&lt;p&gt;&lt;strong&gt;&lt;u&gt;Motivation:&lt;/u&gt;&lt;/strong&gt; The long, successful history of scientific ballooning, coupled with tightening budgets, has led to a surge of interest in the scientific potential of high-altitude balloon flights. Powerful new payloads are being enabled by advancing technologies (e.g. in detectors, high-speed computers, composite materials, etc.), and these experiments will open new discovery spaces for science at a small fraction of the cost of a space mission. Access to much of this discovery space will depend upon the ability to both measure and control instrument pointing to high precision.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;u&gt;The Experiment:&lt;/u&gt;&lt;/strong&gt; The Precision High Altitude Star Tracker (PHAST) is an unpressurized, high-precision, high-bandwidth star tracker for night and day operations aboard scientific ballooncraft. It will enable pointing knowledge using commercial, off-the-shelf (COTS) hardware, and open-source code development. PHAST will take advantage of advances in detectors and ruggedized computers to design &lt;em&gt;without a pressure vessel&lt;/em&gt;. The low-cost design (&amp;lt;$70k) will be demonstrated and validated on a shared-ride balloon flight. Subsequently, &lt;em&gt;all drawings, design documents and software will be made available to the scientific community,&lt;/em&gt; &lt;em&gt;upon request, at no cost&lt;/em&gt;, broadening access to this burgeoning field.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;u&gt;Significance:&lt;/u&gt; &lt;/strong&gt;The high performance afforded by this tracker will permit the development of pointing control architectures of reduced complexity and cost due to the elimination of redundant motion transducers such as multiple fiber-optic rate sensing gyros.&amp;nbsp; PHAST will be designed without a pressure vessel, thus significantly reducing launch mass.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&lt;u&gt;Relevance to NASA:&lt;/u&gt;&lt;/strong&gt; The PHAST development and testing program will advance our understanding of the limits of pointing knowledge for ballooncraft. A timely and successful PHAST program will reduce cost and scientific risk for future balloon-borne missions and will be a &lt;em&gt;fundamentally enabling component&lt;/em&gt; for experiments pushing the envelope of ballooning capabilities.&lt;/p&gt;&lt;p&gt;1.2 Objectives and Expected Significance&lt;/p&gt;&lt;p&gt;By developing a new low-cost star tracker, with high angular precision, fast readout, and the capability of operating in both day and night conditions, we will be providing a new tool that promises cost savings for a wide range of future balloon missions. The capabilities provided by PHAST will be enabling for a number of potential science investigations.&lt;/p&gt;