RocketLab Discussion Thread

[sevenperforce]

Someone pointed out that while RocketLab claims Electron has a 4.5-meter fairing, it also claims the overall rocket is 40 meters long, which would make the diameter as shown just 4.2 meters. Maybe the 4.5-meter fairing is aspirational?

I also made a scaling error on Superheavy which has been corrected.

At a tank diameter of 4.2 meters, the total propellant load of Neutron (both stages) shrinks to just 405 tonnes, which drops the GLOW to around 446 tonnes, which makes a little more sense. To match Falcon 9's TWR off the pad with just four engines, Neutron would need to develop 1500 kN engines. Which is still pretty significant. Of course, I doubt Neutron will be as sporty off the pad as Falcon 9, but still.

[.50calBMG]

Have we heard anything regarding propellant? I would think if they were to stay with electric pumps, switching to methalox would be a trivial thing. Deal with different propellant densities by adjusting the rpm of the pumps, maybe a slight change in diameter. I only assume methalox because it's close to kerolox in density, and everyone and their brother seems to be using it now.

Edited March 2, 2021 by .50calBMG
Clarification

[sevenperforce]

1 minute ago, .50calBMG said:

Have we heard anything regarding propellant? I would think if they were to stay with electric pumps, switching to methalox would be a trivial thing. Deal with different propellant densities by adjusting the rpm of the pumps, maybe a slight change in diameter.

They say they are doing kerolox.

Electric pumps don't scale up well, due to battery weight. 

10 minutes ago, magnemoe said:

Soyuz is lightweight because its has the orbital module, the launch and reentry module is tiny. 
Reuse has an cost penalty. 

Yep, the Soyuz-TMA re-entry module is just three tonnes.

[sevenperforce]

4 hours ago, sevenperforce said:

There's no way engines that size could fit in that tiny interstage with a properly-sized expansion nozzle, so I suspect they will do a pair of vacuum Rutherfords for the upper stage.

Wait, that can't work. The vacuum Rutherford only pushes 24 kN while the render (even at 4.2 m) puts the upper stage at around 89 tonnes. You'd need 10 vacuum Rutherfords to even get a TWR as high as the (very low thrust) Centaur.

I think this is just a bad render.

[tater]

Here's a better image from rocket lab's page:

https://www.rocketlabusa.com/themes/base/production/images/neutron.png

(won't inline png... hang a sec)

 

 

 

[sevenperforce]

4 hours ago, tater said:

Here's a better image from rocket lab's page:

https://www.rocketlabusa.com/themes/base/production/images/neutron.png

(won't inline png... hang a sec)

 

 

 

Spoiler

 

 

That's the same image I used.

[RealKerbal3x]

Looks like 4 engines to me.

[Flying dutchman]

They should name the first launch "Jimmy"

[tater]

2 hours ago, Flying dutchman said:

They should name the first launch "Jimmy"

Spoiler

 

 

[Spaceman.Spiff]

It's kinda weird, and probably wrong, but is the fairing in that picture the same material as the rocket body? 

[sevenperforce]

5 hours ago, RealKerbal3x said:

Looks like 4 engines to me.

I don't think they've made any actual engine choice yet so putting four engines down below is just notional.

Obviously if they do put four engines down there, there's no way they can deep throttle enough to land on two of them, so they'd need a Rutherford (or maybe two or three) to perform the landing burn. 

[RyanRising]

15 hours ago, sevenperforce said:

I don't think they've made any actual engine choice yet so putting four engines down below is just notional.

Obviously if they do put four engines down there, there's no way they can deep throttle enough to land on two of them, so they'd need a Rutherford (or maybe two or three) to perform the landing burn. 

Assuming the first stage has a dry mass similar to that of the Falcon 9 v1.0 first stage at ~14 tons, you'll need 137.2 kN of thrust to hover, meaning you'd need at least six 25-kN Rutherfords, and with that number you'll probably incur pretty rough gravity losses (~1.09 TWR). While the main engines would obviously be too big for this application, Rutherfords are really too small. I do like the idea of using electric-pumped landing engines, they lend themselves well to that if I understand their characteristics right, but they'd need to have a scaled-up version to do that effectively.

Edited March 10, 2021 by RyanRising

[RCgothic]

I agree with your analysis that a 1st stage for a rocket with half the payload of Falcon 9probably weighs about half as much, ~14t, and that six Rutherford's aren't going to cut it for a landing.

Probably needs at least 9 auxiliary Rutherfords, (octoweb arrangement?) and they'd have to be firing on ascent so as not to be dead weight whilst retaining enough charge for a landing. Rutherfords are only 25cm across though, so it's easy to squeeze 9 into a 1.5m diameter, leaving a 1.5m wide annulus for the main engines.

For a takeoff TWR of 1.5 Neutron would need ~4MN of thrust. Nine Rutherfords barely dent that. And it'll need four more engines more powerful than Merlin 1D. Or alternatively six 640kN engines.

Feasible. 15 is a lot of engines for a first stage though.

