Speed of a Space Vehicle on its Journey

[Geof James]

Saturday 7th August, 2010

Hello……..This Geof James, from Redland Bay, Queensland. 4165, “speaking”.

If anyone could please answer a small question. It is regarding a space vehicle’s speed, when it leaves the Earth’s gravitational field and travels to its ultimate destination in space.

I know that the escape velocity from Earth is 11.2 kilometres per second (40,320 km / hour). Does the vehicle continue on, upon its journey at this above "land speed", until it is eventually slowed to land upon the “target destination”.

I have been recently asked this question, and my thoughts are ‘yes’, the speed of 40,320 kms / hour would be correct, until it arrives at its destination.

Can anyone please either confirm or deny my answer, or enlighten me further on this particular matter? Than
Most Sincerely………Geof James (geof.james@internode.on.net)

[TrevorW]

Hi Geoff

there are a number of articles on this subject available from the web but initally it may be a good idea to understand the idea of escape velocity

http://en.wikipedia.org/wiki/Escape_velocity

simplisticly a space ship can accelerate and slow down, brake etc much like any other vehicle but this is very dependent upon the amount of fuel available to it

under constant acceleration over time an incredible amount of speed can be acheived but constant acceleration requires a vast amount of fuel current space ships don't have that luxury, so once a calculated velocity to reach a particualr target is acheived the ship would coast continually at that speed until its destination

[Blue Skies (Jacquie)]

Originally Posted by Geof James

I have been recently asked this question, and my thoughts are ‘yes’, the speed of 40,320 kms / hour would be correct, until it arrives at its destination.

Yes, that would be right over a short distance, say to the Moon, but the longer and further you travel in to the outer solar system you'll find things slowing down as the Sun pulls back on it - I'm thinking of what is happening to New Horizons on the way to Pluto at the moment. It was sent off with an fast velocity around 60,000 km/hr and max speed was 84,000km after a gravity boost from Jupiter - but its not doing that now. It's past the orbit of Saturn, which is about half way, and it will take longer to do the second half of the journey than the first half.

Another example - Cassini arrived at Saturn in 2005 doing 80,000km and they had to slow it down to go into orbit around the planet, a bit of aerobraking on the far side, an amazing feat that was pulled off flawlessly - it was a blind risk as if it had collided with anything significant as it ducked through the inner part of the rings it wouldn't have survived at those speeds. This technique has also been used for probes to Venus and Jupiter, IIRC.

[Jen]

Gday Geof

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