_Augustus_

Okay, so it's been a while! I was in Florida to watch the FH launch and got back a few days ago and neglected this thread. I got back to refiguring on the 11th and noticed that my wooden turntable didn't rotate evenly and wasn't staying level, which I thought was odd. Turns out that it has buckled into a saddle-like shape, probably because it was stored in the garage for a while before I used it. I did get around half an hour or so in before I realized this. I have a new turntable, but I haven't bothered working on the mirror yet since. I did some further Ronchi/Foucault (I sort of understand how to do the latter now) after my work session, and I found the following: The astigmatism is nearly gone. It's still noticeable and distorts the bands a little, but I can now actually read the Ronchi bands and they're not curvy. I rotated the mirror just to make sure it wasn't some sort of coincidence of the astigmatic axis being dead horizontal or vertical, and still saw the same thing. The mirror is slightly overcorrected. I don't know by how much, but doesn't differ a whole lot from the "ideal" patterns for a 16" f/4.9 (I remeasured the ROC to be around 157") on Mel Bartels' Ronchi page, so I'm not too concerned. Why it's not spherical is anyone's guess, but I'm not complaining...... There's a 3" diameter "hole" (depressed zone) at the center of the mirror. I'm not sure how it got there, and I'm not sure if it was there before and I just didn't notice, but since it'll be behind the secondary mirror I don't particularly care. Since the mirror is probably capable of throwing up a good enough image that I can determine the focal point, I've started working on the scope itself. I currently have the mirror box (not the cell or bearings, just the box) finished and am about to move on to the mirror cell.

I remember reading somewhere that Boeing could probably build two a year if needed.

SLS actually still wins in this category since it has more payload capacity and a cryogenic upper stage, but FH would be a lot better than flying it on an Atlas V.

Use Sigma Dimensions........

In Florida now, going to Playalinda on Tuesday. Can't wait!

1. Nope. 2. I've done some afocal Moon shots with a phone but that's about it (I might be able to get some decent planetary shots, too, but still nothing amazing). Serious planetary AP requires a fancy webcam with a tiny chip and tiny field of view, which without tracking means the target drifts out of the field after a few seconds. Long exposures? Forget it....... 3. No worries, bought an identical new one for $15.

I leave for Florida tomorrow morning. Let's go!

So my hot plate self-destructed and I had to buy a new one yesterday. I poured the lap and carved the channels with a hacksaw. Using this thing is an annoying process as it can't overhang the mirror, but I have to be careful not to place it on the mirror too hard, otherwise the edges will chip. I put the mirror on the tester and it's much better than before, but the astigmatism is far from gone.

A single booster exploding on a nearly empty tank would not be much of an explosion. Look at the videos of failed landings; the barge at most suffered from some scorch marks and debris.

I'll be down there on Sunday. Can't wait!

Poured the lap base. I wanted to have it match the curve, but I don't have a 12" wide wooden ring so keeping the mold rigid and having it be sub diameter wasn't possible. I ended up pouring it against the back of the 12", so it's pretty much flat. Since I'm pouring pitch on it anyway and this is an f/5 mirror, I'm not concerned. More tomorrow.

I bought boat tickets to watch the launch from just south of the port.

No, I'm saying that having the MAV and MDV as separate vehicles when you have in-orbit refueling available is stupid.

My new plaster somehow got here today, so I can vacuum the shop tonight and pour a new lap tomorrow.

That was so cringey. Wow.

This isn't a huge violation of science but it's interesting and I pointed some of this out to Weir himself once. He answered and sort of agreed that these were plot devices. In The Martian, Hermes was obviously assembled and fueled in orbit. It can obviously be re-fuelled, in orbit If that's the case, why do the MAV and MDV need to be separate vehicles? I get that the MAV has to land earlier and use ISRU so it can fit on a smaller LV and launch/land on Mars mostly empty, but why? Why not just launch it into orbit and then send a tanker and extra kick stage? There are clearly orbital tankers in this universe; how else do they refuel Hermes? In addition, how does the Ares 4 MAV have enough propellant to take off with Watney? I know Watney was on Mars for a pretty long time, but they mention that the arrival of Ares 4 would still be 4 years away for some reason (I guess it's because they have to clean up Hermes in orbit first?). If that's the case, if they're landing the MAV so long before the mission shouldn't it still need a couple more years to produce propellant? My other nitpicks: Hermes is supposed to use nuclear power in the book, but it has giant ISS solar arrays in the movie.. why exactly? Hermes in the movie looks utterly ridiculous, like some KSP creation, with the Orion command module with an airlock in front of it, ISS solar arrays, etc. The Ares missions are month-long "flags and footprints" missions. Why do they have these giant habitats, multiple pressurized rovers, etc.? CNSA would/will never work with NASA. Does the Rich Purnell maneuver even work? If they used an Earth gravity assist to fly by Mars at a great speed, wouldn't that trajectory put them on a solar orbit with a further out aphelion, somewhere in the asteroid belt, adding years to their journey? And wouldn't they need a lot more fuel to perform Earth orbit insertion?

