Text description in delta-v says "Delta-v needed for various orbital manoeuvers using conventional rockets; red arrows show where optional aerobraking can be performed in that particular direction, black numbers give delta-v in km/s that apply in either direction.[4][5] Lower-delta-v transfers than shown can often be achieved, but involve rare transfer windows or take significantly longer, see: fuzzy orbital transfers. The figure 2.5 for LEO to GTO is higher than necessary[6] and the figure of 30 for LEO to the sun is also too high.[7]" but the reference [6] and [7] look like an original research calculation and seems wrong. They say
"The sum of LEO to GTO and GTO to GEO should equal LEO to GEO. The precise figures depend on what low earth orbit is used. According to Geostationary transfer orbit, the speed of a GTO at perigee can be just 9.8 km/s. This corresponds to an LEO at about 700 km altitude, where its speed would be 7.5 km/s, giving a delta-v of 2.3 km/s. Starting from a lower LEO would require more delta-v to get to GTO, but then the total for LEO to GEO would have to be higher.
The speed of the earth going around the sun is 29.78 km/s, equivalent to a specific kinetic energy of 443 km2/s2. One must add to this the potential energy depth of LEO, about 61 km2/s2, to give a kinetic energy close to Earth of 504 km2/s2, corresponding to a speed of 31.8 km/s. Since the LEO speed is 7.8 km/s, the delta-v is only 24 km/s. It would be possible to reach the sun with less delta-v using gravity assists. See Parker Solar Probe."
Perhaps it would be better if the line went from the Sun to "earth C3=0" ? - Rod57 (talk) 13:58, 29 May 2018 (UTC)
