couldn't/can't/could/can have done?

1.The spaceship couldn't have reached the correct altitude by the time the rockets separate from it.

2.The spaceship could have reached the correct altitude by the time the rockets separate from it.

3.The spaceship can't have reached the correct altitude by the time the rockets separate from it.

4.The spaceship can have reached the correct altitude by the time the rockets separate from it.

(The situation is that I'm as a spaceship engineer briefing, pointing to the correct altitude and the time on the screen, before launching the spaceship)

Like in the above examples, can I use "couldn't/could/can't/can have reached" as referring to the past from the future point that the rockets separate from it?

To illustrate the timeline,

Present(briefing)------->-----Future(1) The spaceship couldn't/could/can't/can have reached the correct altitude---->----Future(2) The time the rockets separate from it----So, as relatively Future(1) is preceding Future(2), can we say 1,2,3,4?I have learned that we can say "couldn't/could/can't have done" in the past perspective, but in this case, Future(1) is also in the past from the point of Future(2), so I think they're all correct.

Please check whether I'm correct.

2 Answers

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  • 2 months ago
    Favourite answer

    you left out "wouldn't have"... which seems best, but your paragraph with future1 and 2 is confusing, don't know what you want. 

    Any of them are correct, it depends on the context, the point you are making.

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    • billrussell42
      Lv 7
      2 months agoReport

      future 1, rocket will or can or could separate.
      future 2, separation is in the past so it did or did not separate.

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  • IOM
    Lv 7
    2 months ago

    3 and 4 are incorrect.

    1 and 2 are correct, but they mean very different things, as you surely know.

    Cheers.

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