Water Found Deep Inside the Moon • Hacker News Board

Re: Water Found Deep Inside the Moon

#271

Post by stcredzero » Fri, Aug 25, 2017, 7:26 PM UTC

adrianN wrote: post #269

stcredzero wrote: post #268

Earlier quoted context omitted.

Is it any more amazing than doing an orbital rendezvous?

You brake before getting close to whatever you want to rendevous with. You couldn't brake if you wanted to hit the nozzle of your mass driver to use it for braking.

You brake before getting close to whatever you want to rendevous with.

This makes me question whether you actually understand how orbital rendezvous works. How about as an exercise, you explain why I would say this. Otherwise, I think the resulting conversation would be tiresome and not worth my time.

Re: Water Found Deep Inside the Moon

#272

Post by adrianN » Fri, Aug 25, 2017, 8:20 PM UTC

stcredzero wrote: post #271

adrianN wrote: post #269

Earlier quoted context omitted.

You brake before getting close to whatever you want to rendevous with. You couldn't brake if you wanted to hit the nozzle of your mass driver to use it for braking.

You brake before getting close to whatever you want to rendevous with. This makes me question whether you actually understand how orbital rendezvous works. How about as an exercise, you explain why I would say this. Otherwise, I think the resulting conversation would be tiresome and not worth my time.

How about you, just as an exercise, compare the difference in velocities of the mass driver and the incoming space craft with the difference of velocities of a capsule docking at the ISS.

Re: Water Found Deep Inside the Moon

#273

Post by efefefe » Fri, Aug 25, 2017, 9:28 PM UTC

Iv wrote: post #249

Calm down. From the article: "the glass beads contain only 0.05 percent water." It is much drier than Sahara sand where soil moisture can reach 1%. Dune's scenario would be a piece of cake compared to what you would need to do to feed a colony off of this water. I suspect that energy-wise it would be cheaper to import water from Earth and recycle like crazy.

>Calm down.

It must be tiring to be so logical and parental.

Re: Water Found Deep Inside the Moon

#274

Post by stcredzero » Fri, Aug 25, 2017, 9:33 PM UTC

adrianN wrote: post #272

stcredzero wrote: post #271

Earlier quoted context omitted.

You brake before getting close to whatever you want to rendevous with. This makes me question whether you actually understand how orbital rendezvous works. How about as an exercise, you explain why I would say this. Otherwise, I think the resulting conversation would be tiresome and not worth my time.

How about you, just as an exercise , compare the difference in velocities of the mass driver and the incoming space craft with the difference of velocities of a capsule docking at the ISS.

Ok, you clearly don't understand enough to understand what you don't understand. You don't have to make the velocities or the positions of specific points on the mass driver and the orbit coincide. All you have to do is to make an orbital path coincide with a great circle pathway on the moon. We can already guide spacecraft with this degree of precision. Anyone suggesting that you'd need to make specific point on the mass driver coincide in position and velocity -- that you'd need to brake first -- just doesn't understand what the discussed device is for in the first place. Basically you've just "proved" that you can't land airplanes, because they come in too fast to brake the same 1/10th of a second they touch the tarmac. o_O

If you can't explain my analogy, then I'm just going to conclude you're trolling based on my previously stated disdain for DK syndrome.

Re: Water Found Deep Inside the Moon

#275

Post by valuearb » Fri, Aug 25, 2017, 11:43 PM UTC

neaden wrote: post #121

valuearb wrote: post #117

Earlier quoted context omitted.

The point is it's really hard to impose laws and forms of government on peoples living days or months away from you. Sooner or later they'll want to make their own.

Says who? Plenty of empires had people living that far without rebellions breaking out. Yeah the US rebelled against Britain but Canada, Australia, and a bunch of other places didn't. Hell, most of England was more than a couple days away from London for most of English history without breaking away. Let alone a larger country like China.

How much of the British Empire still reports to Britain?

