Which begs the question, why haven't we at least even tried to have done anything like this already?

Do we really need to repeatedly spend comparable amounts of money on yet another dramatic TV special about humans traveling to Mars, as narrated by a favored celebrity? We really are running out of time. And it almost seems like it's pre-determined to happen. :\

The engineering issues are really tough, though surmountable. Currently, we just can't engineer the parts that will last that long in hard vacuum. Mostly because we can't test in that environment easily. Also, what do you do when all the light bulbs have burned out or gone haywire, what does that fault-tree look like for the billion and one parts on the craft? For a short journey of ~7 years, it's not a very big deal, it's just engineering issues. When you get into generation ship discussions then it becomes a human rights nightmare to trap newborns in a ship for their entire life and the lives of their descendants.

With a round trip parts delivery time OF a generation, and a communications delay of almost a decade (two for duplex), I don't see any reason not to classify such a mission as a short-range 'generation ship' / complete colony effort.

Getting our 'eggs' out of a single cosmic basket is really important, however I think we need to at least take the baby-crawl to establishing an outpost in the asteroid belt. That would be far closer, have far more reasonable communications/parts delays, and if we can actually send up some robots to build things ahead of us, might actually be a good manufacturing base.

I feel that advancements in quantum mechanics will solve the communication problem.

No, it almost certainly won't. Our current understanding of quantum information theory simply doesn't allow transmitting classical information faster than light. There's no room in what we don't understand that could plausibly contain FTL communication. This is a pretty fundamental result of quantum information theory. https://en.m.wikipedia.org/wiki/No-communication_theorem

> it becomes a human rights nightmare to trap newborns in a ship for their entire life and the lives of their descendants.

Which is exactly why we should get some people off this ship, and colonizing others!

Oh, you meant the generation ship, not the Earth; nevermind.

Yeah I'm to be honest just trying to awaken people to the priority being that we need to establish a self-sufficient colony somewhere other than Earth.

Honestly, as long as humans stay stuck to earth, losing all humanity on earth won't hurt anyone. As long as the extinction is instant. If we have colonies, those colonies need to suffer through the knowledge that we lost earth.

Establishing colonies is only imperative if the continuation of the human race is. I'd argue that humans have value only due to other humans. There is nothing inherently valuable about human life from a non-human perspective.

That is not to say I don't support space colonization, just that I don't think its a moral imperative.

"There is nothing inherently valuable about human life from a non-human perspective."

How would you know?

It's a perfectly reasonable assumption until there's some evidence there is. Given the vastness and scale of the universe, it seems quite likely that our disappearance would never be noticed.

Going unnoticed is not the same as inherently not valuable. Imagine aliens finding us extinct, wringing their little tentacles in dispair at the lost probing opportunities. :)

Well, HN is not the most optimal place to do that. There are not many of us on here and we all already know these things. 1600 Pennsylvania Pl. is a better bang for your buck.

I think you probably mean 1600 Pennsylvania Ave. (not Pl.), Washington, D.C.

Though I don't share your assessment that that is a productive place to direct citizen input on this (or any other) issue.

Thanks!

Elon Musk is working on that.

http://www.spacex.com/mars

And you're certain enough that he's going to be able to do it in time and that he's doing it properly enough that you don't have to do anything about it. And you'll continue to go about doing the exact same things. Got it.

In no way attempting to deflect from my own regrettable inaction, I'm curious to know what you're doing about it?

Based on his previous achievements I feel like he is likely to move the field forward by big steps. And if not him the people after him. I'm not sure if pushing myself into field I don't understand much would help the progress. Scientists do science, not activists.

Are you a space activist of some sort?

The launch cost of launching the mass of the pyramids of gaza into orbit would bankrupt the richest economies. No your hypothetical engine won't be 100% efficient. This is completely unfeasible.

