Practical propulsion methods for manned interplanetary travel

[Rakaydos]

A NERVA is safer than three mile island was. And while Three mile island and Chernoble spread radiation around, they didnt go up in a mushroom cloud.

At worst, a NERVA will radioactivly contaminate it's payload. Probaby not the best for passangers, but not catestrophic for a cargo flight.

[maccollo]

Is nuclear powered.

RTGs pose contamination risk.

Nobody cared.

Edited February 6, 2014 by maccollo

[mdatspace]

I will restate a part of my comment from the last post of page 5:

"I weighed down nuclear propulsion with real political and environmental problems so it would not be the easiest way out. Anybody who has used an LV-N in KSP knows why NTR is a good idea for interplanetary travel."

[KASASpace]

Interestingly enough, that's not banned by this treaty, as a quick glance at it would tell you. It only bans the placing of nuclear weapons in orbit. As for the dates, 1967-1988.

I would hope it would, given being able to 'go critical' is literally the definition of what a nuclear reactor is. With regards to the definition, feel free to petition the UN if you think they should be using yours.

There's nothing in the design even capable of 'going boom'; at most, it'd melt. Do you get all of your physics from bad films? Having 'nuclear' in the name≠will go off like little boy.

By that definition, you're a nuclear weapon; you're fundamentally held together by nuclear forces, and you're capable of inflicting suffering on people. I really shouldn't have to say this isn't actually how international treaties work.

In orbit, eh? Well, wait, if the reactor can go supercritical while in orbit, then it can be a nuclear weapon. Now, by nuclear I mean involving the reaction on the atomic level of the atoms that make up a material which causes it to release energy. Now, when it goes critical, it's "controlled", however, a meltdown is not going supercritical. anyone who thinks it won't go BOOM is dumb, sure, it releases radiation, but that IONIZES the particles of the ship, which isn't exactly dangerous, but the rays would damage everything, and the reactor would be gone., if it goes supercritical, your toast, your cargo is toast, and your rep is toast. All that money, gone to waist. Now, the Soviets had a space program wrapped in secrecy, unlike ours. So, they got away with it. And it's not like it can be enforced. It's just there.

Edited February 6, 2014 by Specialist290
Nothing to see here...

[Kryten]

In orbit, eh? Well, wait, if the reactor can go supercritical while in orbit, then it can be a nuclear weapon.

Then it's a perfectly good thing it can't then, isn't it? Try and think for a little while here; it took thousands of people, three years and billions of dollars of infrastructure and equipment to go from something going critical (Chicago-pile 1, 1942) to something going supercritical (trinity, 1945). Do you think this really would have been necessary if a nuclear reactor could just do it on it's own with minimal provocation?

[Specialist290]

It has recently come to the attention of the moderation staff that the discussion in this thread has gotten rather heated, and that tempers have been flaring as a result. Please remember to keep things civil.

[SargeRho]

I wonder, wouldn't it help putting the crew "in" the fuel tanks to reduce radiation? By that I mean: Put the fuel tanks around the crew quarters, and put the water tanks into the walls without fuel tanks covering them.

[nhnifong]

Funny story, I showed this picture to a Taiwanese girl at the bar tonight and said "Do you know what robot this is?" She said "Wall-E!"

[Nuke]

I wonder, wouldn't it help putting the crew "in" the fuel tanks to reduce radiation? By that I mean: Put the fuel tanks around the crew quarters, and put the water tanks into the walls without fuel tanks covering them.

if the fuel was lh2 this could get ugly. if a micrometeorite managed to puncture the fuel and into the cabin, this could cause a fire.

also there is an issue that the tanks will likely be mostly empty for the return trip (especially if you intend to aerocapture at earth). so you would get the full unshielded dose.

makes me wonder what a two way aerocapture mission would look like. use an impulse trajectory over a hohmann transfer on the earth->mars transfer gives you some surface time. both plannets have atmosphere so why waste the fuel on slowing down? heat shields may be neccisary. on the earth aerocapture you can separate from the mother ship in a return capsule and let the mothership fly on by.

Edited February 6, 2014 by Nuke

[SargeRho]

The puncturing the cabin part is relatively easy to solve, using whipple shields and cushions made of something like kevlar between the layers. As for the return trip: There wouldn't need to be one, and the cabin should be made of non-metal things anyway to prevent secondary radiation. Polyethylene is apparently a good radiation shield.

