PROGRESS AND RECENT DEVELOPMENTS IN THE GAINS PROGRAM C.M.I.R. Girz(1), A.E. MacDonald(1), F. Caracena(1), R.S. Collander(2), B.D. Jamison(2), R.L. Anderson(3), D. Latsch(3), T. Lachenmeier(4), R.A. Moody(4), S. Mares(5), J. Cooper(5), G. Ganoe(6), S. Katzberg(6), T. Johnson(7), B. Russ(7) (1)
NOAA Research - Forecast Systems Laboratory, R/FS1, 325 Broadway, Boulder, CO 80305-3328 USA, E-mail:
[email protected] (2) FSL/CIRA, R/FS1, 325 Broadway, Boulder, CO 80305-3328 USA, E-mail:
[email protected] (3) Basic Automation, 1101 Rainbow Way, Boulder, CO 80303 USA, E-mail:
[email protected] (4) GSSL, Inc., Hillsboro, OR 97124 USA, E-mail:
[email protected] (5) NMSU Physical Science Laboratory, Las Cruces, NM 88003-8002 USA, E-mail:
[email protected] (6) NASA Langley Research Center, Hampton, VA 23681-0001 USA, E-mail:
[email protected] (7) Aerospace Innovations, Hampton, VA 23681-0001 USA, E-mail:
[email protected]
ABSTRACT The GAINS (Global Air-ocean IN-situ System) network of long-duration, high-altitude vehicles is proposed as a means to provide critically needed in-situ observations worldwide. This need is increasingly apparent, for example, in the Arctic where there is growing concern around the shrinking of the ice cap and sea ice extent with concomitant decreases in habitat for animal and plant species. In the mid-latitudes, the sustainability of sufficient soil moisture in grain producing regions is questionable under several climate change scenarios. Preparatory steps using smaller balloons and prototype payloads have been taken toward demonstrating the GAINS balloon concept. The balloon envelope recovery system (BERS) has been tested and radio frequency interference, compatibility and distance checks of the prototype command and communication systems were performed. Electronic and mechanical systems have been integrated in preparation for a 48-h flight of an 18m diameter prototype. 1. INTRODUCTION The Global Air-ocean IN-situ System (GAINS) is predicated on the concept that the greatest danger of human-caused climate change - profound modification of regional climates - could be predicted with a larger and more directed program. The debate on global warming, framed on one side by those who see a long-term gradual warming of global surface temperatures, and on the other side by those who see only small and potentially beneficial changes, misses a very important possibility. A real threat is that the greenhouse effect may trigger unexpected climate changes on a regional scale--and that such changes may happen fairly quickly, last for a long time, and bring devastating consequences.
Reliable prediction of climate change is achievable within the early decades of the 21st century. Climate, unlike weather, is not inherently unpredictable beyond certain periods. The unpredictability of weather arises because a very small change in initial conditions (butterflies flapping their wings) can be shown to result in a large change at a later time (a few days). Climate, even with its feedbacks, is a forced system--it reaches an equilibrium base on energy balances such as radiation. Our regional climate models will be reliable when the estimates of forcing, such as that caused by carbon dioxide, and the estimates of feedbacks are properly accommodated. It is both feasible and compelling to design a comprehensive global program to determine the future forcing and feedbacks that will cause regional climate changes. The strengths and weaknesses of the current global observational system lie in the surface and upper air measurements and satellite observations that make up the system. Our surface stations and atmospheric sounding sites lie, for the most part, in the Northern Hemisphere and are situated primarily on land. The bulk of aircraft measurements of pressure, temperature, wind, and moisture are again over the Northern Hemisphere continents. Satellites have the advantage of perspective-a geostationary satellite continuously scans an entire hemisphere, while a polar orbiter looks at the entire Earth sequentially. The great strengths of satellites are counterbalanced by their great weakness--they are far from the substances (air, land, water) they are trying to measure. For example, the satellite microwave radiometer cannot measure the most important geophysical parameters needed to determine the fate of the Arctic ice: the detailed temperature, humidity, and wind in the boundary layer just above the ice, and the temperature and interaction of the water immediately below the ice. Scientifically, the best combination is often to use the satellite and an in-situ sensor (such as the
radiosonde) to arrive at the comprehensive picture needed for understanding. The realization of dramamatic and long-lasting changes to regional climate and the need to characterize the evolving geophysical systems call for a global obseving network with a strong component of in-situ measurements. We propose that straospheric balloons and aircraft be developed as the world-wide delivery system for such measurements. Computer simulations of network management [1] have indicated the difficulty of maintaining a regular spacing of shear - directed balloons in the winter hemisphere. Directional changes in the vertical wind around winter storms are small and thus unable to overcome the concentration of balloons in the developing baroclinic systems that bring rain, snow, strong winds, and cold temperatures at the surface. A solution using remotely operated aircraft in the midlatitudes and polar regions of the winter hemisphere (Fig. 1) is proposed. Above the polar circle, fueled ROAs will operate for days to weeks. In the midlatitudes where storms still make balloon control difficult, solar-powered ROAs will deliver sounding instruments with a longer inflight time of weeks to months. Superpressure balloons will operate from the subtropics of the winter hemisphere to the summer-hemisphere pole, fueled by the sun