Adieu from Palmdale, CA, for now, until returning for SOFIA commissioning flights

Reposted from

We completed night 2 of line ops for the mid-IR camera FORCAST on SOFIA. Our tests included script validation of the main observation modes for the imaging and spectroscopic (grism) channels, optimization of detector bias, and exploring a new way to improve the flat fields for the imaging modes. During part of the night, we were slowed down by debugging of scripts, an activity we were glad we found issues with now, rather than inflight. As a result of the delays, not all the planned tests were completed,but May 28th is the next line ops for this instrument.

We did manage to get our first grism spectral tests in, but more testing remains for May 28th where my colleagues will take over the testing. I will be on call for data analysis.

I head back to my home in Boulder, CO, today, after a powernap. I will be returning to experience a flight on SOFIA on Jun 11th.Until then another line ops is scheduled for May 28th, followed by commissioning flights on May 30, June 4, June 6, and June 11th.  I’ll be on call for data analysis and wishing my colleagues clear skies, good script runs, and completion of the readiness tests. SOFIA soon enters formal science flights at the end of June, and we want to give the larger community a high performing instrument with an observing strategy to optimize time and signal-to-noise.

SOFIA on the runway at NASA’s DOAF, Palmdale, CA during FORCAST line ops May 2013.

Who’s Sitting in the Driving Seat when you Fly the Infrared Friendly Skies?

Reposted from

Note: The pictures in this blog are taken from a recent line operations (when SOFIA is not in flight, but being operated on the runway) on May 23, 2013. As the program is in its iterative operations phase, these pictures capture the inside of SOFIA on this date. There will be additional preparations to enable the required safe readiness for the flights, the first set for May 30th.

At one level SOFIA is quite simple: you want to point the telescope at for target, hold there on the instrument sensor array for a set amount of time, maybe repeat the observation to allow for better signal-to-noise, and then move on to the next target. At another level, SOFIA is quite complicated as you have a moving observatory (in several degrees of freedom, i.e., forward, left, right) that is trying to target, “peak up” and stay on target for several minutes by which the observatory and/or the target has moved enough.

Mission Director: He/she is responsible for ensuring the flight meets the success criteria and is safe. They run the readiness reviews and summary the milestones for the flight campaigns. They also make decisions if needed to deviate from plan. They keep track of how well we are executing the plan.

The Flight Planner: On the plane he/she sits next to the Mission Director. Lots of work is done ahead of the actual flights to map out an optimized series of “flight legs” to maximize the time spent on target. As the telescope has a fixed position within the aircraft (aft-port), a leg towards the West (in the Northern Hemisphere) means the sky target is in the south; a leg towards the North means the sky target is in the west, etc. When SOFIA flies in the Southern Hemisphere, this gets reversed.

More information about SOFIA Flight Legs can be found at SOFIA Flight Plans.


The Telescope Operators. Sitting close to the telescope, they monitor the telescope set-up and operations and real-time interfaces with the science instrument. Each science instrument will have different requests for the telescope assembly. They also perform the Line Of Sight rewinds periodically. Normally this is scoped out in advance but this is envisioned to be a manual operation performed with agreement the Instrument Scientist’s okay. For example, you don’t want to interrupted an observation, so you are watching the clock and the angles in real time to know when this activity is needed.

More information about SOFIA Line of Sight can be found at SOFIA Line Of Sight Rewinds.

Instrument Scientist. Each science team will have an Instrument Scientist who knows the “ins and out” of the instrument and the subtleties of changes to observations or techniques. He/she is in constant communication with the Telescope Operator as well as the Principal Investigator of the observations. Science Instrument observations are run mainly by pre-written and pre-tested scripts, but sometimes there are some manual observations that the Instrument Scientist can execute.


There is also a lead for the MCCS, the Mission Controls and Communication System, to supervise the performance of that critical subsystem. This software controls the communication between the science instrument and telescope as well as all the archiving of any data taken during the line ops or flight.

There is the Science Team who is on board for the in-real-time data reduction and assessment, in case an observation needs to be redone again or done differently,  a Principal Investigator who decides the priorities of the science observations for the flight and directs the science team and  two pilots and a flight engineer for flying the aircraft.

Finally, there is space allocated for ride-along teachers and other guests who can participate in SOFIA science.

To learn more about the SOFIA Airborne Ambassador program check out SOFIA Airborne Ambassadors Program.

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

Reposted from

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.


