It's also cheaper, but at $45/kg for niobium (not the specific alloy) maybe not a huge one. Still, manufacturing costs and such add up.
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I tried doing calculations for it. I found rough dimensions and a description of the layered design, but the numbers got high really quickly. The design is an Inconel-copper-Inconel-ceramic sandwich, with the copper machined to create channels. But all that stuff is so heavy that a bell even a few mm thick adds hundreds of kg to the engine. The V2 Raptor is supposed to mass only 1,600 kg, and nobody ever mentions a distinction in mass between vacuum and sea level variants.
True the cut the nozzle size, but that’s a different trade space. The short vac nozzle is solely a cost saving measure, explicitly leveraged in a situation where every kg doesn’t matter.
I did a quick Googs of Merlin and speculation is +10-20% on total mass for the longer nozzle.
0th order then, it’s a ~150-300kg upper (or so) on raptor.
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That sounds SUPER high-tech, but SPECTACULARLY expensive- do we have an idea of the cost /engine??
In 2019, folks were going with a $1 million number. SpaceX's goal is $250,000.
The nozzle expansion section isn't anything crazy-futuristic. Each of the material types has been worked with for many decades. I'd think that the full flow staged combustion innards would be the more impressive, by far. Such engines have been built before, but none ever flew until Starship Super Heavy lifted off.
Inconel is around $6/kg. Copper is around $9/kg. Plus the cost of shaping, forming, machining, etc.
The ceramic may be the fanciest bit, but I didn't see any details on exactly what it is. Clearly something that tolerates heat well. Lots of speculation, but nobody outside SpaceX seems to know.
Thanks.
I think inconel is extremely difficult to work, and combining it with ceramic must be a trek. So 250K sounds almost aspirational to me. SpaceX continues to change the face of launches to space....
Must Starship be human rated? For the moon, the moon lander version of SS will pick up and drop off astronauts from/to other space ships. Could that strategy be used for Starships headed to Mars and back.
I have such a hard time envisioning an escape pod for Starship being launched to low orbit on top of Super Heavy.
I have such a hard time envisioning an escape pod for Starship being launched to low orbit on top of Super Heavy.
Sure. It depends on how many people you want to put into a Starship and how many you can carry per trip on the human-rated system that you're using. If a Mars-bound Starship is already in LEO, loaded and ready to go, you could use Dragon to move up to seven passengers at a time. Each seven passengers requires a Falcon 9 launch. If Starship carries 100 passengers to Mars, that's 15 launches. How long would that take? Probably weeks. What would it cost? Probably hundreds of millions of dollars.
What if Starship was human rated? Well, all 100 passengers could go up in one flight and the Starship could be turned around in a couple days. That one flight would cost around $30 million, perhaps much less.
The human-rated Starship is probably not going to be the Starship we see today. It also won't be the stretched version. It'll be some conservative beast with a lot of its hardware devoted to passenger safety. If the human-rated Starship can loft only 100 tons of mass to LEO, and we say that it's going to take 100 people to orbit, then that's one ton of mass devoted to the safe passage of each passenger to LEO. That's a pretty nice budget to work with.
So my answer is that Starship doesn't need to be human rated for NASA-scale goals of putting a few people on the Moon. But if we're ever going to get serious about moving hundreds or thousands of people at once, we're going to need a vehicle that can get them to LEO en mass.
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Just amazing that we can have this conversation and it is not a hypothetical ...it is about how best to accomplish one of the most amazing feats of exploration. What an age.
That price for Inconel, a high-performance alloy used for stuff like rocket engine parts, turbocharger impellers, etc..., being cheaper than copper surprises me.
It's hard to find prices for it not formed into parts already, but about the cheapest I see for sheets of it is $20/kg, but admittedly that's a quick glance... is it really $6/kg?
I had not thought about that before and it makes a lot of sense. A ship like that would be optimized for trips to LEO and back and for passenger safety. So it could have specialized abort systems and emergency landing legs that Mars cargo ships and ships designed to take people from LEO to Mars would not have (or course Mars ships would have legs but a different design).
Yes, in the future there will be a variety of specialized ships designed for specific missions. Fun to think about.
It surprised me as well. I probably should have looked at the numbers harder, but I took the first hit that I found. I just now asked Copilot about it and it says that it's more like $40-$60 per kg. This is the web site it drew from, and while there are no dates on the numbers, I found other sites that were in the same ballpark.
