StarChild Question of the Month for April 2002

Question:

How long does it take to fly to Saturn?

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Answer:

How long it takes to travel anywhere depends on how far you want to go and how fast you move. For example, if you want to travel to the store located 10 km from your house, and you drive at 50 km/hr, it would take you 10/50 hours to get there (in other words, 1/5 of an hour or 12 minutes). Of course, you will take some time to accelerate up to 50 km/hr and some time to slow down so you could stop at the store, but 12 minutes is a good approximation to how long it would take.

For space travel, distances are very large. So the rate at which you travel is very important. However, two other factors play an important role. One is that you rarely travel in a straight line between any two destinations and the other is that if you want to stop some place (like Apollo missions to the Moon), you spend a great deal of your travel time slowing down. If you can't slow down, you would just shoot right by your destination and keep going into deep space! For example, the Apollo spacecraft took about 3 days to travel to the Moon even though it only covered a distance of about 375,000 km and at times reached a speed of 8 km/sec.

Spacecraft destined for the outer planets such as Voyager have reached sustained speeds of around 17 kilometers/sec. To achieve this speed, they traveled in paths which allowed them to use the gravitational pulls of objects in our solar system to increase their speed. It took these two spacecraft about 3 years and 2 months to reach the ringed planet of Saturn.

The nearest star (after our Sun, of course!) is Proxima Centauri at a distance of 4.2 light years. At a speed of 17 km/sec (such as what the Voyager 1 spacecraft currently has), it would take about 75,000 years to reach Proxima Centauri. This may explain why we are not planning any trips there at present!

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