(May 26, 2019 08:30 PM)Yazata Wrote: Tim Dodd the Everyday Astronaut has a youtube video explaining rocket engines. It's an hour long but entertaining and fun to watch. [...] You can find a link to the video and read the text in written form here
excerpt: "Remember how airships or zeppelins used to be filled with hydrogen to make them 'lighter than air'… That’s because Hydrogen is so much less dense than our atmosphere, it makes for an excellent, albeit flammable gas for a balloon. I mean, we all remember the Hindenburg… right?"
Hmmmm... yeah, I guess all the alternative theories that tried to exonerate hydrogen, or demote it to only jointly sharing the blame with something else, have been taken to task. That is, if one goes by places like this loudly declaring it by bullhorn.
The new news concerns the Raptor engines and what the timeframe is for the Hopper to receive the one it's been waiting for while it received its control system upgrades.
The first Boca Chica Hopper tests in early April used engine SN2. (SN1 had earlier been damaged in testing at McGregor.) SN2 fired very short burns a couple of times, then was removed from the Hopper and trucked off to parts unknown. It's now revealed that it was returned to Hawthorne California for inspections. (Elon insisted in a tweet that there wasn't anything the matter with it.) SN3 was already at McGregor for a full-scale test series. It's unknown (to me, anyway) why it isn't being sent to the Hopper. (I can speculate though. Perhaps the testing was testing-to-destruction, where they crank it up until it breaks, so that they learn what its limits are. But maybe SN1 had already done that, if it happened at all.)
SN4 will go to the Hopper. So where is SN4 right now and what has it been doing? Last week it was at McGregor undergoing acceptance testing. Every rocket engine SpaceX builds is test-fired at McGregor before it is installed on a vehicle where it's test-fired again in a static test, before actually flying. (The article above includes a great photograph of SN4 on the McGregor test stand.) SN4 should be arriving in Boca Chica very soon for installation later this week.
Meanwhile, methane tankers were arriving yesterday and the flare stack is once again lit.
The plan seems to be to run methane and LOX tanking tests, then igniter and pre-burner tests (spinning up the turbopumps without lighting the main combustion chamber in other words), then probably a short static fire like we saw in early April. All leading up to a first-flight, vertical to about 20 meters altitude. (About as high as the thing is tall.) That may come as early as next week. (Of course that's aspirational "Elon-time", what they would like to do, and things may well slip.)
Edit: Still no sign of the engine on Tuesday 5-28. (Lots of trucks arrive and leave, so it could already be there. But it hasn't been installed on the Hopper where people can see it.) But Cameron County has announced new Boca Chica road and beach closures for June 2, 3 and 4.
Still no FAA Temporary Flight Restrictions, which we would expect to see prior to testing, even if the vehicle doesn't fly, if there's an explosion danger that could hurl shrapnel at low-flying aircraft.
Might still be wrapped under whatever camouflage cover they smuggled it on. Oh, I forget that's only for military trucks transporting top-secret drones which onlookers speculate are actually captured flying saucers.
Friday May 31 AM: The engine still hasn't appeared at the 'junkyard empire'. Technicians with scissor-lifts are messing around under the hopper's base, perhaps preparing it for engine installation, but the engine hasn't come out of hiding.
Cameron county has pushed back the beach closures. But only one day. Now they begin Tuesday and run through Wednesday and Thursday of next week. So unless the engine appears today, I'd guess that they will slip again.
Subsequent edit: From watching the live-feed, it's pretty clear that the engine still isn't attached to the Hopper. It appears to be supported by the yellow lift and I see guys physically muscling it back and forth. They are probably at that frustrating point where they are trying to get the bolts to line up.
YazataJun 3, 2019 01:31 AM (This post was last modified: Jun 3, 2019 07:35 AM by Yazata.)
More engine news. It now seems that the Hopper won't be using the engine that just arrived (SN4) for actual flights. It will be using SN5, the newest engine completed which is currently undergoing acceptance testing at McGregor.
Another very good article (with what appears to be inside information) by Michael Baylor, here:
"...up until recently, the company was planning to utilize Raptor SN4 for the untethered hops. However, the company has now decided to utilize this engine only for fit checks, and will instead perform the hops with SN5... SN5 is already at SpaceX's test facility in McGregor Texas for verification testing before being shipped south."
No word on the reason for the engine switch.
My own speculation (that's all it is) is that last weeks's delay in the engine arriving suggests that SpaceX wasn't satisfied with some aspect of its performance during test-stand firing at McGregor. (Perhaps its ability to throttle down, which is necessary for propulsive descents but hard for rocket engines.) Since they are learning from experience and incorporating many small changes in each new engine that rolls out, SN5 may include modifications meant to improve whatever it is that they didn't like about SN4.
Well, this is why they do all the testing. It's probably important to remember that SpaceX's Raptor is only the third rocket engine of its type in history, and the first of that three to progress off the test stand to an actual vehicle (such as it is, in this case). Everything they do from now on will be a first, so it's very much learn-by-doing.
Edit: tropical storm brewing off coast of Mexico, but NOAA doesn't seem very concerned about it. It might deliver rain and wind to Boca Chica though.
Yesterday interim engine SN4 was being subjected to gimbal testing. It was observed by BCG and others to be moving on two axes and pointing different ways so as to vector thrust. The engineers examining the photos were of the opinion that the engine reached fairly extreme angles which should give the vehicle lots of control authority. So the mounting and actuators appear to be ready to go.
Now engine SN4 has been removed from the Hopper again (still don't know why they don't want to use it) and everyone has returned to engine-watch waiting for SN5's promised arrival. (Assuming that it behaves as desired at McGregor.)
May 29, 2019 05:35 AM
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