totm nov 2023 SpaceX Discussion Thread

[darthgently]

45 minutes ago, Ultimate Steve said:

1 hour ago, Terwin said:

 

I wouldn't be surprised but I don't think so. From a velocity standpoint at mars you're looking at a 6ish km/s entry. IFT 4 was still melting at 4ish km/s

Thin or thick atmo, decelerating from 6ish km/s to landing speeds via friction is going to entail a lot of heat.  I was wondering if the plan could be to make multiple aerobrake skips and hops over more than one orbit

[tater]

Didn't see this here yesterday (sorry if I missed someone else posting it):

 

[zolotiyeruki]

2 hours ago, darthgently said:

Thin or thick atmo, decelerating from 6ish km/s to landing speeds via friction is going to entail a lot of heat.  I was wondering if the plan could be to make multiple aerobrake skips and hops over more than one orbit

From a quick google search, it appears that orbital velocity at a low Mars orbit is about 3.3km/s, so it might be an option.  The trick is with the later aerobrakes, where your orbit spends longer and longer in the atmosphere.  At least, that's what I learned in KSP.

[darthgently]

37 minutes ago, zolotiyeruki said:

From a quick google search, it appears that orbital velocity at a low Mars orbit is about 3.3km/s, so it might be an option.  The trick is with the later aerobrakes, where your orbit spends longer and longer in the atmosphere.  At least, that's what I learned in KSP.

Me too.  I also learned in KSP that one can tune one’s upcoming periapsis at the preceding apoapsis with a typically tiny prograde burn

[magnemoe]

1 hour ago, darthgently said:

Me too.  I also learned in KSP that one can tune one’s upcoming periapsis at the preceding apoapsis with a typically tiny prograde burn

At Duna you can come in very hard and fast.

Firebird 1 at hardbrake, entry velocity was 3.8 km/s, this is at max Q. burned 1 km/s before final adjustment of Pe, so yes was coming in very hot dropping from Minmus into LKO for injection 
Obviously putting couple of Km/s dv has to be paid back at entry. Over an week testing and modifying the ship for stability at 8g moving center of drag.  
Followed by Firebird 2, less mass and a bit slower. 
I say its the coolest thing I done in KSP. 

I also simulated some Layte injections and the result was not survivable. 
 

[tater]

B12

[GuessingEveryDay]

2 hours ago, magnemoe said:

I say its the coolest thing I done in KSP. 

[magnemoe]

On 9/20/2024 at 4:44 AM, GuessingEveryDay said:

It is, but heating was not the main issue with this it was aerodynamic as in keeping the heat shields in front of the rest. 
This worked at Duna. On Eve heating was an issue but you could burn into an orbit there Ap was inside Eve SOI and then aerobrake into low orbit. 
Laythe, no it does not work KSP 2 it also don't work for large ships, it work for capsules. With an 5km/s intercept velocity shields poppe at once. 
This was also an KSP 2 issue, but at orbital velocites you did not need shields landing at Duna but dont expose sensitive stuff. 

An lander / rover in KSP 2 had the probe core on the bottom because stupid. It blew up during landing, I could still deploy parachute and used an autopilot for landing burn but could not turn on hand brake so second landing on Duna involved an car chase. 

Rover from fist lander slowing down the rover/lander from second mission. 
 

Edited September 21 by magnemoe

[Exoscientist]

On 9/19/2024 at 12:59 PM, Ultimate Steve said:

I mean you do have to have a few screws loose to try going to space at all, so...

One of the big points of Starship is that it is supposed to be the lander. Stripping off the reusability hardware means you no longer have a lander.

I'm having trouble envisioning a reasonable 250 ton Mars capable manned vehicle, even with ground equipment launched separately. If Starship does the TMI and we assume optimistic numbers (40t dry Starship, propellant is equivalent to LEO payload for a combined number of 250 tons, 3.6km/s to Mars, 382s isp for the burn), then you get 70 tons for the Mars vehicle itself. And that is an unrealistic upper bound.

I'm having even more trouble imagining that anyone could develop a Mars vehicle of any mass before SpaceX gets reusability and refueling working.

 Robert Zubrin has argued numerous times that the multiple refueling approach is a poor approach to lunar or Mars missions:

 If you give it a small 3rd/lander stage you can do the missions with no refueling flights required at all

  Robert Clark

On 9/17/2024 at 11:48 AM, zolotiyeruki said:

There's a heavy implication here that SpaceX owes the public this information about exploding engines and stages, and by not divulging it, they are somehow trying to hide it or deceive the public or the FAA. 

