‘To Chop, Nod, or not Chop, Nod. That is the question.’ SOFIA FORCAST May 23, 2013, line-ops.

Reposted from https://blogs.nasa.gov/mission-ames/2013/05/23/post_1369351626283/.

I am out here in Palmdale, CA, not for a SOFIA flight (yes I know that’s where most people’s interest peaks) but for a critical step called line-ops, or operations on the flight line. Essentially we are going through exactly what we plan to while the plane is at altitude and work on end-to-end data testing, assessing observation timing, and communication, both among the different people needed to complete the observation and also between we humans and the highly complex software subsystems.

At 2130h May 22, crew briefing. We covered the main readiness topics: Weather (winds, humidity), Required Personnel, AircraftStatus and Configuration (System Engineer reported out), Telescope Status,Mission Systems Status (Flight Systems reported out), Operational Timeline(roll out, people on, telescope door open, telescope door closed, people off,roll back to hangar), Mission Rules (don’t connect laptops to the internal system and wireless at same time, bring drinks in closed containers, get permission before entering roped off areas, etc.), Safety & Emergency Procedures (exit doorway locations, footwear required), and Test Summary.

Being on SOFIA is not like flying on a normal 747 jet. I hope from the various photos in this blog entry and others, you’ll see it’s got“other things” like computer racks, a whole data collection and archiving server farm on board (the MCCS), conference tables, and various electrical panels needing access for maintenance or operation. It’s got airline seats(with the normal seat belts) for takeoff and landing and places to store your laptop bags, but the similarities end there.

So last night we got through some key tests. We did a pupil check (to optimize alignment of the FORCAST instrument to the telescope). Next were a series of inspections of the telescope boresight (telescope centered ona star) and how that appeared on all the imaging (all filters) and spectroscopy(for all grism and slit combinations) modes. We learned we had a systematic offset in our slits, but we updated the .ini file to address this. Then we did some testing of the basic modes. We tested chop-nod-dither in the SIRF and ERF coordinates. SIRF=Science Instrument Reference Frame (rows & columns on the detector array). ERF=Equatorial Reference Frame (RA/DEC on the sky). There is also a third coordinate system, the TARF=Telescope Assembly Reference Frame (elevation,x-elevation angles). Yes, astronomers love their coordinate systems.

Below is a photo of one of the chop-nod tests, on a bright target star. It’s chop-nod-match mode. Left is the Science Instrument Console with quick look software showing a reduced subtracted image (you see the positive and negative star images). The right image shows a series of display for the telescope guide camera and telescope display.


With the remaining hours for this night, we started probing the space of the chopping throw vs. angle. Below is an example of a large chop that was bumping up against a hardstop of the secondary, so we spent the rest of the night investigating that issue. The scale bar on the lower left of that guide star camera image is 1 arc minute.

The telescope door was closed at 0500h. Sunrise was at0545h. We’ll regroup later tonight to address the series of tests for tonight. There will be a crew briefing at 2130h to assess readiness for tonight.

Oh, surprise to me, we had internet on lineops, so I was tweeting away in near-real time we did our testing and I also got some IDL coding done for the pipeline end-to-end tests.


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