totm nov 2023 SpaceX Discussion Thread

[tater]

1 minute ago, CatastrophicFailure said:

That 24-hour turnaround won’t be standard practice at all.

Yes, and no.

Yes, in that turning around a rocket and relaunching in 24 hours will indeed be a stunt.

No, in that the labor required will be identical, even if the turn around is 24 DAYS, or 24 months.

I think the man-hours required to ready a flight are really the issue.

 

Actual news:

 

[StrandedonEarth]

11 hours ago, Streetwind said:

Re-flying same block 5 core within 24 hours next year

I dunno, that sounds to me like they really want to get the same core off the pad within 24 real-time hours, not labor time. 

As for a quick ASDS turnaround, a year or two ago Elon was considering giving it a quick “gas’n’go” at sea with just enough propellants to hop from the ASDS back to the pad. I wonder if that is still on the table...

Edited May 11, 2018 by StrandedonEarth

[tater]

Operationally, such a turn around helps for BFR operations planning, I suppose. I think that the notional refilling of BFR doesn't address some non-trivial orbital mechanics, honestly, particularly WRT putting BFS into an elliptical orbit.

 

Related to today's launch... sad that it got scrubbed, since yesterday;s delay allowed my son to watch, sadly he's now in school. Least he's wearing his FH tee shirt

 

[zolotiyeruki]

5 minutes ago, StrandedonEarth said:

I dunno, that sounds to me like they really want to get the same core off the pad within 24 real-time hours, not labor time. 

As for a quick ASDS turnaround, a year or two ago Elon was considering giving it a quick “gas’n’go” at sea with just enough propellants to hop from the ASDS back to the pad. I wonder if that is still on the table...

Hmmm, now *that* is an interesting idea.  How much fuel would they need to load in order to make that hop back?  Aerodynamics would not be in their favor, but there'd also be no 2nd stage to loft.  Also, what would they do with the landing legs?

[tater]

 

[sevenperforce]

53 minutes ago, sh1pman said:

It may actually be longer, because staging will happen further downrange, and possibly at higher speed. Remember, you still need to burn off 2+ km/s of prograde velocity first. 

Well, more margin is always better. Obviously they are not going to burn further downrange than they have fuel to boostback from.

Also, you don't have to scrub off prograde velocity; you only have to scrub off downrange velocity. Gravity is your friend. Let's take a look at CRS-12 in the above graphic. A triangle with the hypotenuse tangent to the velocity vector at staging has a horizontal component that is 78% of its magnitude (thanks, Pythagoras). A quick glance at the CRS-12 webcast on YouTube tells me that staging velocity was 1.66 km/s. So scrubbing out horizontal velocity will cost the naked first stage 1.29 km/s.

At zero horizontal velocity, the stage is now 96.5 km downrange and at an altitude of 104 km. Using basic kinematic equations, the stage would need 663 m/s to get back to land, assuming a ballistic trajectory. However, vertical velocity is not zero, so your extra hang time means you only need 338 m/s to get on a trajectory which hits the landing pad.

Now, the "dense" atmosphere begins at 30 km, when the CRS-12 booster was only 6 km downrange and speeding back. However, with titanium grid fins, the booster can hit the denser portion of the atmosphere 30 km downrange, because its L/D ratio can take it the rest of the way. So instead of 338 m/s, the "return" segment of the boostback burn only needs to provide 233 m/s.

So CRS-12 had a boostback of about 1,628 m/s, but if it had been equipped with titanium grid fins, it would have needed a boostback of about 1,523 m/s. At least some of that extra ~105 m/s could have gone to the upper stage before separation, giving just a slightly larger kick to the upper stage.

23 minutes ago, StrandedonEarth said:

I dunno, that sounds to me like they really want to get the same core off the pad within 24 real-time hours, not labor time. 

As for a quick ASDS turnaround, a year or two ago Elon was considering giving it a quick “gas’n’go” at sea with just enough propellants to hop from the ASDS back to the pad. I wonder if that is still on the table...

I don't think that was ever on the table. That was on the digital menu they were considering but never actually got around to printing out.

The logistical challenge of refueling at sea and flying the stage back to land is......unbelievably immense.

22 minutes ago, tater said:

Operationally, such a turn around helps for BFR operations planning, I suppose. I think that the notional refilling of BFR doesn't address some non-trivial orbital mechanics, honestly, particularly WRT putting BFS into an elliptical orbit.

