and the wikipedia article:
In short, it's an experiment to directly measure the mass of the electron-type neutrino. Very occasionally, when tritium beta-decays, the electron carries away all the energy. If the neutrino has mass (and we are rather certain  that it does), then there's a little less energy to carry away. The giant MAC-E spectrometer (actually a chain of them, of which the big one is the last) is the only known way of resolving the 13,000 electron-volt electron to less than an electron-volt.
It's a very hard experiment, but it's important, and nobody knows an easier terrestrial path to the same knowledge (cosmology limits are equal to or better than KATRIN, but there's a big difference between the cosmos and something you can do on Earth).
(Edit: and for you vacuum jocks out there, that entire volume operates at UHV. It's electropolished internally, and for their vacuum test, it pumped to below 10^-7 Torr on a single 6-8" turbo before bakeout.)
However, after hearing about this comeback for at least a decade, I'm a bit skeptic it will ever come true.
Luckily, they found a new use for the structure:
edit yes, "over the long term" they say they could build an airship with a 500 tons lift capability, but that seems far away.
All this for an unsucessful zeppelin that could carry less than the required 200 tons. You'll be convinced very quickly that it doesn't trump simply carrying by land.
I wished there would one fly over me from time to time.
edit: Note here that they started planning at or before 2001 http://www.katrin.kit.edu/130.php#Anker10
An airship might be a better alternative.
It worked poorly: https://www.youtube.com/watch?v=_7jENWKgMPY
Consider a line of three helicopters. According to Wikipedia the rotor diameter of the Mi-26 is 32 metres. Assuming that each helicopter is separated so that the tips of the rotors are also separated by 32 meters from its neighbours . This gives us a distance of 128 metres between the rotational centre of the two outermost helicopters.
The corresponding distance between the front and rear rows of helicopters would be 160 metres.
So you'd need a 128x160 metre frame to carry the 24 metre long spectrometer. Due to its size and the need to support the 200 ton weight of the instrument, the frame itself (including the necessary cross-braces) will be extremely heavy. So you'd need to add more helicopters to lift the frame, which means it would have to be bigger to allow for their necessary separation... And making it bigger makes it heavier...
 A guess. I suspect they'd need more than that.
 I am not a mechanical engineer
or just one of this, though you'd need to arrange for transport to/from the airports
Seems it's not so insanely useful that a second one is needed.
What about an off road heavy transport trailer for the sections of road they can' t fit through. Or a quick build bridge structure similar to what is used by the military? Or some sort of land version of a lock (water transport)?
I presume the height of it means it won't fit under bridges on either road or canal.
The scale of this thing is staggering. In one incident it accidentally scooped up a bulldozer: http://imgur.com/gallery/rU3XU
Also shown there is what it looks like when it's on the move along a carefully planned and prepared route: http://i.imgur.com/51x5NIR.jpg?1
I'm sure the budget for moving a scientific device isn't as huge as something involved in mineral extraction where time equals money.
With optics you definitely would, but with optics you can see a single human from space.
It's not just the digger, there's this conveyor system that's an integral part of the system that looks miles long.
Any company building this kind of stuff will be familiar with the problem of shipping stuff to the customer.
So, I guesstimate that this problem and the solution were foreseen before they started construction.