totm nov 2023 SpaceX Discussion Thread

[IncongruousGoat]

1 minute ago, sh1pman said:

They probably could make it bigger, since FH has higher TWR at liftoff.

They could, but that would mean more tooling and a different tank production line, all of which are expensive. And since SpaceX's whole shtick is doing things cheap by using the same exact stuff over and over, they're unlikely to set up such a production line.

[sh1pman]

1 minute ago, IncongruousGoat said:

They could, but that would mean more tooling and a different tank production line, all of which are expensive. And since SpaceX's whole shtick is doing things cheap by using the same exact stuff over and over, they're unlikely to set up such a production line.

I guess I understand now. So the next logical thing for them to do will be slapping even more F9 boosters together and calling it Falcon Super Heavy.

[tater]

^^^if they were mass limited, or had a larger US.

The side boosters have to RTLS, so they really have to separate at about the same velocity as a single-stick RTLS launch does (so they have the reserve props to return and land). The core is in the same boat, it either gets expended, does stage sep for a "hot" ASDS landing, or perhaps can be hotter than a single ASDS landing would allow, but it does so with some extra props, and can extend the braking burn.

[CatastrophicFailure]

58 minutes ago, sh1pman said:

Is FH upper stage any different from F9 upper stage?

 

54 minutes ago, tater said:

No.

?

I thought it required a significant redesign and is now quite different from the boosters? That was one of the big reasons for the delays, as I recall. 

Also, if they’ve incorporated some of the upcoming Block 5 upgrades into the design, which seems likely, it should be able to take those hot re-entries much better than the existing stock. 

41 minutes ago, sh1pman said:

guess I understand now. So the next logical thing for them to do will be slapping even more F9 boosters together and calling it Falcon Super Heavy.

You know you’ve been playing too much KSP when that mess doesn’t look the slightest bit outlandish. 

[Bill Phil]

54 minutes ago, sh1pman said:

I guess I understand now. So the next logical thing for them to do will be slapping even more F9 boosters together and calling it Falcon Super Heavy.

The issue with that idea is that a big upper stage would be very useful. That tiny upperstage would have so much work to do...

[sevenperforce]

21 minutes ago, CatastrophicFailure said:

I thought it required a significant redesign and is now quite different from the boosters? That was one of the big reasons for the delays, as I recall. 

The core took major redesign; the upper stage is still identical.

6 minutes ago, Bill Phil said:

The issue with that idea is that a big upper stage would be very useful. That tiny upperstage would have so much work to do...

A 4-booster Falcon Heavy would very nearly have an orbital core.

[Bill Phil]

1 minute ago, sevenperforce said:

The core took major redesign; the upper stage is still identical.

A 4-booster Falcon Heavy would very nearly have an orbital core.

Yeah. The upper stage of the heavy is more for sending payloads beyond LEO than to LEO. 

[Ultimate Steve]

1 hour ago, sevenperforce said:

A 4-booster Falcon Heavy would very nearly have an orbital core.

"Elon! Falcon Heavy won't be enough and BFR will be 6 years late!"

"So do asparagus."

"But we can't!"

"It works in Kerbal space program."

"But Elon! It's impossible to do that in real life!"

"Hold my beer."

 

[CatastrophicFailure]

Not impossible, just very very hard. Considering they never could get crossfeeding to work in the first place. 

[harrisjosh2711]

57 minutes ago, Ultimate Steve said:

"Elon! Falcon Heavy won't be enough and BFR will be 6 years late!"

"So do asparagus."

"But we can't!"

"It works in Kerbal space program."

"But Elon! It's impossible to do that in real life!"

"Hold my beer."

 

Man....... I wanted to see the launch. 

[Mitchz95]

10 minutes ago, harrisjosh2711 said:

Man....... I wanted to see the launch. 

This is the closest I could find on YouTube...

 

[PB666]

4 hours ago, sh1pman said:

I guess I understand now. So the next logical thing for them to do will be slapping even more F9 boosters together and calling it Falcon Super Heavy.

You probably would not be able to recycle the core F9. it would end up as space junk. (Its not impossible, but probably difficult)

Nice rocket, you need more struts, you have not boosted enough your rocket until you have at least 200 or 300 struts.

[YNM]

2 hours ago, Ultimate Steve said:

...

"So do asparagus. It works in Kerbal space program."

...

"Hold my beer."

...

N-1 and OTRAG in the same time. How convenient.

