A new secondary for the one-meter is being made. We started that process about a year ago. We have continued imaging with the flawed secondary, but recently we had to ship the old secondary to the polisher so that it could be used to validate the test setup for the new mirror. We are unable to operate the telescope until either the old one is made available again, or the new one is completed.
The work on the new secondary has been very involved. (The original has a dimple and must be replaced.)
First, the mirror itself is a complicated thing. It’s a ribbed silicon-carbide mirror. It is ultra light in weight, and very rigid. These qualities are important because the secondary is a high-speed tip/tilt corrector: it sits on a very fast tip/tilt table from Physik Instrument, and will be able to make AO corrections at up to 100 times per second.
That last bit turned out to be a big deal for making a replacement. Again and again, as the manufacturer tried to machine the raw materials into the required shape, the mirror blank would shatter – it was too thin. The problem was that we had to find a way to make it stronger without making it any heavier.
So we moved things around. The ribs were made fatter, but shorter. We then had to do FEA (finite element analysis) on the new design to discover its resonance frequencies, and make sure that none of them were in the range of the operating frequencies, or in a close harmonic with them. Basically, we had to make sure that any resonances were > 300Hz.
That all took more than half a year. The redesign went manufacturing late this summer, and is finally nearing completion. The substrate has been machined and hardened, and will be coated with the polishable material via CVD (carbon vapor deposition). (We need to measure the substrate very precisely before and after coating, so that we can make sure the coating is thick enough to contain the final curvature of the mirror surface. That’s another few weeks right there!)
Once the mirror goes to polishing, it will be another three months before it’s completed and shipped to New Mexico. At that point, we’ll mount it up and begin commissioning of the telescope. At that point, we will have finished up all systems, and it’s only a matter of making them all behave properly. We’ll be open for business shortly after, but it’s fair to say that during the first year of operation, we will be honing our skills, writing software to make use of the more advanced systems, and otherwise perfecting operation.
Here’s a photo of the mirror, after machining and before it has been coated with the CVD layer.
Uncoated blank (substrate) for one meter secondary mirror (M2)