I still think Mars to Stay is the best way to go, although quite a bit of R&D is needed before that can be done, specially in terms of long term life support.

And even so, if you can largely mitigate the radiation dose on the way there, it'll help tremendously.

Edited February 6, 2014 by SargeRho

[Soda Popinski]

Funny story, I showed this picture to a Taiwanese girl at the bar tonight and said "Do you know what robot this is?" She said "Wall-E!"

Wow, times have changed since I was on the singles scene. Showing girls pictures of space robots was never my go to thing...

I wonder, wouldn't it help putting the crew "in" the fuel tanks to reduce radiation? By that I mean: Put the fuel tanks around the crew quarters, and put the water tanks into the walls without fuel tanks covering them.

If we're talking radiation from the nuclear rocket (whether it be conventional NERVA or some future tech, like gas core fission or some fusion drive), it's good enough to put the fuel BETWEEN the reactor and the crew, as radiation moves in straight lines. On the other hand, if you surround the whole crew compartment, you have less shielding directly between the reactor and crew. Another method common when working with radiation is distance. Taking advantage of the inverse square law, as doubling the distance from a light/radiation point source decreases exposure 4 fold, just put the crew as far from the reactor as possible. This was the thought for the Discovery One in 2001: A Space Odyssey, also emulated in NASA's nuclear fusion powered Discovery Two proposal , which I also ripped of for my own Discovery 2: Mission to Jool.

Of course the problem with using propellant for shielding is, you loose shielding as you burn propellant. But at least it minimizes your exposure time to more radiation prior to it being burn - so say on a Mars mission with a 6 to 9 month travel time, you have that fuel shield there until retro burn. Come to think about it, I would expect the greatest radiation flux to occur only WHEN the engine is being fired. During those burn sequences, the crew could sit in a highly shielded compartment.

Now, cosmic radiation...that would require 360 shielding. Crew water, and even waste material has been considered. I recall there was some promising work on using a magnetic field, and it turned out to be way way easier than originally thought. That could drastically reduce physical shielding requirements.

[SargeRho]

I'm talking about space radiation, not radiation from the propulsion system. If you can solve that without adding too much mass to the ship, you can go with chemical to Mars.

[Soda Popinski]

I'm talking about space radiation, not radiation from the propulsion system. If you can solve that without adding too much mass to the ship, you can go with chemical to Mars.

Looking through the NASA write-up they propose 5 g/cm^2 of aluminum for radiation shielding (about 1 inch thick aluminum), would reduce exposure of a Mars surface mission to about 1 Sievert (table 3-8). That increases cancer incident by about 5.5%, according to Wikipedia.

Based on NASA's Deep Space Habitation Module, based on existing ISS modules, that's a surface area of about 1.3e6 cm^2, or 6.5e6 grams (6.5 metric tons) of aluminum shielding. The concept they have there uses drinking water about 10cm thick (1.3e7 grams - 13 tons), which I presume would be slowly replaced with waste water they can't recycle (Chris Hadfield mentioned about 5% of water can't be reclaimed).

I did come across an old article about using a 1 tesla magnet to provide a miniature magnetic field.

[Simon Ross]

Wonderful to see the Luddites coming out on threads like this

So, just a wake up call to those of you who think the 'N' word is a bad thing

Without it, we don't have a manned space programme, not now, not in 20 years time, not ever !

Please feel free to sit back, protest and watch us all slowly fall back to a position where the world cannot afford to do the things this generation and maybe only this generation has the resources to do the things that we can possibly do to prevent another dark age.

Feel proud of yourselves, pat yourselves on the back while the lights slowly dim, while billions starve and console yourselves that at least you saved the planet.

[Soda Popinski]

Without it, we don't have a manned space programme, not now, not in 20 years time, not ever !

Yeah, it's too bad nobody is currently using nuclear thermal rockets. That explains why we don't have a single manned space program on the planet Earth. Those 6 folks up on the ISS are just a figment of our imagination...

A bit alarmist Simon? Or do you just mean a manned space program to Mars and beyond? I'd agree with that. I personally support NTRs and nuclear power in general (I'm an environmentalist with half a brain).

[Simon Ross]

Yeah, it's too bad nobody is currently using nuclear thermal rockets. That explains why we don't have a single manned space program on the planet Earth. Those 6 folks up on the ISS are just a figment of our imagination...

