One of the most famous rocket engines in history – the Apollo/Saturn’s F-1 – could one day fly again, providing Alabama company Dynetics, teamed with Pratt and Whitney Rocketdyne (PWR), win the advanced booster competition for the Space Launch System (SLS). Their liquid booster approach would advance SLS’ capability to launch payloads of 150mt to orbit.

SLS Booster Evolution:

Initially, SLS will launch in the 70mt configuration, ultimately designed to validate the Heavy Lift Launch Vehicle (HLV) for its exploration roles with the Orion spacecraft.

Known as Exploration Mission-1 (EM-1), the SLS will loft Orion for a short uncrewed mission to the Moon.

For this Block 1 configuration, SLS will consist of a core stage using four Pratt and Whitney Rocketdyne (PWD) RS-25Ds – formerly used by the Space Shuttle Program (SSP) – two ATK five segment Solid Rocket Boosters (SRBs) and an Interim Cryogenic Propulsion Stage (ICPS), highly likely to be a Delta Cryogenic Second Stage (DCSS).

The crewed follow-on flight – known as Exploration Mission-2 (EM-2) – is currently scheduled for 2021, while there is also potential for a cargo mission in-between EM-1 and EM-2.

Overall, the exploration roadmap continues to be largely undefined, especially past the opening couple of missions, citing only the vague references of journeys to a Near Earth Asteroid (NEA) and crewed missions to Mars. The potential for an Exploration Gateway to be at the center of NASA’s BEO ambitions continues to be heavily supported within the walls of NASA centers.

Despite the lack of a complete exploration roadmap, the SLS program continues to firm up their plan to evolve the HLV, with the 2020s set to be dominated by the Block 1A or 1B configuration – a 105mt capable launch vehicle that can be used for crew or cargo missions.

One of the main questions surrounding the 105mt capable vehicle relates to the boosters it will utilize for the opening two minutes of its ascent uphill – a choice between ATK’s Solids or an alternative liquid booster. As such, NASA will hold a competition, a trade-off between the suitors.

ATK – with their tried and tested Sold Rocket Motor history with the Shuttle Program – are always cited as being in pole position, per sources, not least because they will be flying with their five segment booster on SLS Block 1 and likely through to first half of the 2020s with the 105mt capable vehicle.

Also, evaluations are being made for baselining the 105mt SLS as the Block 1B, delaying the debut of the advanced boosters until near the end of the 2020s.

The main consideration for staying the course with the Block 1B is from an engineering standpoint, given analysis with the Block 1A – sporting advanced liquid boosters – shows it to be a “high-acceleration” launch vehicle. As such, it has been noted the environments (vibration, loads, etc.) caused by the high acceleration may be higher than Orion will allow.

With this consideration in mind, the SLS teams want to take the Block 1B design to the same level of maturity as the Block 1A, then make a decision on which way to proceed. Source information notes there is enough RSRMV material to conduct 10 SLS missions prior to the need to move to the advanced booster.

ATK are also classed as favorite for remaining as the booster supplier via the outcome of the competition, resulting in two five segment solid-propellant Advanced Composite Boosters (ACBs) being added to SLS. Details are restricted, but sources claim ATK’s Advanced Booster plans have impressed the SLS team.

(Image taken from the amazing 220mb DM-2 Five Seg Motor Ground Test Super Slow engineering Video – available in L2).

However, if a decision is made to switch to liquid boosters, SLS is designed to accommodate them on both the Block 1A and Block 2 – the latter being the fully evolved SLS, capable of at least 130mt to orbit. Attach points and integration considerations mean little impact will be suffered by the HLV, regardless of the future decision into its boosters of choice.

Dynetics Advanced SLS Boosters:

As part of NASA’s SLS Advanced Booster Engineering Demonstration and/or Risk Reduction (ABEDRR) procurement, 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 October.

During the ABEDRR effort, the Dynetics Team will apply state-of-the-art manufacturing and processing techniques to the heritage F-1, resulting in a low recurring cost engine while retaining the benefits of Apollo-era experience. The end goal will be to use NASA test facilities to perform a full-scale F-1 powerpack hotfire for risk reduction engine testing within a 30 month program.

The proposed booster features a robust structural design based around an 18 foot diameter core, paired with two F-1 engines, evolved from the most powerful LOX/RP engines ever flown.

“The Apollo-Saturn F-1 produced by Pratt & Whitney Rocketdyne is still the most powerful U.S. liquid rocket engine ever flown. The F-1 is well suited to the Advanced Booster, providing a combination of high thrust-to-weight and reliability in a low-cost package,” noted the Dynetics presentation, acquired by L2 – LINK.

“PWR brings unique cost and performance lessons from having recently working to modernize another Saturn-era engine, the J-2X.”

Citing their “superior booster solution”, Dynetics note the performance margin inherent to the proposed two-engine F-1-based booster enables a robust approach to structural design.

