SpaceX’s Full Size Raptor Rocket Engine Revealed By Elon Musk - Scott Manley discusses
The common misconception with anything is that it usually takes a lot of engineering to make anything work.
How small of boats are you talking? How do you recover the fairing after its landed on the net without getting it in the ocean? How do you store the net so it doesn’t fall in the water either? How do you deploy the net? How do you get 4 small boats 300 miles offshore and to make the trip back to LA or the cape in formation with a fairing?
Boats are always more expensive and they stand for Bust Out Another Thousand for a reason.
I’ve worked on exactly one boat that has gyroscope stabilization. It was a sunseeker which is a pleasure party boat which you wouldn’t want for this kind of work. No other boat I’ve ever fished on or worked on has had it and I’ve been on some(in my opinion) insanely nice boats.
4x Captains and crew aren’t cheap either
How small of boats are you talking?
Whatever creates the minimum cost that meets the requirements of the task.
How do you recover the fairing after its landed on the net without getting it in the ocean?
Maintain tension, create a lowering maneuver.
How do you store the net so it doesn’t fall in the water either?
A combination of mechanical and manual motion, i.e. do whatever they do to store Mr. Stevens’ net.
How do you deploy the net?
Just hook it up, let it sit loose on the deck and let tension take care of the rest. You could hook the net to the deck and release it from hooks as the net is unfurled in a very careful maneuver. This could be done at sea.
How do you get 4 small boats 300 miles offshore and to make the trip back to LA or the cape in formation with a fairing?
Driving them in tight formation for 10-15 hours. Or, since you only need three boats to create a triangle, one of the boats could release its tension and drive under the fairing. Or, you could have a fourth (if you only use three) or a fifth boat come with just to grab the fairing as you release the tension. Then drag the net onto that boat after releasing the corners from the other boats.
I mean, this would solve their problem.
I think you woefully underestimate the difficulty of maneuvering boats in the ocean. I actually had to look up gyroscopic stabilization of ships, as I’d never heard of it before, but you’ll find that it’s not a commonly used mechanism.
I happen to work on ships for a living: while hooked up to another ship for fuel, the rocking at <30’ off the surface of the water varies the distance between us more than 10 feet, and that’s when going in the same direction at slow speeds and relatively calm seas. EDIT: Note that 10’ is a very small number in this case, I’ve seen it exceed 40’ in terrible weather.
Now you want to have four boats, connected by what will be a very heavy net (and it doesn’t matter what you make it of, it will be very heavy), moving away from each other in a sea state that is going to be unknown and will vary from glass smooth to heavy swells, maintaining a huge amount of tension (run the math on force exerted by a body on a taut sheet, the numbers grow to be surprisingly huge), and then perform some sort of precise maneuver to lower the net without getting it in the unknown sea state?
I won’t deny it’s possible, but it is WAY more than “a little engineering.”
Also, as noted by Skyentist, captains aren’t cheap. Skilled captains, even less so, and “skilled” is a modest description of someone who can maneuver with three other captains in such a precise manner on smooth waters, much less the open ocean.
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I don’t think I’m being clear enough.
We’re talking about recovering roughly 100 million dollars a year in fairings until BFR fully replaces Falcon 9.
No, I wouldn’t run it at ultra high tension. I’d run it at a greater height with some slack. It takes infinite force to pull a rope perfectly straight under gravity.
Also, as noted by Skyentist, captains aren’t cheap. Skilled captains, even less so, and “skilled” is a modest description of someone who can maneuver with three other captains in such a precise manner on smooth waters, much less the open ocean.
Paying an elite captain for 15 hours of piloting ~20 times per year is a lot less costly than paying a small team of world class engineers full time for 3-6 months (2000-4000 engineering hours for a 4 man team. Also, not as precise with enough slack in the net and proper ship modifications to manage the load, such as counterweights and gyro stabilizers (which SpaceX could engineer themselves, maybe use Tesla tech to spin it very fast).
Also, finally, I’m not saying absolutely that this would work, but it’s an idea that if you were running SpaceX, you’d want to ask your engineers if they didn’t bring it to the table. You might think not because it would be lacking humility, but fresh eyes bring new solutions all the time.
I.e. I used a floor heater to solve the condensation problem of a microscope incubator - the microscope costs about 150,000 dollars. This was in a biophysics lab, and I think that most of the people in there, especially my professor, are smarter than I am. But, I just happened to have a different angle.
That’s why I’m saying, don’t shoot the idea down so quickly as a feasible solution. And again, by no means am I convinced that it would work, but I’m not convinced yet that it wouldn’t save a lot of time and money by the engineering being quicker and dirtier.
Although, another idea I just had is a large inflatable raft, then crane the fairings up onto the ship.
