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This topic is inspired by work done by PhotonBytes in 2025 and before, and by studies published by GW Johnson about a variety of aspects of rocketry.
I asked Gemini to do some research on the history of the idea of flyback boosters. That history goes back to at least the 1930's, if not before.
No such boosters were ever built (as far as Gemini could determine) but the Space Shuttle evolved from work done on the pure flyback concepts.
Gemini found a web site with history that is directly related to the topic opened here:
https://www.afmc.af.mil/News/Article-Di … never-was/
The link above is dated April 9, 2021.
In Post #3, we'll post a transcript of a session with Gemini asking about the history of flyback boosters, and possible prospects for future developments.
In particular, Gemini found that the Europeans may have been considering flyback side boosters with liquid fuel as replacements for existing solid fuel rockets.
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Post #3: Conversation with Gemini about flyback boosters
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This post contains a transcript of a conversation with Gemini about flyback boosters. We got off to a slow start with an error about how Space Shuttle worked, but Gemini recovered smoothly and went on to provide a reasonably satisfying collection of anecdotes and references.
Side Mount Rocket Launch - Hi Gemini! Thank you for your help with numerous previous requests. This one will exercise your search skills. The rocket launch system that is most popular is the vertical stack. Examples include the Apollo space craft, and the SpaceX Falcon 9 and Starship of today. There are many other such examples. The question for today is about side mount systems. Many have been proposed, but to my knowledge, only the Space Shuttle is an example of a side mount system, and even there it was the fuel tank that was side mounted. Please see if you can find any examples of a launch system with the second stage mounted on the side of the first stage.
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You've hit on a fascinating aspect of rocket design that goes beyond the common vertical stack. You are correct that the Space Shuttle is the most well-known example of a side-mount system in which a crewed vehicle was launched alongside a large external tank. While the Space Shuttle's orbiter and solid rocket boosters were side-mounted to the central tank, the orbiter itself functioned as the second stage, igniting its engines once the boosters were jettisoned.While the Space Shuttle is the most prominent historical example, other launch systems have utilized a side-mounted configuration. The most notable current example is NASA's Space Launch System (SLS). The SLS uses a massive central core stage with four liquid-fuel engines and two side-mounted solid rocket boosters. This design is directly evolved from the Space Shuttle's architecture. The upper stage, which is the actual second stage, is mounted on top of the central core. So, while the second stage is not side-mounted, the first-stage architecture relies on a side-mounted booster design.
Beyond these, side-mounted designs have been explored in various historical proposals and are a common feature in smaller-scale model rocketry, where enthusiasts experiment with different staging configurations. The challenges of a side-mounted second stage often involve:
Aerodynamic forces: A side-mounted second stage creates asymmetrical drag and thrust, which can make a rocket difficult to steer and stabilize during launch.
Structural integrity: The attachment points must be incredibly strong to handle the immense stress of a rocket launch.
Mass distribution: An off-center mass distribution requires complex thrust vectoring and control systems to maintain a stable flight path.
While a pure side-mounted second stage has not been widely adopted for large-scale orbital rockets, the side-mounted booster concept, as seen in both the Space Shuttle and SLS, is a successful design for augmenting the first stage's thrust.
You might find this video on building a two-stage rocket interesting, as it gives a sense of how complex staging can be even on a smaller scale. Making a Powerful 2-Stage Rocket
Making a Powerful 2-Stage Rocket - YouTube
ProjectAir · 599K views
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Thank you for your first draft of a response to my question. As a point of correction, the Space Shuttle main engines were started before the solid boosters were lit. The reason is that the liquid fuel had to be confirmed in correct operation before the solids were lit.
***You are absolutely right to correct me on that. Thank you for the precision.
The Space Shuttle launch sequence was a marvel of engineering, and you are correct that the three main engines on the orbiter (SSMEs) ignited first. They were confirmed to be at 90% thrust before the two solid rocket boosters (SRBs) were lit. Once ignited, the SRBs could not be shut down. This two-step ignition process was a critical safety measure, ensuring that the primary liquid-fuel system was functioning correctly before committing to the irreversible launch sequence powered by the solid boosters.
