The Solid Booster is a boost rated 8.7/10 on the Thrust Evaluation bar. It is a 4-shot boost.
The Solid Booster requires the Omega Catalog to be purchased in the Bonus Shop, at which point it is then available in the shop for $25000.
"Often seen on space shuttles, these 4 booster engines offer uncomparable thrust in their category!"
- Oddly enough, the Solid Booster shares a description with the "Lift-Off" word for word.