It's burning a bit of copper when it gets up to power. Good for a first test though, and that's what testing and tuning is all about.
Over the past week in space, SpaceX pressed go on the first flight Raptor, the Lucy mission inched closer, and the ISS crew battled with some dodgy plumbing. SpaceX fires up the first flight engine for Starship Ol' Musky was justifiably chuffed with his band of boffins as a team of engineers fired up the first flight Raptor. …
"Could the rocket scientists in the viewership explain what you do to fix it?"
Hard to say unless you know what the problem is. The Haynes manual for the Saturn V rocket explains that Rocketdyne's J2 hydrogen fuelled engines burnt their solid copper injector plates in the early versions. The fix was to make the injector plates out of sintered metal, so as to make them porous. That way, the entire injector plate could be cooled by gaseous hydrogen seeping through it: it says here that 3.5% of the hydrogen fuel entered the combustion chamber that way.
The fix had previously been discovered by Pratt and Whitney in developing its RL-10 engine, but Rocketdyne didn't want to know due to "not invented here" syndrome. NASA did the required arm-twisting.
But I suspect that isn't the problem in this case. The green tinge to the flame doesn't look "spectacular" as described in the Haynes Saturn V book, and in any case I'm sure Musk's rocket engineers are more than a little bit better informed about rocket engines than me so wouldn't have repeated a mistake from the 1960s.
The effect could indeed be a camera artefact, or maybe there's a little bit of rough copper burning off somewhere inside? If there is a real problem, I'd be willing to bet a decent sum of money that the engineers will be able to fix it without much bother. I do wonder if it's a problem with the spark plugs - even ordinary road vehicle piston engines can melt spark plugs if they're the wrong sort, or if the fuel/air ratio's lean (i.e., low on fuel). Certainly the suggestion from "Persona" that adjusting the fuel/oxidiser ratio is a good place to start is a definite maybe.
I very much doubt that it's a problem with the nozzle (bell, whatever you want to call it): SpaceX's early engines were ablatively cooled, but they've been actively cooled using fuel for some years now and that's a very mature technology which has been in use since the 1930s.
It of course depends on the root cause.
If copper is vaporizing, you'd look to cool it better as one fix.
a) Make the copper liner *thinner*, which would reduce thermal resistance between the hot liner surface and embedded regenerative cooling channels.
b) Redesign the size/shape/placement of the cooling channels for the same reason as in a).
c) Maybe it's cavitation bubbles in the coolant channels inhibiting heat transfer, in which case, modeling and redesign to eliminate cavitation would be the thing.
The flight engines are supposed to be using spark ignition rather than the TEA-TEB mix used on the Merlins. Tests of the prototype Raptors have used TEA-TEB though, so the spark igniton may still be coming Soon (TM).
I believe Musk indicated that this test was using spark ignition - which is why he narrowed the green to either camera saturation or burning copper, not TEA-TEB.
This is more or less a flight-spec engine (albeit this specific one may never fly if they continue to tweak the design, or may only be used for "hopper" tests), as opposed to the previous Raptor tests which were using scaled-down test articles and did indeed use hypergolics for ignition.
What's in that rig is a full-scale Raptor in (more or less) its final form. Which is awesome.
If I understand correctly the copper is actually the direct lining of the combustion chamber and throat, so what is happening is probably a bit of engine rich combustion.
What can be done to fix it can involve many things. Among them: Changing fuel/oxidizer mixture ratios, changing the flow balance in the wall to improve cooling in the hotspots, altering wall thickness (either thinner or thicker, depending on what is happening), changing the injector pattern or slightly altering the flow in certain spots.
There is no TEA/TEB being used in the full size Raptor, so it's definitely not the starter system causing the tinge. On top of that the flame starts out yellow and then turns green. It'd be the other way around if it was ignition fluid.
I also doubt it's the camera as different angles show the same discoloration, and I'd find it strange if several cameras with different lenses, at different angles all showed exactly the same sensor saturation issue.
Another thought would be this: rather than "saturation," many (video) cameras can "see" Infra Red, but report the color as green. Since the flame is hot, there's a lot of IR being released.
Example: point a hand held, IR LED remote control at a video camera lens and push the remote button. While the Mk I Mod 0 eyeball won't see anything, the camera will see the LED(s) light up green.
Presumably, even with an IR filter covering the lens, which would be a sensible precaution given the heat, some hot things may still show green.
As Musk explains, the engine uses "Gaseous CH4/O2 & heavy duty spark plugs. Basically, a [Dashing Away Emoji] of insane power" to ignite the igniter torches.
Clever design for a crewed vehicle. Don't need to carry much of the stuff if you've got some methane-producing bio reactors already on board.
> "Don't need to carry much of the stuff if you've got some methane-producing bio reactors already on board."
Won't work. The propellant mass would have to be beans or maybe brussels sprouts, and the sulphur in the beans is dead weight, dramatically reducing efficiency.
Can't vouch for the footage myself but I note that elsewhere someone stated that the entire image had "greened"—i.e not just the exhaust flame but some shiny stuff elsewhere in the frame, unlit by the flame, had also changed hue. If that is correct, we're over-analysing things.
The design and engineering teams deserve some serious kudos, whatever: a test that ends with an intact engine is a good result. In these days of general pessimism about the state of the world (and the abject f**king w**kers that run things, not to be too rude) it is heartening to see so many really serious-minded and practical ventures in spaceflight. I'm a child of the late 50s, so of course I still believe that humanity's real future, and assurance of longevity as a species, is Out There. If I could see a Moon- or Marsbase in my lifetime, I'd consider myself very lucky.
(And if Richard Branson's dumb stunt in the desert doesn't kill him, he should consider himself very lucky ... Spaceflight, it ain't.)
Why does it cause such severe gastrointestinal symptoms (to wit: Stinky rancid gas) ?
Never had anything like it.
It was in the reduced pile but I can't see any reason for such an extreme reaction.
Not intolerance per se as had a similar reaction to hot curry with lentils.
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