Rockblock is so much easier and cheaper if you do not already own the Ham radio hardware.
KB3SF since 1980.

It works everywhere.  They can send you as many units as you want.  Can't beat the price.

He did it!  Works great!  Rockblock Library for Arduino:

http://arduiniana.org/libraries/iridiumsbd/

I have gotten it to work last year without any special audio library.  Sampling to RAM is trivial.  The only problem with my code is the skipping when it allocates another cluster on SD card.  This can be overcome with a simple to use library which pre-allocates the clusters.  What's the problem Mike?

Worldwide coverage?  Rockblock is difficult to obtain?

He did it!  Works great!  Rockblock Library for Arduino:

http://arduiniana.org/libraries/iridiumsbd/

He did it!  Works great!  Rockblock Library for Arduino:

http://arduiniana.org/libraries/iridiumsbd/

I have a paying application for this service.  Hence my motivation.
Does anyone see the value of this hardware?

I've got the Bescor.  Would like to see the code!

8 seconds will take about as much power as 1 second interval.  At least 1/2.  It takes time to initialize the GPS on powerup.  If you really want to save power record a data point every 2 minutes.  You might get the average down to 1-2ma in this case.  http://www.adafruit.com/products/746 can run without a microcontroller taking power at all.  It only draws 20ma.  But I do not recommend this.  Because then you will have no control over the period or to stop sampling when there is no movement.  It is also difficult to access the stored data with Arduino code.  If you store the data in EEPROM, you could store 500 data points.  That's 1000 minutes or 16 hours of hiking.  if you want 3 days you will have to sample less often or use SD card.  This is what I'm working on.

I've been talking with Nick, he promises soon.  Has anyone already made it work with Arduino?

See link for cost.

http://soloshot.com/

Uses GPS for much longer distances...

Anyone want to work together at interfacing Rockblock with Arduino?
http://rockblock.rock7mobile.com/?page_id=15

I have the hardware and Node.JS library.
http://rockblock.rock7mobile.com/?p=332

I have been unable to find any Arduino code online...

If you use the PPS pin from a cheap GPS, then you no longer have to Ping both directions or round trip.  If all the units are in sync, you only need to go one way from transmitter to receiver.  The time difference will give you an accurate distance.  This time measurement is SO accurate you can almost do it with light or radio speeds.  Sounds can be accurate to inches, or the time between peaks of the sine wave.

The video would be boring, it was a boat navigating a mile out into the lake. 
I posted my code in a different thread when they asked for it.

Even though it seems obvious to you, a picture or diagram of your circuit would help.

It would be trivially easy to make them go the same speed.  Just a couple lines of code.  Not much harder to go half speed.