totm nov 2023 SpaceX Discussion Thread

[Exoscientist]

3 hours ago, Elthy said:

Someone compiled a list of all answered questions, way easier to read than the whole thread:

https://www.reddit.com/r/space/comments/76e79c/i_am_elon_musk_ask_me_anything_about_bfr/dodhawf

 

 Thanks for that. I like the part where he acknowledges that the new version of the upper stage which he calls BFS will be given hovering capability for landing on Earth.

 Bob Clark

[tater]

5 hours ago, Nibb31 said:

I think ZUMA could be a followup for PAN and CLIO, which were both codenames for top-secret launches with an unknown payload. They ended up being identified as Nemesis-1 and Nemesis-2, which are SIGINT birds that are supposed to shadow other countries' satellites to intercept their comms. This could be Nemesis-3 or a followup program.

The only issue here is the guy saying that it's a commercial payload, unless he was knowingly or unkowing fed a cover story.

[magnemoe]

15 hours ago, RedKraken said:

"Wouldn't call what BFS has a delta wing. It is quite small (and light) relative to the rest of the vehicle and is never actually used to generate lift in the way that an aircraft wing is used.

It's true purpose is to "balance out" the ship, ensuring that it doesn't enter engines first from orbit (that would be really bad), and provide pitch and yaw control during reentry."

They wanted to increase drag on the heavy bottom to avoid it go bottom first on reentry rather than sideway, don't think the delta wind generate much lift. 

[Exoscientist]

16 hours ago, RedKraken said:

So a third SL engine on the BFS....

Interesting implication for stage sea-level testing....before the BFS could take off @ ~ 280t wet....... now 420t (5370m/s of deltaV)

Can't wait to see the BFS practicing its landings!

 

 That's puzzling. This screen grab from the IAC 2017 video only shows two sea level engines:

 

  Bob Clark

 

Edited October 15, 2017 by Exoscientist

[tater]

Yeah, they decided to up it to 3 engines for redundancy (lands on 1).

 

[Exoscientist]

16 hours ago, tater said:

 

 This simulation shows the upper stage of the original ITS from last year as an expendable SSTO could get a total 190 metric tons to orbit, including the stage and the payload: 

https://www.youtube.com/watch?v=Kzyzwr-5XXY

Since the stage was estimated to weigh 90 tons, this would mean 100 metric tons payload as an expendable. Then the question is how much mass would be taken up for propellant for return using vertical landing?

 If the new version of the upper stage, the BFS, is about half size, then we might estimate the expendable SSTO payload as ca. 50 metric tons. But again the question is how much would be taken up for reusability systems? The discussion here is this should be a small percentage of the landed weight:

http://yarchive.net/space/launchers/horizontal_vs_vertical_landing.html

 So it should still be feasible with significant payload as a reusable.

  Bob Clark

 

 

[tater]

Musk said flat out in the AMA that the spacecraft is ssto with a very small payload. 

Gotta be smaller than 50.

[Exoscientist]

1 hour ago, tater said:

Musk said flat out in the AMA that the spacecraft is ssto with a very small payload. 

Gotta be smaller than 50.

 Musk prefers the vertical, propulsive landing approach. If you look at the discussion here:

http://yarchive.net/space/launchers/horizontal_vs_vertical_landing.html

one side of that debate argues you can save significant mass using the winged, horizontal landing approach over the vertical landing approach.  When you take into account carbon composites can save significantly on the wing weight, it may very well be the reusable SSTO can carry significant payload as a point-to-point transport.

  Bob Clark

 

 

Edited October 15, 2017 by Exoscientist

[_Augustus_]

Someone on NSF pointed out that a secret government payload doesn't need FAA clearance to launch, so Zuma is definitely a commercial payload.

All bets are on it either being an internal SpaceX mission, or SpaceIL.

 

[.50calBMG]

Since they are switching to three sea level Raptors on the BFS, would they also go to three vac Raptors to keep it symmetric or would they stay with four?

[tater]

 

[Nibb31]

4 hours ago, tater said:

The only issue here is the guy saying that it's a commercial payload, unless he was knowingly or unkowing fed a cover story.

