How do I find G2V stars from here to side of arm

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selden
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Re: How do I find G2V stars from here to side of arm

Post #21by selden » 01.04.2011, 12:14

rrrraygun wrote:I'm going to have to change the title of my book from "The Scientifically Plausible Spaceship Adventure Story" to something else now, or seriously gut the thing so the farthest the characters get to is the Oort cloud. Depressing.


Space travel is *hard*. The quip about "I'm no rocket scientist" has a reason for existing. Interstellar space travel is even worse.

Many people don't realize just how far apart things really are, for example. It's why many authors resort to a currently-unknown method of space travel in order to make the travel time reasonable. Hibernation, extended lifetimes and multi-generation ships are some of the other solutions... but things fall apart with age.

Another thing is that any spacecraft with the technology to get up to a reasonable speed incorporates the technology to completely destroy the Earth many times over. The energy requirements are *enormous*.
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Re: How do I find G2V stars from here to side of arm

Post #22by rrrraygun » 01.04.2011, 20:42

I'd like to share two chapters that I wrote four years ago for the book that ended up as Appendixes. They explain how a speck of dust can, over time, accumulate mass from its gravity--growing into a star, growing til it goes supernova, grows as a neutron star, grows into a quark star, then supernovas again as a Big Bang. I felt I had to write these chapters in order to define things for myself and to make the Big Bang theory more reasonable compared to how it was taught to me in Physics class. This is how I came up with an idea of a sub-periodic table lifeform, the supercomet mold.

Appendix 1: From a speck of dust to a black hole.

A tiny chunk of random stuff floating in space that is large enough to attract hydrogen does. This tiny chunk of random stuff eventually collects a lot of this hydrogen over a certain amount of time the way a snowball grows as it rolls downhill. Hydrogen, being the smallest atom of the atoms, has only a single electron (that is always negatively charged) orbiting around a single proton (that is always positively charged). Being the smallest element, it is the element most easily attracted to small forces of gravity. Hydrogen piles up in a layer until it is so abundant and so heavy upon itself, the hydrogen atoms squish together to become helium near the core. Helium is the second lightest atom being two electrons orbiting around two protons. This chunk is now technically a star the size of our sun. 90% of a star's average lifespan in the known universe is spent growing to this size. Planets around these stars form in proximation of their densities. Earth’s stone-covered iron core, for example, has a very different density than Jupiter or Mercury, and therefore, accounts for its place in the order of planets in a solar system.

However, some stars will continue to grow larger. The bigger they get, the hotter they get.

After a while, this massive thing in outer space becomes large enough to attract and collect hydrogen to the point where those helium atoms will squish together to become carbon. More hydrogen will collect and, eventually, the carbon will be under such pressure as to fuse together with other carbon to create oxygen. Even more hydrogen will cause the oxygen to squish together against other oxygen to become neon in the core. Neon squished together with neon produces silicon. Silicon and silicon sulphur. Lastly, for a star, sulphur and sulphur will fuse together to make iron. Like layers of an onion, layers of these elements will pile up onto each other from the core out… decreasing in density outward.

At some point, in a very large star, the weight of all the iron squishing against iron in the core will overwhelm the electromagnetic force that keeps the electrons and protons in those atoms separate from one another, and therefore, cause the atoms to collapse into themselves. The shockwave from the occurrence of the electromagnetic force being overwhelmed (the protons and electrons slamming together to form one slightly bigger chunk instead of a chunk and a little chunk separated by an electromagnetic force) will cause an explosive release of energy and hurl pieces of the various layers out towards the various stars in its own galaxy in chunks as small as neutrinos (in massive quantities) to chunks as massive as planets, which will again eventually rest in orbits around other stars in proximations due to their densities. This implosion and then explosion is called a supernova. The squished together electron and proton is called a neutron. The 3 quarks that make up a proton normally have a +2/3 charge, a +2/3 charge, and a -1/3 charge. This makes a total charge of +1 which isn't surprising as protons are positively charged. The 3 quarks in the newly-formed neutron now have a +2/3 charge, a -1/3 charge, and a -1/3 charge, giving it a total charge of 0. This isn't surprising as neutrons are electrically neutral. The electron's -1 charge has effectively lowered one of the quark's charges by -1 (changing one quark's charge from +2/3 to -1/3). The gravitational pull of a neutron star left over from a supernova can be so strong, it will attract photons (visual light particles) that happen to be shining past within a certain distance. Neutron stars are commonly referred to as black holes. They too will slowly grow as they accumulate more mass that is gravitationally attracted to them. These have been known to consume entire solar systems and act as a hub at the centre of galaxies.

