Photon propulsion (split from 3 facts maybe you don't know about antimatter)

[Curious layman]

On 6/17/2019 at 12:35 PM, swansont said:

Unless you can go and "mine" antimatter (e.g. positrons from a radioactive decay), it's not an energy source. It's more like a battery — energy storage. You have to put energy in to create it, and the ways we do that are really inefficient.

Apparently a photon rocket is the most promising engine for interstellar flight.

https://en.m.wikipedia.org/wiki/Photon_rocket

Edited July 10, 2019 by Curious layman

[Curious layman]

The quote above from Swansont is from the "is time travel possible?" thread, in the general philosophy section by the thinkertank.

Edited July 10, 2019 by Curious layman

[swansont]

4 hours ago, Curious layman said:

Apparently a photon rocket is the most promising engine for interstellar flight.

https://en.m.wikipedia.org/wiki/Photon_rocket

Interstellar? Not so much. They are overselling the concept. The paper mentions manipulating cubesats, not powering interstellar craft.

https://www.researchgate.net/publication/323390665_Demonstration_of_a_mN-Class_Photonic_Laser_Thruster

Yes, you can get more propulsion by "recycling" the photons. But even at 3.5 mN, if you are accelerating a 350 kg payload (a human in a tiny pod, no food or supplies), that's 10^-5 m/s^2. Want to go 300 m/s? It'll take you a year before you're going that fast.

That tiny acceleration is not sustainable, because the laser is getting further and further away from the payload, and the beam spreads out, lowering the intensity. The cubesat experiment used a smaller mass and was at a distance of only a few meters. (3.5 kg would be an acceleration of 10^-3 m/s^2, meaning it would move a meter in less than a minute, which is basically what their lab demo was)

 

 

[Curious layman]

Starting to think getting people to the nearest star is completely impossible. Maybe better to just send small probes that can assemble into something bigger. Use bio-tech to make us there instead, with artificial wombs and stuff.

[Bufofrog]

I agree, based on the current physics and the cost involved I can confidently say we will never travel to another star system.  I think if there is any sentience that would be able to achieve interstellar travel it would be AI.  No food, atmosphere or radiation damage to worry about and the AI could go into sleep mode for the 1000 years it takes to reach a close star.  The vehicle could be quite small also.

[zapatos]

15 minutes ago, Bufofrog said:

I agree, based on the current physics and the cost involved I can confidently say we will never travel to another star system.  

I suspect that if our star was going to no longer be an energy source for us in the relatively near future that we would begin work on an inter-stellar ship for people. I don't see current physics stopping us. 

[Bufofrog]

2 minutes ago, zapatos said:

I suspect that if our star was going to no longer be an energy source for us in the relatively near future that we would begin work on an inter-stellar ship for people. I don't see current physics stopping us. 

I certainly do.  Maybe it would be the technology more than the pure physics that would prevent us from successfully* leaving the the solar system.  It will never happen and there is no place to go anyway.

*I think in the distance future we could send a ship full of dead people to another star...

[zapatos]

2 minutes ago, Bufofrog said:

I certainly do.  Maybe it would be the technology more than the pure physics that would prevent us from successfully* leaving the the solar system. 

We already have a spacecraft that has left the solar system. No need to wait for the distant future, we could have already sent dead people on their way to another star.

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It will never happen... 

Please be specific with some issue preventing us from traveling to another star that we will never overcome.

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and there is no place to go anyway.

Wow. Not even sure how to respond to this one.

[Moontanman]

On 7/10/2019 at 6:58 AM, Curious layman said:

Starting to think getting people to the nearest star is completely impossible. Maybe better to just send small probes that can assemble into something bigger. Use bio-tech to make us there instead, with artificial wombs and stuff.

It depends on if you think the same people who launched will get there. 

16 minutes ago, Bufofrog said:

I certainly do.  Maybe it would be the technology more than the pure physics that would prevent us from successfully* leaving the the solar system.  It will never happen and there is no place to go anyway.

*I think in the distance future we could send a ship full of dead people to another star...

We could, with only controlled fusion plus our current technology, colonise the entire galaxy is something like 250,000 to 250,000,000 years. As far as where to go... where ever you want to go as long as you are taking your own environment with you the destination becomes only means to refuel, repair, and reproduce. Planets and gravity wells are to be avoided if possible.. 