Or he's just full of fecal matter. This is reddit we are talking about after all.

[Ultimate Steve]

12 hours ago, insert_name said:

A week in a spacesuit with minimal suppliers on a spacecraft that isn't man rated without an abort system? I'm sure you're going to be overwhelmed with volunteers.

 

10 hours ago, Steel said:

I mean... It might be 'possible', but considering the X-37 is unmanned the only internal space you have available is the payload bay with no life support systems (or windows for that matter). You'd basically ride to the moon in a large space coffin

My point wasn't to say that it would be practical, but it is doable.

The 300kg was for an internal habitat (think tiny metal cylinder with just enough room to take off your spacesuit) plus life support (its a bit of a stretch but probably workable). The X-37 was actually considered for crew at one point (X-37C) but it was dropped for some reason.

And it doesn't have to be manned, actually. I was using the lander as an example. Any other payload (NRO moon satellites [why would you even need those]) is also doable with everything being reusable except for the second stage of Falcon Heavy.

[Bill Phil]

2 minutes ago, Ultimate Steve said:

 

My point wasn't to say that it would be practical, but it is doable.

The 300kg was for an internal habitat (think tiny metal cylinder with just enough room to take off your spacesuit) plus life support (its a bit of a stretch but probably workable). The X-37 was actually considered for crew at one point (X-37C) but it was dropped for some reason.

And it doesn't have to be manned, actually. I was using the lander as an example. Any other payload (NRO moon satellites [why would you even need those]) is also doable with everything being reusable except for the second stage of Falcon Heavy.

Yeah, sure, they proposed a crewed version... which was also scaled up by at least 165%.

[Ultimate Steve]

Just now, Bill Phil said:

Yeah, sure, they proposed a crewed version... which was also scaled up by at least 165%.

Correct. However, that was for up to 6 astronauts.

 

Again, my point is not that it should be done, but that it could be done should the need arise.

[wumpus]

4 hours ago, magnemoe said:

They wanted to increase drag on the heavy bottom to avoid it go bottom first on reentry rather than sideway, don't think the delta wind generate much lift. 

I suspect that "vertical drag" is more the issue than lift: getting any sort of glide ratio would be tremendous help.  The shuttle had a glide ratio of 4:1 and was considered a falling brick.  KSP vertical landing works well after gliding in at 1:1, I wonder if that is close to realistic.  I wonder how hard it would be to make an elliptical rocket (probably manufacturing costs would be painful, especially if *anything* gets done on a lathe).

One question I have about spacex plans is about landing this (or similar) on Mars (or the Moon if NASA is paying).  Elon talks about "vertical launch and land" but NASA tends to avoid such things.  The LEM (or correctly "LM") used two separate rocket engines, allowing the landing rockets to be damaged during landing.  There was a pitch for a rocket-propelled lunar vehicle (the rover made infinitely more sense), that required a "launch blanket" placed underneath it to avoid damage from moondust.  Curiosity was dropped by a "skyhook"that kept the rockets from covering Curiosity with dust.  All these show that NASA really doesn't like landing on uncontrolled surfaces (completely different from the platforms that Spacex lands on now) and hasn't changed their opinion with plenty of experience.  I've heard there are explanations for why they think they can launch with landing rockets on Mars, but I wonder if any actual landing engineers are convinced.

[Nibb31]

Yes, that's one of the big problems with SpaceX's plan. I think that BFS landings on unprepared surfaces are going to be presumed as one-way cargo flights. After the first few flights, they will have prepared surfaces.

At least the IAC 2017 sits a bit higher above the ground. Last year's version had the engine bells a few inches above the surface. There is no way that would have been survivable.

[tater]

In addition, the 2017 version has the bells entirely inside the rear "docking ring" assembly.

 

[cubinator]

SpaceX should try covering one of their landing pads with dirt and rocks such as might be expected on the Moon or Mars, then land a rocket on it to see what sort of damage occurs.

[tater]

6 minutes ago, cubinator said:

SpaceX should try covering one of their landing pads with dirt and rocks such as might be expected on the Moon or Mars, then land a rocket on it to see what sort of damage occurs.

