecraft observation. Thus we need to establish stable procedure
to detect fringe by searching wide range of fringerate. One solution will be enlargement of rate window via decreasing integration period. Although
increase of ﬁle size of intermediate correlation output (several tens of Mega Bytes to a few Giga Bytes
per ﬁle) will accompany with it. The other solution
will be searching fringe by repetition of correlation
processing with changing rate parameter.

Analysis Software for Finite VLBI Astrometry

Observed VLBI delay data set obtained in series of NOZOMI VLBI observations [Ichikawa etal., 2003] were submitted to ISAS for orbit determination analysis with joint data set with R&RR
data. Independently from ISAS, we have been constructing our own software for coordinates estimation of spacecraft. Our analysis system is composed from two parts: precise apriori and partial
derivative computation package ‘calc skd’ and leastsquare analysis package ‘lsq src’, as similar with
CALC/SOLVE system. We wanted to make platform independent system rather than using MarkIII database binded with HP computer, so most of
the data used in the analysis are in form of ASCII
text ﬁles. We may use PIVEX format 1 [Gontierand Feissel, 2002] as data system in future. The
CALC version 9 was used as base to implement ﬁnite VLBI delay model. The analysis system runs
on FreeBSD PC-unix system. The calc skd computes apriori delay/rate and partials by following
a ﬁle of scan list and with using a set of parameter ﬁles (planetary ephemeris DE405/DE406, EOP,
and etc...) as the same with the CALC/SOLVE.
The lsq src is a simple multi-baseline least squareanalysis software with minimum functions. It use
observed delay/rate, apriori delay/rate, partials,
and constraints for estimating a subset of the parameters (source coordinates, proper motion, clock
oﬀset/rate, dry atmospheric zenith delay/rate, delay gradient of dry atmosphere, wet atmosphericzenith delay/rate). Since spacecraft may move
rapidly on the celestial sphere, proper motion of
the radio source may be included in estimation pa1 http://lareg.ensg.ign.fr/feissel/pivex.html

June 200315

rameters.

Fukushima, T., Lunar VLBI observation model, A&A,
291, pp.320–323, 1994.

5.

Gontier, A-M., and M. Feissel M., PIVEX: a Proposal
for Platform Independent VLBI Exchange Format,
2002 IVS General Meeting Proc.(N.R.Vandenber
and K.D.Baver eds.)
NASA/CP-2002-210002,
pp.248–254, 2002.

Summary

We are investigating a VLBI technique for application of spacecraft navigation. As a ﬁrst step,
we have developed a ﬁnite VLBI delay expression
with taken into account relativistic eﬀects, and aredeveloping analysis software packages. We will beable to report more detailed result of the analysis
in future issue.

Ichikawa, et al., VLBI Application for Spacecraft Navigation (NOZOMI) Part I – Overview –, TDC News
No.22 (this issue), pp.10–11, 2003.
Kondo, T., R. Ichikawa, Y. Koyama, M. Sekido, and
H. Osaki, VLBI observation using IP-VLBI systemfor orbit determination of deep space spacecraft –Group delay measurements of GEOTAIL and NOZOMI telemetry signals –, TDC News No.21, pp.18–
22, 2003.

Acknowledgement: We thank members of the NOZOMI VLBI observation working group in Japanand W.Cannon, B. Mario, and S. Novikov for supporting series of VLBI observation for NOZOMI.
We also thank VLBI group of Goddard/NASA for Osaki, H, Advancement of versatile scientific sampling processor (VSSP), TDC News No.21, pp.16–
providing us CALC 9 package and permission of17, 2003.
modiﬁcation.
References

Sekido, M. and T. Fukushima, Relativistic VLBI Delay
Model for Finite Distance Radio Source, 2003 (to besubmitted to J. Geodesy.)

Border J. S., et al., Determining Spacecraft Angular
Position with Delta VLBI: The Voyager Demonstration, Proc. of AIAA/AAS Astrodynamics Conference, AIAA-82-1471, 1982.

Sovers, O. J. and C.S. Jacobs, Observation Model andParameter Partials for the JPL VLBI Parameter Estimation Software “MODEST”-1996”, JPL Publication 83-39, Rev. 6 pp.6–8, 1996.

Eubanks, T. M., A Consensus Model for Relativistic Effects in Geodetic VLBI, Proc. of the USNO workshop
on Relativistic Models for Use in Space Geodesy,
pp.60–82, 1991.

Yoshikawa, M., et al., Present status and future problems of the Orbit determination for Nozomi spacecraft, TDC News No.19, pp.37–43, 2001.

Kashima 34m radio-telescope annual maintenance (cont. from page 4)

Photo. 34m telescope and a crane truck. Elevation motors are removed and sent back to thefactory for overhawl. (see topics on page 4 for details)

“IVS CRL Technology Development Center News” (IVS CRL-TDC News) published by theCommunications Research Laboratory (CRL) is the continuation of “International Earth Rotation Service - VLBI Technical Development Center News” (IERS TDC News) published by CRL.
In accordance with the establishment of the International VLBI Service (IVS) for Geodesy andAstrometry on March 1, 1999, the function of the IERS VLBI technical development center was
taken over by that of the IVS technology development center, and the name of center was changed
from “Technical Development Center” to “Technology Development Center”.
VLBI Technology Development Center (TDC) at CRL is supposed
1) to develop new observation techniques and new systems for advanced Earth’s rotation observations by VLBI and other space techniques,2) to promote research in Earth rotation using VLBI,
3) to distribute new VLBI technology,4) to contribute the standardization of VLBI interface, and5) to deploy the real-time VLBI technique.
The CRL TDC newsletter (IVS CRL-TDC News) is published biannually by CRL.

This news was edited by Tetsuro Kondo and Yasuhiro Koyama, Kashima Space Research Center,
who are editorial staﬀ members of TDC at the Communications Research Laboratory, Japan.
Inquires on this issue should be addressed to T. Kondo, Kashima Space Research Center, Communications Research Laboratory, 893-1 Hirai, Kashima, Ibaraki 314-8501, Japan, TEL : +81299-84-7137, FAX : +81-299-84-7159, e-mail : kondo@crl.go.jp.
Summaries of VLBI and related activities at the Communications Research Laboratory are on theWorld Wide Web (WWW). The URL to view the home page of the Radio Astronomy Applications
Section of the Kashima Space Research Center is : “http://www.crl.go.jp/ka/radioastro/”.

IVS CRL TECHNOLOGY DEVELOPMENT CENTER NEWS No.22, June 2002
International VLBI Service for Geodesy and Astrometry
CRL Technology Development Center News
published by
Communications Research Laboratory, 4-2-1 Nukui-kita, Koganei, Tokyo 184-8795, Japan