The development of a small satellite laboratory should not be regarded as a single once off project. There are many stages in its development that are very suited for student engineering projects. It should be regarded as providing both educational and inspirational 'hands-on' opportunities as well as a product that can then be used to provide further science and engineering student opportunites.
Assembling even a basic satellite tracking station should be given a high priority as the many orbiting satellites transmitting data can help define the paths staff and students may wish to persue, as well as generate the excitement of involvement with actual space projects.
Various other aspects of laboratory development can be undertaken in accordance with personal interest, student numbers and available finance.
There are a few satellites that can be received with omnidirectional antennae, especially those that transmit around a frequency of 145 MHz in the two metre amateur band frequency allocation. As the frequency is raised an omnidirectional antenna typically does not have sufficient collecting area to produce an adequate signal to noise ratio, and so a higher gain, narrow beamwidth antenna is required. This then necessitates that such an antenna is moved to track the satellite as it moves across the sky.
A majority of smallsats use both the two metre (145-145 MHz) and the seventy centimetre (435-438 MHz) amateur bands for communication and control purposes. Two metres may be used for the uplink frequency and seventy centimetres for the downlink frequency, or vice versa. A complete satellite tracking station for such satellites would require a transceiver (TRX) for both the 2m and 70cm bands. These can both receive and transmit on the bands in question. Many commercial models are available to fulfill these functions.
Two separate antennae are required, one for each band. To track a moving satellite whose attitude may change as it moves across the sky, circular polarisation is generally used. This may be achieved by using crossed yagis, or possibly a helix type antenna. The antennae must be mounted on a combination of two rotators, one employed for azimuth movement and the other for motion in elevation. These antennae need to be moved by an antenna mount controller which is driven by a computer that calculates a satellite empheris (a table of position versus time).
A controller and modem is required to drive the transceivers. This will both control the transmit/receive functions, and for transmission will feed the transceiver with an appropriate modulation code. For reception, the modem needs to decode the receiver output into a form that can be input to a computer. A Terminal Node Controller (TNC) may be used to handle many of the control and modem functions, and/or software may be used to handle the many data formats that satellites currently used.
Two computers are probably ideal, one to handle transceiver and antenna control, and a second to be primarily devoted to data decoding and formatting, storage, analysis and display. A single computer may also be used to perform all these functions.
A complete high end tracking station may be developed in stages as finances permit. A single frequency receiver connected to an omnidirectional antenna may be the place to start. Low cost software defined radio 'dongles' can provide an easy entry point, but as their limitations are encountered (typically high susceptibility to radio frequency interference), they can gradually be replaced with hardware dedicated to specific amateur bands.
ELECTRONICS TEST EQUIPMENT
Equipment for the electronics work bench should include:
An anechoic chamber may need to be used to test for electromagnetic compatibility (EMC) between the various subsystems on the satellite, and/or to perform interference free calibration of the satellite RF systems.
There are several environmental tests that satellites must undergo and pass before they are launched into space. These will depend on the launch provider and the method of deployment into the space environment (eg from the International Space Station (ISS), etc). The final tests will need to be conducted by an accredited laboratory. In Australia this might be the Advanced Instrumentation and Technology Centre (AITC) of the Australian National University (ANU) at Mount Stromlo in Canberra.
However, this should not preclude local testing to the extent possible. The development of such testing equipment can provide a number of very worthwhile student engineering projects in itself. A vibration table, a vacuum chamber and thermal cycling facility are possible projects. Such projects should also include the development of calibration instruments or mechanisms.
Vibration testing is to ensure that the satellite can withstand the noise and vibration encountered during the launch phase of the mission. Research into the required frequencies and accelerations would set the parameter goals for the instrument. A cheap vibration table might be based around one or more sub-woofer drivers.
The space environment presents its own unique challenges for satellite design. Vacuum, thermal and radiation tolerance are all areas that might be investigation. A small vacuum chamber could be employed to examine component outgassing - the ISS has restrictions on the amount of outgassing permitted. Heat lamps could be added for bakeout purpose and thermal cycle testing. The external surfaces of the ISS can easily vary between -100 and +100 oC each orbit of 90 minutes period. Providing the high temperatures is probably not a problem, but the low temperatures may be an engineering challenge. More advanced additions might include special lamps to simulate the intense solar UV radiation that will be experienced in space.
Such environmental testing equipment can also be used in scientific investigations of different materials and sub-systems that might be used in the space environment. Search the literature on "material degradation in space" for ideas along this line.
There are many opportunities in the development of a small satellite laboratory. Engineering and science projects can serve to reduce constructional costs as well as provide valuable student experiences and training toward various degrees.
Flying a satellite to orbit involves many skills and disciplines including power engineering, attitude control, environmental design and management, communication, project design and management, data analysis and promotion, fund raising, networking and coordination, and actively seeking launch opportunities.
While waiting for a launch opportunity it may well be worthwhile considering a balloon flight to practice tracking and recovery, and to experience some of the problems that will occur in an actual space launch - to iron out real-world problems that always occur outside the laboratory environment.
Australian Space Academy