Milestone-Proposal:Usuda Deep Space Center and Associated Deep Space Control System

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Docket #:2024-19

This is a draft proposal, that has not yet been submitted. To submit this proposal, click on the edit button in toolbar above, indicated by an icon displaying a pencil on paper. At the bottom of the form, check the box that says "Submit this proposal to the IEEE History Committee for review. Only check this when the proposal is finished" and save the page.


To the proposer’s knowledge, is this achievement subject to litigation? No

Is the achievement you are proposing more than 25 years old? Yes

Is the achievement you are proposing within IEEE’s designated fields as defined by IEEE Bylaw I-104.11, namely: Engineering, Computer Sciences and Information Technology, Physical Sciences, Biological and Medical Sciences, Mathematics, Technical Communications, Education, Management, and Law and Policy. Yes

Did the achievement provide a meaningful benefit for humanity? Yes

Was it of at least regional importance? Yes

Has an IEEE Organizational Unit agreed to pay for the milestone plaque(s)? No

Has the IEEE Section(s) in which the plaque(s) will be located agreed to arrange the dedication ceremony? Yes

Has the IEEE Section in which the milestone is located agreed to take responsibility for the plaque after it is dedicated? Yes

Has the owner of the site agreed to have it designated as an IEEE Milestone? Yes


Year or range of years in which the achievement occurred:

1984

Title of the proposed milestone:

Usuda Deep Space Center and Associated Deep Space Control System, 2024

Plaque citation summarizing the achievement and its significance: Text absolutely limited by plaque dimensions to 70 words; 60 is preferable for aesthetic reasons.

Usuda Deep Space Center and the control system for deep space exploration were built in 1984 by ISAS in collaboration with Mitsubishi Electric Corporation and NEC Corporation to perform Halley’s comet observations in the 'Halley Armada'. Facilities such as the 64m antenna were equipped with the most advanced technologies, and were optimized for easy operation. Thereafter, this system contributed to the success of many deep space missions and scientific observations.

200-250 word abstract describing the significance of the technical achievement being proposed, the person(s) involved, historical context, humanitarian and social impact, as well as any possible controversies the advocate might need to review.

The International Geophysical Year (IGY) project urged the observation of Halley's Comet, which approached the Earth in 1986. The Institute of Space and Astronautical Science began to design facilities to deal with this problem. It was required to communicate at a far distance of about 300 million km, which was opposite the Sun from the Earth. At the Usuda Space Observatory (Usuda Station), a large antenna, a low-noise amplifier, and a high-power transmitter were required. Observation information received from the deep space probe should be sent to the control headquarters at the Sagamihara Campus via a communication line, and command information to the spacecraft was sent to Usuda.

   In the realized Usuda antenna, the reflector structure was designed in homology technology to cope with the deformation due to gravity. Beam-waveguides was installed  to connect the antenna reflectors and input/output ports, so the connected devices can be fixed to the building floor and it is easy to refurbish the antenna for  multiple new frequencies. The total facility at Usuda and Sagamihara was designed for easy operation and maintenance by adopting the beam-waveguides and electric driving system, and by compromising between the electric performance and operation conditions. 
   After the completion in 1984, this system worked hard for the observations of Halley's Comet in the Halley Armada consisted of the spacecraft of Japan, the USA, ESA and USSR. Later, this system  contributed to the successes of many subsequent spacecraft  missions, and experiments in space science and radio astronomy.

IEEE technical societies and technical councils within whose fields of interest the Milestone proposal resides.

Antennas and Propagation Society, Geoscience and Remote Sensing Society, Instrumentation and Measurement Society, Professional Communication Society, Aerospace and Electronic Systems Society

In what IEEE section(s) does it reside?

IEEE Tokyo Section and IEEE Shin-etsu Section

IEEE Organizational Unit(s) which have agreed to sponsor the Milestone:

IEEE Organizational Unit(s) paying for milestone plaque(s):

Unit: IEEE Tokyo Section
Senior Officer Name: Kiyoharu AIZAWA

IEEE Organizational Unit(s) arranging the dedication ceremony:

Unit: IEEE Tokyo Section
Senior Officer Name: Kiyoharu AIZAWA

IEEE section(s) monitoring the plaque(s):

IEEE Section: IEEE Tokyo Section
IEEE Section Chair name: Kiyoharu AIZAWA

Milestone proposer(s):

Proposer name: Tadashi Takano
Proposer email: Proposer's email masked to public

Proposer name: Yasuhiro Murata
Proposer email: Proposer's email masked to public

Please note: your email address and contact information will be masked on the website for privacy reasons. Only IEEE History Center Staff will be able to view the email address.

