What do you think would be the limiting factor on the speed of an interstellar spacecraft?

Question

...the inability to feasibly achieve a greater speed, or the inability to protect the vessel from micro-impacts? I'd like to hear ideas on what kind of shielding would be needed at speeds of 300 to 3000 Km/sec., considering what would be the effect of hitting a micrometeoroid at that speed. Or even the effect of interstellar gas, as sparse as it may be. Also, would there be any practical way of detecting a dangerous object which would destroy any reasonable sized shield, in time to alter the ship's course the tiny amount needed to avoid it? Say, for example, the size of a baseball.

Astronomy, duce, for almost 50 years.

Amansscientiae, I tried to think of a better way to ask the question. Perhaps I should have said assuming you could get to a speed of 300 or 3000 Km/sec, would you be able to consider going at that speed because of the effects of high speed collisions with small objects. I wanted to see if people thought these speeds would be prohibitively dangerous, that there wouldn't be any reasonable way to protect from certain kinds of collisions. I also didn't mention that there is a much greater risk of collision at those speeds than there is at speeds we typically use in space flight, especially for the time spans we are talking about. So let's say a steady acceleration from nuclear bomb propulsion. I don't think 1% of light speed is relativistic enough for the energy problem to be impossible to solve.

Zahbudar, true. But let's assume a technology that could consider building such a vessel. Yeah, it would take an enormous amount of energy to build and fuel the ship. And then it would have to escape the sun's gravity, but if built in space, that isn't so hard to do using planetary accelerations like we did with Pioneer and Voyager and others. No doubt, the thing would be huge, mainly because of the amount of fuel needed. But only a very small acceleration is needed. It just has to be maintained for a long time. Once it reaches escape velocity, (in a few months), it could drift the rest of the way.

AZ, thanks.

Ericbryce, I wasn't really thinking of a manned mission, but as you suggested, we might discuss one which is carrying valuable equipment or specimens. If you have live people, in a suspended state or not, I can see why speed would be the biggest problem. The whole thing would probably have to weigh two or three times as much if it had living beings aboard. Then the fuel would have to be about six to ten times as much, and so on. So yeah, it's easier to believe that a manned mission would have to go slower and shielding would be less of a problem than fuel. In an unmanned vessel, however, I wonder if the speed would have to be limited because of what would happen to the ship if it hit a baseball-sized chunk of rock at 3000 Km/sec.; or even if it hit a region of slightly denser gas that would be typical in interstellar space.
I'm writing a story where such a mission is taking place. Yes, it involves big ships with small payloads, and takes 6000 years to get to another star system.

Aviophage, I have done some calculations on acceleration, time, and distance. Once built, the ship would only have to accelkerate for a relatively short period of time. Also, at 1/100 the speed of light, it would take only a 1000 years to go 10 LY. I'm not daunted by that because the technology I am assuming has longevity. But the lifespan was not relevant. Only the speed and collision risks. No, I don't expect anything like this perhaps for hundreds of years. We certainly won't be around to see it. But my characters will! (Because they get a little help.) I'm afraid I must invoke a yet unknown kind of propulsion, as well. Not warp drive, though. I'm working on something more credible which could achieve such speeds. Now, how do I protect my payloads?

Also, I see your point about anything mechanical. I have seen people mention the impracti9bility of interstellar travel because of this, but I'm less pessimistic. If some devices are stored and not subjected to any changes in heat or an atmosphere, then why wouldn't they last indefinitely? If some ET finds the Voyager record in 100,000 years, won't it be playable on the equipment we provide?

Answer 1

Indeed, the limit on speed would be your propulsion system...not the shielding.

Answer 2

The inability to achieve a greater speed. Shielding is the least of our problems. The fragility of the human is the weak link. Light speed is something like 670 million miles per hour and even at that speed interstellar journeys can take hundreds or thousands of years. Since we can never hope to go there our own solar system will be the only area that mankind can ever hope to explore.
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If in the future, if mankind was faced with annihilation, perhaps the technology will exist to launch something I'm calling here "seed ships." Ships packed with robots and computers programed with all the knowledge of mankind and frozen human embryos. Sent out into the void to travel perhaps a hundred thousand years with hopes that one or two would make it to an Earth-like world and our race could continue. These embryos or test tube babies would theoretically be raised by the robots on arrival.
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This is not an original idea at all but interesting to think about. It would be weird to be that first human raised by robots on a new world or maybe by that time robots would be so realistic that the human may not even find out until later that he's the only real human. Talk about your rude awakenings?
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Kind of like SUPERMAN right?
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Answer 3

Speed is your limiting factor. Light speed is the cosmic speed limit, and barring some new physics discovery always will be. The issue of microimpacts may be mitigated by numerous means that don't require exotic materials or sci fi technology. Lasers "sweeping" ahead, magnetic fields, composite laminates on the leading edges of the craft, a small craft or shield flying in front a ways, and many other possibilities.

