Orbital ATK is making steady progress on the production of the twin Solid Rocket Boosters that will power NASA’s SLS heavy lift rocket on its maiden voyage in 2018. Those SRBs will be the first five segment Solid Rocket Boosters used to power a NASA launch vehicle and will be the most-powerful solid rocket motors ever flown.
Five segment Solid Rocket Boosters:
Upgrading from the four-segment Solid Rocket Boosters (SRBs) used throughout the life of the Space Shuttle Program, NASA and Orbital ATK have successfully developed a five-segment SRB that will be used in a twin configuration (just as with Shuttle) to power the mighty SLS rocket through first stage flight.
The five propellant segments – Aft, Aft Center, Center, Forward Center, and Forward – will be joined with the Forward Skirt Avionics and Nose Assembly (which will be mated atop the Forward segment) and Aft Skirt with Booster Separation motor (which will be mated over the Nozzle and Thrust Vector Actuators on the Aft segment).
Standing 177 feet tall and 12 feet in diameter, each SLS SRB will weigh 1.6 million pounds fully loaded and use a polybutadiene acrylonitrile propellant to produce 3.6 million pounds of thrust at sea level.
In twin configuration, the two five segment SRBs will comprise 3.2 million pounds of SLS’s liftoff weight and will produce 7.2 million pounds of thrust at liftoff — approximately 400,000 pounds thrust greater than the entire Space Shuttle system produced at liftoff.
In fact, that 7.2 million pounds of thrust at liftoff represents just over 75% of the total liftoff thrust of SLS, with the four core stage RD-25 engines providing another 1.6 million pounds of thrust for a total SLS liftoff thrust of 8.8 million pounds – approximately 2 million pounds of thrust greater than Shuttle at liftoff.
After ignition, the two five segment boosters will burn nearly 6 tons of propellant every second for 126 seconds, 2mins 6secs, before separating from the SLS core stage and destructively impacting the Atlantic Ocean roughly 130 nmi downrange from the launch pad.
SRB changes from Shuttle to SLS:
In addition to carrying 25% more propellant and a new asbestos-free insulation and liner configuration, each five segment SRB for SLS will also carry a new nozzle design to account for the increase in thrust from the booster, new avionics, and will undergo improved nondestructive evaluation processes before leaving the manufacturing facility in Utah.
However, certain elements of the Shuttle SRB design have been eliminated for SLS SRBs, including the onboard engineering cameras added after the loss of Shuttle Columbia on STS-107.
With a switch to an in-line configuration for the SLS rocket, the need for those engineering cameras on the Solid Rocket Boosters no longer exists, and they will therefore not be present on SLS boosters.
However, the biggest operational change from the Space Shuttle Program will be the fact that the SLS SRBs will be a single use commodity and will not be recovered for post-flight inspection, refurbishment, and reuse.
In an exclusive interview with NASASpaceflight.com, Orbital ATK discussed NASA’s decision not to recover the SRBs.
Recovering the SRBs “required the use and maintenance of retrieval ships and additional facilities,” noted Orbital ATK.
“The relatively low flight rate [of SLS] combined with the amount of heritage hardware that was available led to the decision for non-recovery.”
The heritage hardware from Shuttle and the recovery and post-flight inspection of 133 of the 135 SRB sets flown on Shuttle (both boosters from STS-4 and STS-51L were not recovered in their entirety due to a parachute system failure on both STS-4 SRBs and the range safety destruction of the STS-51L SRBs) helped Orbital ATK improve the SRB design significantly over the life of the Shuttle Program.
According to Orbital ATK, “Over the years, recovering the boosters has proved very beneficial in learning where we could improve the design and reliability of the SRBs.
“These lessons learned were incorporated into the Shuttle SRBs and carried over into the design and processing of the SLS boosters.”
Furthermore, the decision not to recover the SRBs means that the weight of the recovery systems and parachutes – over 9,000 lbs – is no longer needed, therefore leading to a higher performance of the booster.
Therefore, at this time, there are no plans to recover any of the SLS SRBs – even intermittently (as is sometimes done with the Ariane 5’s solid rocket boosters).
Nonetheless, Orbital ATK’s commitment to continuous improvement of the SRB design is not affected by the non-recoverable aspect of the SLS SRBs.
“NASA continues to evaluate approaches to improve the performance of the SLS vehicle to support the evolving requirements for the eventual mission of placing humans on Mars,” notes Orbital ATK regarding their “Dark Knight” SRB proposal to NASA.
“There is a long range plan to achieve placing 130 mT of mass into LEO to support future Mars missions, which will require an increase in booster performance.
“As part of our proposal for the NASA Advanced Booster Engineering Development and Risk Reduction (ABEDRR) solicitation, Orbital ATK generated a preliminary design of a solid booster with a graphite composite case, new propellant, and other component improvements that would enable NASA to achieve the 130 mT mass goal.”
In fact, Orbital ATK, as part of their ABEDRR contract effort, has “made significant progress in conducting risk reduction activities associated with composite case, nozzle improvements, more energetic propellant, and enhanced thrust vector control” for their SRBs.
These risk reduction efforts will help enable Orbital ATK to enhance the capability of the boosters used on SLS.
“We will continue to evaluate opportunities to improve the performance of the SLS boosters to meet the evolving performance needs of SLS as they are identified by NASA.”
Nonetheless, as Orbital ATK looks toward the long-range future for SRB enhancements, the company’s primary focus now is on next year’s QM-2 qualification motor test and the build-up of the SLS motor segments for the first SLS flight – EM-1 – in 2018.
As reported by Orbital ATK, “Production has already started for the EM-1 test flight.
“Motor hardware began processing June of this year in Utah. Booster small parts processing will begin at KSC within the next few weeks.”
As such, Orbital ATK is on track to support not only the first test flight of SLS in three years, but also the continued operation of SLS into the 2030s and beyond.
(Images: Via Orbital ATK, NASA and L2 content – which includes the SRB “Bibles” – a huge collection of non-restricted – yet previously unreleased – presentations all in one place.)
(L2 is – as it has been for the past several years – providing full exclusive SLS and Exploration Planning coverage. To join L2, click here: http://www.nasaspaceflight.com/l2/)