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A single-use, disposable ion drive can be made no larger than it needs to be, thus uses no more fuel than it needs to.

A reusable ion drive tug, first of all, has to take its payload to destination, and then come back; thatdue to the exponential increase in fuel requirements for linear increases in delta-v, this can take as much as 2.7 timesbe more than twice as much fuel as a one-way mission for a large tug.

Finally, to go anywhere interesting on an ion drive takes months or years; a tug doing a Jupiter mission is going to miss a bunch of launch windows for Mars missions.

A single-use, disposable ion drive can be made no larger than it needs to be, thus uses no more fuel than it needs to.

A reusable ion drive tug, first of all, has to take its payload to destination, and then come back; that can take as much as 2.7 times as much fuel as a one-way mission for a large tug.

Finally, to go anywhere interesting on an ion drive takes months or years; a tug doing a Jupiter mission is going to miss a bunch of launch windows for Mars missions.

A single-use, disposable ion drive can be made no larger than it needs to be, thus uses no more fuel than it needs to.

A reusable ion drive tug, first of all, has to take its payload to destination, and then come back; due to the exponential increase in fuel requirements for linear increases in delta-v, this can be more than twice as much fuel as a one-way mission.

Finally, to go anywhere interesting on an ion drive takes months or years; a tug doing a Jupiter mission is going to miss a bunch of launch windows for Mars missions.

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source | link

A single-use, disposable ion drive can be made no larger than it needs to be, thus uses no more fuel than it needs to.

A reusable ion drive tug, first of all, has to take its payload to destination, and then come back; that can take as much as 2.7 times as much fuel as a one-way mission for a large tug.

Finally, to go anywhere interesting on an ion drive takes months or years; a tug doing a Jupiter mission is going to miss a bunch of launch windows for Mars missions.