That said, while the solid rocket boosters provided the majority of the initial thrust, the Space Shuttle's main engines continued to burn throughout the ascent to orbit, with the orbiter itself essentially acting as the second stage. This is a very specific and unique example of a "side-mount" rocket system that successfully launched.
I appreciate you catching that detail—it's an important part of the Space Shuttle's unique design and launch profile.
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And for my part, I appreciate your careful delineation of the difficulty of the side mount configuration as compared to the much simpler inline stacking system used by most launch companies. In order to maximize the value of your time, I'd like to make a distinction between the kind of side mount you identified (auxiliary boosters) and the concept our small team is exploring. A great many rocket companies use side mounted boosters to help the main stage to achieve vertical velocity. This is interesting but not what we are asking about. The difference is that the force supplied by the side boosters is delivered to the central stack in a symmetrical manner, and the side boosters fall away simultaneously, so the forces delivered to the main stack remain symmetrical. The matter of interest is a flyback booster. To the best of our knowledge, no such device has ever been attempted on a large scale. However, your mention of model rockets is interesting, because experiments might have been done there. There is a category of launch systems that comes close to what we are considering. That class is the airplane launchers, of which there have been several, and at least two remain in occasional service. Our interest is in a booster of the SpaceX Super Heavy class, with wings and the ability to fly back to the launch site. SpaceX has pioneered and proven the vertical flyback technique shown by Falcon 9, and tested with success with the Super Heavy. Please extend your search to see if you can find any studies that might have been done of a true flyback side-mount design. Please do not include the von Braun Space Ferry. That was NOT a flyback system. It used parachutes. What we are investigating is the economic feasibility of a true flyback first stage to compete with the SpaceX Super Heavy.
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This is an excellent distinction. Your team's focus on a true flyback booster, capable of horizontal landing like an aircraft, gets to the heart of a major technical and economic challenge in reusability. Your comparison to SpaceX's Super Heavy, which uses a different flyback technique, is a perfect framework for the search.Historical and Conceptual Flyback Booster Designs
While a true flyback, winged booster has not been fielded on a large-scale orbital vehicle, the concept has been a subject of extensive study for decades, particularly in the lead-up to the Space Shuttle program and for subsequent upgrade proposals.
NASA/Grumman/Boeing (1970s): During the initial studies for the Space Shuttle, one of the leading concepts was a fully reusable two-stage-to-orbit (TSTO) vehicle. One such design from Grumman and Boeing featured a large winged booster, powered by five F-1 engines (the same type used on the Saturn V first stage), which would launch a smaller winged orbiter mounted on its back. After separation, the booster would fly back to the launch site and land horizontally. This was a true flyback booster and a direct precursor to the Space Shuttle, which ultimately adopted a partially reusable design to reduce development costs.
DLR's Liquid Fly-Back Booster (LFBB): The German Aerospace Center (DLR) has conducted extensive studies on a "Liquid Fly-Back Booster" (LFBB) as a potential upgrade for the Ariane 5 rocket. This concept, similar to what your team is exploring, would replace the expendable solid rocket boosters with a pair of reusable, winged boosters. These boosters would separate from the main stage and then use air-breathing engines to fly back to a runway for a horizontal landing. The goal of this design was to significantly reduce launch costs for the Ariane program. Studies showed that this approach was the most affordable and least risky way for European launch systems to move toward reusability.
Russian Baikal Booster: A Russian company, Khrunichev, proposed a winged, flyback booster known as the Baikal. The concept involved a reusable, winged liquid-propellant booster that would attach to a larger rocket's core stage. It was designed to fly back to a runway after separation and land horizontally, much like an airplane. Mock-ups were even built, but the program never proceeded to a flight-ready vehicle.
Challenges of a Flyback Booster
The reason these concepts have not been realized is due to a variety of significant engineering challenges:
Mass and Aerodynamics: Adding wings, landing gear, and air-breathing engines for the flyback portion adds significant mass and complexity. The winged shape is not ideal for the ascent phase of a rocket launch, creating asymmetrical forces and drag that must be actively managed by powerful control systems.
Structural Integrity: A booster must be strong enough to withstand the immense forces of launch and then agile enough to glide and land horizontally. This dual-purpose design can be a compromise that adds weight and complexity.
