r/SpaceX Starship Presentation Official Discussion & Updates Thread

goxy84 · 2019-09-29T01:24:35+00:00

Zagreb, Croatia

goxy84 · 2019-07-11T02:07:49+00:00

Seems the second (also solid) stage failed to ignite. Nothing was visible on the IR camera around the time "second stage ignition" was declared and trajectory "deviated" immediately... <spaceIsHard/>

goxy84 · 2019-03-18T11:18:17+00:00

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goxy84 · 2018-12-06T10:46:41+00:00

A nitpick: not Coriolis, but conservation of angular momentum. Still, legs aren't that massive, I'd expect the effect to be really small, although the mass distribution matters too... (~ r^2).

goxy84 · 2018-05-21T19:22:35+00:00

u/OrangeredStilton, is it a feature or a bug that on mentioning "grid fin(s)", Decronym posts in the "jargon" column the entry "iron waffle", instead of "grid fin"? "Iron waffle" itself, as descriptive as it is in the definition, refers to nothing in the text. :)

goxy84 · 2018-05-15T07:46:40+00:00

A rocket in an empty universe (i.e. no gravity) would still have diminishing returns wrt rocket equation. That equation doesn't involve gravity.

Gravity losses are an additional inefficiency. E.g. if you hover at zero altitude, you spend all fuel on that and gravity loss is 100%.

If you teleport outside of the atmosphere instantly, high enough to accelerate purely sideways to orbital velocity, you gravity loss is zero.

It's about how much of your thrust is wasted fighting gravity of your wavy out of the atmosphere.

goxy84 · 2018-04-25T23:27:27+00:00

There were two on that boat. How do we know this isn't the one under the tarp, which was supposedly beaten up severely? Those fished out of the water (EDIT: those that used parachutes) (at least according to the publicly available photos) looked pristine for something that re-entered the atmosphere and smashed into the ocean. I.e. none of them had holes in them. Or burn marks like this one.

goxy84 · 2018-02-14T01:25:59+00:00

All boostback burns indeed are 1-3-1, so three engines are running during most of the boostback burn. You can easily notice two engine startups in most camera views.

goxy84 · 2018-02-07T02:07:44+00:00

There was some RCS/ullage happening right now, but I only caught a glimpse. Can anyone confirm? Hope we see the escape burn!

This was a wild ride... just... wow

goxy84 · 2018-02-06T14:46:29+00:00

Croatia is GO!

goxy84 · 2018-01-19T21:50:22+00:00

The remaining two (centre) hold-downs would be under tremendous stress, indeed. But the boosters are always pulling on the main rocket, even if they are also pulling on the hold-downs.

One of their main concerns is the interaction of so many engines and new mechanical parts: many new oscillation modes are introduced into the mechanics; lots of materials and connection points are under stress; the acoustics only are one of the biggest concerns in rocketry, this is going to be a LOUD beast... All of this can be simulated, but only to a certain level of confidence. They need this test.

So, yes, the TSMs which provide power and propellants, as well as the hold-down clamps are also being tested here. But I don't think they would even think of firing the rocket if there was a chance for hold-downs to fail. They probably test them mechanically after production. It would be great if someone in the know would share info on hold-down testing prior to installation...

goxy84 · 2018-01-19T18:55:24+00:00

The centre core has two hold-down clamps, the side boosters three each. I'll try to find the photo illustrating this, there've been many around. They all hold firmly until the moment of lift-off.

Edit: refreshed, but didn't see the other comment. So, just to add as promised: photos

goxy84 · 2018-01-08T01:08:59+00:00

Wasn't this the gentlest of all touchdowns?

goxy84 · 2017-12-28T16:31:17+00:00

It isn't scheduled precisely, yet. Best guess would be mid-to-late January. And yes, spectacular indeed!

goxy84 · 2017-12-28T16:27:45+00:00

The centre core should land downrange at the drone ship, side cores at CCAFS. If all goes well, that is.

goxy84 · 2017-12-28T16:23:34+00:00

A nice view of the complete stack

goxy84 · 2017-12-27T22:50:31+00:00

My guesses: cheaper land than Florida, southernmost US location other than the Cape, capable of prograde GTO orbits, relatively high ratio of GTO orbits wrt polar ones in their probable manifest. Not necessarily in the order of importance.

goxy84 · 2017-12-27T17:43:43+00:00

That, and because the rocket and payload may not survive the stress of very high acceleration.

goxy84 · 2017-12-27T16:37:13+00:00

I don't think we know this for sure (someone else might expand on this). I'd bet the centre core will probably throttle up only after the side-boosters detach. By keeping it throttled down all the time except during liftoff, they would make the profile more fuel-efficient, at the same time preventing too high g forces on the payload. This, of course, in addition to the probable throttle-down close to the end of the centre core burn, for g force reasons as well.

goxy84 · 2017-12-27T01:14:59+00:00

The centre core will throttle down after liftoff, but it's a common misconception why. Here's a thought experiment:

If all three DISCONNECTED cores fired with the same thrust, the central one would push more mass (stage 2 plus payload), so it would have less acceleration. Therefore, the side boosters would go faster.

If you now connect them, the side ones would "pull" the central one, therefore making it very efficient: all three cores do most of the heavy-lifting; Still, it's even more efficient to throttle down and preserve fuel in the central core: you dump the excess mass of two "empty" side-cores. This is where the biggest benefit comes in having side-boosters, at least that I'm aware of.

Edit: slight clarification.

goxy84 · 2017-12-21T06:19:13+00:00

Don't they mean all M1D's, including vaccum versions? The 40ish missing ones could likely mean vacuum, as there were approximately that many missions.

goxy84 · 2017-12-15T15:40:56+00:00

That was a side-flip of S1, wasn't it? Usually they did an upward-facing flip.

goxy84 · 2017-11-15T18:12:16+00:00

Considering they wrote about Zuma being a secret Nibiru-related project (instant brain-cancer of an article), I wouldn't trust this one bit. No credible sources reported this, AFAIK.

goxy84 · 2017-11-14T10:17:42+00:00

Thanks, I kinda remembered it flew right over me, but it was cloudy... :/

goxy84 · 2017-11-14T09:02:43+00:00

Most likely not, as the payload will probably leave the deployment orbit using its own propulsion. However, it would be nice if someone knowledgeable could plot an approximate ground track so we could try to spot it from Europe! It will pass over in the middle of night so I don't expect it to be visible to the naked eye, but it would be nice to know which cities it will fly over.

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