1 engine with multiple chambers/nozzles doesn’t solve their pump issue (turbo/electric/hybrid), is just makes it worse! Because now you don’t need to design a Merlin class pump, you need an F-1 class pump. You aren’t solving anything that way, just making it more complex.
Quote from: Lars-J on 03/06/2021 04:42 am1 engine with multiple chambers/nozzles doesn’t solve their pump issue (turbo/electric/hybrid), is just makes it worse! Because now you don’t need to design a Merlin class pump, you need an F-1 class pump. You aren’t solving anything that way, just making it more complex.You're circumventing all of the combustion instability problems the F-1 had, and making it much easier to throttle down. That's problems solved.
Quote from: JEF_300 on 03/06/2021 04:51 amQuote from: Lars-J on 03/06/2021 04:42 am1 engine with multiple chambers/nozzles doesn’t solve their pump issue (turbo/electric/hybrid), is just makes it worse! Because now you don’t need to design a Merlin class pump, you need an F-1 class pump. You aren’t solving anything that way, just making it more complex.You're circumventing all of the combustion instability problems the F-1 had, and making it much easier to throttle down. That's problems solved.I don't think it's true that dual chamber engines are easier to throttle down.
I can imagine a 7 chamber engine, with a "landing mode" where the pumps are throttled down and the flow to all but the center chamber is cut off.
This idea of yours seems like solution in search of a problem.It all ignores the established fact/wisdom that electric pumps don’t scale. So having one pump for all nozzles just makes that problem even worse.Now you may say that such a statement (not scaling) is just conventional thinking... well, we are about to find out. Whether the masters of electric pumps (Rocketlab) abandon it for this vehicle, that should tell us.
That's fascinating. In that case, it's fair to call RocketLab a US launcher, IMHO, Ed Kyle.
Antares 230+: Current version of Antares. Has a payload to LEO of ~8t with a liftoff thrust of 3,844 kN. Keep in mind that Antares has a heavy solid upper stage weighing it down.
Quote from: JEF_300 on 03/05/2021 06:51 pmAntares 230+: Current version of Antares. Has a payload to LEO of ~8t with a liftoff thrust of 3,844 kN. Keep in mind that Antares has a heavy solid upper stage weighing it down.Castor 30XL only weighs 25 tonnes or so at launch and probably a couple tonnes-ish at burnout. Less than 9% of total liftoff weight. Much lighter than Falcon 9's second stage. Comparable to a Soyuz Blok I stage. - Ed Kyle
Quote from: Lars-J on 03/06/2021 07:07 amThis idea of yours seems like solution in search of a problem.It all ignores the established fact/wisdom that electric pumps don’t scale. So having one pump for all nozzles just makes that problem even worse.Now you may say that such a statement (not scaling) is just conventional thinking... well, we are about to find out. Whether the masters of electric pumps (Rocketlab) abandon it for this vehicle, that should tell us.Problem: Peter Beck wants to have as few engines on the first stage of Neutron as possible, but it would be difficult to throttle deeply enough to land propulsively on one big engine. Solution: Make it a multi-chamber engine with a chamber in the center, and cut off the other chambers and throttle back the pumps when you want to land, effectively turning the big engine into a smaller one. Yes, I ignore the electric pumps problem, because I ignored the pumps entirely because any would work. This concept could use electric pumps or a gas generator or be staged combustion or even expander-bleed. That wasn't my point.And I'm also not saying that this is the best idea or that this is what they'll do. It was just an idea that I thought was interesting. I'm kind of confused by the outright rejection of it.
Anybody body think Rocket Lab with Lockhead could buy the IP for PGA engine from ROC/Stratolaunch make really efficient upper stage engine?
Quote from: Lars-J on 03/05/2021 06:34 pmI haven't done an real calculations, but from a gut level it seems like Neutron would need 5-6 Merlin 1D's - if using Merlin's - to get the capability they announced.So this is a good opportunity to have this conversation:How much thrust does an 8 ton LV need on it's first stage? Let's look at some examplesSoyuz FG: I believe this is the Soyuz variant currently used for crew rotation. It's a ~7t to LEO rocket with a liftoff thrust of ~4,100 kN (I can't figure out if this number is vac or sea level). It's much heavier than it's needs to be, due to being massively overbuilt because it was designed by Soviets in the 1950s.Atlas III: Atlas III was an 8-10 ton to LEO vehicle, depending on the upper stage. Had an RD-180, and therefore a liftoff thrust of about ~3,800 kN. It's design is about as mass efficient as it gets.Delta IV Medium: The totally booster-less Delta IV (using post RS-68A specs) puts ~8.5t into LEO and has a lift-off thrust of "only" 3,140 kN. It get's away with this because the whole thing is hydrolox, and hydrogen is light.Antares 230+: Current version of Antares. Has a payload to LEO of ~8t with a liftoff thrust of 3,844 kN. Keep in mind that Antares has a heavy solid upper stage weighing it down.Falcon 9 v1.0: This was actually a 10t to LEO vehicle, with 9 Merlin 1Cs providing ~3,800 kN of thrust at liftoff.So I generally estimate that we should be looking at 3,500 - 3,850 kN of liftoff thrust for a scratch-built modern 8t to LEO vehicle with a liquid upper stage. That's before any budgeting for reusability. Edit for more: When it comes to thrust level, the Merlin is both the most convenient and most confusing existing option to use in a comparison. You have to remember that while the Falcon 9 started as a medium-lift launcher, it isn't anymore, and it's engine has scaled up accordingly.Having run back through it like this, my numbers for max thrust for the engines (of a Neutron with 3-4 engines) were low to begin with, and then much lower still because I forgot about propulsive landing. it would be more like 1,000-1,750 kN engines.Edit: made another edit to correct some numbers. There's actually a pretty strong consensus around 3,800 kN for expendable rocket's in this class.