Height means greater torque on your boats, making them even harder to use. Also, I don’t think you understand the open ocean: while maintaining a safe distance on perfectly “smooth” days, the swells may cause the ships to rise and fall over 20’ relative to each other at random. On “smooth” days. Now you want to compensate using slack?
Just how small do you think you need a net to be to catch unguided, tumbling fairings? A single ship on its own would have to be overengineered to do 30 knots, three or four in tandem and sailing in opposite directions to maintain tension could never hope to get a fraction of that. That’s not even factoring in ship safety yet, because you need room between each vessel. If they could predict the fall pattern with accuracy, Mr. Steven would be adequate for the job. EDIT: single ship using something that will counter-balance the torque generated by suspending a net between arms that reach…what do you want to go with? 80 feet?
I’m not being a negative nancy because I don’t want to see them succeed, I’m being a negative nancy because the idea lacks merit. With an object that they cannot predict the fall path accurately enough, speed is going to be far more valuable than size, and speed is not the end result of tying multiple ships together. The proof is in the pudding. Do you see the wake that ship is generating? It wasn’t even close to approximating the fall location of that fairing, it made HUGE maneuvers to compensate.
I’d say having multiple ships is not a terrible idea, but instead of trying to tie them together get them spread out to make recovery more likely. Also, as seen in that video, having some mechanism to cut the parachute away/lock down the fairing on landing is going to be needed, while I’m not smart enough to be able to run the numbers on a video alone it looks to me like the parachute dragged it off the net. A little extra slack in the net itself probably wouldn’t hurt either, assuming it is within tolerances to do so.
The raft idea is better than the multi-ship net idea, but it suffers all the same problems. Speed and maneuverability will be next to nothing if you make it large enough to cover the inaccuracy of the fall prediction.
I’m not being a negative nancy
This is purely a technical intuition issue. I literally just am not convinced it isn’t possible, or even infeasible financially. I’m sure they’ll figure it out and it’ll be something different.
A single ship on its own would have to be overengineered to do 30 knots
Mr. Steven sails at 32 knots.
the swells may cause the ships to rise and fall over 20’ relative to each other at random. On “smooth” days. Now you want to compensate using slack?
I was thinking something like 400 feet between each vessel (Mr. Steven is 205 feet long), variable tension coupled with slack to prevent vessels from being pulled over, i.e. slack in the net gives you 20-30 feet and variable tension gives you another 10-20 feet for a 50’ tolerance, in addition to a very heavy gyro stabilizer. For safety, a quick release mechanism that dumps the net if the torque on the boat gets too high could be involved.
The raft idea is better than the multi-ship net idea, but it suffers all the same problems. Speed and maneuverability will be next to nothing if you make it large enough to cover the inaccuracy of the fall prediction.
The raft itself could be explosively deployed, and then a watertight, relatively strong material on the bottom could simply keep the fairing dry, while the fairing itself would simply displace enough water to allow itself to float. So, a big ring with a watertight mesh bottom that just sits on top of the water.
Hell, you could aim and fire it from Mr. Steven in the event of a near miss.
I think it’ll take a little bit more out of the box thinking. I’m sure they’ll figure it out pretty soon, they’re very close. It may just be a matter now of doing several practice runs or writing some code and integrating that new system with the guidance system on the parachute.
Scott Manley discusses - The Story Behind This Green spaceX Rocket Exhaust
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Elon seems to be aiming at the moon right now with his BFR, which is very exciting. TBH, the moon is just a better target for now for a base. Landing on Mars and getting back sounds about as difficult to me as building a small lunar station. Hell, a lunar station sounds possibly profitable with the present levels of economic growth we have right now.
I would absolutely get on a BFR to the moon, but IDK about Mars until it’s proven safe and I’m a lot older.
Hi Alkan,
It’s easy to think that because the Moon is objectively closer it is easier to go to. The reality is a bit more complicated than that. There are certainly trade-offs between choosing to start a base on the Moon or Mars. The biggest one(and the most important one in my opinion) is that time-wise the Moon is ‘closest’. If something were to happen, and I’m sure that something will, the travel time is only 3 days away and rescue is feasible. Mars on the other hand is 3-6 months away in the best of times and up to 18 at the worst of times.
If you look at the energy cost to the surface, I think it will be surprising to find that it’s actually cheaper to get to the Surface of Mars than the Moon. On top of this, the resources to produce propellant In-Situ are much more accessible on the surface of Mars(Frozen water Ice, for H and O and CO2 atmopshere for carbon). To date we haven’t found much carbon on the Moon and water is mostly in the permanently frozen craters in the poles. Luckly that’s where you’d want a base anyways because you want some place with near permanent sunlight for solar power because 2 week nights are hectic. However, because of the lack of accessible resources to manufacture propellant on the surface, that means you have to land your return propellant reducing payload to the surface of the Moon.
