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Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

theguardian.com

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Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#211

Post by eru »

imtringued wrote: post #168
simonh wrote: post #167

Earlier quoted context omitted.

True, but in orbit refuelling means 3 or 4 additional refuelling launches, so now your cost per kg is back up to a few thousand $ per kg again. Still cheap for Ceres though.

Yeah, orbital refueling doesn't change the rocket equation unless you can manufacture fuel in space. The only benefit is that you don't need a bigger rocket.

You are right.

Manufacturing fuel in space would be the way to go.

Or eg have giant solar panels in orbit that power a laser to shine at your spaceships. Either to propel them directly, or to transmit power for their ion thrusters etc.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#212

Post by HourglassFR »

zajio1am wrote: post #198
lopmotr wrote: post #175

Earlier quoted context omitted.

You really shouldn't put that 0.15 on the end. The numbers weren't that accurate to begin with so it gives the false impression that those digits mean something. I hope it doesn't feel like I'm picking on you but I can't help myself saying something because this is a pet peeve of mine. Rounding appropriately is taught in physics class at school but I think most people don't learn that or think it doesn't apply outsid…

Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value and when the accuracy is relevant, it should be mentioned explicitly (or looked for in the original source). Numeric presentation is just too vague way to represent such complex issue as accuracy. Not rounding values after conversion has an advantage that it does not change the meaning of the claim, while rounding…

> Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value and when the accuracy is relevant, it should be mentioned explicitly (or looked for in the original source). Numeric presentation is just too vague way to represent such complex issue as accuracy.

Of course one should assume something about the acccuracy from the number of displayed digits. It's a pretty fundamental concept in physics or even engineering. You can argue that it is just a convention but then again so are numbers in the first place. When writing down a number you will have to make a choice on how many digits to write down (even if its just zeroes), so we might as well use that to convey some meaning. Yes it does not always suffice and so we can use a more elaborate notation when needed, but by default it is a useful convention.

> Not rounding values after conversion has an advantage that it does not change the meaning of the claim, while rounding requires evaulating assumptions of the original claim to ensure it is done properly.

In other words, don't try to understand the claim and just compute. It can make sense in some context but I don't generally think it is the right approach.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#213

Post by valuearb »

walrus01 wrote: post #170
valuearb wrote: post #126

Earlier quoted context omitted.

The Space Shuttle payloads to LEO cost $40,000 per pound. Before SpaceX commercial launch payloads cost $5,000 to $10,000 per pound. Falcon 9 payloads cost around $1,500 per pound. Falcon Heavy payloads cost around $1,100 per pound. Starship payloads will cost between $100 and $500 per pound. It will be able to lift at least 100 tons to orbit. And using in orbit refueling, it will be able to accelerate that 100 ton p…

I am hopeful that Starship will really achieve those figures, but I am also skeptical... I'll believe it when I see it being done. That's still not cheap enough to do lander/surface manipulation science in the asteroid belt without significant philanthropic or government funding. At $500/pound, if a Ceres unmanned probe lander with drill/melting apparatus weighs 15000 kg when placed in low earth orbit (before whateve…

Starship will launch larger probes to Ceres than we’ve sent to Mars, for a lower launch cost. We will do what we’ve done on Mars.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#214

Post by [deleted] »

gizmo686 wrote: post #105
Balgair wrote: post #102

Earlier quoted context omitted.

That neutron star story is wild . Hard recommendation to read. One point I have with Baxter is that his premises are just bananas, but the people acting in them are pretty recognizable. To be fair, if the characters were also nutter-butter, no one would read it, as it wouldn't be a story anymore, just a strangely formatted research paper. https://en.wikipedia.org/wiki/Flux_(novel)

For another life on neutron star: Dragons Egg, Robert L. Forward

[deleted]

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#215

Post by diffeomorphism »

zajio1am wrote: post #198
lopmotr wrote: post #175

Earlier quoted context omitted.