I'm not terribly concerned about an explosion during a landing catch.  After all, SpaceX has more incentive than *anybody* to make sure it's safe.  It's their money at stake.  As for the public or the environment?  Meh, the area is cleared anyway, and the only thing they'd be scattering into the environment is steel, water, and CO2.

Perhaps my reading comprehension is failing me, but I'm not seeing anything in the quote that supports the claim that the FAA is protecting SpaceX (or from what).

 It’s an unwritten rule at the FAA if a company does not want to reveal proprietary formation, then the FAA won’t reveal it either. SpaceX has yet to admit a Raptor exploded during the last landing burn, nor that the booster exploded shortly after ocean touchdown. If SpaceX won’t reveal it, the FAA won’t either.

  Robert Clark

 

Edited September 21 by Exoscientist
Inadvertent double post.

[tater]

[Ultimate Steve]

34 minutes ago, Exoscientist said:

Robert Zubrin has argued numerous times that the multiple refueling approach is a poor approach to lunar or Mars missions:

In the video his point has nothing to do with Mars or the Moon. It seems that he is referring to a way to capture the medium lift segment of the market by offering a fully reusable Falcon upper stage in the style of Starship.

I don't agree with this point, but that's not the point you are making. I did write a response to Zubrin's point, but it is kind of off topic, so I will put it in a spoiler:

Spoiler

I don't think this would work. Making the upper stage of Falcon 9 reusable would greatly hamper Falcon's payload capacity and you'd end up with a light launch vehicle and not a medium one. Starship is taking a significant (I'd wager at least a doubling) of its dry mass in order to be reusable. F9 Upper is insanely light already so maybe even a tripling, maybe even more, as Starship has many square cube law advantages from being that large. Then factor in the propellant needed for de-orbit and landing. There's not gonna be much left.

It also wouldn't be a simple conversion. If you keep it kerolox at F9 diameter, the payload space becomes tiny. Might not be a problem given the tiny mass to orbit. Methalox, you will want to widen the diameter to make sure you're not a pencil rocket, and that also helps with payload space.  I'll ignore what would have to happen to the Falcon to get it to support something that large on top of it.

Then you will almost certainly need to develop brand new engines. Mvac isn't suited for landing, and even a single raptor is 3x as powerful as the already comically overpowered Mvac.

If you've done all that, congratulations, you have a fully and rapidly reusable upper stage that is shackled by the Falcon 9 lower stage with a 3 week refurb time, which is locked into ASDS landings.

I do think a smaller vehicle to capture the commercial LEO satellite market and similar might make sense in the abstract. But not for SpaceX. They want something this big for Starlink, even ignoring refueling, Mars, and the Moon. The category of "smaller stuff" is a very small portion of what SpaceX intends to do with this vehicle. If the time comes when someone shows up with a smaller fully reusable vehicle, they'll doubtless recoup some of the lighter payloads by doing rideshare, like how they are currently gobbling up a bunch of the super light stuff with Falcon rideshare.

But for your point, that Mars would be better served by a mini starship. I will evaluate two cases. Starship style mission to Mars on a mini starship designed to be launched on an expendable Starship+Super Heavy stack with 250 tons of payload capacity. Secondly, an expendable Starship third stage, again on an expendable first and second stage. I have used optimistic numbers where possible to steel man your argument.

 

Case 1:

TLDR: If you are very optimistic, you might just barely get flags and footprints, but you still need ISRU.

Spoiler

For the case of a mini starship massing 250 tons full in LEO, if you use this as the Mars vehicle, with 382s isp all the way (it won't have that), let's figure out what the dry mass would have to be.

Total Delta-V expenditure is roughly 3.6 for TMI, 0.3 for the landing burn, 3.6 for the ascent, 2.5 for TEI, and 0.1 for the landing burn.

Cargo Starship as it exists today has a mass ratio of about 13:1 (1300t full 100t dry, ish, that's not the real number because we don't know the real number but it is a round number in the ballpark of the real number). The mini starship (assumed to be reusable in this case) would get a worse mass ratio because the square cube law really helps with big things. But let's assume it gets 13:1. Structural mass must thus be at least 19 tons.