As it stands today, those are the most compelling reasons to choose between the two. Energy wise, it’s easier to land on Mars. In a Payload to the surface comparison, due to ISRU Mars wins out again. In a distance in case of Emergency the Moon takes the cake(such a precaution shouldn’t be taken lightly, and is why I personally think we will find a return to the Moon happening before Mars).
To go back to your original statement:
I’d say from an energy and resource perspective it’s easier to land on Mars than the Moon. For practical reasons such as getting our toes wet for longer term low-g habitats the Moon is ideal - but requires larger upfront cost and reduced payloads(More launches more $$$$$$$)
I’ve personally gone back and forth between the Mars First or Moon First debate a lot in my own head over time. It’s a tough call from an engineering standpoint - but ultimately safety comes first for our astronauts from a human standpoint which is why I see the Moon happening first. I just wanted to elaborate a bit more about what the larger costs to are to each of those missions.
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It’s easy to think that because the Moon is objectively closer it is easier to go to.
So, you’re saying Aerobraking in the martian atmosphere offsets the higher cost to reach a Mars transfer orbit? I suppose that makes sense, now that I think about it. Though, it’s going to be a bigger pain in the ass getting back to earth from Mars than the moon in both cases.
If something were to happen, and I’m sure that something will, the travel time is only 3 days away and rescue is feasible.
That’s kind of why I’m more presently interested in the moon, actually. Even if you add some delta-v to your credit card, you do get to learn a lot of important lessons before you send people to Mars. Engineering lessons, basically, more than raw energetic considerations.
However, because of the lack of accessible resources to manufacture propellant on the surface, that means you have to land your return propellant reducing payload to the surface of the Moon.
Well, it’s true that you couldn’t use methane on the moon, but liquid hydrogen/LOX would be fine using harvested water. I see this going two ways, and maybe it’s where Blue Origin will develop a niche that is separated from SpaceX with their development of hydrogen fueled engines for this generation of rockets.
I’m hoping that kilopower gets more exposure. Since most of its power output is thermal, it’s best optimized for cold environments, like the poles of the Moon or Mars. I.e. you could melt ice with the heat (harvested by breaking it apart and mildly pressurizing it first), then perform electrolysis. In return, you get more power output since it’s a heat engine and your heat sink absorbs more heat. That’s a pretty solid win.
On both counts, I see nuclear as super useful for space on the surfaces of planetary bodies since the heat output is so high from nuclear in general. Then you can mine/manufacture your shielding (lead) and most of your structures so that you’re just shipping fissile uranium cores. If it works for nuclear submarines, it will work on Mars or the moon with adequate resources mined.
I agree generally speaking though. The moon interests me more right now because it’s easier to get there and back all things considered, and you can get back sooner. Eventually, yes, I would expect more from Mars than the moon in overall population for a lot of reasons. But, as a base to build in 10 years? Moon, hands down.
Both is what I’m going for though, I’m hoping BO (what a terrible acronym, come on Bezos) gets their shit together and gets on the SpaceX development cadence. One for Moon and asteroids, one for Mars.
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It’s part aerobraking, part not having the land to the propellant to get you off of the surface. Not having to spend propellant to land propellant results in a more usable payload to the surface at the end of the day.
A distinct possibility, hydrolox will always be king for ISP reasons but it is very difficult to work with and store long term. No interplanetary missions have ever used hydrolox for maneuvering for that reason. It’s always been either monoprop hydrazine with an iridium catalyst or some combination of the common hypergols(Hydrazine with MMH or N2O4) because there is significantly less failure modes associated with them. For example, the 8x landing engines for curiosity’s sky crane were all monoprop hydrazine thrusters. For that reason I am always wary of the claims of producing depots of hydrolox for deep space exploration. The best solution I’ve seen is the ACES module from ULA designed to use the boiloff in a generator that keeps the propellant cool for longer periods. Pretty ingenious if it ever flies.
Nuclear power would be wonderful but I don’t see SpaceX using it initially. They have a fire burning beneath them where time is of the essence. “Permission” to launch nuclear power sources would take ages and I feel it’s a bit of a catch 22. There is no need for nuclear power sources because there are no offworld bases that could utilize it, but because we can’t launch nuclear power sources it’s difficult to create offworld bases. Until any initial bases are created and a demand for offworld nuclear power sources is created I don’t think we’ll see any progress on that front. Better to accomplish something tomorrow with what we can do easily today than to rely on technology/capabilities that don’t exist yet.
There is no need for nuclear power sources because there are no offworld bases that could utilize it, but because we can’t launch nuclear power sources it’s difficult to create offworld bases. Until any initial bases are created and a demand for offworld nuclear power sources is created I don’t think we’ll see any progress on that front. Better to accomplish something tomorrow with what we can do easily today than to rely on technology/capabilities that don’t exist yet.
