Telecon tomorrow (Thursday) @ 5 pm Eastern time

Hi all,

Telecon tomorrow (Oct. 15 in North America, Oct. 16 in Australia) at the regular time: 5 pm Eastern (2 pm Pacific, 11 am Hawaii, 23.00 European, 8 am Eastern Australia). Electrical engineering student Evan Moore now has an initial design for the little printed circuit boards on which the photodiodes on the sphere itself will be mounted -- a rendering of the assembly can be found here:

and a rendering of one of the new little boards is here:

We additionally have recent updates on AIFCOMSS, and on the 144 MHz transceivers (Raveon and Radiometrix). More discussion items for tomorrow's telecon include: flight/telescope plans and tests; construction and lab tests of the new gondolas/payloads; light sources and light source modelling; goniometric and pre- and post-flight calibration; propulsion work; nanosat bus and payload solid models; computing / website / TWiki forums and e-mails; grant applications; and recap of schedules. I'll send a progress report before the telecon tomorrow.

Here's how to connect:

1) Open Skype on your computer (note that of course, you should first install Skype, http://www.skype.com, on your machine if you haven't already).
2) In the "Contacts" menu, add me ( jalbertuvic ) as a contact, if you haven't already.
3) Just wait for me to Skype-call you at the usual time (5 pm Eastern, 2 pm Pacific, etc).
4) If there is any trouble, or if you don't get a Skype-call for some reason and would like to join, please just send me an e-mail (jalbert@uvicNOSPAMPLEASE.ca).

Here's the tentative agenda:

I) Flight & telescope plans, and upcoming tests
II) Construction, drop tests, and other tests of the new gondola and payload
III) Diffused light source and its modelling, pre- and post-flight calibration, and goniometric calibrations
IV) Solid modelling
V) Computing/website, including recent flight control and simulation progress
VI) Grant applications
VII) AOB

Talk to you all tomorrow, thanks!!!
justin

-- jalbert - 2020-10-29

Hi all,

My apologies for the delay! -- here's an update on recent ALTAIR balloon work, minutes of the meeting two weeks ago (attendees Arnold Gaertner [NRC], Liviu Ivanescu [Sherbrooke], and me), and a reminder of the telecon in 20 minutes(!) from now:

Electrical engineer (no longer a student -- he officially graduated from UVic with his BEng last week! -- but is still very fortunately working for us until end 2020) Evan Moore has now designed the little PCBs onto which the photodiodes will mount, which will be attached directly to the integrating sphere. (I had previously thought he would be fabricating the new version of the transimpedance amplifier board, but he instead will be sending all three new PCB designs -- the amplifier board, these new little photodiode mount boards, and the ORCASat payload motherboard -- for fabrication all at the same time at the end of next week, in order to save on shipping costs.) Here are renderings of the photodiode modules and the assembly:

The day before yesterday I asked Evan the following questions on this new photodiode module design:

Hi Evan, I've got the following questions on the photodiode PCB assembly renderings you sent this morning (which are attached):

1) The square-ish shaped mounts (I suppose bevelled square, or chamfered
   square, would probably be a more correct term to use) on the sphere
   into which the photodiodes fit -- will they also be made of Delrin?  If
   they are made of Delrin or of some other plastic, will they be 3-D
   printed (or subtractively machined)?  And, do you intend to epoxy them
   to the sphere (or some other way of attaching them)?
   And will the gap-filling Delrin seat that will go in between the PCB
   and the photodiode be 3-D printed, or will it be machined?

2) Very important: How will each of the two PD+PCB assemblies be kept from
   falling outwards from the sphere?  Will the new Delrin seat bolt onto
   the chamfered square mount? -- would that be how you plan on doing
   that?  (I don't see any bolt holes in the chamfered square mounts for
   that, in the attached drawings.)

3) What are the 3 holes in each one of the two photodiode PCBs for?
   Hopefully at least one or two of them in each PCB is for some sort of
   fairly strong rod-like connection to the chamfered square mount, in
   order to avoid unnecessary strain on the thin metal legs of the
   photodiodes...?  (But again, I don't see anything on the chamfered
   square mounts for such a connection, at present.)

4) Also important: On each photodiode PCB, would it be possible for the
   thermistor to be placed at least just a little bit closer to the
   photodiode?  (It is intended to be measuring the temperature of the
   photodiode, after all.)

5) Also important: Keep in mind that we might want to be able to have a
   little grounded aluminum RF shield around each photodiode PCB.
   (Obviously, not around the photodiode itself, but around as much of the
   PCB as possible.)  Thus, the _edge_ of that PCB should be ground, not
   guard (although, obviously, the internal guard ring should be guard,
   not ground!) and importantly there should be a way of attaching such an
   RF shield (I don't see such a way, at present).

and I got the following answers, and updated design renderings, from Evan just 15 minutes ago (which I think are very good, but I haven't yet had time to carefully read them!!!):

Hi Justin,

I have attached some more photos that hopefully better explain my plan
for this.

