Tuesday we did a little experiment to make a custom, DIY vac chamber with wire pass throughs out of a tamale pot.

It didn't work. HAHAHAHA....but our vac pump does a great job.

Handsome Dan also does a great job. Folks, I would like to introduce you to GOAT!

After staring at this for so long in applications and Solid Works it was so exciting to see everything hanging out where it goes....and it all fits! Wooooooo! 

We're also pretty excited because Ryan got Phoenix Closures to send up some sample peanut butter jar lids. YAY! 

AND THEN Seth came in to 3D print the dongle box for us. 

Oops. Something is scaled wrong. The space dongle is not the size of an ant.

Seth has left HASP to focus on the Helping Hands Project and FLOW and we're excited because he was just elected the president of Helping Hands.

We met with Spencer in the machine shop and he figured out a way to tighten the gaps in GOAT.

Today Dan has been cleaning up the dongle box, Dan is programming, Kieran is soldering, and Ryan and I are doing thermal testing in the huge incubator. 

As you can see the white board has a lot of things checked off our list and new stuff is being added all the time. We're hindered right now because our new vac chamber (not DIY) that we had rush ordered to be here today is stuck in limbo because the college closed early. We don't know if it is here and if it is here we don't know where it is. It's frustrating because we were counting on the long weekend to give our wire pass through ample time to cure, now we won't be able to do any solid vac testing until Thursday at the earliest. Ryan will be at NASA Headquarters by then so he'll miss some of the larger tests that we were hoping to do.

Still....we've made a ton of progress this week and it's been a very good week for tUR GOAT HASP.

I don't know if anyone reads this who doesn't also read my Facebook, but JUST IN CASE please consider donating to our GoFundMe. We're so close to our goal.

https://www.gofundme.com/hasp-travel-fund

Jurassic Park with DJ Khaled

Now that classes are out for the summer we have the luxury of working on HASP almost full time in the GEL lab. We’ve been able to spread all of our materials out on every surface, set up work stations, bring in power tools and focus on building and testing the payload.

It’s.

Been.

Wonderful.

Seriously, we are having the best time. We clock in every morning, set up the tasks for the day on the white board, make some coffee and then get to work. We have made a ton of progress in a very short period of time. Some of the younger folks on the team have gone home for the summer (but are still working remotely) and some people can only pop in as their other schedules allow. The leads have been coming in unfailingly almost every day and have set up a rhythm in the way they work. These few weeks have really cemented my love of this work and my appreciation of this team.

We had a glorious conference call with SPEC Sensors where you could feel the creative energy crackling over the speakerphone (unless it was just a bad connection). We’ve been really happy that they’ve agreed to work with us and have even made some tentative plans to do more research for them. HASP 2? Maybe?

After Spencer made the plates we set up a testing rig for the pump and the BABI and ran some endurance tests to see if the rig would survive running for hours. We’ve been very impressed with our SparkFun Pump and have been putting it through the paces in vac and out. It had no issues during our endurance tests (although we all grew tired of hearing it successfully chugging along). Since that went so well we decided to move on to some ground based ambient thermal testing. I made a janky little test rig one day (so much fun) out of scrap aluminum that we dubbed “SHEEP” and we lined it with mylar, threw bunch of sensors into it, and ran it for a few hours. It got pretty hot! We’re going to do more of that with the real GOAT to try and see what other issues we can find.

While tests are running Memes is wiring up the spine, Ryan is getting EVEN MORE donations, I’m trying to get our travel forms square, Jimmy is soldering the wires on BABI, and Handsome is drilling. We’ve all gotten used to wearing ear protection…and some of us even employ it as a tool to add focus when things are too raucous and words need to be written.

When tests go well we learn something.

When tests go poorly we learn something.

Thursday night as we were closing up shop we gathered in the lab next door so we could talk without yelling over the pump and outlined what we needed to do to be prepared for mini-integration and thus, integration. It is a long list but we’re feeling pretty good about our ability to realistically get all of this done.

Jimmy was the first to leave and headed out for his internship last Thursday. Ryan’s last day is this Friday. Memes will stick around until next Friday.

We tested the pump in the -80 degrees C freezer on Monday because the rest of the supplies were tied up. GOAT and SHEEP were disemboweled so we improvised with my vintage tin Dark Crystal lunch box, lined with mylar.  We were skeptical about the pump’s ability to survive the cold trip up and down. Well. The thing worked like a champ. It was still running when we took it out and unplugged it hours later. This means that we primarily need to focus on managing excess heat and will spend less time fiddling around with tiny heaters.

End of Project Video for FLOW

The GOAT, the bad, and the ugly

A guest post from Handsome Dan:

I put together a prototype GOAT with the panels that Spencer made for us.  Here's my first reactions

The Good: Bolt up construction for the entire payload took less than an hour.

