Delay lines

This is certainly the hardest item to price, as there are many possibilities and constraints on Mauna Kea. A comparison with other existing interferometers may be instructive at this stage: ESO's VLTI has 4 trolley type delay lines, each with 200 meter delay for an overall cost of 4 million DM (approximately M$1.5). CHARA, also using trolleys, hass 6$\times$50 meter delay lines for a cost of $1 million. However, one single 50 meter delay line would not cost $10⁶/6, but a more reasonnable estimate might be around k$250 (this could actually be less if CHARA made a copy for `Ohana). Finally, the IOTA evacuated delay line with 2.3 meter delay and laser metrology (a device similar to what could be used for phase II) cost k$100, half of which was for the metrology system; therefore, extending such a system to for example 10 meters might end up costing around k$200.

Other possibilities are currently being explored, due to the limited real estate available on Mauna Kea. For example, some baselines might use the KeckI delay lines. Other options might include fully reflective multiple pass devices (where the path length is controlled by the number of reflections). The final solution will no doubt be a compromise between price and the strong constraints of Mauna Kea real estate.