This is book 2 of the "Marsbound" series.

This note contains spoilers for the book.

 

So, our narrator, two martians, her husband, two other scientists, and three spies are picked for the mission to the Other's homeworld.

The ship uses energy from another universe, a technology learned from the martians and hence from the Others. And not really learned; we can build them, but we don't understand them. The ship uses a large comet as its reaction mass.

For a change, the spooks aren't the bad guys, and the people get on well enough in their multiple-year trip.

Things get a bit exciting at turnover, though, when they're boarded by a flying starfish. Containing both an Other, and another human-like construct the Others have built and sent along to communicate (the Others are cryogenic organisms and run very slowly).

They find out a lot more about the Others, much of which might even be true, and visit their planet of origin. Turns out the cryogenic development of their race was artificial, and they eventually killed their planet-bound predecessors. The Martians are about like the organic predecessors (though artificial, or at least heavily adjusted). On the other hand, they've got somewhat peaceful coexistence with 248 other races.

I skipped one thing. They also cause the people in the ship not to experience the time from turnover to arrival in the Other's system.

And then they send them back to Earth that way, too. So we can get to the Earth political reaction. An old professor of the pilot's is now president of the United Americas, which is English Canada and Spanish South America and some of the US (but not of course south Texas). The worldwide government is deeply secret and focused on somehow resisting the Others, who have shown they out-tech us and think on a longer time-scale than us and basically, we shouldn't be trying.

And this book ends with the moon being destroyed, filling near-earth space with so much debris that we lose all our satellites and space travel is impossible (and killing 7000 people directly). GPS goes out, too, and no doubt other important things. Looks pretty exciting when this book ends.

The title of the third book, Earthbound, makes a nice pun on the "bound" occurring in all three titles, and presumably refers to their problem of now being stuck on the Earth's surface.