IPhone 4 as OHKLA flight computer? | Other subsystems | Forum

Hmm.  Interesting.

On the one hand, I feel like this approach is in some degree of conflict with some aspects of our Social Contract, namely:

• When selecting off-the-shelf hardware for use in construction of
  rockets and spacecraft, in situations where other practical concerns
  (cost, mass, reliability) are equal, CSTART shall exercise a preference
  for hardware which makes minimal use of patented designs, proprietary
  firmware, etc.
• All computers onboard CSTART rockets and spacecraft which run operating
  systems will run operating systems whose kernel and basic userland
  utilities satisfy the Free Software Foundation's Free Software Definition.

But then, the Social Contract and Design Philosophy are kind of a balancing act between conflicting ideals and so I feel like we shouldn't reject the idea immediately due to the above, and should consider the technical merits of the idea as well.

Some things that occur to me are:

• How accurate are the inertial measurement units in an iPhone?  I suppose their intended purpose is for fairly basic stuff – like user interfaces where you can control the device by shaking it, etc?  In this case they might be pretty poor with regards to long-term stability.  It's probably possible to find specs on this to double check.
• How possible is it going to be to add extra input devices?  Most high altitude rocket avionics stacks seem to include a barometer and sometimes also magnetometer in addition to GPS and IMUs.  Does the iPhone have USB ports or something we could use to incorporate this kind of stuff?
• How possible is it going to be to get the iPhone to control things.  I'm thinking here mainly about separating the nose from the body to deploy the parachutes.  Ideally this decision is going to be made by software which responds to input from the kind of data we've discovered above, so we need the iPhone to (i) be able to run arbitrary software (and isn't this difficult?  Don't you need to get your stuff approved by Apple or something?) and (ii) send an output signal to some electromechanical construct of ours for performing the separation.  Again, a USB port could support this, but if the iPhone has those at all I'm not sure it will have as many as we may end up needing.  I guess we could use a USB hub or something, I don't really know how those work.

If these issues are easy enough to overcome then the idea might have some merit.  It would also aid with recovery if we did the launch in an area where there was cell phone coverage.

Rocket-To-The-Moon said:

I wonder what Von Braun would have to say about even the consideration of making a telephone the center of a GNC system?

Good question!  I wonder what he'd have to say about the amount of progress manned spaceflight has had since his passing?

Very interesting – nice "save", brmj!  I do feel like using a smartphone as a flight computer does kind of embody a lot of the original spirit of the Design Philosophy.

The biggest questions over this in my mind are:

• How good are the accelerometers, and
• If there's no phone signal at our launch/landing sites, how hard is it going to be to communicate GPS data from the phone to an external radio device?  I suppose not too hard, really the phone has just replaced the microprocessor we'd have otherwise used.
• What does it cost to buy one of these phones outright (i.e. not on some kind of contract that we'll have no use for), and how does that cost compare to rolling our own device using an Arduino or the like?

rpulkrabek said:

 

In general, I think we are a bit away from utilizing a phone to control a rocket, but it may be good to keep in mind for future use.

There's really almost nothing happening in the way of "control" on OHKLA.  The only control thing involved is separating the nose cone from the body, and that's presumably just a matter of sending a single bit signal to some device once we register an appropriate combination of acceleration and barometry values.