Today we added all three soils to one of the hoppers and ran some tests with the entire experiment assembled.
















Here are Jon and Nick working on getting the vibration exciter set up.





















It's good to finally see one of the hopper assemblies complete with all three soils inside. The soils are from left to right: NU-LHT, JSC-1A, and play sand.
















Here's the entire experiment set up. The only components missing in this picture are the charge amplifier and oscilloscope used to measure the vibrations in the hopper. A small accelerometer will make those measurements and will be mounted on the outside of the hopper.

We took some videos of a couple test runs as well.



This first run shows the soils flowing with the vibration exciter running at about 25 Hz.



This second video shows the soils flowing without the vibration exciter running. Surprisingly, the vibrations did not have as much of an affect as we had expected, nor did the NU-LHT simulant resist flowing as much as anticipated. We will be doing a few more tests, but at least we have shown that the equipment works well.

Just two days left to make final preparations before we leave for Houston. Everyone seems excited for the trip, but we're also focused on getting everything ready before we leave. Once we are in Houston, there will be some time on Thursday for equipment assembly when we can make last minute tests and adjustments if needed.

Back inside the lab, some testing revealed a couple problems with our hopper design. One, soil particles would sneak out between the aluminum sliding door and the bottom of the hoppers. Once in there, it would bind up the slider so that the doors would stick half open. To fix this, we shortened the hopper walls a touch and added some felt between the sliding door and the bottom of the hoppers.

Also, we found out that a lack of airflow inside the hoppers caused problems for the flow. We noticed that the sand would flow much faster with free airflow as compared to when everything was sealed up. when it was sealed, we also noticed a small puff of dust at the hopper opening once most of the sand had flowed through. To fix this, we drilled holes in every hopper and added plastic tubes. To keep the soils and dust from escaping with the air, we wrapped the tubes in the filter material from a shop vac bag. It's not the prettiest thing, but it did the trick. Hopefully we have tackled the biggest problems now, and will be able to make our final assembly in the next couple days. It's looking like we'll get done just in time before we leave early Wednesday morning.

Here are a couple pictures of the hopper assemblies now.

We managed to get our frame painted yesterday. It looks a little nicer than just bare metal and welds. It took a couple hours to complete, including a quick run to the store for more paint, and the spray cans left a blister on my finger. Oh, the sacrifices we are making. All joking aside, it is nice to see this come together more and more each day. This picture is of Nick kneeling on a recycling bin by the loading dock where we painted our parts. I'm not really sure if it was necessary, but it wasn't my place to question his methods. The paint job ended up looking great, and with some Nebraska decals, it will sport some Husker red as well.

Here's another shot of the finished frame.

It is officially UNL's Spring Break, and Nick and I are still spending time in the lab. Today we did some structural tests on our steel frame. This was required by the safety officials at JSC, because in the past they have had welds crack. Thankfully, we got some help from the guys in the Civil Engineering Lab and worked out an effective, if not scary looking, test. We set the frame up on one end, slightly elevated by a few steel blocks on the floor, and strapped the top portion of the frame to a concrete pillar. Then, we hung a substantial amount of weight from specific locations to simulate the loads the frame could see in 9G's (under extreme emergency-only conditions during the flight). Here are some pictures of the set up.

This is the frame after being strapped to the pillar before we began handing weights from it. It doesn't even look scared.


The next few pictures are of the frame with all the weights hanging from it. The frame didn't break a sweat, and the welds held up without any problems, just like we had expected.






























Then we threw all the weights on the scale, 808 lb.


















It certainly looks scary, and I was a little afraid of dropping a weight on my foot. But, it's one more thing to check off the list. Next up is figuring out how to measure the vibrations in the hopper during the flight.

Yesterday evening I put the entire thing together for the first time. Here are some pictures.

Well, this is it. The hopper assembly is mounted in the frame by two 5/8 inch bolts. At one end, the mounting bolt is connected to the vibration exciter. This is basically a beefy loudspeaker. At the center of the cone is a mounting point which will supply vibrations to the assembly. The function generator is mounted near the bottom of the frame, and the amplifier is mounted on top.






This is a better shot of the electrical equipment. Eventually, two metal brackets will hold the function generator in place, and two nylon straps will hold down the amplifier.










This picture gives a better view of how the vibration exciter lines up with the hopper assembly.











