NASA has issued a new Request For Information (RFI) that shows there is a deadline for the Space Launch System (SLS) to transition to “Advanced (Evolved) Boosters” no later than the ninth flight. This is due to a future obsolescence issue with the current booster design which relies on Shuttle heritage components of which there is only a limited amount of stock remaining. NASA intends to purchase another six SLS flight booster sets before the stock runs out, prior to moving to the Advanced Boosters.



The Space Launch System includes a mix of former Shuttle and Constellation (CxP) hardware, a winning design from numerous studies conducted by the Marshall Space Flight Center (MSFC) via political guidance provided in the 2010 Authorization Act.

The commonality of design was aimed at protecting flight-proven technology – such as the RS-25 engines that served the Space Shuttle Program with distinction, through to large investments in the Ares I program – ranging from the Mobile Launcher (ML) to the five segment Solid Rocket Booster design that was to serve as the entire first stage of the in-line ‘stick’ rocket.

Development of the five segment booster began during CxP but soon transitioned to SLS, including numerous test firings at Orbital ATK’s test site in Utah.

The motor is now classed as qualified allowing for the production of the first flight booster set for Exploration Mission -1 (EM-1). Production has already started on the booster set for the second mission.

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NASA has already contracted Orbital ATK for the first three booster sets, along with “Flight Support Booster-One (FSB-1)” as a back up to the flight boosters.

NASA’s latest Request For Information (RFI) is a government acquisition requirement where companies can bid and then win future contracts with NASA, although as with most SLS contracts only one company is in the running.

That becomes more obvious for the first element of the document, which notes NASA will purchase six more sets of five segment boosters. Only Orbital ATK will be able to produce the baselined boosters that will ride with the Block 1 and initial Block 1B SLS launches.

“The first launch vehicle being designed, developed, and built as part of the NASA SLS Program is designated as the Block 1 configuration. Beyond this initial configuration, two upgrades are planned – the Block 1B vehicle and the Block 2 vehicle,” noted the RFI.

“The Boosters remain the same in both Block 1 and Block 1B and are based on Shuttle heritage with many components preserved from the Shuttle program.”

Such components include the casings that house the propellant in each segment. Most of the casings were reused from previous Shuttle missions, with the boosters parachuting to the Atlantic Ocean before being recovered and towed back to Port Canaveral.

The main reason for their return was to dismantle them and conduct a thorough review of their performance, with the findings documented in the SRB IFA (In Flight Anomaly) presentations, which in turn fed into the following mission’s Flight Readiness Review (FRR). The casings were then refurbished and eventually found their way into back into the production line.

Other obsolescence items listed are less specific but include “material suppliers; major structures; thrust vector control; motor cases; propellant, liner, and insulation; and nozzle ablative liners and metal housings.”

SLS does not intend to recover the boosters, a by-product of the Constellation Program (CxP) which suffered from performance issues, in part resulting in the deletion of the parachute and recovery systems on the boosters. Despite SLS’ superior performance, the chutes were not brought back into the design, as such they will fire for the first two minutes of first stage flight, separate and then crash into the Atlantic before sinking to the ocean floor.

This ultimately means the loss of hardware that would normally be fed back into the production line. With no plans to restart production, NASA has opted to use up the remaining stock and use it as a catalyst to bring the Advanced – also cited as “Evolved” in some documentation – Boosters online.

“Eventually NASA will run out of the heritage Shuttle components and a replacement design is needed to address this future obsolescence,” added the RFI.

It has always been in the planning for SLS to move to an Advanced Booster, partly in a requirement for its Block 2 rocket, that is required for Mars missions. The Block 2 is not expected to launch until the 2030s based on long-range NASA outlook manifests. Crewed missions to Mars with SLS have been projected internally as mid-to-late 2030s recently.

“That replacement design will be included in the Block 2 version of the SLS. It is expected that the replacement design will provide the same or higher ascent performance than the existing heritage design,” the overview noted, confirming this document was citing the Advanced Boosters as the replacement. “How much extra performance is possible in a replacement design is of significant interest to the government.”

Two Advanced Booster designs have been evaluated for several years, mainly under NASA’s SLS Advanced Booster Engineering Demonstration and/or Risk Reduction (ABEDRR) procurement process.

Nearly six years ago, Dynetics, Inc. and Pratt & Whitney Rocketdyne (PWR) formed a team “to offer an affordable booster approach that meets the evolved capabilities of the SLS” – and presented their overview at the 63rd International Astronautical Congress, Naples, Italy in 2012.

Their liquid booster approach – using the baseline of the famous Saturn V F-1 engines – claims they could advance SLS’ capability to launch payloads of 150mT to orbit.

Orbital ATK’s proposal – nicknamed the “Dark Knights” due to their black casings – builds on their booster legacy, with a motor that is “advanced” on several levels, by “provid(ing) NASA the capability for the SLS to achieve 130 mT capability – the baseline for SLS Block 2 – with significant margin, utilizing a booster that is 40 percent less expensive and 24 percent more reliable than the current SLS booster.

However, the document leaves the door open for a second round of evolving the concepts past the original proposals for the Advanced Boosters.

Due to the aforementioned lack of Shuttle heritage stock for the current boosters, moving to the Advanced Booster must now become a reality by the ninth flight of SLS.

“The intent of this acquisition is to extend the life of the current Booster design through the available Shuttle heritage inventory while developing replacement designs to be ready when that inventory runs out,” noted the RFI.

“Because approximately eight flight sets of heritage hardware were preserved at the end of Shuttle, a new Booster for Block 2 must be developed, certified, and produced on or before the ninth flight of the SLS.”

Despite continued references to the Advanced Booster and SLS Block 2, that ninth flight of SLS will be with the Block 1B, although the more powerful SLS won’t be online until later than originally planned, likely in the second half of the 2020s, as NASA moves to additional Block 1 launches due to a number of factors including the construction of a second Mobile Launcher.