Interstellar Travel in Gwynne Shotwell's Lifetime

[Alberto-Girardi]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Negative mass and negative energy density would permit this, but those are particularly un-physical states of matter.

Oh, yes. I suppose everything is doable with these two things.

But, speaking of doable things in 40 years, are there alternatives to solar/light sails?

[Robotbeat]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Negative mass and negative energy density would permit this, but those are particularly un-physical states of matter.

Oh, yes. I suppose everything is doable with these two things.

But, speaking of doable things in 40 years, are there alternatives to solar/light sails?

Yes.

[Vultur]

But, speaking of doable things in 40 years, are there alternatives to solar/light sails?

Maybe. Depends on whether you mean "what could we do with 40 years of serious investment in the possibilities" or "what could we do with technology that's likely to be developed anyway in the next 40 years".

I don't know what 40 years of serious work into antimatter options would give us.

Nuclear pulse propulsion could probably be advanced pretty far in a few decades technically.

But that would be fairly slow - a nuclear interstellar probe could be launched (politics aside) in our lifetimes, but not arrive in our lifetimes.

And politically it wouldn't be doable for probably a lot longer. (Probably not until nuclear materials can be refined off-Earth, IMO.)

[Robotbeat]

If you go faster than 0.1c or so, there are a whole bunch of challenges that crop up. So unless I live a really long time (120 years) I don't think I'll see a crewed interstellar spacecraft arrive at its destination even with the most optimistic assumptions. But hey, seeing it off would be pretty sweet and a lot more doable.

[Oberonian]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Yes that is why I added according to Einstein...I thought everyone knows his theory.

[M.E.T.]

If a million tons to orbit becomes a trivial challenge thanks to Starship, which part of a terawatt level orbital laser array remains beyond current technology?

Once that is built, propelling an interstellar ship to a significant fraction of light speed becomes quite feasible.

Then you probably require a century or so to build one at the other end too, and back and forth travel between the two star systems becomes run of the mill.

[Oberonian]

If a million tons to orbit becomes a trivial challenge thanks to Starship, which part of a terawatt level orbital laser array remains beyond current technology?

Once that is built, propelling an interstellar ship to a significant fraction of light speed becomes quite feasible.

Then you probably require a century or so to build one at the other end too, and back and forth travel between the two star systems becomes run of the mill.

Why don't you just beat the hydrogen particles in space with giant blades into kingdom come with electric motors and get 100 x thrust more than from an ION drive and travel at n x C speed ?

 

[rakaydos]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Yes that is why I added according to Einstein...I thought everyone knows his theory.

apparently YOU dont, if you thought Einstein's theory had actual age regression in it...

[Oberonian]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Yes that is why I added according to Einstein...I thought everyone knows his theory.

apparently YOU dont, if you thought Einstein's theory had actual age regression in it...

Okay...isn't 2 years younger than your mates in a 20 year voyage ....actually becoming 2 years younger ?

[Frogstar_Robot]

Will the astronauts become younger ( according to Einstein ) and if so how much ?

No, time can't be reverted. Astronauts travelling at high speed will be younger than people that had thei same age at the start, becuse the times passes slowerly  fo higher speeds

Yes that is why I added according to Einstein...I thought everyone knows his theory.

apparently YOU dont, if you thought Einstein's theory had actual age regression in it...

Okay...isn't 2 years younger than your mates in a 20 year voyage ....actually becoming 2 years younger ?

Relativity is strange, because you always travel in space and time. E.g. given twins, if one travels the Earth and the other stays at home, and they meet at the same place 10 years later, one has traveled in space more than the other, but also they meet at not actually the same time, but the difference is normally negligible. If the traveling twin travels very fast, then the time difference is noticeable. The phrase "same time, same place", is actually "same place, different time".

Each twin thinks their time path is correct, so although the traveled twin looks younger to the stationary twin, to the traveling twin everyone on Earth appears to be older than they should be, it is as if everyone on Earth has traveled into the future. Since there is no universal "correct" time, it is relative to the observer, you can't really say that the traveling twin is younger, or that the stationary twin is older. They are both correct, or neither, depending on how you look at it.

[Vultur]

If a million tons to orbit becomes a trivial challenge thanks to Starship, which part of a terawatt level orbital laser array remains beyond current technology?

A terawatt (sustained, not brief pulses) is a lot.