A bit alarmist Simon? Or do you just mean a manned space program to Mars and beyond? I'd agree with that. I personally support NTRs and nuclear power in general (I'm an environmentalist with half a brain).

@Soda

LOL, it's not a manned space programme my friend, heck it isn't even treading water

[Kryten]

LOL, it's not a manned space programme my friend, heck it isn't even treading water

And we should refer to your arbitrary definition because...

Edited February 6, 2014 by Kryten

[Simon Ross]

And why should refer to your arbitrary definition because...

Because 45 years ago my friend I watched an incredible thing, two human beings landed on another planet with primitive technology and if you were not around at that time you simply will never understand what it meant or the passion it evoked.

And these days, I'm 45 years older and I strongly suspect both you and I are never going to feel that sense of awe in our lifetimes again :-(

For once as a species we put all the crap behind us and did something we can all be proud of. I don't ever see it happening again in my life time, but I hope it will in my children's

Edited February 7, 2014 by Simon Ross

[Headhunter09]

I think the main arguments in this thread are fundamentally flawed.

1. Any plan involving the Moon is worthless. Phobos is closer, in terms of deltaV, than the Moon.

The first step would be to test robotic ice mining and refining technologies on either a near-earth asteroid or Phobos. This way, when a mission arrives in Martian orbit, it can top up at Phobos. As for ISRU from the Martian surface or atmosphere: this is a much more difficult option. For one, the Martian atmosphere is very thin and dry. More importantly, the surface is much farther away in terms of deltaV and disallows any abort mode from Mars orbit (if they were planning on refueling). Having a fuel depot in orbit from Phobos means you don't have to move fuel from an asteroid into Martian orbit (another complication), or up from the Martian surface (inefficient).

2. NERVAs, or any other exotic propulsion system, aren't needed. Any plan can be accomplished with straight-up chemical rockets. Honestly, this is the best option because we have the most experience with it. Even ignoring the potential political aspects (which I don't think would be insurmountable), NERVAs would require many years of research, development, and testing.

With a small number of heavy launches, we could assembled a habitat and booster capable of reaching a Mars orbit, where it could then refuel. It doesn't even need to carry landing equipment, just a deep-space habitat. Which brings me to...

3. It need not be a single mission. What would most likely happen is that any surface and orbital equipment (like heavy life support equipment, such as aerocultures) would be launched years before hand. That way, if anything fails, it can be replaced before astronauts arrive.

So the most realistic profile for a mission is that pieces of equipment are designed and launched steadily for a number of years. Finally, a crew transfer vehicle is assembled and sent on its way. At the other end, the transfer vehicle is parked and the pre-arrived equipment is used for landings, etc. Then the transfer vehicle is refilled by the Phobos ice miner and replenishes its perishable supplies from pre-launched caches, and then returns to Earth.

This profile also makes sense politically. If you have four pieces of expensive equipment already in Martian orbit, the program is less likely to be cancelled. It spreads out the cost, and works against cancellation. Also, it can take advantage of new technologies developed in the mean-time (AKA, you only have to develop a few technologies at a time).

[KASASpace]

I think the main arguments in this thread are fundamentally flawed.

1. Any plan involving the Moon is worthless. Phobos is closer, in terms of deltaV, than the Moon.

The first step would be to test robotic ice mining and refining technologies on either a near-earth asteroid or Phobos. This way, when a mission arrives in Martian orbit, it can top up at Phobos. As for ISRU from the Martian surface or atmosphere: this is a much more difficult option. For one, the Martian atmosphere is very thin and dry. More importantly, the surface is much farther away in terms of deltaV and disallows any abort mode from Mars orbit (if they were planning on refueling). Having a fuel depot in orbit from Phobos means you don't have to move fuel from an asteroid into Martian orbit (another complication), or up from the Martian surface (inefficient).

2. NERVAs, or any other exotic propulsion system, aren't needed. Any plan can be accomplished with straight-up chemical rockets. Honestly, this is the best option because we have the most experience with it. Even ignoring the potential political aspects (which I don't think would be insurmountable), NERVAs would require many years of research, development, and testing.

With a small number of heavy launches, we could assembled a habitat and booster capable of reaching a Mars orbit, where it could then refuel. It doesn't even need to carry landing equipment, just a deep-space habitat. Which brings me to...