Low mass spacecraft are our only real options. A nano-sized solar sail craft powered by the sun or lasers from Earth can hit up to 20% lightspeed theoretically and its launch costs would be affordable, if not relatively cheap. We could have a spacecraft at Alpha Centauri in merely 20 years. Or simply launch them by the dozens or hundreds to various locations. Stephen Hawking has proposed this system in the past and we've had trial launches of solar sails via the planetary society and others. Its a solid and most likely doable concept at scale. Yes, your kids or grandkids will hear the results, but not you. Is that such a problem, especially when the alternatives are never launching a probe to those systems?

To be fair, the proposed Centauri mission would be within a person's lifetime. 20 years to get there then another 4 and half to get the data. So if we launch when you're in your 40s or even 50s, you'll still see the data.

We can even use this concept on heavier ships in the solar system to get to Mars quickly. How quickly? Three days quickly for a 100kg craft. This is a bit more pie-in-the-sky of course:

http://www.sciencealert.com/nasa-scientists-are-investigatin...

>The launch cost of launching the mass of the pyramids of gaza into orbit would bankrupt the richest economies. No your hypothetical engine won't be 100% efficient. This is completely unfeasible.

Not necessarily. You don't need to launch the mass of the pyramids from Earth, you just need to find a source of fuel somewhere else in the Solar System that's in a shallower gravity well, like on the Moon. This is why a lot of people want to work on mining asteroids, and building mining/refining/manufacturing infrastructure offworld.

You can't really just extrapolate the current cost of launching materials by the kilogram. A project of that magnitude would generate economies of scale and probably some innovations along the way that would bring down the cost. The "nearly perfect" fusion engine is really the hard part.

You are assuming that this mass will be launched using today's chemically powered rockets. But using nuclear propelled rockets will bring down the launch costs by orders of magnitude.

A Russian billionaire is trying: https://breakthroughinitiatives.org/Initiative/3

I'm talking about establishing a self-sufficient colony somewhere other than Earth. We have a major crisis on our hands. And few are even willing to consider let alone research and confirm that we're talking about an extinction event much sooner than we thought, maybe on the order of just a couple years out. Problem is, we don't know. Bigger problem is, we're not doing anything about it.

If its affordable to send people to an off world colony then its affordable to bomb it when war on Earth breaks out. Fleeing isn't going to help in a wartime situation and the idea it will not be targeted by world powers is a little naive.

I said nothing about war..?

There's no other conceivable extinction event that could occur "a couple years out". If you're talking climate change, then I agree that's a major problem, but on the order of at least decades.

Plus climate change would have to get pretty incredibly bad for, say, Mars to start looking easier to live on than Earth.

That's the problem with colonization as an Earth back-up—even Antarctica and the Sahara Desert are more livable than any other body in the Solar System, by a long shot. Another Snowball Earth or a heavily desertified Earth would still be preferable to Mars. Throw in a fair amount of radiation, even—still better.

Cuts down significantly on the sorts of events for which a Martian back-up world is preferable to a shelter-in-place strategy.

But if you could go out now and terraform a planet so that when in future you have problems here you have a place to go to that matches the original environment back on earth. And you learn a lot of things about "geo"engineering, the things you cannot try safely at home, which can come in handy to fix any problem back on earth.

We have no ability to terraform anything, let alone a planet, let alone the economics of it ever being feasible. Life isn't a star trek episode. We can't just go and 'terraform now' as you say. We can barely land anything on Mars without a 50% failrate right now. We're talking technology way, way into the future. Hundreds, perhaps thousands, of years.

This is precisely what we don't know. If you're talking averages, then sure it takes decades to observe a meaningful change. However climate change of the sort we're anticipating now isn't about averages. It's about peaks, it's about records, and possibly major shifts in equilibrium.

Basically what we witness so far and will keep on seeing are spikes in all directions of the spectrums (e.g. record high temps, but also record lows; rain in the Death Valley and droughts in formerly wet areas). More critically, what little we've been able to gather on how fast climate eras shift from one to the next, it appears that whereas in-cycle change happens rather slowly (change within an era, because averages), climate era shifts could happen very quickly (because chain of events). We're talking going from a warm era to a glacial one within a few years, sometimes months even. A high speculation is that some thongs might upset the Gulfstream and you'd observe climate evolve from year to year.