==Edit==
"At any attainable speed using known technology for propulsion, an "interstellar" trip would take tens of thousands or hundreds of thousands of years,"

Not entirely correct. Several proven technologies and some promising experimental techs exist that would allow for transit times of a few hundred years. Ion engines and laser sails for example. There are significant engineering problems that need to be worked out, and perhaps won't ever be, but the physics behind them is solid, and it is premature to call such trips "impossible".

Answer 4

There is a basic problem in accelerating a space craft to high velocities... Fuel and Weight (Mass).

If you wish to accelerate a body to a high speed it takes lots of fuel burning for a long time to add more and more thrust.
But, you can only launch so much weight and accelerate it to a finite speed with a given amount of fuel.

If you wish to go faster than that, you need more fuel.

More fuel weighs more, and requires a larger rocket ship, which in turn weighs more. Well, if the added fuel and larger space ship weigh more, then we cannot possibly accelerate it to the desired speed due to the additional weight. So, you will need more fuel so that the rocket engines will burn longer and provide the needed thrust to reach the desired velocity...

But... More fuel weighs more, and you will need a great big space ship to carry it in space. Now you cannot possibly reach the desired velocity with all of that extra weight being carried, so you need to run the rocket engines longer to reach the desired velocity, which means, you need more fuel.

If you need more fuel, the space ship is going to have to be larger. All that added fuel and the larger ship add a lot of additional weight to your space package so we probably can't reach your desired velocity unless we add.....

So you really fall into this loop....when you utilize current solid fuel or liquid fuel rocket engines... New technologies...well
some are in space right this moment and may be the pathway to future long distance flights. Instead of a big thrust for a short time, these new technologies provide some small thrust continuously over very long time periods. Maybe the thrust potential is on the order of 1 or 2 km/sec/sec acceleration. Over a four year flight that might be a rosey big velocity toward the end of the flight. We can only wait and see what results the most recent launches produce.

There is no reasonable means of avoiding small bits of debris in space if you are traveling at 20-30,000 Miles Per Hour. Even small (slight) deviations in your flight path result in totally new possible unseen hazards ahead... avoid one that you can see and fly into another that you cannot see...

Being hit by a speck of granite or copper traveling at
speeds of 30,000 miles per hour would be 25 - 30 times more destructive than the most powerful hunting rifle you can buy today. Cabin depresurization would commence immediately assuming nothing major was hit by the projectile. Most likely you would be dealing with two holes, an entrance hole and an exit hole, plus lots of schrapnel inside the space craft which might puncture the hull also.

Armor is out of the question because it would increase the weight of the space ship and reduce its speed, and increase the fuel needed to drive it faster and faster through space.
A chunk of rocky or metalic debris the size of a baseball or golf ball would probably mean instant destruction of the entire craft and everyone aboard.

Answer 5

The limiting factors would be the available energy for propulsion and the number of working cycles of the spacecraft's components.

At any attainable speed using known technology for propulsion, an "interstellar" trip would take tens of thousands or hundreds of thousands of years, so your spring-loaded thingie would have to be made so it would never wear out. As we don't know how to do that, interstellar travel is not possible.

Furthermore, it is well understood that the amounts of energy required to propel a spacecraft to even the very low speeds required to make the trips in even hundreds of millenia would be... well... let's say "astronomical."

Sorry. No point in even worrying about what you might run into. It's just not going to happen. I wish someone would prove me wrong, but I am not holding my breath.

Answer 6

For the individuals returned on earth, it takes approximately 8.6 years for the freighter to get returned from a around holiday. For the team on the spaceship, it takes approximately 6.6 months. thinking the flexibility expenditures of increasing to 0.999c and backtrack to 0, the shipment might prefer to be very worthwhile.

Answer 7

Your first problem would be to accelerate the spacecraft to such a high speed. I will tell you my solutions to the shielding problem as soon as you show me your solution to the propulsion problem.

:-)

Answer 8

Hmmm, what have you been smoking