Forum

Since the main point of OHKLA is to do hybrid engine research, we want to keep everything else on the rocket as simple and off-the-shelf as possible.  Let's start thinking about what non-propulsion related stuff we'll need, sticking to the bare minimum.

In order to facilitate recovery of the rocket, we'll need a GPS receiver on board and some solution for broadcasting its position to us.  Would a cell phone based solution work best for this or can we achieve a lower mass by using a small radio circuit that a radio ham can receive signals from?

In order to figure out the altitude of the rocket's apogee, we'll need either an accelerometer and a simple microprocessor capable of doing some intelligent integration, some sort of barometric altimeter or perhaps both.  I think we should only go with both if it is necessary to achieve decent accuracy, otherwise we should go with whatever is simplest.  We could either log altitude readings onboard somehow or broadcast them live, or both.  Note that I am assuming GPS won't work as an accurate accelerometer at the sorts of velocities and altitudes involved here – if this is wrong that would be great news.

We will need a power supply for both of the above.  The total flight time should be quite short so a small battery should be sufficient for this.

We will need parachute(s) to ensure that these things return to Earth at safe velocities.  We could try to use one large parachute for the whole thing or break the nose cone and contained avionics off from the engine after burn out and use separate parachutes for each (this is what CSXT did).  We will need a mechanism for parachute release – if we could reuse our altimeter solution for this purpose, it would be excellent.

Is there anything else we will want/need?

If we used an accelerometer to estimate altitude, we would also be able to estimate velocity with it (in fact, this is an essential step in the altitude estimation).

Measuring fuel levels should be possible by measuring the pressure of the N2O tank.  I have no idea about what sort of electronic devices could be used to facilitate this sort of measurement, but I am sure they exist.

I'm of two minds on the issue of a camera.  On the one hand, the footage from the apogee of the flight would be absolutely awesome and excellent promotional material.  On the other hand, I doubt it would directly contribute to us learning anything useful we could apply later to CLLARE.  I guess it comes down to how much mass we can spare.

I think that our best course of action now would be to find someone who knows their way around electronics, like an EE major, who would be interested in CSTART, show them Rocket's list of requirements above and Sparkfun's page (and maybe to a few other resources, like the PSAS stuff and the Arduino for inspiration) and ask them to find a set of Sparkfun products, each <=$100, which would let us build the kind of avionics system we are after.  I don't know any EEs but I do know a Computer Systems Engineering graduate who may be able to help, I'll ask him about it sometime soon.

Acceleration will go negative the moment the engine stops burning, and this will be an appropriate time to release the chute for the booster component, but the nosecone with the payload will of course continue to rise on a ballistic trajectory after this, with negative acceleration the whole time.  We will want to relesae its chute at its apogee, which will be when its vertical velocity hits zero – but filtering and integrating the accelerometer signal to get velocity measurements will make this easy to detect too.