Demystifying Inconel Costs: A Comprehensive Guide
Explore Inconel costs and pricing in this comprehensive guide. Discover how material composition and production methods affect Inconel alloy prices.
inconel718.in
Chinese sites list Inconel for much lower prices, but I have my doubts.
My apologies for the bad numbers. It probably just means that the inconel shells are quite thin because the price of the bell extension surely has to be kept low. SpaceX is going to have to build a lot of Starships, and that means a lot of vacuum engines. Not so many boosters because they're designed to return to the launch site.
The thought of all those sea level Raptors going to Mars bothers me. Are they going to remove them once on orbit? Put seven vacuum engines on Mars-bound Starships? Put some kind of detachable Earth-specific booster on? Increase the performance of the Starship booster so Starship can make orbit on a minimum number of vacuum engines? So many possibilities.
It surprised me as well. I probably should have looked at the numbers harder, but I took the first hit that I found. I just now asked Copilot about it and it says that it's more like $40-$60 per kg. This is the web site it drew from, and while there are no dates on the numbers, I found other sites that were in the same ballpark.
Demystifying Inconel Costs: A Comprehensive Guide
Explore Inconel costs and pricing in this comprehensive guide. Discover how material composition and production methods affect Inconel alloy prices.
Chinese sites list Inconel for much lower prices, but I have my doubts.
Yeah, I think those sheets I saw were Chinese as well. Domestic bar stock was more like the $45-60 range, similar to what you mentioned.
Yeah, assume as thin as possible... once you have sufficient thickness to withstand the exhaust pressure/heat, the cooling fluid does the rest.... more mass wouldn't buy you anything.
Probably totally impractical, but an Extend-A-Bell mechanism would be cool.
Ben W
Chess Grandmaster (Supervised)
The moon lander version won't need a heat shield, which simplifies things dramatically. But for Earth <-> Mars travel with in-space transfer, Starship would have to be capable of aerocapture into low orbit, which complicates things quite a bit. LEO to low Mars orbit without aerocapture requires about 7 km/s delta-v, which is just beyond the capabilities of the current Starship design, and it would need to be fully refueled in low Mars orbit for the trip back to LEO without aerocapture. So it might make more sense for such a "cycler" to use more efficient ion propulsion, but that technology is still quite a ways off.
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Ben W
Chess Grandmaster (Supervised)
I would expect that a version of Starship that is never intended to return to Earth (or operate in thick atmosphere) would not have sea-level raptors; a seven-vacuum-Raptor configuration makes a lot of sense for that. (The downside is that the center gimbal-able Raptor becomes a single point of failure, whereas the nine-engine configuration is robust to one of the center engines failing.) For the ones that will be refueled on Mars and sent back to Earth, obviously the sea-level Raptors are necessary, unless the plan were to aerocapture into LEO and transfer to a different ship for reentry (and then refuel the vacuum-Raptor-only ship and send it back to Mars), but that probably adds more complexity than it's worth. For trans-Mars injection, and perhaps even for much of Mars ascent, it may make sense to burn the vacuum Raptors only, for the increased ISP.
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Knowing that a ship will never transit between Earth and LEO is a pretty strong simplifying assumption. The actual waypoint for Starships returning from Mars may be the Moon. Get propellant production going at the Moon and it's a different ballgame. Earth becomes just another destination, and there can be non-Starship vehicles that travel between Earth and Moon, appropriate to whatever they're carrying.
So instead of a LEO space station, create an LMO station. Everyone goes there to transfer to Starships because they're returning to there and being fueled there. No worries about atmosphere, hordes of satellites, the deep gravity well, and so on. Reducing the number of launches from Earth would only be for the better.
There's only one teeny weeny little problem with the plan. Getting propellant production going on the Moon. Right now we're at the "landers falling over on the Moon" stage.
Ben W
Chess Grandmaster (Supervised)
Good point about low lunar orbit being a useful waypoint. I think one of the big difficulties in the short and medium term will be maintenance and/or repair of the fleet there. (Difficult enough in LEO, or even on Earth!) Also not clear if CH4 production will be feasible on the Moon at all. Hydrolox much more likely.
As far as "hordes of satellites", I expect that once Starship is yeeting megatons annually into space, they'll really have to spend some serious effort cleaning up derelict spacecraft (not just theirs) to avoid Kessler Syndrome. Even with the current amount of junk up there, we're on the precipice of a runaway scenario. One worst-case head-on Starship-Starship collision at 34000mph could make LEO unusable for centuries.
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