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Aerospike engines are one case where single pump and multiple thrust chambers could work. It does suffer from limited throttle range which is issue for RLV but not for ELV.
Advanced Concepts / Re: Realistic, near-term, rotating Space Station
« Last post by Roy_H on Today at 05:18 PM »
Just for clarification, the hub modules are primarily BA2100s, some modified for ports on the side. The rim modules are not BA330s but a new purpose built design I call BA1400. They are 18m long 12m diameter and have three levels in them, top floor is for state rooms and lower level is for utilities.
ESA Launchers - Ariane, Soyuz at CSG, Vega / Re: ESA - Vega Updates
« Last post by SciNews on Today at 05:11 PM »
EuroNews: Love and rockets: Inside Italy's Vega launcher factory
This is so wrong...   I'm really confused as to why this is not obvious... anyone care to explain?

Yes, it is obvious.

It is because we all here have this strong emotional attachment to space and all things space. If the Em drive and Mach effect drives were pitched as free energy machines (and they could have been) we would sneer at them. But since they're pitched as space drives we embrace them. We make excuses for them like "people thought mas was conserved at one time", or "kinetic energy is proportional to (dv)^2, not v^2" or "it's pushing against the entire universe". We even spend thousands of dollars and hundreds of hours trying to build them.

Deep down we're all still ten year olds when it comes to space. I don't exclude myself.

And that's not entirely a bad thing. Great things come just as often from strong emotional attachment as from detached rationalism. Musk is an obvious example, with his fascination with Mars.
Advanced Concepts / Re: Realistic, near-term, rotating Space Station
« Last post by Roy_H on Today at 04:55 PM »
You guys are quite right in my design I make a gross assumption that there will be no problems with 2 RPM and people working half a day and 1g environment and half a day and 0g. This should be proven out first at a smaller scale.

Last pic shows elevator docked at rim.
I think what the OP is getting at is why one would build a Merlin-class engine and use e.g. four of them on a rocket versus a single engine including a turbopump four times the size of a Merlin and with four Merlin-sized combustion chambers/bells.

The answer, as alluded to previously, is that these days it's really a false choice.

Single-pump/multi-chamber engines are mostly an artifact of Soviet engine development that has survived to the present day. They did a fantastic job with their turbopumps (e.g. ORSC), but they had trouble with combustion stability in larger (e.g. RD-170 or F1-class) designs. As such, they decided to instead feed the pump output to multiple, smaller combustion chambers.

The thing one needs to remember is that computing has come rather a long way. The ability to virtually simulate combustion and incrementally refine your design means that the first time you actually assemble a physical combustion chamber and injection array, you have good confidence that it won't just blow up. Without those computing resources, though, many fewer calculations could be done, and achieving combustion stability required lots of hardware and testing.

So, in essence, multi-chamber engines solved a problem which generally doesn't exist today. A multi-chamber engine is naturally more complex than an equivalently sized single chamber engine and, thus, to be avoided.

As for clustering versus building a larger, single engine, I believe that comes down to development money. To some degree, a smaller engine is cheaper and easier to develop than a larger one. Given modern control systems capable of controlling a large cluster of engines, designs are no longer limited to preferably one and a few at most.

Given SpaceX's success with Falcon 9, I don't think it's surprising that companies with relatively limited development funds tend to lean towards using many smaller engines, hoping to reap the benefits of mass production and gain reliability through being able to withstand some degree of engine failure. For example, Rocketlab uses 9 Rutherfords, Firefly Alpha is now using 4 Reaver engines, Orbex's Prime is using 6 engines, and I believe multiple Chinese microlaunchers are all using clustered designs.

On the other hand, the Branson-backed Virgin Orbit's LauncherOne uses a single NewtonThree engine, and Musk's SpaceX designed Falcon 1 around a single Merlin engine.

However, even for SpaceX, it was easier (read: much faster and cheaper) to cluster five of them together to build a medium-class rocket, rather than design, build, and test an engine five times Merlin's size. And, after that, to just stretch the tanks and add another four Merlins to the rocket when the Falcon 5 wouldn't have been able to lift enough cargo per SpaceX's NASA contract.

So, it seems to me that you use multi-chambered engines if you can't achieve combustion stability for a single large chamber, and you use a cluster of engines to save the development costs of a larger engine.
I believe the purpose is still under debate.  L2 could provide additional insight.
- By Michael Baylor

- Awesome 2,700 word overview of the SpaceX Fleet status (thanks to our community for the photo help).
And many thanks to this thread for helping with this! (Please keep them coming).
- By Michael Baylor

- Awesome 2,700 word overview of the SpaceX Fleet status
See here

For those who don't or can't look thru to that Twitter link it is verifying that the launch of Amos 17 is now scheduled for a three month window in Q2 2019, so well after the announced launch of SpaceIL's moon lander.
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