totm nov 2023 SpaceX Discussion Thread

[Kerbal7]

17 minutes ago, tater said:

Don't conflate BFS with Mars colonization, that's not what BFS is for, economically. BFR/BFS (cargo) is for lowering cost to LEO. Being fully reusable means that costs are vehicle costs divided by number of flights, plus operational costs, plus propellant costs. If that number is below current launch costs, it's a win. It need do nothing else.

A crew variant is a different craft, and clearly has no economic benefit, unless it manages to be safe enough that tourism is a thing, in which case tourism is a fairly bottomless market. Thge only economic driver for a crew vehicle aside from that would be the current customer for same: NASA.

I think BFS cargo is a game changer, and the math on reuse was done in the 1960s, by guys contracting to NASA. It;s the only way to eventually exploit space, instead of just visiting it (aside from satellites).

 

Yeah, he can build a big rocket to put things in LEO. That's very possible. But what's the whole build a city on Mars thing about? Publicity?

[Starman4308]

Just now, Kerbal7 said:

Yeah, he can build a big rocket to put things in LEO. That's very possible. But what's the whole build a city on Mars thing about? Publicity?

It's Musk's long-term goal.

People can have dreams they're working towards, yes? Even ones that don't seem immediately practical?

[PB666]

Question: If BFR is to replace falcon and dragon. How do they plan to return the orbital vehicle back to Earth, all I that I have seen is there intent to land on Mars. I have just been under the assumption that once the orbital vehicle goes up, it will simply never come back to Earth (either via refueling, etc)

[Kerbal7]

Just now, Starman4308 said:

It's Musk's long-term goal.

People can have dreams they're working towards, yes? Even ones that don't seem immediately practical?

He says this operation starts in 2022. I don't really consider that a long term goal. You? That sounds like a close goal for me. 

[tater]

4 minutes ago, Kerbal7 said:

Yeah, he can build a big rocket to put things in LEO. That's very possible. But what's the whole build a city on Mars thing about? Publicity?

It's his dream.

Nothing more.

If that's how he wants to spend his billions, more power to him. That's not the thing that BFS is going to do, it's going to be a real "space truck" if it works. The crew version will utterly change human spaceflight.

My personal feeling is that a first crew version has a smaller crew area at the nose that can leave in a hurry (max-q abort), not some giant cabin capable of holding hundreds. Such a hybrid vessel could contract with NASA, ESA, etc to deliver crew/cargo to their notional Moon Village" concepts.

3 minutes ago, Kerbal7 said:

He says this operation starts in 2022. I don't really consider that a long term goal. You? That sounds like a close goal for me. 

He said that goal (2022 or 2024) was "aspirational" but not impossible. 6 years is a long time, and until someone starts thinking that way, we're not going to do anything interesting. Manned Mars has been 10-20 years off for about 50 years now because they plan on doing it in 20, but lack the ability to follow through in a focused way to achieve that goal, then the goalposts move.

Musk wants people on Mars. For reasons. I am deeply skeptical about that, and flatly think the 2024 timeline is absurd. That said, I think the BFS concept is genius, just as the Phil Bono designs of the 60s were genius. BFS is going to be at least tested in some fashion, however.

[Kerbal7]

1 minute ago, tater said:

It's his dream.

Nothing more.

If that's how he wants to spend his billions, more power to him. That's not the thing that BFS is going to do, it's going to be a real "space truck" if it works. The crew version will utterly change human spaceflight.

My personal feeling is that a first crew version has a smaller crew area at the nose that can leave in a hurry (max-q abort), not some giant cabin capable of holding hundreds. Such a hybrid vessel could contract with NASA, ESA, etc to deliver crew/cargo to their notional Moon Village" concepts.

If he can build the version you're talking about here, yeah that would be great. A kind of giant space truck whose re-usability is actually cheap to use. The space shuttle was supposed to do this and failed miserably. But I think Musk can make this version work. The whole city on Mars thing is like hearing a crazy uncle talk though.

[Ultimate Steve]

22 minutes ago, PB666 said:

Question: If BFR is to replace falcon and dragon. How do they plan to return the orbital vehicle back to Earth, all I that I have seen is there intent to land on Mars. I have just been under the assumption that once the orbital vehicle goes up, it will simply never come back to Earth (either via refueling, etc)

From LEO they just de-orbit it and land as shown in the Earth to Earth video (but with de-orbiting). Like the shuttle did, but without wings. From Mars, IIRC, they Sabatier it for a few months until it has fuel again, and apparently it can SSTO back from there, aerobrake and land like a normal F9 S1. Unless I'm seriously wrong about this.

[YNM]

1 hour ago, PB666 said:

dV required to land is less than 4200 m/s. If you have enough dV (i.e. some refuels your ship in LMO) you don't have to worry about the atmosphere at all. But somehow I don't think you are going to see liquid methane, liquid oxygen refueling stations circling Mars anytime soon.

