Jon mentioned that IÂ argue pumps over pressure fed. That is partially because the first thing I tried to do seriously in rocketry was build a pump for some friendsÂ for a project in Huntsville. I started with the base assumption that turbo-pumps were just too hard and something different was needed. I built a series of pistonless pumps that never did work properly. Steve Harrington with Flowmetrics uses the same cycle only he does it right with a totally different design. Mine was 8 dividers rotating in a cylinder. Jon and I went over it during an hour Â layover in Salt Lake in 1999. That was back when you could get on a plane with large metal objects of uncertain purpose.
During the time I wasÂ trying to get these things to work, we were looking at modifying jet engines for use on an almostÂ space plane. It was pointed out to me that the fans and turbines in a jet engine had a tip speed 5 times that required to pump the sorts of pressure we wanted. These 1950s vintage jet engines had fan and turbine tip speeds of 1,000 feet per second. A LOX pump with a tip speed of 200 feet per second can deliver on the order of 250 psi. So I started studying turbine and impeller technology.
This field is difficult, convoluted, expensive and covers several disciplines that I am not equipped to understand. So I did my thing and reread the references to figure out how to game the problem.Â Eventually I decided that the normal approach was wrong.Â The normal approach seems to be to get the very best rocket engineers, the very best pump engineers, the very bestÂ CFD crew, the very best etc and have them all do their specialty to some tight specs to the best of their ability. Over the years this method has turned out some good technical engines, just not all that affordable.
I think the people making the over all decisions need a general purpose expert to stand back and look at the whole picture. Then they need to do a whole system approach to the engine with an eye to making everyone’s job easier and more team oriented. I know that I am not qualified to do any of the real jobs involved here, but I do think I have identified an approach that experts could turn into an unbeatable combination, until the next unbeatable combination comes along. And competent newspace people could build affordable staged combustion engines with the performance, reliability, maintainability, and cost that would facilitate RLV development.
The sketch at the top is a pumped H2O2 monoprop idea. By putting all the components in a single pressure sphere, heavy housings become unnecessary. By stacking the components in order, pressure plumbing becomes unnecessary. Building a very large L* is less of a problem because it is all one symmetrical housing. Accessing the equipment for maintenance is relatively easy if it separates at the equator. All the parts can be removed through a very large opening.
At the top is a low pressure H2O2 inlet straight to the impeller. The 4″ diameter impeller at 12,000 rpms could create 250 psi minus efficiency losses. A residential water pump impellerÂ is so overbuiltÂ that you can use it if it is compatible with peroxide. The impeller discharges into a bowl volute which is much lighter and simpler than a normal one, at the cost of efficiency in converting the velocity head to pressure head. The catalyst packÂ top support and center bearing support are directly under the volute. Â The catalyst pack surrounds the bearing housing down to the bottom bearing support and catalyst support.
The turbine nozzles connect the lower bearing and catalyst support to the sphere wall. The turbine is powered by the decomposed H2O2 to drive the pump. The sphere shape is to allow the use of a much larger diameter turbine than impeller. Impellers want to run at a few hundred feet per second tip speed, turbines really want over a thousand. The normal solution is a gearbox and weird plumbing. The sphere shape allows an impeller tip speed of 200 fps while the turbine has a 600 fps tip speed. Not efficient for a turbine, but the same 200 fpsÂ as the impeller would not have developed enough power, and a higher speed for efficiency would have mandated a gearbox. By using the whole H2O2 flow, evenÂ this mediumÂ turbine speed can power this system.
The turbine exhaust has more than sufficient time to get organized as rocket exhaust through the throat. There would also be plenty of time to afterburn some fuel in the sphere lower half if you solve the problem of pressurizing the fuel and cooling a lot of surface. The 250 psi theoretical pump pressure could be expected to yield about 100 psi below the turbine after the efficiency losses and pressure drops are figured.
I’m not really a fan of peroxide, but that is more a matter of cost and availability than anything else. Peroxide is a self pumping fluid if done right though. By using decent pump and turbine designs, the above speeds could be doubled which would quadruple the pump pressure and get you well on the way to a more efficient engine with good T/W. By using aerospace design practice, with engineers experienced at it, Final pressures of a few thousand psi could be realized in the lower chamber.
My bi prop ideas will come later. Hill and Peterson is my primary reference. Hutzel and Huang doesn’t get deep enough for good understanding of the issues. Sutton doesn’t help.