3. It need not be a single mission. What would most likely happen is that any surface and orbital equipment (like heavy life support equipment, such as aerocultures) would be launched years before hand. That way, if anything fails, it can be replaced before astronauts arrive.

So the most realistic profile for a mission is that pieces of equipment are designed and launched steadily for a number of years. Finally, a crew transfer vehicle is assembled and sent on its way. At the other end, the transfer vehicle is parked and the pre-arrived equipment is used for landings, etc. Then the transfer vehicle is refilled by the Phobos ice miner and replenishes its perishable supplies from pre-launched caches, and then returns to Earth.

This profile also makes sense politically. If you have four pieces of expensive equipment already in Martian orbit, the program is less likely to be cancelled. It spreads out the cost, and works against cancellation. Also, it can take advantage of new technologies developed in the mean-time (AKA, you only have to develop a few technologies at a time).

This is a good idea, but it needs to be ironed out. How would you maintain the constant Martian Stations? You would need a very capable detection system, to find problems. Then you would have to wait until the launch window to fix it. Thus delaying the manned mission, not to mention that the actual stuff has to get there, and the most efficient rockets we have ever built were NERVAs, allowing for more cargo with the same amount of fuel. But, still, not bad, and needs to be ironed out.

[Kryten]

I think the main arguments in this thread are fundamentally flawed.

The first step would be to test robotic ice mining and refining technologies on either a near-earth asteroid or Phobos. This way, when a mission arrives in Martian orbit, it can top up at Phobos.

You're exactly right; putting up a few extra launches worth of fuel is going to be incredibly difficult. Much easier to send a completely autonomous robotic fuel refinery to a place that's currently 0/3 in terms of landing attempts, and where there quite possibly isn't even anything to refine.

[Headhunter09]

You're exactly right; putting up a few extra launches worth of fuel is going to be incredibly difficult. Much easier to send a completely autonomous robotic fuel refinery to a place that's currently 0/3 in terms of landing attempts, and where there quite possibly isn't even anything to refine.

Nonetheless, we already have the capabilities to robotically visit and test asteroids for ice content, even if we haven't had a successful mission.

ISRU on the Moon would require a whole new regime of development, as the US hasn't landed a robot on the Moon since 1968.

Having a self-replenishing fuel dump in Martian orbit opens up a bunch of opportunities that just aren't available when launching your own fuel.

[Kryten]

ISRU on the Moon would require a whole new regime of development, as the US hasn't landed a robot on the Moon since 1968.

Landing on an asteroid hasn't been done the US, ever. I fail to see how that's anything less of a 'whole new regime of development'. Still, I share your scepticism on Lunar ISRU, I just think ISRU anywhere isn't necessary for this kind of mission. We're talking a visit, not forming a colony.

[Rakaydos]

Landing on an asteroid hasn't been done the US, ever. I fail to see how that's anything less of a 'whole new regime of development'. Still, I share your scepticism on Lunar ISRU, I just think ISRU anywhere isn't necessary for this kind of mission. We're talking a visit, not forming a colony.

Isnt "Colont by 2050" one of the stipulations of this thread?

[Soda Popinski]

I think the main arguments in this thread are fundamentally flawed.

1. Any plan involving the Moon is worthless. Phobos is closer, in terms of deltaV, than the Moon.

The first step would be to test robotic ice mining and refining technologies on either a near-earth asteroid or Phobos. This way, when a mission arrives in Martian orbit, it can top up at Phobos. As for ISRU from the Martian surface or atmosphere: this is a much more difficult option. For one, the Martian atmosphere is very thin and dry. More importantly, the surface is much farther away in terms of deltaV and disallows any abort mode from Mars orbit (if they were planning on refueling). Having a fuel depot in orbit from Phobos means you don't have to move fuel from an asteroid into Martian orbit (another complication), or up from the Martian surface (inefficient).

I would think it would take less delta-V to get onto Mars' surface than establish an orbit and rendezvous with Phobos. With a direct to Mars approach, the spacecraft can aerobrake, and use parachutes like the Curiosity rover. Secondly, the current ISRU plan is to send hydrogen, and combine it with the CO2 abundant in the Martian atmosphere, to create oxygen and water. The technology for that is well established, or at least better established than making fuel from Phobos, which seems to be mostly silicates - not really good fuel material.