### ESA's Solar Orbiter sails safely past Earth despite orbiting debris concerns

#### Re: 10,000ths of a radian per second

This is because nobody really cares about the thrust: you can make more thrust by making more engines: if you have an engine which produces a thrust T and you want nT, you need n engines, simple, just buy them at your nearest engine store.

If on the other hand you have an engine which has an exhaust velocity E, and you want to change velocity by a certain amount, V, then the amount of your vehicle which must be fuel is the exponential of V/E. If you want V to be large then you very, very much want E to be large too.

As example if you want V=100km/s and for your final spacecraft to have a mass of a tonne, then with a chemical rocket with E=4km/s, you must carry about 72 billion tonnes of fuel. If you use an ion drive with E=40km/s ... you need about 11 tonnes of fuel.

11 tonnes is a lot less than 72 billion tonnes.

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