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Rocket Lab Unveils "Electric" Rocket Engine
New submitter Adrian Harvey writes The New Zealand based commercial space company Rocket Lab has unveiled their new rocket engine which the media is describing as battery-powered. It still uses rocket fuel, of course, but has an entirely new propulsion cycle which uses electric motors to drive its turbopumps.
To add to the interest over the design, it uses 3D printing for all its primary components. First launch is expected this year, with commercial operations commencing in 2016.
To add to the interest over the design, it uses 3D printing for all its primary components. First launch is expected this year, with commercial operations commencing in 2016.
It's a rocket engine with 'turbopumps!' And 3D printing!
Ok, de-hyped version: Rocket engines consume huge amounts of fuel. Getting fuel from tanks to engines needs pumps, which usually need their own mini-engines. This design uses electric pumps, saving weight and complexity. They are using 3D printed parts, including titanium, because it lets them iterate through design refinements quickly. The engines themselves still burn fuel as normal, they just weigh less.
About 10 years ago I worked on simulating a rocket with electric turbopumps for fun. The concept was the exact same as theirs - minimize the number of parts that have to operate in harsh environments to reduce cost, maintenance and risk of failure. You don't even need any penetrations of the propellant lines, the rotor of the electric motor is the compressor itself.
I have no clue whether the design will actually be practical. But it's certainly not new. I'm sure I'm not the first person that this concept occurred to.
*Kid Rock runs for Senate* Democrats: We must run Kid Scissors.
Big rocket engines use big propellant pumps. The pump on the F-1 (used on the Saturn V) ran about 55,000 horsepower.
Electric motors won't do that cheaper. And they'll sap the weight of the rocket, since even a dead battery is heavy. Fundamentally, a big rocket will be better served by a gas-generator or staged-combustion cycle.
That's fine for this rocket because it's so small. The payload is 110kg. For comparable rockets, turn to Iran's unflown Simorgh, Israel's Shavit, or North Korea's Unha, all in the 100-160kg range.
To put those numbers in comparison, let's look at SpaceX. The single-engined Falcon 1 put 670kg into orbit. A Falcon 9 runs 10,000-13,000kg. And the Falcon Heavy is supposed to lift 53,000kg.
Or for an older comparison, Sputnik 1 weighed 80kg, and Sputnik 2 weighed 500kg. So they're building a rocket that couldn't even lift the second satellite to ever fly. I'm not particularly impressed.
Maybe there's a niche for small payloads like this, but in all honesty, I expect you could fly several such payloads on one bigger rocket, or just hitchhike on the spare capacity on a big satellite launch. Still, worth a shot. Just don't pretend to be playing in the big leagues.
Ever since their first widespread implementations in the mid 20th century, turbopumps have been powered by rocket propellants - either the same stuff they are pumping (F1 engine in the Saturn V), or a separate propellant dedicated to powering the pumps (Space Shuttle Main Engines). There are excellent reasons for this, and not many good reasons to use batteries and motors instead. Rocket propellant pumps require truly massive amounts of power to move thousands of gallons per minute of propellants at thousands of PSI pressure. The SSME turbopumps require over 70,000 horsepower per engine. Like all other rocket hardware, size and weight are extreme concerns. Power-to-weight ratio is the single most critical design goal. Rocket engines themselves burn the propellants they do specifically because those chemical combinations are the absolute best we have for producing the maximum amount of thermo-mechanical energy from the least mass, no-compromise. Using the same types of propellants to drive the turbopumps also provides the maximum achievable power to weight ratio. The SSME turbopumps produce over 100HP per pound, which is insanely high. No known electric motor technology can even reach that order of magnitude in power density, even considering only the actual motor itself! There is no legitimate contest in performance between a gas-driven turbopump and any other technology besides nuclear, and that's that. To make such a large compromise in power to weight ratio by using electric pumps is very odd. Yes, gas-driven turbopumps are really hard. They are the hardest part of building a large liquid rocket engine. But those challenges were first solved over 60 years ago, and avoiding a tough engineering exercise is no excuse for making a giant compromise in performance. The extra mass of that electric drive system could be replaced with propellant or cargo.
I am a geek attorney, but not your geek attorney unless you've already retained me. This is not legal advice.