Of course you could get a terawatt with say 10 million 100-kilowatt lasers... but I think there will be issues focusing them on the sail at great distances. Accelerating to 10% of lightspeed at 1 g would (unless my math is wrong) require something like 300 AU distance.

I'm not a laser expert by any means, but that sounds hard.

[RanulfC]

If a million tons to orbit becomes a trivial challenge thanks to Starship,

A questionable assumption given the numerous very NON-trivial "issues" with regularly getting that much mass into space let alone actually being able to 'use' it. (And that's not even touching the issues Starship/Superheavy raise)

... which part of a terawatt level orbital laser array remains beyond current technology?

Pretty much all of it since we've never actually DONE either major engineering in space nor operated anywhere near a 'terawatt' level laser on EARTH let alone in space. Everything from power generation to structural engineering will be a 'new' field requiring a huge amount of effort and money to get into service, let alone regular service.

Once that is built, propelling an interstellar ship to a significant fraction of light speed becomes quite feasible.

Fun 'fact' here buddy, it also becomes 'quite feasible' to melt an enemy nation down to the bedrock, knock down any satellites or aircraft, heck wipe out that pesky guy who plays his music to loud at night even, with that same system. It's an "interesting" interstellar 'drive' very much in a "Kzinti Lesson" (http://www.larryniven.net/kzin/worlds.shtml) kind of way

Randy

[Vultur]

Fun 'fact' here buddy, it also becomes 'quite feasible' to melt an enemy nation down to the bedrock, knock down any satellites or aircraft,

The principle is valid, but I think this one could be made relatively "safe" for Earth (though not for satellites) if the laser array used a wavelength the Earth's atmosphere absorbs relatively completely, like vacuum ultraviolet.

(And short wavelength means lower beam dispersion, which you'd need anyway, I think...)

If it's absorbed and turns into heat really high above the ground... that's not much heat on a planetary scale (solar input to earth is about 150,000x that).

I don't know exactly what the effects would be but it would take several minutes, I think, to equal the energy of the Chelyabinsk meteor (IIRC, that's estimated at several hundred kilotons TNT; 1 terawatt is about 200-something tons of TNT per second) so probably not terribly violent on the planetary surface tens of miles below?

[Alberto-Girardi]

If a million tons to orbit becomes a trivial challenge thanks to Starship,

A questionable assumption given the numerous very NON-trivial "issues" with regularly getting that much mass into space let alone actually being able to 'use' it. (And that's not even touching the issues Starship/Superheavy raise)

... which part of a terawatt level orbital laser array remains beyond current technology?

Pretty much all of it since we've never actually DONE either major engineering in space nor operated anywhere near a 'terawatt' level laser on EARTH let alone in space. Everything from power generation to structural engineering will be a 'new' field requiring a huge amount of effort and money to get into service, let alone regular service.

Once that is built, propelling an interstellar ship to a significant fraction of light speed becomes quite feasible.

Fun 'fact' here buddy, it also becomes 'quite feasible' to melt an enemy nation down to the bedrock, knock down any satellites or aircraft, heck wipe out that pesky guy who plays his music to loud at night even, with that same system. It's an "interesting" interstellar 'drive' very much in a "Kzinti Lesson" (http://www.larryniven.net/kzin/worlds.shtml) kind of way

Randy

A part from technical issues the biggest issue IMO is who is going to pay for it, because it will be extremely expensive. Plus scientific results will be minuscule per money spent compared to other mission, and succes is not guaranteed. This architecture is not scalable to bigger mission, because more lasers will be needed.

IIUC the best option we have in a reasonable time is a solar sail extremely close flyby over the Sun. I tried to do the math but it was too complicated for me (but I will discuss that in light sail thread, if there is one). I'm against nuclear fission propulsion, but I should inform more to have a better opionion about that.

[cro-magnon gramps]

As I remember the panel question, it was asked where do you see your company in 20 years. It was Gwynn's answer that took this thread to another level. She said, "I hope we are working on Interstellar Propulsion!" Kinda shook up the panel whose answers were less than memorable. Almost pedestrian in their safe outlook. Only Gwynne could say something like that and keep a straight face
Soooooooo!! To answer the question, where does she think the money is coming from: SpaceX 

[KelvinZero]

Fun 'fact' here buddy, it also becomes 'quite feasible' to melt an enemy nation down to the bedrock, knock down any satellites or aircraft,

The principle is valid, but I think this one could be made relatively "safe" for Earth (though not for satellites) if the laser array used a wavelength the Earth's atmosphere absorbs relatively completely, like vacuum ultraviolet.

