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Why did the Apollo spacecraft go into Earth orbit first?

  1. Dec 1, 2014 #1
    I've been playing Kerbal Space Program. I have found the simplest way to get to an outer planet is to launch straight up at dawn and the simplest way to get to an inner planet is to launch straight up at dusk, and in neither case to mess about with going into Kerbal orbit. This got me to thinking about trying a Mun shot this way. It took a few tries to get the timing right, but when I did, it worked beautifully.

    Clearly NASA's job of getting a man to the Moon from Earth would be a bit more complicated because the Moon's orbit is not exactly co-axial with Earth's rotation and Cape Canaveral is not exactly on the equator. But, I can't think of anything wrong with the principle of it. Time the launch so that going straight up (or nearly straight up) puts you on an intercept course with the object you want to intercept.

    So my question is, what is the point of putting a space craft into Earth orbit before taking off towards to Moon? Or, more generally, towards whatever object is your destination?
     
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  3. Dec 1, 2014 #2

    DaveC426913

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    Staging? Systems, safety checks?
     
  4. Dec 1, 2014 #3

    Bandersnatch

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  5. Dec 1, 2014 #4

    phinds

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    You were playing a video game. NASA had to do it for real. The stakes are a bit different.
     
  6. Dec 1, 2014 #5

    SteamKing

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    You want to make sure everything is OK before you leave the earth to head for the moon.

    http://en.wikipedia.org/wiki/Apollo_program

    Scroll down to the section "Lunar mission profile".
     
  7. Dec 2, 2014 #6
    There are three basic reasons. First to configure the spacecraft for its trip to the moon the command and service module had to turn around and dock with the lunar module before the translunar orbit injection burn. Secondly, to calculate the best burn time it was necessary to know the state vector (orbital characteristics and velocity) to make sure the burn pushed the spacecraft in the right direction to minimise fuel use by additional correction burns during the trip to lunar orbit. Finally, can you imagine the checklist after reaching orbit and getting ready to turn the CSM round to dock with the LEM? You wouldn't want to do any of that on the hoof.
     
  8. Dec 2, 2014 #7

    SteamKing

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    I initially thought this was the mission profile for the lunar flights. However, the S-IVB engine (the third stage) was used to send the S-IVB, the CSM and the LM into the translunar injection phase. Shortly after TLI, the CSM separated from the S-IVB and then executed the maneuver to dock with and extract the LM from the booster. In the early Apollo lunar missions, the S-IVB was sent into a solar orbit; after Apollo XII, the boosters were crashed into the Moon to collect readings from seismic instruments placed on the lunar surface.
     
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