Snowball Hopping

Question

If you take real physics, you could travel to the next star in moving cities.

Imagine independent, self-sufficient mining outposts attached to an asteroid. While the asteroid is being used up, the youth will start to search the next target. People will follow when one is found. Latest when the last scrap of material is used, also the most stagnant family will move on.

You can live that way, in a few generations, from asteroid to asteroid to Jupiter's trojans, to Saturn's rings, into the plutonoids, from there into the Oort cloud.... well and at the end of our Oort cloud, the next star's gravity well begins. From snowball to snowball, in a few 100 years you arrive at Proxima Centauri.

It is doable with today's technology or very little advancement from here. But you have to say goodbye to the dream of going there, taking some photos and coming back to show them your wife.

Instead you have to develop an entirely self sufficient life style which is religiously or philosophically focused on moving on to the next snowball, you have to take your entire family with you and you have to say goodbye to earth.

Question

What tech would be needed that is absolutely not available today? For the sake of this question, I would understand rotating hammers or rings for artificial gravity as existing technology: even if it has not yet been built, the concept is understood and technically feasible.

Which prerequisites are missing today?

What problems could those space faring families encounter?

Answer 1

It is doable with today's technology or very little advancement from here

Not at all. We are still struggling to find a way to protect the astronauts on their way to Mars, which as compared to what you describe is just the grocery store around the corner!

Few months of permanence in microgravity, as seen with the astronauts living on the ISS, just to cite the most recent examples, severely weaken the human body, by weakening bones and immune systems among others.

And the ISS orbits under the protection of Van Allen belts, meaning that the astronauts are not showered in highly energetic particles, which would further damage a living organism.

And then the people living on ISS can rely on constant cargo supplies from Earth, they don't have to grow their own food, do their own laundry and so on and so forth.

We don't even know if a woman can successfully start and complete a pregnancy in microgravity!

If you really want to enable ice hopping, as you call it, you need to:

• mitigate microgravity damages to human organism (pregnancy included)
• mitigate high energy particles damages to human organism (pregnancy included)
• find a way to locally produce food and other needed supplies
• find a reliable energy source to supply the stations
• find a suitable propulsion mechanism: moving all that mass around will require a huge lot of rocket propellant!

I highly recommend reading this NASA informative site

Answer 2

Short hops cost more fuel than long hops

L. Dutch has succinctly pointed out some of the big ticket reasons why humanity is not equipped for long duration space travel yet. There is another key concept though.

To quote Douglas Adams yet again, "Space is big. Really big." Proxima Centurai is over 4 light years from Earth. To get there in even 400 years would require that the average speed during the trip was over 1% of lightspeed. We are not even close to being able to accelerate a spacecraft to that speed, yet the question assumes that most of the time would be spent settling new rocks.

Travel on Earth is fundamentally constrained by friction in a way that space travel is not. Friction (primarily drag) increases with the square of speed, so for a given shape, doubling the speed requires four times the power, tripling the speed requires nine times the power and so on. Most vehicles on Earth can reach their top speed within a few minutes at most and will remain at that speed as long as their thrust equals the drag at the speed they are travelling. So it makes sense to break up long trips into short hops - drive for a couple of hours, stop at a service station (gas station for those who don't speak Australian) for fuel and to stretch your legs, then drive for a few more hours. Repeat a dozen times with some overnight stops for a long trip. While the time spent stopped may add up, the act of stopping consumes very little fuel overall.

Space travel is completely different. Let's assume that there is a spacecraft that has made it out of Earth orbit and wants to go places with a low thrust, high efficiency ion drive or something similar. It has performance far exceeding anything currently proposed - it has enough fuel to accelerate at 1 ms^-2 for 100,000 seconds, this fuel being an insignificant portion of its total mass (yes, this is unrealistic). The spacecraft needs to reach an asteroid ten light minutes (180,000,000,000 m) away which is at rest relative to its current frame of reference. The spacecraft can either travel directly there in one hop or it can stop at a service station along the way.

