Practical propulsion methods for manned interplanetary travel

[K^2]

Right. If you are seriously considering ice-mining, you have to be looking at objects beyond the Sol's frost line, which is located about 2.7AU. That excludes moons of Mars, but does include a large portion of the Asteroid Belt. There are plenty of objects there, including some rather large ones, that are bigger than Phobos, at least as easy to get to, and are likely to contain large quantities of water ice. (e.g. 65 Cybele)

[Headhunter09]

Right. If you are seriously considering ice-mining, you have to be looking at objects beyond the Sol's frost line, which is located about 2.7AU. That excludes moons of Mars, but does include a large portion of the Asteroid Belt. There are plenty of objects there, including some rather large ones, that are bigger than Phobos, at least as easy to get to, and are likely to contain large quantities of water ice. (e.g. 65 Cybele)

Good point. Although if NASA does develop asteroid-moving technology within the next 10 years like they're planning, we might be interested in smaller targets in the Belt.

[Soda Popinski]

Pretty sure asteroid captures that NASA is looking at are only near Earth asteroids. Probably not in the asteroid belt.

[LordOfTheOrbits]

Manned interplanetary travel is difficult, especially because of the launch windows. If you want to go to the mars and then go back to earth without waiting months for a transfer window, you have to use a special window that occurs pretty much every 15 years. The next such window is 2021, but we probably won't have the technology to do a manned landing with return then, but we may be doing a manned flyby.

Bringing enough fuel for return is also a challenge which SpaceX wants to solve by extracting methane and liquid oxygen(I think it was those ones) from Mars, so they can use that as fuel for their way back home.

Another difficulty is bone decay and the human body adapting to no gravity. This could be solved by using a big centrifuge which simulates gravity, but that would be pretty hard to launch into space, and there would be some other difficulties with this.

[Soda Popinski]

Another difficulty is bone decay and the human body adapting to no gravity. This could be solved by using a big centrifuge which simulates gravity, but that would be pretty hard to launch into space, and there would be some other difficulties with this.

I suspect the bone density loss thing wouldn't be such a problem if the trip is less than 9 months or so. From what I understand (listening to Startalk podcast), with their exercise regimen, it can be kept in check fairly well. Unlike on the ISS, where the astronauts are busy all day doing scientific experiments brought up by the latest cargo ship, astronauts going to Mars should have more time dedicated to exercise. You've got some Russian cosmonauts staying in space for over a year. The current pie in the sky NASA plan for Mars includes a 7 month travel time to Mars, followed by 1 or 2 weeks to acclimate to the 40% Earth gravity on Mars.

[shynung]

I suspect the bone density loss thing wouldn't be such a problem if the trip is less than 9 months or so. From what I understand (listening to Startalk podcast), with their exercise regimen, it can be kept in check fairly well. Unlike on the ISS, where the astronauts are busy all day doing scientific experiments brought up by the latest cargo ship, astronauts going to Mars should have more time dedicated to exercise. You've got some Russian cosmonauts staying in space for over a year. The current pie in the sky NASA plan for Mars includes a 7 month travel time to Mars, followed by 1 or 2 weeks to acclimate to the 40% Earth gravity on Mars.

Muscle loss can be reduced by exercise regimens, but unfortunately not bone density loss. To reduce the latter, there must be some way to do weight-bearing exercise that covers the whole body, in order to compress the bones. Strapping the astronauts' hips to the treadmill won't do it, since this leaves upper body bones from having to bear weight. Strapping them by the shoulder leaves the neck bones vulnerable, and so on. Also, human arms normally hung from the upper body sections, which means they have to be given exercise separately (bones need pressure to maintain density, not tension). In the end, some sort of centrifuge would still be necessary, otherwise we're looking at an extensive exercise regime.

Then again, considering the amount of time the astronauts have off duty, such exercise regime would still make sense.

[Headhunter09]

As long as we're assembling transit vehicles in orbit, I don't see the problem with constructing a centrifuge. Orbital construction is, after all, one of the things we actually have experience with.

[MrZayas1]

Let's be honest that shouldn't be very hard considering the amount of space there is in space

[LordOfTheOrbits]

As long as we're assembling transit vehicles in orbit, I don't see the problem with constructing a centrifuge. Orbital construction is, after all, one of the things we actually have experience with.

The main problem with that is the fact that a centrifuge would need 12 separate launches so we could make a large enough ring with all the parts fitting in the fairings of to-date launch vehicles, which would cost a lot of money.

[Headhunter09]

But we don't need a contiguous habitat. Two habitats opposite of each other, connected by longer arcs of structural material would do the trick. Better yet, the whole "use the spent booster stage as a counterweight" idea removes the need to have heavy structural members.

[Soda Popinski]

For the 7 month transit time to Mars (going by the MDRA 5.0), shouldn't be insurmountable. That plan is based on the idea we're no better at launch with dealing with bone density loss than we are today (exercise and pharmaceuticals). I believe the plan is to land them on Mars, and let them acclimate to the 40% Earth gravity over the course of 2 weeks before they start doing any real work.

For a longer trip to Jupiter, take a look at NASA's Discovery II idea. That has a 3 part centrifuge. Unlike the MDRA, this requires technology that REALLY doesn't exist (fusion rocket).

http://www.ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20050160960_2005161052.pdf

[LuckyLu]

New research from NASA into warp drives seems to have had some fortunate results into Q-Thruster tech. Impressive stuff:

TL;DR: Quantum thrusters are using the quantum vacuum fluctuations to propel through space so they don't need to carry reaction mass, allowing for some impressive specific impulse numbers, putting to shame any ion or Hall thrusters.

Here's the origin discussion thread on reddit: http://www.reddit.com/r/Futurology/comments/1xe2c7/presentation_by_nasas_advanced_propulsion_leader/