Quote:
Originally Posted by Marasmusine
Why pick another engine over an extra fuel tank? Am I right in saying that this would be better for travelling a shorter distance faster?
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Not really. A higher acceleration means that, well, you can accelerate faster. The delta-V is still a measure of the fastest speed the engine can attain. If one engine has 0.5G acceleration and a delta-V of 0.45 and another has 0.05G acceleration and a delta-V of 0.8 the second engine can accelerate to 0.8 mps - 0.8 miles per second - which is (obviously) faster than the 0.45 mps the first engine is capable of attaining.
The difference is that the first engine has a higher acceleration, meaning it can accelerate to 0.45 mps in less time than the second engine can, but at that point it's out of fuel. The second engine may take longer to reach 0.45 mps, but it still has considerable fuel reserves and can continue accelerating to reach it's maximum speed of 0.8 mps.
Also keep in mind that delta-V is a measure of change in velocity, not just top speed. If you're going somewhere like another planet you normally have to accelerate to start going there, coast for a long while, then decelerate to stop at your destination. This means that you will usually use ~1/2 of your delta-V to accelerate and the other ~1/2 to decelerate, and spend most of your journey in between coasting. Since you're spending most of your time coasting the engine with the higher delta-V, not the higher acceleration, is far more efficient for the journey. For instance, to go from Earth to Mars at their closest pass is still 49,000,000 miles. Even at 0.8 miles per second that's going to take a considerable amount of time (~700 days), almost all of it spent coasting with the engines off. Even Earth to the Moon is ~239,000 miles, which is 3.45 days at 0.8 mps. Most engines have only a few minutes of fuel, however the really efficient ones might have a few weeks worth of fuel.
Higher acceleration only becomes more efficient when you have to escape from a gravity well - take off from a planet - because if you don't have enough acceleration you simply cannot take off from the planet. Higher acceleration is also useful in combat - efficiency be damned, the important thing here is that you can either catch up to or run away from your enemy in the shortest amount of time.