NASA's Global Hawk Pacific (GoPac) mission was the first mission using the Global Hawk Aircraft to study trace gases, aerosols, and the dynamics of the upper troposphere and lower stratosphere (Dunbar) using ten different exteroceptive instruments packages.
Instrument Packages
Airborne Compact atmospheric mapper – two spectrometers to measure how sunlight is absorbed and scattered throughout the atmosphere, and two high definition cameras to identify cloud types and features on Earth's surface.
High Definition Video System - forward looking, time lapsed imagery to identify cloud types and provide situational awareness for the plane, allowing the mission team to change altitude and course to investigate interesting atmospheric phenomena
Microwave Temperature Profiler – This radio meter detects naturally-occurring emissions of microwaves from oxygen molecules in the atmosphere a measurement that is translated in a picture of temperature field above, at, and below the flight path of the plane
Focus Cavity aerosol spectrometer and Nuclei-mode Aerosol sized spectrometer – These spectrometers measure these size distribution and abundance of aerosols. Aerosols play an important but incompletely understood role in climate change and atmospheric dynamics.
Ultra-high sensitivity aerosol spectrometer – This spectrometer looks down a column of air from the plane down to Earth's surface and measures the properties of light in the atmosphere to determine the concentration and size of aerosol particles.
Unmanned Aerial System Hygrometer – This advanced form of Hygrometer uses a continuous beam of laser light and two mirrors to sense the amount water present in the air. Water vapor is a potent greenhouse gas.
UAS Ozone- NOAA Unmanned Aerial System Ozone Instrument – The instrument directly samples the ozone in the atmosphere. Taking a sample of air from outside the aircraft and passing it between a lamp that emits ultraviolet (UV) radiation and a UV detector.
Unmanned Aerial System Chromatograph for Atmospheric Trace Species – the instrument collects air samples and uses two Chromatographers to separate out different molecules and detect the presence and amount of greenhouse gases, ozone-depleting gasses, carbon monoxide, and hydrogen.
Cloud Physics Lidar – This instrument pulses laser light into the atmosphere and observes the reflections – a process known as light detection and ranging, or LIDAR – to reveal the structure and brightness of clouds and aerosols.
Meteorological Measurement System – This package of instruments measures atmospheric temperature, pressure, air turbulence and the direction and speed of the winds (both horizontally and vertically) immediately around the plane. (Dunbar)
Global Hawks flight Characteristics
Global Hawk's maximum endurance of 42 hours and an on-station endurance of 24 hours, range of 3000 NM, and maximum altitude of 65,000 feet which is above significant weather occurrences (Ivancic and Sullivan) enables it to monitor the development of weather patterns in the Pacific Ocean. Electrical sensors are power by a 28 VDC, 186.3 A (5.2 KW) engine driven generator and a 115 VAC, 3-phase 400 Hz, 71.8 A/phase (8.3 KVA) hydraulic powered generator (NASA Armstrong…). The electricity created by these two generators power all of the electrical sensors on the Global Hawk.
Data Delivery
The Global Hawk mission used a 2 Mbps bidirectional link provided by the Ku-band satellite link. The system was capable of 50 Mbps but the cost to operate at such rates was prohibitive (Ivancic and Sullivan). The Global Hawk used a method to deliver data to ground stations called store and forward. The aircraft network uses a standard ethernet TCP/IP LAN with airworthy switches using 10/100T ports. The Link Module system acts as a router between the aircraft and Global Hawk Operation Center networks. Additionally, the Link Module system acts as an on-board file server and database as well as a wide-band router (Sorenson). The data collected from the instrument packages is stored internally within the aircraft and transferred to a ground station when signal coverage of the KU band supports data transfer. This way scientists can evaluate the data as close to real-time as possible. Data is backed up onboard in case of signal failure or corruption.
Recommended improvements
The data relay operation of the GoPac Global Hawk is heavily reliant on satellite coverage to transfer data to ground stations throughout its flight. The Global Hawk actually losses satellite signal coverage around 75 degrees north latitude and during satellite handoff. Because of the store and forward protocol the Global Hawk is able to retain data and transfer once satellite communications are restored. However, if the Global Hawk would be lost during this time data may not be recoverable.
One Possible solution is the use of smaller high endurance Unmanned Aerial Systems (UAS) that can act as network nodes with ground stations. These small UASs could also act as data system backups by also utilizing the same store and forward protocols that Global Hawk utilizes. If one of the UASs is lost the remaining UASs would still be able retain and transfer valuable data. Utilizing UAS platforms would decrease or eliminate the reliance on satellite network coverage therefore decreasing high operational data transfer costs.
References:
Dunbar, Brian. August 2013. GPAC 2010. Retrieved February 7, 2015 from http://www.nasa.gov/externalflash/Glopac/
Ivancic, William D.; Sullivan, Donald V. Delivery of Unmanned Aerial Vehicle Data (January 2011)
Sorenson, Carl. Global Hawk Payload Network Communications Guide. (November 2008).
NASA Armstrong Fact Sheet: Global Hawk High-altitude, long-endurance science aircraft. Feb 28, 2014). Retrieved February 7, 2015 from http://www.nasa.gov/centers/armstrong/news/FactSheets/FS-098-DFRC.html
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