for months-long periods. All vehicles will be programmed to maintain a 10° latitude by 10° longitude spacing from adjacent vehicles. Preprogrammed instructions will be updated via satellite communications to correct for the clustering of vehicles by the ambient atmosphere. Both the ROA and balloon vehicles are designed to carry tens to hundreds of dropsondes for in-situ measurements. A complement of 500 meteorological sondes, 200 ocean sondes and 100 air chemistry sondes are envisioned for the payload of the balloon and the solar-powered ROA. (The fueled ROA would carry a smaller number of sondes). Data from these air and ocean sondes would, for example, provide defintive answers on heat flux at the air-ocean-ice interface for monitoring and predicting climate change at the poles. Balloons alone are proposed from the winter subtropics to the equator and for the Southern Hemisphere. Balloons will be more cost effective in the Southern Hemisphere, where the number of possible launch and recovery locations is smaller than in the Northern Hemisphere. Politically sensitive regions, where overflight by an uncontrolled balloon could be a problem, are virtually non-existent in this hemisphere. We also anticipate that the balloon vehicle will be less expensive than an ROA by an order of magnitude.
2.
GAINS PROTOTYPE DEVELOPMENT
In the development of prototype systems for GAINS, we have emphasized the balloon vehicle and the radio command and control systems. The GAINS superpressure balloon is leveraged from the WindStarTM program. The highly integrated balloon system involves a composite envelope, close-coupled payload, and a proprietary Balloon Envelope Recovery System (BERS). The balloon is a triple-layer design with a SpectraTM fabric envelope that encloses concentric polyurethane helium and air cells. Ambient air is pumped into and vented from the air cell to change the density of the balloon. The command and control package is a prototype, built from commercially available, off-the-shelf components. Insulation provides a controlled environment and for the longer flights, heaters are added so that the instrument compartment never cools below -40°C, and the batteries are kept warmer than 0°C.
Table 1: GAINS Flight Tests
Test Date Objective Balloon Payload Altitude Distance Duration (Mo/Yr) (diameter) (kg) (km) (km) (h) 12/99 Balloon PII-LF 7 8.5 4 01:00 termination (4.5 m) 04/00 Balloon PII-LF 7 8.8 193 04:14 descent rate (4.5 m) 05/00 Radio PII 9 6.7 59 01:33 termination (4.9 m) 07/01 Concept PIII 150 16.0 ~625 48:00 demo (18.3 m)
Flights with smaller GAINS prototype balloons (Table 1) were made in 1999 and 2000 to test BERS (discussed in the next section). A flight to confirm the radio frequency interference analysis was made in May 2000 (discussed in section 2.2). 2.1 Balloon Envelope Recovery System Traditionally, scientific balloon systems use a deployed parachute to suspend the payload below the envelope. At termination, the parachute is cut away from the balloon envelope, and descends separately with the payload. During this separation, shock loads of 7-10 g’s are induced on the payload as the parachute rapidly snatches the payload in a fully open configuration. Unlike the high-shock loading created by the traditional flight termination, BERS termination loads are less than 1 g and the entire balloon system descends as one unit. BERS takes advantage of the composite envelope’s porous structure transforming this shell into a parachute on descent. Payload suspension lines are spaced evenly around the circumference of the shell and attached at reinforced seams. Flight terminations are executed by tearing out panels in the gas-tight internal membranes
with a rip line and allowing the air and helium to escape through the porous shell. The portion of the envelope below the suspension line attachments is not rigidly connected to the payload. As gas continues to diffuse throughout the shell, the descent velocity increases and the dynamic pressure on the lower portion of the envelope forces it upward into the upper section still attached to the payload. During this process, the envelope transforms from a sphere into a hemispherical parachute. This critical transformation was tested with flights of the 4.5m diameter PII-LF balloon in December 1999 and April 2000. The December test was terminated by a timer at an altitude of about 8.5 km. Since this altitude was below the balloon’s float altitude, the balloon was not a fully inflated sphere when its helium was released. Consequently, the balloon shell did not transform into a parachute; it was ineffective for deceleration and streamered behind the payload as the velocity increased in the last kilometer AGL. Descent was too fast at ~ 3 m s-1. This equipment was recovered within 4 km of the launch location. The PII-LF balloon was once again the test balloon for the April flight. The rip panel was redesigned to open a larger area. Approximately four minutes after reaching float altitude (8.8 km), the balloon was terminated by a timed release of the rip mass. There was a small initial climb, the shell became a fairly well formed hemisphere, and system slowly descended at 0.4 m s-1. After 30 minutes, the top valve was opened by radio command, and descent rate increased to 1.1 m s-1. Although the balloon landed safely, it was clear that descent speed needed to be increased to more quickly remove the balloon from domestic airspace. 2.2 Radio command and control The PIII configuration carries a number of radio frequencies in the primary and backup command and communication systems. On 18 May 2000, we flew a subset of the PIII radios (Table 2) to qualify the FSL radio termination device. Of particular concern was desensitization of the termination antenna by either the aircraft transponder or a real-time video (RTV) frequency. A slight modification of the rip-line bladder destruct system was made and BERS descent rates were again measured.
