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Let a hundred reusable missiles bloom

In 2013, when Musk was just about to reuse the first stage, I made a post with the calculation and estimates of the mass costs for different landing methods. Now that reusable steps no longer surprise anyone, it’s interesting to look at which options fly and are being developed.


Landing of the side blocks Falcon Heavy, photo SpaceX

Engines


In the initial post, the minimum possible fuel supply was calculated based on one final braking at a speed limited by air resistance. In reality, the Falcon 9 stage brakes up to three times - the first inclusion brings it to the landing path, the second time the engines are turned on to reduce the heat load and only the third inclusion is made directly for landing. Exact data directly from SpaceX is not available to us, but there is a mission simulation from flightclub.io . Let's try to compare.

Calculations in 2013 yielded a minimum of 2 tons of fuel for braking from a free fall speed of 260 m / s. In the first successful landing on April 8, 2016 in the SES-8 mission, the flightclub simulation gives a speed for the moment the engine was turned on 288 m / s (guessed by chance, but the order of the numbers should not have been different), but more fuel was spent, 6 tons - and the rocket in three years it got heavier, and in the simulation it is believed that as a result, almost 5 tons of fuel will remain in the stage.



But this, in general, does not matter much, because before the first inclusion in the steps, the stock is about 50 tons, which is more than two times the dry weight of the step.



For a mission with a step back to the landing site near the start, the supply, of course, turns out to be large, but not at times - braking for aiming at a barge consumes much more fuel than it might seem. In the first return-to-launch mission, Orbcomm OG2-2 (December 2015), the flightclub simulation fuel reserve is estimated at 61 tons.



For heavy payloads, a step can make only two starts, and the barge is placed further along the flight path. For example, in a recent Starlink 3 mission, the fuel supply was supposed to be approximately 24 tons, which is comparable to the mass of the dry stage (presumably 26.3 tons).



Parachutes


Like any engineering solution, parachutes have advantages and disadvantages. On the one hand, they are great for slowing down a fall and can reduce speed to a few meters per second. But for a very soft landing, the required area begins to grow irrationally - some additional solutions are required. And with precision landing even on controlled domes there are problems. SpaceX catches the head fairings by the ship, while the softness of the landing is ensured by a huge net, but so far the fairings often miss the target. Space Shuttle side boosters landed on parachutes - their design was tighter than that of the steps with liquid engines, and landing on water softened the blow. The side boosters of the Energia launch vehicle were supposed to parachute,and the impact on the surface was supposed to be mitigated by soft landing engines and bearings with shock absorbers, but in practice they did not manage to verify this concept. Exos Aerospace's SARGE suborbital rocket is now landing in parachutes, which, due to its light weight and structural strength, can survive an impact on the ground.

You can evaluate the rigidity of landing by video from the side of the rocket, large steps will definitely not withstand this.

https://youtu.be/64cWvxnaG0M


Wings


Winged steps in metal have not yet appeared. The Adeline project for the European Ariane 6 was closed, although they managed to test a large-scale model. On the basis of the Russian Baikal, work is underway on the Krylo-SV project, in 2017-2018, work was carried out as part of the pre-project, technological demonstrators are expected no earlier than 2021.


Full-size “Wing-SV” and a smaller demonstrator

Air pickup


In fact, air interception allows you to realize the advantages of parachutes without their disadvantages. The helicopter catches the stage descending by parachute and allows you to gently land it in the right place. Theoretically, this option should require a minimum of additional mass on the rocket - not even landing supports are needed. And it is very joyful that they did not forget this idea and will try to implement it.

Rocket Lab, initially not planning to reuse the first stage, changed its mind in the fall of 2019. At the end of 2019 and the beginning of 2020, in real launches, the operation of new equipment was checked, which provided controlled descent of the stage. And last week, successful tests of picking up a prototype helicopter took place. An attempt to catch a real step can be made already at the end of 2020.



The United Launch Alliance is developing a concept for tailing the tail section of the upcoming Vulcan launch vehicle. Its first flight will take place no earlier than 2021, and it is not known whether it will immediately become reusable, or whether it will be introduced later.



Conclusion


The assessment given in 2013 that landing on engines would be one of the most heavier on the rocket was confirmed. But this does not interfere with the successful operation of the method - today there are simply no several competing in the same weight category and striving to derive the maximum payload of missiles, where a method of landing the first stage that is more effective in terms of mass could give a noticeable advantage. The more different reusable systems will be implemented, the more questions can be answered by the experience gained. Maybe by the second half of the century there will be optimal solutions that will become the standard.

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