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Starship Prototype Unveiled

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Re: Starship Prototype Unveiled

#231

Post by doomlaser »

rjf72 wrote: post #224
doomlaser wrote: post #186

Earlier quoted context omitted.

I'm no rocket scientist, so bear that in mind, but something has been bugging me about the flight paths for this vehicle [0]. It has to make some very large, specific orientation changes several times during descent, using the heat shield on one side of the vehicle, and then only rotating to upright orientation in the lower atmosphere, after quite a lot of falling sideways. The orientation maneuvers seem much more co…

A lot of the complexity is hidden in the second video. It's the exact same deal, it just doesn't look like it. In particular those innocuous 'waffle irons' on the side play an incredibly important role. You miss the scale in the video thanks to how big everything is. Those fins are each 4' x 5' large. And each of them can independently yaw/pitch/roll. And of course the exact angle that the rocket is at when it fires…

> Do that exact maneuver on Earth and you'd get an 'unplanned rapid disassembly' during reentry thanks to the thicker atmosphere

That is the planned Earth re-entry maneuver. Belly first almost all the way down, using the heat shield on one side, then flipping and completely re-orienting near the ground so that the vehicle is pointed upwards, and then the final burn to land upright.

But it does make sense that this path has arisen from a secondary capability: to land on planets or moons with less atmosphere. It still doesn't make me less nervous about their ability to pulli it off reliably. Here's hoping.

Re: Starship Prototype Unveiled

#232

Post by semi-extrinsic »

avar wrote: post #68
hoorayimhelping wrote: post #20

380s for ISP for the Raptor vacuum engine seems durn good, considering the tradeoffs between hydrogen and methane. The most efficient engines we've flown, the RL-10 [0] (used on the Delta IV and Atlas rockets as part of the Centaur Upper Stage) and the RS-25 [1], (the Space Shuttle Main Engine) get around 450-460s for their specific impulse. These engines use liquid hydrogen and liquid oxygen. The issue with liquid h…

> This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level. They're optimizing for "real" reusability, as in eventually aiming for airline-like turnarounds. None of the earlier engines you noted were reusable except the RS-25, and given how long it took to turn the Shuttle around one coul…

> But raw performance on a single trip doesn't matter much if you can just deliver the same payload in two trips to orbit instead.

Except that you're doubling the cost if you have to do two trips.

Re: Starship Prototype Unveiled

#233

Post by test6554 »

semi-extrinsic wrote: post #232
avar wrote: post #68

Earlier quoted context omitted.

> This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level. They're optimizing for "real" reusability, as in eventually aiming for airline-like turnarounds. None of the earlier engines you noted were reusable except the RS-25, and given how long it took to turn the Shuttle around one coul…

> But raw performance on a single trip doesn't matter much if you can just deliver the same payload in two trips to orbit instead. Except that you're doubling the cost if you have to do two trips.

You just need twice as much methane. So just have PF Chang’s catered and you’re back in orbit in a couple hours.

Re: Starship Prototype Unveiled

#234

Post by cbhl »

semi-extrinsic wrote: post #232
avar wrote: post #68

Earlier quoted context omitted.

> This is basically how SpaceX seems to operate: rather than optimizing a single part of the system (like trying to get the most efficient engine), they try to optimize from a systems level. They're optimizing for "real" reusability, as in eventually aiming for airline-like turnarounds. None of the earlier engines you noted were reusable except the RS-25, and given how long it took to turn the Shuttle around one coul…

> But raw performance on a single trip doesn't matter much if you can just deliver the same payload in two trips to orbit instead. Except that you're doubling the cost if you have to do two trips.

If you throw away the rocket, sure, you're doubling the cost if you have to do trips.

If the rocket is reusable, then the vehicle cost gets amortized over the total number of trips, and the per-trip cost gets closer to just the cost of fuel (hopefully at least an order of magnitude less than a new vehicle+fuel on each flight).

Re: Starship Prototype Unveiled

#235

Post by test6554 »

paragraft wrote: post #144
35787 wrote: post #119

Earlier quoted context omitted.