Appendix 2: From a big black hole to a big bang.

Neutron stars (black holes) can continue to attract and consume particles with its gravitational field and grow larger. At some point, the weight of too much neutron squishing against neutron will overwhelm the strong nuclear force between the 3 quarks in a neutron and cause neutrons near the core to become a quark-gluon plasma. The quark-gluon plasma consists of quarks and gluons which interact with each other in a liquid state in the core of what is now called a quark star. Normally, gluons cause gluons to interact with each other like rubber does with itself in an elastic band. This rubbery gluon glue normally causes quarks to interact with other quarks by pulling them together when stretched apart and being loose and non-effective the closer the quarks are to each other. Since the quarks have fractional charge in thirds, they normally electromagnetically bond together in threes. These groups of quarks (“hadrons”) in threes (“baryons”) are bound together for balance, similar to the way the three primary colours mix together to become white. These three "colour charges" bind together to total a zero charge in a neutron and a positive charge in a proton. If a baryon (a proton or neutron) gets close enough to another baryon, the “colour” charge within the different baryons will cause the protons and neutrons to stick together. This force is actually the gluon interaction. The gluons cause the “colour” charge, this three pole electromagnetic interaction. Gluons are carriers of the electromagnetic-like “colour” charge (a.k.a. the strong nuclear force) between quarks the way photons (visible light particles) are carriers of the normal electromagnetic force among electrons. Photons come from electrons and gluons come from quarks. The only difference, really, between a gluon and a photon is that a photon does not carry any sort of “colour” charge. This extra feature is due to the high concentrations of gluons orbiting around the quarks due to the gravitational pull of the quark upon the individual gluons. Quarks are many times larger than electrons, whereas the sizes of photon and gluon particles are practically the same. In effect, photons radiate away from electrons freely when the gluons act like elastic bands between the quarks and between the gluons themselves.

(Take a 15 minute break. Drink a glass of water.)

If a quark star becomes large enough, a dense ball of pure quark will form at the core. This core is surrounded by a layer of quark-gluon plasma, which is itself surrounded by a layer of neutrons. The layer of neutrons is covered by a “thin” layer of plasma made up of compressed electrons and protons as they fuse together. Above that, an electric field of beta radiation (high-energy electrons) crackles as heavy atoms fuse together, creating neutrinos and high-energy photons. The high-energy photons (a.k.a. gamma radiation) are pulled toward the centre of the star. Neutrinos continue to shine outwards without the effect of gravity imposing on them. However, neutrinos will not be able to pass through the solid quark core. Any neutrinos created from the star itself or from passing cosmic radiation will accumulate on the surface of the solid quark core.

As more neutrinos accumulate on the surface of the solid quark core, the quark core will remain its original size, the neutrino layer will grow thicker and thicker, and the quark-gluon plasma will continue to grow thicker and thicker as well.

The massive amount of neutrinos collecting on the quark core by the consumption of galaxies eventually causes the quark core to heat up to a point where it becomes plasma and melts the neutrinos at the surface of the quark core down to pure quark plasma with it. Quark plasma magma will make its way to the surface of the neutrino layer, expelling quark lava into the quark-gluon plasma. At this stage, it is the maximum size a star can get before it destroys itself. It enters the final phase of evolution, releasing the energy of the quark. The quarks at the very centre of the plasma core will finally reach the boiling point for quark plasma from the heat caused by extreme pressure under the sheer weight of the entire star. Convection will cause the plasma quark core to rotate, creating a pressure outwards in the star at the poles. Once it reaches the surface, it explosively expels highly-pressurized polar jets of pure quark plasma. This immediate shift of quark plasma from the core causes enough of a collapse to create the supernova of all supernovas. A shockwave carrying very high concentrations of neutrino/quark plasma, crystallized neutrinos, quark/gluon plasma, neutrons, etc., is sent outward. The dangerous force from this transition is known as the Big Bang. A galaxy may contain up to a trillion stars. A Big Bang can annihilate up to a trillion galaxies, something bigger than the size of our known universe. But remember, space is infinite and these Big Bangs will always be occurring somewhere in the universe.

