Detecting ET

[barbos]

1) You're looking at Earth's orbit--but you double it and then call it a radius.

I did no such thing.

 

[barbos]

You asserted certain numbers

No, I did not. I calculated these numbers.

 

[lpetrich]

 Spacecraft propulsion - lots of technologies, from successfully flown to various levels of testing, development, theoretical work, and speculation. Using  Technology readiness level

1. Basic principles observed
2. Technology concept formulated
3. Experimental proof of concept
4. Technology validated in lab
5. Technology validated in relevant environment
6. Technology demonstrated in relevant environment
7. System prototype demonstration in operational environment
8. System complete and qualified
9. Actual system proven in operational environment

I've been sticking to level 9 as far as possible -- anything that has been successfully flown in some mission.

• BepiColombo - QinetiQ T6 - 4300 s - 42 km/s
• Dawn - NSTAR - 3100 s - 30 km/s

Much better than the chemical ones, but powering the spacecraft is a big problem. One will have to use an onboard nuclear reactor to get a good enough energy density.

 List of nuclear power systems in space - mostly radioisotope thermoelectric generators (RTG's), but some nuclear reactors, like in Soviet spy satellites Cosmos 954 and 1402, which crashed.

 

[lpetrich]

Effective exhaust velocities:

At level 9: flight proven:

• H2 - O2: 4.6 km/s
• kerosene - O2: 3.5 km/s
• MMH - N2O4: 3.2 km/s
• Solid fuel: 2.9 km/s
• Electrostatic ion engine: 42 km/s

At level 8: flight qualified:

• FEEP ion engine: ~ 100 km/s

At level 7: prototype demonstrated in space
At level 6: prototype demonstrated on ground
At level 5: component validated in vacuum
At level 4: Component validated in lab

• Magnetic sail, electric sail - a few hundred km/s - works by making a stellar wind drag the spacecraft

At level 3: Validated proof-of-concept
At level 2: Technology concept formulated

• Nuclear pulse engine, fission-fragment engine ~ 10,000 km/s
• Antimatter engine ~ 100,000 km/s

 

[lpetrich]

Antimatter is very hard to produce. You have to smash ordinary particles into each other, and with enough energy per particle, there is a chance of making antimatter by pair production. A small chance, but enough to make enough for elementary-particle experiments.

Production of slow positrons with a 100‐MeV electron linac: Applied Physics Letters: Vol 40, No 8 - 1982
Found a yield of 10^-6 positrons per electron, and scaling that to the electrons' energy and using E = m*c² gives 10^-8. That's not even counting the energy efficiency of the linac itself.

Fermilab's Antiproton Source - ". The Main Injector sends 120 GeV protons to a nickel target. (GeV stands for a billion electron volts and represents how much energy a particle carries.) It takes one hundred thousand to one million protons to make a single antiproton."
That also gives an energy efficiency of 10^-8.

Copious positron production by femto-second laser via absorption enhancement in a microstructured surface target | Scientific Reports - I calculate a projected energy efficiency of 10^-5 relative to the laser light.


One's troubles with antimatter don't end there, because there is the problem of storing it. Since antimatter is just like ordinary matter but with some signs reversed, we can extrapolate from ordinary matter. If one only has positrons and antiprotons, one can make antihydrogen. It will have the same low boiling point, 20 K. What makes antiprotons will make antineutrons, so one can irradiate antihydrogen with antineutrons. That will get to helium, but no further.

That's because every nuclide with 5 or 8 nucleons is unstable.

One has to ram nuclei together to get past those barriers.

Boiling points: H: 20 K, He: 4.2 K, Li: 1600 K, Be: 2700 K, B: 4200 K, C: 3900 K

So one could stop at antilithium.

 

[lpetrich]

That's not even getting into the details of how one would store antimatter, since it rather violently reacts with ordinary matter. One kilogram of antimatter reacting with one kilo of ordinary matter will yield almost the energy release of Tsar Bomba, the most powerful nuclear bomb ever tested.

So one would have to isolate antimatter from ordinary matter, and magnetic confinement could work. One would also have to decelerate the antiparticles that were produced so that they can easily settle in.

 

[Loren Pechtel]

Interstellar travel is VERY difficult. To see why, let us look at Konstantin Tsiolkovsky's rocket equation:

Which is why the most viable ideas we have on interstellar travel do not care about the rocket equation.

Lightsail should give about .01c, there's no way to figure the upper limit for laser-boosted lightsail as that comes down to how reflective and how refractive the sail can be made.

 

[steve_bank]

With a laser you still have to supply energy. To change velocity work ignoring efficiency energy equals work done.

 

[Swammerdami]

Am I wrong that something like magnetic sails, harnessing the power of natural magnets at a destination, should solve BOTH the energy and impetus problems, at least for deceleration? To decelerate from 0.01 c would need only a tiny fraction of a g-force.

Even with just 0.001 c as travel velocity, a civilization which started in the Jurassic Period could have taken over the entire Milky Way by now.

 

[bilby]

Am I wrong that something like magnetic sails, harnessing the power of natural magnets at a destination,

Natural magnetic fields at solar system scale are utterly pathetic. Even by comparison to gravity, which is almost unbelievably weedy.

