Could we actually build an interstellar probe ?

[K^2]

You can determine the precise distance between the spacecraft with laser interferometry, and it is accurate to the required precision for optical interferometry. How can this not be extended to kilometer+ distances?

Because of limited coherence length of the laser beam. If we had lasers with arbitrary precision in holding frequency, we'd have clocks with arbitrary precision in keeping time. And we don't have these. We do have lasers that would be able to measure distances precisely enough over a few km. They are the size of a small building. This is a very, very hard problem. And limitations we are running into are no longer just a matter of engineering. We have no physical principles to extend coherence length with.

[Nuke]

i say we wait till we can build a large railgun on pluto, capable of solar escape velocity and then some. fire off cubesat sized probes en masse. then we can send thousands of probes to thousands of potential systems. of course we need to work on power supplies and figure out how to extremely long range radio. it would probibly allow you to get spectroscopy data on exoplanets. with such large numbers of probes you might get lucky and manage an aerocapture maneuver on a few of them, since you will be carrying a very limited quantity delta-v for course corrections and holding orientation for observations, though this is unlikely.

Edited December 18, 2013 by Nuke

[-Velocity-]

Because of limited coherence length of the laser beam. If we had lasers with arbitrary precision in holding frequency, we'd have clocks with arbitrary precision in keeping time. And we don't have these. We do have lasers that would be able to measure distances precisely enough over a few km. They are the size of a small building. This is a very, very hard problem. And limitations we are running into are no longer just a matter of engineering. We have no physical principles to extend coherence length with.

"You must spread around some reputation before you can give it to K^2 again."

Thanks for the info! I didn't know about this technical challenge. Do you have some good technical references on it? I could look up some IEEE papers, but technical papers are not a good place to start on something that you don't know much about, unless you can find one of those rare "An overview of -" papers. I did take a class on lasers, but we didn't mention this topic at all, not that I remember. If I remember, maybe I can dig out the textbook we used tonight to see if it there's mention of coherence length.

[TechnicalK3rbal]

Isn't voyager (or pioneer, I always forget) technically out of our solar system now? So that would be interstellar?

[Kilmeister]

It depends on your definition of Solar System and the prefix "inter" . But in the context of this thread, no, it is not an interstellar vessel (At least not on purpose).

Edit: It's Voyager I.

Edited December 18, 2013 by Kilmeister

[rhoark]

A 1x3 cubesat with solar sail will ride along for SLS EM-1 in 2017. It's supposed to go interstellar, but I don't know where or how fast.

[AngelLestat]

Of course like many of you said, we need explore our solar system first that we know so little.

But following the question of this topic. My answer is: Possible in the next 25 or 35 years.

Method: Graphene Solar Sail with a mesh weaves, where the weave "spaces" are less than 1/2 the wavelength of light. This will make the graphene reflect some kind of light with high efficiency.

All the instruments would be imprented in the same Sail structure, maybe with a little payload in the extreme (parachute design) that it would be the signal transmissor and receptor that uses the sail like parabolic. This saves weight and also make it capable to resist high acceleration.

It will use just the Sun light to receive propulsion. So no laser-masser battery needed.

Suns gives a lot of energy if we close enoght. Meanwhile at earth orbit (1au) we have 1366 w/m2, at 0,01 Au we have 13660000 w/m2, finally at 0,007 au we have 27710285 w/m2.

(sun radius is 0.00465 AU), flares at magnetic loops raice over the surface with a distance of 0,001 au)

At 0,01 au a final velocity of 6% speed of light (with payload) is possible. We still can get a lot more speed if we close even more, but we dont understand yet why at some height over surface, temperature seems raice until 1 millon degrees. Of course is not maybe a real temperature, becouse there are just particles, but still the invisible effect that heat them, is unknown.

For that reason Nasa will send a probe in 2018 to explore that sun region.

So we will need to wait until that mission to know how close we can get.

Using the same method, the sail would be able to brake at alpha centauri. (In fact it would be easier becouse is a binary system)

About the safety of the sail, is almost garantize (not sure the payload), graphene does not melt becouse is carbon, it sublimates at 5500 celcius degrees. It will reflect mostly all light, but even if it doesn´t, by Stefan-Boltzmann Law will stop to rise their temperature at 2500 celcius or less.

Also the instruments would be expose short time, first the sail needs to fall to the sun using extra weight to accelerate, this will serve like heat shield until the sail deploy in its periapsis.

Actually, Telescopes can't answer if there's life on a planet. It can give you compelling indications, but it can't give you a deffinite answer, and a telescope could only answer if there's civilisation there, if they have night-time lighting. They could be nocturnal after all.

