totm nov 2023 SpaceX Discussion Thread

[cubinator]

7 hours ago, SunlitZelkova said:

it is going to cause some major strategic problems. If the industry is in space, nuclear strategy becomes partially obsolete as a good portion of the enemy industry and population would survive nuclear attack.

This is not a problem.

[tater]

6 hours ago, kerbiloid said:

I'm laughing reading the thread about the S_enateL_aundryS_ystem (notice, that's not me who called it so) and telling that things work different way.

The difference is we all see the sausage being made. Every cent for SLS is voted on. The OIG audits them (and excoriates them at times). They are not hiding the ball.

The idea that there is some secret cabal is the part we take issue with, it's just not a thing for a civilian agency (and military "skunkworks" projects don't have 24 hour HD cameras pointed at them).

[tater]

BN2.1 (test tank) has been put on a test stand:

 

[tater]

@sevenperforce this guy is covering his model with tiles to work the thing out:

I'll be interesting to see what he comes up with for the curves.

[JoeSchmuckatelli]

19 minutes ago, tater said:

'll be interesting to see what he comes up with for the curves.

The chorus agrees. 

[sevenperforce]

On 5/30/2021 at 2:25 PM, tater said:

Musk tweeted about using an expendable SS to throw a large number of probes into the outer solar system. Starlinks have ~3.6 km/s dv as it is, so they might be a decent bus for that.

I will note that Starlinks use Earth’s magnetic field to unload their reaction wheels, so an interplanetary Starlink would need either a separate hyperbolic thruster system or a pair  of ion thrusters on single-axis gimbals.

The latter is probably the best solution. If you go to a multi-axis gimbal it’s even better (you don’t need differential thrust and you even have engine-out capability).

On 5/30/2021 at 4:30 PM, RealKerbal3x said:

(Probably Elon time, but exciting to see nonetheless)

This confirms, indirectly, that the first orbital test will expend Superheavy at sea. If it was going to land on Deimos, Elon would have suggested so in this tweet. 

[sevenperforce]

16 hours ago, SpaceFace545 said:

I think EELV's (I am a ULA fanboy) really allow for the specialization that reusable launchers can't achieve. The Atlas V can launch a GPS satellite one day, a spy satellite the size of a school bus another, then it can send a probe into deep space a week later. All by changing the number of SRBs.

Well, one Atlas V can launch a GPS satellite one day, and then another Atlas V can launch a schoolbus-sized LEO spy satellite another day, and then another Atlas V can send a probe into deep space another day. All by expending a different number of SRBs.

In contrast the exact same Falcon 9 booster can launch a GPS satellite one day and land downrange, launch a schoolbus-sized LEO spy satellite a month later and RTLS, and then act as the side booster for a deep space probe launched on FH a month after that. And you still have the same booster with most of its duty cycles remaining.

Dial-a-rocket is a great technology but it can also be matched by a recoverable booster that can adjust its performance to match its recovery mode.

[CollectingSP]

Just now, sevenperforce said:

Well, one Atlas V can launch a GPS satellite one day, and then another Atlas V can launch a schoolbus-sized LEO spy satellite another day, and then another Atlas V can send a probe into deep space another day. All by expending a different number of SRBs.

In contrast the exact same Falcon 9 booster can launch a GPS satellite one day and land downrange, launch a schoolbus-sized LEO spy satellite a month later and RTLS, and then act as the side booster for a deep space probe launched on FH a month after that. And you still have the same booster with most of its duty cycles remaining.

Dial-a-rocket is a great technology but it can also be matched by a recoverable booster that can adjust its performance to match its recovery mode.

Both have pros and cons, but the Falcon heavy argument doesn’t really apply, considering most FH contracts are LEO contracts 

[sevenperforce]

15 hours ago, kerbiloid said:

ou don't need a huge 3d printer to print the whole Starship and buildings like those mushroom-like ant-heaps from the videos previously posted.

All you need is to replace the rolling machines where it's possible.

You should print not the whole assembled rocket, but metal sheets, bars, beams, screws, wire, forms for stamping, hollow shaped bricks for building walls and floors.

With same 3d printer you can print sheets of custom thickness, composition, texture, and size.
So, it can replace a whole workshop of rolling machines.

All this talk of trying to 3D print Starships on Mars seems absurd to me. Yes, if we want colonies on Mars, we will eventually need manufacturing on Mars. However, Starship is not a rocket that would be built on Mars because a rocket built on Mars would not necessarily look anything like Starship.

By the time we have a functioning colony on Mars that is developed enough to need its own manufacturing capabilities, we are going to be well beyond Starship.

Therefore, there is absolutely no purpose to doing something more expensively on Earth just to learn how to do it on Mars when we will never do it on Mars.