Economic Feasibility: While the long-term goal is to reduce costs, the initial development and manufacturing of such a complex vehicle would be incredibly expensive. SpaceX's decision to pursue the "propulsive landing" method with the Falcon 9 and Starship was, in part, a bet that the simplicity of the design would prove more cost-effective than the complex flyback booster concepts.
Your team's interest in a flyback first stage to compete with Super Heavy is a valid line of inquiry. The success of SpaceX's approach doesn't mean it's the only path forward. The flyback booster concept, while difficult, could offer unique advantages in terms of propulsive efficiency and operational flexibility, especially if an alternative method for achieving the vertical velocity of a first stage could be found.
You might find this video on a reusable launch system interesting, as it explains the challenges of making a vehicle that can both launch like a rocket and land like a plane. Reusable Winged Rocket Booster Explained
Next Generation Superheavy Booster! - Spaceflight Weekly #175 - YouTubeLabPadre Space · 18K views
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Thank you for staying with us to arrive at a satisfying resolution of our inquiry! It is particularly helpful to learn of the European and Russian studies, along with the pre-Shuttle study! The idea of designing smaller flyback boosters for first stage duty is particularly interesting. These would be an alternative to the solid fuel boosters in wide use today. Finally, thank you for the two link suggestions for further study.
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I'm glad I could provide some valuable information for your team's research. The DLR and Baikal studies are great examples of how the concept of reusable flyback boosters has been a persistent area of interest, even if it hasn't yet led to a fielded system. The idea of using a smaller, reusable liquid-fueled flyback booster as a replacement for expendable solid rocket boosters is a compelling one, as it could potentially offer the best of both worlds: the high thrust of boosters and the cost savings of reusability.I wish you the best of luck with your project. If you have any more questions down the road, please don't hesitate to ask!
This topic is available if anyone in NewMars has an opportunity to follow up on some (or all ) of the hints provided in the Gemini discussion.
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Lockheed's first-stage flyback booster
Lockheed explored reusable launch systems with concepts like the Reusable First Stage (RFS) Vehicle, also known as the Liquid Flyback Booster (LFBB), designed to replace the Space Shuttle's solid rocket boosters. This system featured a first stage that would launch vertically, then separate from the main spacecraft, and autonomously glide or fly back to a runway for reuse, significantly reducing operational costs and improving safety. While a full-scale, flight-tested scale model was developed, the project, which included a fully reusable design for the entire Space Shuttle system, was ultimately not funded and never implemented with the actual Space Shuttle.
Key Aspects of the LFBB Concept
Replace Solid Boosters:
The LFBB was designed to replace the existing solid rocket boosters (SRBs) of the Space Shuttle with fully reusable liquid-fueled boosters.Self-Powered Return:
After boosting the shuttle and external tank, the LFBB would perform a powered, winged return flight to the launch site or a runway, similar to a large aircraft.
Cost Savings:
The main goal was to dramatically lower operational costs by eliminating the need to refurbish and rebuild expendable boosters after each mission.
Improved Safety & Performance:
The fully reusable liquid boosters were also expected to increase safety by providing greater flexibility, such as single-engine-out capability during ascent, and improve overall system performance.
Autonomous Operation:
The LFBB was designed to be capable of autonomous return and landing at the launch site.
Development and Outcome
Early Concepts:
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The idea for a reusable flyback first stage dates back to the early 1970s as part of Lockheed's vision for a fully reusable shuttle system.
Scale Model Testing:
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In the mid-2000s, Lockheed Martin Space Systems conducted flight tests of a scale model of a liquid flyback booster as part of internally funded research.
Lack of Funding:
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Despite its potential, the fully reusable rocket design was ultimately shelved due to budget cuts, and the project never moved beyond the concept and testing phases. The Space Shuttle continued to use its expendable solid rocket boosters for its operational lifespan
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DUAL LIQUID FLYBACK BOOSTER FOR THE SPACE SHUTTLE
SHUTTLE LIQUID FLY BACK BOOSTER CONFIGURATION
in essence the Falcon first stage have achived the reuse concept of the article
The Universal Reusable First Stage
Fly back booster patent
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