[amsat-bb] SSTV Clarification

Frank H. Bauer ka3hdo at comcast.net
Thu Apr 2 13:58:33 PDT 2009


I wanted to clarify some statements made by Miles, based on where ARISS was
when I stepped down.  

In his e-mail he states:

SSTV Status:

We have two SSTV systems on ISS. One is the Kenwood VCH1 sstv microphone.
This is the system which th4 crew has been using the most.  The system only
runs on AA batteries at this time due to flight safety limitations.

The second system is the Marex Software system called SpaceCam1.  This
system will run manually for fully automatic.  The software system has not
been used much because of a problem with the VOX cable that goes to the D700
transceiver.  When the Vox cable is used the radio sticks in the
Transmitting mode until 3-minute watchdog timer expires.  ARISS has tried
two different cables with the same results.  The Vox gets its power from the
D700 and it appears the dc power has too much RF and is causing Vox circuit
to keep the radio stuck transmitting.

Marex is proposing a completely different VOC using that has been tested

The ARISS-provided VC-H1 currently does run on AA batteries.  The use of AA
batteries was not due to flight safety limitations at all.  Given the tight
schedule that we had for Richard Garriott's flight and the need to fly a
hardware-based SSTV system, we concentrated on certifying the VC-H1 with the
understanding that there was a surplus of AA batteries on ISS.  On ISS,
batteries for critical functions are taken out of service and replaced
before they are fully used up.  These partially-used batteries can easily be
used for non-critical devices like the VC-H1. The ARISS team is working on a
battery eliminator (power supply) for the VC-H1 that will be flown at a
later date.

There are 3 SSTV systems on board, one hardware system (VC-H1) and two
software-based systems, MMSSTV and SpaceCam.  The primary rationale for
making the VC-H1 prime is that the ARISS team gets very limited use (read
as: almost no use) of an on-board computer.  So the SSTV operations over the
past few years was nearly zero.  Only when the VC-H1 was introduced in
October 2008 did SSTV on ISS really take off.  Some self-interference issues
have been observed on the software-based system that were not observed on
the ground prior to flight. As of right now, it is unclear what is causing
this issue.   The ARISS team has not had an opportunity to fully debug this
issue on-orbit.  (It is very hard to get a computer and the crew time at the
same time)  So I would not speculate what the issue is.  Also, there are
some subtle differences in the radio system on-board ISS as compared to the
ground-based equivalents.

Any proposals for new amateur radio hardware and software systems need to be
approved by the ARISS project selection and use committee.  They then need
to be presented to the space agencies.  The space agencies then determine if
there is volume/power/mass available on-board for the system and give the
ARISS team a yes/no answer as to whether they are willing to fly the
equipment.  The proposal then needs to get a final concurence from the ARISS
international delegates to move forward as an official project.  

Miles' proposal (above) has not gone through that process yet.

I hope this clarifies.

73,  Frank Bauer, KA3HDO 

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