Hard to see how ten helicopters could maintain enough horizontal separation to work safely while carrying the load.

An airship might be a better alternative.

Or combine both, and you get a Piasecki PA97 Helistat.

It worked poorly: https://www.youtube.com/watch?v=_7jENWKgMPY

Great share! That frame looked weak to the naked eye. Screw engineering calculations: anyone who's played a bridge-building game should have seen it coming!

video blocked in the UK due to legal complaint :(

They could build a wide platform beneath it so the anchor points would be further apart.

Assuming the 10 helicopters fly a 3-2-3-2 formation at the same height.

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 [1]. 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...

[1] A guess. I suspect they'd need more than that.

[2] I am not a mechanical engineer

only 5 of these

http://en.wikipedia.org/wiki/Mil_Mi-12

or just one of this, though you'd need to arrange for transport to/from the airports

http://en.wikipedia.org/wiki/Antonov_An-225_Mriya

I never understood why, if the AN-225 is so insanely useful, only one has ever been build. Surely there would be economic benefit in building another few?

The An-124 is the useful large cargo plane. The 225 is more or less a larger version of that for specialized cargo that is rarely needed thus one being enough to service the entire world. If the demand was there I'm sure a second one could be finished quite quickly.

Quote the first paragraph of the linked article: "A second airframe was partially built; its completion was halted because of lack of funding and interest."

Seems it's not so insanely useful that a second one is needed.

If even that single one isn't fully booked, how would multiple planes with 10% utilization each justify their building costs?