BeechTalk - BT

Username Protected · **Posted:** 03 Feb 2021, 19:43

Username Protected wrote:

I’m not an expert but my common sense does wonder why they don’t start all three briefly and then shut one down again if they all start or keep the two that start if only two fire up.

It may be the case that this is just testing and in the full up build they’ll have enough mass left on landing that the difference between too much thrust and not enough thrust is within the throttle range of both n engines they plan to start and n-1 or n-2 engines in case one or two don’t come back to life.

I also am not an expert, but if I were considering a space tourism adventure I would not want to be in a landing vehicle where the required engines did not ALL light off RELIABLY. Every time! :cheers:

I would be a lot less interested if they have to try to light 3 engines to get one to light reliably...

Username Protected · **Posted:** 03 Feb 2021, 19:50

Rockets are cool!!

Attachment:

SN9-Feb-2-2021-7280-1440x960.jpg

Quote:

Prior to the Starship SN8 test launch in December 2020, SpaceX sought a waiver to exceed the maximum public risk allowed by federal safety regulations,” an FAA spokesperson said Tuesday. “After the FAA denied the request, SpaceX proceeded with the flight.”

https://spaceflightnow.com/2021/02/02/faa-approves-next-starship-launch-after-saying-spacex-violated-safety-rules-on-previous-flight/

Quote:

"The FAA's top priority in regulating commercial space transportation is ensuring that operations are safe, even if there is an anomaly," an agency spokesperson said in a statement, using the industry term for a launch failure. "The FAA will oversee the investigation of today's landing mishap involving the SpaceX Starship SN9 prototype in Boca Chica, Texas. Although this was an uncrewed test flight, the investigation will identify the root cause of today's mishap and possible opportunities to further enhance safety as the program develops."

https://www.cnn.com/2021/02/02/tech/spacex-starship-sn-9-test-launch-faa-scn/index.html

Username Protected · **Posted:** 03 Feb 2021, 19:57

I wonder what it is about the events and environment prior to relight that is making this so difficult.

Username Protected · **Posted:** 03 Feb 2021, 20:11

Username Protected wrote:

I’d want them to be able to say something like “99.9999% of the time (999,999 times out of 1 million attempts) they all light fine, but in case they don’t we don’t need all of them anyway.”

There’s no such thing as a mechanical device that works as expected EVERY time. Reliability engineering is about planning for and mitigating the consequences of failures that will eventually happen.

OK, sure, for the sake of my argument what you said is fine. But to only hit one out of three... not so much!

Username Protected · **Posted:** 03 Feb 2021, 20:18

Username Protected wrote:

But to only hit one out of three... not so much!

They hit one out of two. They didn’t try to light the third.

Username Protected · **Posted:** 03 Feb 2021, 21:11

Username Protected wrote:

I wonder what it is about the events and environment prior to relight that is making this so difficult.

I bet it's caused by shock cooling when they shut them down on the way up

Username Protected · **Posted:** 03 Feb 2021, 23:42

Username Protected wrote:

I wonder what it is about the events and environment prior to relight that is making this so difficult.

I bet it's caused by shock cooling when they shut them down on the way up

Username Protected · **Posted:** 04 Feb 2021, 11:33

Username Protected wrote:

They hit one out of two. They didn’t try to light the third.

That's an idea, try to light all three, if you get all 3, shut one down prior to landing. If you get 2, go with that. Shutting down is highly reliable, starting, not so much.

You would have to fail 2 of 3 to not land.

There's a lot of violence going on inside that skirt. I see flames and high velocity gases, so it doesn't take much to break something. It feels like things need to get hardened.

Starting the engines with lots of air blowing up the nozzle sideways might be quite hard.

Mike C.

Username Protected · **Posted:** 04 Feb 2021, 22:05

Username Protected wrote:

This thread reminds me that on the internet, everyone is an expert.

https://twitter.com/elonmusk/status/1357422126161145856

Quote:

It was foolish of us not to start 3 engines & immediately shut down 1, as 2 are needed to land

Username Protected · **Posted:** 07 Feb 2021, 00:16

As a younger man... I only ever contemplated adding Fuel to a fire to make it go.

Now (well) in to my 2nd half and spending countless nights studying orbital mechanics and Rocket propulsion I’ve discovered the other way is far more effective sometimes.

Attachment:

8A4BC300-3F61-445E-A37D-978773F335A7.jpeg

Username Protected · **Posted:** 07 Feb 2021, 12:48

Now spray some aerosols into the intake of the leaf blower for the real fun

Username Protected · **Posted:** 07 Feb 2021, 13:28

Username Protected wrote:

Now spray some aerosols into the intake of the leaf blower for the real fun

That's how you make a home jet engine.

Username Protected · **Posted:** 07 Feb 2021, 13:58

Username Protected wrote:

Now spray some aerosols into the intake of the leaf blower for the real fun

That's how you make a home jet engine.

Username Protected · **Posted:** 07 Feb 2021, 14:43

Username Protected wrote:

A chimnea and a leaf blower with aerosols is where the real fun is

Somewhere on the internet I once read a story about using a shop vac to clean up a petroleum/aromatics/flammable stuff spill. The motors in those aren't really intended to isolate the electricity from the air flowing through, in other words... ignition source.

I've done some dumb stuff but that one's a science experiment I'm content to merely read about.

Pesky fire triangle tetrahædron.

Username Protected · **Posted:** 07 Feb 2021, 20:59

Username Protected wrote:

Now spray some aerosols into the intake of the leaf blower for the real fun

That's how you make a home jet engine.

Bravo SpaceX