Street address(es) and GPS coordinates in decimal form of the intended milestone plaque site(s):

3-1-1 Yoshino-dai, chuo-ku, Sagamihara, Japan GPS coordinates: N35.5581444 and E139.3864524

Describe briefly the intended site(s) of the milestone plaque(s). The intended site(s) must have a direct connection with the achievement (e.g. where developed, invented, tested, demonstrated, installed, or operated, etc.). A museum where a device or example of the technology is displayed, or the university where the inventor studied, are not, in themselves, sufficient connection for a milestone plaque.

Please give the address(es) of the plaque site(s) (GPS coordinates if you have them). Also please give the details of the mounting, i.e. on the outside of the building, in the ground floor entrance hall, on a plinth on the grounds, etc. If visitors to the plaque site will need to go through security, or make an appointment, please give the contact information visitors will need. Institute of Space and Astronautical Science, Sagamihara Campus:

 It houses various research and testing facilities as well as the headquarters of the institute.
 Various computers calculate the trajectory of spacecraft such as deep space probes and satellites, calculate the control of the spacecraft, and create commands for mission execution. There is a display device for that.
 The results of their calculations are sent to the Usuda station via the communication network.
 It is transmitted from the Usuda station to the spacecraft by radio waves.
 Telemetry data representing the status of the spacecraft and observation data generated by the spacecraft are received by the Usuda station and sent to Sagamihara via the network.
 Visitors will be able to see these facilities during the opening period. In addition, the history of the institute's spacecraft and the results of its research are displayed in the Space Science Exploration and Exchange Building, so you can learn about the activities and positions of the Usuda Station.
 It is also an advantage that it is close to the station of the Yokohama Line and has good access. 
 

Are the original buildings extant?

Yes.

Details of the plaque mounting:

The Space Science Exploration and Exchange Building on the Sagamihara Campus is a one-story building with a hall, so it will be installed there.

How is the site protected/secured, and in what ways is it accessible to the public?

At the Space Science Exploration and Exchange Building, visitors fill out the form at the entrance and go inside.

Who is the present owner of the site(s)?

Japan Aerospace Exploration Agency (JAXA)

What is the historical significance of the work (its technological, scientific, or social importance)? If personal names are included in citation, include justification here. (see section 6 of Milestone Guidelines)

1. Historical Background (1) International Geophysical Year and Halley's Comet exploration • Since the 1950s, research and development on space has been scientifically and socially required by the International Geophysical Year (IGY) project. In particular, when Halley's Comet approached the Earth in 1986, exploration of deep space beyond 2 million km became an urgent task. • The research institute in charge of this field in Japan was the Institute of Space and Astronautical Science (ISAS), and began to study facilities to deal with this problem. • As a result, it was required to communicate at an ultra-distant distance of about 300 million km, where Halley's Comet is opposite side of the Sun from the Earth. At the Usuda Space Observatory, a large antenna, a low-noise amplifier, and a high-power transmitter were required. • Observation data from the deep space probe were received, and sent to the control headquarters at the Sagamihara Campus via a communication line, and command information to the spacecraft was sent to Usuda. • Both the Usuda Space Observatory and the Sagamihara Control Headquarters were required to operate with a small number of people. • ISAS was an independent institute belonging to the Ministry of Education at that time, and became a part of Japan Aerospace Exploration Agency (JAXA) in 2003.

(2) Follow-on missions after the Halley's Comet observations • a huge antenna was required to provide communication and tracking capabilities for space probes involved by the Institute of Space and Astronautical Science and other institutions. • In particular, it was indispensable for the control of explorers Hayabusa and Hayabusa 2, contributed to the success of the world-first sample-return from asteroids. • Those explorers used new frequencies so that the station capability should have been improved. (3) Space science, radio astronomy • A huge antenna was required for space science, radio astronomy, • In particular, Usuda facility was used for the preliminary experiment of the Space Very Long Baseline Radio Interferometer (Space VLBI), and the development and operation of the Space VLBI satellite. • For those objectives, it was necessary to receive multiple frequencies.

