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SpaceX test flight of Starship SN-5 [video]

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Re: SpaceX test flight of Starship SN-5 [video]

#361

Post by cookingrobot »

ncmncm wrote: post #319
Jach wrote: post #217

Earlier quoted context omitted.

Easier is a downside.

It would be smart to demonstrate ability to do thing A before attempting thing B that is 1000 times harder. With any luck, things you learn actually doing A, and then A' that is 10 times harder, and then A'' that is 100 times harder, will all turn out to be useful, even necessary, in tackling B. Failure is always an option, but there is no point in choosing it at the outset.

Maybe SpaceX should practice colonizing in Antarctica. They could fly all their gear in on Starships and do a dress rehearsal.

Re: SpaceX test flight of Starship SN-5 [video]

#362

Post by bryanlarsen »

credit_guy wrote: post #353
sobani wrote: post #346

Earlier quoted context omitted.

> the propellent is O2 and CH4 [1] > that results in CO2 and CH4 The chemical reaction of O2 + CH4 -> CO2 + CH4 does not compute. More likely is the reaction 2 O2 + CH4 -> CO2 + 2 H2O. So no methane emissions, that's the actual fuel. Only CO2 (and water) emissions.

Sorry, I skipped some steps in my calculation. The chemical reaction is indeed CH4 + 2 O2 -> CO2 + 2 H2O. So, for each 16 grams of CH4 you get 64 grams of O2, that's a stoichiometric mass ratio of 1:4. The fuel ratio for the Raptor engine is 22:78, according to Elon Musk's tweet. So, for each 100 g of propellant mixture you get 19.5 g of CH4 to burn using 78 g of O2 and you are left with 2.5 g unburned CH4. I simply…

From what I've heard there is a significant fraction of carbon monoxide in the exhaust, so there will be a lot less CH4 in the exhaust than you have calculated. CO is only a weak greenhouse gas.

Re: SpaceX test flight of Starship SN-5 [video]

#363

Post by credit_guy »

bryanlarsen wrote: post #362
credit_guy wrote: post #353

Earlier quoted context omitted.

Sorry, I skipped some steps in my calculation. The chemical reaction is indeed CH4 + 2 O2 -> CO2 + 2 H2O. So, for each 16 grams of CH4 you get 64 grams of O2, that's a stoichiometric mass ratio of 1:4. The fuel ratio for the Raptor engine is 22:78, according to Elon Musk's tweet. So, for each 100 g of propellant mixture you get 19.5 g of CH4 to burn using 78 g of O2 and you are left with 2.5 g unburned CH4. I simply…

From what I've heard there is a significant fraction of carbon monoxide in the exhaust, so there will be a lot less CH4 in the exhaust than you have calculated. CO is only a weak greenhouse gas.

That is very interesting. Do you happen to have a link? I'm not doubting you, I think you are right, but a link that goes into this type of detail would be a very interesting one to read.

Re: SpaceX test flight of Starship SN-5 [video]

#364

Post by bryanlarsen »

credit_guy wrote: post #363
bryanlarsen wrote: post #362

Earlier quoted context omitted.

From what I've heard there is a significant fraction of carbon monoxide in the exhaust, so there will be a lot less CH4 in the exhaust than you have calculated. CO is only a weak greenhouse gas.

That is very interesting. Do you happen to have a link? I'm not doubting you, I think you are right, but a link that goes into this type of detail would be a very interesting one to read.

I probably heard that here: https://everydayastronaut.com/rocket-pollution/

Otherwise it would have been in a comment on an Eric Berger Ars Technica article.

Re: SpaceX test flight of Starship SN-5 [video]

#365

Post by mpweiher »

chrisjc wrote: post #233
mpweiher wrote: post #128

Earlier quoted context omitted.

> game changer Absolutely, and the quantitative analysis is just stunning. In 2018 all of humanity launched a total of 111 payloads into space (out of 114 attempts). At around 5t per launch, that would be 555 tons. Starship is supposed to have a payload to LEO of > 100 tons. So 5-6 launches would handle all of that, by weight. But SpaceX says their goal is to fly these up to 3 times a day. So let's assume they can do…

Perhaps a stupid and naive question, but is there even the demand to lift that much mass into orbit? I may just be lacking in imagination. Obviously most of that mass would have to leave orbit in order for it not to end up looking like an LA freeway in rush hour. edit: i guess propellant/fuel would be one of the heaviest and important payloads we would need to get up there.

> demand to lift that much mass into orbit?

Well, 1 million people ain't going to get to Mars by themselves[1].

But once you have that sort of capacity, at those sorts of prices, many things that are now unthinkable become very possible and possibly useful.

Asteroid mining has been mentioned. Putting huge telescopes into orbit or the Lagrange points. How about a nice and big radio-telescope on the far side of the moon, where there is no EM interference. Or maybe even further out? How about some very, very long baseline-interferometry[2]?

Put manufacturing in space. There appear to be some useful materials that can only be made in low-gravity environments, but currently the Price is not Right™[3]. Bezos wants to put large space habitats into orbit instead [4]

Others have mentioned Starlink, with up to 12000 satellites. Nowadays they're talking about 42K satellites.[5]

Space-based solar power might become feasible[6]. Maybe put up a sunshade[7] to control global warming.

How about some manned deep-space probes? Maybe with some Vasimir rockets[8], a nuclear reactor and lots of reaction mass.

