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The recovery and reuse of launch vehicles is a hot-button issue. Many believe that any vehicle being developed that does not incorporate a system to recover and reuse at least some of its core elements is an antique unfit for the modern world. Others, however, believe that these systems are not applicable to all classes of vehicles and that microlaunchers, in particular, do not have the payload capacity for recovery and reuse systems.
This is not a debate that can be easily settled. As a result of this ambiguity, some European launch startups have chosen to develop these systems in the background without much publicity to ensure that, if needed, they don’t have to start from scratch. A few have chosen to steam ahead with their reusability efforts hoping to be the first to prove their concepts or to develop tech that can be applied to larger vehicles. The result of all this is the development of a number of really interesting recovery and reuse systems.
The Isar Aerospace solution isn't singular. The patent filed by the company includes a number of slight variations, but all of them employ a single core mechanism. This core mechanism is the use of “lifting gas” to inflate a deployable structure. One iteration of the design includes an airship-like structure with a steerable propulsion unit that would be used to guide the rocket to a landing zone to be recovered and then reused. Variations of the system call for the use of either a small parachute, grid fins, or the reigniting of the stage's main engines to slow the vehicle from supersonic reentry speeds to a velocity that would allow for the deployment and inflation of the airship structure. The addition of grid fins could also be used for attitude control during the rocket stage's ballistic flight after separation. A small drogue-like parachute would be employed to pull the inflated structure out of its compartment within which it's stored once the rocket’s velocity was arrested sufficiently to allow for the deployment.
The patent also outlines some interesting solutions for powering the flight of the airship structure. One version of the proposed recovery solution employs a steerable propeller or ducked fan connected to an electric motor. The motor would be powered either by a battery or even by a flexible solar panel seamlessly attached to the hull of the rocket stage.
Utilising what is essentially an airship to recover the first stage of its Spectrum launch vehicle would likely limit the conditions in which it could operate. However, as wind speed is generally a key factor in launch conditions, the ideal conditions for its operation may not be all that different from those required for launch. However, that is assuming that conditions at the launchpad are at least similar to those downrange of the pad, which is certainly not a given.
PLD Space offers a diagram of its reusability system on the Miura 5 page of the company’s website. The diagram shows the rocket's first stage reentering Earth's atmosphere after separation and deploying a parachute to decelerate its descent. The stage splashes down in the ocean before being recovered by a ship and returned for refurbishment and reuse.
This kind of recovery method is always going to have two main drawbacks. The first is that the ocean is unpredictable, which will make recovering a 20.37-metre rocket stage from its waters challenging on even the clearest of days. The second is that the second the stage splashes down, the salt water will go to work corroding any number of key components. That's not to say that these components can’t be refurbished and reused. However, the refurbishment process will likely be significantly more involved than it would be if the stage had avoided the salty waters of the ocean altogether.
An ocean recovery may, however, only be the start for PLD Space. In an early iteration of the company's reuse efforts when its rocket was still called Arion, PLD Space proposed the use of multiple parachutes to reduce the rocket's velocity from supersonic speeds. This version of its recovery system also utilised a paraglider that would have allowed a controlled descent. This design may have allowed for a more refurbishment-friendly recovery. However, by 2021 the company was exploring using propulsive means to reduce the rocket's velocity to a point that parachutes could be safely opened. This approach appeared to ditch the paraglider, although that was not explicitly stated by PLD Space.
MaiaSpace is the only microlaunch startup pursuing reuse via propulsive landing and there's a good reason for that, clearly illustrated by examining the rocket's max payload capabilities under its two configurations. When the rocket is being reused, the Maia vehicle will only be capable of launching with payloads up to 500 kilograms. However, when launched in an expendable configuration the rocket will be capable of tripling that payload capacity with up to 1,500 kilograms. That means that implementing propulsive reusability reduces the rocket's payload capacity by two-thirds. So, why even pursue this method of recovery and reuse? Because it's not really about Maia. It's about what comes next.
MaiaSpace is a wholly owned subsidiary of ArianeGroup. The company is currently working hard to get Ariane 6 to the launch pad for the first time. However, the company also has an eye on what comes next. ESA has outlined a future of European launch capabilities that revolves around a modular launch system that can be used for small to heavy launch capabilities. Maia is about developing the core technology that will form the backbone of ArianeGroup's bid to fulfill ESA's requirements for a next-gen European launch system.
To build out this core tech, MaiaSpace is making use of both ArianeGroup’s Themis and Prometheus projects which the company is under contract from ESA to develop. Maia will utilise three Prometheus engines aboard its first stage and a single vacuum-optimized Prometheus engine aboard its second stage. The core elements of the recovery system that will be utilised for Maia are being developed for Themis, a single-stage booster demonstrator that is expected to begin initial hop tests in 2024.