Wow what an incredibly substantive comment. I remember pretty clearly he said that there would be a single seam weld. Maybe I’m remembering wrong. Or maybe they’ll seam weld multiple rolls into a really wide roll and the only weld required to turn the final roll into the shell is that final hotdog weld.

I think the idea's to go like a Pringles can, with a spiraling single seam.

If getting out of your yoga pants is like opening a can of biscuits, then making a starship is like putting your yoga pants back on...

Re: Starship Prototype Unveiled

#236

Post by bryanlarsen »

bobsil1 wrote: post #220
starpilot wrote: post #194

Earlier quoted context omitted.

The Model X doors are terrible. It's an SUV that you can't put a roof rack on. Does seem like a case of geek myopia over usability.

Or… optimized for a different case (ease of access for small kids).

Sliding minivan doors get you both.

Re: Starship Prototype Unveiled

#237

Post by elif »

kwk1 wrote: post #230
CriticalCathed wrote: post #215

Earlier quoted context omitted.

I don't know about his general claim, but a detail within his comment is right. Smaller grain size leading to stronger material -- this is a result of more grain boundaries as the scale of the grain goes down. Hall-Petch strengthening.[0] A secondary effect is that with smaller grains oriented in random directions the metal is more resistant in general from stresses in all directions; whereas with larger grains you t…

The GP comment is claiming the opposite--that larger grain size results in a stronger material.

Actually I said strong is too ambiguous of a term to use. For instance, do you want it "strong" enough to not bend under x force at y temperature, or do you want it "strong" enough to bend rather than shear at z force?

It is more practical to discuss the hardness and ductility at specific temperatures, as well as its ability to keep its carbon content under those temperature conditions.

Re: Starship Prototype Unveiled

#238

Post by test6554 »

martythemaniak wrote: post #21

That was a very dense an informative presentation last night, but I think the main take away is that rapid reusability is a game changer. In fact, game-changer is probably an understatement, basically every intuition and rule-of-thumb we have about space launches and travel will have to be rethought. And this will be true even of SpaceX falls well short of meeting their stated targets (2020 orbit, 150t capability, mu…

I always figured I would need to shell out $250K for the privilege, but I’d probably be better off investing that in asteroid mining companies.

Re: Starship Prototype Unveiled

#239

Post by test6554 »

vardump wrote: post #65
newguynewguy wrote: post #60

Earlier quoted context omitted.

Aren't there some pretty serious health and ecological problems with such large-scale microwave transmission?

Perhaps, but several orders of magnitude less bad than health and ecological problems from sunlight.

How can you get more power from an orders of magnitude less powerful beam than from an orders of magnitude more powerful beam (sunlight) over an equal surface area? And if you can’t, why do it? This blows my mind.

Re: Starship Prototype Unveiled

#240

Post by fluffything »

strainer wrote: post #159
elif wrote: post #92

Earlier quoted context omitted.

I know there are 1000 of them 100x smarter than me at all of this, but I have my doubts that the specs for "cold rolled" stainless will hold up after tens of re-entries, as it is effectively being tempered over and over.

From the sounds of it steel structure can basically handle much greater temperatures routinely and also even more in rare situations that might mean retiring the ship afterward but not losing everything. In his presentation Elon says that aluminum alloy or carbon fiber structure is basically done for at 300 to 400 Celsius, well that's the temperature at which stainless steel can just begin to get conditioned by heat,…

What do you mean by Handle?

Steel won't melt at 300-400 Celsius but "handling" those temperatures for 10 minutes will change the properties of the material, possibly by a lot, so you don't need "melting" for structural collapse (Twin Towers style).

As the GP says, if you put cold rolled steel, which has an elastic yield strength of >1500 MPa, at 300-400 Celsius, then it is only a matter of time (30-120 min) till the elastic yield strength sinks to 500 MPa or less.

So either this is a single use device, or the steel isn't reaching temperatures over 250 Celsius, or the steel isn't cold rolled but is a low strength steel instead (although that would have other problems).

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