totm nov 2023 SpaceX Discussion Thread

[StrandedonEarth]

2 hours ago, sevenperforce said:

Trouble is, the BFR needs to RTLS, which means every m/s of dV carried beyond its design separation velocity is reduced by more than half, since it has to cancel downrange velocity AND boostback.

By way of example: The booster typically stages at 2.4 km/s, reserving enough fuel to cancel that 2.4 km/s, boost back, and land. Let us suppose that adding a pair of Falcon 9 boosters gives 2 km/s more to the booster. Unfortunately, that doesn't mean separation happens at 4.4 km/s. The booster can only afford to add about 1 km/s to staging velocity, because it now has to slow down from 3.4 km/s instead of from 2.4 km/s.

Why RTLS? Beef up the heat shielding (inflatable heat shield?) and land it wherever it is ballistically and logistically convenient.

[sevenperforce]

2 minutes ago, StrandedonEarth said:

Why RTLS? Beef up the heat shielding (inflatable heat shield?) and land it wherever it is ballistically and logistically convenient.

Well, no legs.

[StrandedonEarth]

1 minute ago, sevenperforce said:

Well, no legs.

So you build (yet another) launch/landing site in Africa somewhere. Which is what I meant by “logistically convenient”

[Nightfury]

Just now, StrandedonEarth said:

So you build (yet another) launch/landing site in Africa somewhere. Which is what I meant by “logistically convenient”

Would a Falcon 9 S1 fit in an airplane or do you need a ship ?

[Jaff]

I’ve been having thoughts on this recoverable top bit (fairings and upper stage etc)

 

would keeping the fairings on as some sort of heat shielding not make it recoverable from Orbit if it came in nose first?

the bells fragility could be overcome with some fancy aerodynamics maybe? Like diverting air from around the outside of the upper stage through some sort of Venturi that keeps the engine bells structure?

[PB666]

2 hours ago, sevenperforce said:

Of course then you'd need to plumb all nine engines for TEA-TEB but that's not too hard to do. Alternately, the Merlin 1D can throttle all the way to minimum and it gets the job done just as well.

The actual real-world problem with a five-core Falcon Super Heavy is the same problem with the real-world Falcon Heavy: stresses on the core. The core has to lift the payload AND transmit the impulse from the boosters, and so you'd have to rebuild the core a second time to make it sturdier.

Not to mention that you'd either have ridiculously massive payloads and EXTREMELY low TWR on the upper stage, or you'd have an orbital core every time, which makes it just slightly difficult to recover.

From a Tsiolkovsky perspective, strap-on Falcon 9s are fantastic. Their lower isp drains fuel quickly and kills gravity drag. Trouble is, the BFR needs to RTLS, which means every m/s of dV carried beyond its design separation velocity is reduced by more than half, since it has to cancel downrange velocity AND boostback.

Of course, if you want to fly a BFR core expendable, then slapping on Falcon 9s is perfect. But the cores will never be intentionally expended.

By way of example: The booster typically stages at 2.4 km/s, reserving enough fuel to cancel that 2.4 km/s, boost back, and land. Let us suppose that adding a pair of Falcon 9 boosters gives 2 km/s more to the booster. Unfortunately, that doesn't mean separation happens at 4.4 km/s. The booster can only afford to add about 1 km/s to staging velocity, because it now has to slow down from 3.4 km/s instead of from 2.4 km/s.

The core it going to be sacrificed right. IMHO they should take a look at Russian rockets. Q is not going to increase (or at least it doesn't have to unless you increase the cross-sectional area of the PL), just T x Q for the bottom of the second stage. That is not a problem.

So the only real problem is the skin of the core. To handle this problem and keep F9 core just create bolt attachment point on the skin. Then when you need to add pairs of booster, bolt an aluminum bar to the bolt holes and the bar itself has the attachment points, then on the F9 head have a riser that rides the bars once they are attached that adds the additional structure. If you look at Russian rockets they do not pay alot of attention to form drag in the mid-section, what for you are just going to dump it. Some of their rockets don't even use fairing. There is a lesson there in that if you got all kind of crowdy junk around the core, detailing aerodynamics has no reward. You can see the boundary layer on the nose cone, once it starts getting close to Mach the boundary begins to separate and pretty much all the dynamic resistance is transferred to the nosecone.

As to the other point, yes fire up the engine to get rocket off the pad then throttle it down to 5%, you can do the same thing as asparagus just by carefully timing throttle down along the core, dispose of two boosters, then the second pair and then rethrottle the core. The core cannot be salvaged anyway so no need to worry about having landing legs or spoilers.

The deal is that if they want to land the core, I guess then they need to due more in aerobraking department before adding thrust to land. The whole prospect is bad business IMHO, if you get 1000 more dV out of the launch stages, your ability to land-target the core becomes more difficult across the board. Landing predictions are harder, there is more heat on reentry, less control of craft on renentry, more weight on the core because of structure (although the structural outmounts can be bolted and theoretically unbolted to land). This isn't silly blue origin stuff, they are trying to sell PLs (heavy's in LEO). For all intents in purpose the LEO is the contract point, any other service provided is fluff. So they need to decide the most efficient way to get a rocket in the cheapest, immediately stable LEO. The heavier the payload the better. If you can quadruple the PL at the expense of a core, you take it.