Crystallized neutrino/quark comets are the result of Big Bangs and are rarely noticed by intelligent lifeforms. They initially begin as steamrolling chunks of debris, but eventually slow down enough to become part of other systems. They slow down by traveling past large gravitational forces of black holes as well as by running into normal particles which easily bond with the particles on the surface of the comets as they travel through nebulas and through the crossfire of cosmic radiation and debris. They will eventually adopt an elliptical orbit around a cluster of galaxies. Fragments from these giant comets will break off and eventually adopt their own sub-galactic orbits between solar systems.

The strange combinations of matter created in and near the cores of these massive pre-Big Bang stars will remain in large quantities on these strange comets. The unique mess of forged sub-atomic particle rarities will eventually combine together to form many different combinations in many different environments. They bind together as normal chemicals do in the Periodic Table until one ordinary day, when the acidity and temperatures and surrounding environment are just right… the sludge begins to move on its own - self-organizing toward a greater complexity, driven by a sub-atomic organic chemical reflex to bond with similar sub-atomic chemicals, growing….

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What do you think about this?

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Re: How do I find G2V stars from here to side of arm

Post #23by MKruer » 01.04.2011, 22:39

For interstellar space travel the best bet would be to use lasers powered by the sun to push solar sail. In this respect you don't need to carry fuel with you except to break and that could be done in another system by some areo and gravity assisted breaking. There may some more exotic materials, mathematically proven and as yet unverified methods such as Negative mass. That may or may not be proven correct. The real problem with those approaches would be that the amount of energy to make those exotic materials is greater then just doing the trip the conventional way. I worked a passable power method by tapping into and pulling energy from other dimensions, in a nutshell energy bled-over which got me around the whole carrying full with me.

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Re: How do I find G2V stars from here to side of arm

Post #24by Hungry4info » 02.04.2011, 04:49

MKruer wrote:... you don't need to carry fuel with you except to break and that could be done in another system by some areo and gravity assisted breaking.

Are you seriously entertaining the idea of aerobraking from a velocity that would make interstellar travel feasible?
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Re: How do I find G2V stars from here to side of arm

Post #25by ThinkerX » 02.04.2011, 06:20

Are you seriously entertaining the idea of aerobraking from a velocity that would make interstellar travel feasible?

I can't really see this being done with a (physical) solar sail...

...but I have seen it proposed as an option for slowing down a Bussard Ramjet.

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Re: How do I find G2V stars from here to side of arm

Post #26by Hungry4info » 02.04.2011, 07:26

I can't imagine any way that could work without being instant death for a number of reasons.

1) Hitting the atmosphere at such velocities is going to produce one heck of a meteor. All that kinetic energy has got to go somewhere. Probably a combination of both the vaporization of the spacecraft and producing a mess out of the local environment of the planet.

2) Inertia. Sudden deceleration is going to hurt. At the speeds we're trying to slow down from, that atmosphere is going to feel worse than a brick wall.
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Re: How do I find G2V stars from here to side of arm

Post #27by selden » 02.04.2011, 14:51

Hungry,

The "aerobraking" proposals I've seen don't actually use atmospheric braking. They brake against the magnetosphere and stellar wind of the destination star.
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Re: How do I find G2V stars from here to side of arm

Post #28by MKruer » 02.04.2011, 18:33

ThinkerX wrote:
Are you seriously entertaining the idea of aerobraking from a velocity that would make interstellar travel feasible?

I can't really see this being done with a (physical) solar sail...

...but I have seen it proposed as an option for slowing down a Bussard Ramjet.

You are not using the the sail to break just to get moving.

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Re: How do I find G2V stars from here to side of arm

Post #29by MKruer » 02.04.2011, 19:04

selden wrote:Hungry,

The "aerobraking" proposals I've seen don't actually use atmospheric braking. They brake against the magnetosphere and stellar wind of the destination star.

That would be correct. If I remember correctly the numbers of atoms per cubic meter in the interstellar medium are one to two orders of magnitude less then that were is found around a star. So by definition entering any system would act as a break, how much so depends on a host of factors. Also there is really no true upper limit to an atmosphere until it gets carried away by the solar winds. If someone was entering this system they would probably target the planets Exospheres and/or Magnetosphere on the way into the sun. It would not be like 2010's film where they would drop into the mesosphere. Doing that first would be suicidal.

You can also use the gravity of the planets to burn off speed.

Another way that might be faster would be to send a lighter weight portable laser array that would enter the system and land first then by the time the second ship reach half way point it the second array would be used to slow down the ship before entering the destination system.

