Re:Starship – SN8 – High-Altitude Flight Test
by codeulike on Wednesday December 09, 2020 @06:23PM
(#25366932)
I'm wondering if the engine shutoffs on the way up were deliberate, so they could get data on running on 3,2 and then 1 engine.
Re:Starship – SN8 – High-Altitude Flight Test
by smiley1437 on Wednesday December 09, 2020 @08:03PM
(#25368084)
If you look at the timer, it's almost certainly planned
Engine 1 cuts off 1m45s after launch
Engine 2 cuts off 1m28s after engine 1
Engine 3 cuts off 1m28s after engine 2 and then SN8 goes into glide testing.
The extra time on all 3 engines is probably to gain sufficient height?
Re:Starship – SN8 – High-Altitude Flight Test
by qayxc on Wednesday December 09, 2020 @07:14PM
(#25367576)
They looked planned. I think they tested the full array of required operations: shutdown, gimbal, throttling, re-ignition.
Re:Starship – SN8 – High-Altitude Flight Test
by wongarsu on Wednesday December 09, 2020 @07:38PM
(#25367840)
Even in normal operation it might have been useful to throttle down the engines in order to ascend a bit slower (less drag). If you have multiple engines, shutting some of them down is a convinient way to throttle.
Re:Starship – SN8 – High-Altitude Flight Test
by seg_lol on Thursday December 10, 2020 @01:46PM
(#25376935)
It was a wonderfully designed test. I'd love to hear a presentation on test design, the mission profile and what data they were looking at with each one.
I assume SpaceX has the same video feed with superimposed telemetry. I'd love to know turbo pump pressure and rpm during landing.
Re:Starship – SN8 – High-Altitude Flight Test
by grishka on Wednesday December 09, 2020 @06:01PM
(#25366582)
> no idea if it was supposed to be running on two, then one engine
Yeah and then something caught fire near the engines. I expected it to explode that very moment.
Re:Starship – SN8 – High-Altitude Flight Test
by oska on Thursday December 10, 2020 @12:24AM
(#25370091)
> Yeah and then something caught fire near the engines.
This is an artifact of air flow vortices around the base of the rocket and its skirt and is completely normal. This video [1] explains it well.
Re:Starship – SN8 – High-Altitude Flight Test
by AnimalMuppet on Wednesday December 09, 2020 @06:10PM
(#25366720)
Delayed gratification by a few minutes, but we got the pretty fireball in the end...
Re:Starship – SN8 – High-Altitude Flight Test
by Filligree on Wednesday December 09, 2020 @06:05PM
(#25366636)
I think that was the ignition system; the green flame matches. Which makes sense if they lost an engine, of course.
Re:Starship – SN8 – High-Altitude Flight Test
by Gwypaas on Wednesday December 09, 2020 @06:16PM
(#25366815)
The merlin engine uses TEA-TEB which causes the green flame seen on Falcon 9. The raptor uses electric spark ignition, which is harder but doesn't require any awfully poisonous chemicals and you can't run out.
Re:Starship – SN8 – High-Altitude Flight Test
by grishka on Wednesday December 09, 2020 @06:43PM
(#25367197)
No, not that, I meant the moment when one of the three engines shut off mid air and then moved away a bit so the remaining ones point straight down.
Re:Starship – SN8 – High-Altitude Flight Test
by remarkEon on Wednesday December 09, 2020 @06:13PM
(#25366762)
What's the reason that the flame produced by the ignition system is green?
Edit: ah, it's answered here https://news.ycombinator.com/item?id=25366736
Re:Starship – SN8 – High-Altitude Flight Test
by elteto on Wednesday December 09, 2020 @06:57PM
(#25367369)
That’s incorrect. Raptor does not use a TEA/TEB igniter like Falcon. It uses a spark igniter.
The green flame here is unintended engine ablation :) The chamber was melting.
Re:Starship – SN8 – High-Altitude Flight Test
by ArPDent on Wednesday December 09, 2020 @08:01PM
(#25368059)
specifically it's copper being vaporized i believe
Re:Starship – SN8 – High-Altitude Flight Test
by remarkEon on Wednesday December 09, 2020 @09:13PM
(#25368743)
Nice. Flashbacks to highschool chemistry. I'm assuming this isn't something you want to have happen ...
Re:Starship – SN8 – High-Altitude Flight Test
by SAI_Peregrinus on Wednesday December 09, 2020 @11:12PM
(#25369613)
No, engine-rich combustion cycles are definitely not something you usually want. Especially not on a re-usable craft.
Re:Starship – SN8 – High-Altitude Flight Test
by enraged_camel on Wednesday December 09, 2020 @06:01PM
(#25366577)
>>I wasn't sure if the ascent looked OK - no idea if it was supposed to be running on two, then one engine.
I realized that this may have been done to slow down the acceleration to make sure it doesn't go past the 12 km limit. I may be wrong though.
Re:Starship – SN8 – High-Altitude Flight Test
by endymi0n on Wednesday December 09, 2020 @06:03PM
(#25366615)
I also wasn't entirely sure whether the engine shutoffs were fully intended... at least the sideways acceleration of the Raptors at shutoff looked scary.
Re:Starship – SN8 – High-Altitude Flight Test
by apendleton on Wednesday December 09, 2020 @09:03PM
(#25368649)
As engines shut off, the remaining ones that were still going had to rapidly re-center to keep the direction of thrust aligned with the center of mass of the vehicle, and the ones that had shut off had to move out of their way to make room.
I'm sure they'll learn an immense amount from it, and it was amazing to see it nearly pull off the landing. Given the way that Falcon 9 early landing attempts went, it'll go the same way with Starship, and it'll be landing soon.