It is not necessary, like in some replies, to use a program specifically built for these computations, and/or providing 9+ digits accuracy for the absolute distance. I don't have the data for Apollo missions, but for ground, aircraft and ISS standard prediction software plus simple estimates are sufficient. Using a point 6375 km below the sub-Martian point, SkyMap shows me ISS 19.5 degrees from Mars, at a range of 6767.8 km at 10:02:50 (somewhat stale elset). With the cosine of 19.5, I get 6377.6 km along the Mars vector, ie 2.6 km above Earth's surface, so no mountain close to this location is high enough. I also plotted a more normal view (but 1 km above to account for mountains on nearby Tahiti) This shows that pass just 0.2 degrees above horizon, at a range of 2303 km, corresponding to about 8 km. At first sight this should be refraction in this (stereographic=alt/az) plot mode, but I had expected more (.5 degrees = 20 km extra?) To check for the effect of small time errors, it is sufficient to get three distances and use a quadratic approximation through them. The same technique can be used for satellites (conidering the slight change in radius due to orbital eccentricity), aircraft, and rotation of Earth's surface. I have from JPL Horizons for Mars: 2003-Aug-27 09:00 55757931 km 2003-Aug-27 10:00 55757921 km 2003-Aug-27 11:00 55757948 km so the small precession in RA of the ISS orbit (~30 km/orbit) will at most produce 10 km along the Mars vector (at 19.5 degree distance), so Mars' movement will negate the gains. Likewise, a small shift along Earth or ISS' orbit will not reduce the distance significantly. ----- Original Message ----- > It occurs to me that tomorrow, August 27th, some human may have a chance > to pass closer to Mars than anyone else in recorded history. This could > be someone at or near the sub-Martian point or someone on ISS. > According to a very quick calculation based on a recent elset, this last > might occur at about 2003-08-27 1005 UT. Or possibly some astronaut on > a previous mission, especially an Apollo mission. ----------------------------------------------------------------- To unsubscribe from SeeSat-L, send a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@satobs.org List archived at http://www.satobs.org/seesat/seesatindex.html
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