This is actually an interesting idea. Use a booster you don't expect to refly, and put a regilith simulant down, making sure to have some rocks as well to look at the way higher thrust engines project debris.

A grasshopper would suffice, as well.

[1101]

2 minutes ago, tater said:

This is actually an interesting idea. Use a booster you don't expect to refly, and put a regilith simulant down, making sure to have some rocks as well to look at the way higher thrust engines project debris.

A grasshopper would suffice, as well.

Wouldn't it be rather a worst case scenario, given higher local g(and so more thrust needed) and the presence of atmosphere narrowing the plume, amongst other issues?

[cubinator]

13 minutes ago, tater said:

This is actually an interesting idea. Use a booster you don't expect to refly, and put a regilith simulant down, making sure to have some rocks as well to look at the way higher thrust engines project debris.

A grasshopper would suffice, as well.

Right, they could do it with a grasshopper BFS and study the effect it has on the engines. They don't necessarily have to fly it again, you just need to go and look at the engines. We have lots of sand and rocks on Earth, after all, might as well use them.

 

9 minutes ago, 1101 said:

Wouldn't it be rather a worst case scenario, given higher local g(and so more thrust needed) and the presence of atmosphere narrowing the plume, amongst other issues?

I actually think that it might not quite be as bad as on the Moon or Mars, because in a lower gravity environment the rocks and dust that get sprayed upwards will fly further and potentially cause more damage. Of course, when the engines are running they will tend to push things away from the bells, but there will certainly be rocks flying. You can also do a more in-depth study of the effect the terrain has on the rocket when it's a five minute car ride away as opposed to on another planet. The rocket is meant to be reliable, so it has to work in a worst-case scenario anyways.

Edited October 15, 2017 by cubinator

[tater]

I can only assume nasa messed with this a little before Apollo. Still, you're talking about a much larger craft with higher thrust, and the engines are mission critical for return.

[RedKraken]

Some interesting ssto speculation.

[magnemoe]

4 hours ago, wumpus said:

I suspect that "vertical drag" is more the issue than lift: getting any sort of glide ratio would be tremendous help.  The shuttle had a glide ratio of 4:1 and was considered a falling brick.  KSP vertical landing works well after gliding in at 1:1, I wonder if that is close to realistic.  I wonder how hard it would be to make an elliptical rocket (probably manufacturing costs would be painful, especially if *anything* gets done on a lathe).

One question I have about spacex plans is about landing this (or similar) on Mars (or the Moon if NASA is paying).  Elon talks about "vertical launch and land" but NASA tends to avoid such things.  The LEM (or correctly "LM") used two separate rocket engines, allowing the landing rockets to be damaged during landing.  There was a pitch for a rocket-propelled lunar vehicle (the rover made infinitely more sense), that required a "launch blanket" placed underneath it to avoid damage from moondust.  Curiosity was dropped by a "skyhook"that kept the rockets from covering Curiosity with dust.  All these show that NASA really doesn't like landing on uncontrolled surfaces (completely different from the platforms that Spacex lands on now) and hasn't changed their opinion with plenty of experience.  I've heard there are explanations for why they think they can launch with landing rockets on Mars, but I wonder if any actual landing engineers are convinced.

blast then landing might is an issue. Sill if the Apollo lander took damage during landing it would been an problem anyway. Think they did two stage because of simplicity also an hard landing or large rocks could easy damage the landing engine. two stage also let you leave the landing gear and stuff and have an backup engine in case something went wrong during decent. 

The mars rover hang directly between the engines, you would anyway had the issue of getting rid of the landing module afterward. 

BFR is far more solid build than the LEM or Mars rovers, however it might have an separate issue with its bottom layout, could you get rocks bounching of wall and engine bells hitting fragile engine parts higher up?  This would not be an issue on LEM as the engine was the lowest part except the legs. You could armor for this however 

Now for an moon base you would want an landing pad, one serious issue with landing on Moon is that because no atmosphere dust will go far and fast and it can easy damage windows or spacesuits.