What does 'break up on re-entry' to Earth mean?

[Nona m.]

English Language Tests, Intermediate level

ESL/EFL Test #148 "Idioms with the phrasal verb break", question 2

Nasa is currently in the process of trying to work out how to avoid any more of its spaceships from ......... on re-entry to Earth.

(a) breaking off
(b) breaking away
(c) breaking out
(d) breaking up

English Language Tests, Intermediate level

ESL/EFL Test #148 "Idioms with the phrasal verb break", answer 2

Nasa is currently in the process of trying to work out how to avoid any more of its spaceships from breaking up on re-entry to Earth.

Correct answer: (d) breaking up
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I don't really understand what is this sentense mean.can you please explain for me?

[Alan]

This means that scientists at NASA are trying to work out the best way of preventing their spaceships from falling to pieces when they come back to earth.

A
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