46 minutes ago, Bufofrog said:

I agree, based on the current physics and the cost involved I can confidently say we will never travel to another star system.  I think if there is any sentience that would be able to achieve interstellar travel it would be AI.  No food, atmosphere or radiation damage to worry about and the AI could go into sleep mode for the 1000 years it takes to reach a close star.  The vehicle could be quite small also.

 

On 7/10/2019 at 6:58 AM, Curious layman said:

Starting to think getting people to the nearest star is completely impossible. Maybe better to just send small probes that can assemble into something bigger. Use bio-tech to make us there instead, with artificial wombs and stuff.

Sorry repeat.. 

[Bufofrog]

32 minutes ago, zapatos said:

Please be specific with some issue preventing us from traveling to another star that we will never overcome.

Distance.

I know it sucks.  I would love a universe where Star Trek or Star Wars was a real thing but it ain't.  We are celebrating man reaching the moon 50 years ago.  Why haven't we been back?  Distance.  And the distance to the moon is nothing.

I fear the chance of successfully sending people to Mars and having them return within the next 20 years is 75% at best.

16 minutes ago, Moontanman said:

We could, with only controlled fusion plus our current technology, colonise the entire galaxy

The Fermi paradox isn't a paradox at all.  The answer is unpleasant but obvious, "you can't get there from here".  

I am not going to argue this, since it is pointless, but i do think that if we didn't have this idea in the back of our minds that we have all these new planets to escape to, then just maybe we wouldn't treat the earth like it is something we could throw away after crapping it up.

 

Edited July 11, 2019 by Bufofrog

[zapatos]

4 minutes ago, Bufofrog said:

Distance.

There is a simple solution for that. Time.

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I know it sucks.  I would love a universe where Star Trek or Star Wars was a real thing but it ain't.  We are celebrating man reaching the moon 50 years ago.  Why haven't we been back?  Distance.  And the distance to the moon is nothing.

Really? We haven't gone back to the moon because it is too far away?

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The answer is unpleasant but obvious, "you can't get there from here".  

Well thought out and presented argument.

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I am not going to argue this, since it is pointless...

Circular logic. I agree, it is probably pointless to discuss this with you.

[Bufofrog]

3 minutes ago, zapatos said:

Really? We haven't gone back to the moon because it is too far away?

Yes.  We can live in space fairly easily as shown by the ISS.  But the moon is too far away and hence expensive.  Why do you think we haven't gone back?

3 minutes ago, zapatos said:

Well thought out and presented argument.

It actually is.  The distances are just too difficult to overcome.

I know everyone will hate me for stating what seems obvious to me, because it is not want we want.  But a famous philosopher once said, "you can't always get what you want".

So I will stop here since it will only get uglier from here.  I will state for the record, I so hope that I am wrong and we figure out some whiz-bang way to get off this rock and move to the stars.

[Moontanman]

21 minutes ago, Bufofrog said:

Distance.

I know it sucks.  I would love a universe where Star Trek or Star Wars was a real thing but it ain't.  We are celebrating man reaching the moon 50 years ago.  Why haven't we been back?  Distance.  And the distance to the moon is nothing.

I am not suggesting any magical technology, and distance is meaningless if you live in a space habitat. 

 

21 minutes ago, Bufofrog said:

I fear the chance of successfully sending people to Mars and having them return within the next 20 years is 75% at best.

I'm not sure what this has to do with star travel. 

21 minutes ago, Bufofrog said:

The Fermi paradox isn't a paradox at all.  The answer is unpleasant but obvious, "you can't get there from here".

Why? 

21 minutes ago, Bufofrog said:

I am not going to argue this, since it is pointless, but i do think that if we didn't have this idea in the back of our minds that we have all these new planets to escape to, then just maybe we wouldn't treat the earth like it is something we could throw away after crapping it up.

 

I would not suggest escaping to other planets, such an assertion is foolish. Not taking care of the Earth is foolish and short sighted in fact I see a time when the majority of humans live in space habitats and the earth is more of a nature reserve. 

Just now, Bufofrog said:

Yes.  We can live in space fairly easily as shown by the ISS.  But the moon is too far away and hence expensive.  Why do you think we haven't gone back?

No reason to go back yet? 

Just now, Bufofrog said:

It actually is.  The distances are just too difficult to overcome.

We put a lander on Titan using nothing but chemical rockets... I doubt you have a clue to what you are talking about. 

