Rocket Labs mean business, Brits stick pin in Mars map, and Japan celebrates HTV-7’s dive into the atmosphere
Hippy-friendly hybrid-electric rocket motors
I'm still boggling at the use of electric turbopumps on the Rocket Lab's Electron, but if you only need 1 megawatt (those 9 engines are tiny) for about 2 minutes then that's about 33kWh and not too bad.
The engineering and development advantages are interesting. You entirely eliminate all the turbomachinery of the fuel pumps, so that makes development easier. You're not diverting propellant to run turbines, so the engine can gain efficiency without the plumbing complications of a staged combustion engine.
The drawback is a heavy battery pack, but it'll be lighter than an electric car's because you don't care about reusability and good recharging characteristics.
I wonder how electric pumps would scale to larger rockets that use turbopumps in the tens of megawatts.
Re: Hippy-friendly hybrid-electric rocket motors
> I wonder how electric pumps would scale to larger rockets that use turbopumps in the tens of megawatts.
Short answer is, they just don't.. Specific energy of the power source, and weight of the machinery, are going to be hugely limiting factors. The energy density of say RP-1/LOX is just so much better and turbopumps just produce a massive amount of power given their relative weight, something no electric motor can come close to as it scales up, using any current or projected technology.
Rutherford made a great choice using electric for the Electron, it hugely simplifies the engine design (and probably hugely increases reliability to boot) but electrically driven engines will never be more efficient than a more traditional turbopump driven engine.
The gains here are in simplicity, not efficiency, basically.