Meadowgold Mobile Observatory

For quite some time I have wanted to build a mobile observatory. The night sky at my home is OK for observing, but not great – rated a Bortle 5.  So a goal was to have something that can be set up and ready to use at home, but portable enough to take to a dark site and enjoy observing there.

Design

My early thoughts considered a roll-off design, using a cargo trailer or camper and slicing the top 2 feet or so, and putting that on a rail to slide either forward or back off the trailer, opening up half the trailer to the sky. This had a lot of challenges around sourcing a rail large enough that didn’t require support (basically a huge drawer slide). Also challenges in what to do about the doors, and sealing it from insects, water, etc.
Then, I considered placing a dome roof on a cargo trailer. This required a step-down roof design to keep the height to a reasonable level. Kind of like this rendering:
Neither design was ideal, and they still left me with a lot of work to do in making the ‘warm room’ part of the observatory livable.

Enter the Toy Hauler

I was looking into toy hauler campers, which are, as the title suggests, RV trailers meant to haul ATVs, etc while also having a living space. I ran into the front deck toy hauler design and knew immediately this was the best shot at making the mobile observatory.

I found a really clean used Forest River front deck toy hauler that some nice folks in Michigan had for sale, and purchased it in Fall 2019.

Choosing the Dome

The deck on the toy hauler was 8ft square, so there were several domes available that would fit on that size deck. I chose to go with NexDome, mainly on a cost/features comparison. It had everything I needed.

I’ll have a separate writeup on my thoughts on NexDome, what I like, what I don’t, and some changes I have made to my dome.

Placed the order and had lots of time while waiting to work out the next challenge – mounting the pier…

Mounting the Pier

Since starting this project, I had continuously been pondering how best to stabilize a pier in this kind of system. I knew it had to be isolated from the trailer and very solid.

I arrived at a 3 legged tripod for a triangle base that the standard NexDome pier would bolt onto. This was the simplest to fabricate. The legs would be square 5000lb capacity trailer jacks with a hand crank. Getting the size just right was important, to have the legs miss the floor supports of the trailer deck, which were 16″ on center.

I had this fabricated by the great folks down at Wolfe Metal Fabrication in New Kensington and it turned out great. I planned 3/4″ steel, but they had some 1″ instead, so I figured why not? The heavier the better!

Borrowed a magnetic drill press from my brother, and drilled all the holes. Broke one of his bits — sorry.

Mounted the Nexpier on it, and cut holes in the deck for the jacks to go down through. While in transit, the jacks are raised far up by loosening the clamps. The plate rests on rubber stops on the trailer deck, and can be secured with tie-downs.

Assembling the Dome

Next came the task of assembling the dome. A pretty easy job, but does require 2 people to place the dome on the walls.

Making it Roadworthy

It goes without saying that the NexDome was not intended to travel down the highway on a trailer, at highway speeds with wind and the elements. The dome itself rides on rollers and only its weight holds it onto the walls. Some steps had to be taken to make this rig roadworthy so it could withstand traveling.

First, additional bracing was added from the walls to the floor. This bracing is removable if I want more room inside after traveling.

Also this image shows the ABS plastic sheets that close up the holes in the floor and slide nicely as the trailer moves separate from the mount.

While in transit, the pier is strapped down with cargo straps to the floor of the dome to prevent it from moving. The scope and counterweights are removed in travel, but the telescope mount itself can remain on the pier.

A full custom tarp was built to cover the entire dome and serve to both protect the dome as well as help hold it down onto the trailer.

Automation

This observatory marks a new stage of automation for my observing, and I am really enjoying it. The dome itself has the rotation and shutter automated. The mount is driven by EQMod software and KStars/Ecos open source astronomy automation software. The scope now has a motor focus and motorized filter wheel.

The Warm Room

With the dome and telescope fully automated, the entire observation session can be operated remotely, from inside the RV portion of the rig. To accomodate this, I removed this couch from the front of the trailer:
and replaced it with this L shaped desk and some monitors.
I now have enough room to comfortably observe during the evening, and work remotely during the day. I can also start an hour long imaging session and hop in the bunk for a nap!

Power Control

My goal is to be able to run the entire trailer using battery power if no electricity is available.

First, this requires that all equipment can run from 12 volt DC. I found Spectre brand monitors that run on 12V, and my laptop can run from 12V. Of course all the scope equipment and mount can run 12V. The trailer is already suited to run lights, water pump, refrigerator, and furnace from 12V and propane.

I found a toolbox that mounts on the trailer A frame tongue and holds 5 deep cycle batteries, giving me a total of 450 amp-hours of power.  This should be enough to run several evenings.

In the warm room, I run (2) 30-amp circuits to a control box at the desk. There, I have a control box to select (6) different 10-amp circuits for the various components. Voltmeters and ammeters allow me to keep an eye on the current draw, to watch for problems like a motor hanging up.

Both AC and DC power is monitored by power meters.  The AC side is useful for monitoring how much AC power is being used when plugged in at a star party.   The DC side has a Coulomb counter to measure the amount of energy used and the amount of energy remaining in the battery bank.

StellarmateOS Server

The system is operated by a Raspberry Pi4 running StellarmateOs. This little computer is mounted on the pier.

The Pi controls everything in the observatory. Inside the warm room, I connect the KStars application to the Pi4 server.

The Raspberry Pi is a Pi4 in a Vilros case with a fan. I have included a real time clock module, which was a little challenging to fit in the case. Bending the pins over allowed it all to fit.

Scope

The scope for this setup is a 190mm SkyWatcher Maksutov-Newtonian. It is f5.2 focal length. Mounted on an Atlas Pro AZ-EQ, it is near the weight limit for that mount.
Cameras include a QHY163C 16megapixel cooled color CCD camera capable of being cooled to -20C. That camera is mounted on a QHY filter wheel with several narrowband filters for imaging. A QHY5L-II-C camera performs autoguiding using an Orion 50mm guide scope. A PoleStar polar alignment camera is used for aligning the mount during setup.

Keeping Tabs on Things

It is surprising how unnerving it is to command a telescope mount to slew and not be there to watch it, to make sure everything is going OK. What if a cable gets caught, or the coordinates are wrong? It is nice that I have a power control box next to me in the warm room, but without eyes on the scope, it isn’t much help.

So, that was addressed with … more cameras.

These little cameras are inexpensive and easily mountable: ELP Sony IMX322 USB camera with 170deg lens

Mounted two of them in the dome. One to view the interior of the dome, and another on the scope to see where it was pointing. This helps ensure that the dome is rotated to the right place for the scope to see out the shutter opening.

For these cameras, I added .. yet another Raspberry Pi. This one runs MotionEyeOS, an open source security system software. So in a browser window, I can keep tabs on everything in the dome:

Preparing the MMO for a dark site involved adding blackout blinds, and shielded red lights to illuminate the steps at night.

KStars

There’s a lot to say about how much I like KStars. That will be a separate topic altogether.

Future Work

There are features of the NexDome that need to be improved.  The shutter needs to work more smoothly, and the dome slaving to align the shutter opening with the telescope is not as accurate as it should be.