Edited March 10, 2021 by RCgothic

[YNM]

7 hours ago, RyanRising said:

I do like the idea of using electric-pumped landing engines, they lend themselves well to that if I understand their characteristics right, but they'd need to have a scaled-up version to do that effectively.

Perhaps a dedicated electric turbopump just for landing ? For liftoff up to separation they can use gas generators or whatever.

[Ultimate Steve]

36 minutes ago, YNM said:

Perhaps a dedicated electric turbopump just for landing ? For liftoff up to separation they can use gas generators or whatever.

Has a two-cycle rocket engine been done before?

[YNM]

1 hour ago, Ultimate Steve said:

Has a two-cycle rocket engine been done before?

Probably not, but 'all they need to add' (famous last words, to some) is an electric motor and some batteries to keep the turbopumps running, plus some valve to turn off the gas generators (or bypass shunt for whatever main cycle they end up using). To my knowledge current turbopumps require an external means of power to start up in the first place right ? An electric motor for turbopump startup doesn't sound too much out of the world, it's how we power up turbojet and turbofan engines (as well as normal engines in general), although most of the time it's just powered by the tank pressure to start for now. Engine startup before liftoff will use GSE power, for landing it'll use onboard batteries (and throughout the landing sequence as well).

Say, if they put in 7 engines (6 around a circle + center engine), assuming the 6*640 kN that works out to ~550 kN per engine for maximum liftoff thrust, for landing you need ~250 kN (9*25 kN), that's around a half of a single engine thrust. 40% thrusting should be easy with electric turbopumps ?

Edited March 10, 2021 by YNM

[magnemoe]

8 hours ago, YNM said:

Probably not, but 'all they need to add' (famous last words, to some) is an electric motor and some batteries to keep the turbopumps running, plus some valve to turn off the gas generators (or bypass shunt for whatever main cycle they end up using). To my knowledge current turbopumps require an external means of power to start up in the first place right ? An electric motor for turbopump startup doesn't sound too much out of the world, it's how we power up turbojet and turbofan engines (as well as normal engines in general), although most of the time it's just powered by the tank pressure to start for now. Engine startup before liftoff will use GSE power, for landing it'll use onboard batteries (and throughout the landing sequence as well).

Say, if they put in 7 engines (6 around a circle + center engine), assuming the 6*640 kN that works out to ~550 kN per engine for maximum liftoff thrust, for landing you need ~250 kN (9*25 kN), that's around a half of a single engine thrust. 40% thrusting should be easy with electric turbopumps ?

They could draw power from the turbo pumps to power the electrical pumps then they are running, even using them as vernier trusters Soyuz style during accent and braking burn. Then kill the main engines and land on the electrical pumped engines who would be scaled up Rutherfords. 

Not sure about most engines but Raptor uses nitrogen to spin up the turbo pumps, think this is common, know that large IC engines also uses compressed air to start so this is pretty common. 

[CatastrophicFailure]

9 minutes ago, magnemoe said:

using them as vernier trusters Soyuz style during accent and braking burn.

Hmm... it would be pretty complex, but might be a certain elegance to four pairs of gimballing Rutherfords surrounding a small number (or single) large central main engine. Rutherfords provide vernier directional control as well as landing thrust, maybe even with engine-out redundancy. And a large, non-gimbaling main engine could be easier (read: quicker) to develop....

[YNM]

8 hours ago, magnemoe said:

They could draw power from the turbo pumps to power the electrical pumps then they are running, even using them as vernier trusters Soyuz style during accent and braking burn. Then kill the main engines and land on the electrical pumped engines who would be scaled up Rutherfords.

It is a second possibility as well, the vernier/landing engines are not necessarily the same as Rutherford engines.

But yeah honestly the most surprising consequence coming out from this announcement is just the engine, esp. with the perceived deadline of merely 4 years, an impressively short time for a rocket engine development if they start from scratch. Plus that'll mean they would have at least two engine production lines out, if the verniers and upper stage ends up being not Rutherford that goes up to three lines.

8 hours ago, magnemoe said:

Raptor uses nitrogen to spin up the turbo pumps, think this is common, know that large IC engines also uses compressed air to start so this is pretty common. 

Yeah, not saying that electric pumps can do everything.

 

Just realized that Merlin used to make about 690 kN, although now it's rated up to 980 kN of thrust. 550 kN engine is a pretty big engine to run with electrics I suppose, unless RocketLab have a lot of confidence. Found this paper for electric pump engine performances which aligns with what Rutherford is doing. Uprating it to 550 kN - or even 250 kN - would be quite a challenge.

Edited March 11, 2021 by YNM

[tater]

 

[tater]

24 hours:

 

[YNM]

Going live, t-15 mins

 

Overlaying graphics on the fairing...

[tater]

So far, so good!

SECO.

Supposedly Peter Beck will come on and do a Q&A on Neutron during the coverage.

[RyanRising]

the interview was a whole lot of nothing, but i guess you can't really expect much. They are hiring.

[tater]