Eye on the TIGRE

Today’s major news is that TIGRE did a compatibility check with CSBF and should declare flight readiness tomorrow.  Compatibility, as the name suggests, is an all-up check of all the physical and electronic interfaces between the science instrument and the CSBF crane, communications packages, and ballast systems.  It’s also a good time for the rest of us to take a look at other payloads in their flight configurations.

TIGRE up close.

Attaching crush padding and ballast hoppers.

On the crane.

Unfortunately, the surface winds don’t look good for launching for the next few days–there’s a cyclone lingering on the northern coast of Australia.  Hopefully by the weekend TIGRE will get a launch opportunity.  The float winds are rather variable, but they look pretty good.

As for us, we keep adding and testing gondola systems.  We got some bad news, though–some calibration sources we’ve ordered from the US are not here yet.  The company told CSBF they would be shipped a week ago.  Turns out they’re still in the States…

(At this point I want to note that my great little pocket camera–a Fuji FinePix F30–is still showing a full battery.  I haven’t charged it since I left the States!)

Blowing in the Wind

With TIGRE nearing flight readiness–they are planning for compatibility tomorrow morning–today CSBF held the first of what will be ongoing daily weather briefings.  The news was that the upper atmosphere winds will begin turnaround by the end of the week.  Turnaround is the best time to fly balloons, as the prevailing winds are shifting from blowing west to blowing east (or vice versa).  The transition stage tends to have low overall wind speeds, so balloons can float for a long time without going very far.  With the size and emptiness of the Australian continent, catching the peak of turnaround is somewhat less crucial for flight duration than it is in New Mexico.  Nevertheless, we left the meeting motivated to get ready.

Thankfully, Jane and Steve have decreased the noise we were seeing through judicious rerouting of the cables, so tomorrow we will return to integrating the remaining gondola systems.

The regional news station did a report on the balloon launching station and the upcoming campaign recently.  See if you can spot the NCT team member who makes a cameo!

Weekend Assortment #3

A tough old bird.

This truck will lay out the tarp which protects the balloon and parachute from the ground.

Sunset over the MacDonnell Range.

In the Dark #2

Once again today we found ourselves in both the literal and metaphorical dark, as the hangar power went out as we were grappling with a tricky problem.  (This time, though, all of our most crucial electronics were safely on battery backup.)  Since completing what we had hoped would be our final routing of the signal cables, we’ve developed a bit of a noise issue.  There seems to be an interaction been electrical grounds which should be isolated that we haven’t seen before.  Jane and Steve spent a hard day trying to isolate the problem.  It can definitely be a bit of a black art.

With limited means of helping that process, the rest of us worked on other projects.  Alan updated some of the software we use to control the gondola from the ground.  Zach attached cables to all of the newly-installed shield pieces.  I spent some time looking at our science targets.  The Southern Hemisphere sky is rich in gamma-ray sources:  pulsars, x-ray binaries, active galaxies, supernova remnants, and of course our primary target, the Galactic center.  Making the best use of our observing time requires a good deal of planning!  I hope to say more about our science goals in an upcoming post.  For now, though, we’ve got to get ready to get off the ground first!

Isolation

Today had an unexpected hiccup–we found a devil amongst the details.  In the morning, Jane, Alan, and Zach continued with the final harnessing.  Steve completed the battery boxes.  I worked on a bit of thermal analysis before installing the rest of the shield pieces with Alan.

One completed battery box.

After lunch, though, Jane was taking a look at the shields and the cryostat-side harness to make sure everything was fitting right.  When she checked with a multimeter, though, she found an electrical connection between the cryostat and the gondola!  To minimize electrical noise, the detector-cable-card cage chain is electrically isolated from nonessential parts of the gondola, typically with insulating spacers.  Since there is precious little play in the shields or the detectors, we were fretting about how to find and remove the electrical contact.

By this point the whole group was taking a look at things, and it got worse–the card cages themselves weren’t isolated from the gondola!  So, potentially we had problems on both ends of the chain.  On closer inspection, we found that the metal card cages were directly touching to the metal rails holding them.  We had to interpose an insulating layer to give us the isolation we needed.  After brainstorming about cutting mylar film or using Kapton tape to insulate the rails, we asked ourselves why we didn’t have this problem in the New Mexico flight–the isolation check was part of our preflight checklist.  Eventually, we figured out that we had omitted half of the fiberglass washers surrounding the bolts which attach the rails to the card cages!  I had simply misremembered how they were mounted.

Those little washers are what we forgot.

Fixing that oversight took a couple of hours and involved removing all the card cages from the ebay (again!).  The good news was that adding the washers isolated the cryostat from the shields as well, so the shields don’t have to be moved.  We’re back up and running as we expected again.  As our old family saying goes, if you don’t have it in your head, you’ve got it in your feet!  It does underline the importance of regular, step-by-step testing.

Shields Up

This morning’s nerve-wracking installation of the shields went off without any apparent hitches, thankfully.  Alan, Zach, and I were able to work smoothly through a proceedure we’d developed last December which minimized the risk and the stress involved.  What I had not anticipated, however, was how challenging it would be to get the bottom shield pieces positioned correctly!  To minimized leakage of photons coming up from below the instrument, which are only background, we have to tile the three large bottom shield pieces seamlessly underneath the cryostat.  Geometrically, this essentially involved making three triangles meet point to point to point.  However, in this case the three triangles were extremely heavy, with their travel impeded by their securement bolts and the points of the triangle hidden by the cryostat!  I spent a frustrating afternoon shifting the shields around trying to line things up as best I could.

The bottom shields (plus a few side pieces) installed.

Not much clearance underneath!

