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Has SpaceX provided any details on their specific plans for the trajectory of the Falcon Heavy payload propulsion on its trip out as far as Mars orbit? I'm wondering if they have made public whether they are launching directly towards Mars orbit or if they will orbit the earth for a few rotations first.

Also, will the 2nd stage Merlin Vacuum engine provide all of the thrust necessary to get to Earth orbit and then use the same engine to get out of Earth's gravity towards Mars orbit? I know the Merlin Vacuum engine can be re-fired multiple times, but I do not know if getting to earth orbit, then getting out of Earth's gravity field will run the motor significantly longer than it's ever run before on a flight.

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  • $\begingroup$ Downvote. Just wait for a couple of days. $\endgroup$
    – Everyday Astronaut
    Jan 27, 2018 at 14:26

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It is pretty much decided that it won't actually orbit Mars, but rather touch the orbit of Mars going around the Sun. See for example the answers to this question.

As far as it rotating the Earth for a few rotations, that also won't happen. The only reason someone would do that is if one was testing out a system prior to committing, like a manned mission. There isn't a payload to check out, thus the sooner they can get it going to its final destination, the better. There is a chance that it will have some kind of a "Drift" phase, where it needs to wait for a few minutes between firings of the second stage, but that hasn't been made public yet.

Bottom line, I'm quite sure they will get to the final trajectory as quickly as they can. The timeline isn't public yet, but should be a day or two before launch, if not longer. There might be a small coast phase.

Edit- So it turns out there was a large coast, but it was to demonstrate a new capability. There is a desire to put a satellite directly to GEO. This requires a coast of about 6 hours. The mission tested that ability. It was not to check out the payload.

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    $\begingroup$ Testing before committing is not the only reason for staying orbiting earth. They also can use a parking orbit waiting for a more appropriate time window to travel to mars. $\endgroup$
    – Manu H
    Jan 26, 2018 at 6:53
  • $\begingroup$ That is true, but they would do that for at most an orbit, otherwise it would make sense to leave later. $\endgroup$
    – PearsonArtPhoto ♦
    Jan 26, 2018 at 11:05
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    $\begingroup$ Staying in earth parking orbit until an optimal orbit departure time might also give more flexibility in ground launch windows. If it were me planning a mission, I'd rather get off the ground and into orbit early, just in case there is an issue on the ground (weather, sticky valves, etc.) that would delay a launch past my optimal orbit departure timeframe. Then I would know I'm at least part way there and past one of the biggest hurdles of getting into orbit in the first place. $\endgroup$
    – Milwrdfan
    Jan 29, 2018 at 14:49
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    $\begingroup$ This answer is incorrect as it did in fact spend 6 hours orbiting Earth. $\endgroup$
    – kasperd
    Feb 11, 2018 at 11:28

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