The panels fit well together assuming well manufactured corner brackets with 90 degree angles..

The No 10 Bolts are also a great fit.  There's about .01" of wiggle room, which is a good thing.

The hull is a freaking tank.  We could throw it down a flight of concrete stairs and nothing would move.

The Bad

The McCorner Brackets from McMaster are indeed McCrud.  They had to be made with large tolerances because there's even inconstancy between some of the brackets which exacerbates spacing of the panels (below).  Once tightened, the brackets flatten which creates about a 1/8" gap between top/bottom and the side panels.  Only good thing is that the gap is consistent along all the edges.

We will definitely have to spot weld hex nuts to some of the brackets.  It can be just the lower brackets for two panels, but there's no way we will be able to put the last panel on without them or without finding someone with 10 cm arm circumference and tiny, strong fingers.

The GOAT

If we can't find brackets that are made with tight tolerances then we can use the McCrapster brackets.  Shaving them down isn't an option because of the amount of material that would have to be removed, but we could adjust the mount hole placements by 1/8" to compensate.  Not all of the angles of the brackets are exactly 90 degrees which causes warping (see pic below) so we would have to adjust them with a little elbow grease.  It'll be somewhat time consuming but doable.  Plus we would have brackets very specific to this hull.  Not ideal, but an option.

How to Make a Ginger Snap

As our time runs out in the semester we are having to think critically about how to get everything done in time for Integration. One of the things that we've been itching to do is to actually build the GOAT hull.

We were able to gain access to the Durham Tech machine shop so that our consulting machinist would be able to cut and punch the panels for GOAT.

The initial fabrication process took about 12 hours and the machining shop is not too invigorating if you're not allowed to touch anything. So we had to make our own fun while Spencer did all of the hard work.

OK actually it was still pretty cool.

Even though the hull is essentially just an aluminum box, it's a box we've spent a long time looking at in Solidworks, so it was gratifying to see it in real life after all this time. 

 

Look it works! It caught a jar of peanut butter!

Just a BABI

If you want to get the attention of someone at CSBF in a negative way just include the word "pressure" post scripted by the word "vessel." CSBF was concerned that our Bernoulli Air Bath Intensifier (BABI), a 28 oz. plastic (PETE-1) container modified as an atmospheric accumulator (a.k.a. a Great Value peanut butter jar) might be a pressure vessel but it's specifically designed to not be a pressure vessel. BABI has a single design goal: to circulate air across the sensors in order to sample fresh air throughout the flight, so that we are not taking stagnant readings of the air inside our hull. We can not reach the pressures preferred by our sensors, but testing shows that we can improve the amount of air available at float, and we are hopeful that we’ll be able to record some meaningful data. This challenge of this project has moved away from our original science and has morphed into an engineering design quandary about moving air in the stratosphere.

CONSTRUCTION

For reproducibility throughout our prototyping, we make our capillary holes with a Cobalt Steel Micro-Size Drill Bit (0.0020" diameter) in a thin piece of aluminum from the wall of a beverage can. We then drill a 1/16” hole in the wall of the plastic jar and seal the perforated aluminum patch over it, aligning the holes. We have yet to settle on epoxy or silicone caulk as the best sealant; both have benefits and drawbacks and we have to consider what will react with our sensors.

For each BABI, ¼” brass hose nipples are mounted in the sturdy plastic at the “bottom” of the jar, sealed, secured in place by washers sandwiched onto the plastic, then left to cure in low vacuum. Our 7.5-to-15 PSI (0.52-to-1.03 bar) safety valve is similarly mounted.

A slot is drilled into the lid through which the wiring is fitted and then sealed. This is currently an unsatisfactory and fragile seal, and we are investigating better ways to install a pass-through.

The plastic lid threads are wrapped in 5 turns of teflon plumber’s tape before the lid is sealed. Structural elements such as the mounting brackets and sensor standoffs have been omitted from this drawing/description for clarity. The pump in question is a SparkFun ROB-10398 that runs on 12VDC and outputs a stated flow of 2.50x10-4 kg/s (12 LPM stated by manufacturer, and assuming standard atmospheric density at sea level.)

The BABI (bottom left) inside our BestValueVacs 3 gallon vacuum chamber with our SparkFun pump and Arduino Mega.

NORMAL OPERATING PRESSURE for GROUND AND FLIGHT OPERATIONS

We have made several tests both at local ambient pressure as well as inside our vacuum chamber. All tests have been made at room temperature; thermally-controlled tests at -40°C and at +40°C are planned.