What about a comet impact? That's extinction level and comes with very little warning.

Given our limited sky coverage, we can't really rule out killer meteor on the time scale of "a couple of years", or even a couple of hours, though the probability is extremely low (like, sub-1-in-100 million, for the couple of years time frame.)

Still probably higher than extinction from war in the same time frame.

> There's no other conceivable extinction event that could occur "a couple years out".

Life on earth could end in the next five minutes. :) https://www.youtube.com/watch?v=RLykC1VN7NY

The resources and practically to gently shoving a comet or asteroid out of the way are probably a billion less than building self-sustaining colonies elsewhere. Worse, now we have two planets to defend, not one.

I don't see the "we must migrate now" types saying "lets put migration away for a while so we can better build anti-asteroid solutions and detection systems."

Arguably, we're just a couple launches and deployments of mass drivers away from fixing this issue. This is all known tech that could be deployed relatively quickly. A self-sustaining Martian colony is probably hundreds of years away considering the work it would take to terraform the planet.

The resources involved in preventing a GRB from hitting us, on the other hand, are . . .

. . . actually I have absolutely no idea how you would practically do that at all.

He appeared to be speaking of a known, ongoing crisis, not a minute possibility of a killer meteor.

Haha! My link doesn't go to a video about meteors. Your point is taken, though. I was just being cute and/or hoping you hadn't heard about this.

But I have heard the possibility of a GRB discussed seriously as a motivator for expanding, not just through the solar system, but through the galaxy.

Lots of good reasons to establish a space colony, fleeing the earth is not one of them. By this sort of argument you actually discredit the idea of space exploration.

> fleeing the earth is not one of them

Why not? If a big asteroid is going to hit earth (for example), fleeing is a pretty reasonable response. It's also a reasonable defense against technobiological hazards.

The impact would have to be absolutely massive to cause enough damage to the Earth that it is less liveable than Mars.

To compare, the Triassic–Jurassic extinction event created an Earth still more liveable than Mars. Even if we go way back in time, to when there was no land-life on Earth and a poorly oxygenated atmosphere, the Earth is still better off than Mars for supporting human life.

If the goal is to save the human race, then it'd be better to have a few high orbit or lunar habitats, then if something wipes out the majority of civilisation on Earth, we immediately begin recolonisation of our home planet.

Let me ask you this question: Would you consider the Titanic, oh, I don't know -- a success story?

Because that's basically what this sort of thing comes down to, at the end of it. There's basically nothing that is going to be existentially, immediately threatening to earth on a timescale that Mars is actually a more livable environment.

Where else in the Solar System could we even get the amount of water we would need?

Isn't Mars full of water? Source: I read the Mars trilogy by Kim Stanley Robinson.

The chance that an asteroid hitting Earth that actually matters is extremely low. It is even lower chance that we can detect it on time. It is much higher chance that politicians will start a nuclear war that wipes out most of humanity from the face of Earth.

I'm not certain what you mean by "fleeing", but we sure as hell aren't going to move seven billion people. A bunch of engineers and rich people may be able to get out, but that's about it. To save the rest, we'll need cheaper methods.

Isn't part of the problem that any ship capable of interstellar travel is also capable of being turned into a WMD? I imagine a lot of people would get really nervous if someone for instance parked a bunch of radioactive material in low earth orbit, and even with fusion there would be the fear that someone could turn the ship around.

To be fair kinetic bombardment is stupid easy to do once you can put stuff into orbit. Put a few, 20 foot long tungsten rods into orbit and you can effectively nuke, without radiation, any location that you orbit over [1].

Sure this is a problem but it's one that already exists today, not necessarily only when we start building space craft in orbit.