I haven't done an real calculations, but from a gut level it seems like Neutron would need 5-6 Merlin 1D's - if using Merlin's - to get the capability they announced.
https://www.nasaspaceflight.com/2021/03/rocket-lab-reveals-neutron/ - By Thomas Burghardt - talking to Peter Beck,https://twitter.com/TGMetsFan98/status/1368354747770626048
“Certainly additive manufacturing. But more traditional pumps are required at this scale.” Beck says that Neutron’s first stage will be powered by multiple engines, but not as many as Electron’s.“Nine engines is great if one shuts down, but otherwise is a bit of a pain,” citing manufacturing and testing required for every single engine. “A small amount of engines is optimal, but large engines have limited throttleability.” Beck says Neutron will have the “least amount of engines practical.
Forgive me in advance but why do you rule off mixed engines?A couple of RD-191 or similar surrounded by some Rutherfords (say ~40, not many, just as 4 Electrons, giving about 1000 kN).Rutherfords are external because used as attitude control thrusters. Most of them are cut of early after liftoff to save batteries.Reentry burn and landing is performed restarting some Rutherfords. Up to 1000 kN is well enough, electric-pump feed cycle provide the best control and you can throttle as you want. Probably multiple engine-out capability at landing. The big central engines are not restartable, possibly not throttleable and perhaps even gimbaling is not required.No new engines to design, this way. If it's really required not to purchase the big central engines they could just copy by a proven design . Lego mode off, and sorry for that.
Beck quote from local newspaper."For the US, engines are strong core of expertise. In NZ, structure, anaylsis and design is a key strength, in Canada (Sinclair) spacecraft elements."Make sense for US develop engines, has large pool of expertise to hire from plus NASA test stands. Engine production is also there. Going need Grasshopper for landing tests, could use Electron and fly out of Mahia. Have spare launch pad, just need to build landing pad. Sent from my SM-G570Y using Tapatalk
As far as achieving recovery for reuse, Beck does not anticipate a SpaceX-esque “hop” test program.“Our priority is to get into service and deliver a customer satellite. Reusability can not work, and the mission can still be successful, so we can take some risk there.”The first stage recovery is expected to take place on an ocean platform stationed downrange. While the option of performing Return To Launch Site (RTLS) landings is not off the table, it’s also not expected to be useful for Neutron.“I’ve learned to never say never to anything. Otherwise, it results in some unpleasant dining experiences. But we’ve baselined a flight profile with a downrange landing.”“It’s a propellant trade between RTLS and downrange landing. RTLS begins to grow the vehicle.”
Quote from: indaco1 on 03/07/2021 12:34 amForgive me in advance but why do you rule off mixed engines?...Reentry burn and landing is performed restarting some Rutherfords. Up to 1000 kN is well enough, electric-pump feed cycle provide the best control and you can throttle as you want. Probably multiple engine-out capability at landing. The big central engines are not restartable, possibly not throttleable and perhaps even gimbaling is not required....Need one big engine for reentry and final braking burn, Rutherfords aren't powerful enough for high deceleration needed.
Forgive me in advance but why do you rule off mixed engines?...Reentry burn and landing is performed restarting some Rutherfords. Up to 1000 kN is well enough, electric-pump feed cycle provide the best control and you can throttle as you want. Probably multiple engine-out capability at landing. The big central engines are not restartable, possibly not throttleable and perhaps even gimbaling is not required....
Quote from: TrevorMonty on 03/07/2021 03:07 amQuote from: indaco1 on 03/07/2021 12:34 amForgive me in advance but why do you rule off mixed engines?...Reentry burn and landing is performed restarting some Rutherfords. Up to 1000 kN is well enough, electric-pump feed cycle provide the best control and you can throttle as you want. Probably multiple engine-out capability at landing. The big central engines are not restartable, possibly not throttleable and perhaps even gimbaling is not required....Need one big engine for reentry and final braking burn, Rutherfords aren't powerful enough for high deceleration needed.I've not made accurate calculations, but assume a mass ratio of 15 (like F9), say 10% mass at landing including spared propellant. Rutherfords give about 20% of liftoff thrust: 4 MN by RD-191 (2 x 2000 kN) and 1 MN by Rutherfords (40 x 25 kN). Suppose T/W at liftoff is 1.5.This give a max T/W = 3 at landing (that is 20 m/s2 deceleration) throttleable to a single Rutherford so you can even hover and sucide burn is not required.Most of deceleration came by aerodynamics. If you start landing burn when subsonic at 300 m/s it takes 15 sec and 2.25 km to stop.To save propellant a small parachute could used and jettisoned before burn or skydive or other aerobrakes, but it's for efficiency not because thrust is not enough.As far reentry burn is concerned we don't even know if they will do it. Tests with Electron have been totally passive reenty. But even if done you could just start engines earlier during parabolic coasting, I have not access to a trajectory oprimizator but I don't thing a longer reentry burn will be that inefficient.Of course Peter Beck said they will use less engine as possible and it makes sense. But I repeat, 40 reusable Rutherfords are the same number expended for just 4 Electron missions.