[Need some help] Simulation on mission to Alpha Centauri

[corous]

Hi, my fellow Kerbalnauts,

I have a favor to ask.

I'm working on a rough simulation on a mission to Alpha Centauri and would like some help. Back of a napkin calculation says it should be possible with existing rockets, I'm also setting the mission up using NASA's General Mission Analysis Tool (GMAT), but a second set of eyeballs is always welcome.

The mission is to send a 50kg payload into a direct ascent solar escape trajectory towards Alpha Centauri at 50 km/s, i.e. no gravity-assist trajectory around Jupiter etc. and using chemical rockets only. And don't forget that Alpha Centauri lies outside of the Earth's plane of motion. From GMAT, it looks like it's generally in the southwest with respect to the Earth's axis of rotation.

To do the simulation in KSP, you will need the Real Solar System mod and possibly other realism mods for existing rockets / launchers etc.

So, again, the mission parameters:

1. Spacecraft dry mass: 50 kg

2. Min. Velocity (after final burn of upper / kick stage): 50 km/s

3. Existing launch vehicles preferred: Soyuz, Proton M, Delta IV, Atlas V, SpaceX Falcon etc.

Please post your results of velocity achieved with the type / fuel mass of launch vehicle used.

Thanks in advance,

corous

[Ralathon]

You do realize that a spacecraft moving at 50km/s will take roughly 26 thousand years to reach the alpha centauri system? That's 5 times older than the oldest man made structures. What would be the point of launching a mission like this? By the time it arrives in the alpha centauri system we'll have space bases there to watch it fly past.

[corous]

You do realize that a spacecraft moving at 50km/s will take roughly 26 thousand years to reach the alpha centauri system? That's 5 times older than the oldest man made structures. What would be the point of launching a mission like this? By the time it arrives in the alpha centauri system we'll have space bases there to watch it fly past.

Yes, I do. And, I'm also aware that it will take the Voyager 1 40,000 years to do a 1.7-light-year flyby of Gliese 445 / AC +79 3888, but people are still talking about the flyby itself.

I thought the problem I posted originally is an interesting one and worth spending an hour or so if someone on here already has the mods installed. If not, so be it, I'm not holding a gun to anyone's head.

As for the merit and economics of the mission itself, maybe I'll be able to convince some financiers. Who knows?

[meve12]

I honestly wouldn't bother with something that slow. Maybe a Europa mission, but not a Proxima Centauri flyby.

[dharak1]

Isn't solar probe + supposed to hit 200+ km/s near the sun? A quarter of the time isn't THAT bad for another star.

[KerikBalm]

http://en.wikipedia.org/wiki/Bi-elliptic_transfer

You would want to do this, not a direct escape transfer.

Drop your PE inside mercury's orbit, then burn there to reach speeds well beyond escape velocity

[peadar1987]

http://en.wikipedia.org/wiki/Bi-elliptic_transfer

You would want to do this, not a direct escape transfer.

Drop your PE inside mercury's orbit, then burn there to reach speeds well beyond escape velocity

And transfer windows for gravity assists from both Mercury and Jupiter will come by fairly frequently.

[1of6Billion]

How does one plot an interstellar course?

Do you aim in the right direction (where you suspect your target will be when you get there) and fire them engines. Or are we talking about a glorified Hohman transfer?

[Ralathon]

How does one plot an interstellar course?

Do you aim in the right direction (where you suspect your target will be when you get there) and fire them engines. Or are we talking about a glorified Hohman transfer?

Interstellar travel is really just point and burn. The orbital period around the galactic center is so long that you can pretty much assume that the stars are stationary relative to each other. The problem in interstellar travel is the immense dV needed to get anywhere within a human lifespan. If you want to reach the nearest stars within a century you are talking about dV requirements 3 orders of magnitude higher than we usually use in spaceflight.

[Hattivat]

AFAIK it's only point and burn if we assume an antimatter-burning engine made out of unobtainium to achieve velocity high enough to make all the external gravitational influences irrelevant, and reach the destination in 50 years, letting us disregard the relative velocity of the stars involved. And even then, considering how tiny is the target in respect to the distance involved, the accuracy of the resulting fly-by may turn out to be rather disappointing.

With the timeframe that the OP proposes, the answer is a resounding no - we have pretty much no idea how to aim a probe to fly reasonably close to a star 40 000 years into the future. Keep in mind we don't even really know what the interstellar space is like yet.

[cantab]

You need to take into account relative velocity of the stars. It's something like 25 km/s for Alpha Centauri, and in about 30,000 years it'll be the best part of a light-year closer than it is today.

You may though be able to ignore any change in the magnitude of that relative velocity, and consider it as on a straight-line trajectory.

[corous]

http://en.wikipedia.org/wiki/Bi-elliptic_transfer

You would want to do this, not a direct escape transfer.

Drop your PE inside mercury's orbit, then burn there to reach speeds well beyond escape velocity

An excellent thought. Will test that out. Thank you, sir.

[corous]

AFAIK it's only point and burn if we assume an antimatter-burning engine made out of unobtainium to achieve velocity high enough to make all the external gravitational influences irrelevant, and reach the destination in 50 years, letting us disregard the relative velocity of the stars involved. And even then, considering how tiny is the target in respect to the distance involved, the accuracy of the resulting fly-by may turn out to be rather disappointing.

With the timeframe that the OP proposes, the answer is a resounding no - we have pretty much no idea how to aim a probe to fly reasonably close to a star 40 000 years into the future. Keep in mind we don't even really know what the interstellar space is like yet.

