So the J58 has the bypass capability but it will only bypass in the high mach. One can also see it has paid the price in complexity at the turbine end. Mind you this a design from the 60’s. So at high speeds this engine is very similar to drawings I have been doing. The turbine is bypassed at about mach 2.1 and above. Engine pretty much just converts in to a big ramjet. It sounds simple enough but it has some complex features to deal with pressure build up. The Aerospike has to move and so on. Regardless it is yet another example a compound system that worked great.
So I am taking a look today at the various CFD options. I’ve looked around to see who is using what software. Basically it would seem to me the people doing real engineering and actually building things are using a variety of solutions. Some of which I have never heard of. I just assumed everyone was using ANSYS but it would seem not.
Copenhagen Suborbital – Solid Works / Open Foam
XCOR Aerospace – http://www.metacomptech.com/
Space X – Ansys
JPL – Whole bunch of things including ANSYS.
Also it would seem my ideas about hypersonic combined flow system. Precooling. Non direct coupled impellers. Piston pumps. Pretty much all of it is right on the bleeding edge where I should be. Rather satisfying to contemplate these ideas and to then realize this work is actually being done.
Some general observations about the new F1B engine vs the Apollo era F-1 engine.
1. Ditching the Turbo pump after flow injection makes for a simpler engine but it also shows to much academia not enough intuition. Those Apollo guys made a big deal of turbo pump through flow injection to the primary chamber for a reason. Anybody who has ever built anything fast can tell you why.
2. Ditching the radial tube arrangement due to manufacturing complexity assumes you were going to manufacture a radially arrayed tube structure the same way the Apollo engineers did. This does not have to be the case. It is a brilliant design that gets the maximum flow for the minimum mass. Do the simple math for the tube area vs a double chamber layer design + supporting internal baffles. It is good to note the Redstone engines and the V2 were all part of a long history of double wall design. They abandoned it for a REASON. I can think of at least 3 different ways to manufacture that original Apollo chamber design that are economical and low in manual assembly / labor.
3. Your still building your grand parents rocket engine. While I understand that aerospace is typically conservative WTF for. We are so far beyond this standard rocket combination and we need to move on. The next generation of engines will clearly be hybrid rocket jet compounds with some ambient air breathing facility and this engine isn’t it …..
4. After a bit of study it is really quite exciting to realize that you don’t need to be either JPL or a large research institute to build a decent engine any more. All you need is to be half competent prepared to acknowledge the reality of risk and to push the boundaries.
This is my second pass at a thrust chamber. By building it from tubes like the F-1 series engines I was greatly able to reduce the 3D printing costs. Also I halved the size. Few issues to resolve with hole sizes that are to small for the SLS process to handle. Also I not sure how the final exit portion of the engine bell will be joined and it has no supporting bracket points on the top mount. I think for trial runs it will just flow direct from an oxygen bottle and kerosene driven by a standard high flow fuel pump …
General sketches suggesting how to contemplate the Sabre cycle principle. Basically this is all about Turbo Pumps and Compressors. How do you combine a high flow rocket engine with a low flow ambient compressor. You can start to contemplate complete cast blocks with the rocket chamber portion at one end. Will be drawing one of these in the entirety shortly. Least anyone thinks I just wanted to copy some tired old F-1 design. We are well beyond that now but …. physically have to begin somewhere ….
Really all the problems … are production problems … should completely not at all think about these problems like our grand parents .. this complex … . multi component carrying .. .bolted together .. masterfully welded … kaboodle .. .. So the F1B is down to less than 200 parts .. or so they claim ….
This is an Apollo Turbopump impeller. It is about 2 feet long from end to end and weighs a lot. This is a very, very, very precise piece of equipment. Either from F1 or J-2 engines, but it is impressive, regardless. The partial paperwork that came with this explains that it is as perfectly balanced as was humanly possible back in the 1960’s. Remember, this was before CNC milling, when metal things like this had to be jigged and run by hand. Precision was really, unbelievably hard back then, and yet they made this. Actually, many of these. Impellers for pumping LOX or Kerosene or Liquid hydrogen, which was capable of spinning at 28,000 (Yes, twenty-eight THOUSAND) RPM. This is the finest example of precision engineering and milling I have ever seen.
These are some pictures of the original Redstone engine.
So I just finished watching Don Pettit on the Tyranny Of The Rocket equation and I think he sums up beautifully the current problems with our multi stage to orbit capabilities and has captured my thinking exactly.
In a nut shell a turbo compressor driven high exhaust velocity liquid fueled rocket engine does a terrible job while it is going slow and must carry an enormous penalty in the form of highly pressurized mass to get to the point where it can get fast enough to be efficient and hit that magic 11180.6 m/s. This requires multiple staging complex sub systems complicated ground handling and expertise in dangerous oxidizers like super concentrated hydrogen peroxide and toxic hypergolics.
If you look at the companies involved in getting us in to orbit at the moment ( note here I am just supposing that Nasa is a dead loss by default ) they all have different approaches to the tyranny and I find them all lacking.
If you look at what SpaceX are doing it is all about cycle time. Sure they want to build cheaper more efficient rockets but no matter how well they design these systems unless they do something really radical they are still constrained by the same problems as any other rocket system. They aim to address some of these problems by building cheaper recoverable rocket systems and having a turn around time measured in days not months. They aim to build rockets that are simply BIGGER to lift more mass. But observe that none of this solves the basic problem of having to loft an enormous tank of oxidizer/fuel mass all the way to the edge of the atmosphere.
(b) Copenhagen Suborbitals
To my mind Copenhagen Suborbitals are not really INVENTING anything. Rather they are following a very specific well trodden path for a sub orbital shot and trying to do so on a small budget using open source hardware. I am all for this and it is excellent to see them throwing together items like turbo pumps from used turbines and so on. This is all commendable but once again none of this solves the basic problem.
(c) Armadillo Aerospace
Armadillo for the most part seem to be messing around in a highly focused but pointless kind of way. Powered descent capability. Various kinds of hybrid engine. This is all well and good but once again none of this is addressing the tyranny.
(d) Virgin Galactic & Scaled Composites
Both of these companies are repeating what I would call the ‘X’ flights. These are essentially small aerodynamic jet type vehicles lifted by a secondary flying vehicle from which they drop and make a shot. Vehicles like White Knight will get us to sub orbit but they wont be carrying much in the way of useful mass. Once again none of the tyranny is being solved here.
(e) Reaction Engines Limited
Now this is where it at last gets interesting. These guys are directly addressing the tyranny in a way nobody else is. The Sabre system is accepting the harsh reality that for us to get single transition to orbit systems with decent turn around and conventional landing and take off ability we are going to have to fundamentally rethink our rocket systems and think of something new.
So where does that leave us. Well I think the Sabre guys have pointed the way to a whole different conception of the traditional rocket engine. We can now begin to do the math to ask serious questions about hybrid systems. As soon as you begin to think about replacing the tank mass and going partially ambient the rocket tyranny starts to look less and less like a problem. If all your assumptions about transfer to orbit are not based on an enormous highly pressurized expensive one shot tube of metal you get a lot more options.
At the moment I am busy working out compressor sizes for a given flow rate to get some given mass in to orbit. It gets interesting. For example I can see that even a 20% reduction in total fuel mass to orbit would be pushing the engineering in to the realm of achievable for an organisation like Copenhagen Suborbital. Basically solve the high pressure tank mass problem and figure out a way to harness some of that air mass your already flying through and everything looks better. This is also changes how you think about the design of the vehicle. So for example so what if you need a compressor with a 3 meter inlet diameter. Nobody said a system like this had to all be in a long tall thin metal tube.