2016 Scientific Ballooning Technologies Workshop Title The APL Balloonborne High Altitude Research Platform (HARP) Author P. Bernasconi, D. Adams, S. Arnold (JHU/Applied Physics Laboratory) Abstract The Johns Hopkins University Applied Physics Laboratory (APL) has developed and demonstrated a multi-purpose stratospheric balloon-borne gondola known as the High Altitude Research Platform (HARP). HARP provides the necessary electrical power, mechanical supports, thermal control, and data transmission capability for operational support of almost any form of high-altitude scientific research equipment. APL, now well into its second decade of developing and operating scientific balloon missions, builds and operates HARP which has flown on five occasions first as Flare Genesis from Williams Field in Antarctica in 2000 and most recently as the Balloon Observation Platform for Planetary Science (BOPPS) from Fort Sumner, New Mexico in 2014. HARP’s sixth mission will be known as Stratospheric Terahertz Observatory 2 (STO2) originating from Antarctica in December 2015. The gondola is customized to match the required payload mechanical support, thermal control, articulation and pointing needs. A light-weighted structure, capable of supporting Ultra-Long Duration Balloon (ULDB) flight is available. ULDB missions originating from Antarctica can operate for more than 100 days. The structure, composed of an aluminum framework that is connected by machined aluminum fittings is designed for easy transport and field assembly while providing ready access to the payload and supporting avionics. Scientific research payloads as heavy as 600 kg (1322 pounds) and requiring 500 Watts electrical power can be supported. The gondola comprises all subsystems required to support and operate the science payload, including both line-of-sight (LOS) and over-the-horizon (OTH) telecommunications, the latter provided by Iridium Pilot systems. For multi-day missions solar panels are used to generate electrical power. For single-day missions batteries are used to provide electrical power. The avionics design is primarily single-string; however, use of ruggedized industrial components provides a high level of reliability. The avionics features a Command and Control (C&C) computer and a Pointing Control (PC) computer housed within a single unit. The avionics operates from ground pressure to 2 Torr and over a temperature range from -30 C to +85 C. Science data is stored on-board and also flows through the C&C computer where it is packetized and encoded prior to real-time downlink. The telecommunications subsystem is capable of LOS downlink in excess of 3000 kbps and OTH downlink in excess of 250 kbps. The pointing control system (PCS) has high heritage and provides three-axis attitude stability to 1 arcsec or better in both daytime and nighttime operating environments. The PCS has multiple modes of operation that can be used to aim at a fixed point for science observations, to perform science scans, or to track an object ephemeris. This paper provides a detailed description of HARP, summarizes its performance on prior flights, describes its use on upcoming missions and outlines characteristics that can be customized as needed to meet the needs of the high altitude research community. 2016balloontech.umn.edu