Why light speed wouldn't matter

[Temstar]

14 minutes ago, 11of10 said:

I imagine it might actually miss the planet in that case, what with it being faster than it's supposed to be, and just flying straight past us.

However, this now occured to me: Can ground based laser stations actually make that lightsail ship enter a stable orbit around Earth?

I think so. You can always angle the sail by angling the whole ship so that the laser bounces off with some angle and you can get thrust in any direction up to 180 degree off axis from the laser source. Basically much like the sail on a tall ship.

I'm not 100% certain but I think there are ways to actually sail light sail against the motion of the incoming photon, but I think that requires several mirrors and a few bounces.

[magnemoe]

1 hour ago, 11of10 said:

I imagine it might actually miss the planet in that case, what with it being faster than it's supposed to be, and just flying straight past us.

However, this now occured to me: Can ground based laser stations actually make that lightsail ship enter a stable orbit around Earth?

Not ground based, the wast heat from the lasers would be more than the energy earth get from the sun. 
Only way to build it would be in space. I would build it around Mercury orbit. So the starship aim pretty much at the sun for the initial braking, only for the final part you move towards earth orbit. Does not have to take it into Earth orbit, once you are close you switch back to the internal engines for the last 100 km/s or something braking 
 

[magnemoe]

59 minutes ago, Temstar said:

I think so. You can always angle the sail by angling the whole ship so that the laser bounces off with some angle and you can get thrust in any direction up to 180 degree off axis from the laser source. Basically much like the sail on a tall ship.

I'm not 100% certain but I think there are ways to actually sail light sail against the motion of the incoming photon, but I think that requires several mirrors and a few bounces.

yes some interstellar ideas drops an outer sail who is reflected and brakes the second stage, sounds very complicated to me, also getting an stable beam all the way to the other solar system. 
Venture stat uses an better system here, one interesting idea is to use the interstellar molecules for braking, think bussard ramjet but you only redirect the molecules, not sure how much force you get out of it but main benefit is that its reactionles

[mikegarrison]

Humans as we know them have only been around for about 50,000 years or so. A little more, a little less. Depending on your definition, you might go back 10x longer than that for "anatomically modern" humans, but there is no evidence that they were "behaviorally modern" humans. The main difference seems to be that language developed about 50,000 years ago.

Hominids have been around for about 2,500,000 years. Maybe a little longer. The last common ancestor with chimpanzees was about 5-7 million years ago.

100 million years is such a vast time that it would be ridiculous to expect there will still be humans. Yes, some species seem to stay unchanged for that long, but those are usually species that live in one small ecological niche. If the niche doesn't change, then they don't change. If there is anything that defines humans, it is that we don't restrict ourselves to a small ecological niche.

[Shpaget]

53 minutes ago, mikegarrison said:

If the niche doesn't change, then they don't change. If there is anything that defines humans, it is that we don't restrict ourselves to a small ecological niche.

No, but we certainly don't suffer and are selected by whatever environment we come across. We modify it to our liking. We put on a jacket if it's cold, burn a tree or two if it's really cold, or install an air conditioning if it's a bit too warm.

[WestAir]

To be fair, the age of transhumanism is arguably less than one lifetime away. With designer babies and genetic modifications so close to our future, I don't see how natural humanity will survive. Two hundred years from now parents will nit-picking every one of their off-springs attributes, from eye color to what type of cool new organs / features they'd like on their child. I can't imagine what will be on Earth in 100,000,000 years but by then it won't be human.

[NovaSilisko]

what the hell happened to this thread

[fredinno]

10 hours ago, magnemoe said:

No, and yes jumping rogue or even rouge planets might be an way this can work out, starting and stopping is not an major issue, you are moving slow and refueling is the easy part. 
More of an issue to find other stuff, planets between stars are likely to have thick ice layers, too thick to drill trough as pressure at depth will collapse anything.  
Smaller objects are probably better. 
And yes this will require an self replicating system, either an machine or colony ship both being able to build copies of itself in practice.

Larger objects are easier to see, and if we have the technology to send a interstellar spacecraft economically, we would almost certainly have the insulation to mine a rouge planet without making it collapse.

[magnemoe]

5 hours ago, fredinno said:

Larger objects are easier to see, and if we have the technology to send a interstellar spacecraft economically, we would almost certainly have the insulation to mine a rouge planet without making it collapse.

Issue is not insulation, issue is that ice get plastic at 50 meter or something probably later at low temperatures but temperature and pressure will rise as you go down. pressure will increase like water pressure as you drill down, if the ice layer is 200 km you will face an insane pressure at the bottom.
Good luck mining here. Smaller bodies will have less pressure and as gravity is low stuff will be more even distributed. 
 

[fredinno]

32 minutes ago, magnemoe said:

Issue is not insulation, issue is that ice get plastic at 50 meter or something probably later at low temperatures but temperature and pressure will rise as you go down. pressure will increase like water pressure as you drill down, if the ice layer is 200 km you will face an insane pressure at the bottom.
Good luck mining here. Smaller bodies will have less pressure and as gravity is low stuff will be more even distributed. 
 

