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Re:Water Found Deep Inside the Moon by andars on Thursday August 24, 2017 @01:41PM (#15092255)
In terms of distance, sure.

In terms of delta-v, the budget for the moon is upwards of 50% that for Mars.

EDIT: The 50% figure is from memory, and upon further reflection is probably not quite right, so take it with a grain of salt. I just wanted to point out that distance is not the only relevant metric.

Re:Water Found Deep Inside the Moon by rory096 on Thursday August 24, 2017 @02:03PM (#15092486)
>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 transfer windows every two years. If there's an emergency or resupply is needed (or you just want to expand the mission), another lander can be sent at any time. (With some restrictions, like hitting your desired landing spot and making sure the sun wasn't in the Apollo crews' eyes at landing. But regardless, no longer than 28 days between windows.)

Re:Water Found Deep Inside the Moon by WalterBright on Thursday August 24, 2017 @02:31PM (#15092691)
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.

Re:Water Found Deep Inside the Moon by Robotbeat on Thursday August 24, 2017 @06:53PM (#15094765)
Years? Absolutely not. Transfer can be done in about 90 days, less (30 days) if you pursue aggressive entry, high orbit refueling, and nuclear thermal propulsion. Assuming you're settling the place and not just doing flags and footprints, transfer time is the important part.
Re:Water Found Deep Inside the Moon by OtterCoder on Friday August 25, 2017 @01:40AM (#15096367)
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.
Re:Water Found Deep Inside the Moon by Tepix on Friday August 25, 2017 @11:29AM (#15099120)
Nowadays ships cross the Atlantic in less than a week.
Re:Water Found Deep Inside the Moon by OtterCoder on Saturday August 26, 2017 @02:58PM (#15106837)
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 by foxylad on Thursday August 24, 2017 @11:41PM (#15095941)
For the journey, yes. But for permanent settlement, in both cases you'll need of the order of years-worth of supplies while you become self-sufficient.

Back on-topic, the discovery of water on the moon makes this more achievable there; otherwise Mars's resources might have actually meant less resources were required.

Re:Water Found Deep Inside the Moon by adrianN on Friday August 25, 2017 @12:31PM (#15099757)
You don't have to send all the supplies at once though (you shouldn't actually). You can send many small missions, each providing some parts of a Mars base before sending any humans. See for example the Mars Direct plan by Zubrin: https://en.wikipedia.org/wiki/Mars_Direct
Re:Water Found Deep Inside the Moon by jhgb on Friday August 25, 2017 @12:50PM (#15099999)
But the presence of water on the Moon is more limited than the presence of CO2 and H2O on Mars. That could be significant for self-sufficiency. Especially if we could find a way to make plastics from CO2 and H2O in a reasonably small mobile device. Just grow your colony out of the stuff you suck out for the atmosphere...
Re:Water Found Deep Inside the Moon by valuearb on Saturday August 26, 2017 @10:25PM (#15108750)
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 by tjmojo on Thursday August 24, 2017 @03:47PM (#15093392)
Shared this video[1] about the same topic above[2]

[1] https://www.youtube.com/watch?v=h2nqgKL2JQU [2] https://news.ycombinator.com/item?id=15093353

Re:Water Found Deep Inside the Moon by valuearb on Thursday August 24, 2017 @04:09PM (#15093625)
The aerobraking advantage only works getting there, not coming back.
Re:Water Found Deep Inside the Moon by jacobush on Thursday August 24, 2017 @04:44PM (#15093884)
ACKSHULLY - aerobraking on Mars is a chore. The atmosphere is dense enough to burn you to a crisp, thin enough it won't help you slow down - much.

Look at the marvel that is the Skycrane. Not needed for the Moon.

Re:Water Found Deep Inside the Moon by rory096 on Thursday August 24, 2017 @05:02PM (#15094027)
>thin enough it won't help you slow down - much.

No. It's thin enough you can't land with parachutes alone. It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit.

Is landing on Mars more complex than a thick atmospheric landing on parachutes or an exoatmospheric landing on propulsion only? Yes. But the atmosphere still saves you a lot of delta-v.

