This is a fairly ambitious project, and there will be many challenges to face and solutions to find. Here is a document where I am linking pages that I find useful during my research.

In order to guide my preparation, I’m going to try to predict some the issues I will have to tackle. These are roughly grouped together:

Power

Firstly, power. How will my device be powered during it’s long journey to “the edge of space” and back? The simple answer is batteries, but it gets much more complicated when we consider what this power supply will have to do:

• survive temperatures below -40C
• supply upwards of 6000mAh
• deliver at multiple voltages (most likely 5v and 12v)
• tolerate violent shaking
• tolerate very lower pressures

Servos

Servos are motors with a limited range of motion. In airplane applications, they are used to control the position of the control surfaces. For this application, the servos will need to:

• survive temperatures below -40C
• tolerate very lower pressures
• tolerate temporary high stress from violent winds
• potentially tolerate moisture from cloud layer
• draw minimal current
• be very reliable (not get stuck)
• operate at a convenient 5V

Minimizing the number of servos required to control the craft will be important.

Airframe

My design will be constrained by several ideals.

• It must be cheap.
• It needs to be fairly easy to construct and repeatable.
• It must be built out of fairly common supplies.

For this specific high altitude application, there are several other constraints which will come into play:

• It must be fairly strong to resist violent gusts which may stress the airframe. Wing flutter is unacceptable.
• It must have a fairly large (and potentially insulted) bay for electronics.
• It must be essentially immune to flat-spins which are likely to develop in upper atmospheric conditions.
• It must have a fairly sufficient glide-slope in order to traverse to the landing site.
• It should have a fairly small lateral profile to reduce the effect of crosswinds.
• It should require as few servos as possible to operate
• It should perform well through a wide range of airspeeds (15mph-200mph)
• It should have good mounts for camera placement.
• It must be easy to control autonomously.
• Related to environment:
  • survive temperatures below -40C
  • tolerate very lower pressures
  • potentially tolerate moisture from cloud layer
  • tolerate extremely high speeds (200+mph)

All of these requirements hint at some form of delta-style aircraft.

Autopilot (Electronics)

This may turn out to be the hardest part of the project for me. I will explain in later post what exactly stands to be so challenging about this, but for now let’s go over the performance requirements.

• Related to environment:
  • survive temperatures below -40C
  • tolerate very lower pressures
  • potentially tolerate moisture from cloud layer
  • tolerate violent shaking
  • Function at or above the target altitude (for the GPS and barometer)
  • tolerate potential radiation exposure
• The electronics must be highly reliable.
• They should be fairly easy to interface, debug, and initialize to make launching easier.
• They must fit within the airframe neatly.
• Related to the power supply:
  • draw minimal current
  • function at standard voltages (5V, 12V)
  • not require extremely smooth supply voltage
  • tolerate voltage sag throughout the flight
• Related to control of the craft, the autopilot must
  • function for long duration and long distance flights
  • have a sleep mode during the ascent
  • activate autonomously on release from the balloon
  • tolerate a wide range of speeds and possible flight characteristics
  • Re-plan flight path should the glider end up in an unanticipated position
  • Account for different atmospheric pressures when determining ideal glide slope

 

Balloon

This one is pretty simple in comparison. My challenges for the ballon are;

• It must be able to lift the payload easily and quickly (ideally <2kg)
• It must be affordable if I am to perform multiple launch tests.
• It must be able to lift the payload above the target 100,000 ft altitude.
• It should be environmentally friendly

I’ll lump in the release mechanism for the payload with this one. This will be the mechanism to detach the payload from the lifting balloon.

• It needs to be very reliable. This means
  • Releases consistently
  • There is no risk of the aircraft detaching accidentally
• It should be fairly low weight and small.
• It should require minimal energy to activate.
• Once released, the portion of the mechanism that remains with the glider must not affect its aerodynamics.

Camera

And finally, the camera. This one is also very straight forward:

• It should be powered by the aircraft’s main power supply (no peripheral battery)
• draw minimal current
• produce HD video with minimal vibrations
• Related to environment:
  • survive temperatures below -40C
  • tolerate very lower pressures
  • potentially tolerate moisture from cloud layer
  • tolerate violent shaking
  • tolerate potential radiation exposure

So as you can see, I have a lot of stuff to get right in order for the payload to complete it’s goal of autonomously returning to a target landing site! And this isn’t even everything….

Over the next couple of weeks I will begin to amass components for testing and building the first prototype.