Just now, Bufofrog said:

I know everyone will hate me for stating what seems obvious to me, because it is not want we want.  But a famous philosopher once said, "you can't always get what you want".

Yes and a famous scientist said we would never travel faster than 60mph blah blah blah... 

Just now, Bufofrog said:

So I will stop here since it will only get uglier from here.  I will state for the record, I so hope that I am wrong and we figure out some whiz-bang way to get off this rock and move to the stars.

We already have, evidently just not fast enough for you... 

[swansont]

52 minutes ago, Bufofrog said:

Yes.  We can live in space fairly easily as shown by the ISS.  

That's "easy"?

 

53 minutes ago, Moontanman said:

 I'm not sure what this has to do with star travel. 

The ability to survive for a period of time in space with no umbilical for resupply would be one relevant (and I would have thought obvious) connection.

[Moontanman]

3 minutes ago, swansont said:

That's "easy"?

 

The ability to survive for a period of time in space with no umbilical for resupply would be one relevant (and I would have thought obvious) connection.

The ability to survive depends on the ability to break the umbilical, space is full of the stuff we need to live... 

 

[swansont]

5 minutes ago, Moontanman said:

The ability to survive depends on the ability to break the umbilical, space is full of the stuff we need to live... 

Full? No, it most decidedly is not. On an interstellar scale, the stuff we need is localized and those oases are far apart.

[Moontanman]

4 minutes ago, swansont said:

Full? No, it most decidedly is not. On an interstellar scale, the stuff we need is localized and those oases are far apart.

Depends on what you mean by full,a habitat the size of the ISS would have problems surviving the journey to Mars, a McKendree cylinder many miles long could exist for centuries if not millenia and chunks of icy rocks are not uncommon and dust could even be harvested...   

I am not talking about firing up a Mckendree cylinder and heading for the nearest star, the expansion would be slow, centered around our own star and thousands if not millions of habitats slowly expanding in all directions making use of materials we encountered to top up, store, and even build new habitats. It would take tens of thousands of years to make it to one star but the expansion would be in all directions eventually resulting in combined speeds greater than light as the bubble of humanity expanded...   

Edited July 11, 2019 by Moontanman

[swansont]

1 hour ago, Moontanman said:

Depends on what you mean by full,a habitat the size of the ISS would have problems surviving the journey to Mars, a McKendree cylinder many miles long could exist for centuries if not millenia and chunks of icy rocks are not uncommon and dust could even be harvested...   

You were the one who said full (pace is full of the stuff we need to live), so you need to define it and provide a reference, and we are talking about interstellar trips. My objection is that we have not yet gone to Mars, and undtil we have, there is no hard data that longer trips are possible.

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I am not talking about firing up a Mckendree cylinder and heading for the nearest star, the expansion would be slow, centered around our own star and thousands if not millions of habitats slowly expanding in all directions making use of materials we encountered to top up, store, and even build new habitats. It would take tens of thousands of years to make it to one star but the expansion would be in all directions eventually resulting in combined speeds greater than light as the bubble of humanity expanded...   

And therein lies the problem. You cannot have slow expansion. You have to have something at each destination. 

It's like going into the desert — your endpoint of the trip has to be an oasis. Or on the ocean — the endpoint has to be land. You can't go 1 km a year into the ocean to get across it. 

McKendree cylinder represents an unproven technology, and we have never, ever demonstrated a small number of people surviving on their own, in isolation, for any length of time anywhere near to what is required, regardless of the size of their cupboard. Biosphere-2 failed pretty quickly, and the ISS gets resupply on a fairly short interval. Submarines aren't an apt analogy, because they can easily make water and air, but even then, they will run out of food. In space, any mass you want to bring with you has a fuel cost, which, in turn, increases the fuel cost.

 

[zapatos]

2 minutes ago, swansont said:

And therein lies the problem. You cannot have slow expansion. You have to have something at each destination. 

 It's like going into the desert — your endpoint of the trip has to be an oasis. Or on the ocean — the endpoint has to be land. You can't go 1 km a year into the ocean to get across it. 

What is the endpoint of our trip on Earth? We are effectively on a spaceship right now going nowhere.

People on islands are moving across the ocean at much less than 1 km per year.

While creating a self-sufficient spacecraft is not something we will achieve anytime soon, it hardly seems out of the question.

 

[swansont]

43 minutes ago, zapatos said:

What is the endpoint of our trip on Earth? We are effectively on a spaceship right now going nowhere.

