TechSat/Gurwin-II

TechSat/Gurwin-II is a microsatellite, built by students of the Haifa-based Technion (Israel Institute of Technology) with industrial and government support (the S/C is also referred to as TechSat-1B, as well as OSCAR-32 by the AMSAT community; the COSPAR ID is: 1998-043-D). TechSat is a microsatellite family of Asher Space Research Institute (ASRI) of Technion. As a university, Technion is involved in the development of space-qualified systems based on advanced and innovative technologies. The microsatellite is named in honor of Joseph and Rosalind Gurwin whose long-term support for space research at Technion enabled the TechSat mission. ^{1) 2) 3)}

The TechSat development started in 1993. TechSat-1a, a technology demonstration microsatellite (50 kg), was launched March 23, 1995 on a Russian Start launcher (a newly converted Russian intercontinental ballistic missile) - unfortunately, this mission experienced a launch failure.

Spacecraft:

The TechSat/Gurwin-II satellite is of cubic shape with a size of 445 mm x 445 mm x 445 mm. The platform is three-axis stabilized, using a momentum wheel and three magnetorquers as actuators, and a three-axis magnetometer as attitude sensor. All attitude instruments have a total power consumption of about 3 W. The power consumption for all housekeeping functions is less than 10 W (including transmitters, receivers, on-board computer, and power conditioning. The satellite attitude history, based on the magnetometer telemetry processed both by the onboard and ground station Kalman filters, was statistically analyzed, to summarize the long-term performance of the attitude control system. The analysis made it evident, that throughout the most part of the flight, the magnetic control provided the 3-axis stabilization of the satellite with nadir-pointing accuracy of about 2º-2.5º.

The solar cells employ thin-film photovoltaic cell technology (developed in Russia); they are mounted on four sides of the six outer aluminum panels. A NiCd battery is provided for eclipse operations. The fifth panel, pointing toward Earth, includes antennas, the retroreflector, the UV spectro radiometer (OM-2) and an imaging camera. When 3-axis stabilized, the satellite would have its sixth panel unlit; it is not exposed to the sun and therefore does not include any solar cells. The structure plays a major role in the thermal design. The heat flows from the solar illuminated panels to all parts of the structure that are used as radiators. The S/C mass is 48 kg, the total payload mass is 6.6 kg, power = 20 W. The S/C design life is one year. ⁴⁾

Figure 1: The TechSat/Gurwin-II satellite and its components (image credit: ASRI/Technion)

Launch: The Earth-pointing satellite was launched as a secondary payload on July 10, 1998. A Russian Zenit-2 vehicle carried the Resurs-O1-4 satellite (primary payload) and five piggyback payloads (TMSAT, TechSat/Gurwin-II, FASat-Bravo, and SAFIR-2) from the Baikonur Cosmodrome into orbit.

RF communications: Communication is realized via receive and transmit antennas. Three uplinks in the 145 MHz VHF band (2 m), three uplinks in the 1270 MHz L-band (23 cm), and one downlink in the 435 MHz UHF-band (70 cm). Data is transmitted at two available rates: 1200 bit/s and 9600 bit/s. At 1200 bit/s the carrier modulation is BPSK (downlink) and FM (uplink). At 9600 bit/s the carrier modulation is FM (downlink & uplink).

Satellite operations are conducted from a ground station at Technion. The S/C features a digital store and forward multi-user system, compatible with existing store and forward facilities already in use on microsatellites (use by the international amateur radio electronic community). ^{5) 6)}

Figure 2: Illustration of the TechSat/Gurwin-II spacecraft (image credit: ASRI/Technion)

Orbit: Sun-synchronous circular orbit, altitude = 820 km, inclination = 98.8º, period =101 min, local time of equator crossing is at 10 AM in descending node.

Mission status: TechSat/Gurwin-II is operating nominally as of 2007 (9 years after launch - surpassing many times its design life). Lately, the satellite is providing services in two interchangeable modes of operation: 1) amateur service, or 2) space experiments, over the TM downlink. ^{7) 8)}

The mission duration and design flexibility allowed for more experiments to be conducted than originally planned. Additional investigations of significance were testing of the new attitude control algorithms and evaluation of the solar panel deterioration.

ACS (Attitude Control System): For most of the time the TechSat attitude control system operated in a standard, 3-axis-stabilization mode. The checks of the satellite's attitude have been done periodically, with the latest one in December 2006.