A basic fridge magnet is weak as piss; Yet it is massively stronger than the Earth's magnetic or gravitational fields, even at the absolute surface of the planet. It's so strong, that it easily supports itself against a thin (typically 24 gauge, or 0.51mm) layer of steel, overwhelming the gravitational and magnetic fields of an entire planet, located a mere metre or so away.

 

[steve_bank]

To use natiral magnetic you would have to create a magntic field that oppose. That brings you back to an energy source.

Mag lev trains use electromagnets.

On of my favorite movies as a kid was First Men In The Moon. HG Wells.

Dr Cavor an eccentric British scientist creates a substance he calls Cavorite that shields gravity.

He paints it on shutters on a sphere. Close the shutters facing the Earth and open the ones facing the moon and off it goes.

 

[Loren Pechtel]

With a laser you still have to supply energy. To change velocity work ignoring efficiency energy equals work done.

You still need the energy but you aren't accelerating the fuel.

 

[steve_bank]

With a laser you still have to supply energy. To change velocity work ignoring efficiency energy equals work done.

You still need the energy but you aren't accelerating the fuel.

Where and what is the fuel for a laser? That is the question. Especially out in deep space.

For a solar sail drven by a laser Newton's Laws apply. The sail and the connection points to the ship have to withstand the acceleration force.

F = m*a where m is the mass of the ship.

Also.

I am in deep space standing on a flat plate with a wall. No matter how hard I push on the wall velocity of the plate does not chagae,

In the solar system te laser woud have to be external. There would be collimation problems, the beam diverges.

 

[Jimmy Higgins]

Interstellar travel is VERY difficult. To see why, let us look at Konstantin Tsiolkovsky's rocket equation:

Which is why the most viable ideas we have on interstellar travel do not care about the rocket equation.

Lightsail should give about .01c, there's no way to figure the upper limit for laser-boosted lightsail as that comes down to how reflective and how refractive the sail can be made.

I'm curious the accuracy you need for bearing on a trip to something 4 light years away. If one is going 0.01c, how hard is it to adjust course?! (somewhat of a rhetorical question)

 

[Swammerdami]

To use natiral magnetic you would have to create a magntic field that oppose. That brings you back to an energy source.

Yes, i still need the energy. I think my tritium-tritium or lithium-tritium reactor will be good enough.

But I've avoided the many tons of massive impetus for braking (and acceleration!)

 

[steve_bank]

Navigation and maneuvering is a big issue.

Head for a tart and constantly change course to keep in a cross hair?

In ST one easliy navigates with precision to a set of coordinates, referenced to a fictional navigation system. A galactic GPS.

When leaving Earth you could initalze an inertial navigation system and refence oosition to the that point. But electronics can drift.

The old LORAN stsrem in some form might work, butwould require a lot of power. A chain of trasmitters in a timed sequence.

LORAN - Wikipedia

en.wikipedia.org

 

[Loren Pechtel]

Interstellar travel is VERY difficult. To see why, let us look at Konstantin Tsiolkovsky's rocket equation:

Which is why the most viable ideas we have on interstellar travel do not care about the rocket equation.

Lightsail should give about .01c, there's no way to figure the upper limit for laser-boosted lightsail as that comes down to how reflective and how refractive the sail can be made.

I'm curious the accuracy you need for bearing on a trip to something 4 light years away. If one is going 0.01c, how hard is it to adjust course?! (somewhat of a rhetorical question)

Yeah, you need accuracy far beyond what we can currently do. The spacecraft has to ride the beam because if it loses the beam it has no way to get back, there can be no steering other than very slow maneuvers initiated by the laser facility--they tell the spacecraft to tack at such-and-such an angle as the beam is moving.

 

[lpetrich]

Returning to the original subject,  Search for extraterrestrial intelligence notes several potentially-detectible kinds of evidence that ET's could produce:

• Broadcasts
  • Radio waves
  • Visible light
• Large-scale engineering
• Spacecraft

The canals of Mars were a putative example of ET engineering, though those alleged structures were eventually discredited.

 

[bilby]

Head for a tart and constantly change course to keep in a cross hair?

Sounds like a fun Saturday night out...

 

[lpetrich]

SETI, METI, CETI, IETI

• SETI: Search for Extraterrestrial Intelligence
• METI: Messages for Extraterrestrial Intelligence
• CETI: Communication with Extraterrestrial Intelligence
• IETI: Invitation to Extraterrestrial Intelligence

IETI? If any ET's are monitoring our Internet communications, an invitation to them to contact us.

But an over-the-Internet invitation has a great difficulty. It is difficult to reverse-engineer Internet transmissions, especially satellite Internet transmissions, for reasons that I explain here. So one has to be covertly present on our planet to do so, complete with using Internet-client end nodes, the desktop and laptop computers, the smartphones, and the tablets that Internet users access the Internet with. Server nodes and telecom-company hardware are usually less accessible.

I then explain why. Internet packets have structure (link header - for hardware) (internet header - for the network) (transport header - for the networking layer) (app data) (optional link footer). The app data may have published formats, like HTTP/HTML/CSS/JavaScript, or else proprietary.

Satellite Internet service adds further difficulties. Satellite transmissions typically have error-correcting coding and they are often encrypted. So without knowledge of the protocol details, they would be very hard to reverse-engineer.

So if one was eavesdropping on Internet communications, one could tell that we have some digital communications protocol, but not much more.