Here are a couple of code files that provide a realtime update of balloon position on google earth etc.

The 1st KML file is the outer shell kml that you launch from google earth - it just tells google earth to read the 2nd file (every10.kml) once every 10 seconds.

The 2nd KML file (every10.kml) contains kml to draw a balloon track and the “launch” and “current position” placemarks. This whole file is completly re-written every time the the balloon position needs updating. The google earth display will be updated upto 10 seconds later. Typically this file would be created and updated by code parsing GPS data being sent on a radio downlink.

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.1">
<Document>
  <NetworkLink>
    <Link>
      <href>every10.kml</href>
      <refreshMode>onInterval</refreshMode>
	<refreshInterval>10</refreshInterval>
    </Link>
  </NetworkLink>
</Document>
</kml>

every10.kml:-

<?xml version="1.0" encoding="UTF-8"?>
<kml xmlns="http://earth.google.com/kml/2.1">
<Document>
    <Style id="track">
      <LineStyle>
        <color>fff010c0</color>
      </LineStyle>
      <PolyStyle>
        <color>3fc00880</color>
      </PolyStyle>
    </Style>

    <Style id="place">
      <IconStyle>
        <scale>1</scale>
        <Icon>
          <href>http://weather.uwyo.edu/icons/purple.gif</href>
        </Icon>
      </IconStyle>
    </Style>

      <Placemark>
        <name>Launch</name>
        <styleUrl>#place</styleUrl>
        <description>Launch location was ... at ...</description>
        <Point>
          <altitudeMode>absolute</altitudeMode>
          <coordinates>-0.092096,52.250872,55</coordinates>
       </Point>
      </Placemark>

    <Placemark>
      <name>Flight Path</name>
      <styleUrl>#track</styleUrl>
      <LineString>
        <extrude>1</extrude>
        <altitudeMode>absolute</altitudeMode>
        <coordinates>
  -0.092096, 52.250872,   55
  -0.089721, 52.252995,  166
  -0.082192, 52.258184,  379
  -0.072153, 52.263721,  597
  -0.059924, 52.269104,  819
  -0.030587, 52.277540, 1279
   0.002241, 52.283403, 1761
   0.035656, 52.288259, 2269
   0.069353, 52.292391, 2803
   0.102276, 52.297056, 3368
   0.132938, 52.303864, 3970
        </coordinates> 
     </LineString>
    </Placemark>

      <Placemark>
        <name>Position Now</name>
        <styleUrl>#place</styleUrl>
        <description>Current Position is ... at ...</description>
        <Point>
          <altitudeMode>absolute</altitudeMode>
          <coordinates>   0.132938, 52.303864, 3970
          </coordinates>
        </Point>
      </Placemark>

  </Document>
</kml>