Stairway to the stars. Climbing aboard the SOFIA Airborne Telescope

Reposted from

We got the “go” to proceed with line ops. SOFIA, a 747SP,was towed out of its hangar onto a side-runway, and away from any air traffic. The heading is 130.5. This is important as it tells us what view angles are available from the telescope. The telescope looks out the aft-port side of the aircraft. (Aft=back of wing, Port=left side, when viewed from the back, facing the front). So at this heading, we are looking at the N-E portion of the sky. Our calibration targets include TDra, NSV25184, RUCyg, muCep, and TCass, all pretty bright stars.

We walked out from the hangar to the craft and can come/go from the craft during the night. Of course, this is not what will be like during the flight. Below is a picture of our ingress/egress path on the plane,

A “true stairway to the stars.”  I learned that for the flights, we would do a similar activity, meaning we do not board within the hangar, but board after the craft has been towed out to the runway.

Using the waiting time wisely to make the best use of the remaining ops ahead

Reposted from

Line ops last night were cancelled due to a “no-go” by the telescope assembly subsystem. A problem had been found that could not enable observations tonight. It was a call the science team did not want to hear, but it was the right call. This exercised the reason why there is a “readiness review” before going out to execute a complex activity. A plan was put in place for the 1st shift when they get in at 7am (0700h) today (Wed) to address the problem and report back during the day. If all goes well, a crew-briefing will be scheduled again at 2130h tonight and we can resume line ops at 2300h.

If we were observing using a ground-based telescope, we watch the weather. A seasoned ground-based observer watches the humidity. You can often get obsessed looking at trends in pressure, temperature, etc. It’s important as you may need to replan your allotted observation time if you lose a night  (or nights) to the weather-gods.When I assisted with a balloon launch last summer at Ft. Sumner, NM, we’d gather daily to address the winds. Winds were most stable at dawn so we’d have our “crew briefing” at 3 or 4am with readiness to roll out at 5am with the hope to launch in the next hour or so (it would take nearly an hour to do the roll-out of the balloon and the He fill). Yes, sometimes the call would be made at 3am for a “no-go” or even as late as right before the fill. And then you roll back the balloon to the hangar. Last Sept, we launched on the 3rd attempt. All rocket launches also watch the weather and have various sub-system “go/no-go” checks.

SOFIA ops are not so different from those other examples.

So, we replan again. We have three remaining nights left in the schedule, two this week and one contingency night next week, which now seems to be required. Also, we’ve started looking at the flights scheduled for next week, to see what tests planned in flight would supersede the line ops tests to allow to compress our “line ops” schedule. Now, this is a calculated risk since the purpose of line ops is to test the system end-to-end before flight. So essentially you want to run the key components you plan to test inflight on the ground first.

What are line ops anyway? It’s not as “dramatic” as the actual flight, but it serves very important purposes to follow our observation plan end-to-end, address timing issues, and most importantly, communication between people and communication between people & machines. The plane is towed out on the runway to a viewing position safe from any active runway traffic, and preferably in a location far from buildings or lights to obstruct viewing angles.We operate on plane-provided power. We command the telescope door to open,configure the telescope, check it out, power the science instrument, and start running through a series of discrete tests, some of which are to be run exactly on the flights, and other diagnostic tests that are needed that would otherwise take up the valuable flight time.

One of the tests we want to do is test the “nod” function of the telescope and how the data sets we collect affect our observing strategy optimization (ahem, improve signal to noise). In mid-IR astronomy, the sky background is “brighter” than our targets. In fact, we often cannot see our targets in the original raw data until we do a “background subtraction.” So we use the telescope’s secondary mirror to “chop” a source back & forth (as it would appear on our detector) at a fast rate. And then we would command the telescope to “nod” to a different part of the sky. And repeat the process of“chopping” and “nodding” over a pre-planned orientation, both “throw distance”and “angle.”

You can read more about Chopping at Nodding at Why Chopping & Nodding is needed for SOFIA FORCAST Observations.

An example taken from PDF on Signal to Noise Improvement by Chop/Nods sums it up nicely.

example_forcast_chop_nod_imagesSo we’ll be exercising things like this during the line ops, exploring the same technique for different roll angles because when it comes to your science target which can be anywhere in the sky, we’d like to understand the system performance and, if any, limitations.

We have other tests planned like assessing the detector bias performance, looking at flexure of our alignment, particular for our grism mode where we have narrow slits, optimizing a new flat field technique, and running through the science scripts to checking for timing and fix any commanding errors.

So fingers crossed, we will get on sky tonight, on the tarmac at Palmdale, CA. The skies have been clear the last two nights, so we the weather gods have been kind. We now need the electrical-power-subsystem gods to be kind.