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Starship / Super Heavy

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Re: Starship / Super Heavy

#291

Post by simonh »

throwaway316943 wrote: post #237
simonh wrote: post #154

Earlier quoted context omitted.

More than that actually, it takes I think 3 tankers to fully top up a Starship in orbit, and the Lunar model needs to go into an elliptical orbit towards the moon and have at least one more top up again before having enough fuel for the rest of the mission.

I thought the full refuel was only necessary for a Mars mission?

It’s interesting. Going to the moon, propulsive my landing, and propulsively taking off and returning to Earth takes more dV than just a boost to Mars. If you think about it boosting to Luna and Mars aren’t much different in dV, but then you have lunar landing and takeoff again to do. Even with a very thin atmosphere, you can still shed the vast majority of your interplanetary velocity with aero braking at Mars.

As a result the Lunar variant actually needs a lot more fuel delivered to it than the Mars version. Even one full refuel in LEO isn’t enough, and it needs to boost part way to an intermediate elliptical orbit and get another top up.

Re: Starship / Super Heavy

#292

Post by morlockabove »

Koiwai wrote: post #287
MartinodF wrote: post #196

Earlier quoted context omitted.

The rocket weighs quite a bit less at the end, having used most of its fuel, so only two engines are needed to land. The engines cannot be throttled down more than ~50% (as all rocket engines), so a third one would add too much thrust. Falcon 9 does the same, relighting 3 engines (out of 9 total) for the boostback burn, 3 for the entry burn and then just 1 for landing.

Thanks for the explanation! it this also the reason why Raptor is (relatively compared to like F-1) small and BFR uses so many of them?

That, and for redundancy. I've heard it's designed so that even if a significant number of engines malfunction, others can be used to compensate.

Re: Starship / Super Heavy

#293

Post by morlockabove »

colechristensen wrote: post #112
mrlonglong wrote: post #21

Earlier quoted context omitted.

What are they going to do with all the brine. It's quite toxic and I don't think it's a good idea to dump that back in the sea.

Dilute it? There’s a whole ocean right there.

If you dump industrial amounts of salt in the ocean, it kills sealife in the immediate area.

Re: Starship / Super Heavy

#294

Post by markonen »

baq wrote: post #207
maccam94 wrote: post #127

Earlier quoted context omitted.

Note that the $2M is to launch a fully loaded (100 tons of payload) Starship into low earth orbit (LEO). Launching it further, such as to the Moon or Mars, requires refueling while in-orbit. I've seen estimates from Musk that it would take 6-7 launches of a tanker variant of Starship to deliver enough fuel to fill an empty Starship (it could be stockpiled in an orbital depot ahead of the main payload launch). So the…

ask any astronomer what they could do with extra $150M per launch and watch them salivate. also, this thing could lift JWST pretty much without that complex unfolding mechanism. genuinely exciting.

I've always wondered whether payloads weren't super-expensive precisely because the launches were, too.

I mean, if you are spending hundreds of millions to launch something, that something better work once up there, right? So you spend 20 years engineering a "perfect" payload, the costs do what they always do, and now you have a billion-dollar payload.

But if a launch was $2M and bookable with a month's lead time, you'd just de-risk the whole thing by having a simple-to-build, likely-to-work payload. Or ten.

(This might not apply to something like the JWST specifically, since even a terrestial mirror of that size is a huge challenge. But I bet a lot of other kinds of science payloads will be built very differently a decade from now.)

Re: Starship / Super Heavy

#295

Post by fbender »

ChuckMcM wrote: post #275
mabbo wrote: post #9

> The fully integrated Starship/Super Heavy launch vehicle will be approximately 400 feet tall and 30 feet in diameter. For reference, the Saturn V rocket from the Apollo program was 363 feet tall. It was 33 ft wide at the first stage, while Starship is 30 ft wide all the way to the top. It's just massive. And it's fully reusable. What a game changer.

Yes it is. Starship, the part that will end up in orbit is longer than the truss section, which is the longest section of the ISS and has the solar panels on it. At the crash sight of SN8 watching the people walk around the wreckage, it gave a good indication of scale.

Starship alone (the orbiter) is 50m. The truss of the ISS is 109m[1] long. While massive, Starship will still be dwarfed by the station (other than planned habitable volume or individual modules/elements).

[1] https://www.nasa.gov/feature/facts-and-figures

Re: Starship / Super Heavy

#296

Post by blackrock »

nickik wrote: post #208
juanbyrge wrote: post #152

Earlier quoted context omitted.

I don’t mean to trivialize what SpaceX is accomplishing, but maybe we are overestimating the degree of difficulty of building rockets in the 21st century, given the advances in technology over the past few decades? With the immense improvement in compute power, materials, accelerometers, welding techniques, etc.. since the 60s, maybe SpaceX was the first to recognize that building rockets is not as hard as it used to…

Well, we actually have a large amount of companies trying to do it. Like 40-60 different companies. Not to mention government projects. Of all of those, only RocketLab has managed to do it, and their rocket is basically as tiny as you can build a orbital rocket. SpaceX did an orbital rocket bigger then RocketLab in 2008. RocketLab doesn't yet have real competition, despite many billions invested. SpaceX at the same t…

Is RocketLab able to 3D print larger rockets?

Re: Starship / Super Heavy

#297

Post by ubertoop »

kybernetikos wrote: post #185
simonebrunozzi wrote: post #172

Earlier quoted context omitted.

Ah, what would be the most common incorrect way to use it? Being a non-native English speaker I'm always fascinated to learn new things like this one.

It's often used for a "trivial or minor fact" but by comparison with planetoid (something like a planet but not a planet) or cuboid (like a cube but not an actual cube) or asteroid (looks like a star but is not a star) or humanoid / android (having the form of a human or man while not actually being one), you can see what the 'correct' usage should be. Trivial fact would perhaps be better as 'factette' or 'microfact'…

I have also heard people use it to describe a "bite sized fact". The "oid" part of the word, for some people, seems to mean "small" or "compartmentalized".

In this incorrect usage of the word, take the following sentence: "Nice little factoid!", could also be written as "Nice little nugget of info!"

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