I guess what I am saying is there is many ways to bleed off speed in a system; it’s just finding the correct way that is the trick, and also hoping that to don't have so much delta-v that you will be ejected from the system before the gravity of the star will capture you. The irony is that it may take you longer to slow down enough then to reach the destination system.

I thing that any attempt really depends on how badly you want to get there in a short period of time. The faster you want to do it, the more aggressive you need to be and the more technologies you need to use in concurrence.

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Re: How do I find G2V stars from here to side of arm

Post #30by selden » 02.04.2011, 19:16

The late Dr. Robert Forward described how one could use a laser (or maser) + reflective sails both to accelerate on the way to another star and to brake for arrival. Braking would involve separating the sail into two parts, one of which reflects light back toward the decelerating spacecraft. The sail which reflects light back toward the spacecraft continues to accelerate, of course.

Such a method of interstellar flight also depends on long-term maintenance of an extremely powerful laser system in the system of origin, but you don't have to depend on robotics having already arrived in the destination system.

See http://en.wikipedia.org/wiki/Beam-powered_propulsion

(He also wrote a couple of SF novels about it.)
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Re: How do I find G2V stars from here to side of arm

Post #31by Hungry4info » 02.04.2011, 21:06

selden wrote:The "aerobraking" proposals I've seen don't actually use atmospheric braking. They brake against the magnetosphere and stellar wind of the destination star.

Ahh okay. That makes a lot more sense.
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Re: How do I find G2V stars from here to side of arm

Post #32by starguy84 » 10.04.2011, 07:20

Just some random notes:

There are plenty of G2V stars in the galaxy. That 10-15 light year distance Hungry4info quoted isn't bad for G2V stars; (all the other types are much rarer). There are 2 G-type dwarf stars within 15 light years/5 parsecs of us: Alpha Centauri A (G2V) and Tau Ceti (G8V). I don't know how far it is to the edge of the arm, but the number of G stars should remain roughly constant everywhere in the galaxy (they live ~10 billion years, and the galaxy is only a bit older than that, so it's not like you'll only find them newly born in the star-forming regions of the arms). As for how many stars are between those two stars... there are 50 star systems within 15 light years of us, a density of 0.0035 systems per cubic light year. At that rate, the average distance to the next star system is ~4 light years (ie, 0.0035 x 4/3 pi 4^3 = ~1), while the average distance to the next G dwarf is ~12 light years.

Second... The only way I can think of to make interstellar travel realistic is to account for LOTS of time. Either the travelers have to be robots, in cryogenic sleep, or some kind of generational ship (I know none of THOSE are terribly realistic, of course). If you can allow for thousands or tens of thousands of years traveling between stars, your fuel and acceleration/deceleration requirements become less... although the survival of a spaceship/crew for that long becomes more difficult.

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Re: How do I find G2V stars from here to side of arm

Post #33by ThinkerX » 10.04.2011, 07:41

So Starguy...you don't think much of Bussard Ramjets, then as a viable means of getting from star to star within the lifetime of the crew? Biggest problem I see (aside from generating the 'scoop') is getting up to sufficient speed to use the dang thing before exiting the relatively plentiful full rich environment of the solar system...hence my idea to head a few dozen au in the opposite direction first. Also...maybe don't have the scoop at its full diameter to start with - maybe only 10% or 20% of its maximum diameter, scaling up bit by bit until ramscoop crusing speed is reached.

Apart from that...I've found myself wondering if some form of zero point energy (or is it vacuum point energy?) that might be made into a stardrive that wouldn't require either a million to one fuel to payload ratio and/or a trip time of several centuries, if not millenia. As I understand it, ZPE is currently doable via the very close set plates (forget the exact name) and the so called 'blue light' or 'cavitation' effect; trick would be to somehow convert that energy into motive power. (read about one scheme that involved literally millions of the pairs of close set plates, which has me wondering).

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Re: How do I find G2V stars from here to side of arm

Post #34by selden » 10.04.2011, 10:53

Unfortunately, relatively recent studies have concluded that Bussard ramjets would have a rather low cruising speed. The gigantic ramscoop area results in a substantial resistance. See http://en.wikipedia.org/wiki/Bussard_ra ... easibility
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Re: How do I find G2V stars from here to side of arm

Post #35by ThinkerX » 10.04.2011, 22:59

Seldon, the article doesn't completely rule out all forms of the Bussard Ramjet.