Through a bizarre series of events, I managed to get a complete homemade 8" Dob with a dual-speed focuser, a bunch of testing equipment, a bunch of grit, and a 16" f/5 polished mirror for the whopping price of $150. The 8" scope is abominably heavy (the mount is entirely constructed out of 3/4" plywood), and the primary needs recoating, so I'm parting it out because a) I don't need it and b) if I can reclaim some/all of my investment by selling the optics, why not? I am keeping the mount because while the paintjob could be better (Black mount and black tube? Really?) and it weighs about as much as a small child, it does have nice construction and even an adjustable tube cradle - and it's not worth the cost of shipping anyways. The focuser I'm keeping as well, obviously - it alone is nearly worth the price I paid for all of this. The seller told me an interesting story. He wanted to make his own scope so he bought a kit to make his own mirror grinding machine (a mirror-o-matic kit to be exact) , and proceeded to make an 8" on it. He dropped the 8" during fine grinding and bought a GSO primary to build a scope with. Then, despite having no prior skill in even polishing a mirror, he proceeded to make the 16", and gave up during figuring because he had no idea what he was doing. Now he has an 8" Skywatcher collapsible scope and has given up on the whole ATMing thing, so he sold me everything but the machine (I don't really have the money for it nor the space). In addition to having no prior skill in polishing/figuring, this guy used Burgundy pitch (which if you remember from when I started making mirrors is unreliable and bad) and ROUGE (messy and slow-working) to polish despite having PLENTY of cerium oxide and zirconium oxide (the latter works slower and leaves a slightly smoother surface than cerox - like rouge but without the mess). There's still rouge on the test stand he made for it that gets on my fingers whenever I touch it, and the entire side of the mirror is stained with it (though thankfully it doesn't come off). I plopped it on the Ronchi tester (which I had to position a little over 13 feet away!), expecting either a somewhat decent sphere (assuming he just gave up on figuring without actually trying it) or a mess. I got the latter. The mirror is pretty astigmatic, as well as hyperbolic (though the astigmatism makes it hard to tell and it may not be that severely overcorrected). Just to make sure the astigmatism wasn't caused by the glass itself having issues, I tested the mirror for strain - I found none. So the messed-up surface is his fault, and I can fix it. Despite the issues with the surface, correcting this 16" will take far less time and effort than working the 12". So once I pour a new tool and finish with #80 on the 12", at which point I'd have to clean up my work area anyway, I'm going to put everything away and focus on finishing the 16" instead. Does this mean I'm abandoning the 12"? Heck no! I just don't have the money to complete both at the moment and I'd rather work on the one that will take less time and has more aperture. The 12" may get redesigned to be either a faster and more portable instrument or a slower (f/7-f/8) Chief with no central obstruction, but I will still finish it. Just not right now.

All to test a not-fully-functional version of a 1970s rocket and an unmanned, over budget, delayed Apollo CSM on steroids.

LOL, like it even matters. You could launch all of these CubeSats on a Falcon 9 and it'd probably be cheaper than the #*^(@ adapter.

My tile tool is toast. The center tiles aren't wearing down at all, there's no contact at the center, and it appears that the worn and non-worn tiles have completely different radii. In addition, the edge tiles are so thin that they might disappear after the next work session. I ordered more plaster (I'm pretty much out and don't have enough for a new tool), should get here Saturday, but I leave for Florida on Sunday and get back the following Saturday. This time it's blue instead of pink.

But then the money doesn't go to our lord and savior Elon.........

Still cool, makes me want to make one myself.......

5 or 6 days before my birthday, I appreciate the present as well.

I can fit 2 dimes in the sagitta, so I'm pretty much at the target. I did the pencil test and switched to center-over center and to my surprise the mirror and tool are in pretty good contact, even at the edge. I attribute this to my use of circular strokes like what Udjat uses instead of the regular chordal stroke. I'm debating whether to continue with #80 or just switch straight to #120. The difference in size between #60 and #80 pits is small, and I don't see the point in working to get rid of all of the #60 pits then having to work to rid myself of #80 pits.

I'm about to go downstairs and work on the 12". I just bought a 16" blank and an 8" homemade Dob I'll likely part out for very little money, so it appears I've found the material for my next project.