Interstellar Flight, slowboat mode.

[SargeRho]

Avatar and Firefly/Serenity aside, pretty much every sci-fi movie featuring interstellar civilisations also features a form of faster than light travel. But I've become more intrested in imagining ways for civilisation to make due without such physical shenanigans.

The fact aside that interstellar civilisation is likely not practical, and assuming an average human lifespan of 100ish years thanks to medical advances, what do you think would be the best way to achieve interstellar flight well within human lifetimes, to a point where it'd be possible to go back and forth a few times?

I'm thinking initially, well before an interstellar civilisation is actually established, ships might be built in a way similar to the ship envisioned by Project Daedalus, but as sleeper ships, taking decades to a century to reach nearby stars, using magnetic sails as interstellar parachutes, to reduce the fuel needed when braking. Later on, large particle beam stations might be built in a low-ish solar orbit, pushing against the magnetic sails used by such ships, reducing fuel requirements, or shortening the trips by accelerating them further than they otherwise would go. Those ships would be multiply redundant, and each carry a few 100 frozen colonists along with tens of thousands of frozen embryos. Such colony fleets would only be sent to planets known to have an atmospheric composition and temperature suitable for human life.

Another thing I wonder about: How do you keep a starship powered for the journey? You might have to keep it powered for over a century after all. I'm thinking either some sort of fission reactor with a purification plant, or a fusion reactor. I think it'd take roughly 20 tons of deuterium and helium 3 to keep a 1.5Gw reactor going for a decade, but I'm not sure there at all.

Something like this perhaps?

The Tsiolkovsky, the first manned interstellar spacecraft ever built, accelerates away from the Solar System with a crew of 100 frozen colonists. Using pulsed fusion propulsion, it powers it's way up to nearly 20% the speed of light. At such tremendous speeds, the diffuse gas and dust of the interstellar medium becomes a hail of deadly projectiles. To protect the the ship from the occasional collision with dust grains, a massive triple-layer impact shield absorbs the majority of impacts. By the time the Tsiolkovsky reaches it's target, the shield will be blasted and scarred with impact craters and radiation damage.

After it has achieved coasting velocity, the main engine is jettisoned. Once it is time to decelerate, a magnetic sail, a loop of superconducting wire many hundreds of kilometers wide is deployed, acting as a parachute by braking against it's destination's stellar wind. A smaller fusion-pulse engine then slows it into a capture orbit.

Edited March 11, 2014 by SargeRho

[Scotius]

I'm not sure jettisoning main engine halfway would be practical. Or safe. If something happened to the magnetic sail ship would be unable to decelerate. And keeping the engine means there is no need to carry second one for in-system maneuvers. Better to keep it simple

[Winter Man]

Thing is with non-relativistic sublight interstellar travel, if your journey is longer than 40 years the technological advances made back on Earth make your craft pretty redundant. It's always worth waiting that little bit longer for that extra bit of tech, and it never goes ahead.

[SargeRho]

Jettisoning the engine is very practical actually. You shave a few 100 tons off your mass by the time you decellerate. It's a 2-stage ship. The main engine stage is jettisoned once empty, but there's a second, smaller stage. Project Daedalus would have used that engine to accelerate further. But you kinda want to stop at your destination, not blast past at 20% the speed of light. The first stage is several times as heavy as the second stage, counting only the engine section, not what it's pushing. At some point the mass of a second engine and the jettison mechanism is compensated for by getting rid of the dead mass you no longer have to accelerate.

If everyone thought that way, we wouldn't ever get anywhere. It's what's kept us from going to Mars, and is a way of thinking that needs to die.

Edited March 11, 2014 by SargeRho

[Red Iron Crown]

Slowboat travel falls into two camps as near as I can tell: Put Everyone to Sleep, and Reproduce Along the Way.

Put Everyone to Sleep: A "sleeper ship", people are frozen or hibernated somehow so they consume few resources and experience little time passing on the journey.

Pros:

- The colonists (volunteers, one would hope) arrive within their own lifetimes, pretty much in the same condition as when they left.

- Fewer consumables required for life support.

- Less living space required.

Cons:

- Crew needs to be available to deal with unexpected situations, perhaps on rotating awake periods, so crew will be older upon arrival.

- Needs reliable, proven hibernation technology.

Reproduce Along the Way: A "generation ship", the crew reproduces along the way, with the people arriving at the destination being descendants of the original crew.

Pros:

- No hibernation tech required.

- Ship provided enough space for living until colony living arrangements are made.