[1] https://en.wikipedia.org/wiki/Kinetic_bombardment

Contract SpaceX to bring the rods into orbit, then bill per strike. KBaaS, disrupting warfare since 2017.

Back of the envelope calculation: rods with length of 6m and radius of 5cm weight little over 900kg. Falcon 9 can bring 22.8 tons to LEO. So we can get up about 24 of these in one go. If we want to use the USAF dimensions of 6.1m and radius of 0.15m, then it's only 2 of them, maybe 3 with some adjustments to the rocket.

I always wondered how to de-orbit those rods. It's not like you can just 'drop' them as they are already in free-fall. You'd need to cancel quite a bit of orbital velocity to get the things to de-orbit. Aiming'd be even more of a bitch.

> ...a 6.1 m × 0.3 m tungsten cylinder impacting at Mach 10 has a kinetic energy equivalent to approximately 11.5 tons of TNT (or 7.2 tons of dynamite).

Well, that's a bit underwhelming. Sounds a bit like Russian polonium tea, that is, less like a matter of efficiency, and more like showing off the sheer extravaganza of killing somebody in the most colorful, expensive way.

Kinetic bombardment is silly and inefficient science fiction. Conventionally armed ballistic missiles can strike any point on Earth almost as quickly at a far lower cost and with greater survivability.

Well today sending a rocket up, putting these things in orbit and then dropping them would probably be a bit obvious and inefficient. But in the near future when we're mining asteroids? As long as they can be captured closed enough to Earth I would imagine kinetic bombardment would be pretty effective. They would be rather difficult to shoot out of the sky as ballistic missiles can be blown up prior to reaching target but kinetic would require an much, much larger amount of energy to destroy enough so as to not hit and damage the target.

Asteroid mining on any sort of commercial scale is far future, not near future. Even with fully reusable rockets, asteroid mining wouldn't be profitable; anything we need can be obtained cheaper on Earth.

Small asteroids are too irregularly shaped to be useful as precision-guided projectiles. As soon as they hit the atmosphere they're going to veer off course.

Kinetic bombardment satellites — whether fully artificial or asteroids guidance and propulsion strapped on — would be in known orbits with limited maneuvering capability and thus highly vulnerable to antisatellite weapons. It takes very little energy to kill a satellite; you don't have to vaporize it, just break any critical part in the communication, propulsion, or guidance systems. Satellites are generally easier targets to hit than ballistic missiles.

> Asteroid mining on any sort of commercial scale is far future, not near future. Even with fully reusable rockets, asteroid mining wouldn't be profitable; anything we need can be obtained cheaper on Earth.

It's certainly in the future, it just all depends on what is far to you. Many companies who want to get in on this are hoping to attempt within the next 10-15 years (obviously commercial mining would come some years later after a successful attempt). If it can be successfully navigated it would have the potential to be crazy profitable!

It's too expensive to bring materials up but if you can mine materials in space and deliver them to the various space companies / government departments is where you'd make your money. Mining water, in theory, should be crazy cheaper as long as you can capture the asteroid efficiently enough. NASA has already said they would love to see more work in this space so they can purchase materials cheaper while in space and they're even hoping to capture an asteroid in the mid 2020s as a type of test for this scenario.

> Satellites are generally easier targets to hit than ballistic missiles.

This misses my entire point: in order to destroy the kinetic projectile you would have to launch a preemptive strike against the satellite. There is no way around it. You won't be able to defend yourself against a large projective being precision dropped onto your location without a lot of energy (so depending on what country you are maybe you can knock several into a few direction or vaporize with a high enough yield but you only get one chance at destroying it). Meanwhile a ballistic missile, while faster, can be destroyed with a hot enough laser.

I understand they're not practical and if you want to use an asteroid itself that's even more awkward. But when we start mining asteroids, in my opinion, it's going to become crazy practical and cheap.

That's not how it would work. Incoming kinetic projectiles are just as vulnerable to defensive systems as ballistic missiles. Hit it hard enough and you can knock out the guidance system. They would need very precise and sensitive guidance systems to hit anything from orbit.

