[amsat-bb] High LEO for cubesat?

[Bruce Robertson]

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