why does it take so long for probes and the like to get anywhere?

Question

surely they should keep accelerating and eventually get just below the speed of light? or does this acceleration take too long to achieve?

they must keep accelerating because in space there in no force to stop them, like friction

why does everyone keep saying they need a continuous thrust to keep accelerating? its basic physics, if u throw a ball in outer space it keeps going faster and faster because theres nothing there to stop it... admittadly gravitational pulls from distant bodies may effect it a bit but it cant be very much considering the distances involved

Answer 1

Wow. You are so misinformed, it isn't funny. Newton's first law: A body in motion continues in uniform motion unless operated on by a force. The speed doesn't change if there is no force!

F=ma. If F=0, then a=0 which means that velocity is constant.

*BOGGLE*

Answer 2

Basic physics, as you say, states that acceleration is in direct proportion to the force exerted. If you don't exert a force (by means of thrust) , you don't go faster and faster. If you want to send the probe toward the edges of the solar system, you have the Sun's gravity working against you and you're slowing down. You can do intelligent things by feeding off celestial bodies' momentum, gaining speed but still, you're slowing down overall

Answer 3

Newton's first law says that an object will continue at constant speed unless acted on by a force. So unless a thrust force is exerted, the space craft will not speed up. It coasts at whatever speed it got after using up all it's rocket fuel. It definitely does not speed up on its own, but because there is no friction in space, it doesn't slow down either.

Answer 4

The problem is, they don't keep accelerating. The amount of fuel it would take to continue to accelerate, would be counter productive. Getting out of the atmosphere is difficult enough, but if you're lugging tons of extra fuel, it makes you much to heavy. The goal is to put them on a tragectory that will reach their destination safely, not quickly. In the realm of space exploration, the amount of time we're talking about isn't very long. We're talking about a universe that is billions of years old. And the distances they travel are also very far compared to the relative distances we are used to here on earth. These probes do travel quite fast.

Answer 5

You're asking why the transit time for transfer orbits is usually several months.

t1 = departure time
t2 = arrival time
m = mean motion in the transfer orbit
a = semimajor axis of the transfer orbit
GM = solar gravitational constant
AU = astronomical unit
M1 = departure mean anomaly in transfer orbit
M2 = arrival mean anomaly in transfer orbit

The "mean anomaly" is the angle, subtended at the sun, between a line going through the perihelion and another line going through the orbiting object's current position. For most fuel efficient transfer orbits, the change in mean anomaly during flight, M2-M1, is about pi radians.

GM = 1.32712440018E+20 m^3 sec^-2
1 AU = 1.49597870691E+11 meters

The semimajor axis, a, is converted from astronomical units to meters for use in the formula.

m = (86400 sec/day) ( GM / a^3 )^0.5
t2 - t1 = (M2 - M1) / m

For example, suppose your space probe underwent a difference in mean anomaly of 2.55454855 radians while in a transfer orbit having a semimajor axis of 1.319533 AU. The mean motion would be 0.011349 radians per day, and thus the transit time would be 225.1 days.

Answer 6

The closest star system is 1 parsec away which is roughly 1.5 light years away. That means if you travel at the speed of light it would take 1.5 years to get to Alpha Centary. Since there is no way to get to the speed of light with conventional equipment we can only travel at a faction of the speed (less then 1%). If we travelled 0.01 the speed of light it would take 100 years to reach the closest star system (1/0.01 = 100). Now this is a broad generalisation but you can figure it out with raw math using the amount of fuel an engine can burn to get to max speed (using E = MC^2) and taking that speed and dividing the distance by it (1 / 0.01). This will get the actual time to get to Alpha Centary (around 100 years).

Answer 7

We could develop the technology for a space probe that would accelerate continuously as you suggest, but right now such a thing is cost prohibitive. The idea is to get as much data from these probes as possible, therefore most of their size is devoted to instrumentation instead of a propulsion system.

Answer 8

If you want to accellerate towards the -very fast- speed of light, you need to have a VERY BIG ROCKET, AND A VERY BIG FUEL SUPPLY. All this needs to be got off the Earth, either by shuttle or rocket, where every gram is critical! So the scientists ensure they launch probes and fly them towards other planets, to put them into 'sling-shot' orbits, to speed them up, and then steer them out to their intended path. This can really help, but still not get them near to the VERY high speed of light. And what's the rush? If it gets to the planet you want to study, and has to spend a month braking, what's the point?

Answer 9

No they don't just keep accellerating. They do finally get to such a distance that the perturbations of gravity from planets, moons, etc. are so infintesimally small that they just "coast" untill they finally escape the gravitational pull of any solid objects.

There is only one place where a solid object would actually accellerate to nearly light speed from the effects of planetary bodies; the event horizon of a black hole. Once past that horizon it could possibly accellerate to the speed of light.

Answer 10

Coz the distances involved are STUPENDOUSLY large, and the probes etc only carry a limited amount of fuel.
Given an unlimited fuel supply etc then they would arrive at their destination somewhat quicker. But don't forget that it would still take time to achieve that really high end speed.
Good question though!