Pangea Aerospace filed a patent in 2020 for one of the most unique recovery methods utilizing turbofans, turboprops, propfans, propellers or ducted fans” which would be mounted in a pair of side pods to decelerate and recover the company's Meso rocket. However, Pangea has since pivoted away from not just developing this recovery system but from developing complete rockets altogether. The company has formed a group of Spanish companies with the aim of jointly developing a launch vehicle with Pangea providing its 300 kN ARCOS aerospike engine and recovery expertise to the project. The company hopes to receive €42 million in funding for the project from Spain's Centre for the Development of Industrial Technology (CDTI). However, PLD Space is also competing for the CDTI funding.
The Pangea-led consortium building the launch vehicle is comprised of GMV, ITP Aero, Aenium, and URAX. I got a chance to speak to Pangea Aerospace CCO Xavier Llairo who shared a few details about the consortium’s recovery and reuse plans. According to Llairo, the ARCOS aerospike engine “facilitates passive atmospheric reentry (without engine ignition) due to its geometry and regenerative cooling system, effectively acting as an actively cooled heat shield. This is very important as you minimize the payload penalty.”
Following reentry, the company plans to utilise a parachute for recovery operations and will focus on a solution that does not require the stage to splash down in the ocean.
“Regarding the recovery system, in order to maximize the competitive advantages of the aerospike engine and achieve full reusability for our clients, we want to avoid its exposure to seawater,” explained Llairo. With this idea in mind, we had the opportunity to lead the RRTB project, funded by the European Commission, in which we explored several landing technologies. Among them, we studied the parachute as a recovery configuration that enables us to retrieve the vehicle, drastically decrease the payload penalty and reuse it with minimal refurbishment operations. This approach allows us to fully leverage the competitive advantages offered by the aerospike engine, as it eliminates the need for re-entry and landing burns (so reduces even more fuel consumption) and facilitates reusability with minimal refurbishment.”
According to its bid for the CDTI funding, Pangea Aerospace is exploring utilising a helicopter to recover the stage midair following parachute development.
Orbex has publicly stated that recovery and reuse are part of the plan for its Prime vehicle but has offered very few details. A patent filed in 2018 does, however, give a glimpse into the company's efforts. The primary goal of the design is to incorporate a mechanism that would allow for the slowing down of the stage during reentry without affecting the aerodynamics of the rocket during launch. To do this, the company proposed the incorporation of drag-enhancing elements to the top of the stage that could be deployed after the first stage separation. These elements would, unlike grid fins, take on the shape of the rocket, essentially being indistinguishable from the rocket’s main body at launch. The drag-enhancing elements will allow the stage to be slowed down with a high degree of orientation stability and controllability.”
According to the patent, the drag-enhancing elements would measure between 0.5 and 2 metres long or between 12 and 17% of the total length of the stage. The number of drag-enhancing elements is suggested to be four, but the patent examines the use of as few as two and as many as eight. The exact number used would be defined by a balance between complexity, effectiveness, and operability.
The patent casts a wide net in terms of defining what material the drag-enhancing elements will be constructed from. Carbon-fiber-reinforced polymers or metals such as aluminum, stainless steel, or titanium alloys could be used in a honeycomb or foam core structure. A ceramic, polymer, or metal-based protection coating may also be employed as surface protection from the high temperatures that will be faced during reentry. The drag-enhancing elements would also be required to do double duty as a structural connection between the first and second stages of the rocket.
The addition of a parachute is proposed to further arrest the rocket stage's velocity. However, according to the patent, the drag-enhancing elements are expected to slow the stage to such a large extent that only a comparably small parachute system would be necessary. The restart of at least one of the rocket's main engines is also floated as a possible addition to further slow the rocket during the final stage of the descent.
There are a few other reusability efforts, but they're not given a dedicated write-up here as details on the particular systems are few and far between.
Sirus Space in France is developing a range of launch vehicles built from a common booster core. Renders of the vehicles feature grid fins similar to that which one would find on a Falcon 9. Interestingly, the company claims to be aiming to recover and reuse 100% of each launcher's elements. This would mean the recovery of both the second stage and fairings in addition to the first stage. The recovery and reuse of a microlauncher's second stage is an incredibly ambitious goal, to say the least.
HyPrSpace is another French launch startup developing a range of launch vehicles that will also utilise common architecture. The company's OB1-MK2 vehicle is the primary recipient of HyPrSpace's reusability efforts. According to the company, the rocket's booster will be reignited several times during reentry to allow for a soft landing in the ocean. The rocket features grid fins that will enable attitude control.
Recovering and reusing small launch vehicles is by no means a simple task. Not only do recovery systems need to function as designed, but they need to do so without a significant payload cost. If the solution demands too steep a price on the payload capability of a vehicle, recovering and reusing that vehicle will simply not make sense. In larger vehicles that balance is far more forgiving. In microlaunchers that balance is on a knife’s edge. There are some interesting solutions being pursued with many having the possibility to allow for the recovery and reuse of at least some of each rocket’s key components. It does, however, remain to be seen whether or not any of these systems will make it to the launchpad.
Dawn Aerospace is flying from NZ, but a large part of the development, funding, and team is from the Netherlands and should be considered a European launch startup. Rapid reusability was recently demonstrated with three rocket-powered flights in three days.
Curious to see Hyperspace pursuing reuse of their hybrids, given that the solid fuel grain has to be replaced every flight
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