Solid fueled rocketry itself is very simple, as in fireworks. I even once managed to make one with Potasium Nitrate (KNO3) after seeing DIY rocketry youtube video.Things like Ammonium perchlorate and aluminium powders are widely available and very cost effective. Why did it took so long?
( btw, my knowledge about rocket sceince is very basic )
Real rocketry for space mission would need a better solid fuel mix called Hydroxyl-terminated polybutadiene (HTPB), and the secret sauce to make it burn long enough and deliver thrust high enough is the big deal. There's also things like nozzle design, control etc.
Here's an RX 550 nozzle getting blown, likely caused by imperfect connection between propellants.
As for Indonesia's liquid fueled engine progress u can check it here
Indonesian Strategic Industries
https://www.kemhan.go.id/pothan/2023/01/20/diskusi-penguatan-industri-pertahanan-bersama-safran-group-perancis.html some interesting point from above : "The Safran Group also guarantees AASM-HAMMER compatibility on the T-50 and KFX/IFX aircraft made jointly by PTDI and KAI and hopes to be...
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