Edited December 7, 2017 by YNM

[KSK]

6 hours ago, CatastrophicFailure said:

The engine bell would get torn apart in very short order. That thing is incredibly fragile when it’s not firing. 

This. I definitely remember one launch where there was a problem with the upper stage engine bell - cracks or some such. The solution was to have an engineer take a pair of tin snips to it and cut away the damaged portion. I imagine they lost some vacuum ISP that flight but it got the job done.

[Nefrums]

Just making the fuel tank of the second stage larger makes more sense.

[NSEP]

7 hours ago, Ultimate Steve said:

"Elon! Falcon Heavy won't be enough and BFR will be 6 years late!"

"So do asparagus."

"But we can't!"

"It works in Kerbal space program."

"But Elon! It's impossible to do that in real life!"

"Hold my beer."

 

That looks like one of those illegal fireworks.

[Racescort666]

10 hours ago, sevenperforce said:

A 4-booster Falcon Heavy would very nearly have an orbital core.

5 Core RTLS...

It's just that the center core does a once-around before landing. 

Actually, some back of the napkin maths tells me that with 4 boosters, you could wait to light the center core until mid-flight (a la Titan).

[NSEP]

10 minutes ago, Racescort666 said:

5 Core RTLS...

*opens Realism Overhaul

[StrandedonEarth]

I wonder how BFR would do with (2,  4,6,8?) F9’s as strap-on boosters. Maybe it could get a nearly full tanker into orbit.....

[NSEP]

3 minutes ago, StrandedonEarth said:

I wonder how BFR would do with (2,  4,6,8?) F9’s as strap-on boosters. Maybe it could get a nearly full tanker into orbit.....

*Realism Overhaul intensifies.

A BFR with F9 boosters reminds me of the Energia, and the Energia is my favourite rocket that i also miss the most.

[sevenperforce]

58 minutes ago, Racescort666 said:

5 Core RTLS...

It's just that the center core does a once-around before landing. 

Actually, some back of the napkin maths tells me that with 4 boosters, you could wait to light the center core until mid-flight (a la Titan).

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.

51 minutes ago, StrandedonEarth said:

I wonder how BFR would do with (2,  4,6,8?) F9’s as strap-on boosters. Maybe it could get a nearly full tanker into orbit.....

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.

[NSEP]

After processing the numbers down on this website:

http://silverbirdastronautics.com/cgi-bin/LVPcalc.pl

it calculated that a BFR, with 4 Falcon 9 First Stage boosters can send 200-300 tons to LEO. (Expendable that is)

EDIT: I deffinitly did something wrong, since the expendable BFR without boosters can already send 250 tons to LEO. Shoot

Edited December 7, 2017 by NSEP

[sevenperforce]

36 minutes ago, NSEP said:

After processing the numbers down on this website:

http://silverbirdastronautics.com/cgi-bin/LVPcalc.pl

it calculated that a BFR, with 4 Falcon 9 First Stage boosters can send 200-300 tons to LEO. (Expendable that is)

EDIT: I deffinitly did something wrong, since the expendable BFR without boosters can already send 250 tons to LEO. Shoot

What were you using for the BFR booster's dry and wet mass?

[NSEP]

22 minutes ago, sevenperforce said:

What were you using for the BFR booster's dry and wet mass?

For the BFR i used 240 tons dry and 3220 tons wet.

[sevenperforce]

49 minutes ago, NSEP said:

After processing the numbers down on this website:

http://silverbirdastronautics.com/cgi-bin/LVPcalc.pl

it calculated that a BFR, with 4 Falcon 9 First Stage boosters can send 200-300 tons to LEO. (Expendable that is)

EDIT: I deffinitly did something wrong, since the expendable BFR without boosters can already send 250 tons to LEO. Shoot

Upon review, you're probably using 85 tonnes as the dry mass of the BFR. But that's the dry mass of the spaceship. If we're talking expendable, then you should really be looking at the dry mass of the cargo BFR, which will likely be closer to 40 tonnes.

3 minutes ago, NSEP said:

For the BFR i used 240 tons dry and 3220 tons wet.

240 tonnes dry seems WAY too high. The ITS dry mass was quoted at 275 tonnes and it's twice as big.

Setting the booster dry mass at 140 tonnes, the cargo BFR dry mass at 40 tonnes, and the fuel capacity of the booster at 3,075 tonnes, I get 225 tonnes to LEO without strap-on boosters. Adding 4 strap-on Falcon 9s increases payload to 309 tonnes.