In this video you can see the summit team pushing a large metal cart on rails. The cart is used for installing and removing a heavy structure on the telescope mount: a 52,600-kilogram (~58-ton) “surrogate mass.” The surrogate mass is standing in for the primary mirror and its steel supporting structure (called the “cell”), providing the balance necessary for moving the telescope mount during tests. The real primary mirror and its cell will be installed later this year, using a different custom-built cart.
The carts that carry heavy equipment from the maintenance floor up to the telescope travel on rails installed in the floors. Some sections of the rail system are permanently fixed in place, but there are also transition areas that need to be connected with temporary, removable rail pieces. For example, there are permanent rails installed on the floor of the vertical platform lift that moves equipment between floors, but temporary rail sections are installed to connect these rails with the permanent rails leading from the lift to the floor of the dome. If these sections were left in place, they would interfere with the rotation of the dome, so when the team is finished using the cart to transport equipment to and from the telescope, they remove and store the temporary rail segments. Other removable sections connect the rails between the maintenance floor and the lift, and the rails between the dome and the telescope platform.
This test campaign verified that the cart moves smoothly and consistently along the entire rail system, including the removable sections at the transition areas. The tests also confirmed that the hydraulic jacks on the cart, which will be used during the installation and removal of the surrogate mass, are working properly. The cart by itself isn’t that heavy (4800 kg, or ~5 tons), so it can be pushed along the rails manually. Once the surrogate mass is attached to the cart, the team will use electric winches to move it along the rails.
At the end of the video, you can see the cart being moved from the telescope floor back down to the maintenance floor on the observatory’s vertical platform lift.