Testing Grounds and Ground Testing
For the upcoming June 16th launch our mission goals are:
- Launch the IIT high altitude balloon club’s first payload
- Test a new miniature MicroDAQ data logger
- Test Jeff’s GPS data logging unit in flight
- Attempt our first rocket ignition at altitude!
Goal 1 is keeping with our philosophy of lending a hand in increasing the numbers of near space exploration teams. For their first flight the IIT team has built a payload with a variety of sensors including a 360° sun sensor array utilizing multiple photo diodes. They are also sending up either a GoPro or Flip Camera for imaging. The good news is that they have procured funding for next year and will be able to expand their program.
We recently purchased an amazing miniature data logger. The MicroDAQ MSR145 measures a mere 52mm in its longest dimension and is a complete, self-contained 3-sensor unit capable of recording 2 million data points. Our unit has external temperature and humidity sensors and an internal pressure sensor. This Saturday, Ted was able to learn the ins and outs of the unit and prepped it for flight. Jeff built an inset mount for it in one of our Big Red Bee trackers – right next to his GPS unit – and now it’s ready to fly!
What The Heck
The last goal, was a late decision in the spirit of, “What the heck. Let’s give it a shot.” Jeff and I attended the NIRA club meeting June 1st and we were able to get some valuable advice and feedback from the members. There was a spirited exchange of ideas about near vacuum ignition and stabilization challenges. Suggestions for stabilization included a gimbal-ed motor which was shot down quickly for its complexity and possible DoD restriction (since a controlled motor could be construed as active navigation). A method of “rifle-ing” the rocket on a spiral launch rail ran into opposition when the length of rail and force exerted on the needed body-mounted guide pins was brought up. A short discussion involved the idea of using a canted motor (possibly an auxilliary motor) to spiral the rocket. This may be an idea worth exploration. So, we’re back to a motorized spin up. This seemed to be the most palatable solution though with a mixture of trepidation including the ability to stabilize the rocket body while spinning up to the necessary rpm to make it effective.
I posed the question about ignition at altitude and after some sage advice from Bob Kaplow and some of the other members, Jeff and I figured we should give it a shot. We’re going to attempt to ignite a small Estes rocket with a C-motor at altitude. One of the bits of advice from Bob was that the standard black powder Estes motors tend to fail when they are exposed to temperatures 70° (I’m assuming °F) below their normal temperature. Because of this, we built an insulated launch tube (more of a box, actually). The trigger will be a Basic Stamp with a timer. The Basic Stamp will activate a transistor and dump 6V from 4AA lithium batteries through the igniters. We’re setting up two GoPros to monitor the ignition… and launch?
We tinkered with a few ideas for safeing. The first idea was to cap the top of the launch tube with flexible plastic flaps to contain the rocket in all cases though the force of the ignited rocket would be able to push aside the barrier. We settled on a different direction. The concern was that the force needed to hold the rocket safely would possibly impair the launch. We decided to use a tie-down of mono-filament fishing line to hold the rocket down. The line is attached to the motor support and is pulled across the nozzle of the motor. At the moment of ignition, the mono-filament should instantly burn away and release the rocket. If there’s an ignition failure, the rocket should remain tightly tethered within the launch tube.
Last Saturday we ran a set of experiments to look at the response of the igniters and propellant in a near vacuum. The video is posted on our YouTube page or you can link to it here. Pardon the focus – we decided at the last minute to video the procedure – but you’ll get the idea. On the left side you see the experiments in the vacuum chamber and on the right are the comparative experiments in the open air. The first view is of the igniter – standard Estes types – in real time followed by a half-speed slow motion of the same clip. The same pattern follows in a test of propellant ignition. Not wanting to blow off an entire motor inside the vacuum chamber, we extracted some of the propellant for the test. Both views on the split screen are synched at the ignition point.
A few notes and observation about the test… Due to the ignition wires we could only get the pressure down to 10% atmosphere not the 1-2% we experience a 100,000ft. At first glance, the igniter respond without much difference, though it appears the vacuum test may be slightly less explosive. Because of this we decided to use 2 igniters for the flight. The difference in the propellant experiment is far more dramatic. In the vacuum only propellant in direct contact with the igniter burned. This is probably due to the fact that once the black powder is broken up the internal oxidant loses effectiveness and external air catalyzes the reaction. So, though it is not an accurate depiction of conditions, it is still informative. We’ll see on Saturday!
This weekend guests from Mach 30 – a group dedicated to “the advancement of humanity into a spacefaring civilization through sustainable leadership, open design practices, and a bias toward mature technology” will be at the Adler. As part of their mission of sharing technological development with anyone interested in space exploration, they’ve designed what they call the Open Design Engine (ODE). Think of it as a Sourceforge for hardware – for space hardware as well. They’ll be in the lab Friday to help document our efforts over the past 6 years so it can be accessed by any prospective near space adventurers out there. They’ll also be joining us on the flight Saturday. Some of you may have met J. Simmons when he and fellow Mach 30-ian, Maureen Carruthers, joined us for our December 10th flight.