Author Topic: Falcon 9 Q&A (Read 74129 times)

su27k · « **Reply #40 on:** 04/01/2018 05:12 am »

From the reddit comment of an ex-employee who welded the octaweb:

Quote

2219 aluminum/lithium alloy

This is from a year ago, but I doubt they'll change it for Block 5.

Bananas_on_Mars · « **Reply #41 on:** 04/01/2018 12:55 pm »

Somewhere along the way(Block 4ish?) they changed to an octaweb that's bolted instead of welded.
So the material might have changed.

LucR · « **Reply #42 on:** 05/11/2018 06:49 pm »

From Elon's Block 5 phone presser transcript:

Quote from: theinternetftw link=https://gist.github.com/theinternetftw/5ba82bd5f4099934fa0556b9d09c123e

But this is a much stronger octaweb structure. It's made of a much higher strength of bolted aluminum. A 7000 series instead of a 2000 series.

So they did change it for block 5.

kevinof · « **Reply #43 on:** 05/11/2018 07:00 pm »

Used to be welded together, now it's bolted which (according to Space X) makes building and refurb easier.

IanThePineapple · « **Reply #44 on:** 11/12/2018 05:53 pm »

Is it known which core F9R Dev2 is/was? I thought I read somewhere that it was core 1007, but I couldn't find any of this info again.

Thanks for the help!

Slarty1080 · « **Reply #45 on:** 02/17/2019 01:57 pm »

What are those short towers around the launch pad of Falcon 9 used for?

Orbiter · « **Reply #46 on:** 02/17/2019 01:58 pm »

Lightning protection.

Jim · « **Reply #47 on:** 02/17/2019 03:09 pm »

Leftovers from Titan IV

ugordan · « **Reply #48 on:** 02/17/2019 03:26 pm »

Plus, they're not exactly short. They're what, 250 feet tall just to the bottom of that white cylinder, which is another 150 ft high?

PM3 · « **Reply #49 on:** 02/17/2019 04:38 pm »

https://www.google.com/search?q=cape+canaveral+lightning+protection&tbm=isch

Slarty1080 · « **Reply #50 on:** 02/17/2019 06:21 pm »

Why not just a metal spike at the top? What's with the white cylinder bits?

ugordan · « **Reply #51 on:** 02/17/2019 06:27 pm »

Because the towers themselves are not meant to be isolated ligthning rods. If you look carefully at SLC-40 imagery, you'll see catenary wires going between all four towers and a middle grid inside that one. The purpose of the towers is to create a "net" by shielding the launch vehicle from high electric field tension when a lightning strike hits, sort of like a Faraday cage does. It's not supposed to *attract* lightning.

PM3 · « **Reply #52 on:** 02/17/2019 07:12 pm »

Quote from: Slarty1080 on 02/17/2019 06:21 pm

What's with the white cylinder bits?

"The big top rods are insulators ... spun fiber in polymer matrix structure ... at the time the biggest such cylinder in the world."

"The fiberglass (FRP) tubes on the top of the launch platforms are a part of a lightning protection system and are insulators with cables that form a cone of protection for the launch tower. They were designed by my former company CH2M HILL, (Gainesville,FL)an engineering firm, and were manufactured by Starline Fabricators, Astatula, FL"

https://space.stackexchange.com/questions/2958/what-are-the-towers-around-the-spacex-launch-pad-used-for

Slarty1080 · « **Reply #53 on:** 02/17/2019 08:38 pm »

thx - does that mean that Starship will need an even bigger set up? Or will that be different because its made of Stainless?

cebri · « **Reply #54 on:** 05/26/2020 06:03 pm »

Do we know how much thrust the RCS of the first stage of the falcon 9 produce?

gongora · « **Reply #55 on:** 08/15/2020 11:20 pm »

Quote from: brejol on 08/15/2020 11:16 pm

Ariane 5 just launched 3 satellites to GTO. How many launches would it take the falcon 9 to launch them?

two

Lisa_R4 · « **Reply #56 on:** 09/02/2020 03:49 pm »

Amazing photos. Seems so surreal it can light engines on the way back when the forces must be pushing some plume back on to the engines themselves. Sorry for the newbie question, but how do they protect the bottom of the Falcon 9 from that?

CorvusCorax · « **Reply #57 on:** 09/02/2020 05:26 pm »

Quote from: Lisa_R4 on 09/02/2020 03:49 pm

Amazing photos. Seems so surreal it can light engines on the way back when the forces must be pushing some plume back on to the engines themselves. Sorry for the newbie question, but how do they protect the bottom of the Falcon 9 from that?

The bottom of Falcon9 has a heat-shield for that reason. I's design changed a couple of times over F9's design iterations. The rigid parts are easy, they are simply coated in a sufficiently heat resistant material. But the engines gimbal and that makes it necessary that parts of this shield are flexible. In the past SpaceX used something that looked like asbestos cloth you find in furnace-mits and similar, but these have shown holes and other signs of burn through after booster-recovery. The block5 iteration has something better, but the exact design is probably a trade secret

Nevertheless SpaceX has encountered heatshield failures on some extreme reentry recovery attempts. (B1057 - Falcon Heavy Center Core suffered from TVC failure on center engine after a heat shield burn-through -> aborted landing)

The nozzles themselfes don't need protection, they are designed to cope with rocket exhaust and have active cooling channels in their walls.

CorvusCorax · « **Reply #58 on:** 10/12/2020 03:05 pm »

I think Shotwell was quoting Musk though when she said [Re: Elon Musk criticized Grasshopper's test campaign as having been "not aggressive enough" as the test article ended up surviving all tests.]. I don't have the exact source/video, though.

Link/Reference anyone? It should be public, but I don't know where to look.

AS_501 · « **Reply #59 on:** 04/22/2021 09:51 pm »

I'm puzzled why Falcon 9 throttles down through Max Q. I can understand why Falcon 9 Heavy (as well as Shuttle, Delta IV Heavy, etc.) does this to reduce aerodynamic loads on the booster attach points. But F9 is single stick. My best guess is that the vehicle velocity approaching Max Q dictates the need for throttle down. Or this is required by Dragon, not the booster? Or if Space X built Dragon and Falcon 'beefy' enough to endure full Max Q, there would be a weight penalties.

Sidebar coments:
- I just watched the last Delta IV Medium (two SRBs) launch. Didn't hear an RS-68A throttle down comment.
- I think the Shuttle was first vehicle to utilize throtte down simply because it had the first throttleable engines.
- The original Atlas rocket is an interesting case. It was famous (or infamous!) for it's thin-skin construction. As far as I know it survived Max Q every time with its fixed-thrust engines.
Thanks