Sense and Avoid Sensor Selection - UAS under 55lbs

     The inevitable integration of Unmanned Aircraft Systems (UAS) within existing airspace
has to be carefully controlled to ensure the safety and efficiency of not only the National
Airspace System (NAS) but the world’s airspace is not degraded.  Aircraft collision avoidance
can be separated into two categories, cooperative aircraft and non-cooperative aircraft.  The
technology to separate aircraft operating in these two categories is readily available; however,
the biggest problem is integrating this technology into a relatively new system so it can
satisfactorily perform its function.  There are a number of products on the market that claim to be
the best option for Sense and Avoid (SAA) technology which include: Traffic Collision
Avoidance System (TCAS), Automatic Dependent Surveillance-Broadcast (ADS-B), Electro-
Optical (EO) cameras, Light Detection and Ranging (LiDAR), radar, and acoustic systems.  In a
perfect world any UAS, regardless of size, would/should integrate all available technology to
ensure airspace integrity; however, this is currently not possible with UAS under 55 pounds.  In
order to detect and avoid cooperative, non-cooperative aircraft and wildlife, the combination of
these two SAA systems will be the best option for small UAS: Sagetech’s ADS-B transponder
and SARA’s Passive Acoustic Non-cooperative Collision-Alert System (PANCAS).

     The biggest challenge with smaller UAVs is getting the SAA sensory package small
enough to fit alongside numerous other electronics and still permit UAV maneuverability. 
Sagetech Corporation has solved that problem with their revolutionary transponder.  It is the
smallest transponder in the world and is easily the choice for UAS where size, weight and power
are needed for efficient operations (SAGETECHCORP, 2015).  Sagetech Transponders measure
just 3.5” x 1.8” x 0.7” and weigh only 100 grams.  Compliant up to 60,000 feet; the flight
computer can read altitude data from the transponder providing backup altitude information.

Supply Voltage is 10-32V and power consumption is 8 watts (typical) 14 watts (max).  The
company offers three variations to their transponder (SAGETECHCORP, 2015):

• Mode C Transponder – Small, high reliability solution for Mode A and Mode C requirements (Mark XA AIMS certified version is also available)
• Mode S Transponder with ADS-B Out – Enhance your safety of flight, thanks to increased visibility afforded by NextGen's ADS-B
• Mode S Transponder with ADS-B Out and GPS – Include your GPS location in Mode S communications

Even though this tiny transponder will revolutionize the UAS industry in the next 5-10 years, it
will not be very beneficial at the present time.  Until all aircraft are equipped with ADS-B
transponders and receivers, UAV SAA systems must rely on other equipment to identify other
aircraft and take evasive maneuvers.

     Solving the problem with detection and avoidance of obstacles in today’s airspace is
SARA’s PANCAS.  PANCAS enables UAVs to meet FAA standards for detecting and tracking
aircraft.  The PANCAS uses an array of four lightweight acoustic probes and a custom-designed
digital-signal processor (SARA, 2012).  Eliminating the worry of an unbalanced or less then
airworthy UAS, the PANCAS uses windscreen technology and mounting hardware that eliminate
the effect of wind noise and aircraft vibration (SARA, 2012).  The digital-signal processing
board filters the acoustics, detects, tracks targets and produces an avoidance command that eliminates an imminent collision; simultaneously sending the respective data to the ground
control station via data downlink for operator awareness.  The total weight of the sensory
package is 250g and uses around 7 watts of 6-volt DC power.  An advantage with using an
acoustic sensory suite over other optical or radar based alert systems is:

• Offers all-weather collision avoidance capabilities
• PANCAS can be integrated into and Class UAV hardware
• Provides 360 degree (spherical) coverage
• Ability to detect objects day or night, through clouds or fog

     In summary, the combination of the Sagetech’s ADS-B transponder and SARA’s
PANCAS will allow small UAS to operate safely and efficiently within the NAS and airspace
around the world.

- Garrick


References

SAGETECHCORP.com, (2015). XP Family Of Transponders.  Retrieved from
http://www.sagetechcorp.com/unmanned-solutions/
SARA.com (2012). UAV Acoustic Collision-Alert System.  Retrieved from
http://www.sara.com/ISR/UAV_payloads/PANCAS.html