[amsat-bb] $50sat update

[Howie DeFelice]

The following status of $50sat/MO-76, one of the first Pocketqubes, was recently posted by Michael Kirkhart,KD8QBA on the 50dollarsat Yahoo group. Here is an excerpt:
                17 Months in Space, Still Working, and How Long Will a $10 Camera Battery last        
        
      
       
    
   
      
        Sat Apr 25, 2015 11:56 am        (PDT)        . Posted by:      

      
        
        
                 michael.kirkhart at att.net         
        
      
    
   
        
             Tuesday, April 21, 2015 marked the 17 month anniversary of 
the launch of $50SAT/MO-76/Eagle-2, and believe or not, it is still 
operating.  Unfortunately, the battery capacity has degraded to the 
point where the satellite spends a significant amount of time with the 
battery voltage below the 3300 mV minimum required for enabling the 
transmitter.  As a result, those of us who live in the northern 
hemisphere no longer hear any transmissions during the evening passes, 
and for now, rarely hear any during the daytime passes as well.  The 
last telemetry packet I captured here in EN82 land was April 21, and the
 last one which was error-free on April 10.  Fortunately, I have been 
able hear it operate over Anton's (ZR6AIC) WebSDR station in South 
Africa during the evening passes (which occur between 4:00 and 6:00 PM 
Eastern Daylight Time), and occasionally am able to capture error-free 
telemetry packets.  The last one available is from April 24 at 21:25 
UTC.





This situation was fully expected; when looking at the battery voltage 
chart (which, along with all the other telemetry, is available from our 
Dropbox at https://www.dropbox.com/sh/l3919wtfiywk2gf/AABRl4iM5BFqVAcLQGSmdsVga/Telemetry-analysis/Current-Telemetry),
 the readings took a large drop sometime after February 12.  Given this 
was a $10 camera battery that had gone through over 6,000 orbits, each 
with temperature swings of -30 degrees C to +30 degrees C, it is 
surprising it has lasted this long!  At this point, it is starting to 
behave more like a large capacitor than a battery.

As we get closer to summer here in the northern hemisphere (and after this winter, it cannot come soon enough), $50SAT/MO-76/Eagle-2
 will spend more time in the sun before it makes each pass; this means 
it will be warm enough to enable solar power sooner in the pass, and 
makes it more likely it we will be able to hear it transmit before it 
disappears over the southern horizon.  Those of you who live in the 
southern hemisphere, however, should still be able to hear it during 
both daytime and evening passes.  If you could, we would certainly 
appreciate any telemetry you could gather and post.





The orbit continues to decay at an average rate of about 1.5 km/week; 
apogee is just below 570 km at 569.8 km, and perigee is at 538.2 km.  
Someday, I will attempt to determine when it might actually de-orbit.  
If any of you have access to STK or some other fancy software which 
might be able to do a de-orbit prediction, please feel free to run a 
simulation and let us all know.  Some basic parameters you might need 
are as follows:





TLEs as of 2015-04-24, 23:53:15 UTC:


EAGLE 2                 


1 39436U 13066W   15114.82864817  .00033340  00000-0  23789-2 0  9991


2 39436  97.7463 190.7550 0022811 281.2509  78.6152 15.04244039 77466





Using these, the following can be computed:


Semi-major axis =  5743.7488705249 km


Apogee = 569.7766621696 km


Perigee = 538.1516552847





Average cross-sectional area = 0.014252 m^2


Mass = 210 g


Area/mass ratio = 0.06787 m^2/kg





In the meantime, I will continue to update the Dropbox with any new 
telemetry gathered.  Please keep it coming, even if it has errors or is 
incomplete.  At this point, we are happy to simply know that it is still
 operating.