Oh by my calculations, you'd "only" need an interferometer baseline of around 22 km to resolve the disk of Earth at the distance of 50 light-years in visible light-

Astronomer? Or just hobby? I would like to save your contact in case some day need some help with optic calculations.

There is other option I guess. Not easy of course.

To use our sun gravity to focusing light at 700 Au (alpha centauri-Sun focal point). This will be a lot easier with radio signals, also very usefull to comunicate with our probe.

But seems also possible with light.

Even we are dealing with a narrow annulus shape, the final area is huge. With this will be possible to see planets in the alpha centauri system like we were almost there.

So you "just" need a fleet of space telescopes flying in formation across a few dozen kilometers of space, station-keeping with respect to each other with nanometer precision. Sounds tough, but this is achievable with today's technology, believe it or not. Just expensive. BUT A HELL OF A LOT LESS EXPENSIVE THAN AN INTERSTELLAR PROBE!!!! The cost of each space telescope would also be significantly lowered because you'd be effectively mass-producing them.

And then we go to the big problem. Space. First of all, holding station with required precision is impossible. Just forget about that.

At the end of this video there is a way to accomplish that.

Edited December 18, 2013 by AngelLestat

[Nibb31]

A solar sail, by definition, is useless for interstellar propulsion. Even at our distance, it would have to be massive if you want to get some thrust out of it, much more massive than an ion drive, a bit of xenon, and solar panels.

[-Velocity-]

An object inside the Sun's corona will not heat up to 1 million degrees. Probably, some kind of process with magnetic fields there is causing the ionized gases to heat up, and despite the fact that I don't know what it is (and I don't think astronomers really know either) one thing is for certain - it's not going to affect a blackbody. You have to have an electric charge (and be moving, but everything is moving to some degree), a magnetic susceptibility, or a flow of charge (all three of these are really just different ways in which you can have a difference between the movement of positive and negative charges) for a magnetic field to affect you. In the case of the corona, it's the electric charges of the ionized gases that allows them to be affected by the Sun's magnetic fields. A solar sail isn't going to have an electric charge!

So your solar sail isn't going to be subject whatever processes are heating up the gases in the Sun's corona. It's not a problem of temperature- anything that absorbed a bit of heat from the superheated gases of the corona would quickly re-emit it into space as EM radiation (mostly as IR, but some visible will be mixed in too if it's hot enough to start glowing).

However, you're talking about a ridiculously thin membrane of carbon, that would be bombarded by very high speed (as atoms heated to millions of degrees are moving really fast!), ionized atoms. Luckily, they would be very light atoms. Even so, that could very well damage your graphene, but I don't know enough about chemistry to say. All I know is you're going to have A LOT of electron-hungry atoms hitting your carbon at very high speed...

Edited December 18, 2013 by |Velocity|

[-Velocity-]

A solar sail, by definition, is useless for interstellar propulsion. Even at our distance, it would have to be massive if you want to get some thrust out of it, much more massive than an ion drive, a bit of xenon, and solar panels.

No, not necessarily. If you make it very thin, you can get high speeds out of it, because the force applied by the sunlight does not change as you make the sail material thinner and thinner. You just reduce mass, which, of course, increases acceleration.

But, while it's fairly easy to make small samples of a thin sail material that would be suitable for an interstellar (~0.01c+) laser-pushed light sail or even possibly an interstellar SOLAR sail, it's a WHOLE OTHER MATTER to try to make a lightweight rigging system, and to produce the hundreds or thousands of square kilometers of material that is necessary to carry a useful payload.

Edited December 18, 2013 by |Velocity|

[Kerbart]

How do we get information back? Radio signals diminish with the square of the distance. Given how weak the signal is that we receive from the Voyagers, how would we get it from our Alpha Centauri probe?

[-Velocity-]

But anyway, if we CAN find some way to mass produce sail material in space, and IF we could find some way to actuate it and make it maintain precise shapes (within an accuracy of like, 80 nm), then you have incredibly good telescopes and mirrors- no need for interferometers. One way to possibly do this is to correct for aberrations in the large focusing mirror in a much smaller, adaptive mirror, similar to how adaptive optics works today. Anyway, you could potentially form some very, very low divergence, Gaussian laser beams for your laser-pushed light sail. You could focus almost all of your laser energy on your light sail, even out to hundreds of AU.

It's fun to dream about.

[-Velocity-]

How do we get information back? Radio signals diminish with the square of the distance. Given how weak the signal is that we receive from the Voyagers, how would we get it from our Alpha Centauri probe?

You would use lasers pulses, probably. It's easy to make highly directive, high-power beams of energy with lasers.