Cons:

- The descendants may not care about colonizing and prefer to stay on the ship on which they were raised.

- Much larger living space per crew member required.

- Needs either a sustainable closed ecology or very large amount of stored consumables.

Personally, I think the sleeper ship is the more viable option, but both options require technologies we haven't developed yet.

[DonLorenzo]

Thing is with non-relativistic sublight interstellar travel, if your journey is longer than 40 years the technological advances made back on Earth make your craft pretty redundant. It's always worth waiting that little bit longer for that extra bit of tech, and it never goes ahead.

While I want to agree with the sentiment (technology goes fast, is inexorable and has a driven purpose etc.), just how close are we to overtaking the voyager and pioneer probes again?

Edit: also, the newer ships could always go to different destinations. It's not like there's a set roadmap. The universe is vast. A quote from a since forgotten sci-fi book: 'Even if you suddenly got the ability to teleport to all the worlds, and would set to exploring one per day, it'd still take tens of thousands of years to check out just our corner of the galaxy'

Edited March 11, 2014 by DonLorenzo

[Canopus]

I guess you would go as fast as you can but still stay slow enough so that relativity doesn't affect you too much. You have already mentioned many technologies that could make that possible. You would search for a perfect planet to colonise in nearby space with telescopes and then you launch a self sustaining colony that also has to work politically so you basically have a new country on that spacecraft instead of a colony that is in need of control from earth. The ship would most likely be a generation ship that stays at the colony after it has been established. Maybe with some advanced facilitys onbaord that are needed for establishing the colony on the ground and then slowly after some years a constant line of supply ships fly from earth to the new world starts.

Thats atleast what i hope for humanity to happen someday.

[Streetwind]

For interstellar travel within human lifetimes, you basically need fusion drives. No form of propulsion currently available to us can achieve the required delta-V because they are not fuel efficient enough. If your Isp isn't at least six digits, you don't even need to try for the Centauri system, which is our closest neighbor.

Then though you need to ask if you even want to go to Centauri. If there's nothing there that we want (such as an earthlike world, which there isn't), we have gas giants and dead rocks aplenty in our own system. They might send a science team or two to research the highly unusual "binary plus extra" star configuration, but colonists are highly unlikely.

This complicates the matter somewhat, because for science missions you don't want any arbitrary human to arrive there, but rather exactly the specialists you chose. Even if you picked people in their late twenties, which is exceptionally young for an astronaut, they would be approaching the end of their natural lifespan by the time they got there on a 40-50 year cruise - along with all that comes with it, such as failing eyesight and hearing, and an old and unflexible brain. And that's not even counting potential effects of long-term space habitation.

Using a generation ship on the other hand could be tricky as well - you'd have to send a number of parent pairs who then conceive offspring in-flight, and from the first day on drill them to become scientists to study the Centauri system. These children would never have seen the earth, and would never live to see it. They would be born enroute, live their life in the pursuit of science for the benefit of a world that's as alien to them as the lifeless place they study, and ultimately die out there once the task is done. Trapped in a small spacecraft from birth to death, lightyears from a place that their parents might have called home but they never could. They'd never even have a choice. Morally a highly questionable affair.

Edited March 11, 2014 by Streetwind

[SargeRho]

You would most likely use Hibernation/Cryostasis systems when going to another star. At 20% the speed of light, you'd take 25ish years to get to Alpha Centauri. Taking acceleration into account, let's say 30?

So far one planet has been found in the Alpha Centauri system, and planets can stably orbit either star as far out as Saturn is from the Sun in our solar system. Since both stars are similar to the Sun, the habitable zone is further in than that. You can't say for certain there aren't any Earth-like stars in ACAB, because it hasn't been studied enough. So far, one rocky planet orbiting very close to ACB.

[NASAFanboy]

Thing is with non-relativistic sublight interstellar travel, if your journey is longer than 40 years the technological advances made back on Earth make your craft pretty redundant. It's always worth waiting that little bit longer for that extra bit of tech, and it never goes ahead.

There was a short story I wrote about a colony on Glise 581g celebrating the arrival of the first interstellar probe. Apparently, humankind had perfected the acclubierre drive a decade after the probe was launched using breakthroughs in quantum physics or something.

[Simon Ross]

Sorry, but waiting for technological advances is like waiting for a train that will never arrive.

40 years ago, we could land a man on the Moon, today the US cannot even get a man into LEO.

No NERVA, no Shuttle, no Vision

Technological advances don't just come out of thin air, men make them happen

[Canopus]

Sorry, but waiting for technological advances is like waiting for a train that will never arrive.

