Much of the debate on the board here arises from our common desire to see the launching of satellites with a larger footprint.
A fine analysis of one approach to this is the video and ppt of David, G0MRF, discussing his ideas for a bird that reaches the financial sweet spot, between LEO and HEO, a 'middle earth orbit, or MEO.
http://www.batc.tv/vod/AMSAT-UK_MEO.flv and http://www.uk.amsat.org/2009/2c_Bowman-MEO.pdf
He points out that a bird at 7000 km altitude is beyond the inner radiation belt and yet has a pass duration of 90 minutes and a footprint diameter of over 13,000 km.
Here's the great thing, though: it is possible to do an orbital transfer from LEO to MEO.
David points out some difficulties, though: VLSI electronics components are not as tolerant of radiation than others, and the attitude control of the second burn might be tricky.
Another approach (also gleaned from David's rich harvest), which would be even more simple, and perhaps within the realm of a 3x cubesat, would be to raise a typical cubesat from its 650km altitude to the 1400km or so that has made AO-7 so popular.
An elliptical orbit, requiring only one 'burn' might even be seen as an advantage. As David says, it would allow for the bird eventually to be deorbited, but it would also mean that periodically the bird could be used with very simple antennas for local communications, and on other occasions would require a better groundstation affording a wider footprint.Using DH2VA's propulsion spreasheet, I see that delta_v for one half of a Hohmann Transfer Orbit from 650 to 1500 is 212 m/sec ish. Since my understanding of the HTO is that it comprises two burns, one creating an ellipse, the second turning that ellipse into a circle, I've assumed that that number is about right for an elliptical orbit with the final altitude.
Using David's http://g0mrf.com/MEOSAT.htm, I gather that the Isp of a cold-gas thruster is about 60 sec, which should be enough to get the necessary delta_v above.
And then there's the transponder. With William PE1RAH's transponder board in hand, and the work about to be done on FUNCUBE (not to mention Delfi C3 and NE3T), we should have a very good idea of what can be achieved with linear transponders in small LEO vessels. With one or two of the cubes dedicated to thrust, we'd have lots of solar panel area. What about a software transponder vs. hardware transponder shootout with respect to volume and power requirements? Could a software transponder include the modulation/demod of a suitable digital mode, allowing less elaborate stations to work the bird at apogee?
Anyway, that's the sort of fun one can have with the materials that David has provided.
From a promotional standpoint, a project that aims to provide the
functionality of AO-7 could highlight the remarkable success of that bird and at the same time point out the new opportunities and challenges in space.
73, Bruce VE9QRP