Collision during relatively fast interstellar travel

[Ivan Tuzikov]

Let's take as an example a Deuterium-Deuterium fusion spacecraft. The estimated exhaust velocity is fairly high, an estimated 19,000 km/s (0.063 c) which means a 120,000 ton starship attached to 12,000,000 tons of deuterium can do a delta-vee of ~0.29 c. With an efficient magnetic sail that means the journey speed approaches ~0.29 c, albeit with the mass-penalty of the sail.

 

Is it really possible to flight at speed of 0.063*c or faster through Kuiper belt, Hill's cloud and Oort cloud to, say Proxima Centauri and not collide with something.

 

There is an opinion that we are going to collide in case of fast interstellar travel - http://boards.straightdope.com/sdmb/showthread.php?t=689927

 

And there is also an opinion that fusion spacecrafts are unfeasible.

 

http://www.wired.com/2008/08/space-limits/

 

http://physics.ucsd.edu/do-the-math/2012/01/nuclear-fusion/

 

 

So, how probable is collision during relatively fast interstellar travel (0.063*c or faster)?

[EdEarl]

Do you think the probability of collision increases with speed? If so why? How does speed affect your ability to detect and react to a pending collision? What is the increase in damage from collisions? How do size and mass affect collision rate and maneuverability? A big question, that may not have a satisfactory answer is, "How many objects of what size are in interstellar space?" You may be able to make a Drake-like equation to answer your question.

IMO you haven't asked the right question. You are certain to collide with small things, starting with photons and working up in size. You are certain to avoid large things like stars and planets, except by choice. The littlest things do not cause damage. Some small things act like a sand blaster. Large things damage. What is acceptable damage and what must be avoided. Ship hull design is a factor.

The simple answer is you aren't likely to hit anything catastrophic for a long time. Voyager 1 and 2 have been traveling for 38 and 35 years without hitting anything. IDK how many years total travel has occurred within the solar system, nor whether a payload has had an unintended collision, but I'm sure it is rare.

Edited February 16, 2016 by EdEarl

[TakenItSeriously]

At those speeds I'm not sure if gravity assists are going to be much help. Why not just avoid the orbital plane altogether?

 

I get the impression that the ort cloud wouldnt be that big an issue to navigate.

[DanTrentfield]

Let's take as an example a Deuterium-Deuterium fusion spacecraft. The estimated exhaust velocity is fairly high, an estimated 19,000 km/s (0.063 c) which means a 120,000 ton starship attached to 12,000,000 tons of deuterium can do a delta-vee of ~0.29 c. With an efficient magnetic sail that means the journey speed approaches ~0.29 c, albeit with the mass-penalty of the sail.

 

Is it really possible to flight at speed of 0.063*c or faster through Kuiper belt, Hill's cloud and Oort cloud to, say Proxima Centauri and not collide with something.

 

There is an opinion that we are going to collide in case of fast interstellar travel - http://boards.straightdope.com/sdmb/showthread.php?t=689927

 

And there is also an opinion that fusion spacecrafts are unfeasible.

 

http://www.wired.com/2008/08/space-limits/

 

http://physics.ucsd.edu/do-the-math/2012/01/nuclear-fusion/

 

 

So, how probable is collision during relatively fast interstellar travel (0.063*c or faster)?

The probability of a collision at 0.63c would be the same as it is at 0.001c, as velocity is a mute point when it comes to collision probability, what you really have to worry about is how many things there are you can hit, Unless of course you're flying the death star, your speed will have no affect on your collision probability. (And even then a nearby asteroid's trajectory would begin to resemble a line next you rather than a suborbital ballistic trajectory. ) (Insert Han Solo Joke: "Never tell me the odds")

Also the "Interstellar travel will never happen" thing is completely bogus, (Being the major movie buff I am, I'm doing a Jurassic park quote) "Life will find a way", and it forgets to factor in the magical thing that is innovation, It may happen today, it may happen in the year 3067, but innovation happens, and innovation changes everything, And have we thought of everything? No because the universe is infinite.

Edited February 17, 2016 by DanTrentfield

[Ivan Tuzikov]

Well, when the speed is high it is more hard to maneuver, isn't it? As well as to detect any obstacles in advance.

[zapatos]

The probability of a collision at 0.63c would be the same as it is at 0.001c...

Doubt it. When I drive at 100 mph I am much more likely to have a collision than when I drive at 5 mph.

[TakenItSeriously]

The probability of a collision at 0.63c would be the same as it is at 0.001c, as velocity is a mute point when it comes to collision probability, what you really have to worry about is how many things there are you can hit, Unless of course you're flying the death star, your speed will have no affect on your collision probability. (And even then a nearby asteroid's trajectory would begin to resemble a line next you rather than a suborbital ballistic trajectory. ) (Insert Han Solo Joke: "Never tell me the odds")

 

I'd disagree, the higher the speed:

The greater the energy imparted from collisions, regardless of size.

