SLS: BOLE Evolved Boosters On The Way

Northrop Grumman Corporation has completed the first segment of the enhanced BOLE (Booster Obsolescence and Life Extension) boosters that will be part of the Block-2 version of the SLS, Space Launch System.

NASA’s Space Launch System (SLS) rocket with the Orion spacecraft aboard is seen atop the mobile launcher as it rolls out to Launch Pad 39B, Friday, Nov. 4, 2022, at NASA’s Kennedy Space Center in Florida. NASA’s Artemis I flight test is the first integrated test of the agency’s deep space exploration systems: the Orion spacecraft, SLS rocket, and supporting ground systems. Launch of the uncrewed flight test is targeted for Nov. 14 at 12:07 a.m. EST. — *NASA’s Space Launch System (SLS). Credits: NASA/Joel Kowsky*

This will be a radical improvement of the old SRBs derived from the Space Shuttle boosters, which will equip the Artemis missions up to VII.

The first static tests on the new boosters will already be carried out this year.

The main innovations

Goodbye to the metal structure of the old SRBs: the new version will be made of carbon fiber and composite materials with a considerable weight saving, around 30%.

BOLE design changes overview. Credit: NASA — *BOLE design changes overview. Credits: NASA*

The solid propellant, HTPB (hydroxy-terminated polybutadiene), has also been improved for the benefit of efficiency and final thrust, which is estimated to be 11% higher.

Furthermore, the thrust vector control system will be improved by moving from the old electro-hydraulic TVC to an electromechanically controlled eTVC system.

Also new is the coverage of the upper part, which, thanks to a lower aerodynamic load, guarantees better penetration, significantly increasing the efficiency of the lateral boosters.

The Evolution of the Space Launch System

The SLS, planned for the Artemis program, is a heavy launch system that will see two variants evolve in parallel: the manned one and the cargo one.

SLS configuration evolution. Credit: NASA — *SLS configuration evolution. Credits: NASA*

The first version of the launcher called Block-1, used in the Artemis I mission, has a load capacity towards the TLI (Trans Lunar Injection) of 12 tons. The 1-B version will further improve the payload capacity towards the TLI to 39.2 tons, featuring a new upper stage called EUS (Exploration Upper Stage) and the newly built RS-25 engines.

Implementing the new BOLE boosters will transition the SLS towards the Block-2 version, intended for deep space missions with a load capacity towards the TLI of 46 tons.