Minisat 01


The Minisat 01 was a satellite developed in Spain as means to kickstart its space program. The project started in 1990 and was funded by the both Inter-Ministerial Committee of Space Science and Technology and the Instituto Nacional de Técnica Aeroespacial who was also responsible for the project's management. After some feasibility studies, the satellite entered design phase in 1993. The main objectives of the program were to develop a technology demonstrator in order to test and develop the nation's capabilities to produce and manage spacecraft. To this end, INTA teamed up with private enterprises and universities to acquire funds and resources. Nonetheless, emphasis was also put on keeping the costs to a minimum and to ensure affordability.
The initial program was supposed to involve at least four minisatellites but only Minisat 01 was put into orbit. A second design, the Minisat 02, was developed and tested in 2001 but the mission was canceled and the satellite scrapped by 2002.

Mission

The Minisat 01 was conceived to perform Earth observation on a low orbit in addition to four different scientific experiments:
An alternative payload was devised but not implemented consisting on four additional experiments: GOYA, SIXE, DOPA, XRASE. These experiments would be later projected for the Minisat 02 before the whole project was scrapped.

Body

The satellite was build between CASA, who was in charge of developing the platform, and INTA, who mainly devised the different payload and experiment implementation. A great degree of emphasis was put on keeping cost down so the construction was modular, small and projected to have a service life of 4 to 5 years. The body ended up weighting 195 kg and was shaped like an hexagonal prism with the experiments attacked to the top and bottom faces while the sides mounted 4 deployable AsGa solar panels capable each to fully provide the power needed to run the satellite.
The core contained a NiCd battery and the onboard central computing and processing unit with 32 Mb of RAM, 512 kb of EEPROM, 2.4 MIPS of throughput, 32 MBytes of data storage and multiple redundant cores. A bus connection links the microprocessor to the experiments capable of providing point-to-point interfaces while managing the control subsystem. This was divided in two basic units: the thermal and the kinetic units. The first consisted on insulator coating around the body with both, internal and external, thermistors to measure temperature and active internal heaters around experiments and battery in order to keep the temperature within operational ranges. The kinetic unit ensured the Minisat 01 maintained a favorable position to maximize sunlight incidence on the solar panels in addition to stabilize the spacecraft on its 3 axis. This unit consisted on a combination of 3 torque rods placed orthogonaly to each other and a reaction wheel in the spin plane. Data of the current position of the body was provided by two perpendicularly put sun sensors and two biaxial magnetometers which, working in cooperation, could provide accurate information on the satellite's position up to ±3º of error.
Communication with Earth was maintained using bidirectional RF transmitters operating on the S-band with a downlink speed of 1Mbit/s and a uplink speed of 2 kbit/s.

Launch

The S/C was launched from an American Lockheed L-1011-385-1-15 TriStar registered N140SC with a Pegasus-XL rocket from Gran Canaria Airport in the Canary Islands the 21st of April 1997. It was successfully put on a near-circular close orbit of 585 km of apoapsis and 566 km of periapsis with and inclination of 151º and an orbital period of 96 minutes.
After 5 years of successful operation, the satellite reentered the atmosphere on 14th February 2002.
During its whole service life it was operated by INTA, who monitored the satellite from the Maspalomas Station.

Experiments

EURD

Being the result of the joint efforts of INTA and the University of California, Berkeley, this device was to conduct spectrographic observations of diffuse EUV radiation in the interstellar medium in order to examine the Mesosphere's composition. The focus of these observations were oxygen lines and high energy, high mean life neutrinos whose presence may be indicative of dark matter.
To archive that, the device employed two independent spectrometers equipped with modulable spectral band. This allowed to compare and filter the readings obtained in order to minimize systematic errors caused by the ionizing nature of EUV, thus, ensuring a higher degree of precision. Each spectrometer was about 40x40x13 cm in size and 11 kg in weight with acute grating in order to protect the measuring instruments. Under the grating, the Multi-Channel Plate detectors with wedge and strip encoding are allocated, facing the exterior through a lens which provides them with 26º x 8º FOV and four possible positions. These were: open, shielded, magnesium fluoride filter and aluminum filter.
The device was placed at one end of the satellite, facing anti-sun direction and it was operated continuously during the satellite's life.

CPLM

Developed by the Technical University of Madrid the CPLM was experimentation module created to study the behavior of fluids when allocated inside axis-symmetric bridges under conditions of microgravity. It consisted on a test cell containing the fluid bridges embedded between several optical detectors, which were capable of measuring changes in position and shape of the fluid, and a command unit. This unit was itself built with a motor, able to change the direction of the bridges and to reset the experiment, and an accelerometer which measured the forces acting on the test fluid. The module was allocated inside a cylindrical container which also held the power supply, several temperature and pressure sensors and a back-up memory card.
During its operational run the liquid bridge would be oriented perpendicular to the z-axis and activated for 5 minutes once a week. As a result, the satellite would spin ±0.375 rpm longitudinally as a direct consequence from the accelerations applied at the CPLM.

LEGRI

The LEGRI was developed by an international composed by INTA, the Rutherford Appleton Laboratory, the University of Valencia and the University of Birmingham. The main objective was to build a prototype gamma-ray telescope capable of detecting low energy radiation produced by the dispersion of gamma radiation emitted by celestial bodies such as black holes, binary stars or neutron stars.
The device was to incorporate some cutting-edge technology for its time, such as HgI2 emerging detectors developed by the Centro de Investigaciones Energéticas y Medioambientales capable of providing accurate readings on the operating energy range and a high degree of thermal resistance and a very good efficiency-weight ratio. Originally 100 such detectors where to form the LEGRI sensing sub-unit but the experimental nature of this technology made INTA choose to mix an array of 80 HgI2 20, more conventional and reliable CdZnTe detectors. This decision also allowed to directly compare their performance when working on a 0 g environment and sharing FEE and background noise fluxes. Besides the sensing sub-unit, LEGRI incorporated a filtering unit made of a mechanical collimator supported on a honeycomb tungsten plate which is allocated in front of the detectors, a high voltage power supply needed to feed the device, and a processing unit which manages data and provides continuous attitude readings on the satellite in order to ease image reconstruction while avoiding signal noise.

ETRV

Developed by CASA, the ETRV was a speed regulation mechanism capable of deploying various devices such as solar panels, antennas and proves. It consisted on an electrical motor connected a torsion spring mounted over a gearbox capable of regulating motion and providing a certain degree of stability. To simulate payloads, a small flywheel was added to the end of a deploying arm directly connected to the gearbox. To ensure the correct positioning of the movable arm an electromagnetic Reed switch would measure momentum, gyro angle and rate of the arm providing real-time corrections for the system and allowing a maximum deployment speed of 180º in about 3 minutes.
The time control during the different phases of deployment was ensured by a pyrotechnic nut, responsible for maintaining the system's integrity until the firing of a pyro-kintetic charge which would signal the conditions were met to begin the whole placement process.