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This research involving collaboration between NPS and University of Alabama in Huntsville (Huntsville, AL) was funded by the U.S Army Special Operations Command. The main objective of this research was the development of a prototype of a miniature precision airdrop system to evaluate some advanced concepts in controlling single and multiple (during mass airdrop) autonomously guided parafoils. These concepts included building a peer-to-peer networking frame with multiple ADS being its nodes, achieving a pinpoint accuracy for a delivery of mission-critical payload, developing flocking and collision avoidance (deconfliction) capabilities, computing reachability sets to resupply detached units at multiple locations in a timely manner, using unpowered and powered parafoils in urban warfare and exploring capabilities of larger ADS to deliver and deploy the smaller ones.

The first demonstration of the system took place during the Tactical Network Topology (TNT) experiments at the McMillan airfield (CA62), Camp Roberts, CA on May 15th of 2008 (prior to that several airdrops were conducted at Marina airport (KOAR)). Figure A shows the 5-lb version of the Snowflake ADS and Fig.B demonstrates the original GN&C unit.

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Figure A. The Snowflake ADS.

Snowflake B
Figure B. The GN&C unit.

In total, during the first series of the TNT airdrops, three Snowflake ADS were deployed over the McMillan airfield (Fig.C) from 1,900ft AGL altitude. All three systems were deployed from Cessna-172SP aircraft (Fig.D) flying at about 70kn.

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Figure C. The McMillan airfield.

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Figure D. The Snowflake ADS deployment platform.

All three systems had a clean canopy opening and behaved as predicted switching from one phase of the GN&C algorithm to another. Although the touchdown accuracy was not the main objective for this very first set of experiments, the three deployed systems demonstrated just 55m circular error probable (CEP), which happened to be twice more accurate than any other existing autonomously guided ADS.

After these initial airdrops, an additional series of tests was performed in Yuma, AZ (October of 2008 and May of 2009), Camp Roberts, CA (February and August of 2009, May and August of 2010), Kingman, AZ (May of 2009) and Marina, CA (August and September of 2009), which enabled tuning Snowflake's guidance and control algorithms to achieve unprecedented and unbeatable accuracy. To this end, Fig.Ea features the results of series of airdrops performed in May of 2009 with a 30m CEP, and Fig.Eb – performed in May of 2010 with a 10m CEP!

Figure E

Figure E

Figure E. Snowflake accuracy as of May of 2009 (a) and May of 2010 (b).

The key features that allow Snowflake-N (N stands for networked) to achieve these excellent results are

  • Real-time update of inertial reference trajectory based on the current estimates of ADS parameters and winds/atmosphere (Fig.F outlines six different phases of such a trajectory)
  • Real-time optimization of the final turn into the wind (for soft landing) with an update rate of as high as 10Hz
  • Advanced tracking algorithm based on the model predictive control
  • Communication / networking with the target weather station and multiple descending Snowflakes-N to share winds/atmosphere information

Figure E

Figure F. Snowflake guidance strategy.


Due to these features, the Snowflake ADS exhibits about the same trajectory every time it is dropped (that distinguishes it from other ADS), and softly lands into the wind (or any other predetermined direction if a specific tactical scenario, especially for multiple systems, calls for it). Figure G presents a couple of actual trajectories. Communication with the miniature target weather station(s) and between multiple ADS, and capability to access the descending system from anywhere in the world (global networking) makes Snowflake-N ADS a unique system to be used in a variety of novel applications. (Figure H shows the same trajectory as in Fig.Gb but viewable on-line from anywhere in the world at Google Earth.)



a)Figure G b)Figure G

Figure G. Bird's-eye view of a couple of actual Snowflake trajectories.


Figure H

Figure H. Bird's-eye view of a Snowflake trajectory displayed on-line in the Google Earth environment.


The Snowflake system has been successfully deployed from Cessna-152 and Cessna-172 general aviation aircraft, UH-1A helicopter, Tier II Arcturus T20 and Tier I SIG Rascal 110 unmanned aerial systems, and C-123 transport aircraft from an altitude as high as 10,000 ft MSL and speed up to 110kn (Fig.I). That includes demonstrating Snowflake ADS at PATCAD 2009, where it outperformed not only other same-size systems, but even more stable heavier systems equipped with much better sensors and utilizing flaring.


Figure I
Figure I. The range of Snowflake deployment conditions.