Site: Toshiba Corporation
1-1, Shibaura 1-chome
Minato-ku, Tokyo 105-01, Japan
http://www.toshiba.co.jp/index.htm

Date Visited: June 6, 1997

WTEC: C. Bostian (report author), K. Bhasin, W. Brandon, A. Mac Rae, J. Pelton, S. Townes

Hosts:

BACKGROUND

Toshiba is a large and diversified electronics company. Its space products and activities include the following:

Toshiba is the only Japanese company doing space robotics. It has extensive robotics experience both on the ground and in space. Current projects include robotics experiments on Space Shutte (MFD), ETS-VII and JEM (the Japanese Experiment Module for the International Space Station). Research activities include robotic vision systems that will recognize objects to be handled.Selected Highlights of Toshiba Involement in Flight Programs

RESEARCH AND DEVELOPMENT ACTIVITIES

Antennas

Large Deployable Antennas for ETS-VIII

Toshiba's design uses a modular construction. The modules have a hexagonal cross section which has been reported at different visited sites as having a diameter of 3, 4, or 4.5 meters. ETS-VIII will carry two large S-band antennas (one for transmitting and one for receiving) with 17 meter physical apertures, each constructed from 19 modules. The surface accuracy will be at least lambda/20. The feed will be a phased array.

Our hosts discussed in some detail the problems of compensating for thermal distortion of the antennas, particularly the possibility that thermal distortions may cause the main beams of the two antennas to point in different directions. Toshiba's plan is to use the spacecraft Attitude and Orbital Control System (AOCS) to point the receiving antenna in the desired direction and then adjust the amplitudes and phases of the transmitting feed array elements to compensate for thermal distortion.

Measuring the thermal distortions under field conditions will be difficult. Toshiba has tested one of the modules on the ground. When ETS-VIII is on orbit, the spacecraft can be commanded from the ground to do a conical scan of the antennas. Pointing errors can be determined from the measured patterns, and the transmitting feed array adjusted to compensate for them.

The antennas will be designed and constructed to minimize thermal distortion. Carbon reinforced plastic materials will be used, not metal.

ETS-VIII will not employ orthogonal polarization frequency re-use. The isolation between adjacent beams has not yet been determined. The satellite may either re-use frequencies on every other beam (ABAB pattern) or it may re-use frequencies on every third beam (ABCA pattern).

Other Technologies for Large Space Antennas

About 10 years ago Toshiba investigated inflatable and unfurlable antennas for space Company representatives will not pursue these, however, but will emphasize instead the ETS-VIII modular approach The ETS-VIII antennas are the largest that it is currently considering. Space antennas in the 13-15 m class are sufficient to allow communication with hand-held terminals at S-band.

Toshiba developed a 3.5 meter effective aperture (3.8 meter physical aperture) Ka-band antenna for ETS-VI. It was made of carbon fiber reinforced plastics and achieved an efficiency on the order of 50%.

Our hosts expressed the view that Ka-band was probably the upper frequency limit for mesh technologies. As frequency increases, the mesh density must get higher (i.e., the mesh must get finer) and the modules must get smaller.

L-band SAR Antennas

ALOS (Advanced Land Observation Satellite - to be launched in 2002) will carry an L-band SAR using a Toshiba direct radiating phased array with approximately 400 elements. Its physical size will be 10m by 3m and it will achieve 10 m resolution. (The optical portion of this satellite will achieve 2.5 m resolution.) The mechanical design will provide a lighter weight structure than was used in the SAR carried by the Japanese earth observation satellite (EOS).

Robotically-Assembled Antennas

The 1992 WTEC team was briefed about some proposed experiments involving the use of robots to assemble large antennas in space. These apparently will not be carried out. ETS-VII will do other space robotics experiments. If there were a program to develop robotic techniques for constructing antennas in space, Toshiba would be the company to carry it out. In the past the company made some proposals to the government, but there is currently no experimental activity.

Position Determination

Toshiba is developing a high accuracy clock system which will carry an atomic clock. The spacecraft will transmit a signal similar to that of GPS. The result may be a Japanese GPS-like system that will provide higher accuracy than GPS.

Space Power

Toshiba buys solar cells for its panels from Sharp. The company is working on large-scale solar panels.

Batteries are currently not a hot research topic, although Toshiba is a potential supplier of Ni-H2 batteries for commerical use and is looking at the possibility of using lithium batteries developed for electric cars, in space.

Toshiba is considering cooperating with the U.S. company International Fuel Cells in the development of fuel cells for space applications.

Ion Engines

Toshiba is developing xenon ion engines but they are not ready for the commercial market. Performance is good but cost needs to be reduced. One of its goals is a 150 mN thruster. Toshiba also builds the power supplies for ion thrusters. It does not build chemical thrusters.

Onboard Processing

Toshiba has no special activities in onboard processing. It does develop computers for control applications.

Power Amplifiers

Toshiba built a 200 W 21 GHz TWTA that will fly on COMETS, and which has an efficiency of 50%.

Toshiba manufactures power FETs for the terrestrial market. It has modules that will deliver more than 10 W at L-band, but these are not space qualified. The company has an internal R&D effort on power FETs for space applications. It is looking at HEMT devices for frequencies up to 90 GHz.

Free-Space Optical Communications

Toshiba has a laser communications experiment on ETS-VI. It developed the lasers, optical system, and the fine pointing system. The company's participation in OICETS is limited to the power subsystem; NEC is doing the optics.

Toshiba is conducting research for NASDA on optical detectors in support of the Gigabit Satellite. Our hosts were not familiar with the details, i.e., about which devices are under consideration.

Other Optical Technologies

Toshiba is not presently investigating optical signal distribution onboard satellites, but our hosts view this an important topic.

COMMENTS

We discussed the many proposals for NGSO systems and for Ka-band GEO systems and shared opinions about the strategies and probable success of some of the ventures.


Published: December 1998; WTEC Hyper-Librarian