Ask Slashdot: How Would You Build a Microsatellite? 117
Dishwasha writes "A fellow co-worker of mine turned me on to CubeSat; apparently there are commercial space companies that will launch CubeSat systems from their payload for a modest fee. Is anybody in the /. community involved in amateur microsatellite systems? How would I go about getting involved at an amateur level? Are there any amateur user groups and meetups I can join? I have limited background in all the prerequisites but am eager to learn even if it takes a lifetime. Any links to design and engineering of satellites would be appreciated."
Re:Building is easy, launching is hard (Score:5, Interesting)
One tried and true anti-spin method utilized with CanSats (predecessors to CubeSats, see http://www.arliss.org/ [arliss.org] is to attach a refrigerator magnet to one end of the satellite. The 'sat will flip 180 degrees as it passes over north and south poles, but remains otherwise in stable orientation. Sometimes simple is good :-)
--
A man is rich in direct proportion
to the number of things he can afford
to leave alone.
— Thoreau
Re:Building is easy, launching is hard (Score:5, Interesting)
You can slowly kill the spin by loading the satellite with magnetic torque rods. The rods cause the satellite to orient to the Earth's magnetic field. There are active and passive systems.
For coms that are effective in a spin, a couple of omni whips at right angles should do it. The basic unit is called a 1U Cubesat and it's 10cm x 10cm x 10cm container, but they can have mechanisms to pop out antennas as soon as they get out of the container. Some of the designs I've seen have pop-out arrangements of solar cells so they can have up to 500 cm2 of solar cell area and are made to orbit with them pointed away from the Earth. Cubesats can be stacked several in a launch container. (Like a six-pack.) There are 1U, 2U and 3U designs.
This year's Smallsat Conference is at Utah State University - Logan Utah, August 10 – 15, 2013
Smallsat [smallsat.org]
Re:Building is easy, launching is hard (Score:4, Interesting)
Yeah, you can have omnidirectional antenna coverage for both uplink and downlink. ... This is the preferred method if you can close your link and data budgets because it makes the system vastly simpler and inherently fail safe. ... A secondary directional downlink may be reasonable if you have very high data requirements (e.g. streaming video or ultra high definition imagery)
Most commercial and military satellites have a low-bandwidth omnidirectional uplink and downlink for control. USAF satellites used to have (and may still have) almost a complete separation between the "bus" and "payload" sides, with the "bus" side on omni antennas. At the ground end, the USAF had big steerable dishes at about six tracking stations around the world. The spacecraft was piloted through those. Command and control of most USAF satellites were run from the Blue Cube in Sunnyvale until that operation was moved to Falcon and Vandenberg AFBs.
Once the spacecraft was in the desired orbit and oriented, directional antennas were used by the payload to communicate with the payload user's control center. With directional antennas, smaller ground-side dishes could be used. The big steerable dishes were a scarce resource needed for multiple satellites, so tying them up for payload data like imagery was avoided.
Back in the early 1980s, one of the amateur radio satellites was incorrectly commanded to transmit on its own control receive frequency. This blocked the receiver from receiving further commands. To recover the satellite, the Stanford Dish [wikipedia.org] was used. That 46 meter steerable radio telescope had, left over from old USAF work, a 3MW transmitter. The combination of a huge dish and a high powered transmitter allowed focusing enough power on the satellite to get through to the receiver and tell the satellite to change its transmit frequency. It took two tries (the first time the codes sent were wrong) but on the second try it worked.