totm nov 2023 SpaceX Discussion Thread

[sevenperforce]

Holy crap I thought this was a simulation

 

That's drone footage y'all

[tater]

 

[tater]

 

Ahead at 3 reflights under the assumption the payload mass loss actually matters.

This might be true for Starlink which maxes out payload mass. But for a nominal sat to GTO? What, would they have more sat customers with 40% more payload?

 

[zolotiyeruki]

12 minutes ago, tater said:

 

Ahead at 3 reflights under the assumption the payload mass loss actually matters.

This might be true for Starlink which maxes out payload mass. But for a nominal sat to GTO? What, would they have more sat customers with 40% more payload?

 

That's a great point.  Of course, he's not saying whether the "you" is SpaceX as the supplier, or the customer.

[tater]

 

[cubinator]

There's those high winds again. I'm telling you, he wants to land one on Jupiter. Is TWR above 2.5?

[tater]

48 minutes ago, cubinator said:

There's those high winds again. I'm telling you, he wants to land one on Jupiter. Is TWR above 2.5?

Fewer launch delays.

Less concern about landing ops. You can't be set up for return from Mars (or the Moon, etc), and then realize the winds are too high at the landing zone.

Ditto P2P. As I have said many times, I don't think P2P is a thing, but to the extent they do, then need "all weather ops." The characteristic rise time of a thunder storm is shorter than an antipodal, suborbital trip.

 

[RealKerbal3x]

Wow. Look at that thing. That's one sexy piece of engineering.

In other news, I'm torn on the thing they're building at the launch site. Is it a launch pad or a water tower?

Edited August 19, 2020 by RealKerbal3x

[Codraroll]

20 minutes ago, RealKerbal3x said:

Is it a launch pad or a water tower?

Apparently it's a launch pad FOR water towers.

[RealKerbal3x]

1 minute ago, Codraroll said:

Apparently it's a launch pad FOR water towers.

So a water tower

[AVaughan]

8 hours ago, tater said:

But for a nominal sat to GTO? What, would they have more sat customers with 40% more payload?

I doubt they would get more customers, since they can always launch in expendable mode and/or use Falcon Heavy if the payload mass is an issue.  But 40% more payload mass to GTO might allow them, to co-manifest more payloads, which would save money by reducing costs.  (Of course real reuse with cheap refurbishment also reduces costs even more significantly.  But a ULA led refurbishment would probably involve a teardown and rebuild, which isn't going to be cheap.  And that is before even mentioning the need for a redesigned rocket and all the associated development costs).

[magnemoe]

23 minutes ago, RealKerbal3x said:

In other news, I'm torn on the thing they're building at the launch site. Is it a launch pad or a water tower?

Good question, I think the pillars angle a bit to much inward for it being an high water tower, yes saw the youtube video but why cure concrete pillars? 
On the other hand you have the central pipe, Yes it could be structure for the flame diverter. 

Now they will need both an water tower and at least one launch pad so it does not matter that much 

[RCgothic]

It's clearly a launch pad. The supposed downcomer isn't lined for water and there's no piping beneath the concrete footing for it to connect to. Plus we know the pad will have to be elevated because you can't excavate a flame trench in Boca chica due to the water table.

The centre pipe is either structure for a flame diverter or temporary support for the concrete forms.

[RealKerbal3x]

18 minutes ago, RCgothic said:

It's clearly a launch pad. The supposed downcomer isn't lined for water and there's no piping beneath the concrete footing for it to connect to. Plus we know the pad will have to be elevated because you can't excavate a flame trench in Boca chica due to the water table.

The centre pipe is either structure for a flame diverter or temporary support for the concrete forms.

Yeah, I'm kind of leaning towards launch pad. Those rebar cages are huge (~2m diameter) - I doubt concrete pillars that large would be required for a water tower, unless it's an insanely huge one.

We can also see from aerial photos that they're building it in a hexagonal configuration similar to that of Starship's launch mount.

[sevenperforce]

8 hours ago, tater said:

 

That is fascinating. But I suppose it makes sense. Think about it…you need the engines lit in order to do the actual landing; if they don’t, you’re boned anyway. And with high gimbal it’s not hard to imagine them having a lot more control authority than gas thrusters.

Probably one place where KSP emulates real life. You need to blanket your rocket with RCS to even come close to the control authority you get from a Vector. It’s not even a contest. Any time you can have your engines lit, you have way more authority than any aerodynamic surfaces, RCS, or reaction wheels can provide.

So the kick-flip it is. The best part is no part and the best system is no system. 

2 hours ago, AVaughan said:

I doubt they would get more customers, since they can always launch in expendable mode and/or use Falcon Heavy if the payload mass is an issue.  But 40% more payload mass to GTO might allow them, to co-manifest more payloads, which would save money by reducing costs.

The Ariane 5 can co-manifest and I don’t think it’s a capability that is used often (though I could be wrong about that). Unless you have a single customer sending two comsats to the same GEO destination for whatever reason, you’re always going to end up with a “primary” customer and a “secondary” customer. The GTO delivery will be to the primary customer’s target orbit, and the secondary customer will have to burn extra propellant to move to its target orbit, which reduces mission lifetime. It’s a small burn, but it’s still an issue. And you have the added complexity of multiple integrations. Plus the primary customer will be worried about whether the secondary customer might compromise mission success. 

