Why can spacecraft not travel at relativistic speeds in outer space?

Assuming that a spacecraft had enough fuel to propel itself to any desired speed, why is it that modern spacecraft only travel at relatively slow speeds (~10-20 km/s)? Since there is no friction in space, what is stopping such a craft from traveling so fast? I know that it is physically impossible to travel at the speed of light but surely, we should be able to travel at much faster speeds due to the lack of friction? Why is it that they don't go as fast as they potentially could?Why can spacecraft not travel at relativistic speeds in outer space?You answered your own question: they don't have enough fuel. The problem is not lack of friction, it is lack of anything to push against, so you need to use rockets that push against their own exhaust. There is an equation, called the rocket equation, that can tell you how much propellant (which is basically fuel, but not technically exactly) is needed to get up to such speeds, and it is an amount larger than the whole planet Earth! You need to burn fuel for YEARS to accelerate up to such speeds if you do it at 1 G or some reasonable rate. Our rockets burn up ALL their fuel in 10 minutes just to get up to 17,500 miles per hour. The problem is that the fuel not yet used is part of the weight of the rocket that has to be pushed by the fuel being burned now, so to go faster than 17,500 mph you need enough more fuel to push the still fully fueled rocket up to 17,500 mph before you start burning that last 10 minutes worth to add 17,500 mph more speed. It is an exponential function and the amount of fuel needed gets impossibly large after speeds of "only" a few kilometers per second.Why can spacecraft not travel at relativistic speeds in outer space?
%26gt;%26gt;Assuming that a spacecraft had enough fuel to propel itself to any desired speed, why is it that modern spacecraft only travel at relatively slow speeds (~10-20 km/s)?%26lt;%26lt;



They don't have the fuel. Consider the Apollo Moon landings. They accelerated a manned spacecraft to 25,000mph, but it took an entire Saturn V rocket to do it.



You also have to consider the destination of the spacecraft. Is it going to Earth orbit? Then it can only go at Earth oribital speed or it will fly off into space. Is it going to a particular planet? Then it not only has to get there, it has to be able to slow down once it gets there in order to enter a stable orbit or land. Does it have people on it? Then, whatever its final speed, it can only accelerate at a certain maximum rate or it will turn the crew into salsa.Why can spacecraft not travel at relativistic speeds in outer space?They are limited by the speed of chemical rockets. The combustion gasses escape at that velocity so that is as fast as the spacecraft can go. If greater speeds are needed then gravity assists from planets is the only way to go. Ion rockets have a much faster speed but so far are low thrust and pretty much in the experimental stage.Why can spacecraft not travel at relativistic speeds in outer space?
It all has to do with relativity. As the velocity increases the mass increases also, and the amount of energy it takes to drive the craft increases proportionately. Anything approaching the speed of light would require a HUGE amount of energy.Why can spacecraft not travel at relativistic speeds in outer space?Our technology is not that good yet. The biggest problem is the expense of getting all that fuel off the ground and into space. Some groups are working on solar sail technology, this has the potential to do just that without much more technology than we have now. It does not carry it's fuel with it.Why can spacecraft not travel at relativistic speeds in outer space?
fuel driven spacecraft has a limit but a gravity sling shot craft can go up to 210 m/s
Space is not quite a vacuum. It contains dust and gases - in tiny amounts, true, but those tiny amounts are enough to create a *lot* of friction as you approach light speed.



I recall reading somewhere that by the time you reach half the speed of light, you'd be running into stuff so fast that it would be like slamming into a wall. Think of it: how much space dust could you expect to run into in 100,000 miles? That's how much you'd be running into every second.



The biggest reason why spacecraft move so slowly is because they can't carry enough fuel to provide constant acceleration: they can only accelerate for a few minutes, long enough to make it into orbit. Once they've used up their fuel, they just drift along in free fall. Sure, you could carry somewhat more fuel, but every pound of fuel you carry with you is one less pound of payload on board, and spacecraft have very limited payload capacity as is.



If you had constant acceleration for your whole trip, then you could reach other planets within a matter of days - you'd accelerate for the first half of the trip and decelerate for the second half. Unfortunately, don't have the technology to build ships capable of constant acceleration for days at a time.



Hope that helps!