Well, Gas giant planets should work- they have moons that can be mined. The only problem is likely delta-v to go into a orbit.

[Green Baron]

Hi,

in order to stop by an interstellar body for refueling the ship had to decelerate from it's interstellar speed and accelerate again. I'd think that once accelerated to interstellar speed the ship should keep it until arrival ? It costs nothing ...

 

p.s.: one of many approaches to evolution of language (http://www.nature.com/ncomms/2015/150113/ncomms7029/full/ncomms7029.html) (2015).

Separation estimates http://www.nature.com/nature/journal/v483/n7388/full/nature10842.html  for Human / chimpanzee-separation (2012).

Can't say a word about the future ...

Edited January 26, 2016 by kemde

[magnemoe]

42 minutes ago, kemde said:

Hi,

in order to stop by an interstellar body for refueling the ship had to decelerate from it's interstellar speed and accelerate again. I'd think that once accelerated to interstellar speed the ship should keep it until arrival ? It costs nothing ...

 

p.s.: one of many approaches to evolution of language (http://www.nature.com/ncomms/2015/150113/ncomms7029/full/ncomms7029.html) (2015).

Separation estimates http://www.nature.com/nature/journal/v483/n7388/full/nature10842.html  for Human / chimpanzee-separation (2012).

Can't say a word about the future ...

Its not about refueling, its about getting oxygen to replace leaks and raw materials for spare parts then we talk about generation ships using thousands of years to the target. 
Easier to stop and start as you must be able to do so anyway and it takes short time compared to the travel time.

And no I think an faster ship probably combined with cold sleep is far more practical. 
Only benefit is that an slow and huge colony ship is able to replicate everything, however going to an planet you can live on you don't have to do this at once. You can live with not being able to build space infrastructure for some time. 

[fredinno]

3 hours ago, magnemoe said:

Its not about refueling, its about getting oxygen to replace leaks and raw materials for spare parts then we talk about generation ships using thousands of years to the target. 
Easier to stop and start as you must be able to do so anyway and it takes short time compared to the travel time.

And no I think an faster ship probably combined with cold sleep is far more practical. 
Only benefit is that an slow and huge colony ship is able to replicate everything, however going to an planet you can live on you don't have to do this at once. You can live with not being able to build space infrastructure for some time. 

The problem is that even with such a ship, you would need significant life support- it would take 4 years even at c.

[magnemoe]

2 hours ago, fredinno said:

The problem is that even with such a ship, you would need significant life support- it would take 4 years even at c.

yes, however its an major difference between 40 and 4000. First we can make stuff with an good chance of lasting 40 years, not 4000. 
So you can manage with just some redundancy. Main issue is not life support its repair.

For life support you can bring all your supplies you don't need to grow all the food in the ship. yes you will probably grow some fresh vegetables. 
Second some sort of cold sleep is easier than interstellar travel.

[fredinno]

5 hours ago, magnemoe said:

yes, however its an major difference between 40 and 4000. First we can make stuff with an good chance of lasting 40 years, not 4000. 
So you can manage with just some redundancy. Main issue is not life support its repair.

For life support you can bring all your supplies you don't need to grow all the food in the ship. yes you will probably grow some fresh vegetables. 
Second some sort of cold sleep is easier than interstellar travel.

How would you even power a ship? Orion Dirives run up to 0.06c, and nuclear Fusion might be 0.1c.

[magnemoe]

4 hours ago, fredinno said:

How would you even power a ship? Orion Dirives run up to 0.06c, and nuclear Fusion might be 0.1c.

Well in that setting using an orion you would use 66 years to Alpha Centauri so it would be no need to stop and restock. Restocking an orion is a bit harder than an fusion rocket too as you need an bomb factory.
 

[fredinno]

11 hours ago, magnemoe said:

Well in that setting using an orion you would use 66 years to Alpha Centauri so it would be no need to stop and restock. Restocking an orion is a bit harder than an fusion rocket too as you need an bomb factory.
 

I don't think stopping to restock once would increase the travel time too much though..

[Yourself]

On 1/26/2016 at 11:31 AM, fredinno said:

The problem is that even with such a ship, you would need significant life support- it would take 4 years even at c.

Fortunately it wouldn't be 4 years from the perspective of the ship itself.  From the point of view of a ship travelling at c, it would arrive instantaneously no matter where it was going.  It'd take 4 years from the ship's perspective if it were travelling at ~70% c.

[magnemoe]

17 hours ago, fredinno said:

I don't think stopping to restock once would increase the travel time too much though..

No but chances of finding an cache of nukes halfway to alpha centauri is pretty small.
An fusion ship would have easier to refuel. 
The only reason to stop is if you run out of consumables and raw materials. This is an issue on very long duration trips with an generation ship not then going at 0.05c or faster.
 