The smaller the object that becomes a threat.

The more difficult it becomes to detect intercept trajectories at a distance.

The less time you have to react to those trajectories.

The more you need to armor your craft.

The greater the mass of your craft.

The less maneuverable you'll be for evading objects.

The more you'll cut into your safe detection lead time.

 

These are the potential issues I can think of off the top of my head.

[EdEarl]

Doubt it. When I drive at 100 mph I am much more likely to have a collision than when I drive at 5 mph.

Why is important to answering the OP question.

[Sensei]

At relativistic speed even impact with photons is going to be problematic, because their energies/frequencies will be blue-shifted.

Normal photon in visible spectrum, not harmful, after blueshift could be ionizing spacecraft material.

 

[EdEarl]

If you plot object size (m³) and density (#/km³) then there are many photons (smallest objects) and few stars (largest objects). A first approximation curve between those two points is a straight line. However, it is possible to find estimates or measurements of a few more points, such as planet density and hydrogen atom density. Half a dozen points should allow a good guess at the shape of the size-density curve.

Edited February 17, 2016 by EdEarl

[imatfaal]

At relativistic speed even impact with photons is going to be problematic, because their energies/frequencies will be blue-shifted.

Normal photon in visible spectrum, not harmful, after blueshift could be ionizing spacecraft material.

 

 

The speeds the op is talking about will take red photons and blue shift them all the way to green photons

You would have to be up at just one millionth away from the speed of light to get visible light into the proper hard x-ray band

[DanTrentfield]

Well, when the speed is high it is more hard to maneuver, isn't it? As well as to detect any obstacles in advance.

But if you're flying a bigillity dollar fancy pants fusion spaceship you'd plot your trajectories carefully wouldn't you......

 

Doubt it. When I drive at 100 mph I am much more likely to have a collision than when I drive at 5 mph.

Driving isn't the same as traveling through space, If you were driving through the middle of Montana at 150 mph with no cars in sight, nothing but bushes, and a straight road you wouldn't crash now would you? That's more like flying through space, the probability you'll hit something is very low, But you still have to watch out because there are more asteroids in the solar system than there are people on four earths.

[zapatos]

Driving isn't the same as traveling through space, If you were driving through the middle of Montana at 150 mph with no cars in sight, nothing but bushes, and a straight road you wouldn't crash now would you? That's more like flying through space, the probability you'll hit something is very low, But you still have to watch out because there are more asteroids in the solar system than there are people on four earths.

I don't see where it is much different. In either case I might suddenly find something in front of me that I did not expect, say, an asteroid or a deer. If I am going faster, I will have less time to react and am therefore more likely to collide with that object. That seems self evident.

[DanTrentfield]

I don't see where it is much different. In either case I might suddenly find something in front of me that I did not expect, say, an asteroid or a deer. If I am going faster, I will have less time to react and am therefore more likely to collide with that object. That seems self evident.

But the Probability is what we're talking about, if you hit a grain of sand moving at 0.63c you're suddenly a scattering wreck of debris fuel and oxygen, which is why you don't accelerate to 0.63c right away, you get past the Mars-Jupiter asteroid belt, and then you begin accelerating, slingshot around a planet to save yourself some delta-v and fly through the Oort cloud quickly, as it's widely dispersed. Probability, not what if.

[zapatos]

Hmm. So you are saying that the probability of colliding with an object does not go down as you gain greater ability to maneuver around the object?

[DanTrentfield]

Hmm. So you are saying that the probability of colliding with an object does not go down as you gain greater ability to maneuver around the objITh

That does go up. Probability of collision, does not because collision probability depends on trajectories not pilot error. Also you totally worded that wrong, You can have a computer guidance system do all the maneuvering for you and get through an asteroid field without a scratch.

[TakenItSeriously]

I don't see where it is much different. In either case I might suddenly find something in front of me that I did not expect, say, an asteroid or a deer. If I am going faster, I will have less time to react and am therefore more likely to collide with that object. That seems self evident.

Then you've clearly never driven through the desert on an empty highway where driving a 100MPH feels like your standing still.

 

Things don't just materialize in front of you. A deer suddenly appearing in front of you after you've come around a blind bend is when you get into trouble. A deer that you see approaching the road off in the distance when there's no other objects around to hide it isn't going to be an issue.

 

This kind of problem is important even for satellites today, although the scale is different. It's due to the speed at which objects move in space with no atmosphere to slow them down. Then even tiny lightweight objects such as a paint chip can be traveling at several times the speed of a bullet and would kill any astronaut unlucky enough to be on a spacewalk in its path.

 

Fortunately objects in space are also easy to detect. The main issue is how much debris there is to avoid.