For the no ISRU case (just to have a laugh), dry mass would have to be 17 tons. You have a whole negative 2 tons for crew and cargo and life support.

For the ISRU case, the outbound journey has a Dv of 3.9km/s, and the inbound journey has a Dv requirement of 6.2km/s which will dominate, suggesting a maximum return dry mass of 48 tons. As the structural mass is 19 tons, this leaves, at most, 29 tons for the crew, the life support, shielding, power systems, spare parts, spacesuits, consumables, samples from Mars, etc. This assumes the ISRU equipment has been prepositioned by another ship. Landing mass can be up to 74 tons, which allows for the 29 tons of return mass to not have to include the consumables required to get to Mars, and presumably a lot of equipment can be left on Mars.

And again, I have been using optimistic numbers and assumptions throughout.

29 is more than I thought it would be and is probably doable, but in reality you will get significantly less than this. That mass fits a Salyut, which could support crews of 3 for 8 months (and was likely limited by the humans). Salyut is old, and a significant chunk of its mass is in hull and propulsion and attitude control, which Starship already provides. With prepositioning the ISRU equipment and a very small crew size (low single digits), I'd say that you could probably barely squeeze out a 2 launch (one for ISRU, one for the lander, if you're playing it safe, one presumably F9/Dragon launch for the crew) flags and footprints mission using a mini-starship third stage on an expendable Starship and expendable Super Heavy if I haven't steel manned it too strongly (and I did steel man it a lot).

It would be painfully easy for the dry mass to grow from 19 tons to 25 tons, and the isp to drop from 382 to 355 (this vehicle is sized about right for a single sea level Raptor assuming the thrust wouldn't be too high on Earth, which it probably would be, necessitating new engines), and to want a 200m/s Delta-V margin. Then you only get 14 tons to play around with, which, again, must fit zero boiloff tech, 6 months of consumables for the return trip, the crew, the spacesuits, the airlock, the life support equipment, exercise equipment, solar panels for power generation, landing legs for Mars, samples you are returning from Mars, and a lot more I'm missing.

 

Case 2:

TLDR: Not even in magical fantasy land.

Spoiler

For the case of using a 250 ton Starship stage 3 with a similar mass ratio (~25, F9US is black magic) as the Falcon 9 upper stage as the TMI stage for a separate Mars vehicle, you end up burning 155 tons of propellant, with about 6 tons of structure, for an 89 ton TMI capacity, a 19 ton improvement over not building an expendable third stage.

 

What would it take to fit a monolithic mission inside of an 89 ton payload capacity?

Let's start with Orion because it exists and it can probably re-enter from Mars. Let's ignore the 6 month docked endurance time and assume it can go the full nearly 2 years (assuming an opposition class flags and footprints mission). It is pretty small and can only hold 21 days of supplies. Something like HALO (minimalist Gateway habitation module) is not enough. We also don't know how heavy it is, but it is a deep space habitation module, and it is based on Cygnus, something we do roughly know the mass of. Let's assume that something with the mass of a full Cygnus spacecraft (~7 tons) can provide enough supplies and volume for the crew to survive and remain sane and physically fit. This is a laughable proposition, but let's go with it.

The stack is now 34 tons (rounding down), counting 9 tons of fuel and an engine with 316 seconds of isp.

I'll briefly mention that with these numbers (26t wet, 9t prop, 316s isp), some of the Delta-V estimates for Orion I see floating around (1855m/s) are laughably impossible.

Anyway, this Mars stack gets 953m/s, we need at least 2.5 to get home from Low Mars Orbit. This requires a total of 31 tons of propellant, which I'll store in massless tanks for the sake of argument.

The stack in Low Mars Orbit is now 56 tons.

Now we need a lander. The Apollo Lunar Lander was 15 tons (rounding down). Obviously it cannot do a Mars landing and ascent for reasons that should be obvious, and any serious Mars lander is going to be significantly heavier. But let's assume the Apollo lander can be used just fine.

The stack in Low Mars Orbit, pre landing, is now 71 tons.

Now if you can magically aerocapture the whole extremely unaerodynamic stack that is not structurally designed for aerocapture, with no added heat shield mass, and ta-da! You've done it! With a whole 18 tons to spare!

