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After the launch and six-hour cruise, the Falcon Heavy’s upper stage will fire a third time to send the Tesla into a cycling orbit between Earth and Mars. This should take the Tesla out as far as the Martian orbit around the Sun, or even a bit further. Musk said the vehicle should get as far as 380 to 450 million km from Earth, depending on how the third burn goes. ( source )

80 million kilometers is a huge tolerance. Normally rockets make very precise burns to arrive at specific trajectories and how the amount of fuel carried converts to delta-V and possible trajectory is well known.

What is the cause why the planned trajectory was defined with such poor precision? While I understand they are not aiming at any specific target, they should still know how much delta-V the rocket carries and how far it will get it.

Like, I'm happy your rocket can reach anywhere between Mars and the Asteroid Belt, but I'd be more confident if the word "anywhere" wasn't applied in so literal meaning...

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  • $\begingroup$ Is it Starman or is it the Roadster? $\endgroup$
    – uhoh
    Feb 8, 2018 at 13:05
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    $\begingroup$ They were doing a test to see what would happen to the third stage of the rocket after spending 6 hours in the Van Allen belt, being unsure what amount of boil-off or what effect it would have on the booster left the uncertainty. $\endgroup$
    – Edlothiad
    Feb 8, 2018 at 13:05
  • $\begingroup$ I think it is uncertainty in the maximum possible trajectory, but not necessarily uncertainty in a given, targeted trajectory if they choose to do so. In other words, if they burn until they need to shut down to avoid explosion, they are not sure exactly when it runs out of gas. But that doesn't mean that that would be the uncertainty in a specific orbit as long as SECO3 happens before it runs out of gas. Considering the current projections are for it to pass within 7 million km of Mars and I don't think that's an accident. $\endgroup$
    – uhoh
    Feb 8, 2018 at 13:08
  • $\begingroup$ A small uncertainty here makes a big difference way out there $\endgroup$
    – larry909
    Feb 8, 2018 at 13:18

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The source was that no-one cared; it was a test flight

Elon Musk's stated minimum goal of this flight was: to not blow up Pad 39A.(*)

"I hope it makes it far enough away from the [launch] pad so that it does not cause pad damage," Musk said last year. "I would consider even that a win to be honest."

This was a test to see if the thing flies and makes it to orbit. To achieve high precision of the orbit was not on the agenda. They simply did not care about that, because already getting to orbit — any orbit — was a smashing success all on its own.

(*) The reason for this is that being allowed to use Pad 39A is pretty much like borrowing your grandparents' priceless crystal glasses for your private party: you do want to hand that back in pristine order. Oh, and because SpaceX needs the pad to do business. If it is broken, they cannot use it for launches that earn them money.

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    $\begingroup$ I think they probably care a great deal, Musk has a long history of understatement and managing expectation. $\endgroup$
    – GdD
    Feb 8, 2018 at 13:24
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    $\begingroup$ @GdD Musk was very clear about the expectations in the time leading up to the launch. He clearly stated that anything that is not an explosion on the launch pad is a success. Like he said in the press conference after the launch: his nightmare scenario would have been a wheel coming bouncing down the access way; a Tesla logo landing with a THUD in front of a camera. Anything that was not that, and he was happy. $\endgroup$
    – MichaelK
    Feb 8, 2018 at 13:33
  • $\begingroup$ Comment to down-voters: 1) explain why you down-vote. 2) If you think you can do better, by all means: author an answer. $\endgroup$
    – MichaelK
    Feb 8, 2018 at 13:39
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    $\begingroup$ That no-one cared was the reason for the unimportance of the exact orbit, but is no explanation for why it couldn't be predicted with higher accuracy. SpaceX has expert mission planners, tons of simulation tools and much experience with precise orbit insertions, few-seconds launch windows etc. It all doesn't make sense to me either. $\endgroup$
    – Everyday Astronaut
    Feb 8, 2018 at 15:40
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    $\begingroup$ @MichaelK Someone passive-aggressive? :-P To make it clear: not caring about something means it is irrelevant, not uncertain. The "doesn't make sense" part was supposed to support the question. $\endgroup$
    – Everyday Astronaut
    Feb 8, 2018 at 20:26

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