An experiment was staged onboard the TechSat of a purely magnetic attitude control, able to provide 3-axis stabilization, given a magnetometer as the only sensor, and magnetic torquers as the only actuators, with two different solutions to the problem, namely `Linear Quadratic Regulator' and `No Wheel' controllers, developed, respectively, at Cornell University (Ithaca, NY, USA) and at ASRI/Technion. ^{9) 10)}

• In late 2005, after more than seven years in space, TechSat/Gurwin-II is still working and providing valuable information, showing no significant degradation. ¹¹⁾

• One of the TechSat mission goals was to carry out long-term experiments, and to compare the actual in-flight parameters of the onboard equipment with those at the design stage. power, attitude control, communication, computer, and thermal subsystems performed stably and provided the satellite's normal functioning in any of its possible operational modes. No substantial failures or malfunctions were noticed either in the housekeeping of the whole bus, or in its separate modules.

• All subsystems of TechSat were tested under various operational conditions. Flight experiments with ERIP were carried out only periodically for short durations. The XDEX instrument was stopped because of no correct calibration of the detector. For SUPEX, the tests were finished after 2 years because of cooler degradation. OM-2 failed after 10 months of operations.

• By 2004, the digital store&forward multi-user system on TechSat was able to provide its services to the global amateur radio community. In the initial phase of the mission, there were some difficulties with the amateur BBS (Bulletin Board System) program. Considerable effort was invested to bring about the necessary changes in the satellite software to enable operation of the satellite by the radio amateur community.

Table 1: Duration of TechSat subsystem operations in space

Sensor complement:

OM-2 (Ozone Meter-2). Objective: Measurement of the ozone concentration in the Earth's atmosphere (vertical distribution of ozone and the total ozone amount in the nadir direction). Study of latitudinal, seasonal and planetary-scale ozone variability. OM-2 is a UV spectroradiometer with a total mass of 1.80 kg (optical head of 1.55 kg and the microcontroller of 0.25 kg), "a tiny SBUV instrument," measuring in the spectral range of 252 - 340 nm. The instrument uses a filter-wheel photometer that measures the SBUV (Solar Backscattered UV) radiance.

The optical sensor head consists of the following subsystems: a single lens objective, a filter wheel, a set of apertures, a baffle, and a photomultiplier detector (Rb₂Te, 26 mm in diameter). The mounted objective has an aperture of 10 cm in diameter and an effective focal length of 80 mm. OM-2 conducts sequential measurements of SBUV radiation in seven wavelengths (each of 1 nm width), the sampling time is 30 ms. A total measurement sequence lasts 5 s. The total footprint size is 70 km (along-track) x 170 km (cross-track), the corresponding FOV is 3º x 12º. The data volume of one day of contiguous measurements is about 50 kByte after data compression. ^{12) 13)}

Table 2: OM-2 parameter definition

ERIP (Earth Remote-Sensing Imaging Package). Objective: Collection of snapshot panchromatic imagery in the vicinity of ground stations. The instrument consists of a CCD video camera unit (VCU) and an Image Processing and Control card (IPC). ERIP uses a Nikon objective, f= 135 mm, and a PUL NiX CCD TM-720. On command, a video image is captured, digitized, compressed and stored in an image buffer for later transmission. The compressed image data is transferred to the OBC (On Board Computer) and transmitted to the ground station, where the captured image is decompressed and displayed. Each image contains about 250 kByte of data, or about 60 kByte after compression.

Table 3: Instrument parameters of ERIP

SOREQ (Single Event Monitor for Detecting Protons and Heavy Ions in Space). Objective: measurement of the solar charged particle environment (protons and heavy particles) for a better understanding of the changing radiation environment (interest in the hazardous nature of the environment to long-term effects on S/C electronic systems). SOREQ measures SEU (Single Event Upset) and SEL (Single Event Latch-up) occurrences in six HM65162 (2k x 8 SRAM) devices. [Note: single-event latch-ups manifest themselves in a sudden increase of power consumption.] The devices are arranged in two groups, allowing for the examination of chips from different date codes having different sensitivities. The TechSat computer initializes, twice per minute, a read-write circle (about 1 ms in duration) and serially reads the shift register. This enables mapping of events with a resolution of about 2º. The instrument mass is 0.23 kg, its power consumption is < 30 micro W. ¹⁴⁾