People on islands are moving across the ocean at much less than 1 km per year.

The earth is not a small bunch of people, isolated from resupply. We know that we can make do with a whole planet, near a star. Or even an island of sufficient size, which has access to resources outside of the island.

But we're talking about systems that are smaller and more isolated than that.

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While creating a self-sufficient spacecraft is not something we will achieve anytime soon, it hardly seems out of the question.

I'm looking for more than a hand-waving dismissal of the problem, which is all that I've gotten so far. It's been tried, and the attempt failed (Biosphere II), so it's not like we can say we have a great handle on how to get to a solution.

[zapatos]

2 hours ago, swansont said:

The earth is not a small bunch of people, isolated from resupply. We know that we can make do with a whole planet, near a star. Or even an island of sufficient size, which has access to resources outside of the island.

But we're talking about systems that are smaller and more isolated than that.

Yes, it was only an analogy. The point was that self sufficient systems exist in nature and so should not be dismissed out of hand.

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I'm looking for more than a hand-waving dismissal of the problem, which is all that I've gotten so far. It's been tried, and the attempt failed (Biosphere II), so it's not like we can say we have a great handle on how to get to a solution.

And I was hoping for more than a hand-waving dismissal of the possibility. Simply saying 'we've never been able to do it before' is hardly a damning rebuke. What constraints do we face that are likely to never be overcome? Does slow expansion violate any laws of physics? Is building a self-sustaining system unlikely to ever be achieved due to some demonstrated constraint?

[swansont]

4 hours ago, zapatos said:

Yes, it was only an analogy. The point was that self sufficient systems exist in nature and so should not be dismissed out of hand.

And my point is that relevant ones do not, in fact, exist, and nobody has provided an example that rebuts this.

4 hours ago, zapatos said:

And I was hoping for more than a hand-waving dismissal of the possibility. Simply saying 'we've never been able to do it before' is hardly a damning rebuke. What constraints do we face that are likely to never be overcome? Does slow expansion violate any laws of physics? Is building a self-sustaining system unlikely to ever be achieved due to some demonstrated constraint?

There has been no science presented in support of this wishful thinking. No actual science to critique. Not ever having done something is at least some kind of constraint. 

The violation is more biology, I would think. People need to eat and stay warm. But physics limitations would be an energy source and reaction mass for the rockets.

All I’ve seen in support is a hint of a magic wand and that we need not pay attention to the man behind the curtain.

[zapatos]

12 minutes ago, swansont said:

And my point is that relevant ones do not, in fact, exist, and nobody has provided an example that rebuts this.

Yes, we all know that we have not yet created a self sufficient system. That is why it's being discussed here. 

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The violation is more biology, I would think. People need to eat and stay warm. But physics limitations would be an energy source and reaction mass for the rockets.

All I’ve seen in support is a hint of a magic wand and that we need not pay attention to the man behind the curtain.

So food, warmth, energy sources and reaction mass require a magic wand? 

We made it to the moon.

Do you think a trip to Mars is out of the question?

How about the moons of Jupiter?

At what point do we have to abandon physics, technology and engineering, and resort to the magic wand?

All you are suggesting is that since we don't know the answers now, it will be impossible without magic.

[Curious layman]

I'm with Bufofrog and Swansont, there's a big difference between the edge of the solar system and the nearest star. I've also seen (somewhere on you tube) that the nearest star/planet that could actually be of any use to us is about 120 light years away.

i only think its only impossible trying to get us there, how we are now. Were too specialised for our environment. Too complex. I think it's more of a biological problem. 

I thinks it's about whether we can create life that can survive that long.

I hope Zapatos and Moontanman are right though. 

Edited July 12, 2019 by Curious layman

[swansont]

9 hours ago, zapatos said:

Yes, we all know that we have not yet created a self sufficient system. That is why it's being discussed here. 

And yet I get pushback for pointing this out. And it's not being discussed here, it's being ignored under the assumption that it's a triviality.

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So food, warmth, energy sources and reaction mass require a magic wand? 

We made it to the moon.

Do you think a trip to Mars is out of the question?

How about the moons of Jupiter?

At what point do we have to abandon physics, technology and engineering, and resort to the magic wand?

All you are suggesting is that since we don't know the answers now, it will be impossible without magic.

Are you not reading what I wrote?

There's a difference between going to the moon and Mars and a huge difference between going to another body in the solar system and to another star. It's not simply a linear extrapolation.