Space enthusiasts constantly underestimate costs and schedules. Just because something is theoretically possible doesn't mean that the engineering problems can be solved in an economical way. If there is large-scale asteroid mining in my lifetime then I'll eat my hat.

> Incoming kinetic projectiles are just as vulnerable to defensive systems as ballistic missiles. Hit it hard enough and you can knock out the guidance system

Not true at all. Kinetic projectiles would have no guidance system. It's just a big, dumb piece of tungsten. That's it. You would have to hit it hard enough to make sure that, when it hits, it won't cause damage. This means near complete vaporization. That's very energy intensive.

Ballistic missiles, however, simply need to have their payload exploded at almost any distance away from the target to reduce its power to near nothingness.

> If there is large-scale asteroid mining in my lifetime then I'll eat my hat.

Not sure how old you are but if you're under 40 and not planning on dying sooner than average then, in my opinion, you should start looking up hat recipes :D. At least I hope but it depends because the primary customer for asteroid mining is going to be space companies and government agencies like NASA. A disruptive political system that prevents said purchases could hamper progress significantly.

You seem to be hilariously ignorant about the realities of aerodynamics, rocketry, and orbital mechanics. Due to atmospheric turbulence and normal thrust variations in the rocket motors that would have to be used for de-orbit burns, any unguided projectiles would have such as huge CEP as to make them militarily useless. Unguided projectiles launched from aircraft today can't reliably hit anything at distances over a few miles; satellites are much farther. A (sensitive and fragile) terminal guidance system would be an absolute necessity. Contrary to what arrogant programmers might think, DARPA isn't run by idiots and they gave up on such nonsense schemes for good reason long ago.

As for asteroid mining, hope doesn't count for anything. There is no shortage of essential raw materials here on Earth. No one is going to commit the hundreds of billion $ necessary to do it on more than a trial basis. There's simply no economic incentive nor is there political will to spend that money. Sorry to burst your bubble.

Well I assume is the USG let alone SpaceX decided to put some 20 foot tungsten rods in orbit a lot of people would start raising objections pretty quickly.

If anyone is interested in kinetic bombardment, read Heinlein's "The Moon is a Harsh Mistress". Much like how the Fosterites in his "Stranger in a Strange Land" were a blueprint for Scientology, TMiaHM is a guide on how to plan and conduct a revolution, although in this case it was the Moon against Earth.

Jet planes can also be used to destroy skyscrapers. People don't seem to get really nervous about them.

We've created a giant security apparatus based on Jet planes. They are not something we just let anyone buy or fly and if you deviate from your flight path these days you stand a good chance of getting shot down. People definitely get nervous about them.

Are you implying that rockets capable of transporting several hundred kg of tungsten to orbit are -not- tightly controlled? I imagine if you assembled anything close to this size without seeking extensive permissions you would be quite severely punished

No, I'm just addressed the analogy of jet airplanes and pointing out those are tightly controlled. I understand that current rocked are very tightly controlled, my point is just that any sort of interstellar rocket would be much more dangerous and thus have to be subject to much higher controls. A ship that was capable of reaching a significant fraction of light speed would be the most dangerous weapon ever created though, and existing controls might not be sufficient.

NASA is not standing still. Europa just went to the next stage for exploration.

http://www.jpl.nasa.gov/news/news.php?feature=6755

It just takes a lot of time to plan and build ships for space travel.

You're completely missing my point.

We've known about climate change for a long time. Since the 60s/70s, no? But nobody has been able to realize what it really is, because scientists do not understand gravity yet. I've been begging people to confirm this for themselves instead of believing what others say about it. If people really knew what global warming was they would have started working on ships decades ago.

My point is, people on stable self-sufficient colony outside of Earth is priority number one. Not sending a probe to Europa. But somehow I get the feeling you have no interest in this reality.

