Tag Archives: astronomy

Stairway to the stars. Climbing aboard the SOFIA Airborne Telescope

Reposted from https://blogs.nasa.gov/mission-ames/2013/05/23/post_1369289647791/.

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 https://blogs.nasa.gov/mission-ames/2013/05/22/post_1369242690470/.

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.

Firm Flexibility

Reposted from https://blogs.nasa.gov/mission-ames/2013/05/21/post_1369126163898/.

Tonight’s line operations were cancelled due to open issues recertifying work on reworked parts of the telescope assembly (TA) power subsystem. There are no show-stoppers, just the need for more time for testing and integration. Progress continues to be made. The cautious step was to make the decision to start line ops tomorrow, and there is a contingency day next week to make up time if needed. The schedule for the remaining three nights of line ops will remain tight, but there is a plan. Creative re-ordering of tasks will be the “philosophy” these next three days. Having worked operations on two space missions, I can say that operations of any craft, air or space, is a skill of “firm flexibility.”

This evening, I experienced a Technical Readiness Review(TRR). This consisted of getting all the leads around a table and walking through the status of each subsystem, who is needed where and when, what types of testing will be done during the next few days, and when the daily crew briefings will be held. Also addressed were questions posed by the visiting science team to the operations team, to fill in some gaps. Today was the first time the group had re-assembled since the last line & flight ops, which for the FORCAST instrument, had been back in March. Since then, two other instruments (HIPO/FLITECAM and GREAT) had been installed, tested, and removed,and there have been software upgrades to both the telescope and telescope to science instrument communications. This phase of operations is pretty complex,folding in highly dynamic items that may seem be changing a lot, but it’s actually normal. And the job of operations is to keep to schedule while still achieving the tasks. Sometimes the path is different from the exact original concept, but if the goals are met, it was a successful journey. At tomorrow’s crew briefing at 2130h, open items from today’s TRR will be addressed and closed before line ops begins, set for 2300h-0500h.

I’m still a bit on the sidelines, watching and learning from the experienced SOFIA observers who have worked with SOFIA operations before. During a lull this afternoon, I got a glimpse into the AORs, or AstronomicalObservation Requests, which is how an end-user communicates her requests to enable an observing plan via scripted observational tasks. The AORs for our upcoming line ops have been written, and one of my roles will be quick look data analysis to confirm they executed as expected. My colleague Luke Keller, from Ithaca College, is shown below crafting some new slit-stepping observations.

Oh, I got to step inside SOFIA today. She’s bigger on the inside (compared to what I had expected, that is.).IF

Being in the presence of a cool lady, a 747SP named the Clipper Lindbergh

Reposted from https://blogs.nasa.gov/mission-ames/2013/05/20/post_1369084870713/.

I have arrived here in Palmdale, CA. This is a new place for me, so it has a share of expectations. Palmdale, just 50 miles north-east-ish of Los Angeles is home to the Dryden Aircraft Operations Facility or DAOF, for short.  Upon arrival, I learned that NASADryden Flight Research Center itself is about another 40 minute drive away, so time permitting, I’d like to check out that sister center.

I’ve rendezvoused with two colleagues from Cornell and Ithaca College who have both flown on SOFIA and also have put in so many hours to make the FORCAST instrument a success. They are eager to get back to operations & science observations again. I’ve also met two graduate students, one who has flown already and another, just as green-as-me, this being his first time to Palmdale and checking out the *Stratospheric Observatory for Infrared Astronomy* for himself.

Today marks a special occasion for me to see SOFIA in all her shiny-white-paint with an organized crew getting her ready for this week of line operations, or line ops. The reality is intense. One can read about things on the internet or in papers, but to actually see the physical metal, glimpse at her sleek curves, observe the crews keeping her safe and airworthy, is something else. And that’s just the outside.

The science instrument FORCAST, a mid-infrared instrument, is already installed and had its latest cryogen fill this morning.

Tonight, line operations are scheduled from 11pm-5am and I can share what I learn.  Until then, pieces of the complex set of what goes into operating a facility such as SOFIA,are slowly coming into place.

For now, I just cannot help staring at this amazing beauty.


747SP, the SP means “Special Performance.”