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This ongoing research involving collaboration between NPS and University of Alabama in Huntsville (Huntsville, AL) is funded by the U.S Army Special Operations Command. The main objective of this research is 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 include (but are not limited to) building a peer-to-peer networking frame with multiple ADS being its nodes, achieving a pinpoint accuracy for delivery of mission-critical payload, developing flocking and collision avoidance (deconfliction) capabilities, computing reachability sets to resupply troops at multiple locations in a timely manner, usage of unpowered and powered parafoils in urban warfare and exploring capabilities of the larger powered parafoil system to deliver and deploy smaller ones.

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

Figure A. The Snowflake ADS.

Figure B. The GN&C unit.
In total, during the first series of TNT drops, 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 70kt.

Figure C. The McMillan airfield.

Figure D. The Snowflake ADS deployment unit.

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 first set of experiments, the three deployed systems demonstrated only 55m circular error probable (CEP), which happened to be twice more accurate than any other existing autonomously guided ADS.

After these initial drops, 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 drops performed in May of 2009 with a 30m CEP, and Fig.Eb – performed in May of 2010 with a 10m CEP!

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

The key features that allow Snowflake to achieve these excellent results are:

  • Real-time generation of an inertial reference trajectory based on the current (constantly updated) estimates of ADS parameters and winds/atmosphere (Fig.F outlines 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 100Hz;
  • Advanced tracking algorithm based on the model predictive control;
  • Communication / networking with the target weather station(s) and between multiple descending Snowflakes to share winds/atmosphere information (this version is called Snowflake-N and features below 10m CEP accuracy).

Figure F. Snowflake guidance strategy.

Due to these features, Snowflake ADS exhibits about the same trajectory every time it is dropped (that distinguishes it from all other existing aerial delivery systems), 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 themselves, and capability to access the descending system from anywhere in the world (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.)

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

Figure H. Bird-eye view of a Snowflake trajectory displayed on-line in Google Earth environment.
To date, the Snowflake system has been successfully deployed over 100 times 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 10000 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. The range of Snowflake deployment conditions.

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