 

[fredinno]

On January 28, 2016 at 9:21 PM, Yourself said:

Fortunately it wouldn't be 4 years from the perspective of the ship itself.  From the point of view of a ship travelling at c, it would arrive instantaneously no matter where it was going.  It'd take 4 years from the ship's perspective if it were travelling at ~70% c.

Of course not, I meant from the perseptive of everyone else.

18 hours ago, magnemoe said:

No but chances of finding an cache of nukes halfway to alpha centauri is pretty small.
An fusion ship would have easier to refuel. 
The only reason to stop is if you run out of consumables and raw materials. This is an issue on very long duration trips with an generation ship not then going at 0.05c or faster.
 

 

Generation ships will almost certainly be the primary interstellar ships for at least the first several centuries of interstellar travel, so yes, they are likely useful as resting stops. I'm fairly certain going at a level inside a human generation would require something like a Black Hole Drive to work.

 

If something has a metallic body or mineable core, there's almost certainly enough thorium to make bombs. And yes, you can make bombs out of Thorium. http://www.popularmechanics.com/science/energy/a11907/is-the-superfuel-thorium-riskier-than-we-thought-14821644/

[magnemoe]

4 hours ago, fredinno said:

Of course not, I meant from the perseptive of everyone else.

Generation ships will almost certainly be the primary interstellar ships for at least the first several centuries of interstellar travel, so yes, they are likely useful as resting stops. I'm fairly certain going at a level inside a human generation would require something like a Black Hole Drive to work.

 

If something has a metallic body or mineable core, there's almost certainly enough thorium to make bombs. And yes, you can make bombs out of Thorium. http://www.popularmechanics.com/science/energy/a11907/is-the-superfuel-thorium-riskier-than-we-thought-14821644/

Again why would you stop, it only makes sense for an trip lasting many hundreds years. 
An thorium bomb would probably be larger so you would end up with an far larger fuel faction and the rocket equation kills you. 
Note I'm not sure if orion has the ISP required for getting 0.05c but use that here.

Agree with pineconez
http://www.projectrho.com/public_html/rocket/slowerlight.php

[KSK]

If folks haven't already found it, then the Interstellar Missions of this Wikipedia page provides some interesting figures, complete with references. Interesting that one of the proposals is suspiciously similar to the Avatar starship, right down to mentioning (and linking to) a further page describing the (incorrectly named as it turns out) antimatter catalysed nuclear drive.

However, to reply to magnemoe's last question, a fission based Orion ship could apparently reach around 0.03 to 0.05c, with reference figures provided for a 400,000 ton (fully laden) vessel, that would reach Alpha Centauri in 133 years, reaching a top speed of 0.033c

Edited January 29, 2016 by KSK

[KerikBalm]

if you are on EVA with an MMU at the ISS (acronyms, so many!), 1 meter away from the airlock, you just point and thrust.

The galaxy is 100,000 light years across, that mean the diameter of our orbit (sincewe're at the endge) is roughly 300,000 light years.

4 light years travel is an insiginficant portion of the orbit

Or look at it this way:

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

The sun orbits the center of the galaxy every 250 million years.... more or less

4 years at light speed means the travel time is 4/250,000,000 -> 0.0000016% of the orbital period.

Our orbital velicity around the center of the galaxy is 1/1300th the speed of light. while stuff gets weird very close to light speed, the point is that the orbital velicty is minor compared to light speed

Point and go... alpha centuria will more very slightly relative to where you are pointing, but the angle between where you should point, and where alpha centauri is now... is very very small.

If you were to do a hohm an transfer to alpha centauri, you wouldn't be going light speed, and it would take many millions of years.

Light speed transfers between stars would be like these sort of high dV interplanetary transfers:

 

Edited January 29, 2016 by KerikBalm

[magnemoe]

1 hour ago, KSK said:

If folks haven't already found it, then the Interstellar Missions of this Wikipedia page provides some interesting figures, complete with references. Interesting that one of the proposals is suspiciously similar to the Avatar starship, right down to mentioning (and linking to) a further page describing the (incorrectly named as it turns out) antimatter catalysed nuclear drive.

However, to reply to magnemoe's last question, a fission based Orion ship could apparently reach around 0.03 to 0.05c, with reference figures provided for a 400,000 ton (fully laden) vessel, that would reach Alpha Centauri in 133 years, reaching a top speed of 0.033c

Nice so its works better than I expected. An medusa would be preferable as the engine part is lighter you should also be able to use larger and more efficient bombs.

[Yourself]

7 hours ago, fredinno said:

Of course not, I meant from the perseptive of everyone else.

My mistake.  You'd mentioned the life support of the ship in regards to the travel time, but the life support travels with the ship, so the travel time from the perspective of the ship is all that would matter in that case.  That's why I assumed you were talking about the ship's proper time rather than an outside observer's.