2. Historical Achievements (1) Halley’s comet observations in International Armada • This system, completed in 1984, has been effective in international joint observations of Halley's Comet. First, the Japan spacecraft SAKIGAKE and SUISEI completed their mission as part of the Halley Armada. • It contributed to the control of the U.S. comet probe ICE in collaboration. • Meanwhile, the scientists and engineers had close collaboration with ESA’s probe GIOTTO, and USSR’s probes Vega 1 and Vega 2. (2) Contribution to the follow-on missions • After that, it contributed to the control of the deep space probes such as Hayabusa (launched in 2003) and Hayabusa-2 (2014) , the lunar probe "Kaguya" (2007) and the Earth magnetospheric observation satellite "Geotail" (1992) in shallow space, and so on, leading to the mission success. (3) Scientific observations • The facility was also used for scientific observation, and made significant contribution. • In 1989, when the U.S. deep space probe Voyager 2 flew by Neptune, Japan and the United States jointly conducted radio science by taking advantage of the fact that the Usuda antenna was visible in the rotation of the Earth. The Neptunian atmosphere was clarified. • In 1995, the world-first experiment of space debris detection in a bi-static radar scheme was accomplished between Usuda and another site Uchinoura at 1000km distance using a mock debris of a satellite in orbit. • In 1998, radio science in the occultation phenomenon of Mars was conducted using Usuda facility. • Moon explorer KAGUYA and the associated small satellites OKINA and OONA were tracked and controlled by Usuda facility. In 2007, the gravity distribution on the far-side of the Moon was revealed by analyzing the Doppler shift frequency of the radio wave relayed via the small satellite. Also, the data indicated the existence of caves under the lunar ground. • In 2018, radio science in the occultation phenomenon of Venus was conducted using Usuda facility by Japanese and European scientists.

(4) Radio astronomy • When Japan and the United States jointly conducted the world's first preliminary experiment of space-based Very-Long-Baseline Interferometer (Space VLBI) using the TDRS data relay satellite, this antenna was used as a ground-based radio telescope. • In particular, the world's first satellite specialized for space-VLBI, Halca, developed by the Institute of Space and Astronautical Science, played the role of a radio telescope as well as a high-speed reception of data received from the satellite antenna. • Usuda facility was used for terrestrial radio astronomy, and contributed to many achievements. (5) Findings in the antenna operation • In 1985, the angle error of the antenna in automatic tracking mode was observed in the Acquisition and Loss of signal. The observation and data analysis clarified that the error was caused by the shadow of the terrain onto the antenna aperture, which generated a wrong tracking signal. • In 1987, explorers were lost near the Sun, as was called occultation phenomenon. We studied the phenomenon precisely to clarify the tracking time around the Sun. 3. Impacts on other systems • When NASA sent an engineer to Japan in 1991 before developing a new Deep Space Network (DSN) antenna, we explained the operation status of the 64-meter antenna and provided technical information. • In particular, this opportunity gave NASA people a great influence on the design of the beam waveguide system to supply radio waves from the transmitter and receiver to the antenna. • In designing and constructing a new 54-meter antenna for deep space control in the Usuda area, the design concept of the 64-meter antenna was inherited.

What obstacles (technical, political, geographic) needed to be overcome?

(1) Technological difficulties • In order to receive extremely low levels of radio waves, it was first necessary to build an antenna that could drive in all directions and had the highest gain in the world (i.e., one of the largest in the world). • In the 1980s, the Deep Space Network (DSN) in the United States had the largest antenna in the world with a diameter of 64 m, and it was expanded. For the Usuda antenna, the same performance as the expanded DSN 70m antenna was required. • It was necessary to amplify low-level received radio waves against the noise (thermal noise) that exists constantly. Moreover, since the equipment needed heavy maintenance, it was necessary to design the optimal one.

• The high-power amplifier sent microwave of 20 KW in the 2 GHz band for communication with the Halley's Comet probe. A water-cooled klystron was adopted, but the receiver had to be protected against high power damage and interference. • The position and speed of the spacecraft are obtained as a result of sending a measurement signal, receiving the response, and analyzing those difference. The measurement accuracy depends on the type of measurement signal, the error characteristics, and the accuracy of the reference time (atomic clock). Therefore, atomic clocks needed to be stable for a long time. In addition, short-term stability was required for radio astronomy such as VLBI. • To cope with many applications, it became necessary to support other frequencies. Therefore, it was necessary to add a feed horn and a connecting waveguide that matched each frequency, while the reflectors of the antenna itself and the mirrors in the beam waveguide system were to be used as the same. • This large-scale refurbishment should have been planned and carried out based on the previous operational experience and future technology trends in spacecraft communications.

