Two rockets maintaining fixed separation in an inertial laboratory frame do not preserve their comoving separation. A string connecting them is stretched rather than remaining unstrained; sufficiently large strain can break a real string. The contrast with Born rigidity follows from relativity of simultaneity and does not contradict Lorentz contraction.
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Bell's spaceship paradox is a thought experiment in the realm of special relativity, proposed by physicist John S. Bell. It illustrates some of the counterintuitive aspects of simultaneity and the effects of relative motion on different observers. In the thought experiment, consider two identical spaceships, A and B, which are initially at rest and a certain distance apart in a reference frame. Both ships are connected by a taut string.