Sample Project/Thesis Proposal

AE295A - Master’s Project Proposal
Presented to Dr. Nikos Mourtos
by Joshua Benton

September 1, 2011

Miniaturization, Integration, Analysis, and High-Altitude Flight Testing of a Scalable Autonomous GPS-Guided Parafoil for Targeted Payload Return

Background and Context

A parafoil is a special type of airfoil that is non-rigid and relies on dynamic pressure in flight to retain its shape. Due to their being non-rigid (and therefore foldable/packable), parafoils lend themselves very well to applications where controlled descent is required, but limited stowage is available for any sort of traditional wing structure. Also, compared to a traditional round parachute, parafoils have much greater directional control, improved glide performance, and the ability to adjust rate of descent by deforming the shape of the airfoil via control (or “toggle”) lines. These attributes of parafoils have made them very popular for human aerial descent, where the entire parafoil as well as a redundant backup can be stowed in a backpack and deployed rapidly when necessary.

In addition to manned applications, parafoils provide an attractive means to deliver a variety of payloads (e.g. military supplies, emergency equipment, food packages) to remote or inaccessible locations with a moderate degree of accuracy. This accuracy can be further improved by including an autonomous control system on the payload, which can effectively steer the parafoil in the same fashion as a human would, guiding it with a higher degree of precision to its landing point. In the last decade, several independent research efforts have focused on doing exactly this, providing complete, “intelligent” parafoil systems which autonomously steer themselves to a pre-defined landing point to deliver payloads (typically military supplies). Recent research efforts have improved accuracy of these systems from a few kilometers landing error to orders of magnitude less, depending on prevailing winds and initial drop altitude.

In my work at NASA Ames Research Center, we have identified a need to return small payloads (such as biological samples and small science experiments) from the International Space Station when desired or necessary, independently of the larger manned or supply vehicles which visit the Station with relative infrequency. Our proposed solution to this problem requires a means to guide the payload on the final leg of its journey to a selected landing point, with a high degree of precision, to aid in simple and immediate retrieval. The volumetric space available in the proposed return system eliminates rigid wing structures as a solution, and the gliding device for atmospheric descent must remain stowed until post-reentry. For these reasons, a parafoil system appears to be a very attractive solution.

In addition to ISS return applications, a well-developed autonomous parafoil system could be scaled larger and used for a number of other applications of interest to us, including the return of experiments from sub-orbital sounding rocket flights, which currently relies on slow, expensive, and frequently- unsuccessful water recovery from rented boats.

We have identified and worked with researchers at the Naval Postgraduate School in Monterrey, California, on a GPS-guided parafoil device they are developing. From our collaboration, we have built our own version of their GPS-guided return device, and have drop-tested it several times from low altitudes (~3000 ft. AGL) from an autonomous UAV. We have also collaborated with colleagues and a student team at the University of Idaho in 3 high-altitude balloon drops of the device, but two of these drops resulted in failures: the first, failure to separate from the balloon due to tangling; and the second, failure for the parafoil to fully inflate.

Problem Definition and Approach

Though we have already fabricated a prototype version of the autonomous parafoil return device we wish to use for the ISS, there are still many problems to solve to make it a practical and feasible solution:

1. Miniaturization of the autonomous control system: At present, the autonomous steering system that hangs below the parafoil is much too large volumetrically to fit within the confines of the ISS sample return system. A design of the physical structure and a more efficient packaging scheme are required to miniaturize the control system while still maintaining reliability and functionality. Smaller steering servos, more efficient line rigging and tensioning, and a smaller battery (while still maintaining design margin) are necessary to achieve this.
2. Characterization of high-altitude parafoil aerodynamics: Due to the nature of the application we wish to use this device for, it is advantageous to attain steering authority at as high an altitude as possible. In doing so, the maximum achievable ground range of targeted landing is improved. Unfortunately, the functioning of a parafoil relies on dynamic pressure to maintain its structural shape, and high-altitude use is problematic due to collapse and “nose-diving” of the parafoil over its payload. To understand the maximum glide capability we can achieve with a parafoil return device, the aerodynamics of the parafoil at high altitude/low pressure need to be characterized and validated, through analysis and testing. CFD, vacuum chamber testing, and another high-altitude balloon test in April 2012 will be used to analyze and validate the performance of the parafoil at high altitude.
3. Semi-rigidization of the parafoil structure: To eliminate the problem of parafoil collapse in low dynamic pressure, a method of self-deployment while maintaining packable stowage capability will be developed. A system of lightweight spring-like material will be added to the parafoil to make the structure “semi-rigid” and capable of maintaining its shape in a low pressure environment. Vacuum chamber testing will provide a means of validation prior to balloon flight testing of the integrated system.
4. Software porting of advanced guidance code to a newer control board: At present, our version of the Naval Postgraduate School’s GPS-guided parafoil device uses a different microprocessor board than their device. Previously, I have only programmed our board to steer the device to a specified heading, rather than to a specific set of landing coordinates. A ported version of the advanced code exists, but is written for an older version of our control board, and has yet to be tested/de-bugged. As part of the development effort, the ported code requires modification for compatibility with the new version of the control board, debugging, and ground-testing.

As noted above, an opportunity exists to flight-test the entire system from a high-altitude balloon in April 2012 with the collaboration of the University of Idaho’s RISE balloon team. This is the same team we have worked with in the past and have developed an excellent working relationship and understanding of all necessary procedures and protocols for safe flight testing of the parafoil system. During flight, the payload and balloon are tracked via redundant GPS transponders on the APRS radio network (amateur HAM band), enabling precise recovery of the payload systems.

Data returned from the flight testing includes HD video (one camera up-looking to the parafoil and another looking 45 degrees to the ground); a GPS flight track including time and altitude via the APRS network as well as the data-logging control board of the parafoil device; and three-dimensional component velocity and acceleration of the parafoil payload via an on-board IMU.