You sound a little unhinged to be honest. If you're really worried that climate change on Earth is going to cause big problems for humans (which is not an unreasonable concern; climate change threatens to cause significant sea level rise which will cause big problems for people living in sea-level coastal cities), building self-sufficient colonies offworld is a rather extreme answer to that. A simpler answer is to simply move inland, and make sure your structures can handle extreme weather. That's a lot easier than trying to build an offworld colony.

The real reason to build an offworld colony is because you're worried about a big asteroid strike. But here again, it's a lot easier to just build observation systems to spot these threats, and weapons systems to handle these threats, than to build an offworld colony that's truly self-sufficient.

Finally, offworld colonies have gigantic problems with them: 1) people don't handle radiation well, and no place in the Solar System protects us from radiation the way the Earth does, so we'd probably have to burrow underground to mitigate it, and 2) we really don't know how well the human body can handle low-gravity conditions, but we do know that the human body does not handle zero-g well and that it causes massive health problems. There's no place in the Solar System with close to Earth-normal gravity, except for Venus which is a hellhole hot enough to melt lead (on the surface). Mars is only 1/3g, and the Moon is only 1/6g, and pretty much everything else is even less except the gas giants which obviously aren't livable.

Now what climate change and offworld colonies (in this system at least) have to do with our lack of understanding of gravity, I have no idea.

So all we have to do about climate change is build structures to handle extreme weather? Climate change is and will continue to affect our whole food chain that supports the some ~7 billion people on earth. It's not just the weather we will be dealing with.

And you think it's easier to just pack up and move to Mars than to deal with the climate change? You think it'd be easier to figure out how to grow food on Mars than to mitigate climate change-caused problems with the food chain here?

There's lots of stuff you can do to grow food here even with climate change: greenhouses, indoor/vertical farming, etc. Good luck with all that on Mars.

Scientists understand gravity very well, pick up any book on general relativity.

> We've known about climate change for a long time. Since the 60s/70s, no? But nobody has been able to realize what it really is, because scientists do not understand gravity yet.

We know exactly what climate change is and it has nothing to do with gravity.

What does gravity have to do with climate change?

If you're curious on more than a surface level, this book is an excellent resource from an ex-astronaught on why things are lagging. "Safe Is Not An Option"

https://www.amazon.com/Safe-Not-Option-Rand-Simberg/dp/09891...

It sounds like you have a startup idea on your hands : )

How would this generate returns on investment? Monetary returns, that is.

I mean if I somehow magically become a billionaire I intend to throw money at the problem with no hope of ever making a return because I believe humanity's last hope is an offworld colony, but I doubt I'll convince any VCs to join in.

You've no idea. But for the first step, I need to find one or two very truthful physics grad students / electrical engineers who feel some responsibility for Earth or saving themselves. You wouldn't happen to know someone?

Why don't you become one?

Don't worry your pretty little head. I went to top schools.

I think you mean "Post-truthful"

Politics, specifically the PTBT[1]. Otherwise Project Orion[2] would be a reality now.

[1] https://en.wikipedia.org/wiki/Partial_Nuclear_Test_Ban_Treat...

[2] https://en.wikipedia.org/wiki/Project_Orion_(nuclear_propuls...

Project Daedalus seems more appropriate for interstellar travel:

https://en.wikipedia.org/wiki/Project_Daedalus

How about http://www.mars-one.com/ ?

EDIT: My math was totally wrong. 10 trillion dollars, 0.1x world GDP. (Still a lot of money though) Leaving the old text below so the replies make sense.

---

To move 6,000,000 megatons of fuel into low earth orbit would take 111,111 Falcon Heavy launches, at a total cost of $10,000,000,000,000 dollars. (10 quadrillion dollars, 93x world GDP)

Something that takes the total global economic output of the planet a century just to lift the fuel into orbit doesn't read as plausible in the next 50 years to me.

You wouldn't gather that fuel from earth.. you'd gather it from an icy asteroid or comet or moon (Europa).

I'm not sure if your error is in the number or in the words, but the number you wrote down is 10 trillion dollars.