Indeed, it's thought that the reason that we might not have "heard" from aliens yet is because it's likely that it makes more sense to communicate across interstellar distances by laser flashes... and we've barely begun to search for those. Granted though, we've also barely begun to search for radio signals, so the fact that we haven't detected any really doesn't say much.

So even if it is practical to communicate interstellar distances via radio, if it's MORE practical to communicate via laser, no one is going to be communicating via radio.

Anyway, maybe it MIGHT be possible to use your light sail as a giant radio dish to focus signals back to Earth, but then skin depth considerations come into play big time (your material has to be thick enough to reflect radio waves, the required thickness depending on the material conductivity and radio frequency), and that also obviously ties together communication and maneuvering in undesirable ways. Not to mention, you need to have a way to very precisely control the shape of the sail.

So it's really just easier to use lasers, probably. Probably.

Edited December 18, 2013 by |Velocity|

[AngelLestat]

A solar sail, by definition, is useless for interstellar propulsion. Even at our distance, it would have to be massive if you want to get some thrust out of it, much more massive than an ion drive, a bit of xenon, and solar panels.

By definition is the most convenient. It uses know physsics and the most important (no propellent). If you are talking about interstellar distances (this mean more than 0,2c at DV), the rocket equation would ruin all your hopes if you try to use any kind of propellent (except antimatter).

So even if your fusion or ion engine has an ISP of 5000, 10000, 30000 it would not be enoght. (Maybe if you conbine with a magsail to brake it can work)

So you need antimatter, this mean ISP=300000000.

This plus hundred or reason that I dont want to mention, is why you will find that Beamed propulsion or magsail, or solar sails are the best to-day candidates for interstellar travel. (no mention by me, just look and read).

And the fact that once you are in the alpha centaury system, with just the sail, you can visit all the planets that you want.

So your solar sail isn't going to be subject whatever processes are heating up the gases in the Sun's corona. It's not a problem of temperature- anything that absorbed a bit of heat from the superheated gases of the corona would quickly re-emit it into space as EM radiation (mostly as IR, but some visible will be mixed in too if it's hot enough to start glowing).

However, you're talking about a ridiculously thin membrane of carbon, that would be bombarded by very high speed (as atoms heated to millions of degrees are moving really fast!), ionized atoms. Luckily, they would be very light atoms. Even so, that could very well damage your graphene, but I don't know enough about chemistry to say. All I know is you're going to have A LOT of electron-hungry atoms hitting your carbon at very high speed...

I am agree if the source is magnetic, but according to their calculations this effect it cant be enoght, for that reason some other waves like sound, alfin or gravitational are mentioned.

I also read that a solar sail is the structure that less damage takes from the interstellar medium. Becouse if a molecule hits the sail, just passes right through making a tiny hole, this is almost imperceptible to the sail function.

But if you had a big fussion ship, this molecule will passes right throught the whole ship and fuel. So the molecule will disintegrate releasing radiation and damaging a lot more the ship.

Is not the same case that you mention, but I think it will behave similar.

How do we get information back? Radio signals diminish with the square of the distance. Given how weak the signal is that we receive from the Voyagers, how would we get it from our Alpha Centauri probe?

Like velocity said there are many ways, like I mention before one thing that can be cost effective is to use the sun gravity to focus the signal. Also can work to explore our destination system before send the prove.

ALso the probe needs to have a good autopilot software to react to any drawback, becouse it can not wait for our commands XD

But anyway, if we CAN find some way to mass produce sail material in space, and IF we could find some way to actuate it and make it maintain precise shapes (within an accuracy of like, 80 nm), then you have incredibly good telescopes and mirrors- no need for interferometers. One way to possibly do this is to correct for aberrations in the large focusing mirror in a much smaller, adaptive mirror, similar to how adaptive optics works today. Anyway, you could potentially form some very, very low divergence, Gaussian laser beams for your laser-pushed light sail. You could focus almost all of your laser energy on your light sail, even out to hundreds of AU.

It's fun to dream about.

Yeah is fun.

They already acomplish make a perfect mirror, this will allow many things, like the scalability of lasers or any kind of optic without decrease in efficiency.

About the divergence and how to focus, yes. there is new ways how to mitigate that.

The real problem is how to aim.

To solve that problem, we need to accelerate our sail in less time. Until now, my favorite concept that also decrease the energy consuption is the SailBeam concept by Jordin Kare.

So even if it is practical to communicate interstellar distances via radio, if it's MORE practical to communicate via laser, no one is going to be communicating via radio.

Anyway, maybe it MIGHT be possible to use your light sail as a giant radio dish to focus signals back to Earth, but then skin depth considerations come into play big time (your material has to be thick enough to reflect radio waves, the required thickness depending on the material conductivity and radio frequency), and that also obviously ties together communication and maneuvering in undesirable ways. Not to mention, you need to have a way to very precisely control the shape of the sail..

