Can we file that under lies for children :)? Engine designers recognize that the gas generator output is a waste and often find something to do with it. As you note, on the F-1 the exhaust is pumped into the nozzle for cooling (it doesn’t do much for thrust, as it’s downstream of the combustion chamber). Even in the Merlin, the exhaust goes through a small nozzle and gives a little extra thrust. Other designs may use the exhaust to pressurize the propellant tanks, either directly or via a heat exchanger. In others, it was used for roll control (including the Merlin 1C on the Falcon 1). However, none of these uses reach the efficiency of staged combustion, and there are frequently better ways to solve those problems.
Elon Musk announced this today:
Pretty exciting achievement for the SpaceX team
I’d suppose that the RD-180 probably also exceeded its 267 bar “nameplate rating” in ground testing, but nevertheless that’s pretty awesome to hear. Especially as it’s still without subcooled propellant:
I like the “provided everything holds together”. Never a certain thing in engine bringup…
Thank you — most helpful. In essence, to get the fuel (including oxidizer) moving quickly, you need turbo pumps. To run the turbo pumps, you need to use some of that fuel and/or oxidizer. But what proportion of each, and what do you with the leftover stuff from this action? Interesting how important certain materials are (and how the Russians were ahead of us), and how high chamber pressure is a goal for many of the actions, but not necessarily all of them.
Uh oh…
SpaceX launch: Starman trackers warn Elon Musk’s Tesla Roadster will CRASH into Earth!!!
(within the next ten million years… or probably some other planet, who knows?)
Not so much quickly, but at a very high pressure. Think about filling a bike tire–it’s easy to pump if it’s flat, but it gets harder to pump the more full it gets (as a note, a bike tire is generally 5-10 bar, while the turbopumps here run at 800 bar). The gases in the combustion chamber aren’t moving all that quickly (that happens in the nozzle), but to get the propellant in you still have to exceed that pressure.
Other than that, you’ve pretty much got it. Rocket science is a series of tradeoffs and just about everything you do to improve one thing makes something else that much harder.
Ahh, thanks!
The first Dragon 2 demo mission is tonight:
11:49pm PST, 2:49am ET, 07:49 UTC.
No cargo, aside from some mass simulators and a mannequin named Ripley. No word on whether an orange cat will pop out when the ISS astronauts pop open the hatch.
The Dragon 2 looks like a proper spaceship compared to the Soyuz.
Yep, I can hardly wait. Should be a beautiful flight.
I really, really want the mannequin to be rigged with a chest-burster that pops out when the ISS astronauts enter the capsule.
Woo-hoo! Perfect mission so far. Successful launch, drone ship landing, and Crew Dragon deploy. Sounds like it’ll spend a while doing basic checks before docking with the ISS, but so far it’s going really well.
I agree that their zero-G detector should have been a facehugger :-).
Dunno about perfect, the landing was a few metres off-centre. Tsk tsk.
But we got to see the whole landing without the feed cutting out. That’s gotta count for something.
As a point of comparison in landing accuracy, the Soyuz capsule comes equipped with a gun in order to shoot bears or wolves, since it may land so far off target in Siberia that they can’t get to it in a reasonable time.
Looking at a diagram of a rocket engine and turbopump, it reminded me of ONI with its pipes that efficiently channel flows: https://imgur.com/SZ8OigQ
What kind of metal do they use in the combustion chamber? What tends to be the performance bottleneck in rocket engines?
The piping is quite impressive. The SSME, which you linked to, is worse than most since it includes two low-pressure pumps and because it’s only an ordinary (fuel-rich) staged combustion engine. A similar diagram for the Raptor is actually easier to understand, IMO.
The combustion chamber and throat is typically a copper alloy. A high melting point is obviously important, but even more important is that it has a very high thermal conductivity. The parts are cooled “regeneratively”, which is to say that cold propellant is piped through them before going on to the preburner. Although there are materials with a higher melting point than copper, they all (aside from diamond, maybe) have a significantly lower thermal conductivity. That makes the regenerative cooling less effective.
I’d say temperature is ultimately the biggest performance bottleneck. Given a material that survive as a turbine blade at a higher temperature, you can immediately increase the performance of many engine designs. The FFSC design is useful in the first place because the flow that drives the turbines can only get so hot, and yet if we try to increase power by (say) adding more fuel to the oxygen flow, that raises the temperature too much. FFSC gets a rough doubling on top of partial staged combustion because it uses both the fuel and oxygen flows, but that’s a one shot deal. There’s no more turbopump power to be had without raising the temperature beyond what the turbines can take. But turbopump power is what you need to get even higher combustion chamber pressures.
Dunno if anyone else stayed up late last night for the docking, but it all went splendidly.
This is impressive for a variety of reasons, but the big one is that this was, for SpaceX, an entirely new way of connecting to the station. Previous Dragon missions were (according to NASA terminology) berthed, not docked–which means that the capsule was merely brought close by, and then a robot arm on the ISS grabbed the capsule and brought it the rest of the way in. In contrast, the Crew Dragon does a proper docking, using its own power to bring it into connection with the station. It’s also entirely automated. They were able to test several extra functions, such as the ability to move back from a checkpoint.
At this point, the only pieces left are the undocking and the reentry. Crew Dragon uses a similar mode of reentry as the Cargo Dragon, but the shape of the craft is different and Musk had some minor concern about aerodynamic instabilities. I doubt that’s a serious risk at this point, but you never really know until you test against reality.
Crew Dragon has safely returned to Earth
It doesn’t look like they encountered any problems at all. Musk had been somewhat worried about reentry, and while the capsule obviously arrived safely, I wonder if we’ll hear anything more detailed about it.
The only thing left to test is the launch abort system. That test is scheduled for June. Then, if everything goes perfectly, an actual crew launch in July. I don’t know that anyone’s expecting them to make that date, but given the current results, it’s not yet impossible.
Yeah, this couldn’t have gone better for SpaceX. Great flight.
In the meantime, NASA is saying the date may slip again for the inaugural launch of SLS.
Who did the recovery, Space-x or the Navy?
SpaceX did the recovery using a vessel called the Go Searcher. It has a helicopter pad, speedboat launchers, a medical bay, and some other things. This recovery used a second vessel called the Go Navigator as well, but that isn’t expected to be needed for typical launches. Some more details here.