SUPEX (Superconductivity Experiment). Objective: Conduction of a series of operational tests of the instrument in flight - consideration for later use of power generation. The superconducting device is based on thin film technology (developed at the Physics Department of Technion) made of Y₁Ba₂Cu₃O₇. It uses superconducting filters to separate the channels. The experimental assembly on-board TechSat comprises the HTS (High Temperature Superconductor) device, a cryocooler and electronic instrumentation. An automatic electronic technique is used to measure the transition temperature and critical current in the superconducting state. Cyclic measurements (about 15 minutes) are conducted once a week. The device is mounted into an insulating housing, and is thermally attached to a K-508 miniature cryocooler of Ricor, Ltd., Kibbutz Ein-Harod Ihud, Israel. The overall instrument mass is 0.63 kg, the power consumption is 12 W. The nominal cooling power is 0.5 W at 77 K. ^{15) 16)}

XDEX (X-Ray Detector Experiment). Objective: 1) test of high performance, sensitive X-ray detectors (CdZnTe) with high energy resolution; 2) test of a focal plane array where photon counting and signal processing can be performed and stored; and 3) test of degradation of the detectors/focal plane array assembly in a high-energy particle environment. The instrument consists of solid-state detectors, a sensitive preamplifier, a microcontroller and memory. The experiment is a step towards development of an X-ray telescope based on CdZnTe detectors. The instrument mass is 1.6 kg.

SLRRE (Satellite Laser Ranging Retroreflector Experiment). Objective: High-precision laser ranging measurements from the ground for orbit determination (5-10 cm range). SLRRE is a passive on-board experiment consisting of an array of laser retroreflectors, corner-cube mounted on the Earth-viewing panel (panel 5) of the microsatellite. The SLRRE mass is 0.65 kg.

2) M. Guelman, F. Ortenberg, A. Shiryaev, R. Waller, "Microsatellites for Science and Technology: Gurwin-TechSat in-flight Experiments Results," Proceedings of the 3rd International Symposium of IAA, Berlin, April 2-6, 2001, pp. 67-70

3) http://www.amsat.org/amsat-new/satellites/satInfo.php?satID=14&retURL=/satellites/status.php

4) Information provided by Roni Waller and Fred Ortenberg of ASRI/Technion.

5) http://www.technion.ac.il/ASRI/techsat/

6) http://www.technion.ac.il/ASRI/

7) Information provided by Fred Ortenberg of Technion, Haifa, Israel

8) M. Guelman, F. Ortenberg, A. Shiryaev, R. Waller, "Gurwin-TechSat Microsatellite Long-Term Mission," Proceedings of the 6th IAA Symposium on Small Satellites for Earth Observation, Berlin, Germany, April 23 - 26, 2007

9) M. Guelman, R. Waller, A. Shiryaev, M. Psiaki, "Design and Testing of Magnetic Controllers for Satellite Stabilization," Acta Astronautica, Vol. 56, 2005, pp.231-239

10) http://www.technion.ac.il/ASRI/projects/psiaki/Psiaki.html

11) M. Guelman, F. Ortenberg, A. Shiryaev, R. Waller, "Seven-year Flight Testing of the Gurwin-Techsat Microsatellite," 19th Annual AIAA/USU Conference on Small Satellites, Utah, August 2005, SSC05-V-4

12) A. Devir, F. Ortenberg, ""Space-based small ultraviolet photometer for the measurement of the ozone concentration in the Earth's atmosphere," Proceedings of SPIE, Vol. 3110, 1997, pp. 161-170

13) M. Guelman, F. Ortenberg, B. Wolfson, "Flight Tests of the novel TechSat Satellite Ozone Meter: Algorithms and Measurement Processing Results," Proceedings of the 40th Israel Annual Conference of Aerospace Sciences, 2000, pp. 299-310

14) J. Barak, E. Adler, M. Murat, et al., " The SOREQ Radiation Monitor for Detecting Protons and Heavy Ions in Space and its Preliminary Flights Data on Gurwin II TechSat," Proceedings of the 14th AMSAT-UK Colloquium Space-Communication-99, University of Surrey, July 23-25, 1999, pp. 2-9

15) E. Polturak, G. Koren, et al., "Design and Performance of a Space Based High Temperature Superconductivity Experiment," Proceedings of the 14th AMSAT-UK Colloquium Space-Communication-99, University of Surrey, July 23-25, 1999, pp. 10-14

16) E. Polturak, G. Koren, M. Ayalon, "Space Based High Temperature Superconductivity Experiment," Proceedings of the 40th Israel Annual Conference of Aerospace Sciences, 2000