40 years ago, we could land a man on the Moon, today the US cannot even get a man into LEO.

No NERVA, no Shuttle, no Vision

Technological advances don't just come out of thin air, men make them happen

But can't you see whats happening around you? We may currently not be big in spacetravel but we have come so far in many other fields of sciences and engineering. And the rest will inevitably happen too. You make it sound like nothing has happened in the last 40 years.

[Sirrobert]

Sorry, but waiting for technological advances is like waiting for a train that will never arrive.

40 years ago, we could land a man on the Moon, today the US cannot even get a man into LEO.

No NERVA, no Shuttle, no Vision

Technological advances don't just come out of thin air, men make them happen

Sure we could, if we'd invest the time required in it. We as a species have deceided not to.

Time is not infinite. The time you spend researching one thing, you can't spend researching something else

[AngelLestat]

The fact aside that interstellar civilisation is likely not practical, and assuming an average human lifespan of 100ish years thanks to medical advances, what do you think would be the best way to achieve interstellar flight well within human lifetimes, to a point where it'd be possible to go back and forth a few times?

I trully believe that there is a minimun velocity that we need to achieve to travel interstellar distances.

For example, to the alpha centauri case, it will be close to 10% the speed of light. For a distant star would be more.

Becouse we need to considerer many things to calculate this minimun speed:

-Crew (if we dont have himbernation or something like that, the time presents a problem)

-Technology advance, if we have a ship that arrives in 80 years traveling at 0.05c, then is very possible that we have enoght technology to double that speed in the next 40 years, so this would make almost pointless the first mission. But if we already manage to achieve 10% of light speed, this mean that we can reach alpha centauri in 40 years, so is very unlikely that we can double that speed in the next 20 years..

But if we choose another star that is far away, then this minimun speed rise.

-how much time will pass until we see the benefits.

- etc.

Another thing I wonder about: How do you keep a starship powered for the journey? You might have to keep it powered for over a century after all. I'm thinking either some sort of fission reactor with a purification plant, or a fusion reactor. I think it'd take roughly 20 tons of deuterium and helium 3 to keep a 1.5Gw reactor going for a decade, but I'm not sure there at all.

When you are accelerating, you have no problem with the energy, when you are slowing down with a magnetic sail, you have no problem either, becouse the magnetic loop in the slowing down process generate a lot of energy, enoght to any ship needs.

Something like this perhaps?

http://fc04.deviantart.net/fs71/f/2011/231/1/2/tsiolkovsky_by_smpritchard-d462z32.jpg

Where do you get this image? or is just a draw of some deviantart user?

Sorry, but waiting for technological advances is like waiting for a train that will never arrive.

technological advances always arrive, but I guess your opinion is most founded in policy decisions.

Edited March 11, 2014 by AngelLestat

[SargeRho]

The magsail is actually going to consume power, since you need to charge it up. And you'd have a power problem for the decades long cruise.

The image is a render made by SMPrichard of a Starship of his own design, the Tsiolkovski. He's also among the people I follow on DeviantArt (being a DA user myself). Sauce: http://smpritchard.deviantart.com/art/Tsiolkovsky-252081182

I'm working on a starship of my own, daedalus-derived too right now.

Shameless self-advertising:

Edited March 11, 2014 by SargeRho

[Simon Ross]

With respect to a couple of the posters here

Unless you are driving advances in technology.

Unless you have a clear goal and a vision of how to reach it

Unless you are committed to taking a certain acceptable level of risk

NOTHING HAPPENS !!!

Again, sorry, but actually bugger all has happened to improve our capacity to LEO and beyond. 40 years ago we had the capability to orbit 100+ tons of payload, today we couldn't even put a single man into orbit !

It's a total failure of vision. a total failure of policy and a total failure of courage !

We had so much, now we have so little

Sorry to rattle a few cages, but please wake up and smell the coffee folks

Edited March 11, 2014 by Simon Ross

[Nuke]

id go the generation ship route, using my method from the asteroid ships thread:

what i would do use use an ice dwarf. i would use the ice as fuel for a nuclear water (or ammonia, or whatever) rocket, or perhaps some kind of fusion-electric. the important thing is that melted ice is either used as the propellant, or is used to make the propellant (which could be hydrogen or hydrazine or something). i imagine fields of engines all pointed skyward surrounded by open pit mines gathering ice to feed the thruster farms. the thrusters would be mounted on treads so they can be moved as areas are mined out, and to redistribute thrust as needed. any non-ice materials can be utilized by the inhabitants, or simply thrown overboard to lessen the "ship"'s mass.

habitation would be in underground centrifuges, as any gravity will be too small to be useful. depending on how much gravity is available, you may need a more conic centrifuge to compensate. i imagine these being constructed in deep open pits (perhaps retired mines), and then capped over with a dome of reinforced ice, for radiation shielding.