[RCgothic]

And the secondary customer will be similarly worried about the primary customer's requirements (e.g. CRS-1/Orbcomm).

[magnemoe]

1 hour ago, sevenperforce said:

That is fascinating. But I suppose it makes sense. Think about it…you need the engines lit in order to do the actual landing; if they don’t, you’re boned anyway. And with high gimbal it’s not hard to imagine them having a lot more control authority than gas thrusters.

Probably one place where KSP emulates real life. You need to blanket your rocket with RCS to even come close to the control authority you get from a Vector. It’s not even a contest. Any time you can have your engines lit, you have way more authority than any aerodynamic surfaces, RCS, or reaction wheels can provide.

So the kick-flip it is. The best part is no part and the best system is no system. 

Now I assume they start the flip by folding inn the bottom fins, this will reduce drag on lower part while keeping it high on the top so the bottom should swing down.
As you get more vertical the drag difference goes down but you have momentum and some forward velocity. 
In short i don't see much use in using engines to flip, you will need to use them to stop you rotating, then slow you down and do adjustments so you land on the landing pad. 

Now on Mars its quite possible this will not work as the air is so thin and you have to use the engines to rotate you. 

[magnemoe]

1 hour ago, sevenperforce said:

The Ariane 5 can co-manifest and I don’t think it’s a capability that is used often (though I could be wrong about that). Unless you have a single customer sending two comsats to the same GEO destination for whatever reason, you’re always going to end up with a “primary” customer and a “secondary” customer. The GTO delivery will be to the primary customer’s target orbit, and the secondary customer will have to burn extra propellant to move to its target orbit, which reduces mission lifetime. It’s a small burn, but it’s still an issue. And you have the added complexity of multiple integrations. Plus the primary customer will be worried about whether the secondary customer might compromise mission success. 

Think main problem is if one of the payloads are delayed. Also size and weight has to be within parameters. One issue is that average GEO satellite has become heavier so its hard to find two you can launch together. 

If you take extra orbits with PE low you can select any place in GEO. should not cost extra fuel you just do two burns to circulate. First raises PE so one or more orbits later you are at AP at correct position and you circularize. 

[tater]

Skimming this:

https://en.wikipedia.org/wiki/List_of_Falcon_9_and_Falcon_Heavy_launches

and looking at payload masses, it looks like the recovery performance hit is only occasionally an issue. Things like Iridium might be an issue (10 sats at a time), though they might have been volume limited more than mass at 9,600kg.

GTO launches showed a bunch of expended cores, so clearly it's a legit issue there, though that might change with more utilization of FHr (though that also impacts operating costs). That said, they have recovered some after pretty heavy GTO launches. I suppose there might be some rideshare loss of revenue?

The CRS missions are all gimmes, they don't pish the recovery envelope at all.

SSO launches look like they don't come close to having the 40% payload hit matter.

 

Nice image from yesterday:

https://twitter.com/TrevorMahlmann/status/1295835404529172482?s=20

[Meecrob]

5 hours ago, magnemoe said:

Now I assume they start the flip by folding inn the bottom fins, this will reduce drag on lower part while keeping it high on the top so the bottom should swing down.
As you get more vertical the drag difference goes down but you have momentum and some forward velocity. 
In short i don't see much use in using engines to flip, you will need to use them to stop you rotating, then slow you down and do adjustments so you land on the landing pad. 

Now on Mars its quite possible this will not work as the air is so thin and you have to use the engines to rotate you. 

They may be concerned about the time it takes to transition from belly flop to vertical orientation. I'm guessing the more time Starship spends transitioning orientations, it is travelling off course. I could be totally wrong, I'm just extrapolating from aviation.

[RCgothic]

 

 

Edited August 19, 2020 by RCgothic

[mikegarrison]

The standard answer for how long an airplane can keep flying is "as long as you are willing to pay to keep it flying". The issue with a car, an airplane, a boat, etc. is not that it's impossible to keep it operational. The issue is that it generally gets more and more expensive to do that as it ages. Eventually it becomes cheaper to buy a new one than to keep the old one working.

I'm sure the same applies to rockets.

[cubinator]

5 minutes ago, mikegarrison said:

The standard answer for how long an airplane can keep flying is "as long as you are willing to pay to keep it flying". The issue with a car, an airplane, a boat, etc. is not that it's impossible to keep it operational. The issue is that it generally gets more and more expensive to do that as it ages. Eventually it becomes cheaper to buy a new one than to keep the old one working.

I'm sure the same applies to rockets.

That's a really good direction to be going in for rockets. Up until now, the moment it becomes cheaper to build a new one was when the empty stage dropped into the sea.

[magnemoe]

21 minutes ago, Meecrob said:

They may be concerned about the time it takes to transition from belly flop to vertical orientation. I'm guessing the more time Starship spends transitioning orientations, it is travelling off course. I could be totally wrong, I'm just extrapolating from aviation.

you can offset this however starting burning while horizontal will increase your horizontal velocity and you have to counter that, so you want to tilt before burn. 
Now the safe way to do this is to do it high up so you have more time to correct, yes now your landing burn uses more fuel. have extra fuel in the tanks no issue using it once its settled. Yes it an offset weight but its just good training after all.
I would move some methane up in the nose as you get the fuel for an abort system, have an secondary header tank downward as you will return stuff from space down the line. 

 

[RCgothic]