Kilopower is worth more of a look though. It already has a working concept that weighs 134 kg and puts out a constant output of a single electric kW. Thermally, it outputs a lot more power, but it puts out a nice, constant electrical power of 1 kW.
If you watch a presentation given by the creator, he discusses how its design actually uses less enriched uranium so that it isn’t going to result in some horrendous meltdown. In fact, it’s designed to just heat up and do nothing indefinitely if it has no way to dump its power. So, it’s quite safe.
I was actually kind of stunned by it, and it’s actually a pretty recent (last couple years or so) development. Its path to use is just some work around red tape. Plus, it’s not radioactive until you turn it on, even if it crash lands.
I’ve seen Kilopower before. It would be game changing for any exploration probe, rover, lander, etc. Did you know Curiosity does everything that it does on 100 Watts? Can you imagine what sort of science we could do with 10x the power. Even Cassini was only 660(or 800, I can’t remember) Watts BoL with 3x RTGs.
You and I may know how it works, how it’s not dangerous until it’s “turned on,” but you have to convince the regulators not me. To convince the regulators you have to educate the public and that’s a tall order. I wish I wasn’t generalizing but the majority of the public really is afraid of radioactivity and any fallout associated with it and “nuclear waste”- real or perceived.
Read up about when Cassini was launched all the protests that happened regarding it’s RTGs and its plutonium heaters. People were very unhappy about it. Nuclear power in space is a tough sell unfortunately.
The reaction to nuclear is unfortunate in general. It’s such a powerful source of energy and it has so much untapped potential. If we were researching and using nuclear like we try to research renewables, we’d be a lot farther ahead, probably on better track to curb warming emissions.
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I wonder what you think of this, Skyscientist. It is actually of concern to me because I know that if you have porous material in an airframe and it hits a point of failure, it’s a case of “connect the dots.”
Rivets have to meet a distance from each other or the edge of a panel because of the structural dangers it presents.
I wonder how this issue is being addressed. Most of the time, SpaceX is way ahead of people on this sort of thing, so, who knows. Their one launchpad explosion was a case of a bad strut from an outside manufacturer, not a design flaw. There is a lot of Chinese counterfeit aerospace metal out there, so it’s easy to get duped.
This is just making me more excited for the test flights. 
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So this is technique is actually pretty common in propulsion engine called film cooling. It’s typically employed on the throats of the combustion chamber -> nozzle to help keep it cool. The throats experience the worst of the heating in the combustion process because all of the hot combustion products are compressed through the nozzle at subsonic speeds and speedup to their exhaust velocities. Film cooling works because the heat of vaporization(Liquid to Gas phase change) is usually a large energy sink and prevents the heat from reaching the chamber wall.
The grad lab I used to work in employed film cooling in our first engine that was redesigned to be 3d printed engine to help keep our printed inconel cool because we didn’t have regen cooling in that engine. The newer engine that has 5x more thrust is still in development but utilizes regen cooling and film cooling in the throat. The film cooling outlets tapped off a tiny bit of fuel from the regen lines.
I haven’t worked in that lab in a year though so I’m not sure exactly how they’re doing now.
I can’t speak for structural strength because that’s not my background(I prefer sims and control) so I’m not really sure what to say about that. I’m not exactly sure how you would do it in an airframe but as an example our film cooling channels were milimeters in diameter at most. I think we tried to go even smaller and I would expect similar on the reentry facing side of a vehicle. This makes them structurally pretty strong because of the small size of the outlets.
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And what @skyentist will never understand is the following. 
- Moon is accessible to common people because of the travel time, Mars is not, so you have a choice of doing two 6 month trips and a year stay which would make your away period over a year if you go to Mars.
- You have to be self sufficient if you go to Mars, because the travel time to the Moon is a few days you don’t need to be.
- Any emergency that can’t be handled by the ‘colony’ on Mars can be fatal, the travel time is so long that there can be no rescue from Earth.
- If you are doing 2 year missions, you will be picking ‘astronauts’, not general population, which just continues the status quo that space is not accessible to people.
- Because the Moon is so close time wise, there needs to be no fuel production off-world (technology that doesn’t exist)
- Because the Moon is so close time wise, you can send ordinary people for a week or two off-world during their annual holidays.
There is like a million other things too, all to do with travel time which is an issue for Mars.
You just want to pick a fight and argue don’t you? At least one of your bullet points I’ve already written in a previous post - whether you had taken the time to actually read it I’m not sure.
I enjoy talking about the engineering problems related to spaceflight not arguing with people for the sake of argument. If you weren’t so condescending with your holier than thou attitude I’d indulge you but man it’s really not fun and a waste of my time.