Update 4/24/2016 – It’s all about the telemetry

Hi all,

We flew our testbed rocket another couple times this week with TripoliMN at their launch on the 23rd up in North Branch. This time around during the flights, we were testing our telemetry capabilities. By the way: I’d like to thank Gary Stroick for letting us fly under his certification and letting us call “his” rocket the “Happy Puppy.”

We found some interesting issues with corrupted data packets, but we can see a path to fix all of the issues we found, so good news! In our avionics bay, we flew both an Arduino (which was sending back accelerometer data via Xbees) and a Raspberry Pi (collecting many other data including video, but storing them on-board in an SD card). We have the some of the data, but are still processing most of it. Look for that next week, if you’re interested. We’ll also post on-board video (or a failure of on-board video) taken from the rocket.

LPRD rocketry members walking back after loading rocket onto launch rail

’bout to drop the hottest mixtape of 2016

There’s something about the combination of Alex’s sunglasses, Ginny’s crossed arms and wind-blown hair, Matias’s intense stare down at the ground, Dan’s coveralls, and that random guy’s hat and suspenders that makes this look like it was pulled straight out of an action film or a post-apocalyptic…

Subteam Spotlight: Engine

Engine team has been busy these past several weeks. The knowledge that we can successfully fire a liquid propellant rocket engine has been incredibly freeing. With that confidence, we can experiment with different injectors, different nozzles, etc.

We began working on impinging stream injectors a while ago, but Lee has designed a test rig which will let us test many parameters very efficiently. We’ve ordered the parts and should be building shortly. We’re also working on increasing the evenness of oxygen distribution in our chamber, but we made a few mistakes when meshing our simulation, so we haven’t quite come to a conclusion yet.

With some hard work and a little luck, we plan to have several injectors of both Mk 1 and Mk 2 size CADed and ready to machine over the summer.

The Material Advantage student group is still working on our ceramic rocket engine. They’re still running into an issue with the slip-casting manufacturing method, but appear to be well on their way to figuring it out.

David Deng

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Update 4/17/2016: Solids launch 2 coming up!

Hey all!

A few things to know for this week. First: we’re going to be flying again this weekend on the 23rd at the Tripoli MN launch up in North Branch. I know many of you on this list are rocketeers, so I hope to see you there! Definitely come by and talk to us! We’ll be the ones with the very drab, very plain rocket. Nothing interesting this time ’round except for the wireless communication, we’re afraid. Later on, we’ll try to convince them to let us do some interesting things, but I don’t want to spoil the subteam update.

One more thing: remember how last year, we were asking for “safety approval” to use money from the College of Science and Engineering, and they decided since we weren’t using their money, we weren’t their jurisdiction? Well, now we want to use there money, so we’re going to request approval again. We’ll see how that goes, but if we come out of it intact, we might have some additional sources of funding to go into cool things!

Subteam Spotlight: Flight

In the Flight team, now that we’ve successfully constructed a testbed for avionics in our modified Torrent Madcow rocket, our biggest project is the development of what we call an “asymmetric thrust rocket.” For your visual pleasure, I have inserted pictures from our recent low power asymmetric experimentation below.

That video above is NOT how we’re going to be doing it. We just wanted to see how some rockets would react when we designed them quite wrong. The method we decided on is much less haywire.

Basically, when we attempt to fire a liquid propellant rocket engine, we run into a major issue. When the rocket engines are small (which they must be to avoid scaring the University), their thrust to weight ratio is poor. Fortunately for us, we can reach about a two to one thrust to weight ratio for the entire rocket.

If we had active guidance and thrust vectoring which allowed us to stay upright, we wouldn’t have an issue. Unfortunately, we don’t have thrust vectoring or active guidance, so we must rely on passive, aerodynamic stability to keep ourselves pointed upwards. For general rocketry, the accepted speed off the rail is 45 ft/s, or 14 m/s. Unfortunately, for your standard six foot rail, this means a thrust to weight ratio of about six. Now we have an issue. We can either build a very long launch rail, or we can attempt to boost thrust at the very beginning of our flight. Since building a longer launch rail is easy (in theory), we can do more interesting work and allow for more flexible flights by increasing thrust at the beginning.

LPRD Rocketry launch day on east bank flats near University of Minnesota

Typically, there are two methods to increase that thrust (if we want to still retain our liquid propellant motor. The first is staging, where a first stage solid motor would boost our rocket up to speed before dropping away to allow our second stage liquid motor to push the rocket the rest of the way. The problem? Starting the liquid propellant rocket engine in the air. If it doesn’t start, that’s a flying tube full of fuel and oxidizer waiting to crash into the ground. So staging is tough.