Re: Water Found Deep Inside the Moon

#276

Post by SAI_Peregrinus » Sat, Aug 26, 2017, 2:12 PM UTC

stcredzero wrote: post #271

adrianN wrote: post #269

Earlier quoted context omitted.

You brake before getting close to whatever you want to rendevous with. You couldn't brake if you wanted to hit the nozzle of your mass driver to use it for braking.

You brake before getting close to whatever you want to rendevous with. This makes me question whether you actually understand how orbital rendezvous works. How about as an exercise, you explain why I would say this. Otherwise, I think the resulting conversation would be tiresome and not worth my time.

The relative speed of two objects docking in orbit is very small. You brake or accelerate as you get close to matching orbits.

The relative speed of a capsule and the mass driver will be very high IF you're using the mass driver to slow down substantially. That's in the definition, you're using it to slow down so the initial relative speed at contact must be high. The higher the speed the less energy you have to waste lowering your orbit (slowing down beforehand). If you're slowing down beforehand enough that your relative speed of contact is low then you don't need the mass driver to brake.

Re: Water Found Deep Inside the Moon

#277

Post by OtterCoder » Sat, Aug 26, 2017, 6:58 PM UTC

Tepix wrote: post #255

OtterCoder wrote: post #230

Earlier quoted context omitted.

That's astoundingly quick. 30-90 days is in the same range as crossing the Atlantic via tall ship. With transfer time that low, it really does seem feasible. The two year gaps are a bit rough, but there are plenty of ways to plan for it.

Nowadays ships cross the Atlantic in less than a week.

Well, if any of these silly EmDrives ever work out, maybe we can get Mars down to that time too.

Re: Water Found Deep Inside the Moon

#278

Post by lgats » Sat, Aug 26, 2017, 11:32 PM UTC

http://i.imgur.com/E4jeTmM.jpg

Re: Water Found Deep Inside the Moon

#279

Post by valuearb » Sun, Aug 27, 2017, 2:25 AM UTC

WalterBright wrote: post #68

rory096 wrote: post #56

Earlier quoted context omitted.

>The 50% figure is from memory, and upon further reflection is probably not quite right, so take it with a grain of salt. You're actually underestimating. Mars has an atmosphere, so spacecraft can use aerobraking to significantly reduce the delta-v required to get there. The moon has no such benefit — propulsion is required all the way to the surface. The advantage of the moon, of course, is that it's not limited to…

You need a far bigger (heavier) craft to get to Mars. You'll need years worth of food, water, air, you'll need radiation shielding, much more space per crewmember, more redundant systems and backups, etc. Look at the size of the Apollo.

You don't need radiation shielding to go to or stay on Mars. The health risk from the excess radiation is moderate, should be a very low priority for an adventurer.

Re: Water Found Deep Inside the Moon

#280

Post by computerex » Mon, Aug 28, 2017, 12:12 PM UTC

nine_k wrote: post #251

danielbarla wrote: post #236

Earlier quoted context omitted.

I'm not too clued up on the topic, but I was under the impression that a lunar elevator would potentially require much longer cables than on Earth (primarily due to the lack of spin of the moon). From the Wikipedia article [1] > There are two points in space where an elevator's docking port could maintain a stable, lunar-synchronous position: the Earth-Moon Lagrange points L1 and L2. L1 is 56,000 km away from the Ear…

This is correct, unlike my assumption of a shorter cable above. OTOH due to lower gravity, the tensile strength required is still much lower. To quote the very article you lonked: > the engineering requirements for constructing a lunar elevator system can be met using currently available materials and technology.

So what you are saying is that a space elevator is theoretically possible. I think that's step 0 in building something. Being theoretically possible is the most basic prerequisite.

Just because something is theoretically possible doesn't mean it's feasible or practical to build in real life. For example, we have known that it's theoretically possible to build vacuume sealed trains, aka the hyperloop, since before the first airplane took flight. And yet whilst you see planes fly everywhere, you don't see any vacuum sealed trains.