[sevenperforce]

14 minutes ago, Nightfury said:

Would a Falcon 9 S1 fit in an airplane or do you need a ship ?

A Falcon 9 first stage wouldn't even fit under an airplane, let alone inside one.

It's huge.

[Nightfury]

7 minutes ago, sevenperforce said:

A Falcon 9 first stage wouldn't even fit under an airplane, let alone inside one.

It's huge.

How about this ?

width is enough, and should be long enough too (of course vertical)

Edited December 7, 2017 by Nightfury
spelling is difficult :D

[PB666]

5 minutes ago, sevenperforce said:

A Falcon 9 first stage wouldn't even fit under an airplane, let alone inside one.

It's huge.

When did SpaceX start hiring pygmies . . . . . .

[_Augustus_]

10 minutes ago, Jaff said:

I’ve been having thoughts on this recoverable top bit (fairings and upper stage etc)

 

would keeping the fairings on as some sort of heat shielding not make it recoverable from Orbit if it came in nose first?

the bells fragility could be overcome with some fancy aerodynamics maybe? Like diverting air from around the outside of the upper stage through some sort of Venturi that keeps the engine bells structure?

Not a bad idea.

[sevenperforce]

31 minutes ago, Nightfury said:

How about this ?

width is enough, and should be long enough too (of course vertical)

The BelugaXL's cargo bay will only be about 40-45 meters long.

[tater]

LOL.

[magnemoe]

32 minutes ago, Nightfury said:

How about this ?

width is enough, and should be long enough too (of course vertical)

First stage is 44 meter long, 3.66 meter wide, make a bit above 4 with legs. length is the issue here 64 meter is total length, so if you loose 20 meter on nose and tail it will not fit. 
Cargo hold of both C5 and antanow is around 36 meter. 
You could transport it on rails but not sure if that is assembled, diameter is chosen for rail transport. its also the max width of all tanks outside of the Israel one

[Spaceception]

10 minutes ago, tater said:

LOL.

Beat me to it

I'd love to see some friendly twitter beef between everyone planning to launch to Mars honestly. The world needs that kind of drama.

[_Augustus_]

30 minutes ago, tater said:

LOL.

For SLS to beat Elon to Mars SLS a) has to stay around for more than 2 missions, b) cost less or get more funding so that a Mars mission is affordable and c) BFR/SpaceX as a whole has to massively fail, which won't happen.

Elon knows SLS is a joke, but he can't bash it too much because NASA is one of his customers.

[Racescort666]

31 minutes ago, magnemoe said:

First stage is 44 meter long, 3.66 meter wide, make a bit above 4 with legs. length is the issue here 64 meter is total length, so if you loose 20 meter on nose and tail it will not fit. 
Cargo hold of both C5 and antanow is around 36 meter. 
You could transport it on rails but not sure if that is assembled, diameter is chosen for rail transport. its also the max width of all tanks outside of the Israel one

If the first stage is 44m then an AN-225 might work.

http://www.aircharterserviceusa.com/aircraft-guide/cargo/antonov-ukraine/antonovan-225

 

[PB666]

31 minutes ago, magnemoe said:

First stage is 44 meter long, 3.66 meter wide, make a bit above 4 with legs. length is the issue here 64 meter is total length, so if you loose 20 meter on nose and tail it will not fit. 
Cargo hold of both C5 and antanow is around 36 meter. 
You could transport it on rails but not sure if that is assembled, diameter is chosen for rail transport. its also the max width of all tanks outside of the Israel one

No, this is what you do, haul it to the nearest river, fill the fuel tanks with air and cap . Throw it in the nearest river (legs retracted of course) tug it down to the ocean and haul it from wherever to Florida or Texes. Pull it into a dry dock and and take it over from there. Or you could take an Old russian whaling ship and hoist it unboard from the point of disembarkment, then taunt Greenpeace as you hauled your load into Florida. You could try to land it in the Congo River, its nice and wide and deep. Probably wouldn't make it to the coast in one piece since the aluminum would command a decent price on the black market.

[kerbiloid]

BFR + BFS + water = "Aldebaran: Resurrection"

Spoiler

 

[Nightfury]

Maybe a silly question, but does anybody know why the SpaceX Webcast launches always have this hissy sound? Does they don't have better microphones or is it because the camera is standing right next to the rocket?

[tater]

22 minutes ago, Nightfury said:

Maybe a silly question, but does anybody know why the SpaceX Webcast launches always have this hissy sound? Does they don't have better microphones or is it because the camera is standing right next to the rocket?

Can you provide a clip?

[Nightfury]

It's basicly every launch ( mostly at start)

If you listen to e.g. an Atlas V launch the sound seems deeper and more "rocket-like"

 

[Guest]

2 hours ago, tater said:

LOL.

Best possible answer, tbh. "I dare ya." Everyone wins.

[tater]

Yeah, exactly.

Of course having Boeing do it requires that all of us have a walletectomy every April.

[Canopus]

4 minutes ago, tater said:

Yeah, exactly.

Of course having Boeing do it requires that all of us have a walletectomy every April.

SpaceX won‘t reach Mars on their own money. You‘ll have to pay either way.

[DAL59]

4 hours ago, Nightfury said:

Would a Falcon 9 S1 fit in an airplane or do you need a ship ?

 

The space shuttle was transported via plane, so an empty Falcon 9 might be movable via plane.