> If you accelerate/decel at a sustained 1 g, you can make it to Mars in about 2 days. This is the key calculation where you realize that quick inter-planetary

> If you accelerate/decel at a sustained 1 g, you can make it to Mars in about 2 days. This is the key calculation where you realize that quick inter-planetary travel is totally within the realm of physics. > Using Days and AU (astronomical units) we can see 3 days will get about 2.5 AU (halfway to Jupiter). 4.5 days will get you 5 AU (halfway to Saturn). 9 days will get you 20 AU (more than halfway to the Kuiper belt) Obviously inter-stellar travel seems like a totally different matter, but actually at 1g constant acceleration it works out to about “1 year + the number of light years” to an outside observer. Less time passes for the traveler. Invent an engine efficient enough to allow constant 1g acceleration for years at a time and humans really could become interstellar. The best ion engines get around 200,000 Isp. If you had a 500t ship burning 1t of mass per day, you would need an Isp of ~4.5m to achieve 1g over that first day (it gets easier as you get lighter). The theoretical limit (ejecting mass out the back at 1c) for specific impulse is 300 million. https://space.stackexchange.com/questions/840/how-fast-will-1g-get-you-there https://space.stackexchange.com/questions/840/how-fast-will-...