totm nov 2023 SpaceX Discussion Thread

[magnemoe]

9 hours ago, StrandedonEarth said:

Or just to get a full BFS into orbit, instead of having to refuel it before it can leave LEO.

Not cost effective, you will also have problems finding single payload weighting more than 150 ton, nuclear reactors is one thing I can think of but even here the reactor would be launched cold so you could add shielding later. If you need 300 ton for one launch its cheaper to just ditch first stage. 

You would want an larger rocket if your launch so much its economical to scale up, fewer launchers and larger rockets tend to be more effective. 
This would require multiple BFR launches each day. 

[Wjolcz]

I too believe that ITS would make no sense. BFR is a redesigned and improved ITS not the other way around.

They probably thought "we should go this [ITS] big!" then decided to be more sensible and do something similar to what had flown already except from composites and fully reusable.

By 'flown already' I'm talking here about Saturn V and Space Shuttle. To me BFR is just a stretched shuttle on top of a stretched orange tank with engines.

Edited May 7, 2018 by Wjolcz

[ment18]

1 hour ago, Wjolcz said:

I too believe that ITS would make no sense. BFR is a redesigned and improved ITS not the other way around.

They probably thought "we should go this [ITS] big!" then decided to be more sensible and do something similar to what had flown already except from composites and fully reusable.

By 'flown already' I'm talking here about Saturn V and Space Shuttle. To me BFR is just a stretched shuttle on top of a stretched orange tank with engines.

They shrank the design because it was too costly to create a 12m rocket, but 9m was much less expensive.  There is the possibility that ITS scale vehicle is still planned, just after the BFR, sorta like falcon 9 v1 to v1.1.  BFR is nothing like the space shuttle, like nothing at all.  They serve completely different purposes and have completely different designs.  BFR doesn't have wings, it has control surfaces.  BFR is for interplanetary travel, not orbital maintenance.  BFR is composite, not aluminum, runs on completely different propellants, with completely different engines.  The shuttle had no propellant tanks, and the BFS itself has more propellant storage than the orange tank (by mass).  

BFR heavy is not going to happen.  SpaceX has learned from the FH, and the forces don't make sense.  BFB is designed for very specific force loads, straight through the bottom, so the side forces from other boosters would be very bad.  Require complete redesign of core, much worse then Falcon 9 because carbon fiber is a pain with how it responds to forces.  If you can't break you payload into 150 ton pieces, thats ridiculous.  We have created the ISS out of <30t parts.

[XB-70A]

10 hours ago, tater said:

 NET Thursday.

Now confirmed by the same Tweeter account:

 

 

[tater]

 

[tater]

 

 

Edited May 7, 2018 by tater

[mikegarrison]

https://www.seattletimes.com/business/musks-spacex-is-using-a-powerful-rocket-technology-nasa-advisers-say-it-could-put-lives-at-risk/

General market news article about the controversy over loading oxidizer while crew is already onboard the rocket.

[tater]

 

11 minutes ago, mikegarrison said:

https://www.seattletimes.com/business/musks-spacex-is-using-a-powerful-rocket-technology-nasa-advisers-say-it-could-put-lives-at-risk/

General market news article about the controversy over loading oxidizer while crew is already onboard the rocket.

This thing has been over the wire services for a few days now. Meh.

[sevenperforce]

42 minutes ago, tater said:

 

 

New catcher net looks badass.

24 minutes ago, mikegarrison said:

https://www.seattletimes.com/business/musks-spacex-is-using-a-powerful-rocket-technology-nasa-advisers-say-it-could-put-lives-at-risk/

General market news article about the controversy over loading oxidizer while crew is already onboard the rocket.

Really old news.

[sevenperforce]

I don't understand why propellant loading while the astronauts are on the pad is more dangerous than propellant loading before the astronauts on the pad.

If there is an RUD while the propellant is being loaded, Dragon 2 can abort.

Seems much safer than climbing into a capsule with all the fuel sitting there ready to go boom. The capsule can't abort during ingress.

[tater]

4 minutes ago, sevenperforce said:

Seems much safer than climbing into a capsule with all the fuel sitting there ready to go boom. The capsule can't abort during ingress.

Not to mention all the support personnel involved in putting people into the spacecraft. Those people are vulnerable from the time they get inside the danger area, until the capsule is latched tight, then the support crew have to leave.

Seems like it's a lower probability of accident, but with many more people involved, and for a longer time frame, vs a larger probability of problems, but for a shorter time frame, and with fewer people.

[sevenperforce]

30 minutes ago, tater said:

Not to mention all the support personnel involved in putting people into the spacecraft. Those people are vulnerable from the time they get inside the danger area, until the capsule is latched tight, then the support crew have to leave.

Seems like it's a lower probability of accident, but with many more people involved, and for a longer time frame, vs a larger probability of problems, but for a shorter time frame, and with fewer people.