If aerobraking is not an option, simply use a massless nuclear thermal rocket with 1000s isp and massless zero boil off fuel tanks, and the vehicle comes out to 92 tons, leaving negative 3 tons for margin!

 

There is no way you can get a monolithic manned mission to Mars and back on a single flight using this method, at least while respecting human sanity.

 

Notably, case 1 may have just barely been able to close. In reality I highly doubt it would for reasons I expressed above. But if it did work, sure, we can do a 2 launch flags and footprints Mars mission.

What I don't understand is why you are so concerned with it happening in one launch. The launches are the easy part. The Mars part is the hard part.

Here is a comparison between Case 1 and just using Starship with refueling:

TLDR: I do not believe that building a mass effective mini starship is easier than developing refueling and rapid reusability.

Spoiler

In case 1, you have to go through the effort of building a new vehicle, which is harder to get working than normal Starship (square cube law), and likely also developing new engines (single raptor or rvac, with HLS landing engines in the skirt might do the trick). Part of me is like "And then you just use this tech exclusively for the lander and not for the significantly easier Starship + Super Heavy?" But I might be putting words in your mouth there, I'll assume that the two Mars launches were one off fully expendable missions and shut my mouth.

Which, sure, it could be done. But I do not believe that's easier than getting refueling to work.

Starship proper, you get so much more mass to play with. Even assuming just the 100t to orbit version, hell, even just assuming 75 tons, and a laughably low 355s isp, you can get 100 tons of cargo to Mars for 5 refueling flights. With ISRU as in case 1, this allows you 100 tons for the return trip. (assuming 100t dry and same delta v requirements as in case 1).

To pull off case 1, using optimistic numbers, we have to:

• Expend 2 super heavy boosters
• Specially build 2 expendable starships and fairings
• Design, develop, build, and test a custom mini starship (harder than normal starship, or at least harder for the same mass ratio)
• Build 1 crew mini starship
• Build 1 cargo mini starship
• Possibly develop new engines or accept a stupidly high TWR on a single Raptor
• Fit everything that isn't hull, control, and propulsion into 29 tons on the inbound leg, using very optimistic numbers, you will get less

To pull off an equivalent mission using normal Starship and pessimistic numbers, we have to:

• Build 1 Mars cargo and 1 Mars crew Starships (anticipated to be similar to normal Starships)
• Develop Starship to a point where you can conduct 6 reusable launches in rapid succession
• Conduct 6 launches for the ISRU
• Conduct 6 launches 2 years later for the crew
• Fit everything that isn't hull, control, and propulsion into 100 tons for both legs

I'm not sure what part you're stuck on. Is it the "Conduct 6 launches" part? SpaceX has conducted 6 launches in the past 15 days with a system that is designed to be significantly less reusable than Starship. If we're talking same launch pad, there have been 6 launches from SLC-40 in the past 32 days.

Is it the "Conduct 6 dockings" part? They can dock with the ISS within a day or two of launch with all the restrictions that come with the ISS and crew and they've yet to fail a docking. Knock on wood.

Is it the reusability part? Super Heavy is very nearly a solved problem, and Starship does indeed have a ways to go, but square cube law makes it easier than mini starship. 

Is it the cryogenic fluid transfer part? I don't really have a comeback for that, the IFT-3 transfer reportedly went well but is a somewhat different problem, I'm optimistic but I'll have to wait and see.

At best, mini Starship for Mars just barely gets you flags and footprints.

If that's your goal, then sure, Case 1 can maybe be made to work. That is not SpaceX's goal. They want a large, sustained presence on Mars. Which is very out there, but that's what they are looking at.

 

2 hours ago, Exoscientist said:

It’s an unwritten rule at the FAA if a company does not want to reveal proprietary formation, then the FAA won’t reveal it either. SpaceX has yet to admit a Raptor exploded during the last landing burn, nor that the booster exploded shortly after ocean touchdown. If SpaceX won’t reveal it, the FAA won’t either.

  Robert Clark

Raptor exploded during landing burn:

We all saw it happen live, do they need to write up a whole blog post about it? I mean I would love that. But I don't think they are under obligation to.

I also don't think that the engine out is particularly worrying at this stage. They went from 12 engines out in their first landing burn attempt to one engine out in their second landing burn attempt. During the second attempt they landed right on the mark despite the engine out (I think I heard Elon say this at some point either on Twitter/X or in some interview), giving them enough confidence to try the catch. And this is with outdated engines.