The company believes they can reduce costs by using the new Friction Stir Welding machinery at the Marshall Space Flight Center (MSFC) – which was originally intended for the Ares I launch vehicle. As such, AI 2219 material will be used as the basis for the tanks and skirts of the booster.

While the SLS Block 2 – with advanced Solid Rocket Boosters – is estimated to provide a capability of 130mt to orbit, Dynetics claim that by using the vehicle assumptions for the fully evolved SLS, their proposed booster delivers 150mt, “providing a 20mt (15 percent) margin, even with a conservative, affordability-focused booster.”.

Citing the history of the F-1’s flight record, Dynetics also point to the safety of the famous engine, as “demonstrated on 13 Saturn V flights of 65 engines with no failures.”

“The Dynetics Team identified a modernized F-1 engine as the ideal Advanced Booster engine concept because of the Saturn heritage engine 100 percent demonstrated flight reliability; high thrust; and simple, low-pressure LOX/RP GG cycle,” added the presentation.

“As a liquid engine, the F-1 can be acceptance tested to screen for defects prior to integration and, with the vehicle restrained, can be run on the pad for pre-launch readiness demonstration. Finally, if an engine does shut down, the booster can maintain vehicle control by shutting an engine down on the opposite booster, allowing either mission completion or a safe crew escape, depending upon the timing of the shutdown.”

Dynetics also provided their evaluations into initial load estimates, using data from historical booster loads from the Space Shuttle Program (SSP), assumed with the application of conservative factors

“It is believed that this is a conservative assumption (the loads), because many of the load contributors inherent to solid rocket boosters are eliminated or mitigated by liquid engine boosters,” noted their findings. “Examples include thrust rise, thrust rate mismatch at liftoff, thrust oscillation, and thrust and mismatch at separation.”

For previous SLS Articles, click here: http://www.nasaspaceflight.com/tag/hlv/

The company also referenced the SLS Block 1A, the 105mt capable HLV that – as previously mentioned – is set to be the workhorse of the 2020s.

Most notable is Dynetics’ claim they would be able to achieve 120mt as a non-Block 2 SLS. it is possible this class of HLV would fulfil the requirements of even the most ambitious versions of the NEA missions outlined in the ESD CONOPS (Concept of Operations), and potentially the Mars missions, allowing for the cancellation of the Block 2 to free up money for payloads.

The removal of the Block 2 from the SLS family has been noted as a consideration, albeit “privately” within the SLS program.

“Although the focus of the booster design activity concerned the Block 2 SLS configuration, the performance of the booster concept for the Block 1A SLS configuration (prior to incorporation of the Upper Stage) has also been assessed,” the presentation added.

“For the Block 1A version of the booster, a derated F-1 engine was baselined to provide increased reliability by operating at reduced chamber pressure and thrust while building flight heritage for the SLS F-1 in preparation for Block 2. The SLS Block 1A configuration with the proposed Advanced Booster provides payload capability from 103 mT (F-1 derated to 85 percent) to 120 mT (100 percent F-1 power level).”

Dynetics also note that the F-1 driven boosters provide NASA with greater flexibility, based on the projected multi-mission role SLS will be tasked with in the years to come.

“The F-1 engine design has continuous throttling capability over a sea level thrust range of 1.3 to 1.8 Mlbf to provide flexibility that supports SLS program goals by enabling the ability to tailor the thrust profile for each individual SLS flight and configuration if desired or required,” Dynetics noted.

“SLS is envisioned to fly a diverse range of missions (human, cargo, varying payload mass, varying insertion orbits) using multiple vehicle configurations (Upper Stage, no Upper Stage, varying number of core engines) where the ability to tailor the booster thrust profile provides NASA great flexibility to achieve current and future mission objectives.”

The company is also looking at “commonality and simplification” as Main Propulsion System (MPS) design goals, in order to increase affordability and reliability – leveraging Saturn, Delta IV, and SLS Upper Stage experience to prepare current suppliers to produce large cryogenic components.

“The booster RP feedline is common to the Core engine inlet; coupled with similar or less total propellant, this allows common designs for fill/drain, tank vent and relief, LOX thermal conditioning, and pneumatic system components. (It will) deliver more than 10,000 pounds of propellant each second of operation to a pair of F-1 engines.

“The propellant feed system valves are based on recent engine programs, such as RS-68 and J-2X. An active Pogo suppression system built on Saturn MPS lessons learned has been baselined, and engine feedlines based on S-IC geometries and components have been utilized.

“During flight, the same autogeneous LOX tank and heterogeneous gaseous Helium (GHe) RP tank repressurization systems proven during the Saturn program will be employed.”

While additional options – such as an Ares 1-style “in line” launch vehicle option (see “family” graphic) – are also presented, the key drive will now take place over the next 30 months, as the Dynetics team work to reduce the risk through a series of full-scale risk mitigation hardware demonstrations under the ABEDRR procurement process.

(Images: L2’s SLS Sections, NASA, ATK and Dynetics/PWR)

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