The second option is clustering or essentially using boosters. Instead of a single liquid motor, we would have additional solid propellant motors around the sides. Now the problem lies in lighting all of the motors at once. Probable? Yes. Guaranteed? Not at all. Therefore, best practices will angle the motors into the center of mass so that if one motor doesn’t ignite, it won’t throw the rocket too far off course. Problem? The increased mass and size of the rockets means a larger diameter rocket means more thrust is needed means a larger diameter rocket, etc etc.

Sam Lijo of LPRD rocketry assembling low power asymmetric thrust rocket

Note: this method doesn’t work. We tried it. Don’t do it at home.

So we decided we would experimentally pursue a third option: an in-line solid rocket motor as a booster which is angled slightly off center to allow its thrust plume to clear the rocket body. If we place the motor’s center of mass at the same location as the rocket’s center of mass (and the burn duration is short), then we can place the booster at any arbitrary angle without worrying about it throwing the rocket too far off balance (so long as it cuts out before aerodynamic effects become dominant).

This way, we can hold down the rocket, ensure ignition of the liquid propellant rocket motor, and only then ignite the solid booster. Because there’s only one solid to light, we don’t have to worry about igniting everything at once, and the whole assembly is lighter, easier to fly, and safer, despite its odd look.

This week we will be purchasing the Loc-Precision Aura kit to modify to allow for the addition of an angled motor. The Aura is designed to be extra rugged and minimalist, meaning we can add extra weight and still allow the rocket to take off This means (at least according to Open Rocket) that we can still take off safely even if one of the motors fails to light.  We have selected the 143-G-33 and 53-F-70 motors as our most likely candidates for flight. The G33 gives a nice, long, 4 second burn while the F70 gives a short, sharp kick off the rail, just like our eventual liquid propellant rocket would be using.

Loc Precision Aura design modified by LPRD rocketry to accommodate asymmetric thrust

With any luck, this’ll be an exciting thing to try out. We hope to fly it during the summer.

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Update 4/10/2016 – Whooosh

Hi all,

Here’s the video from last week’s flight, as promised.

Subteam Spotlight: Avionics

After a few hiccups with our primary flight avionics, we think we have figured out what went wrong with our equipment. It looks like a few of our connections were bad and that was what might have impeded communication between boards. However, we have been able to rectify this problem and it looks like we have part of our avionics set up for the upcoming launch on the 23rd of April. This will be our in-flight computer that would communicate with our ground base over RF.

LPRD Arduino and XBee used to collect and send data on our rocket

It would host an accelerometer only but eventually we would like to add in our IMU and GPS modules that we were able to procure.

As for our liquid systems development, we have started working on a feedback loop from our valves to gather position data. This would allow us to know how much our valves are open and would also help us attain the correct ratio of liquids from the channels soon with a high degree of accuracy. We intend to use potentiometers at the valves for this purpose. More details on the circuitry and the code will follow as we continue our development. This is our starting point :

LPRD Schematic of control and feedback loop for rocket engine

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Update 4/3/2016 – When Cows Fly

Hi all,

Short update this week. Unfortunately no high speed video yet from Orbital ATK. I’m told that it exists and is on a hard drive somewhere, we just need to coordinate to get it to campus. Should be here soon, so keep looking for that. If you’re bored and looking for things to read, how about last week’s “summary of everything we’ve done” post?

Subteam Spotlight: FlightLPRD Rocketry Solid 1 on Launch Rail ready to be fired for first time

We flew our first rocket today. MadCow Torrent kit. We built it all the way back during the winter, but there were final touches to the avionics we needed to complete before going. Glen Smith worked quite hard to get it done, so many thanks to him. The parachutes functioned just fine, but we weren’t able to convince our wireless communications to work just quite yet.

LPRD Rocketry solid rocket one avionics bay as made by Glen Smith

The rocket itself is a dual deploy, meaning that the rocket deploys a drogue chute at apogee and a main parachute lower down. This is so the rocket falls relatively quickly (but not too quickly) and avoids using the wind-catching main chute until the last couple hundred feet.

LPRD Rocketry solid rocket one landed after first flight

The MadCow has Landed

This upcoming week, we hope to fly our prototype asymmetric thrust rocket. If all goes well, we’ll be ordering and creating a mid-power version pretty soon, so we’ll see how it goes!

David Deng


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