(2) Political and financial difficulties • Due to the small budget of the institute, it was not possible to devote a great effort to the operation & maintenance of these devices. Therefore, the following compromises were made between the electrical / mechanical performances and the cost to optimize the total system. • The antenna drive system of hydraulic type could not be adopted because of oil leakage. • When connecting the receiver to the antenna, transmission loss could be reduced by connecting it directly to the back of the antenna, as had been adopted in the world. However, this maintenance work was not desirable because it required work at a height of about 70 m. • A low-noise amplifier cooled by liquid-He tends to have a pipe blocked by solidified nitrogen or oxygen, and was not suitable for Usuda Station. So, the low-noise amplifier was cooled by gas-He. • For the maintenance and operation of Usuda's facilities and communication with the Sagamihara Campus, computers, software, and display consoles were required. The design was based on equipment compatible with the former scientific satellites, but it needed to have the performance and operability to track the Halley's Comet probe. Almost the same equipment was needed in Sagamihara, too.

• Initially, the antenna was used only for tracking deep space explorers, but required for science observations and radio astronomy by other institutions. • From Usuda to Sagamihara, it was necessary to realize a high-speed data line of 100 kbps. However, the distance from the Usuda antenna to the nearest telephone office was 7 km so that it was difficult to achieve the bit rate with conventional copper wires. At that time, the telephone company (NTT) did not have optical fiber installed in the local line, but as a special case, optical fiber was drawn to realize the bit rate.

(3) Geographical difficulties • To receive weak radio waves from deep space probes, it was important for the deep space station to prevent radio wave interference from the surrounding area. Therefore, we selected several places where microwave-communication lines did not pass and where car telephone signals did not reach, and conducted on-site verifications. As a result, the site of Usuda was chosen. • The surrounding terrain of the antenna was efficient to shield radio wave interference from the outside. However, the shadow onto the antenna aperture caused a wrong pointing of the antenna, as was analyzed and solved for right operation later.

What features set this work apart from similar achievements?

1. One of the largest antennas that can drive the whole space and transmit and receive radio waves

 The large antenna of Usuda Station can drive the entire space and transmit and receive radio waves.
 There are large antennas in the world. For example, China has an antenna with a diameter of 500 meters, but it is not possible to drive the antenna because it is dug into the ground to create a parabola. Europe has a large antenna with a diameter of 100 m that can drive the entire space, but it is only for reception and cannot transmit
 Therefore, the only antennas that can be compared to the Usuda Station antenna are the 70m antennas of the US DSN and the Russian Deep Space Network. The Usuda antenna achieved an antenna gain of 61.6 dBi, which is almost equivalent to the gain of the DSN70m antenna (63.3 dBi).

2. Measures against the deformation of the giant reflector due to gravity In the Usuda antenna, the structure was designed so that the deformed mirror surface becomes a parabolic surface (homology technology). The change in the parabolic surface is corrected by driving the sub-reflector. This can be flexibly designed according to the environment.

 On the other hand, the 70-meter antenna of DSN in the United States uses a method of placing a flat plate that is deformed by gravity in the radio passage (Deformable Flat Plate) and a method of adjusting the electric field blown on the main reflector (Array-Feed Compensation System) by configuring the primary radiator with an array. This is complex in design and has limited scope.

3. Beam-waveguides

 The Usuda antenna uses beam-waveguides to connect the antenna reflectors and input/output ports, so the connected device can be fixed to the building floor.

In the DSN70m antenna, the communication equipment is attached directly to the back of the antenna. Therefore, since the communication equipment is at a height of about 90 m and at an angle, it is extremely difficult to maintain and operate it.

4. Support for multiple frequencies

 The Usuda antenna responds to multiple frequencies by adding horns to the beam-waveguides.
 On the other hand, the 70-m antenna of DSN in the United States consists of an S band and an X-band discriminating filter (frequency selection plate), and is shared by the Cassegrain antenna type and the Barabola antenna type. Therefore, there is no degree of freedom in frequency expansion, and it is not easy to adjust and change.

5. Antenna drive system

 In the Usuda antenna, the antenna is driven by an electric type.

