Most powerful solid-propellant rocket motor

The most powerful solid-propellant rocket, and the most powerful rocket motor ever constructed, is the SLS Five-Segment Booster (also known as the Five Segment Reusable Solid Rocket Motor, or RSRMV), built by Northrop Grumman (USA) for NASA's Space Launch System (SLS) super-heavy rocket. Each one of these boosters, which will be used in pairs as part of the SLS, generates a peak thrust of 3,280,000 lbf (14,590 kN) at sea level. The boosters were successfully test-fired for the first time on 10 September 2009.

The Five-Segment Booster is a development of a rocket motor first built for the Space Shuttle program in the 1970s. It comprises five cylindrical sections (segments) packed with solid propellants, which are bonded together at NASA's launch assembly facility along with a nosecone/avionics bay and thrust-vectoring nozzle at the top and bottom, respectively. Once fully assembled, the Five-Segment Booster is 177 ft (53.94 m) tall and weighs 1,616,123 lb (733 tonnes).

There are a few key differences between the Five-Segment Booster and the original Space Shuttle solid rocket boosters. The most obvious of which is that the Shuttle SRBs only had four segments, giving them around 20% less propellant to burn. There have also been some refinements to the ways in which the solid propellant grains are mixed and packed, which mean that the Five-Segment Booster has a peak thrust around 10 percent higher than the Shuttle SRB, and burns for 10 seconds longer.

The energy that drives rocket engines comes from the violent chemical reaction between a fuel and an oxidizer (collectively called "propellants"). Internal combustion engines and jet engines work using the same basic reaction, but they pull in air from the atmosphere to act as the oxidizer.

A solid-propellant rocket uses grains of fuel and oxidizer chemicals, mixed together in a dense, plastic like mass. For the Five-Segment Boosters the main source of fuel is aluminium powder, and the oxidizer is ammonium perchlorate. These two substances are then bound together by a polymer called polybutadiene acrylonitrile, which also acts as a secondary source of fuel.

The solid propellant is moulded into a carefully engineered shape within its strong steel casing. The igniter is at the opposite end to the nozzle – at the top of the rocket – and the combustion gases are forced down a cylindrical channel through the fuel block that acts as a combustion chamber.

In the Five-Segment Boosters the composition of the propellant varies depending on where in the chamber it is. This allows the rocket to vary its thrust as the propellant burns from top to bottom, which is required to maintain the stability of the rocket.