Assuming no refuels, direct entry and the ability to turn back to Earth, this could mean that a single BFR would be in Earth-SSTO dV capabilities.

But yeah. It's years and years in deep space. No one has managed to do much improving on those... I'd like to see that but I hope they're threading in the right manner.

 

Actually, the simple question is : if we take a one-way mission to Mars, would that be acceptable ? Is this yet another "exploration" age, where lost parties are just numbers ?

Edited February 19, 2018 by YNM

[PB666]

21 minutes ago, Ultimate Steve said:

From LEO they just de-orbit it and land as shown in the Earth to Earth video (but with de-orbiting). Like the shuttle did, but without wings. From Mars, IIRC, they Sabatier it for a few months until it has fuel again, and apparently it can SSTO back from there, aerobrake and land like a normal F9 S1. Unless I'm seriously wrong about this.

Coming in from 27000 km back into Earth, the video doesn't actually show how they do this, its obviously not retrorocketing all the way in. Skeptical.

[Ultimate Steve]

1 hour ago, PB666 said:

Coming in from 27000 km back into Earth, the video doesn't actually show how they do this, its obviously not retrorocketing all the way in. Skeptical.

Since the ship would be mostly empty at that point, it would have a high surface area to mass ratio so slowing down higher in the atmosphere would be easier. Apollo entered at around 11km/s, and Stardust did about 12.4km/s, after visiting a comet in an orbit higher than Mars, so re-entry velocities for BFS will be lower than 12.4km/s unless you're going on a super fast trajectory, so the speed is doable. After it has slowed down it will land like usual. I remember Elon saying somewhere that the PICA-X will not ablate much for LEO missions or Mars entry, but will ablate some upon returning to Earth from Mars.

Edited February 19, 2018 by Ultimate Steve

[PB666]

33 minutes ago, Ultimate Steve said:

Since the ship would be mostly empty at that point, it would have a high surface area to mass ratio so slowing down higher in the atmosphere would be easier. Apollo entered at around 11km/s, and Stardust did about 12.4km/s, after visiting a comet in an orbit higher than Mars, so re-entry velocities for BFS will be lower than 12.4km/s unless you're going on a super fast trajectory, so the speed is doable. After it has slowed down it will land like usual. I remember Elon saying somewhere that the PICA-X will not ablate much for LEO missions or Mars entry, but will ablate some upon returning to Earth from Mars.

It does not appear to be a shallow trajectory, there would be tremendous g-forces on it. Still skeptical.

[Ultimate Steve]

34 minutes ago, PB666 said:

It does not appear to be a shallow trajectory, there would be tremendous g-forces on it. Still skeptical.

Where are you getting the information on steepness of the trajectory? Going by memory (which is wrong a lot) I don't think we've seen a BFS Earth re-entry animation.

I think the shuttle did about 3G and the Soyuz does about 5 during re-entry, so surface area makes a difference. The Apollos went just above 7G sometimes. The larger surface area on BFS plus the higher velocity should mean that the G's might be about the same... I think... I mean, it's not rocket science or anything, right? Fighter jets have also been known to do 12G for short periods of time.

EDIT: According to a random number found on the internet for F91.1 (should be close enough to 1.2) the first stage has a dry mass of about 15 tons. If we say each merlin can do 600kn at minimum throttle and a three engine landing burn is used, that's 1800kn, 20 tons (for residual fuel), gives us about 9G, so Falcon has withstood these forces before, although not laterally.

Edited February 19, 2018 by Ultimate Steve

[DAL59]

4 hours ago, Kerbal7 said:

10+ billion to develop even according to Musk and he doesn't have that much money.

Yes, he does.  He has 19 billion in SpaceX, and 20 billion in personal money.

3 hours ago, Kerbal7 said:

he whole city on Mars thing is like hearing a crazy uncle talk though.

So?  He's a billionaire, he can do that if he wants.

[PB666]

19 minutes ago, Ultimate Steve said:

Where are you getting the information on steepness of the trajectory? Going by memory (which is wrong a lot) I don't think we've seen a BFS Earth re-entry animation.

I think the shuttle did about 3G and the Soyuz does about 5 during re-entry, so surface area makes a difference. The Apollos went just above 7G sometimes. The larger surface area on BFS plus the higher velocity should mean that the G's might be about the same... I think... I mean, it's not rocket science or anything, right? Fighter jets have also been known to do 12G for short periods of time.

EDIT: According to a random number found on the internet for F91.1 (should be close enough to 1.2) the first stage has a dry mass of about 15 tons. If we say each merlin can do 600kn at minimum throttle and a three engine landing burn is used, that's 1800kn, 20 tons (for residual fuel), gives us about 9G, so Falcon has withstood these forces before, although not laterally.

You don't want your passengers doing >8 g. The shuttle had more wing, and typically enter at an oblique angle, which means it lost alot of forward momentum. Apollo from what I understand had an initial angle (-5 to -6') that did not intercept the surface had a steeper entry angle because it could exit the atmosphere again. 

