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3-axis?




I knew if I waited a bit, someone would address most of the issues, and Jon 
(NA9D) has done a good job.  Thank you.  I haven't dealt with this for a 
while because there has been nothing tangible to report.  As I think I 
discussed a while back, there is a method outlined in principle to take us 
to 3-axis such that, if everything worked properly, we could go into 3-axis 
without the panels deployed and test things before deploying the 
panels.  If we were not satisfied we could, in principle, go back to spin 
mode without deploying the panels.  However, all the issues (and software) 
have not been resolved, bits of critical software have not been tested in 
flight, and the command team feels absolutely no rush to pursue this for 
many of the reasons Jon outlined.  There definitely is concern about 
disrupting our only currently functional HEO satellite. There is a "pucker 
factor" involved, but these come with the territory.  There is also a huge 
time commitment to close, real-time scrutiny of telemetry, re-learning 
control, etc.  We had hoped to pursue some of the testing over the winter, 
but two command stations had to be off the air for a protracted period and 
this raised concerns about adequate coverage in the event of a problem.  In 
addition, there is a considerable push involved in the planning of Eagle, 
P3E, and P5 with regard to a new IHU, software development, etc.  This 
effort is time critical for the development of these new satellites, and 
this is taking up time that might otherwise be devoted to 3-axis.

All this is not to say that 3-axis won't happen, but that we do not feel 
pressured to pursue it until the time is right.  The first critical piece 
of software involved in magnetorque control definitely needs to be 
tested.  This should be safe to do and will undoubtedly be pursued when the 
time is right.  This will not involve getting out of spin mode, only 
slowing down the spin rate to verify that we can still control attitude and 
counteract the ME.  As a side benefit, this should also allow for better 
pictures with the SCOPE cameras (decreased blur).  If this works, then the 
issue of 3-axis will remain open.  If we cannot counteract the ME at the 
slower spin rate, then the issue will be closed once and for all.

Perhaps the strongest argument for pursuing 3-axis is that the spacecraft 
was designed for this mode, and a lot of effort went into the development 
of the momentum wheels and 3-axis sensors.  Proof of concept would be 
valuable for future missions. There would be some end-user benefits, to be 
sure, but not to the degree realized if we had achieved our desired 
inclination and had more functional transmitters.  It is important to 
understand that 3-axis would NOT eliminate the seasonal poor solar angle 
problem that we experience.




-- 
  ________________________________________________________________________
  Stacey E. Mills, W4SM    WWW:    http://www.cstone.net/~w4sm/ham1.html
    Charlottesville, VA     PGP key: http://www.cstone.net/~w4sm/key
  ________________________________________________________________________ 

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