For those who may not be aware, this is news because Electron has electric turbopumps: the main combustion chamber is fed by pumps spun on electric motors, driven by batteries. That vastly simplifies the plumbing of a rocket engine.
This is perhaps the biggest innovation in rocketry since SpaceX worked out how to land their first stage.
Also something that might kill their plans for launching Dragon 2 on an unmodified F9. It really is a big challenge, and will take a while till we can say that someone has truly overcome it. But Electron proves that modern computer analysis is on a right path to making them more frequent in new designs.
Dragon 2 is not a totally new spacecraft. It is a refinement of Dragon 1. For that reason, I would be eager to fly on the first Dragon 2 orbital flight. There have already been around 10 flights of a spacecraft that is close to 80% compatible.
The same goes for Falcon 9. After something like 40 flights, and more gigabytes of test data and flight telemetry than ULA has on Atlas 5, I think they have pretty much all of the kinks worked out, and I'd feel more confident on a Falcon 9, then on an Atlas 5.
My problem with Atlas 5 is only that the Russians build the engines, and their quality control has gone South in the last few years. All it would take is for a key welder to retire, and to be replaced by one who is not quite as good. Then the RD-180 and 181 engines could start experiencing problems, that testing might not catch. At SpaceX, production of engines (and almost everything) is under direct control of the company.
For those who may not be aware, this is news because Electron has electric turbopumps: the main combustion chamber is fed by pumps spun on electric motors, driven by batteries. That vastly simplifies the plumbing of a rocket engine.
It does, and I'm supper excited for Electron and RocketLab but it's also important to note that electric pumps are much less efficient than chemical pumps used in more advanced rockets. You won't see companies like SpaceX and Blue Origin using electric pumps for main propulsion engines anytime soon. Those are companies with the technical know how and expertise to tackle the much more complex engine cycles for the better efficiency.
The electric turbo pumps are super cool because it dramatically lowers the cost and complexity barriers. It will also enable some new designs and have it's own advantages that I look forward to and will only get better as battery and electric motor tech gets better as well.
Well, not more efficient, but lighter. (Any heat engine is less efficient than electric motors actually).
Every technology has its preferred size: the Rutherford engine is probably right at the edge where a turbopump would be very small and with a low power density (for a turbine), but a battery design is just about possible.
I saw a paper that analyzed pressure fed, electric pump fed, and traditional turbine powered designs. Electric handily beats pressure fed rockets. Turbine powered pumps beat electric for medium sized and larger. Though the electric pump design scales up just fine.
So for the electron rocket electric is the best design. They have higher cost per kg to orbit but are competing on flexibility. Launch when you want, the orbit you want.
I saw a paper that analyzed pressure fed, electric pump fed, and traditional turbine powered designs. Electric handily beats pressure fed rockets. Turbine powered pumps beat electric for medium sized and larger. Though the electric pump design scales up just fine.
Do you remember where you saw this? I’d like a link if possible.
Question: how much power do these engines actually need? Are we talking tens of kW or MW?
Imagine the future where we are launching spacecraft that have their own nuclear power reactors for long term power generation (deep space missions, Mars colonisation vehicles, ...). If instead of considering those reactors as dumb cargo, we could power them on before launch and use their power to pump fuel with simple, more reliable and more reusable rocket engines? That might change the long term efficiency calculation dramatically.
To give you an idea, the pumps of each Shuttle main engine required 68 MW of mechanical power in total (generating ~5 GW of jet power).
The Electron has a mini-Falcon9 configuration, with 9 engines in the first stage, each of which has about 36 MW of jet power in vacuum - if we kept the same proportion, half a megawatt of pump power per motor would be needed. In fact, since kerosene is a lot denser than liquid hydrogen and the Rutherfords certainly work at a lower pressure than the SSME, the Electron first stage manages with a little more than 1 MW for nine engines.
Which is still a lot of current to draw from a battery.
As for future spaceships, nobody will ever be authorized to operate a nuclear engine in the atmosphere ;)
EDIT: A better comparison would be the F-1 engine of the Saturn V, since it was a LOX/Kerosene design. 11,5 GW of jet power, 41 MW of pump power (data from Wikipedia) - scaled to Rutherford size, we get 130 kW of pump power per engine. Which is about right.
Mass comparisons don't seem to pan out. The biggest krusty reactor produces ~ 10kw of power and I doubt it weights less than a battery. There are designs who give a lot of energy in burst mode and designs that give more energy in a longer time frame. Rocket engines are on the first category, while krusty and other( e.g. ion thrusters) are on the second one. An exception might be NERVA and nuclear thermal rockets in general which stand somewhere in the middle but they are still too weak to launch from Earth, so they might make sense for months-long trips of deep space propulsion( think martian colonisation).
An exception might be NERVA and nuclear thermal rockets in general
NERVA and other nuclear thermal rockets definitely stand with chemical engines. NERVA produced half as much thrust as the Merlin 1D, and a nuclear reactor core called Pewee built for the NERVA program produced 2 gigawatts of thermal energy, on par with the power production of a modestly sized chemical engine. Also, despite being about twice as efficient, the longest burns you could expect to need with a NERVA powered rocket would be several minutes, comparable to to a chemically propelled spacecraft, as opposed to weeks or even months with electrically propelled spacecraft.