On the other hand, hydraulic antennas were common at that time, including DSN70m antennas. This is difficult to precisely control due to the large number of oil leaks.

6. Antenna angle standard

 When the antenna direction is changed, the paraboloid of the antenna mirror surface and the rotation axis are deformed. At that time, a laser collimator was used as an angle standard that did not change. The overall angle setting achieves a high accuracy of 0.003 degrees rms compared to a beam width of 0.13 degrees. 

7. Low noise amplifier The best performance for a low-noise amplifier was achieved in the United States with a maser cooled with liquid helium, and was equivalent noise temperature of 5 K. However, in liquid helium temperature of 4 K, impurities such as hydrogen and oxygen solidify and block pipes. Therefore, we abandoned liquid-helium cooling, and used a gaseous helium-cooled parametric amplifier developed in Japan. The performance of 9K on a single unit and 26K on the receiving system was obtained. Later, HEMTs were cooled with gaseous helium to achieve sufficient performance of 20 K in total.

8. Prevention of damage and interference from the transmitter to the receiver In order to suppress the transmitter’s high power, a transmission band blocking filter of 110 dB was realized and inserted before the receiver. In order to prevent interference from noise radio-waves generated by the transmitter, a blocking filter of 40 dB in the reception band was inserted.

9. Ultra-high-precision oscillator for time reference (atomic clock) Cesium and rubidium oscillators having excellent long-term stability were used, and hydrogen maser having excellent short-term stability were used for VLBI. However, at present, multiple hydrogen oscillators are operated in parallel to ensure long-term stability.

10. High-speed data line from Usuda to Sagamihara Optical fiber communication lines, which were not commonly used at the time, were introduced, so that a high-speed data line of 100 kbps from Usuda to Sagamihara was realized.

11. System optimization taking into account electrical performance versus maintenance and operation Great effort could not be devoted to the maintenance and operation of Usuda Deep Space Center including Usuda Station and the Sagamihara Headquarter. Therefore, the optimal solution was achieved by balancing electrical performance and cost. For example, the transmitter and receiver were installed on the floor thanks to the beam waveguides, the antenna drive was electric instead of hydraulic, and the low-noise amplifier was cooled by gaseous helium instead of liquid helium.

Supporting texts and citations to establish the dates, location, and importance of the achievement: Minimum of five (5), but as many as needed to support the milestone, such as patents, contemporary newspaper articles, journal articles, or chapters in scholarly books. 'Scholarly' is defined as peer-reviewed, with references, and published. You must supply the texts or excerpts themselves, not just the references. At least one of the references must be from a scholarly book or journal article. All supporting materials must be in English, or accompanied by an English translation.

Media:List of supporting materials.pdf Media:ReferenceT_1R.Akiba, “Status Report on PLANET-A, IAF 1980.pdf Media:ReferenceT_2T.Nomura, Deep Space Projects, AIAA 1981.pdf Media:ReferenceT_3 M.Kawaguchi, “Despin Antenna , ISTS 1982.pdf Media:ReferenceT_4 T.Hayashi, Bubble Date Recorder , ISTS 1982.pdf Media:ReferenceT_5 K.Hirao, System Design of Japan’s First, IAF 1985.pdf Media:ReferenceT_7 T.Nomura, “Communications System, IAF 1985.pdf Media:ReferenceT_8 T.Hayashi, Operation Results of Communications Facilities, ISTS 1986.pdf Media:ReferenceT_9 1986 IEEE MONTEC.pdf Media:ReferenceT_10 1986 ISTS “Design principle.pdf Media:ReferenceT_11 1986 ISTS “Utilization of Usuda to ICE.pdf Media:ReferenceT_12 1986_translated from Japanese_Telecommunications System for Halley’s Comet Exploration.pdf Media:ReferenceT_13 1987 JSTS_Communication Tracking_Halley’s Commet.pdf Media:ReferenceT_14 1988 ISTS “Up-to-date.pdf Media:ReferenceT_15 1994 Japanese deep space station with 64m diameter antenna fed through beam waveguides and its mission applications.pdf Media: Reference E_1 1991 Imbriale_IEICE National Convention_Beam waveguide analysis.pdf

Supporting materials (supported formats: GIF, JPEG, PNG, PDF, DOC): All supporting materials must be in English, or if not in English, accompanied by an English translation. You must supply the texts or excerpts themselves, not just the references. For documents that are copyright-encumbered, or which you do not have rights to post, email the documents themselves to ieee-history@ieee.org. Please see the Milestone Program Guidelines for more information.