15 hours ago, Beccab said:

Looks like the 32 engines configuration will be 3-9-20, not 4-8-20 as people expected given the current configuration. Curious

Really fascinating! I am sure that using 12 engines for the boostback burn is vastly more efficient. I am guessing that the center three engines will fill the same role as the single center engine on Falcon 9, and the ring of nine engines around those will fill the role of the two outboard restartable engines on Falcon 9. Otherwise, same basic launch, boost back, and landing profile.

14 hours ago, CatastrophicFailure said:

IIRC they’re still working on something rather like it, tho probably without the nifty hydrolox V8. Tory was just mentioning it on Twitter the other day. 

Last question of mine he answered was confirming that both IVF and SMART are still in dev.

[sevenperforce]

12 minutes ago, CollectingSP said:

Both have pros and cons, but the Falcon heavy argument doesn’t really apply, considering most FH contracts are LEO contracts 

Uh, what?

The first FH launch went to Mars. The second went to supersynch GTO. The third was a multi-orbit mission that ended up in direct-MEO.

The future FH contracts are, in order: direct-GEO, direct-GEO, heliocentric (asteroid belt), an unknown USSF orbit, heavy GTO, heavy GTO, TLI, TLI, TLI, and TLI.

So of the dozen known FH contracts (not including the also-beyond-LEO test flight), there is only one that **might** be LEO. And that one might use Falcon 9 since it hasn’t been confirmed as Falcon Heavy. It’s a Vandy launch anyway so it’s definitely not a normal LEO flight regardless. 

[RealKerbal3x]

 

[tater]

38 minutes ago, sevenperforce said:

This confirms, indirectly, that the first orbital test will expend Superheavy at sea. If it was going to land on Deimos, Elon would have suggested so in this tweet. 

Might fit on ASOG.

[southernplain]

15 hours ago, CollectingSP said:

I agree completely. Spacex just doesn’t have the capability to do that at the moment. They can’t even get many contracts from the AF because of vertical integration requirements (which they do not fit at this time.)

as for the specialization, that’s what I think as well. Falcon is “one size fits all,” and ULA has many different sizes of delta/atlas for every mission you could possibly think of.

Spacex’s Reusable rockets are good for cheap and quick launches.  Things like GPS, for example.

if you want something in a wonky orbit, or you want to send a mission far out into the solar system, pick ULA’s expendables, as they are better for that. Just look at how many missions spacex has sent outside of LEO. One? Two?

1. The NSSL award includes vertical integration for Falcon 9/Heavy. SpaceX is installing that hardware at the Cape right now IIRC.

2. Falcon Heavy is plenty capable of high energy launches.

Recovered Falcon Heavy is basically identical to Atlas 551 to Mars (C3=12.2), both throw about 4.8t.

Expendable Falcon Heavy is also extremely competitive with other expendable LVs, but SpaceX won't bid expended Falcon Heavy because reuse is the whole point.

[tater]

Yeah, part of the SpaceX contract win (only 40% of launches) is vertical payload integration being added, AND an extended (taller) fairing.

[CollectingSP]

2 hours ago, sevenperforce said:

Uh, what?

The first FH launch went to Mars. The second went to supersynch GTO. The third was a multi-orbit mission that ended up in direct-MEO.

The future FH contracts are, in order: direct-GEO, direct-GEO, heliocentric (asteroid belt), an unknown USSF orbit, heavy GTO, heavy GTO, TLI, TLI, TLI, and TLI.

So of the dozen known FH contracts (not including the also-beyond-LEO test flight), there is only one that **might** be LEO. And that one might use Falcon 9 since it hasn’t been confirmed as Falcon Heavy. It’s a Vandy launch anyway so it’s definitely not a normal LEO flight regardless. 

The first launch didn’t go *to mars* technically.

I should have just said “earth orbits”,  instead of LEO.

[SunlitZelkova]

8 hours ago, cubinator said:

This is not a problem.

I wrote that in the context of nuclear war theory, where having large parts of your population and industry out of reach of enemy nuclear weapons would hurt the concept of deterrence. You could launch a first strike on the enemy and suffer little damage in retaliation. Thus space colonies/factories, things like mass fallout shelters, and other installations designed to save lives en masse from a nuclear strike would be destabilizing and would present a problem within the context of trying to maintain deterrence (part of nuclear war theory).

Personally, I believe that any death at all is a bad thing and should be prevented.

Spoiler

But I am also a realist and I think deterrence will be necessary for the foreseeable future, and is much more likely to save lives on both sides of the globe at this period in time than attempting to build lots of ABM systems and fallout shelters. This is my personal opinion, I am not attempting to bring you to such an opinion or change your mind if you disagree.

To get back on topic, is it known whether MSR is planned as part of SpaceX's hyper ambitious Mars colony program?

[RCgothic]

7 hours ago, CollectingSP said:

The first launch didn’t go *to mars* technically.

