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Please forgive me if I am asking a dumb question. I am a little curious about the orbital parameters of "LEO" used by SpaceX on many occasions specifically those related to payload capability. According to SpaceX's Falcon 9 newest user guide it appears, though I cannot confirm, that it refers to a 200km x 360km orbit:

Official User Guide

but on this website it hints to be a 185km x 185km circular orbit (a little dated):

spacelaunchreport

So which one is more accurate in terms of payload capability? Thanks.

Chris
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Peng
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  • There's almost no such thing as a dumb question! This one however, is a good question. Do you mean that Table 3-2 says "LEO Direct Inject (200 km x 360 km)" for a insertion accuracy spec, but it's not clear if it also applies to a payload mass spec? – uhoh Jun 29 '16 at 03:37
  • Yes that is what I meant. I just did calculaiton using an online calculator and it appears that the delta-v needed to transfer from 200x200 circular orbit into 200x360 orbit is about 50m/s, so perhaps either way it won't affect the payload capability very much? Thanks. – Peng Jun 29 '16 at 03:45
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    As a rough rule of thumb, figure 0.5% payload difference per 10km of altitude difference in circular orbit. (Please do not plan an orbital launch using this information.) – Russell Borogove Jun 29 '16 at 04:26

1 Answers1

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The most believable figure here seems to be the 200km x 360km figure, as it is from the most recent official source. They claim ±10km x ±15km is within three standard deviations, so there is a significant spread. The other source you mentioned, the space launch report, references the source of the data from a seven years older user guide, and a four year older data sheet. (The 185km x 185km LEO orbit is often used when comparing different launch vehicles.)

One more thing though: While SpaceX offers a standardised orbit as a product, they operate in a very specialised niche market where missions are often custom made. As the $\Delta v$ cost of using a slightly different orbit is only minor, you could easily order another orbit for your payload, eliminating the need for having a company LEO definition. Custom orbits are of course much easier if you do not share the launch with many other satellites though.

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