This is probably not too challenging.

[tater]

4 minutes ago, sevenperforce said:

This is probably not too challenging.

The lunar architecture has BFS in a highly elliptical orbit. Given their launch sites, this means that rendezvous launch windows will be tight and infrequent if the period is measured in days (or many hours, even) since launch will be near when perigee is over the launch site.

[sevenperforce]

17 minutes ago, zolotiyeruki said:

Hmmm, now *that* is an interesting idea.  How much fuel would they need to load in order to make that hop back?  Aerodynamics would not be in their favor, but there'd also be no 2nd stage to loft.  Also, what would they do with the landing legs?

Let's see. Assuming a nominal 5-tonne payload, S1 burns 2.75 m/s to get to staging. About three fifths of that goes to fighting gravity drag and aerodynamic drag. If we guesstimate the first stage to have a staging mass of 105 tonnes for an ASDS mission based on 20% propellant reserves for EDL (I may be overestimating this), then we will need around 240 tonnes of props to get back home from the ASDS, including the entry and landing reserves. That's about 60% of a full prop load.

Landing legs for Block 5 can be refolded but you'd need a launch pad of some kind with hold-downs since the legs obviously cannot be refolded mid-flight.

[tater]

 

[sevenperforce]

8 minutes ago, tater said:

The lunar architecture has BFS in a highly elliptical orbit. Given their launch sites, this means that rendezvous launch windows will be tight and infrequent if the period is measured in days (or many hours, even) since launch will be near when perigee is over the launch site.

BFS is infinitely restartable so there's no reason it can't simply inject to a circular parking orbit and then catch up when it needs to. Inclination is always an issue, but....

[tater]

4 minutes ago, sevenperforce said:

BFS is infinitely restartable so there's no reason it can't simply inject to a circular parking orbit and then catch up when it needs to. Inclination is always an issue, but....

It's inclination, plus the whole point of a direct injection into elliptical was to mitigate props use. Seems like optimal for the lunar architecture would be 2X tankers, 1 in LEO, top it all the way off, then wait to rendezvous with spacecraft.

And for the new page:

 

[Barzon]

I sure do hope they have fixed the problem that caused the abort last night!

[DAL59]

4 hours ago, kerbiloid said:

If they replace those four expandable legs with a single titanium spike with a sharp steel bit, they can just stick the rocket into the sand (on land or on barge).
Maybe this would additionally save several tons.

Why use a landing burn at all?  Just a tube that catches it and slows it down. /s

 

[XB-70A]

Falcon 9 has just started to breath.

Already 3 minutes of venting.

Edited May 11, 2018 by XB-70A

[KSK]

And we're live!

 

[tater]

Live!

1 minute ago, XB-70A said:

Falcon 9 has just started to breath.

I always forget you're actually THERE.

[DAL59]

Started!

[KSK]

Commencing pre-flight checklist.

Nibbles?
Go.
Cold one? 
Brrrrappp.  Go!
Router?
Magic internet gnomes reporting in.
Keyboard?
I've got this.
Livestream?
GO.

Science and Spaceflight forum - KSK is reporting Go for launch!

[HebaruSan]

He said the abort was a left-over status from a previous test that wasn't properly reset.

[Brotoro]

Forgot to press the reset button before launch sequence.

Weather conditions at the barge are sunnier today.

Edited May 11, 2018 by Brotoro

[KSK]

Man, those interstage optical illusions are playing with my head again. Is it just me or does that rocket look slightly bent? 

 

[XB-70A]

5 minutes ago, tater said:

I always forget you're actually THERE.

I don’t know if it’ could be a good and realistic idea, but during the last months I was thinking about starting some live coverages for the forum community, just the film and without any comments. Only to give another spot to everyone interested, but at first I must have a better camcorder with an internet connection.

[Nightfury]

Just now, XB-70A said:

I don’t know if it’ could be a good and realistic idea, but during the last months I was thinking about starting some live coverages for the forum community, just the film and without any comments. Only to give another spot to everyone interested, but at first I must have a better camcorder with an internet connection.

Would love watch this

[sevenperforce]

LIFTOFF!!!!

 

(kidding, kidding)

[Nightfury]

Just now, sevenperforce said:

LIFTOFF!!!!

 

(kidding, kidding)

1:30 too soon