[NASAFanboy]

With respect to a couple of the posters here

Unless you are driving advances in technology.

Unless you have a clear goal and a vision of how to reach it

Unless you are committed to taking a certain acceptable level of risk

While NASA lacks a clear goal for now, they are going capability-based rather than destination based. NASA has a mantra, and that's "Build it, and the payloads will come". That's why we are building the SLS. NASA has a clear goal that is limited and only extends to what, 2021? And even that is debatable (I'll be realistic and say that NASA has a clear goal until 2020). Remember the last time we went destination-based? With Constellation and Apollo?, none of which survived a decade? And the last time we went capability based, with an Shuttle program that lasted for thirty years? NASA well understands that capability-based is the way to go.

NOTHING HAPPENS !!!

Again, sorry, but actually bugger all has happened to improve our capacity to LEO and beyond. 40 years ago we had the capability to orbit 100+ tons of payload, today we couldn't even put a single man into orbit !

We, as in the United States, I presume? Last time I checked, we still had Soyuz and Shengzhou.

The United States is quickly closing up the spaceflight gap with private companies who are building spacecraft that are anything if more capable and advanced than the Russians and the Chinese. The Dreamchaser and the CST-100 and most likely the Dreamchaser can carry twice as many astronauts as a Soyuz with computing power that is infinitesmally more advanced. We're holding off for better things. If we didn't cancel the shuttle, we would still be stuck in LEO for the foreseeable future, the shuttle simply had to go if we were to break out of Earth Orbit.

It's a total failure of vision. a total failure of policy and a total failure of courage !

We had so much, now we have so little

The United States has the largest and most successful planetary science program in the world. No other nation except for the United States has an probe on an interstellar trajectory. No other nation except the United States has sent a probe to the outer planets by themselves, and no other nation except for the United States has any probe headed to the outer planets in the foreseeable future (USA has the Europa Clipper in 2025, the Juno in 2016, the New Horizons in 2015). We've demostrated and created technology that will drive us along faster in spaceflight that we ever would have at lesser cost and more safety. The Apollo missions were and lucky streak, some missions like Apollo 8 and Apollo 11 had only an 50/50 chance of succeeding. Future NASA missions will have an much, much greater chance of success.

Sorry to rattle a few cages, but please wake up and smell the coffee folks

Caffiene Drinkers Unite!

[Scotius]

Times are a'changing Current crisis in Europe already considerably chilled relationship between USA and Russia. I would not be surprised to see increased efforts to man-rate Dragon and Boeing capsule, and again give NASA ability to send manned crafts to space.

[SargeRho]

Simon, this thread is making the assumption that there is the motivation, will and ressources to do it.

[Red Iron Crown]

Dreamchaser can carry twice as many astronauts as a Soyuz with computing power that is infinitesmally more advanced.

You keep using that word. I don't think it means what you think it means. /Inigo

[NASAFanboy]

You keep using that word. I don't think it means what you think it means. /Inigo

I'm trying to stress the fact that the US will soon have its own fleet of mini-shuttles going to and from orbit in spacecraft more capable than the Soyuz....

[KASASpace]

I prefer sleeper ships, like in Harry Turtledove's Worldwar series, where aliens attack earth in 1942, using fusion and hibernation tech to get here from Tau Ceti, ~12 ly from Sol.

Send a small fleet, each ship landing in one general location, but being used as production facilities at first, and then getting cannibalized for parts.

Of course, now we need that planet.......

[SargeRho]

NASAFanboy, Infinitesimally means that it's "infinitely smaller than" or "an infinitely small fraction of". The word you're looking for is Infinitely.

Another method I found was using lasers to produce matter-antimatter fuel using enormous solar arrays as power source. Such a probe could travel to a nearby star, refuel, and repeat that procedure several times, lasting as long as its engines will survive the radiation.

Edited March 11, 2014 by SargeRho

[NASAFanboy]

Infinitesimally small means that it's "infinitely smaller than" or "an infinitely small fraction of". The word you're looking for is Infinitely.

I have facepalmed, and now I must headdesk.