[URC] Suit Sat

[David Basden]

On Mon, Jan 30, 2006 at 11:07:49AM +0800, Alwyn Lloyd wrote:
> 
> http://science.nasa.gov/headlines/y2006/26jan_suitsat.htm?list202976
> 
> http://suitsat.org/
> 
> we have a few days.. a
> 
> anyone interested in trying to get something together?

Definately!

The only problem is that Meryki is due in something like 18 hours,
so there's a slight possiblity i'll be busy.

I've got an FM-92 (with a custom ROM so you can set it's VCO directly)
that works well on 2 meters. I've also got a hand-held scanner that
will receive FM in the 2m band if anyone wants to borrow it. The
only other 2M gear I have is a crystal driven rig, and I don't think
it's going to be easy to get hold of a crystal for 145.990MHz in a
couple of days.

If you're interested, and haven't done any LEO satellite listening
before, check out www.amsat.org (good for operational information
on the satelites, and pretty much -the- organisation for amateur
satellite stuff) and www.heavens-above.com (excellent source of
pass times for not only ISS and amsats, but also lots of other
stuff).

Stuff you'll probably want to keep in mind:

	- The polarization[0] of the radio wave 'tumbles' when 
	passing through the atmosphere, and changes from second
	to second. With the wrong polarization/orientation of
	your antenna, you can get a loss of something like 20dB[1].
	One way of dealing with this is to physically hold your
	receiving antenna and (with 2m) wave it around slowly
	like a light sabre[2].

	- Passes for something in a low orbit can be quite fast.
	  Normally only a few minutes, with the object moving a
	  large distance across the sky. A watch accurate to the
	  nearest second, and a laptop with tracking software 
	  makes life a lot easier here. Also a compass if you don't
	  have a pretty good idea where South is. 
	
	- Although it's not as bad at 2m as it is as 70cm, you'll
	  probably have to take into account the doppler effect
	  on the signal. Most satellite tracking software will
	  calculate the frequency difference for you on the fly.
	
	- To use satellite tracking software, you need up-to-date
	  Kepplarian elements for the orbits that you want to track.
	  These are realeased pretty much daily by NASA, but if they're
	  just shoving this thing out the door of the ISS, it might
	  be interesting trying to get hold of accurate ones for
	  the SuitSat ahead of time. They will need to be accurate
	  or the pass information will by out, sometimes by a lot 
	  (i.e. you're pointing an antenna at entirely the wrong
	  part of the sky, 2 hours before or after the pass).

	- Much of the time of a pass is going to be <30' or so
	  off the horizon. Nearby trees and buildings are going
	  to get in the way. Football fields are good, but councils
	  can get upset if you drive your cars on them. The
	  football fields near Steves are good and flat, and also
	  surrounded by the river (which aparrently makes a good
	  ground plane).
	
	- Passes directly overhead are the best to use if you can
	  get them. They are longer, the doppler change is slower,
	  they are easier to track, and the object comes *much*
	  closer. Buildings don't get in the way as much.

	- SSTV stuff has lots of different standards. On the bright
	  side, there is lots of software, and it's quite easy to play
	  with even without using radios. Use a tape recorder, or 
	  mobile phones or something to get a feel for it beforehand.
	  Ben, Bryden and I have gotten it to work over the wackest
	  connections. There is lots of software out there, just make
	  sure that the stuff you use does the mode the SuitSat does,
	  and isn't going to by crippleware.

	- The Amsat people, if given a choice will prefer orbits over
	  North America and Europe. Unless it's in a polar orbit, 
	  Perth might not get that many passes. It might be a good
	  idea to record the audio off any passes you try for in
	  case you mis-time trying to decode it in real-time. It
	  might not work as well later, but might give you a chance
	  to try and do the SSB side of things when you're not
	  juggling everything else.

If anyone is interested in doing this, i'm interested, but quite likely
busy. I'm happy to lend stuff to help (I have a few antennas, feedlines,
connectors etc. as well as the gear above). If you want to practice
there are also am-sats already up there that operatate on 2M FM. Well,
at least one.

David
	  
[0] The axis that the electrical component of the E/M wave is travelling
    along. CB etc is vertically polarised, so you put the antennas
    vertically. TV is horizontally polarised, so you put antennas
    horizontally. There is also circular polarization.
[1] http://www.qsl.net/n9zia/cir_pol_rpt.html
[2] This has led to concerned citizens calling the police previously.
    Some people are just too easily spooked.