Meanwhile, Jane, Alan, and Zach continued the ebay-side harnessing.  Steve wired one of the two battery boxes.  Tomorrow we should be done with harnessing and finish with the shield installation as well.

We’ve had an extremely windy few days here–bad weather for launching, were anyone ready to go.  We may have to wait awhile to fly…

Carpe Diem

We expected today that the centerline crane would be in use by another group.  Finding it was not, we were able to take our gondola off the cart and move ahead  with some important preparations.  Jane and Alan worked heroically all day finalizing the routing and wrapping of the signal cables in the electronics bay.  This wrapping–with wide teflon plumber’s tape (from McMaster Carr, of course)–helps protect the cables and reduces electronic noise.  There’s more to do tomorrow, but it’s an important step forward.

The newly wrapped cryostat connections.

Jane and Alan sort out the harnessing.

Meanwhile, Steve worked on wiring up our battery boxes.  Alfred and Ming-Zhe continued their work on our test solar panels.  I made some modifications to the flight code in the morning; in the afternoon I cleaned off some of the road grit (and mosquitoes!) that had accumulated on the cryostat on the long road trip from Sydney.

Tomorrow will involve a high-stakes operation–installing the heavy BGO (bismuth germanate) shield pieces.  The large base sections weigh nearly a hundred pounds each, they have large delicate photomultiplier tubes jutting out at odd angles–and we have to slide them in through the cradle structure with less than half an inch of clearance from our extremely delicate (and virtually unrepairable) high voltage connectors.  It’s the riskiest element left in our preparations other than flight itself.  Seems like a good night to turn in early and get some rest!

Broadening Our Range

Spending too much time in the hangar can be stressful.  To maintain some perspective, we try to take one day off a week.  Today, we used our rest day for a Tour of the HebridesEast MacDonnell Ranges.  We piled in our vehicles around noon and headed east on the Ross Highway.  The weather was comfortably warm and the skies were clear, making for a pleasant day to travel.  Fly nets, however, were de rigueur throughout the day…

Our first stop, a mere 16 km out of town, was the Emily Gap.  On its sheer rock faces were well-preserved Aboriginal paintings.  With the recent rains, we found to our surprise that wading was part of the order of the day.

Fording the stream.

Emily Gap.

Aboriginal paintings.

Big rocks!

Alan is impressed.

Heading back out.

Not far up the road was Jessie’s Gap, a similar cut through the range.  (This one left me humming, though.)

Jessie Gap

Looking through.

I'm guessing this is often much drier...

Incredible rock layering.

Further afield, we stopped at Corroboree Rock, a strange outcropping sacred to the Aboriginal people.  Frequently we found ourselves wishing we knew more about geology!

Coroboree Rock.

Taking it in.

As we neared our final destination, the road became increasingly interesting.  The two-lane sealed road became a single lane.  (When encountering oncoming traffic, you have to drive with one wheel on the gravel shoulder, taking care that thrown rocks don’t break your windshield!)  After the turnoff to Trephina Gorge Park, the road was mostly gravel, and we had to ford a couple of (very low) streams!

The payoff was immense, though, as the hike through the gorge was magnificent.  After some initial confusion about trailheads, we established that the trail led right through the shallow river.  We once again peeled off our boots and waded in.  We took our time savoring the beautiful red and purple rock faces and the cool water before turning and heading back for home–only an hour’s drive!  Really, it was a spectacular experience of the Red Centre.

Trephina Gorge.

Gorge, us.

Slow Motion

The testing proved a bit protracted, but the detectors seem to be working nominally.  Today we made what we hope are final adjustments to the cabling to pick up a channel that had gone out due to a bad connector pin.  Jane has begun finalizing the harnessing–taping up the signal cables to keep them secure and noiseless.  Alan and I spent a mercifully brief afternoon applying thermal compound to a few boards–most of last year’s efforts are still good.  Next steps include integrating the shields and harnessing the signal cables in the electronics bay–and then we hope to move on to things like rotation tests and full-system calibration.

Time seems to have slowed a bit as we’ve become more familiar with our surroundings.  I don’t think twice about driving on the left anymore, we’re all saying “no worries” a lot, and I find myself wondering what else I can put beetroot on.  I suspect things will start to feel faster as we near flight readiness, though.  TIGRE should declare readiness sometime next week–it will be fun to watch them come together.

Dependencies

With our large project and small team, at any given time each of us has a to-do list longer than we can read in one sitting.  For the most part, we each choose tasks to work on based on mood or momentum.  In the last few days, though, I’ve been trying to determine which of our myriad of checkboxes is limiting our progress towards the distant but looming goal of flight readiness.

The two most immediate items on that prioritized path are finalizing the detector connections and installing the shields.  Our heavy bismuth germinate (BGO) shields surround the NCT detectors on the bottom and the sides, reducing background from the atmosphere.  Installing them is a risky and dicey procedure, though, so we want to make sure our detectors are behaving as they should and the connections are all good before we wall them off.  All this takes time, consultation, and reference to archival data.  We’re making progress, but it’s not as clear cut as determining that things turn on.

For their part, the shields turned on fine, but we found higher background rates than we expected.  With ground backgrounds poorly characterized and influenced by everything from the presence of smoke detectors to the composition of the hangar cement, sorting this issue out has been a headache.  So far, though, careful tests by Jane and Zach suggest the shields are working as they should.

Steve has been busy building an electronic isolator to report the cryostat temperature.  Alfred and Ming-Zhe are working on the test solar panels.  I’ve made a few minor changes to the flight software, and Alan continues to improve our ground support software.  Alan and I are also discussing our calibration plans–if and when the sources we need arrive!

Keeping it all straight is a task in itself, but we’re helped by great support from team members still at home.