 

All objects in Earth orbit down to the size of a baseball are tracked and satellites or the ISS must occasionally move in order to avoid collisions. Satellites that have lost the ability to maneuver become a threat since they may be hit creating many more pieces of debris.

 

The ISS can has shielding material that can offer some protection but I think there's a gap in what it can handle and debris that's tracked. Because of this, I believe there are plans to move the space station into a higher orbit that's not as dense with space junk.

 

Space junk has become a serious issue since there's so much of it. A large collision could suddenly create much more debris which could cause a chain reaction of collisions making satellites that depend on orbits in high traffic areas such as geosynchronous orbits no longer viable. It's a statistical problem which has already been worked out for determining a tipping point for the density of items which I believe we are very close to surpassing.

[DanTrentfield]

Then you've clearly never driven through the desert on an empty highway where driving a 100MPH feels like your standing still.

 

Things don't just materialize in front of you. A deer suddenly appearing in front of you after you've come around a blind bend is when you get into trouble. A deer that you see approaching the road off in the distance when there's no other objects around to hide it isn't going to be an issue.

 

This kind of problem is important even for satellites today, although the scale is different. It's due to the speed at which objects move in space with no atmosphere to slow them down. Then even tiny lightweight objects such as a paint chip can be traveling at several times the speed of a bullet and would kill any astronaut unlucky enough to be on a spacewalk in its path.

 

Fortunately objects in space are also easy to detect. The main issue is how much debris there is to avoid.

 

All objects in Earth orbit down to the size of a baseball are tracked and satellites or the ISS must occasionally move in order to avoid collisions. Satellites that have lost the ability to maneuver become a threat since they may be hit creating many more pieces of debris.

 

The ISS can has shielding material that can offer some protection but I think there's a gap in what it can handle and debris that's tracked. Because of this, I believe there are plans to move the space station into a higher orbit that's not as dense with space junk.

 

Space junk has become a serious issue since there's so much of it. A large collision could suddenly create much more debris which could cause a chain reaction of collisions making satellites that depend on orbits in high traffic areas such as geosynchronous orbits no longer viable. It's a statistical problem which has already been worked out for determining a tipping point for the density of items which I believe we are very close to surpassing.

Exactly what I've been trying to use statistics and logic to prove to zapatos.....

Edited February 17, 2016 by DanTrentfield

[TakenItSeriously]

Exactly what I've been trying to use statistics and logic to prove to zapatos.....

Your right, I neglected to credit your post which I find irritating myself. Sorry about that.

[DanTrentfield]

Your right, I neglected to credit your post which I find irritating myself. Sorry about that.

Its fine, just probability, not speed.

[EdEarl]

A successful trip is one in which you do not encounter a potentially damaging object, or if you do then you can dodge it, or if you can't dodge then you can repair the damage.

 

P [math]\doteq[/math] 0 [math]\leq[/math] probability [math]\leq[/math] 1

 

Ps = probability of successful trip

P_{[math]\heartsuit[/math]} = probability of clear path

P_{[math]\diamondsuit[/math]} = probability of dodging an object

P_{[math]\spadesuit[/math]} = probability of repairing damage

P_{[math]\clubsuit[/math]} = probability of damaging collision

 

Ps = P_{[math]\heartsuit[/math]} + P_{[math]\diamondsuit[/math]}+ P_{[math]\spadesuit[/math]}P_{[math]\clubsuit[/math]}

 

Hope to get this right, it's been a long time since I did any statistics.

Edited February 19, 2016 by EdEarl

[TakenItSeriously]

A successful trip is one in which you do not encounter a potentially damaging object, or if you do then you can dodge it, or if you can't dodge then you can repair the damage.

 

P [math]\doteq[/math] 0 [math]\leq[/math] probability [math]\leq[/math] 1

 

Ps = probability of successful trip

P_{[math]\heartsuit[/math]} = probability of clear path

P_{[math]\diamondsuit[/math]} = probability of dodging an object

P_{[math]\spadesuit[/math]} = probability of repairing damage

P_{[math]\clubsuit[/math]} = probability of damaging collision

 

Ps = P_{[math]\heartsuit[/math]} + P_{[math]\diamondsuit[/math]}+ P_{[math]\spadesuit[/math]}P_{[math]\clubsuit[/math]}

 

Hope to get this right, it's been a long time since I did any statistics.

It's close but I think it's more correct to just subtract the failures from 1

 

Pc should be failure to repair so that collision and failure to repair = an unsuccessful state.

Ps = (1-Ps PC)

 

If you wanted to include maneuverability in that equation

Ph = probability of intersecting trajectory

Pc = probability of failure to avoid collision

Pd = probability of failure to repair damage

Ps = 1-Ph*Pc*Pd

This avoids overlapping probabilities

Edited February 19, 2016 by TakenItSeriously