[amsat-bb] Re: Phase 3

[Daniel Schultz]

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