GSLV looks strange: 1. It has liquid fuel boosters and solid fuel core, while all other launchers with boosters have solid fuel boosters 2. Its boosters finish to work after core, so actually they are not boosters, but together with core it is very complex first stage

Why they made such decisions? Whey they do not enlarge the core to throw boosters while core still is working?

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    $\begingroup$ If you want a precise trajectory, you need controllable engines - that is, liquid fuel, so you definitely want the LF engines to operate after the solid fuel engine is extinguished. But why the LF boosters and solid core? This is beyond me. $\endgroup$ – SF. Mar 29 '18 at 17:32
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    $\begingroup$ Short answer: it was a quick-and-dirty evolution from the earlier PSLV launcher. $\endgroup$ – Russell Borogove Mar 29 '18 at 18:03
  • $\begingroup$ @SF - the second and third stages are liquid fueled, so there would be no control issues if everything below that were solid-fueled. $\endgroup$ – Russell Borogove Mar 29 '18 at 18:18