Super Heavy Booster Explosion:

It's a 70 meter tall soda can filled with explosive gas, being dropped into the water from a height of a few meters, the base is not designed to take that shock and any damage causes a big methane leak, why would it survive?

Remember a few years ago how they did have that Falcon survive an ocean landing? And then they had to figure out how to sink it safely. It was a headache. Super Heavy surviving a water landing is probably something they wanted to actively avoid.

And we still don't know that happened for sure, last I heard. If you have new info on that, please let me know.

 

[CatastrophicFailure]

On 9/19/2024 at 3:37 PM, darthgently said:

Me too.  I also learned in KSP that one can tune one’s upcoming periapsis at the preceding apoapsis with a typically tiny prograde burn

I learned in KSP that a blood sacrifice to an eldritch abomination from outside reality can turn living beings into spaghettified Cronenberg horrors experiencing a new definition of pain and suffering and they STILL. DON’T. DIE.  

 

On 9/19/2024 at 6:44 PM, tater said:

B12

I thought this was KSP. 

[tater]

50 minutes ago, Ultimate Steve said:

TLDR: I do not believe that building a mass effective mini starship is easier than developing refueling and rapid reusability.

Zubrin's ideas have been fairly useless for a long time, his "mini Starship" nonsense is more of the same, as SpaceX are going to do what they are going to do. He has a simple mechanism to put his money  (and presumably someone else's who has very deep pockets) where his mouth is, he could commission such a variant, then fly a test mission.

I tend to think there will be variant ships worked on at some point (I have proposed a few myself), but all reasonable ones are predicated on the current conops being worked on (rapid reuse, orbital refilling).

[mikegarrison]

5 hours ago, Exoscientist said:

It’s an unwritten rule at the FAA if a company does not want to reveal proprietary formation, then the FAA won’t reveal it either.

Uh, no.

It is a WRITTEN rule that government agencies will protect CBI (Confidential Business Information) to the extent that they are legally allowed.

[tater]

 

[cubinator]

I don't think it's ever going to stop bugging me that they named this planetship "Starship".

[tater]

These pics are during stacking, but NSF Starbase live cams show it in fact stacked right now.

[Ultimate Steve]

2 minutes ago, cubinator said:

I don't think it's ever going to stop bugging me that they named this planetship "Starship".

Tbf it's a lot more of a Starship than Starliner is a Starliner.

[tater]

2 minutes ago, cubinator said:

I don't think it's ever going to stop bugging me that they named this planetship "Starship".

You still raw about Saturn V not actually being a Saturn rocket?

 

[darthgently]

1 hour ago, Ultimate Steve said:

Tbf it's a lot more of a Starship than Starliner is a Starliner.

Related, this brings to mind that the recent launch named Thousand Sails had a much more accurate name in hindsight, but alas, not in the way intended

[cubinator]

1 hour ago, tater said:

You still raw about Saturn V not actually being a Saturn rocket?

 

Not really, actually. I always 'got' it being named after Saturn, sure that's cool. You can make an argument that this vehicle is named after the stars or something, but the common use of the word is something fundamentally different. 

I'll never be any less stoked about anything Starship does over that, though. And it does incur a theme of being 'overly optimistic' that has been producing great things at SpaceX...

Edited September 21 by cubinator

[tater]

16 hours ago, cubinator said:

Not really, actually. I always 'got' it being named after Saturn, sure that's cool. You can make an argument that this vehicle is named after the stars or something, but the common use of the word is something fundamentally different. 

I'll never be any less stoked about anything Starship does over that, though. And it does incur a theme of being 'overly optimistic' that has been producing great things at SpaceX...

I'm pretty unsure that starships in the common meaning will ever be a thing at all.

Also, what about "star sailors?" What do they ride in? Universe sailors? (astronaut and cosmonaut, respectively)

(I'm actually not a fan of the name, either, I just got past it faster, probably).

Edited September 22 by tater

[darthgently]

Wen “floofdangle”?

 

[tater]

Booster in catch position before OLM mounting it:

7 minutes ago, darthgently said:

Wen “floofdangle”?

Spoiler

 

 

[Pthigrivi]

Im still pretty surprised they’re going for the catch on this one. The last one was very on fire when it hit the deck. They really want to risk the olm and tower? Seems like one nominal hover should be the minimum.