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This logbook entry is about Falcon’s not yet but hopefully soon reusable upper stage. As every space enthusiast is aware of, SpaceX is recovering and reusing their first stage boosters. The first stage turns around and guides itself like a missile after separation, using grid fins to hit its target drone ship out in the ocean. Then, just before impact, up to three engines ignite to land on the floating platform which is stabilized and held in place by the ship’s extremely powerful and foldable propellers. This still one of a kind maneuver is what makes SpaceX so different from other rocket companies which all throw away their boosters crashing them into the ocean.
Having figured out how to land the booster safely SpaceX also decided to recover their multi million dollar payload fairing. While it looks simple this fairing pushes against all the aerodynamic pressure during launch to protect the payload up top. It’s normally separated once the rocket leaves the atmosphere to then also crash into the ocean. A rather simple solution SpaceX came up with is to equip each of the fairing halves with a parafoil and cold gas thrusters. The thrust keeps them oriented and stable while they re-enter back into the atmosphere before the parafoil is released. Operating a parafoil above such a giant piece of hardware is extremely challenging due to all the turbulences and SpaceX is yet not able to land land their fairings routinely but they’re of course working on it. Each half is supposed to land on a second ship out in the ocean called Mr. Steven. It has a giant net stretched over four enormous pillars and I assume they will have two of those ships in the future. (www.kNews.space) That’s what Elon Musk refers to as a bouncy castle btw.. It’s bouncy but castle mmh not so much but let’s not start to nitpick here because there will probably be no party balloons recovering the upper stage either.
The last part of the rocket that remains crashing into the ocean is that upper stage. Recovering and reusing it has not the highest priority for SpaceX since they are working on their next gen rocket, the BFR, which stands for. It’s the Big F***on Rocket.
However, they are going to try it, improving it progressively. Similar to the fairings the upper stage is supposed to land on a ship probably also using a parafoil of some sort only bigger. The most difficult part though is to re-enter back into the atmosphere without breaking up which is a completely different endeavour flying at orbital speeds. One important thing to keep in mind is every kilogram added to the upper stage means a kilogram less payload since the upper stage goes wherever the payload goes naturally. So I assume this is only an option for either light Falcon 9 payloads or the Falcon Heavy.
The most popular method on the internet to get the upper stage back is a so called ballute. Not that balut guys from the philippines. This one is a fusion between a balloon and a parachute. Ha! It inflates itself like a parachute without the need of any gas while providing a huge surface area to act as a giant drag brake essentially. The idea is to decrease the speed as fast as possible during reentry and keep the nose of the stage pointing downward. (ww w.kN ews.spac e) Without it the heaviest part would face the hot plasma which would be the engine section. It could then double to either land the upper stage safely on a ship, or maybe even allow to catch it with a giant drone like the United Launch Alliance plans to do with their Vulcan rocket’s engine section.
However, latter sounds a little too complex for SpaceX as this recovery is not a priority right now. But who knows. I’m not quite sure how all of that would work out especially since the ballute had to be heat resistant. But that’s just one way they could do it and I want to explore a more crazy method.
While the ballute idea sounds really good and was even tried before, I’m still a bit sceptical about this approach. The reason is it can only be used during reentry and they couldn’t deorbit and lose speed before that happens. Such a ballute also had to be mounted next to the engine which could have unknown consequences to a launch and I doubt they will do a test launch with it or recertify their upper stage. Mounting inflatable stuff as a secondary payload inside the fairing on the other hand should be no big deal. So I think they will at least start putting stuff there to gain experience before they make changes in more dangerous areas.
So what could they do in order to reenter without destroying the expensive engine? The solution is to get rid of as much speed as possible while still in space. It’s of course highly speculative at this point but the upper stage tanks are pressurized with Helium gas as they drain. Once the mission is over this gas is vented into space to make sure the upper stage tanks do not rupture from heating up in the sunlight. As you can imagine this gas could also be used to inflate a giant balloon. (www.kNews.space) To make things a little less complicated and stable SpaceX could omit the rope and mount the balloon or multiple balloons directly to the payload adapter. However, doing it like this they had to mount a pipe at the side of the vehicle since all the necessary connections are at the bottom where the engine is. I’m not sure if SpaceX is willing to do changes to its fuel piping system to reuse the upper stage but for this video I assume they do. If not it’s probably going to be a self inflating ballute as mentioned in the beginning that does not require internal gas.
A benefit of such side mounted balloons would be they could act like giant inflatable fins basically. Varying the pressure and size they could even steer the upper stage and point the bottom section in the right direction to bounce off the atmosphere a little like the Space Shuttle used to do in order to lose as much velocity as possible before they hit the thicker more dense layers where the real heating begins. (www.kNews.space) Whatever they come up with and which orientation the upper stage will reenter, they will not be able to get rid of all the velocity so some kind of heat shield will be needed. SpaceX plan is to add more and more insulation to its upper stage similar to what they’ve done to their Block 5 booster. They covered all the parts that are exposed to the reentry heat with their black insulating material. They will either shield more of the engine or come up with a payload adapter shielding solution, where they can still mount the payload safely.
Though, I personally only see it as a backup plan should the development of BFR not go as smoothly and take much longer than expected. Having a completely reusable rocket would make a big difference and would drop the costs to launch Falcon down to single digit million values competing with even the smallest of launchers. Even if it was Falcon Heavy. Do you have some thoughts on it as well? Feel free to leave a comment below the video I read all of them!Written on June 20th, 2018 by Lukas