You don't need the zipline or whatever other egress nonsense if you have nothing explosive until your LES is armed.

[tater]

3 minutes ago, sevenperforce said:

You don't need the zipline or whatever other egress nonsense if you have nothing explosive until your LES is armed.

It seems pretty unlikely that there would ever be an event such that a zipline would actually save anyone, too.

[YNM]

How long is the propellant loading ?

I know that I presume most (if not all) of the time, crew goes in before propellant loading, but perhaps, somehow SpX is a bit longer ?

[sevenperforce]

15 minutes ago, tater said:

It seems pretty unlikely that there would ever be an event such that a zipline would actually save anyone, too.

That's what I said when I first heard about it. I mean, sure, you want every possible egress available...but there are just really no failure modes which give you enough time to jump on a zipline.

[StrandedonEarth]

8 minutes ago, tater said:

It seems pretty unlikely that there would ever be an event such that a zipline would actually save anyone, too.

Difficult to say. In the absence of large solid rockets, the only way to get a conflagration would be to have a structural failure, or a huge leak. It’s conceivable that a small fuel leak could start a fire that, if uncontrolled, would still take awhile to cause a failure that would lead to a fireball. Still, much less pucker factor to simply “pop the cork” in that situation than have everyone racing for the zip lines 

[CatastrophicFailure]

58 minutes ago, sevenperforce said:

You don't need the zipline or whatever other egress nonsense if you have nothing explosive until your LES is armed.

Well, there’s still a few hundred pounds of hydrazine, but yeah... 

I was just watching a thing about a Titan missile explosion in Georgia back during the Cold War. They were stored fully fueled (because we were all a bit MAD back then...), and a technician dropped a great big socket down the silo that pierced the fuel tank, and one thing led to another. 

Now presumably modern man-rated boosters are a bit more thick skinned, but it seems like common sense to me that having as few people as possible around a fully fueled rocket is the safer bet. 

[DAL59]

17 hours ago, Bill Phil said:

That's something like over a thousand tonnes, right? At that point you'd have... well, some serious capability. I'd be launching a lot more than a fully fueled BFS, that's for sure...

This could launch 35 fully fueled BFRs.  

[cubinator]

1 hour ago, sevenperforce said:

I don't understand why propellant loading while the astronauts are on the pad is more dangerous than propellant loading before the astronauts on the pad.

If there is an RUD while the propellant is being loaded, Dragon 2 can abort.

Seems much safer than climbing into a capsule with all the fuel sitting there ready to go boom. The capsule can't abort during ingress.

That's a good point. 

[tater]

https://www.bizjournals.com/jacksonville/news/2018/05/07/midnight-ride-spacex-preps-for-2-rocket-launches.html?ana=e_sjo_tf&s=newsletter&ed=2018-05-07&u=%2BtTOa5Jp5%2B79Pqi%2FoH2Lgw0e32faf0&t=1525721581&j=81444671

About the upcoming couple of launches in FL. The date is wrong for block 5, but Thursday looks pretty firm now.

[Bill Phil]

38 minutes ago, DAL59 said:

This could launch 35 fully fueled BFRs.  

Child's play.

https://en.m.wikipedia.org/wiki/Project_Orion_(nuclear_propulsion)

[tater]

 

[Tullius]

1 hour ago, YNM said:

How long is the propellant loading ?

I know that I presume most (if not all) of the time, crew goes in before propellant loading, but perhaps, somehow SpX is a bit longer ?

A few hours.

For the Space Shuttle (https://en.wikipedia.org/wiki/Space_shuttle_launch_countdown), the propellant loading took 2 hours, which meant that fueling started about 11 hours before launch, while the crew started boarding the shuttle about 4 hours before launch. Also during the propellant loading, nobody was at the pad.

So in case of STS, NASA was expecting the propellant loading process to be one of the more dangerous parts of the countdown. Also one should not forget that it was during the propellant loading for the static fire that the Falcon 9 for Amos-6 exploded (although one can hope that the problem that caused this is now solved).

It is clear that SpaceX wants to shorten the countdown of any launch as much as possible (the Space Shuttle countdown started nearly 3 days before launch), but that will of course mean that they will have to take additional risks. It all depends on how much risks you are able to mitigate and how much risks you are willing to take.

[tater]

Prop loading on F9 begins at ~T - 1:10.

It looks like Shuttle had vehicle crew, and associated workers on the pad for at least 5.5 hours, or which ~3 hours were just the vehicle crew.

So 2.5 hours with many people, then 3 hours with 7 people on the pad with no plausible escape from any catastrophic failure, vs 70 minutes with the Dragon crew on the pad, with a LES capable of mitigating most any massive failure.

 

[sh1pman]

13 minutes ago, Tullius said:

It all depends on how much risks you are able to mitigate and how much risks you are willing to take.

(also applies to Mars colonization)

Edited May 7, 2018 by sh1pman