Note to mention that Falcon Launches would get significantly cheaper if we have to do 100,000 of them.

Oops.

Is it plausible for anything we'd build to travel .998c and survive the journey?

Just going that fast isn't really risky at all (assuming you don't hit anything, which isn't actually a safe assumption). The tough part is making something capable of a constant 1g of acceleration for a 7 year trip. Most of the craft we make only accelerate for the first small percent of a trip. We can do accelerations that high, but not for very long, and we can't even manage acceleration for such a long duration even at a small fraction of 1g.

You have no idea how scary traveling at near-lightspeed actually is. Isaac Arthur has a great video covering it. https://www.youtube.com/watch?v=s6BQSgidbmc

If you go fast enough doesn't any incoming radiation just get blue shifted into gamma rays? Just running into cosmic dust at the speed of light would not be fun.

>Just running into cosmic dust at the speed of light would not be fun.

That's why you need a navigational deflector dish. http://vignette1.wikia.nocookie.net/memoryalpha/images/b/b4/...

Isn't that the whole relativity theory: that if you emit a photon while at celerity 1c, it looks like it goes away at 1c both from you and from a still reference? hence blue is still blue at 1c?

The spectrum of light depends on the frequency of the vibrations in the electromagnetic field, not the velocity of the wave. For both red and blue light the wave is traveling at 1c but the peaks of the wave are at 700 nanometers or 400 nanometers depending on the color. And under Special Relativity distances distort so that you do in fact see light shifted to higher frequencies/shorter wavelengths in the direction you're traveling.

I'm talking about radiation from other stars or what ever. Imagine if every star in the star field in front of you shifted from visible light to gamma.

I'm sure there is a study out there that describes the exact amount of radiation exposure you would receive at reletivistic velocities due to blue shifting.

The speed doesn't change but the wavelength does. That's why we see light from other galaxies redshifted.

> The tough part is making something capable of a constant 1g of acceleration for a 7 year trip.

Isn't that just a building with an engine in the basement? Seems like one of the harder parts would be making sure it can survive freefall at launch, turnaround and arrival.

> Isn't that just a building with an engine in the basement?

No, it turns out that the requirements of generating thrust (which require generating energy and using it to toss something out the back of your ship) end up running into hard limits in the delta-V you can carry based on the available thrust-generating technology. Surviving 1g of constant acceleration in easy (well, I mean, it requires a certain degree of structural strength, which as mass gets large--which it will even with something delivering a minute payload--becomes challenging because of square/cube issues), but building something that can actually generate 1g of constant acceleration for 7 years is a non-trivial engineering challenge.

> Seems like one of the harder parts would be making sure it can survive freefall at launch, turnaround and arrival.

No, surviving free fall is a non-issue. Literally, that means surviving not having external forces acting on it. There's nothing to it.

My layman's reading of physics-for-layman books has taught me that if we were to travel at the speed of light, we'd convert into energy. However, I'm not so sure about 99.999999% the speed of light. That's really OK, as far as we know?

You are technically travelling at 99.99999% of the speed of light right now, relative to something.

You are actually traveling faster than the speed of light relative to some distant galaxies. The "speed limit" in special relativity refers to an inertial reference frame (in general relativity, this would be a reference frame with no/negligible spacetime curvature). As soon as you have significant gravity/acceleration relative to things with mass, the answer becomes much more complicated (and not fixed).

What determines my speed limit? Is it set at 0 here on earth? What if I travel to another galaxy, this one was going at .5c relative to me when I was on earth. Then after trillions of years, inflation causes all of the galaxies to separate beyond sight from me in this new galaxy. Now, the centre of this galaxy appears at rest. Does my velocity get "reset?"

Special relativity says that no matter what your velocity is relative to Earth you can proclaim that you're actually at rest and it's the other guy that's moving. So your velocity is always continuously being "reset". And in each of the frames of reference of everything in existence nothing else is traveling faster than the speed of light.