(And short wavelength means lower beam dispersion, which you'd need anyway, I think...)

If it's absorbed and turns into heat really high above the ground... that's not much heat on a planetary scale (solar input to earth is about 150,000x that).

I don't know exactly what the effects would be but it would take several minutes, I think, to equal the energy of the Chelyabinsk meteor (IIRC, that's estimated at several hundred kilotons TNT; 1 terawatt is about 200-something tons of TNT per second) so probably not terribly violent on the planetary surface tens of miles below?

I think there is a whole subject on what is politically feasible HSF-scale beamed propulsion in the future. Safe wavelengths could be one part of the solution. Other requirements could be international inspection to verify that these things are far more fragile than they are useful as weapons and that you are building exactly what you say you are building. Probably better if they are fully open international projects that only continue to exist by mutual consent of all super powers, and have to share time to everyone so no one has to build their own. I do wonder if this means we will never be able to allow different nations to just do their own thing in different corners of the solar system. Which is a pity. I would like to see humanity's future asap not all wired up to the same hair trigger.

[edzieba]

Kzinti Lesson or Jon's Law, whatever variety of interstellar drive you dream up (be it pulsed fusion, beamed power, etc) involves handling sufficient energy to glass continents. If you can't trust anyone to handle building such a propulsion system because they may misuse it, you won't be visiting any other stars.

[Robotbeat]

Kzinti Lesson or Jon's Law, whatever variety of interstellar drive you dream up (be it pulsed fusion, beamed power, etc) involves handling sufficient energy to glass continents. If you can't trust anyone to handle building such a propulsion system because they may misuse it, you won't be visiting any other stars.

meh, a macron beam propulsion system would make a crappy weapon. The macrons cannot penetrate the atmosphere (would burn up at about the Karman Line) and you’re “only” dealing with Terawatts, not Petawatts. You cannot “glass” anything. At best, you could double the amount of sunshine over a ~100km radius. And aiming it would be slow and extremely hard to pull off on a rapid timeframe as it’s 1000km long.

Conventional ICBMs would be a bigger threat.

[Robotbeat]

100 years ago, nearly everything about Apollo was in the TRL 1-3 range. Yet 50 years later we were on the Moon.

What matters is first principles. Tsiolkovsky showed spaceflight was possible. Then we did it. Exact TRL doesn’t matter that much at this point.

We are at 1921 levels of tech with respect to Interstellar travel. What matters is first principles (which also determine how much resource is required, thus economic feasibility as well).

It is quite likely we WILL have propulsion tech developed in Gwynne’s lifetime that will allow us to start building the ship in her lifetime. It’s not a crazy thing to think. Gwynne seems healthy so could well see 100 years old, in time to see the “Saturn V” of interstellar flight take shape.

[Vultur]

I think there is a whole subject on what is politically feasible HSF-scale beamed propulsion in the future.

I think this is far enough into the future that the question is unanswerable. If/when this becomes a real issue, that implies that space industrialization is already a major economic force IMO. This would probably mean significant, and not now predictable, shifts in politics.

We still don't really know what kind of legal/political regime space settlements will be under (sure, there's the OST, but how will it be interpreted in practice, and will it change?)

Kzinti Lesson or Jon's Law, whatever variety of interstellar drive you dream up (be it pulsed fusion, beamed power, etc) involves handling sufficient energy to glass continents.

That's a bit of an overstatement. Sure, it's massive amounts of energy and therefore potentially quite dangerous -- but "glassing continents" would be a whole other scale.  Even large asteroid impacts don't do that.


Anyway, a propulsion beam would I think want the shortest possible wavelength, for less beam dispersion, so it would be a significantly different setup than a laser weapon to shoot at targets on Earth's surface.

It also depends if we're talking human spaceflight or automated probes -- some small interstellar probe concepts use less than a terawatt (Starwisp was 56 GW according to wikipedia, Breakthrough Starshot "up to" 100 GW).

meh, a macron beam propulsion system would make a crappy weapon.

What's a macron beam?