I find the assumptions of Zubrin/Andrews to be overly limiting:

Robert Zubrin and Dana Andrews analyzed one hypothetical version of the Bussard ramscoop and ramjet design in 1985. They determined that their version of the ramjet would be unable to accelerate into the solar wind. However, in their calculations they assumed that:

1.The exhaust velocity of their interplanetary ion propulsion ramjet could not exceed 100,000 m/s (100 km/s);
2.The largest available energy source could be a 500 kilowatt nuclear fission reactor.
In the Zubrin/Andrews interplanetary ramjet design, they calculated that the drag force d/dt(mv1) equals the mass of the scooped ions collected per second multiplied by the velocity of the scooped ions within the solar system relative to the ramscoop. The velocity of the (scooped) collected ions from the solar wind was assumed to be 500,000 m/s.

The exhaust velocity of the ions when expelled by the ramjet was assumed not to exceed 100,000 m/s. The thrust of the ramjet d/dt(mv2) was equal to the mass of ions expelled per second multiplied by 100,000 meters per second. In the Zubrin/Andrews design of 1985, this resulted in the condition that d/dt(mv1) > d/dt(mv2). This condition resulted in the drag force exceeding the thrust of the hypothetical ramjet in the Zubrin/Andrews version of the design.

However, that same article goes on to mention that there are circumstances in which the Ramjet would be feasible:

For example, a ramjet might collect 1 gram of incoming ions per second from interstellar space beyond the heliopause, at a velocity of 50 km/s relative to the ramjet driven spacecraft. In this case d/dt(mv1) is (0.001 kg/s) (50,000 m/s), yielding a drag force of 50 newtons.

If the gram of ions is then accelerated to 500,000 m/s then d/dt(mv2) is (0.001 kg/s) (500,000 m/s) = 500 N.

Therefore, -50 newtons + 500 newtons yields a net force forward of 450 newtons.

The typical velocity of the solar wind within the solar system is 500 km/s. The typical velocity of the interstellar wind is 50 km/s beyond the heliopause. In the solar system, if the exhaust velocity of the ramjet exceeds 500 km/s there will be a net thrust that will accelerate the ramjet. Figures here assume the spacecraft is travelling towards the sun (since the solar wind is directional), under the worst conditions for thrust.

If the example were set in the solar system, the drag force, d/dt(mv1), would be about (0.001 kg/s) (500,000 m/s), or 500 newton.

If the exhaust velocity of the ramjet were 1,000,000 m/s then d/dt(mv2) = (0.001 kg/s) (1,000,000 m/s) = 1000 N of thrust, and -500 newtons + 1000 newtons = net thrust of 500 newtons to accelerate the ramjet forward.

If the Zubrin/Andrews assumption were correct then d/dt(mv1) = 500 N, and d/dt(mv2) = 100 N, and the drag forces would exceed the thrust of the ramjet. Under those conditions, the ramjet would likely only function along vectors perpendicular to the solar wind.

This design negates the vast bulk of the 'drag' effect of the classic Bussard Ramjet, though you still get into severe fuel problems once past the bounds of the solar system:
Electrostatic ion scoopOne possible modification of the ramjet design is to use an electrostatic ion scoop, instead of an electromagnetic ion scoop to achieve the ion collection from space. In an electrostatic scoop a negative electric field on a forward grid electrostatically attracts the positive charged ions present in interstellar space and thus draws them into the ramjet engines. This can be a 100% electrostatic scoop in which an electromagnetic field is not used at all. There will be no converging electromagnetic field lines that can potentially generate drag effects by scooping the ions from interstellar space if this pure electrostatic approach is used. The scooped ions will however have an electric field-induced velocity when they are drawn inside of the ion ramjet engine. So long as the velocity of the ramjet engine exhaust jet is greater than the electric field-induced velocity of the incoming scooped ions there can be a net force in the direction of the ramjet's flight that will accelerate the spacecraft.

Furthermore, the net potential difference of the galactic electric field in interstellar space is only 1.6?10?19 volt[citation needed]. The effective ion collection radius of an electrostatic ion ram scoop will be the range at which the ramscoop electric field has a greater potential difference from the galactic electric field. This potential difference declines proportionately to 1/d? for distance d from the source of the ram scoop electric field

It might actually be a preferrable way to go, as far as interstellar travel is concerned. The trick would be to attain a high enough velocity to attain a significant percentage of C before the 'free' fuel becomes too thin to be of use. (At that point, you scale back the drive and 'coast' most of the way to your destination.)

Went and quoted from the wiki article so others would be able to follow the discussion. The author of the OP might find it of interest.


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