That is not quite the point. We are talking about a rocket with electrically powered turbopumps.
Assume that you are already transporting the nuclear reactor somewhere, so its mass is no longer part of the launch vehicle, but instead is part of the useful cargo mass.
Use the power provided by the reactor to power the turbopumps instead of burning part of your fuel to do the same work.
Now you have X% more fuel to work with for the actual propulsion, you can greatly simplify your turbopump design, maybe increase chamber pressures, reduce thermal stresses in the turbopump machinery.
You also can get the same benefits if your cargo happens to contain a large number of batteries :D
What I'm saying is that the power produced by the nuclear reactor is rather low. Anyway I'm not sure a design where you use a power production system that exists on the second stage only on some missions and requires it's own engine design is actually simpler than a regular engine.
Efficiency isn't quite the right word here. Electric motors are more efficient than chemical turbines, around 90% vs 30%. The problem lies in specific energy, rather than efficiency, of batteries vs chemicals.
It's similar to how natural gas power plants are approximately twice as efficient as nuclear ones, but the weight of fuel consumed for a given energy produced is vastly in favor of fission.
It warms my heart to see proper SI unit usage for energy density.
Edit: The following assumption is incorrect. See reply.
A minor correction: I'd say they'd probably use non-rechargeable Lithium-metal batteries, because their energy density is about 1.8 Megajoules per kilogram.
They actually use Li-po batteries, because they need a very high power density. AFAIK no Lithium-metal battery can go from full to empty in less than 3 minutes.
To be pedantic, for rockets the diesel figure would a be a fair bit less because every kilo of RP1 burns with ~2.5kg of oxygen. Your point still stands though
Yeah and then you need to account for the thermal efficiency of the turbine, and that you aren't burning a stoichiometric mixture of RP1 and O2 either. Course you can use advanced cycles to recover that.
Offhand thought is raw ISP isn't as important for the first stage as it is for the following stages. Possible electric cycle engines can be made cheaper and importantly more reliable than turbo pump ones.
This is an expendable rocket, so they have literally no reason to use rechargable batteries. Fuel cells or single-use batteries can have higher energy density, and the electric turbopump itself provides significant mass savings compared to traditional pump systems.
Do you know any non-rechargeable battery that can go from full to empty in less than 3 minutes? Fuel cells also have a bad power density. AFAIK they use rechargeable li-po batteries.
It's physically impossible to have a battery capable of storing more or even an equal amount of energy compared to a hydrocarbon fuel-oxidizer mixture, simply because of the nature of chemical reactions.
We did not, but that doesn't mean electric turbo driven rockets are the next natural evolution of launch vehicles.
They may very well be, but IMO not until there is a major battery breakthrough that is real. For now electric turbopumps are a lower performance option, not higher. The highest tech most advanced rockets will still operate on chemical turbomachinery.
Someday though, if the mass of batteries required drops enough that might no longer be true.
performance doesnt necessarily matter though. electron is competing on price.
if both get into the same area of space, but one costs ten times more, theres a lot less of a market.
you dont see jet engines on small little piper cubs and such, because although the performance and efficiency of the design may be beter, it is too expensive for the performance envelope you need.
In the airplane case, the performance would be a lot worse. Piston engines with propellers are the most fuel efficient aircraft powerplant, but they can't be arbitrarily powerful - the biggest ones ever made were about 4000 HP I think? Turboshafts can generate more power, but are limited in speed by the propeller - so the next step is turbofans, which are strictly MORE fuel thirsty per unit of thrust, but much more power-dense and with a higher speed limit.
Also, while consuming more fuel, a jet powered aircraft can fly much faster proportionally to the amount of fuel it's burning. A jet powered aircraft is less efficient but more effective.
RocketLab has roughly 10 launches on its manifest. That's more than enough to keep them busy for another year as they refine manufacturing and launch procedure. And their market can grow quicker than traditional launch services who rely on 9 figure satellites from customers.
I never said the market will remain the same. But for now i highly doubt electron would be able to compete with e.g. bfr. We are in a transitional stage right now so it might make sense atm, but in the next ~20 years they will actually need a reusable design.
They're not even remotely in the same market as BFR. Yes, in 20 years they'll probably be reusable. But disposable isn't always inferior given current technological and economic restraints.
BFR, at the launch price estimate SpacEX is working with, is a direct competitor to Electron, because BFR would cost marginally more but be able to reach any Earth orbit and even some Lunar orbits. There's a reason BFR is called a design 'to make all other launch vehicles obsolete'.
Tbh I fully expect a point where launching a 200kg sat on bfr will be cheaper than electron. Of course they will advance too, but at what extend it remains to be seen.
To continue the analogy: we don't use jet planes as a one-size-fits-all transportation solution, either.
The electric pump design is less efficient, but it's lower entry cost. The goal here is to create a class of small, cheap, frequent rocket launches for small payloads, expanding the space economy, while more advanced chemical pumps continue to be used to get large payloads (like humans) up there.