I should have just said “earth orbits”,  instead of LEO.

Atlas V's upcoming launches are:

GEO, LEO, GTO, SSO,

Heliocentric

GTO, LEO, GEO, GEO, LEO, SSO, GEO, (Unknown air force orbit - unlikely beyond earth's SOI), GTO, GTO, LEO, LEO, LEO, LEO.

Delta IV Heavy has only 3 NRO contracts remaining which will probably be to GEO or GTO. Vulcan currently has no missions beyond the earth-moon system on the public manifest.

 

Missions beyond the earth-moon system are rare. Those that do exist, Falcon is getting an increasing share of. Most notably, it will almost certainly get Europa Clipper. It also has DART, PSYCH, and IMAP. That's not counting TLI missions.

Edited June 1, 2021 by RCgothic

[mikegarrison]

Atlas tends to have a payload mass advantage in some high delta-v missions because it uses a really light second stage compared to Falcon.

[magnemoe]

On 5/31/2021 at 7:24 AM, CollectingSP said:

*EXTREME BIAS WARNING*

I agree completely. Spacex just doesn’t have the capability to do that at the moment. They can’t even get many contracts from the AF because of vertical integration requirements (which they do not fit at this time.)

as for the specialization, that’s what I think as well. Falcon is “one size fits all,” and ULA has many different sizes of delta/atlas for every mission you could possibly think of.

Spacex’s Reusable rockets are good for cheap and quick launches.  Things like GPS, for example.

if you want something in a wonky orbit, or you want to send a mission far out into the solar system, pick ULA’s expendables, as they are better for that. Just look at how many missions spacex has sent outside of LEO. One? Two?

not saying that they can’t, but the government probably wants to pick the company that has more experience doing that kind of thing.

This is pretty correct, falcon 9 has the downside of an fairly heavy and low isp upper stage it works well for heavy payloads to leo  but not so then if you want to get an small probe up to high velocity here light and high isp upper stages like centaur is perfect. 
An kick stage for falcon 9 would help here.

Note that this is even more true for starship but it can be refueled, and you can carry an 100 ton 3rd stage. 

[RCgothic]

This keeps getting repeated, but actually hydrolox is not necessarily the best choice for probes to high C3. The high ISP gets handicapped by poor mass fraction.

Leaving aside the impossibilities, if Falcon Upper Stage were to be replaced with a notional 116t wet RL10 (462s ISP) stage with similar mass fraction to Centaur III, Falcon's maximum C3 would actually reduce by 290m/s, and that's discounting the likely less efficient trajectory due to lower thrust. For most probes that probably doesn't make too much difference, and the higher payloads to lesser C3 from hydrolox would probably be generally more useful. Probes to high C3 are a rare use case.

But an equivalent methalox (380s) FUS would have 1407m/s more than the hydrolox version and have better DV for payloads 8.6t or less.

 

The best use case for Hydrolox isn't small probes. It's massive payloads.  The Hydrolox upper stage would increase falcon's ASDS recovery payloads from 15.6t to ~23t. The large stage size for Hydrolox also lends itself well to large payload fairings.

Edited June 1, 2021 by RCgothic

[RCgothic]

 

 

 

[Nothalogh]

9 hours ago, RCgothic said:

The best use case for Hydrolox isn't small probes. It's massive payloads.  The Hydrolox upper stage would increase falcon's ASDS recovery payloads from 15.6t to ~23t. The large stage size for Hydrolox also lends itself well to large payload fairings.

So, a hydrolox expendable upper stage for Superheavy?

[tater]

 

[RCgothic]

1 hour ago, Nothalogh said:

So, a hydrolox expendable upper stage for Superheavy?

I discounted the impossibilities above, but in practice a hydrogen upper stage fitted on top of an existing booster would have a lot less propellant by mass due to hydrogen's much lower density.

An equivalent mass upper stage would be a lot larger and wouldn't practically fit on top of a booster not designed for it. Either that or it ends up an abomination like Ares-1.

[sevenperforce]

10 hours ago, RCgothic said:

The best use case for Hydrolox isn't small probes. It's massive payloads.  The Hydrolox upper stage would increase falcon's ASDS recovery payloads from 15.6t to ~23t. The large stage size for Hydrolox also lends itself well to large payload fairings.

Hmm. This makes me wonder...given basic assumptions about engines and propellant choices (and avoiding an inordinate number of staging events), is there an ideal vehicle configuration for any given orbit? Assume gross liftoff thrust is the limiting factor.

1 hour ago, Nothalogh said:

So, a hydrolox expendable upper stage for Superheavy?

Hydrolox would perform better in comparison to kerolox for certain large LEO payloads, but methalox typically beats them both. One of the great things about methalox is its high O/F ratio means its bulk density is not much different from kerolox but its specific energy is much higher.