Regarding your questions:

1) All the mounting pieces will be made from delrin, to keep everything
electrically isolated and happy. I imagine that the mount and seat will
both be subtractively machined. The mount will be glued to the side of
the sphere probably with the same epoxy we will glue the heatsink on
with. This mount has no thermal or electrical requirements, so any glue
that works somewhere else on the satellite will work for this.

2 and 3) See photos, two of the holes on the side of the PCB are meant
for bolts. I had not added the holes in the mount piece yet because I am
getting Josh to redesign that to be more easily machined. The third hole
is for a thermistor that will tunnel down through the seat piece and
contact the photodiode case, to have as direct a thermal connection as
possible.

4) As per above the thermistor will have direct contact with the
photodiode. I think we will pot the thermistor into this hole using the
same stuff we pot the other thermistors with.

5) All the pours around the PCB edge are ground, and the pour in the
middle is guard (see the following further design reconsideration).

One other thing that I think I am going to change is how we get the
guard trace up to the photodiode board. Before, I had measured the
leakage between any two conductors in the photodiode cable and found it
was less than 2 picoamps (or some other very small value). Regardless we
decided to have the surrounding braid of the photodiode cable assembly
be at GUARD potential and install a further braid around that to be at
SHIELD (GND) potential to be safe. However, now that I have been going
through with the design of the photodiode modules, I think that having
the USB casement at GUARD and trying to install a further braid around
that at SHIELD is going to be a lot of effort for very little actual
added value. Since the cables do not actually leak to each other anyway
in any meaningful way, then having the entire surrounding braid at GUARD
is not going to add any benefit.

So moving forward, I propose going to 5 conductors (as show in the
attached photo) surrounded by a GND SHIELD braid. This will simplify the
cable assembly design significantly, and still means that we can get the
guard trace up to the photodiode board itself.

Radiometrix still has our four SHX1-144 transceiver modules (they arrived there on Apr. 6) and is doing their firmware update that solves the BUSY output issue. They'll then test them out and send them back to us. Due to the COVID-19 situation in the UK, they've been taking a long time. Very fortunately, the COVID situation is slowly starting to improve in the UK (although everyone is of course very wary of a likely second wave). I asked Radiometrix about this yet again on Monday, and they haven't replied yet. We've also been doing more connecting up and testing out of our two new 144 MHz Raveon M8S data modem transceivers here in Victoria:

After checking them out with Raveon's Windows-based Radio Manager software, I've started to connect the radios up to Arduino Megas -- in the next few weeks I'm planning to get them talking to one another, and then I'll check out their effective ranges.

Once we get those 144 MHz transceivers settled and back into the ALTAIR gondola, we'll do some outdoor drop testing of the actual gondola. (We've done all the outdoor drop tests I can think of doing with our dummy gondola.)

And we also still need to test out our new DFRobot SEN0177 payload aerosol monitors that we have here:

Engineering students Josh Gage and Evan Moore found that the "wings" that Josh had found in the laser diode light output distributions:

were due to how the diode was mounted in the heat sink. When the diode is mounted properly and carefully, the wings go away.

We also have our 10 Hamamatsu S12698-01 photodiodes and 3 Thorlabs FDS100-NOCAN photodiodes (those Thorlabs ones have their windows removed) here in Victoria:

I've given them to Evan to try out -- he's taking a few weeks to ramp up, and will produce some linearity, etc., plots from them soon.

The survey-tripod-mounted device to cross-check yaw-pitch-roll information from the gondola (e.g., on days before/after flights) is also constructed now, thanks to Mark Lenckowski -- photo at:

and all that remains to be done is to finish the small fitting between the device and the bottom of the payload. The purchased hardware in it includes both the survey tripod (http://www.cpotools.com/cst-berger-60-alwi20-o-aluminum-tripod-with-quick-release--orange-/cstn60-alwi20-o,default,pd.html), two adjustable angle mounts (http://www.thorlabs.com/thorproduct.cfm?partnumber=AP180), and a rotation mount (https://www.thorlabs.com/thorproduct.cfm?partnumber=RP01). That last fitting to attach (temporarily, pre- or post-flight) the upper adjustable angle mount to the payload landing gear has been started and will be completed here in the next couple weeks.

We're currently revising the draft initial contractual agreement from our colleagues at Globalstar Canada regarding 2 initial SPOT Trace devices (and their service plans) for the educational side-project for the upcoming NATO SPS application, in which classrooms in elementary and high schools could launch company-donated SPOT Traces using party balloons (or a more environmentally-friendly version thereof), and track them to learn more about winds at different levels in Earth's atmosphere.

Houman will send Cordell and/or us updated sections of his master's thesis soon -- that information will be extremely useful to us going forward. Also, Susana and Nathan, it would be very helpful for us all to get the JHU students' final writeup when you have a chance.

Next grant application will be a NATO "Science for Peace and Security" application (together with Australian colleague partners).

Our next telecon is in 20 minutes (!!!) from now -- see below for Skype instructions.

Cheers, talk in 20 mins (!) from now -- thanks all!

justin

-- jalbert - 2020-10-29