ARTEMIS SRBs: THE POWER AND HISTORY

 

By Wes Oleszewski; Aero-News Network Spaceflight Analyst

Propelling the Artemis II launch vehicle will be two types of rockets. At its core the Space Launch System (SLS) booster has four liquid fuel RS-25 engines. But most prominent are the two Solid Rocket Boosters (SRB) strapped to each side of the core. When the Artemis II launches toward the Moon, it will do so by way of these incredibly powerful and fairly historic SRBs.

Developed for the Space Shuttle program the Artemis SRBs are longer. Each stands 177 feet tall and weighs in at 1.6 million pounds. Burning a polybutadiene acrylonitrile (PBAN) propellant, the combination of the two SRBs produces 7.2 million pounds of thrust at liftoff. To put that in historic perspective, the Apollo 17 Saturn V that sent the last crew to the Moon produced 7.7 million pounds of thrust at liftoff. So, when combined with the Artemis II core stage of the SLS booster lifts off with 8.8 million pounds of thrust. The total burn time is just two minutes and six seconds before the SRBs are jettisoned into the Atlantic Ocean. Unlike the Space Shuttle, the Artemis SRBs are not recovered for reuse.

Additionally, the unusually cold weather in Florida this week has drawn a number of myopic and uninformed questions as well as countless social media posts citing the Challenger disaster and comparing that to now. Challenger was destroyed by one factor. Engineers were ordered by managers to “Take off their engineer’s hat and put on their management hats” in order to push for the launch to take place outside of the test data temperature envelope. That caused the burn through of the SRB segment joints which triggered the disaster. Artemis is NOT Challenger. The current SRBs have been specifically re-engineered to assure such will not happen again.

A foundational element of the SLS booster is that it was developed to leverage Space Shuttle technology. In its earliest concepts the Shuttle did not have SRBs but instead was composed of two huge airplane-like vehicles. By the end of 1971 there was only one aircraft in the system which was boosted by two SRBs and three liquid propellant orbiter engines fueled by an external tank. This configuration was first shown in model form to President Richard Nixon on January 3, 1972. Nixon was fascinated by the model and two days later released a statement where he gave it, not only his approval, but also the name “Space Shuttle.”

Large Solid Rocket Motors (SRM) were nothing new in 1972. Because on June 8, 1965, the largest SRMs in the world boosted the first Titan IIIC from Cape Canaveral Launch Complex 40 for the U.S. Air Force. Those 120-inch diameter, five segment boosters combined to produce 2.647 million pounds of thrust making the Titan IIIC the most powerful launch vehicle in the world at that time. Thus, in the early 1970s NASA elected to use two SEBs consisting of four segment each to boost the Shuttle. Those SRBs were 147 inches in diameter and the combination of the two produced 5.6 million pounds of thrust at liftoff. Over 135 launches only one of those boosters failed and that was due to it being fired at temperatures outside of its published performance limitation. Most of the other SRBs were recovered and reused.

Thus, Artemis SRBs are assembled from former Shuttle SRBs. One adaptation is the SLS will fly on five segment SRBs rather than the Shuttle’s four segment boosters. As a result of all this, Artemis II SRBs are composed of an assortment of sections with an amazing Space Shuttle history. As an example, a combined 84 different Shuttle missions total will fly on Artemis II. The left SRB has portions with a history of being used in nine ground test firings and 47 Shuttle missions. As an example, that SRB’s forward skirt has flow 14 times. Meanwhile, the right-hand booster has also been used on nine ground test firings, and its forward skirt has also been flown on 14 missions. But that SRB has an accumulated record of an amazing 64 missions overall. Additionally, the same SRB’s upper most segment, cylinder 86, is the oldest of the segments on Artemis II and dates all the way back to STS-5 when it boosted the orbiter Columbia on November 11, 1982.

In the Artemis program the SRBs are no longer recovered for re-use. This is because the cost of recovering, refurbishing, transporting and reloading a single SRBs has, over the history of their use, added up to a good bit more than simply making a new SRB. The same rule applies to the RS-25 engines on the SLS core stage.

Yet, when you see Artemis II launch, you now know the both the power and the history.