This is a closeup of the vibration exciter and how it connects to the mounting bolt. The idea was to use washers and rubber o-rings as a sort of spring to push the assembly against the exciter, but a few quick tests proved that this might not be a good idea. It seems to damp out almost all of the vibrations, so we'll have to make some adjustments.






The reason why we are supplying vibrations to the assembly is because of the difficult flow characteristics of the lunar soil simulants. In lab tests on the ground, our Principal Investigator showed that the soils (especially the NU-LHT simulant) would not flow at all. The particles in the soil are so irregular that they interlock with one another and stop flow. Therefore, we are supplying vibrations to force the stuff to flow, and are investigating exactly how this works in lunar gravity.

Once we get everything working properly, we will disassemble everything to do load testing on our frame. NASA would like us to show proof that the welds on our frame are good ones by hanging weights from the frame. As part of the equipment design, the frame and assembly must withstand 9Gs in one direction. This puts some severe loads on the structure, and they want to make sure everything will be ok in the event of an emergency landing. Our plan for this test is to hang the frame vertically from the anchor points and hang weights off the corresponding mounting points for each individual piece of equipment. I'll certainly get some pictures up of that test as well. Personally, I'm not worried at all about the strength of the frame, because it looks like you could park a car on top of it with no problems.

That should pretty much get everyone caught up to where we are right now. I'm going to be in the lab again this afternoon with Nick to work through some more bugs. I'll make another post hopefully in the next couple days to update everyone on our progress.

Here are a few more pictures of our equipment from Friday.

This is me (Brett) with Nick standing next to our two hopper assemblies. I'm on the right. One assembly has an 18 mm opening and the other has a 25 mm opening.











Here is another picture of the two assemblies. The electric solenoid which opens the hopper doors is activated by the switch seen in front of the assembly on the left.










Here's a shot of our workspace in an old lab in SEC. We were pretty fortunate to get access to this room, as space is a fought after commodity in the engineering building. The other microgravity team will be sharing this space with us, so it might get a little crowded once they start assembling their project.

Well, it's Friday, and I've spent most of the day in Scott Engineering Center. Our first hopper assembly is coming together. There have been a few hangups, but nothing to serious yet. I should probably take a little time to explain the idea behind our equipment.

As part of their study of lunar soils, NASA has created lunar soil simulants, which mimic the behavior of actual lunar soil. We will be working with these simulants, JSC-1A and NU-LHT for those of you keeping track at home. We will be building two complete hopper assemblies which will each contain three soils, the two simulants and sand as a control. The three hoppers are designed basically like egg timers. There are two sections in each divided by a door in the middle. When a test is to be run, an electric solenoid open the doors simultaneously and lets the soils pass through to the bottom. Then, the solenoid is turned off, two springs pull the door back closed, and the entire assembly can be rotated 180 and the test can be repeated. I've added some pictures of this assembly as it was being put together.

The first picture shows the hopper doors open. You can also see where bolts will be added to hold the entire thing together. One of the main concerns with this design was if the aircraft cabin lost pressure at 35,000 feet. The sudden change in pressure between the air inside the hopper and the air in the cabin would basically turn the hopper into a pressure vessel. The bolts were then added, including two in the middle to hold everything together even in an emergency situation.




Here's another view of the assembly as it is going together. The protective covering was left on one side to protect it until it is put together for the final time. We had to remove one side, however, to be able to see how the inner pieces lined up as we put it together. The two big sides were CNC milled to have grooves which match up with the hopper walls and sliding door inside.

Our machine work has been completed. Now begins the long process of putting everything together and making necessary adjustments so that everything works properly. What now looks like a pile of scrap lexan (a more robust version of plexiglass) and a beefy steel frame will hopefully transform into a dedicated experiment platform. It is exciting to finally see everything begin to come together. With such a short time frame to complete this project, we will have to move quickly to get everything together.

Next week is UNL's spring break, but it's looking like ours will come a little later this year. A few of us are planning on staying in Lincoln to work on testing our equipment. We leave for Houston the Wednesday after spring break. With the trip quickly approaching, it seems like there's a bunch of work left to do, but I have great confidence in our team and am sure we will have everything together in time. I've really been impressed with this team's effort so far. I'm privileged to be working with such a group of hard working individuals.

I will get some pictures posted as everything starts to come together, hopefully in the next few days.

Labels: assembly, equiment, lunar soil, microgravity