In the seti case, maybe they use many frecuencies at the same time with weird error correction algorithms that would look like just noice for us. And why not neutrins instead electromagnetic to send the signal... who knows xd

If your sail was made to reflect one kind of frecuency, then you use a laser of the same freacuency to send the signal. I guess.

Edited December 19, 2013 by AngelLestat

[Lighthouse_Power_Beaming]

The Longshot probe, might be built with today's tech. I have attached the report for all toreview. Basically it is a preliminary design of an interstellar probe

to the nearest star, based on current and emerging technology. Also Orion still should be considered because it can be built with todays tech.

If we can build 1000 rounds of W48 nukess for the 155mm gun, then certainly at least we can build the smallest version of Orion.

Longshot: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19890007533.pdf

Orion: http://www.islandone.org/Propulsion/ProjectOrion.html

Cheers Bert

http://www.lhdev.com/People.html

[Nuke]

i say we build a large nuclear powered rail/coil gun in the outer solar system (perhaps on a kuiper belt obeject), which could hurl a small probe at fairly high velocities towards whatever star we wanted to probe. thing about this kind of structure is that it can be used again and again and again, you could do a thorough analysis of all nearby systems.

[AmpsterMan]

Necro here. Closing this thread.

Edit: I kinda shot from the hip there; it seems the post was on topic and added new stuff to the discussion. Apologies all around.

Edited July 29, 2014 by AmpsterMan

[KASASpace]

Fission fragment propulsion has the possibility of millions of specific impulse. We could use that. Antimatter, *shivers* is tough to deal with, so probably no. How efficient is nuclear energy again? Much more than chemical, but still low. If we could get some sort of interim between antimatter, with its efficiency, and nuclear energy, with its relative ease of use, we could probably do it.

Either that or get lucky with wormholes.

[Seret]

I think we could actually do it now

I agree, but flight times would be so long it might be of dubious benefit. Quite apart from the possibility mentioned above that propulsion advances could have our probe outrun during it's journey, it's also highly likely that imaging advances would render it obsolete. We're talking about a flyby probe after all, it may well be that in the decades or centuries it was en route that telescopes and instruments back here were able to gather the same sort of data remotely. Even in the nearish future things like spectroscopy of exoplanets is going to yield an avalanche of data.

I think it's too soon to even think about interplanetary probes. For a start we don't know where to send them. I say wait until we've got a better picture of which destinations look really interesting.

[G'th]

To be frank I'd say that it'd probably be more of a benefit to just send probes into interstellar space rather than aiming for any particular star. As has been said, getting to any other star would take centuries, even with ideal propulsion. But, just getting out of the solar system wouldn't take that long, particularly if you dedicated a launch to that end (Instead of having probes end up leaving the system after sling shotting around the planets). There's still quite a bit to learn about interstellar space from what I understand that would likely be more immediately valuable (and thus worth the cost of launching a probe) than anything we send to another star.

Granted, a probe aimed at specific star would still be able to provide the same benefits, but if you aim it at something, then you're inevitably going to end up putting more resources into it so that it gets there as fast as possible. A probe just for interstellar space won't have that.

[SargeRho]

WIth ideal propulsion you can get to another star in under 20 years...less if you don't intend to brake there.

[Ralathon]

WIth ideal propulsion you can get to another star in under 20 years...less if you don't intend to brake there.

With an ideal anything you can do everything. Engines that can hit 0.25c are a looooong way off from a technical PoV.

[SargeRho]

Magnetic sails combined with particle cannons. They have the advantage that you can use them to brake in the interstellar medium.

[rkman]

So the question is, could we actually reach any of them ?

Sure, if you have a lot of patience.

Two probes are already on the way since the 1970's.

Maybe a modern probe could be a 10 times faster (which i doubt would be feasable), but it hardly matters whether it takes 100,000 years or 10,000 years to get there.

42,000 AD  Voyager 1 is passing near the red dwarf star, AC+79 3888

298,000 AD  Voyager 2 is approaching Sirius

http://www.futuretimeline.net/beyond.htm

And then still we'd be limited to nearby stars. Who wants to wait a couple of centuries for the results to be radioed back to Earth? Not to mention that the probe would need a stupidly powerful transmitter and hugely large antenna. It would need to have capabilities similar to one of the Deep Space Network ground stations. We'd better invent subspace communication first, and as of yet there is no indication such a thing is possible.

Edited July 29, 2014 by rkman

[Javster]

Could Voyager 1 be interstellar if we waited long enough?