Table 2: Transmitters flown on 18 May 2000
Transmitter Purpose LOS Telemetry Real-time communication of flight data (to ground) and termination command (to balloon) Argos Backup (satellite) transmission of balloon position Transponder FAA traffic control RTV Onboard real-time video with balloon in field of view Recovery Beacon High power, short-lived beacon for recovery Animal Beacon Low power, long-lived beacon for recovery GSSL Terminate Backup termination command Launched from the Tillamook Balloon Facility at 15:33 PDT, the balloon was in the air for 1 hour 40 minutes, attaining a maximum float altitude of ~6750m (Fig. 2) and traveling 57km northeast from Tillamook, Oregon (Fig. 3). The payload consisted of the FSL primary controller, containing LOS telemetry, radio terminate, and GPS location. The balloon also carried: backup communications (through the Argos satellite); an aircraft transponder for FAA control; an upward looking realtime video (RTV) to view the transformation of the SpectraTM balloon during termination; a high powered, short-lived radio beacon for recovery; a low powered, long-lived animal beacon for recovery; and the GSSL standard terminate package with back-up termination capability by radio command and timer. Once it was confirmed that the GPS, telemetry, aircraft transponder, and RTV were working well, the balloon was terminated at ~16:10 PDT by a rip line destruct device commanded by radio. A safety timer automatically opened the helium vent at 16:35 PDT. The test was an unqualified success. All transmitters (GPS, FSL telemetry and radio terminate, RTV) worked as planned, and a command on the FSL LOS radio frequency terminated the flight. A slight modification of the rip-line bladder destruct system improved the balloon’s descent time. Maximum descent rates (between 3.5 - 4.0 m s-1 ; see Fig. 4) were 3 to 6 times greater than the April test and were adequate to satisfy our descent rate requirements. Launch, chase and recovery procedures were honed with this test. The balloon landed in a grassy area and was retrieved less than an hour after it hit the ground, aided by the chase aircraft directing the recovery team to the landing spot.
3.
PROTOTYPE-III FLIGHT
3.1 Objectives of the flight The fourth flight scheduled for July 2001 (Table 1) is a demonstration of the superpressure balloon using a onesixth-scale vehicle (Fig. 5). The objectives of this test are to (1) float the 18m diameter (PIII) balloon with a maximum payload at an altitude of 16.5km, (2) acquire performance data on the superpressure balloon over two day-night cycles, (3) acquire data on solar power generation, (4) fly the FSL payload with supplemental systems from collaborators, (5) exercise the launch, chase and recovery systems, (6) recover the balloon and payload, and (7) test the GPS glistening experiment on a balloon platform. The PIII flight will be the first to test GAINS components that have been mechanically and electronically integrated, and also to fly the payload in the closely coupled torus (Fig. 6). Because the torus requires that the balloon be fully inflated, the air bladder will have a slight superpressure at launch, and this air will be vented during ascent. The PII-LF and PII flights have been daytime flights of up to 4-h duration. During the PIII flight, the envelope will be instrumented with pressure and temperature sensors to monitor the effect of incoming solar and outgoing longwave radiation on the vehicle. Altitude will be determined from both a barometric sensor and GPS. The balloon will be launched from the small balloon facility in Tillamook. A chase aircraft will follow the balloon to monitor it visually, keep it in line-of-sight (LOS) radio contact at all times, and to terminate the flight. Upon termination, the aircraft will direct ground vehicles to the landing location for balloon and payload recovery. 3.2 Payload The FSL payload consists of a primary controller with real-time LOS communications. The primary controller acquires data from the onboard sensors and transmits them through an LOS link. Measurements are made of the balloon envelope’s internal environment (superpressure, temperature), and the instrument package (temperature, battery voltage, battery current, solar cell current). Balloon position obtained from an onboard GPS (latitude, longitude, altitude, number of satellites) is also telemetered. While this first flight will demonstrate neither dropsonde capability nor altitude control, in-situ data at float altitude will be taken. Direct measurements of the ambient environment (acquired from altimetry, temperature, and relative humidity sensors) will be made; vector winds at altitude will be computed from GPS positions. The ARGOS satellite is a backup communications link, but only a minimal data set will be transmitted. Because there can be up to a 12-h delay in acquiring ARGOS