You really shouldn't put that 0.15 on the end. The numbers weren't that accurate to begin with so it gives the false impression that those digits mean something. I hope it doesn't feel like I'm picking on you but I can't help myself saying something because this is a pet peeve of mine. Rounding appropriately is taught in physics class at school but I think most people don't learn that or think it doesn't apply outsid…

Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value and when the accuracy is relevant, it should be mentioned explicitly (or looked for in the original source). Numeric presentation is just too vague way to represent such complex issue as accuracy. Not rounding values after conversion has an advantage that it does not change the meaning of the claim, while rounding…

> Or perhaps one should not assume anything about accuracy just from the numeric presentation of the value

One common convention is that the value is written in a way that matches the accuracy. For example, you would never write 73.458 +/- 0.1 because the last digits are meaningless given the accuracy. Similarly, if you measure distances with a tape and round you inputs to the nearest cm, you wouldn't give areas in square mm. In turn, if you give the area in mm^2, then this implies that you think your error bounds are precise enough for this to make sense.

So it is not about readers not "assuming things" but a pretty explicit, though wrong, claim of precision on part of the previous post.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#216

Post by valuearb »

simonh wrote: post #167
valuearb wrote: post #126

Earlier quoted context omitted.

The Space Shuttle payloads to LEO cost $40,000 per pound. Before SpaceX commercial launch payloads cost $5,000 to $10,000 per pound. Falcon 9 payloads cost around $1,500 per pound. Falcon Heavy payloads cost around $1,100 per pound. Starship payloads will cost between $100 and $500 per pound. It will be able to lift at least 100 tons to orbit. And using in orbit refueling, it will be able to accelerate that 100 ton p…

True, but in orbit refuelling means 3 or 4 additional refuelling launches, so now your cost per kg is back up to a few thousand $ per kg again. Still cheap for Ceres though.

A fully expended Falcon 9 launch costs around $50M. A partially reusable Falcon 9 launch costs around $25M.

Starship will be fully reused. It will launch a 5x larger payload than the partially reusable Falcon 9 at a lower launch cost. So somewhere in the $5M to $20M range.

Starship can be fully refueled in LEO with eight tanker flights, Even at $20m per flight, that costs no more than the Atlas V that just launched perseverance to Mars, only with 40 times more mass.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#217

Post by valuearb »

imtringued wrote: post #168
simonh wrote: post #167

Earlier quoted context omitted.

True, but in orbit refuelling means 3 or 4 additional refuelling launches, so now your cost per kg is back up to a few thousand $ per kg again. Still cheap for Ceres though.

Yeah, orbital refueling doesn't change the rocket equation unless you can manufacture fuel in space. The only benefit is that you don't need a bigger rocket.

Orbital refueling absolutely changes the rocket equation in a huge way. The standard NASA human Mars plan involves a mega rocket large enough to lift the humans and their supplies in one shot from earth, along with the fuel to get to Mars and the fuel to get back.

Starship enters LEO with empty fuel tanks, meaning it can lift much more payload per pound of fuel. Being refueled in orbit is cheap, because fully reusable flights are cheap. And for Mars, Starship only needs enough fuel to get there, it can make fuel on Mars. That means it doesn’t have to carry even more fuel to fly the return fuel to Mars.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#218

Post by shadowprofile77 »

Nitpicking, I know, but to call it "Planet Ceres" in the title is more than a bit wrong. This is a dwarf planet at best and is also often classified as a really big asteroid (the only one in the asteroid belt that's rounded by its own gravity). If even the much larger Pluto can't get the "Planet" title, Ceres hardly deserves to be called that in a headline from a major newspaper.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#219

Post by valuearb »

rbanffy wrote: post #183
imtringued wrote: post #168

Earlier quoted context omitted.

Yeah, orbital refueling doesn't change the rocket equation unless you can manufacture fuel in space. The only benefit is that you don't need a bigger rocket.

We'll eventually get to the point where Starship-like rockets only ferry people, cargo, and, maybe, propellant to LEO for transfer to spaceships that don't need to go deep into any gravity well. These ships will then take you to orbit around your destination so you can board another shuttle to the surface.

That would be massively inefficient for travel to Mars, because you can Aerobrake to land and make fuel on Mars for your return.

Re: Planet Ceres is an 'ocean world' with sea water beneath surface, mission finds

#220

Post by ColeyG »

JohnBooty wrote: post #140
marcusverus wrote: post #92

Earlier quoted context omitted.

>They conclude that the mantle transition zone--410 to 660 km below the Earth's surface--acts as a large reservoir of water. Sadly there will be no eyeless space whales in our basement, given that the temperature at that depth on Earth is around 2,000° Celsius.

eyeless FIRE whales

I like this line of thinking way better lol
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