Interstellar Navigation (10)

1 Name: Anonymous Scientist : 2011-05-10 12:02 ID:pGXR8nNn

In interstellar space, how do you know where you're going? If you want to visit Proxima Centauri you can look into your telescope on earth and see where it was. You can only estimate where it is now (or more importantly, where it’s going to be when you get there) and surprisingly, not with the degree of accuracy you’d hope for. It seems observed distance is off by fractions of a light year and its movement relative to earth each year potentially off by fractions of a milliarcsecond. These unknowns could put any mission to this star off by millions of miles and this is the star nearest us!

These problems almost eliminate the option of navigating by the stars to get to the stars. Often you’ll hear the option of navigating by pulsars as though it’s as simple as a GPS system, but that’s not the least bit true. Now your probe must also be a complex radio observatory and again these positions change naturally and relative to the movement of any space craft over time. Add to that problems of timekeeping at high speed and there are even more problems to overcome.

This isn’t impossible but it is extremely complex. Any thoughts on this? I was thinking one of the better ways to improve our future odds would be to build observatories elsewhere (by which I mean Mars and beyond).

2 Name: Anonymous Scientist : 2011-05-10 22:02 ID:ZPF54YLb

It's not as if you'd intentionally stray millions of miles from your destination when, the closer you get, the more certainly you can tend towards it.

3 Name: Anonymous Scientist : 2011-05-10 22:07 ID:1y/oZJ5a

There's no real problem with it, stars (mostly) don't move that fast relative to each other and their speeds relative to sun are generally well known for our star neighbors. Navigating our own planetary system is harder because planets affect each other more than stars do and travel over significantly more curved trajectories.
Apart of that, you can always apply corrective maneuvers during the flight.
Much worse problems with interstellar travel are time and energy needed for that with our current technology.

4 Name: Anonymous Scientist : 2011-05-11 08:20 ID:c5OiyqCX

>>2 OK... So my thinking here was that we'd be sending a probe. You know, unless there are volunteers for a one-way mission to die in space after seeing maybe one or two fairly uninteresting stars. With that in mind, here we go:

This probe is going to very quickly be beyond the point at which communicating with it at all is the least bit useful (so we can't send updates). It's going to have to be artificially intelligent to a high degree to be able to aim itself over time. It just seems like there's a possibility that if we're the least bit off with our earth-based observations, we're going to expend a lot (as in all) of our fuel in making corrections on our approach.

On the other hand, if we end up missing our target (or crash into it or hit Ptolemy's spheres on the way or whatever) it would still teach us a great deal about the flaws in our current understanding of astronomy... so win-win?

5 Name: Anonymous Scientist : 2011-05-12 01:13 ID:ZPF54YLb

There is really just a finite set of conditions we'd have to account for - optical distortions, orbital eccentricity, debris interference, gravitational wells of intermittent bodies. And I'm sure changes in trajectory would most efficiently occur in single bursts; the greatest fuel expenditure being the continuous action of closing distance within the general vicinity.

But then, there are ways to incorporate refueling and conservation along the itinerary of the craft's journey. How about aiming for the nearest star in the path of its travel, so that it hooks onto the orbit for a bit, collecting electromagnetic energy which it uses to gain speed as it gradually recedes, eventually slinging itself away?

6 Name: Anonymous Scientist : 2011-05-18 23:41 ID:1pLVVbkJ

I always wonder how one would get their o2 for long periods of time.
I suppose you could just have a bunch of plants on board.

7 Name: Anonymous Scientist : 2011-05-19 08:46 ID:ZPF54YLb

Larry Niven used an interesting concept called a ``ramscoop field'' - electromagnetic wings some tens, hundreds or thousands of kilometers wide which collect stray gasses and synthesize them for various purposes. I suppose the direct product could be breathable air with fuel as a byproduct. The catch though is that for this to be even remotely effective you must either be sailing through a nebulous cloud or traveling fast enough that you collect the stuff faster than you burn it. shrug

8 Name: Anonymous Scientist : 2011-05-20 10:11 ID:c5OiyqCX

Well plants are not exactly the way to do things. They're not terribly efficient so you'd need lots of them. You'd have to expend energy to provide them with light and if you're going to do that, why not just use that power to mechanically scrub the air?

For long distance cruises around the solar system at reasonable speeds, we'd probably give people plants for fresh food and yet another hobby to keep them occupied. They'd do more for the sanity of the crew than they would for the atmosphere.

I said reasonable speeds above for a reason. If you want to get totally crazy (and this being 4-ch's "science" board, let's go ahead and do that) then understand that if you manage to get your space ship going fast enough VTEC... er, I mean, special relativity kicks in. At speeds approaching the speed of light, your ship is gone from earth for many decades but your perceived time on board is greatly reduced. The faster you go, the fewer supplies you'd need. Get going fast enough and you might be able to cover tens of light years with only a couple years' worth of supplies.

It takes enormous machinery buried below Switzerland to get bits of atoms up to the speeds we're talking about here. The step up in energy to get something as massive (and yet still cramped) as a Vostok capsule up to that speed is well beyond our reach at the moment.

9 Name: Anonymous Scientist : 2011-05-23 21:18 ID:dqH49jxd

>>Larry Niven

moar liek Robert W. Bussard, amirite guise?

10 Name: Anonymous Scientist : 2011-05-23 22:04 ID:ZPF54YLb

I said used, not invented, dumbass. Read A World Out Of Time, The Integral Trees and The Smoke Ring.

This thread has been closed. You cannot post in this thread any longer.