We are so conditioned to think that anything space has to be small, super-lightweight and super-high-performance/expensive that it's really kind of hard to think about the consequences of those constraints no longer applying.

And of course tourism, like the already-announced circumlunar flight[9], space habitats etc.

Think big!

[1] https://www.syfy.com/syfywire/elon-musk-mars-colonization (or just google it)

[2] https://en.wikipedia.org/wiki/Very-long-baseline_interferome...

[3] https://en.wikipedia.org/wiki/Space_manufacturing#Materials_...

[4] https://www.businessinsider.com/jeff-bezos-proposes-floating...

[5] https://observer.com/2019/10/spacex-elon-musk-starlink-satel...

[6] https://en.wikipedia.org/wiki/Space-based_solar_power

[7] https://en.wikipedia.org/wiki/Space_sunshade

[8] https://en.wikipedia.org/wiki/Variable_Specific_Impulse_Magn...

[9] https://en.wikipedia.org/wiki/DearMoon_project

Re: SpaceX test flight of Starship SN-5 [video]

#366

Post by mpweiher »

baq wrote: post #241
chrisjc wrote: post #233

Earlier quoted context omitted.

Perhaps a stupid and naive question, but is there even the demand to lift that much mass into orbit? I may just be lacking in imagination. Obviously most of that mass would have to leave orbit in order for it not to end up looking like an LA freeway in rush hour. edit: i guess propellant/fuel would be one of the heaviest and important payloads we would need to get up there.

starlink/oneweb/similar constellations, assuming US folks really hate comcast as much as they say on the intertubes. these are up to 12k sats with very short (couple years?) life time, so regular flights will be necessary to keep the fleet at desired capacity. this beast can lift i-don't-even-know-how-many hundreds of birds in one go.

One Starlink satellite is apparently 250 kg at this time. They currently get sent up using Falcon 9, which can lift 15t to LEO when reusable, so that checks out.

At 100t, that would be 400 a pop.

Re: SpaceX test flight of Starship SN-5 [video]

#367

Post by maccam94 »

jcun4128 wrote: post #329
HPsquared wrote: post #324

Earlier quoted context omitted.

Things have different scaling laws. Very large rocket engines might not be practical for a range of reasons: wall thickness required to contain the high pressures (this is probably a big one) combined with the temperatures, combustion instability, controllability, and general ability to manufacture. Why are elephants and ants differently shaped? Another example is piston engines: large ones generally have lots of (re…

I never quite got the Orion(nuclear?) engine design eg. is it literal "nuclear explosions" or just using nuclear as a heat source. I think they push fluid through the bells, maybe other materials(like ceramic) for the larger nozzles... can they use magnetic field to contain heat... probably not assumes it's ionized or something ha... heat still goes through magnetism. I got it, active heat destructive interface ha.

Nuclear thermal rockets are much more interesting IMO because they were actually viable and in development until Nixon killed them for no good reason. They're coming back now though.

https://en.wikipedia.org/wiki/NERVA

https://spacenews.com/momentum-grows-for-nuclear-thermal-pro... (2019)

Re: SpaceX test flight of Starship SN-5 [video]

#368

Post by ben_w »

nickik wrote: post #358
ben_w wrote: post #349

Earlier quoted context omitted.

Self driving cars done right will be able to do full speed while literally , not metaphorically, touching bumpers. Traffic jams with human drivers happen spontaneously when the cars get close enough that overcompensation turns into a negative spiral.

So in the city of the future you gone have 1000s of self driving cars going full speed threw the city? It makes much more sense to open up the city for people and ban cars for the most part. Move the transportation under ground.

Please, millions.

The roads are already there, electric cars are quiet, road trains are even more efficient.

I am no fan of American city design, having half encircled Davis CA on foot, having found the suddenly-terminating sidewalks in Salt Lake City, and having walked the really boring route from San Jose railway station to the hotel in the top left corner of the Apple Maps icon.

(NYC is surprisingly pedestrian friendly though).

Re: SpaceX test flight of Starship SN-5 [video]

#369

Post by nickik »

ben_w wrote: post #368
nickik wrote: post #358

Earlier quoted context omitted.

So in the city of the future you gone have 1000s of self driving cars going full speed threw the city? It makes much more sense to open up the city for people and ban cars for the most part. Move the transportation under ground.

Please, millions. The roads are already there, electric cars are quiet, road trains are even more efficient. I am no fan of American city design, having half encircled Davis CA on foot, having found the suddenly-terminating sidewalks in Salt Lake City, and having walked the really boring route from San Jose railway station to the hotel in the top left corner of the Apple Maps icon. (NYC is surprisingly pedestrian fri…

In Europe we are already trying to make more space for pedestrians specially around the city center. The value of the land above ground is incredible. Freeing up those spaces from cars makes sense and is incredibly nice.

Re: SpaceX test flight of Starship SN-5 [video]

#370

Post by peter303 »

martythemaniak wrote: post #205

I really love the out-in-the-open development process. It doesn't cost SpaceX anything, yet they attract lots of internet media where people set up streams, discuss progress etc. The next year should be pretty exciting as they develop things further. Starship has a number of big innovations, which are: - the raptor engine. This was developed behind closed doors and is sort of finished. We won't see much of it, but it…

SpaceX using $3.6 billion investors money to build Starship.

It will probably circle the Moon before NASA SLS.

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