A: A tardigrade is a microscopic animal, a bit smaller than dust specks. They look horrifying under a microscope, but are quite harmless to humans. They're also known for their ability to survive in hard vacuum (read: space) for an extended timespan, a quality that the Federation greatly appreciates.
Q: Why doesn't the Federation expand onto other planets in the Solar System?
A: The Federation could technically expand onto other planets, but it doesn't make economic or logistic sense to do so. Why? Because they simply can't get around fast enough. The Hydrogen Drive is a miracle of science and technology, but it still has limitations - higher efficiencies require more space, which eats into personnel space onboard, while more personnel space eats into drive room and therefore efficiency. The most efficient a drive can be before humans cannot live reasonably onboard is still too low for fast interplanetary travel, taking a few months to get around - far too slow to make colonizing other planets economically profitable, not to mention that colonial control grows more difficult with travel time between the parent nation and colony. Manned Federation missions have been to other planets, including Mars, Jupiter, and Saturn, but these flights took anywhere from 3-7 months (one-way) and were purely scientific in nature.
Q: How does space travel work with the hydrogen drive?
A: Ships follow what is referred to as a "brachistochrone" trajectory, in which the ship accelerates continuously for half the distance to its destination before flipping around and decelerating over the second half. This is extremely fast - at one gravity, or 9.8m/s^2 of acceleration, a one-way trip to the Moon takes only 3 hours. Mars and Jupiter would be no more than a week off if the hydrogen drive was more efficient. For comparison, the Apollo missions took three days to complete a one-way Lunar transfer, and NASA missions to Mars usually take around 9 months.
Q: Where do stations get water/air/fuel from?
A: Ice asteroids. Stations get regular deliveries of what amounts to massive ice rocks, which are then melted down into water. Water can be used for drinking and reaction mass, or it can be split for hydrogen (reactor and drive fuel), and oxygen (air.) Of these, only hydrogen must be resupplied on a continual basis; water and air can be recycled with very little loss.
Q: Why no sea or air forces?
A: This is explained somewhat on the Military page, but to expound on that: the Federation has no planetary territory other than a few spaceports, none of which are in any position to be equipped with any extensive naval or air facilities. Some have proposed hauling such assets back and forth from orbit, but the logistics involved are unbelievably complicated to the point where it's just not known how it would be done. (How easy do you think it would be to regularly move an entire naval battleship between an Earth ocean and an orbital drydock?) If the Federation requires Naval or Air assets, it has plenty of allies to call on.
Q: How do the stations of the Federation handle orbital decay?
A: Good question! Any object in orbit experiences orbital decay due to a variety of causes, including friction with Earth's upper atmosphere, solar wind, and tidal forces. Rather than doing periodic large-scale boost burns with chemical engines (like the ISS) or hydrogen drive, Federation stations constantly fire low-thrust, high-efficiency ion engines to maintain their orbits. The delta-V needed is relatively low, as the decay forces experienced at station altitude are minimal.
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