SpaceX Starship SN9 High Altitude Test – Live [video] | Hacker News Reader

SpaceX Starship SN9 High Altitude Test – Live [video]

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38 pointsfirebaze24 comments

SpaceX will be conducting a 12.5 km test flight of their SN9 prototype vehicle. This flight will be a repeat of the largely successful SN8 test flight, with some possible minor flight profile changes.

SN9 will lift off from Boca Chica, Texas under the power of its three Raptor engines. The Raptor engines will shut off one by one during ascent to decrease loads and acceleration on the vehicle. At apogee, the single Raptor engine still burning will initiate the vertical-to-horizontal flip before shutting off. SN9 will make use of its body flaps to keep it stable during descent. Prior to landing, SN9 will ignite two of its Raptor engines to reorientate itself back into a vertical position and perform a propulsive landing.

So the engine shut-offs for the SN8 test were indeed deliberate.

> So the engine shut-offs for the SN8 test were indeed deliberate.

Yes. As you burn the fuel, the ship gets lighter and you need fewer engines. The big surprise was the engine-rich exhaust during the landing burn.

I just love all the aerospace euphemisms.

They have a harsh job. Interesting metaphors are a defense against that.

The NASASpaceflight channel (not NASA related actually, just annoyingly scammy name) covering the same event https://www.youtube.com/watch?v=lPRfJxz-ECE

Agreed that the name is a bit unfortunate, but they mention their non-affiliation every chance they get. And they do produce some pretty high quality live coverage of these events.

Hope to see the changes to the flight control software & header tanks work! The last flight was neat, just seeing it perform the belly flop maneuver. Today we might see it land if there's enough pressure in the reserve tanks.

What's insane about this flight profile is that fuel tanks aren't supposed to do this. The flip it does right before it hits the ground makes all the liquid fuel splash around and slosh to one side. So instead, it uses some of the hot gasses from the rocket engine to pre-heat a small amount of fuel and use it to pressurize a small reserve tank that is used to get the engines going. One of the causes of the explosion from the last test was that they ran out of pressure in the fuel tank, causing oxidizer rich combustion which eventually burnt up the engines. So hopefully they tweak the system a little and we get to see a belly flop and a successful landing!

> causing oxidizer rich combustion which eventually burnt up the engines

Which sometimes is called "engine rich exhaust". I love these sarcastic terms in rocketry. RUD, lithobraking, etc.

> So instead, it uses some of the hot gasses from the rocket engine to pre-heat a small amount of fuel and use it to pressurize a small reserve tank that is used to get the engines going.

I think they are still using helium or nitrogen to pressurize the tanks. Autogenuous pressurization is definitely what they want to do (or „have to do“ if you like) but afaik they are not there yet.

They were using autogenous pressurization for SN8, and that's what failed with the header tanks on landing.

For SN9's flight (hopefully today), they'll just use regular helium pressurization for the header tanks. It's a temporary fix to continue testing the rest of the system while they work that particular kink out.

Is there any analysis regarding how the tiny legs are meant to work? By the look of it, the smallest percentage residual velocity or vertical rotation is going to crunch whichever hits first. The Falcon 9 legs are huge and clearly very strong. The SNx legs just seem ... incongruous? Or are they still in int the 'zero volicity splash-down for modelling' stage?

(Edit: Not to mention how any of this is meant to work on Mars.)

i think its just temporary.

Yeah, I remember Elon saying that they want to get rid of the legs.

Only for the booster. Starship (2nd stage) will need legs for landing on the Earth, Moon, and Mars.

Elon basically tweeted that the legs are one of the single biggest 'battlegrounds' inside of SpaceX. There are tons of ideas and different approaches.

We will see what SN15 goes with. The current ones are defiantly not a final product.

Don't know if it's just me, but I'm finding it enormously frustrating to work out when this launch will be. I know things change, but would it be so hard to have it prominently displayed somewhere the expected time in local, with the timezone, and GMT so others can work out what time it will be where they are?

Currently on this stream it says 15:30 ... what time zone is that?

The YouTube popup gives local time. 15:30 seems to be UTC.

UTC is the only civilized timezone.

Thank you.

Apologies if I'm covering something you're already aware of, but that time is just Tim's (Everyday Astronaut's) best guess at when to start streaming.

The actual launch time is unknown to everyone outside of SpaceX. For SN8 SpaceX published a live stream of their own a few minutes before launch, but we don't even know if they'll do that this time.

Noted ... thanks.

(I did know, but it's useful to have the comment here for anyone else who's reading this).

It's internal testing. I don't think they actually want to encourage people watching.

For good reason, I suspect. Most of the friends/family I showed the SN8 belly-flop and "landing" to were like, "oh no, is SpaceX screwed now?" I had to explain that giant explosions are a fact of life when testing rocket prototypes.

The launch time changes constantly, as there's no real time provided by SpaceX: everything is an estimate based on road closures and NOTAMs.

If you want to keep track of this launch (and all other launches that happen), I've made a tiny Telegram bot that sends notifications before a launch happens: https://t.me/rocketrybot

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