Test Run	External Pressure Max (bar)	External Pressure Min (bar)	Internal Pressure Max (bar)	Internal Pressure Min (bar)	Comments	Hole (in.)	Pump
PB BABI - 1.1 (03/29/17)	ambient	ambient	1.660	ambient	bottom dimpled out	none	SparkFun at 18V
PB BABI - 1.2 (03/29/17)	ambient	ambient	1.061	ambient	leak rendered this test useless	none	SparkFun
PB BABI - 1.3 (03/29/17)	ambient	ambient	1.056	0.07	Considerable and consistent leaks at lid threads	none	SparkFun
PB BABI - 1.4 (03/29/17)	ambient	ambient	1.035	0.07	No deformation. Small leak at lid threads	none	SparkFun
PB BABI - 2.1 (04/9/17)	1.005	0.069	1.555	0.09	Minor Leaks through lid	.008”	SparkFun
PB BABI - 2.2 (04/9/17)	1.003	0.071	1.555	0.09	Minor Leaks through lid	.008”	SparkFun
PB BABI - 2.3 (04/9/17)	ambient	ambient	1.015	ambient	Minor Leaks through lid	.008”	SparkFun
PB BABI - 2.4 (04/9/17)	ambient	ambient	1.04	ambient	Found leaks part way through our test. Covered it up with our hand to bring us up to our max pressure.	.008”	SparkFun
PB BABI - 3.1 (04/12/17)	1.01	0.05	1.563	0.06	Minor Leaks through lid	.008”	SparkFun
PB BABI - 3.2 (04/12/17)	1.01	0.05	1.170	0.06	Massive leakage	.008”	SparkFun
PB BABI - 3.3 (04/12/17)	1.009	0.05	1.163	0.06	Massive leakage	.008”	SparkFun
PB BABI - 3.4 (04/12/17)	1.01	0.05	1.166	0.06	Massive leakage	.008”	SparkFun

Maximum Pressure Testing

METHODOLOGY

We performed these maximum pressure tests to observe the behavior of BABI at extreme internal pressures. We manufactured several BABIs with only an inlet port (¼” barbed hose nipple). We used much stronger pumps for two early trials, then the SparkFun pump for all later trials. One trial used an air compressor capable of 250 PSI and the other a standard bike pump.

CONCLUSIONS

The result was a consistent maximum pressure reading of 1.56 bar after 40 seconds, with minor leaking around the threads. The two ‘extreme’ trials resulted in a breach where the lid was forced off the threads. There were no projectiles created from the breach and no permanent deformations of the assembly.

Test Run	Ext.  Max P (bar)	Ext. Min P (bar)	Int. Max P (bar)	Int. Min P (bar)	Comments	Capillary Hole Size (in)	Pump
PB BABI (3/29/17	ambient	ambient	1.38 ± 0.69	ambient	jar lid came off threads	none	Bicycle Pump
PB BABI (03/30/17)	ambient	ambient	2.89 ± 0.13	ambient	Considerable and consistent leaks at lid threads	none	250 PSI Air Compr.
PB BABI (4/16/17)	ambient (1.00 ± 0.01)	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	Minor leaks through lid	none	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	none	plugged for overpressure test	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	none	plugged for overpressure test	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	Consistent pressure despite leaving pump on for longer	plugged for overpressure test	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	Perhaps minor leak at hose fitting	plugged for overpressure test	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.56 ± 0.01	1.00 ± 0.01	none	plugged for overpressure test	SparkFun
PB BABI (4/16/17)	1.00 ± 0.01	1.00 ± 0.01	1.57 ± 0.01	1.00 ± 0.01	Perhaps pump cannot handle back pressure	plugged for overpressure test	SparkFun

RISK MITIGATION

We understand that CSBF has a vested interest in equipment that does not explode. To that end, we have implemented a complementary array of safety features to prevent an overpressure disaster, listed here in descending order of probability/reliability:

1. Intelligent automation of pump:

We are not running the pump until our barometers indicate that we are at ~100,000ft altitude (~0.01 bar), and the pump will automatically shut off when ambient pressure rises over 0.01 bar. Similarly, if the pressure inside BABI rises over 1.25 bar, the software shuts the pump off. This is our first and best defense against overpressure.

Our vacuum chamber can only draw down to around 50 mbar, which is significantly higher than the 5 mbar expected at float. However, at 50 mbar we saw that the pump could only create a pressure differential of approximately +20 mbar (50 mbar ‘ambient’, 70 mbar inside BABI); mathematical modeling shows that at 5 mbar this will be even less. In our estimation the likelihood of a breach is minimal.

Ambient tests have shown that, with the pump off, BABI de- and re-pressurizes only slightly slower than our vacuum chamber. We are not concerned about a rupture (neither implosion nor explosion) due to ambient pressure differentials on ascent/descent. Note how closely the curves of the BABI and its “ambient” vacuum chamber pressure align over time as shown below.

