SEDSAT-2 Payload Design Notes 20070422
From SEDSWiki
SEDSAT2: Payload Study –
Contents |
Radio emission detection
This idea has NOT been recommended by the Payload team. Reason: The miniscule aerial we could bring would not add anything to observations, and we would never pick up anything anyway.
Purpose: To detect radio emissions from deep space. Possibly look for signs of intelligent communications from extra-terrestrial cilvilizations.
Approach
To achieve this it would probably be required to have a parabolic dish mounted somewhere on the cubesat. Potentially one whole side of the cubesat can be utilized as a parabolic antennea. However effective diameter would only be a maximum of 0.1m, and this would result in the antenna having a vey low gain, as the gain of the parabolic antenna increases proportionally to the effective surface area. We we would also be quite limited in the frequencies we could look at, both in terms of onboard processing(requirements increase with higher frequencies) and because of the physical dimensions of the parabolic dish.
In addition to this we would only point towards specific targets for very small periods of time , due to our orbital speed.
Conclusion
It might be interesting if we had a very specific wavelentgh to look at, but the gain of being outside parts of the atmosphere is negated by our limited reception capabilities. Ground-based radio telescopes would offer a significantly better gain despite the atmoshperic distortion that they are subject to.
Radiation detection
This idea has been recommended by the Payload team as a possible secondary payload for SEDSAT-2. Reason: Radiation detection can be done on a very limited resource budget, and would provide data that might be useful to others. Pro: Modest requirements. Con: Is an entire, extra payload.
Purpose: To measure the radiation exposure of the spacecraft.
Approach
Our idea is to use a semiconductor component to measure the radiation exposure the spacecraft is subjected to. When the PN junction of the device is exposed to ionizing radiation, it will in turn be imbued with an additional charge. This will change the properties of the PN junction and so it will affect the threshold voltage of the device. By measuring the change in this voltage we can determine the amount of ionizing radiation which the spacecraft is subjected to.
It might be possible to accomplish this using a realtivly simple semiconductor device, such as a transistor or a diode. This would make this a very cheap venture as it would be require very cheap components. We should be able to do the signal processing in an eventual payload controller, so it would not add a lot of complexity to our system. The footprint of these components should in addition be small, so it would not greatly compromize our main imaging objective. This would however need to be researched further to give any estimate on the accuracy we can hope to achieve.
There are however premade commcerical circuits available. These are based on a modified P-type MOSFET and are known as RADFETs. These are available in ready-to-use DIL packages and can be configured to detect radiation levels as low as the millirad range.The cost of one these devices is around 1000USD(minimum order)
Since these are based on semiconductor devices there might be a requirement for active temperature compensiation based on the ambient temperature in the cube. We do not see this a major problem.
Conclusion
This secondary concept should be possible to implement without any major impacts on the primary imaging payload, and does not add a lot to the complexity of the payload system, as long as there is a minimum surplus of power/space to implement the detector circuit. This data might be usefull both to future cubesat missions and to sucessor missions to the SEDSat-2.
ISS beacons
This idea has NOT been recommended by the Payload team. Reason: Added complexity and resource requirements do not seem worthwile considered the (lack of) benefit.
Purpose
Listening to the HAM radio beacons on the ISS. Possibly sending messages to HAM radio operators using the ISS.
Approach
The ISS operates a HAM radio digital repeater(digipeater) for eduactional/public interest purposes. We could potentially either contact the ISS, send a message to be repeated or just listen to the traffic on the ISS channel. This would require an antenna tuned to 145.99 for uplink and 145.80 on the downlink pointed in the general direction of the ISS. For more info see thee ARISS system
Conclusion
Might be interesting from a PR point of view. Our orbit would however have to correspond to the ISS orbit in such a way that such communication is possible.
