Autonomous Mobile Observatory Stations – Development in Progress Bill Hanna IOTA North American Annual Meeting July 29, 2016 Stillwater, OK

Issues With Multi-Station Deployments There is a lot of “stuff” to deal with It takes time to align to the pre-point target – Reduces the number of stations that can be set up prior to the event, especially if it occurs shortly after sundown – There are workarounds for this, but at the expense of visiting the observing sites multiple times over more than one day

Concepts Being Examined Self-contained unit – No (or almost no) fiddling with “stuff” on site – Requires only an initial coarse manual alignment Able to steer the optical axis as necessary – To the pre-point target – Track thereafter? “Inexpensive” – Commercial mounts can align themselves autonomously, but at significant expense

Self-Contained Unit A single housing to integrate all of the components – Telescope – Camera – Battery / Power Controller / (Solar Cells?) – Executive Computer – Recorder – GPS / Time Inserter – Dew-Suppression Heaters – Cables – Optical Axis-Steering Assembly and Controller – Rain Sensor? – Security Sensors?

All of the Physical Components Are Available The amateur robotics community is an excellent source for the mechanical components – Rotational and Linear Servos Analog and Digital – Stepper Motors – Gears, Belts, Pulleys, etc. Wide selection of executive computer platforms – Raspberry Pi – Arduino – Micromite – Single-Board Computers

Initial Manual Coarse Alignment Want to point the default optical axis to the nominal from Occult Watcher Manual coarse alignment, possible even in daylight, based on three components – Level – Elevation – Azimuth Referenced to a celestial body – Sun – Moon – Bright star Referenced to a ground target – Mountain peak – Transmission tower – Building / Structure Should easily get the default axis within 5°, perhaps within 2°

Freely-Available Information The easiest way to do something is to get someone else to do it for you – Sun AZ and Moon AZ from the USN Observatory – Star positions from C2A or similar – Ground targets from Google Earth Will require a “pre-processor” to collect (and compress?) the necessary information for a given event – Shared among multiple deployed units

Optical Axis Steering Pan/Tilt Mirror Control – Two rotational servos – Worm gears X/Y Mirror Control – Two galvanometers Housing Alignment Control – Two (or three?) linear servos changing the lengths of the legs

Pan/Tilt With Two Analog Servos The cheapest option, but is it suitably accurate and repeatable? Lynxmotion SSC-32U USB Servo Controller – 32 servo channels, in two banks of 16 each Provision for separate voltages on the two banks – Accepts ASCII text commands via USB or RS-232 serial – Controls 500µs to 2500µs pulsewidths in 1µs increments – Additional functions using minimal external components Hitec HS-422 analog servos – Speed and torque are not significant factors – Want a small deadband

Pan/Tilt Test Rig Pan/Tilt assembly mounted over an Orion 80mm Short Tube OTA First-surface mirror to minimize false images – Edmund Scientific Astrovid StellaCam3 (Peltier-cooled Watec-120N+) Pinnacle Dazzle to VirtualDub on a Lenovo laptop SSC-32U commanded via USB to a virtual COM port using Tera Term – µs counts = 180 degrees = arc-minutes – 1 1µs count = 5.4 arc-minutes

Pan/Tilt Mirror w/ Analog Servo Evaluation Rig

Pan/Tilt Assembly Close-Up

Pan/Tilt Target Ruler 30 arc-min 1 count

Results Arbitrarily chose 30 arc-minutes (the apparent diameter of the moon) as a repeatability goal Reasonably accurate and repeatable, to within ~16 arc- minutes (3 1µs counts) but only after making a large (≥ ~5-degree) slew Small moves (such as those necessary for tracking) were essentially impossible due to the typical ~5µs to ~8µs deadband of a standard analog servo Good position holding after removing power to the servo – The mirror assembly has an extremely small mass Overall assessment: good, but not good enough

Next Test Will Use Digital Servos More expensive Need to be programmed individually prior to use – Only need one programmer Higher power consumption The deadband can be programmed to zero at the expense of continuous “hunting” – This will have a minimal impact on the servo lifetimes because the powered use will be relatively intermittent Significant parameters to be evaluated – Position hold after power removal – Small motion (i.e., tracking) performance In particular, the effect of any resulting vibration on image stability

Software Issues If using an analog camera, need a reliable driver for the various available video digitizers (e.g., eMPIA Technology em28xx chips) for various small platforms (e.g., Raspberry Pi) – Able to capture a single frame Plate-solving routines

Looking Forward Design for the future – Internet of Things (IoT) – 3D Printing The number of different cameras currently (and projected to be) in use may mean that it will be simpler to have a separate (and standardized) camera for the alignment process – Also means that only a single version of plate-solving software will be necessary

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