2. Pump physically incapable of overpressuring jar

Our pump has shown itself incapable of pushing more than an extra 0.5 bar of pressure. In sea-level-pressure tests without any capillary holes and a safety valve set to 25 PSI (1.72 bar), we were unable to exceed 22.6 PSI (1.56 bar). We heard a distinct fluttering noise and isolated it to the pump housing; this was repeated on subsequent tests. While the stated max output of our SparkFun pump is 32 PSI (2.26 bar), we have found that it just can’t push that hard.  The only time the lid came off the threads, we were using more powerful pumps (air compressors and bicycle pumps.) Even in these extreme cases the threads of the jar gently gave out before a fatal burst could be considered.

3. Safety valve

The pop safety valve is set to activate when the internal pressure of BABI rises 0.5 bar (7 PSI) above ambient pressure and testing has shown that the safety valve is effective. The mass flow rates for the safety valve, capillary hole, and the pump were derived experimentally and mathematically. The pump’s maximum mass flow rate at ground level in Raleigh was consistently observed to be 1.405 * 10-4 kg/s, despite its higher specifications. Taking the combined mass flow rates of the capillary hole and the safety release valve, we observed a combined mass flow rate of 9.05 * 10-5 kg/s.

In the appendix are two samples of our data and calculations. We were able to measure ΔP/s and, assuming atmosphere is ideal, apply the law PV=mRT.  We considered the mass differences per second to give us a mass flow rate for each individual flow component of BABI: the capillary hole, the safety valve, and the pump.

The results of this experiment provide evidence that, when the safety valve is opened, the mass flow rate out of the BABI is less than the mass flow rate of the pump. This means that even when the valve is open we are still able to achieve a slight gain in air being delivered to our sensors.

The team would like to do more testing in order to optimize the BABI. Ideally, we would be able to maximize the airflow through the container while still providing a sufficient leak. We are working on a combination of testing, mathematical modeling, and engineering the assembly.  The BABI assembly leaks when the internal pressure is raised; we have been unable to accurately account for the mass flow through the various leaks, which result in a lower calculated mass flow rates for all three components. Further experiments with our wiring, materials used for patching holes, adhesives, and valve placement should help us fine-tune the BABI. We want it to not be a pressure vessel but we don’t want it to be this much of a non-pressure-vessel.

4. Sealant faults

Our recorded “best” pressure (running the pump at 12V) was 1.56 bar, after which point (while testing at sea level pressure) we are distinctly able to identify leaks through our lid threads as well as through some of our homemade vents. The more the pressure, the greater the surface area of the leak.

(NOTE: even with these leaks, we are still building up a small ΔP; just nowhere near enough of a differential to be dangerous.)

5. Threads fail before jar

In overpressure tests with a proper air compressor able to output 250 PSI, we found that the jar/lid interface deforms enough to allow large volumes of air to escape at the lid. The deformation occurs consistently around ~2 bar. During several trials the pressure then declined with the large volume flow rate of the compressor still active and lid still attached.  Two of the trials resulted in the lid coming off the threads with minimal momentum. Our bracket will constrain the lid from carrying completely away, but likely will not constrain the lid enough to prevent it from lifting slightly and venting. Further tests for this scenario are planned.

6. Tube fastener fails before jar

In one other overpressure test, the vinyl tube with small zip ties popped off the barbed fitting before the jar lid popped loose. In all other tests the jar lid let go first.

7. Contained in 0.0625” aluminum hull

Worst-case scenario: If our pump has somehow stayed stuck in the on position, and our code can’t cut its power, and we can’t override it remotely, and the pump surpasses all previously recorded efficacy, and the safety valve has stuck, and the jar self-seals all of its various leaks due to the heat, and the low-grade threads hold, and the tube stays on, then our BABI will become a true pressure vessel and may rupture. In this worst-case scenario, our hull is bolted together on all 6 sides with solid 6061 aluminum; any ‘shrapnel’ will be contained within and should provide no danger to HASP/CSBF hardware or personnel.

PAST FLIGHT HISTORY OF PRESSURE VESSEL

To the best of our knowledge and research, no one has ever flown a partially-pressurized perforated peanut-butter jar to near-space; this will be a first.

Fig. 13: An engineering concept image showing BABI operating at float altitude. All dimensions to scale.

CONCLUSION

The common definition for a pressure vessel describes it as a container that has a pressure radically different than its surroundings. Our data shows that our container does not meet that definition and will not build enough pressure to ever become a flight risk. Our team is confident that the possibility of dangerous pressure buildup is miniscule.