Are you sure about this?

Sure, the exact conditions in interstellar space is not known. There could be "waves" of radiation pressure due to cosmic rays etc., but the motion of nearby stars should be relatively easy to predict. On a macro scale, they should be more or less Keplerian. Plus, Alpha Centauri is in the same galactic arm as the solar system and all.

[peadar1987]

Are you sure about this?

Sure, the exact conditions in interstellar space is not known. There could be "waves" of radiation pressure due to cosmic rays etc., but the motion of nearby stars should be relatively easy to predict. On a macro scale, they should be more or less Keplerian. Plus, Alpha Centauri is in the same galactic arm as the solar system and all.

I think it's more sort of strange, Pioneer Anomaly-type effects that we may not have anticipated. The motion of the probe might only be affected a tiny amount, but over 40,000 years, any effect will add up.

[Hattivat]

Basically what Peadar wrote. All the hypothetical unknown influences, even if tiny, plus the minor inaccuracy of our current measurements, added up over 40 000 years, would in all probability be more than enough to make us miss. Keep in mind how tiny the star systems are in comparison to the void surrounding them - the distance from Pluto to the Sun is 4.4 billion km at the closes point, and Alpha Centauri is roughly 44 trillion km away from the sun. Even assuming this rather underwhelming accuracy target (getting a fly-by which at its closest point is no further from Alpha Centauri than Pluto is from the Sun), that is still the equivalent of hitting a 1m x 1m target from 10 kilometers away.

[corous]

I think it's more sort of strange, Pioneer Anomaly-type effects that we may not have anticipated. The motion of the probe might only be affected a tiny amount, but over 40,000 years, any effect will add up.

And @Hattivat , thank you for the input, gentlemen.

The Pioneer Anomaly seems like more of an engineering oversight, rather than a previously unknown cosmic phenomenon. The thermal recoil force theory and initial modeling error explanations seems to fit the scenario well.

So yes, I agree with your point that any miniscule effect can add up to something significant over 26,000+ years (not 40,000 -- that's the Voyager's trip to Gliese 445). But on the same token, the earlier a trackable spacecraft can be launched to "test the water", the better. Isn't it?

[Hattivat]

While I agree in principle, the "trackable" aspect is another part of the plan that I see potential problems with - granted I know next-to-nothing about data transmissions, but 250 kg weight limit doesn't exactly sound like it could include a dish capable of interstellar transmissions to me. There is also the "minor" problem that designing a spacecraft that could function for 26 000 years without any maintenance would be quite a challenge. Or actually, more like "impossible" with current technology. If you are going to assume that some sort of a breakthrough will enable us to build electronics that can survive for thousands of years, you'd be better off assuming such a breakthrough will take place in the field of propulsion, so that's we don't need to wait for 26k years in the first place. And even if our electronics could survive for that long, you'd still need to develop some exotic energy source to keep it going that long, no RTG can keep on working for that long, and solar panels obviously won't cut it in interstellar space.

[cantab]

If you *can* design something that will last 26 millenia, surely you can design it to be capable of making course corrections, obviating the need for silly initial precision.

[Hattivat]

Do we trust some humans 23 000 years in the future to transmit the correction instructions to the probe, or do we assume that the engineers striving to design something to last for 26 000 years somehow felt that it wasn't enough of a challenge and decided that this "something" should be a supercomputer with high-precision measuring instruments, to be able to calculate the necessary corrections by itself?

[cantab]

Automatic star sensors and guidance systems aren't that difficult to make. OK so an interstellar trip adds a few wrinkles, but it's still a simple, well-defined problem with uncomplicated image processing needs (stars on a black background, how much simpler can you get?)

Anyway, presumably we do think that ground control is going to keep an eye on this for tens of thousands of years, since it needs to receive the close-ups when the probe finally reaches Alpha Cen. Otherwise what's the point of the mission?

[Hattivat]

Otherwise what's the point of the mission?

Considering that at the dawn of anno 28014 humans will in all likelihood be either

a) extinct / technologically regressed, or

possessing telescopes capable of collecting data on Alpha Centauri with much better fidelity than an ancient 250 kg probe on a highly imprecise course

I'm afraid that my conclusion is that there is no point, other than purely symbolic value.

Launching an interstellar probe with chemical rockets makes about as much sense as crossing an ocean with a paddle boat.

[1of6Billion]

..snip..

Launching an interstellar probe with chemical rockets makes about as much sense as crossing an ocean with a paddle boat.

Which has been done numerous times as well..

[Hattivat]

Paddle boat, not paddle ship. You know, the silly human-powered watercraft that can be found in amusement parks, like this one:

...unless I'm unaware of something and someone actually did cross an ocean in one of these, in which case please link a video or some photos, I'd love to see it

[Nibb31]

Crossing the Atlantic in one of those would be orders of magnitude easier and faster than travelling to Alpha Centauri on chemical propulsion, actually.

Interstellar travel with current technology would be more like emptying the Atlantic Ocean with a teaspoon.

[magnemoe]

Paddle boat, not paddle ship. You know, the silly human-powered watercraft that can be found in amusement parks, like this one:

http://blog.kerplunc.com/wp-content/uploads/2013/06/p19.jpg

...unless I'm unaware of something and someone actually did cross an ocean in one of these, in which case please link a video or some photos, I'd love to see it

Should be possible to cross the Atlantic in one of them yes you would need to make it more weatherproof by adding a roof, someone did row over Atlantic alone in a boat not much larger.