1. Express trip: The spacecraft accelerates for 50,000 seconds, reaching a speed of 50,000 m/s and covering 12,500,000,000 m. The spacecraft then cuts its engines and coasts for 3,100,000 seconds before turning end for end and decelerating for 50,000 seconds, during which it covers the remaining 12,500,000,000 m and comes to rest relative to its destination. Total travel time is 3,200,000 seconds (or about 37 days.)
2. Pit stop trip: The spacecraft accelerates for 25,000 seconds, reaching a speed of 25,000 m/s and covering 625,000,000 m. The spacecraft then cuts its engines and coasts for 3,550,000 seconds before turning end for end and decelerating for 25,000 seconds, during which it covers the remaining 625,000,000 m and comes to rest relative to the space-going service station. Then it has to repeat the entire process again in order to reach the destination asteroid. Even assuming that the service station is the super-deluxe-instant-service version and no time is spent there, total travel time is 7,200,000 seconds (or about 83 days).

In other words, even one stop of zero duration along the way in space will more than double the travel time. Stopping ten times along the way will slow the trip by a factor of more than one thousand, even ignoring the time spent stopped. Even if humanity can build ships that can accelerate up to 1% of light speed, figure on the slow migration route taking hundreds of thousands or millions of years to reach the nearest star.

Answer 3

There are many interrelated problems that we are not currently able to resolve.

Chemical propulsion limits the speed achievable regardless of the mass of the space craft to a minuscule fraction of the speed of light making journey times of the order of tens of thousands of years and stopping off at a range of locations on the way does not help.

Energy becomes an increasing problem as you move away from the sun. Beyond the orbit of Jupiter solar power is hopelessly feeble. Nuclear fusion fuel would only last a few decades and fusion power is still not with us.

Another major issue is production capability. It is one thing being able to easily produce a spacesuit or rocket engine on Earth, but it is quite something else to produce the same item in orbit, on the Moon or on some distant icy comet. This point in particular deserves to be emphasised.

If we can make it on Earth it does not mean we can (with current technology) make it elsewhere. Modern technology relies on a globe spanning network of industry which simply would not exist in the remoteness of space. If more Titanium plate was needed all manner of other technologies and materials would need to be provided. It would need cutting and forming and those machines would need repair and replacement, chlorine would be needed which in turn requires electrochemical processing and brine.

It would be no good to say that we can use other technologies instead of those I have mentioned because ultimately they all have similar issues of interconnectedness and complexity. And it would be no good to say that there is salt or frozen brine at the location, because in most cases we won’t know how much there is, and how accessible it is and what level of what other impurities are present.

An even better example might be reprocessing spent nuclear fuel rods or prospecting for Uranium. Think of the myriad of subsidiary processes required from nuclear enrichment to protective clothing, where will these come from and where will the machines that produce them come from?

Sorry to be so pessimistic I wish it were different, but such is life, perhaps in the decades and centuries to come we may slowly overcome some of these obstacles.

Answer 4

That sounds really easy and funny in your description but I don't think it is. It is not that easy to generate a self-sufficient base up in space, as you need to produce all resources, every little bit, by yourself. The first problem you will come into contact with is fuel. Our technology is mainly propulsion-based and you will not find that much materials in space you could generate acceptable fuels from. Solar sails as a drive could be a solution but our knowledge in this technology is not advanced enough at the moment. Another problem is food. We are able to grow plants in space, yes, but not on the long term. Especially soil (or fertilizer) still have to be brought up from earth and your asteroids and most of the planets/moons will not give what our plants need to grow.
These two problems alone forbid to try this with our current technology-level, still not thinking about getting the vast amount of materials and humans you need for a community living for generations (so at least a few thousand humans) up in space. And keeping them living (body degeneration in zero gravity.)

Still gave you +1 for the fresh idea of humans doing the grasshopper on a interstellar scale.

Answer 5

The key critical requirment is a clossed Life Support System. Essentially you are going to create closed ecosystems in space colonies that can last for centuries, while in the present we have no idea how to do this.

The "Biosphere 2" experiments eventually failed as the people inside the dome needed to have outside materials imported (like oxygen) as the various biomes destabilized and outpust became erratic - all in less than a year. Compounding the problem, the experiment was ended and no real follow up has ever taken place (I believe the entire Biosphere 2 compound was later sold). Some issues were not even really known at the time (the concept of "microbiomes" was barely understood in humans, much less the idea of microbiomes in plants, the soil and virtually everything else. We still don't have a clear understanding of that even today).

So with enough money, you can currently get to Mars and even live there for a while with a huge import pipeline, the knowledge to build and sustain a closed life support system is lacking. Until that cam be addressed, long term survival in space is going to be diffficult and expensive (and perhaps a workable CLSS will be equally difficult and expensive - we just don't know).