[0] https://mars.jpl.nasa.gov/mgs/sci/aerobrake/SFMech.html

Re:Water Found Deep Inside the Moon by keenerd on Thursday August 24, 2017 @05:40PM (#15094287)
> It's still enough that Mars Global Surveyor used it to make up a 1,250 m/s delta-v deficit.

It took MGS 15 months (not counting delays) of aerobraking to do that. MGS only weighed 1000kg too. Maybe it could work for shipping large, pre-assembled, empty hab modules to Mars before people get there. (Low density, higher drag, no rush.) But not practical for actual human bodies or even resupply since the Hohmann transfer takes a mere 8.5 months. Adding an aerobraking maneuver could easily triple the transit time.

Re:Water Found Deep Inside the Moon by simonh on Thursday August 24, 2017 @06:41PM (#15094695)
It only took that long because MGS was aerobraking into orbit and wasn't designed to survive the stress of lower atmosphere turbulence, so only used the uppermost layer of the atmosphere for braking. If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do.

Surface probes do direct descent trajectories. There is no extended series of repeated braking passes. You do it in one go.

Re:Water Found Deep Inside the Moon by dragonwriter on Thursday August 24, 2017 @06:48PM (#15094737)
> If your going to land, obviously you get to use all the atmosphere and also can use parachutes. Something a problem braking into orbit can't do.

Also, you can use lithobraking.

Re:Water Found Deep Inside the Moon by niftich on Thursday August 24, 2017 @04:49PM (#15093927)
For a dramatic coverage of this exact subject, I highly recommend 'Curiosity's Seven Minutes of Terror' [1] from NASA JPL.

[1] https://www.jpl.nasa.gov/video/details.php?id=1090; or on Youtube: https://www.youtube.com/watch?v=h2I8AoB1xgU

Re:Water Found Deep Inside the Moon by Robotbeat on Thursday August 24, 2017 @06:54PM (#15094768)
Note this is before SpaceX proved supersonic retropropulsion works just fine. Atmosphere is now a huge asset for Mars EDL.
Re:Water Found Deep Inside the Moon by Robotbeat on Thursday August 24, 2017 @06:51PM (#15094758)
7 minutes of terror is a fantastic video, but that line in it always bugged me. Atmosphere is an enormous asset for Sending large payloads to Mars now that we know supersonic retropropulsion works just fine.
Re:Water Found Deep Inside the Moon by valuearb on Thursday August 24, 2017 @04:08PM (#15093610)
Re:Water Found Deep Inside the Moon by hutzlibu on Thursday August 24, 2017 @02:46PM (#15092844)
BUT ... getting from the moon back to earth is very easy and fast. From the mars not so much.
Re:Water Found Deep Inside the Moon by kurthr on Thursday August 24, 2017 @07:23PM (#15094942)
However, you might use a space elevator at L1 or L2 (or both) that allow capture of HEO or launch or inter-system vehicles with only efficient high impulse rocket motors.

Note that you could use Spectra/Kevlar or other common high strength materials with a taper ratio of only 4:1 with a lunar elevator. It might take "only" ~50 tons of spectra to hang the weight and allow lifts of a 1000kg or so... its much more doable than earth or mars.

https://en.m.wikipedia.org/wiki/Lunar_space_elevator

Re:Water Found Deep Inside the Moon by zamalek on Thursday August 24, 2017 @01:45PM (#15092295)
It makes much more sense to use the moon as a stepping rock. At least my KSP experience has taught me that :)
Re:Water Found Deep Inside the Moon by TomK32 on Thursday August 24, 2017 @01:58PM (#15092434)
Every experienced KSP player uses Minmus of course, not the Mun.
Re:Water Found Deep Inside the Moon by Dodgeit on Thursday August 24, 2017 @02:20PM (#15092609)
My experience in KSP usually ends with an explosion
Re:Water Found Deep Inside the Moon by andyfal12 on Thursday August 24, 2017 @04:29PM (#15093783)
Yes, so those two metrics boil down into time cost and fuel cost? Any other costs for just the transit?
Re:Water Found Deep Inside the Moon by Robotbeat on Thursday August 24, 2017 @06:49PM (#15094746)
Nope. Mars is actually lower than the Moon due to atmosphere.