[FPSPACE] How come ISS keeps 'gaining' altitude?

[James Oberg]

After the first 'gain' on Mar 29, I asked JSC PAO and they said
there had been no maneuvers, nothing to raise the station's
altitude. I wrote it off to a computation fluke.

Now it's happened twice more, the last two days in a row.

What is going on?


http://www.hq.nasa.gov/osf/iss_reports/index.htm


ISS On-Orbit Status 03/28/09
Mean altitude loss in the last 24 hours -- 167 m 

ISS On-Orbit Status 03/29/09
Mean altitude gain in the last 24 hours -- 15 m 

ISS On-Orbit Status 03/30/09
Mean altitude loss in the last 24 hours -- 70 m 

ISS On-Orbit Status 03/31/09
Mean altitude loss in the last 24 hours -- 96 m 

ISS On-Orbit Status 04/01/09
Mean altitude loss in the last 24 hours -- 53 m 

ISS On-Orbit Status 04/02/09
Mean altitude gain in the last 24 hours -- 46 m 

ISS On-Orbit Status 04/03/09
Mean altitude gain in the last 24 hours -- 62 m 
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