Comments on: SpaceX successfully tests new engine (VIDEO)

By: Ben H.

Ben H. — Fri, 06 Jul 2012 04:13:17 +0000

I think this is really cool, and I’m glad to see SpaceX making advances. That being said, the SpaceX PR campaign is disingenuous, and on the edge of lying, from a technical perspective.

They state that the engine has “An enhanced design makes the Merlin 1D the most efficient booster engine ever built”

Now, they explicitly state that they mean it has the best thrust-to-weight ratio. Sure, nice. But this isn’t how the industry measures efficiency, we use ISP (specific impulse). ISP is basically telling you how much impulse the engine gives you per weight of propellant. This value is independent of the mass of the engine or rocket, which is what makes it a better measure of efficiency. A great thrust-to-weight ratio doesn’t do you all that good if the propellant tank guys at SpaceX design a sloppy heavy tank system, for instance. But a great ISP is a great ISP.

I’m disappointed in SpaceX, at least their PR wing, for pushing a technically inaccurate statement that their engine is “the most efficient booster engine ever built”. And I’m disappointed that the media and bloggers are happily repeating it like all the engineers at SpaceX are geniuses.

Congrats to SpaceX on the engine test and on their recent successes, but please reign in the propaganda and conduct yourselves like engineers, not pitchmen.

Thanks,
- Ben H.
Mission Control, TX

By: Jared

Jared — Fri, 29 Jun 2012 11:54:10 +0000

> I’m really a fan of more exotic means of getting a large space craft off the ground

You’d be a big fan of the Launch Loop, then.

http://en.wikipedia.org/wiki/Launch_loop

By: Peter B

Peter B — Fri, 29 Jun 2012 01:06:50 +0000

Kent @ #25: Okay, regarding the white smoke blasting downwards from a pipe at the rim of each engine bell, I’m still not sure. It’s certainly likely to be a very cold vapour, based on what appears to be a block of ice at the end of the pipe which disappears soon after the engines ignite. So that means it’s probably either liquid oxygen, liquid hydrogen or liquid helium vapourising on contact with the relatively warm air. And given the fact that the sparks don’t suddenly burn more vigorously on hitting the vapour, I’m guessing it’s helium.

However, I’m happy to be corrected by someone who knows what they’re talking about.

By: Peter B

Peter B — Fri, 29 Jun 2012 00:31:56 +0000

Kent @ #25 asked: “…at 2m:40s in the following video, what is all that other action besides the engines themselves : sparks going horizontally, other streams firing across the test zone, etc. – I’ve always wondered about that.”

Regarding the spray of sparks, according to Wikipedia: “At T-minus 10 seconds, hydrogen igniters were activated under each engine bell to quell the stagnant gas inside the cones before ignition. Failure to burn these gases could trip the onboard sensors and create the possibility of an overpressure and explosion of the vehicle during the firing phase.”

I’m not sure what you mean by the “other streams firing across the test zone”.

By: puppygod

puppygod — Thu, 28 Jun 2012 12:07:04 +0000

I always thought that choice of the name was intentional – as a homage paid to the aforementioned Rolls-Royce Merlin.

Re-using names is a long standing tradition in aerospace industry. How many, for example, lightnings do we have?

By: Blargh

Blargh — Wed, 27 Jun 2012 20:27:24 +0000

Did they really have to name it “Merlin”? Sometimes name collisions are unavoidable, but in that case you at least pick something that isn’t in the same field (in this case: aerospace, and possibly the most famous aircraft engine ever – the Rolls-Royce Merlin)…

By: Jay29

Jay29 — Tue, 26 Jun 2012 19:30:50 +0000

Holy f$%&! No wonder we can put things in orbit — that’s freaking powerful!

By: Joseph G

Joseph G — Tue, 26 Jun 2012 18:37:08 +0000

@24 Gunnar: Thanks so much for that interesting article about the Energia/Buran program! It was very well written, as well as being a fascinating read!

Thanks!!! That’s very nice to hear. I wrote it for a website that accepts reader submissions covering various odd and interesting topics. Unfortunately, I never heard back from them

By: Gary Ansorge

Gary Ansorge — Tue, 26 Jun 2012 16:40:17 +0000

I’m really a fan of more exotic means of getting a large space craft off the ground, like a mag lev launcher or Leik Myrabos Light craft concept. Once in orbit, we can use extremely high specific impulse engines. The nuclear salt water thrusters have an ISP around 10,000 vs 450 for a liquid H2 and lox engine. Some of the ion thrusters we’ve built are better than that but they’re not able to provide high acceleration, which would be necessary for lunar landings and such.

The only problem with space elevators is that first, we have to actually BE in space to build them and second, they take so long (over a week) to get to geo sync orbit.

I guess we’re stuck with these primitive chemical rockets for a while longer. I’ll tolerate nearly anything to get humans off this planet.

Gary 7

By: Kent

Kent — Tue, 26 Jun 2012 16:26:20 +0000

That’s cool !

Got me wondering about previous rocket engine tests . . . for instance, at 2m:40s in the following video, what is all that other action besides the engines themselves : sparks going horizontally, other streams firing across the test zone, etc. – I’ve always wondered about that. Perhaps sometime you could do a little write-up on what goes on with a rocket engine ?

NASA Space Shuttle – “Best of Launches”
http://www.youtube.com/watch?v=mjrpuG2HOuI&feature=related