Media:List of supporting materials.pdf

Media:ReferenceT_1R.Akiba, “Status Report on PLANET-A, IAF 1980.pdf Media:ReferenceT_2T.Nomura, Deep Space Projects, AIAA 1981.pdf Media:ReferenceT_3 M.Kawaguchi, “Despin Antenna , ISTS 1982.pdf Media:ReferenceT_4 T.Hayashi, Bubble Date Recorder , ISTS 1982.pdf Media:ReferenceT_5 K.Hirao, System Design of Japan’s First, IAF 1985.pdf Media:ReferenceT_7 T.Nomura, “Communications System, IAF 1985.pdf Media:ReferenceT_8 T.Hayashi, Operation Results of Communications Facilities, ISTS 1986.pdf Media:ReferenceT_9 1986 IEEE MONTEC.pdf Media:ReferenceT_10 1986 ISTS “Design principle.pdf Media:ReferenceT_11 1986 ISTS “Utilization of Usuda to ICE.pdf Media:ReferenceT_12 1986_translated from Japanese_Telecommunications System for Halley’s Comet Exploration.pdf Media:ReferenceT_13 1987 JSTS_Communication Tracking_Halley’s Commet.pdf Media:ReferenceT_14 1988 ISTS “Up-to-date.pdf Media:ReferenceT_15 1994 Japanese deep space station with 64m diameter antenna fed through beam waveguides and its mission applications.pdf

Media: Reference E_1 1991 Imbriale_IEICE National Convention_Beam waveguide analysis.pdf Media: Reference E_2 1992 CCDS Packet Telemetry.pdf Media: Reference E_3 2006Fujiwara_Rubble-Pile Asteroid Itokawa_Science.pdf Media: Reference E_4 2015Yoshikawa_Hayabusa_sample return mission.pdf Media: Reference E_5 2007 Bistatic Radar System Using VLBI Technologies for Detecting Space Debris.pdf Media: Reference E_6 - 2020Tsuda_Hayabusa2 mission status_acta astronautica.pdf

Media:Reference S_1 - 1986 science_Levy_Very Long Baseline interferometric Observations .234.4773.187 Science.pdf Media:Reference S_2 - 1987 Acta Astronautica_Levy_REssult and communications.pdf Media:Reference S_3- 2002 HIROSAWA_ActaAst_Space VLBI 1-s2.0-S0094576501001710-main.pdf

Media:Reference P_1- 1992 Elect and Comm in Japan “Receiving System in Voyager 2 experiment.pdf Media:Reference P_2- 1992 Voyager Radio Science_e75-b_7_665.pdf Media:Reference P_3 - Farside Gravity Field of the Moon_2009 Science.pdf Media:Reference P_4 - Possible lunar lava tube_Haruyama_2009_GRL_3972.pdf Media:Reference P_5- Fine Vertical Structures at the Cloud Heights of Venus_Imamura_etal2018JGR_RadioHolography.pdf Media:Reference P_6- Observation of the Solar Corona Using Radio Scintillation_Chiba_etal_2022_SolarPhys.pdf

Media:Reference R_1 - 1998 science.281.5384.1825_Overview and Initial Results.pdf Media:Reference R_2 - 2004 THE VSOP 5 GHZ ACTIVE GALACTIC NUCLEUS SURVEY_Horiuchi_2004_ApJ_616_110.pdf Media:Reference R_3 2016_Takefuji_Very Long Baseline Interferometry Experiment on Giant Radio PulsesPASP_128_084502.pdf Media:Reference R_4 - 2021science.abd4659_Enhanced x-ray emission.pdf

Media:Reference M_1 _Design and Operation.pdf Media:Reference M_2 _Application Achievements.pdf Media:Reference M_3 _Halley's comet DenshiTokyo 1985.pdf

Media:Reference F_1- Solutions to Low-Frequency Problems_1992-01-07_Imbriale_SOLUTIONS TO LOW-FREQUENCY PROBLEMS.pdf Media:Reference F_2- Novel Solutions to Low-Frequency Problems_1998 IEEE TAP Imbrialems.pdf Media: Reference F_3- “Large Antennas of the Deep Space Network”_Descanso_Mono4_web_Imbriale.pdf

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