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.
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