The 1905 Special Relativity Theory (1905 SRT) version of reciprocity implies that the other guy in a different inertial frame than your own will be the one that is moving. The consequence of this implication is the "Twin Paradox" (i.e. both twins in different inertial frames have been accelerated and are both aging slower than the other twin). A different version of reciprocity that implies that the accelerated twin is moving and the apparent movement of the twin that has remained stationary is only an aberration (or mirage) is axiomatic because movement first requires acceleration.

Assuming spacetime is not expanding, let's say 1 galaxy is moving away from us at .9c. I leave our galaxy and catch it by travelling at .99c. Then a citizen of that galaxy, at rest, accelerates to .9c. So his velocity relative to earth is .89c? I think I need to go watch a youtube video on special relativity. Intertial reference frames are really weird.

inflation/expansion of space is not limited to the speed of light.

I know. That understanding is already illustrated in my question... I don't see what that has to do with answering it?

As far as we know, as long as you don't actually reach light speed (which is currently thought to be impossible anyway) you can pretty much get as close as you want and be fine.

Thanks. It's quite counter intuitive to think about. You'd be going along at 99.99999999999999999999999999999999% and then hit that last bit and poof now I'm photons.

Well, achieving that "last bit" takes an infinite amount of energy, so it's not surprising that that has some effect.

Yes, as long as you don't hit anything or care about the time dilation you will experience.

Also, and I'm not an astrophysicist, but I believe going fast _relative to Earth_ doesn't make it any more or less likely that you're going to hit anything. Moving at .998c relative to Earth and hitting something that is stationary relative to Earth is the same thing as not moving and being hit by something going .998c relative to you.

EDIT: Right, as chris_va pointed out, we're all traveling at .998c relative to something out there.

> Also, and I'm not an astrophysicist, but I believe going fast _relative to Earth_ doesn't make it any more or less likely that you're going to hit anything.

OTOH, given that it is (like most of the stuff around it) orbiting the center of mass of the Milky Way Galaxy, shouldn't Earth be moving relatively close (within a very small fraction of light speed) to the speed of most of the interstellar dust, etc., in its immediate galactic vincinity, such that moving at 0.998c relative to earth is also moving at a very similar fraction of c relative to lots of other things you are going to potentially hit on a journey from earth to a nearby star system?

Of course. Thanks. This is why they don't put me in charge of our next interstellar trip.

>doesn't make it any more or less likely that you're going to hit anything.

I believe that would be wrong. Also not an astrophysicist but I would guess that most of the stuff in our galaxy is moving at speeds which are, on average, relative to our galaxy, and moving at some average rotational speed around it. Of course there could be stray bits moving quite quickly on through.

So moving at c relative to the planets and solar systems swirling around our galaxy probably would make you more likely to hit something.

Not a physicist, but wouldn't a spacecraft standing on Earth's surface already feel 1g because of Earth's gravity (https://en.wikipedia.org/wiki/Equivalence_principle)?

You can look up Project Daedalus's report online. They considered all these issues in great detail and came up with an affirmative answer.

> Is it plausible for anything we'd build to travel .998c and survive the journey?

The first half is actually a bigger problem than the second half.

The problem is far easier to state than implement.

All about funding. NASA, for example, is about 35 years behind schedule by my math, solely from funding.

Now whether throwing money at a public agency would have made advancements in lensing, transistor along with propulsion technology happen quicker. Thats a tougher question that leans towards the "unlikely".

Funding is not the only issue. Their planning was also a disaster. The Space Shuttle wasted so much money with very little return. If NASA continued with Project Orion and NERVA a Mars colony would have been well established by now.

The Space Shuttle was fundamentally flawed because NASA compromised with DoD to get it funded. Had NASA been fully funded for space exploration alone they would have made better choices.

The rocket equation is the biggest block. Getting a constant thrust of 1g for 7.3 years is hard.

It takes an incredible amount of fuel, and an incredible specific velocity.