Shuttle had 6400 km horizontal = 174 km vertical (comes to 1.5' sure it was higher though) for shuttle with more rapid drop per distance at the end of the flight. 

[CatastrophicFailure]

48 minutes ago, Ultimate Steve said:

Where are you getting the information on steepness of the trajectory? Going by memory (which is wrong a lot) I don't think we've seen a BFS Earth re-entry animation.

I think the shuttle did about 3G and the Soyuz does about 5 during re-entry, so surface area makes a difference. The Apollos went just above 7G sometimes. The larger surface area on BFS plus the higher velocity should mean that the G's might be about the same... I think... I mean, it's not rocket science or anything, right? Fighter jets have also been known to do 12G for short periods of time.

EDIT: According to a random number found on the internet for F91.1 (should be close enough to 1.2) the first stage has a dry mass of about 15 tons. If we say each merlin can do 600kn at minimum throttle and a three engine landing burn is used, that's 1800kn, 20 tons (for residual fuel), gives us about 9G, so Falcon has withstood these forces before, although not laterally.

The shuttle could manage only 3g because it’s a lifting body, just like BFS will be. That allows for a much gentler re-entry, since the vehicle can use aerodynamic lift to decelerate more in the thin upper atmosphere. The BFS will likely do a similar earth entry to what we see in the video, using lift vectored down to “pull” itself down into the atmosphere where it would otherwise skip off. That lets it fly right in a sweet spot for both G loading and heating. 

[Jaff]

Am I the only one not particularly looking forward to BFR?

 

that means replacing Falcon where we get awesome launches at least every month (9 or heavy) for bfr that will accumulate payloads and do them all at once only a few times a year.

 

id rather more awesome launches than less awesome launches 

[sh1pman]

15 minutes ago, Jaff said:

Am I the only one not particularly looking forward to BFR?

 

that means replacing Falcon where we get awesome launches at least every month (9 or heavy) for bfr that will accumulate payloads and do them all at once only a few times a year.

 

id rather more awesome launches than less awesome launches 

You got it wrong. BFR cost per launch will be much lower than any other rocket, even Falcon 1. It won't accumulate payloads, instead it will launch payloads that are way smaller and cheaper than what's economically viable for Falcon 9, and still make profit.

Edited February 19, 2018 by sh1pman

[Jaff]

13 minutes ago, sh1pman said:

You got it wrong. BFR cost per launch will be much lower than any other rocket, even Falcon 1. It won't accumulate payloads, instead it will launch payloads that are way smaller and cheaper than what's economically viable for Falcon 9, and still make profit.

 

Why would they not accumulate payloads? 

Why risk multiple launches when 1 will do it? 

 

[sh1pman]

Just now, Jaff said:

 

Why would they not accumulate payloads? 

Why risk multiple launches when 1 will do it? 

 

1) Different satellites have different launch windows, inclinations and orbit heights.

2) Sometimes waiting for half a year is not an option.

3) Launching them all at once bears a risk of losing them all at once. Multiple launches are safer that way.

[YNM]

21 minutes ago, sh1pman said:

You got it wrong. BFR cost per launch will be much lower than any other rocket, even Falcon 1. It won't accumulate payloads, instead it will launch payloads that are way smaller and cheaper than what's economically viable for Falcon 9, and still make profit.

Ever heard of SS Great Eastern ?

[KSK]

5 minutes ago, Jaff said:

Why would they not accumulate payloads? 

Why risk multiple launches when 1 will do it? 

Because being able to launch payloads when required by their customers, rather than waiting to accumulate enough payloads to justify a launch, is a big selling point. Especially for comsat operators for whom more time on orbit equals more money made.

[YNM]

55 minutes ago, KSK said:

Because being able to launch payloads when required by their customers, rather than waiting to accumulate enough payloads to justify a launch, is a big selling point. Especially for comsat operators for whom more time on orbit equals more money made.

@sh1pman

57 minutes ago, YNM said:

Ever heard of SS Great Eastern ?

Spoiler : Great Western worked, Great Britain succumbed, Great Eastern flopped.

Edited February 19, 2018 by YNM

[KSK]

I fail to see the relevance of your post to mine. Are you actually going to make a point, or just throw links at us?

Edited February 19, 2018 by KSK

[Jaff]

So the bfr with 150t capability will be used to launch a 5t payload?

[YNM]

25 minutes ago, KSK said:

I fail to see the relevance of your post to mine. Are you actually going to make a point, or just throw links at us?

I'm referring to yours and @sh1pman as well.

Great Western ~ F9

Great Britain ~ FH

Great Eastern ~ BFR

Engineering-wise the last in the series are the best most possible. But economy-wise you need them to be somewhat full. Sending them with only a puny 3*1 ton sats in it won't work, as was 3000 pax's Great Eastern with only 38 passengers onboard flopped.

Great engineering maybe, great economics it's not.

Edited February 19, 2018 by YNM