Gordonjcp MM0YEQ wrote:
You could conceivably rip the RF board out of a UHF and VHF one and couple
it
with your own CPU and audio board, and have a ~150 gramme mode V/U
transponder
on a standard 10x10 cubesat board. You could use a 10m SDR and a wee DSP
board
like the ones that TI does for a few beer tokens and build Bob Bruniga's crossband PSK transponder. You could do all this for the price of the
buffet
for four and a couple of pints at my local Indian restaurant, and you could
do
it in a weekend.
You can cram a lot of radio into a tiny space these days, and with a
cubesat
you've got a bit of space about the size and weight of a bag of sugar. You could just about tape two big old Motorola GP340s together and fit them in a
2U
launch. There's no excuse.
I agree that you can pack a lot of electronics into small packages these days. I disagree that it is feasible to use commercial radios that were not engineered for space flight. Many student groups have in fact used HT guts for their LEO beepsats but if you want a mission that lasts ten years instead of six months, you need to do some serious engineering.
The reason why Cubesats are too damn small is not about the electronics inside the cube, but the questions you need to ask are:
Can the satellite deploy enough solar cells to generate sufficient electrical power?
can the satellite deploy a large enough antenna to direct a usable signal to users on Earth?
Can you keep that antenna pointed at the Earth, at the same time that you are keeping the solar array pointed at the sun?
Is there sufficient external area on the satellite to radiate waste heat from the electronics?
A Cubesat with a Chinese HT inside and 100 square centimeters of solar cells on all six surfaces can generate one or two watts into a whip antenna, but put one of those in high altitude orbit, 10,000 km from Earth, and only hams with EME class stations will be able to make use of it.
This is the reason why LEO Cubesats are easy and HEO Cubesats are hard.
I appreciate the motivational stories about deaf frogs who don't know what is impossible, but sometimes you do have to pay attention to the ugly laws of physics. That's why someone once defined an Engineer as a "Disciplined Dreamer". One of my favorite New Yorker cartoons was of a motivational speaker standing in front of a room full of people wearing Superman costumes, telling them "Now go out there and fly!". I guess that's the reason why Superman Halloween costumes come with a warning on the box that "wearing this cape will not allow you to fly"...
Dan Schultz N8FGV
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Daniel Schultz