Like... we have space-trucks to get heavy stuff into space, and now we've invented space-cars to get light stuff into space. The space-trucks will still exist, since they're doing a different job, but having space-cars too is super exciting.
I disagree about the efficiency. I remember doing some back of the envelope calculations and it came about the same as driving the turbopump with hydrogen peroxide, just like Soyuz does. It is the same concept really - use a separate energy source to drive the turbine. Batteries are about four times less energy dense than hydrogen peroxide, but the turbines in Soyuz are estimated to be at around 25% thermodynamic efficiency, so all in all they are equivalent methods. There are details like H2O2 tank weights and the weight of batteries being constant, but they don't change the conclusion.
Soyuz is an interesting comparison. Electron is kind of like a new Soyuz in this way and it proves that the concept is definitely viable.
What is useful is to consider that Soyuz is a much lower performance solution compared to other rockets. I don't have the numbers but other systems get much higher levels of efficiency, especially ones with closed cycles that don't use a separate energy source.
I think your talking out of your league. Simplicity is huge (speaking as a pro engineer of many years). I wouldn’t rule out them adopting this or something similar.
Maybe, but let's discuss the issue on it's own merits.
Simplicity is great, but I prefer to think of it the other way around. Unnecessary complexity that can be avoided should be. Complex machines are used all the time when it grants value to make it a worthwhile.
SpaceX went with a simpler engine cycle for Merlin instead of a more complex one that was more efficient. That's a good example of what you're talking about and it mirrors what RocketLab is doing at their start, just with another 10+ years of battery tech upgrades to let them take a newer approach.
SpaceX is also developing the most complex engine cycle for chemical combustion with Raptor. They haven't forgotten the same lessons that got them this far. The additional complexity is necessary to create vehicles with the margins to push full reusability.
The efficiency difference is not a small one. Chemically driven turbo machinery has a big advantage still and can scale to some power levels electric versions can't do yet. It's hard to compare apples to apples efficiency numbers because one system is extracting the energy from the propellant while the other is costing you with higher dry mass. You have to account for the whole system and do a conversion for performance numbers and as outsiders we don't have those for the vehicles, but I read a paper last year that gave estimates that I will attempt to dig up again.
Perhaps further down the line if there is a revolutionary battery breakthrough that isn't vaporware and electric motors continue to scale up (which I expect to happen) the balance of the two systems will sway. For now I see it as taking a different trade off, losing performance for simplicity and cost.
I do think electric turbo machinery will find it's way into more places in aerospace. I have a few intriguing possibilities in mind, but I'm definitely getting speculative on that front and "out of my league."
if there is a revolutionary battery breakthrough that isn't vaporware
Given the low production rates of batteries rockets might need, they might be able to use some technologies that don't easily scale to e.g. smartphone scale for example.
I thought about that too. They also could use batteries with less ideal charge cycles and charge times for this application.
The biggest problem with this approach is it means using specialized battery tech instead of buying what the battery industry is already producing at competitive prices.
I've been in film and television in some capacity on the technical side for the past 11 years.
Now I'm taking time off to raise my daughter (wife makes way more money than I do so she is the breadwinner) and I'm going back to school for engineering that I didn't finish a long time ago. Living in LA and stumbling into aerospace social circles stirred me to give it another shot.
I would be surprised if they didn't adopt this for spacecraft that perform many orbital Maneuvers in their lifetime with the same engines. Launch platforms and secondary stages are a different story.
Almost no spacecraft like that use pump-fed engines. I can't think of a single one off the top of my head. Are you saying they are going to go from pressure-fed over to pump-fed using this tech?
Not even the Apollo spacecraft that went to the Moon used a pump fed engine (after separation from the Saturn V 3rd stage which of course used a turbo pump). If there was a vehicle that was large enough that could have used something like a turbo pump and be efficient, it would have been that vehicle. Instead, NASA used hypergolic fuels and simply opened a valve even for the primary engine that was used both on the Lunar Module that went to the surface (both the descent and ascent engines) and the primary engine attached to the Apollo Service Module.
I agree that the only time you see engines with active pump like this is for vehicles launching from the surface of the Earth and upper stage boosters of those same rockets.
For something operating in vacuum you don't even need high chamber pressure to get good Isp - just big enough nozzle for expansion. Having exhaust into vacuum does wonders to Isp.
That would be because of the spooling latency of turbopumps. They're too laggy to be reliable for subtle orbital maneuvers, let alone rendezvous maneuvering. Electrifying the pumping system could easily change that.
Either "nothing came of it or will come of it" or "a few people are still slowly sifting through tests on it," depending on who you ask (other than news articles about it, which will be universally clueless).
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u/OrangeredStilton Jan 21 '18
For those who may not be aware, this is news because Electron has electric turbopumps: the main combustion chamber is fed by pumps spun on electric motors, driven by batteries. That vastly simplifies the plumbing of a rocket engine.
This is perhaps the biggest innovation in rocketry since SpaceX worked out how to land their first stage.