data, their usefulness is limited to times when the LOS telemetry cannot be obtained. For instance, on an earlier flight, ARGOS positions were received when the balloon was on the ground and LOS telemetry was no longer operating. Had the LOS signal been lost in the last half hour of the flight, these ARGOS positions would have been critical in directing the recovery crew to the payload. Backup position information is available from the New Mexico State University/Physical Science Laboratory (PSL), and Edge Of Space Science, Inc., (EOSS) packages. Both PSL and EOSS acquire and transmit GPS position, the latter in the amateur radio band. Doppler location information will be computed in the ARGOS data stream, too. Safety of the domestic airspace is of the utmost importance in executing GAINS flights. Air traffic control personnel will be cognizant of the balloon’s position at all times through signals from an onboard aircraft transponder. Additionally, during ascent and from termination through landing, the crew of the chase aircraft will communicate position information in the Very high Omni Range (VOR) format to the Air Route Traffic Control Center (ARTCC). There are multiple termination modes for this flight. Primary termination of the flight is a rip line on the helium bladder under the LOS radio command of the FSL device on the chase aircraft. Backup to this is radio command from the LOS GSSL termination device in the chase aircraft. If radio modes to activate the rip line destruct device fail, the secondary termination mode is activated by venting helium through the top valve on the balloon. This is triggered by an “out-of-box” or “out-oftime” determination from the FSL microprocessor. A prelaunch forecast of balloon trajectory is used to define a geographic box and a surrounding “frame” beyond which the balloon is not allowed to stray. If a fixed number of balloon positions, for instance 10, are located outside the box in the frame (or beyond), the FSL microprocessor opens the vent. Likewise, if elapsed flight time reaches a predetermined length, the vent is opened. Backup termination on the helium vent is a radio command on the ground from the LOS PSL C3 system in the recovery vehicle. A GPS glistening experiment, which has been flown on research aircraft [2], will undergo its first test from a balloon platform. The GPS instrument consists of a PC104 bus stack consisting of a Pentium processor and a specially modified GPS dual front-end receiver in a rugged enclosure, and two GPS antennas. One antenna oriented upward receives direct signals from GPS
satellites, and the other with reversed polarity and oriented downward receives signals reflected from the surface of the earth. This technology was initially used to investigate the measurement of sea surface roughness by performing a cross-correlation between the diffusely reflected signal and the pseudorandom noise that underlies all GPS transmissions [2]. The current version of the GPS instrument to be flown on the balloon has been redesigned to be more compact, use less power, and withstand a greater variation in environmental conditions than previous versions. This instrument has also incorporated a new data collection mode and other software modifications needed to begin the exploration of another potential use of the reflected GPS signal, which is the remote detection of ground surface soil moisture conditions. The new data collection mode was developed to track 5 direct satellites (providing a continuous navigation solution) and multiplex the remaining 7 channels to track the reflected signal of the satellite tracked in channel 0. The new software mode has been shown to increase the signal-to-noise ratio of the collected data and enhance the science return of the instrument. While there is no coordinated effort on this mission to compare measurements with ground truth, the testing of the instrument in a relevant environment along with the potential qualitative data expected will provide valuable information with which to proceed toward further development of a soil moisture measurement capability. Flight status is that the mechanical and electronic systems have been integrated into the torus (Fig. 6). In preparation for the PIII flight, distance and radio interference checks were made in June 2000 with the ground recovery vehicles and the chase aircraft. The torus was hoisted (Fig. 7) off the ground while the base and recovery vehicles tested signals from 8 to 48km away. The aircraft flew at 3.1km at 8 to 48km distances. All vehicles confirmed receipt of telemetry at their ground stations, and receipt of destruct signals by the balloon from them.
Thanks to N. Fullerton and M. Govett for their helpful comments in reviewing the paper, and to B. Johnson for finalizing the text and graphics.
6. REFERENCES 1. Girz C.M.I.R. and MacDonald A.E. Global Air-ocean IN-situ System (GAINS), Proceedings 14th ESA Symposium on European Rocket and Balloon Programs and Related Research, European Space Agency, 1999. 2. Garrison J. L. and Katzberg, S. J. The Application of Reflected GPS Signals to Ocean Remote Sensing, Fifth International Conference on Remote Sensing for Marine and Coastal Environments, San Diego, California, Oct. 1998.
Fig. 1. The GAINS global observing network comprising fueled remotely operated aircraft (ROA) at the winter pole, solar-powered ROA in the winter midlatitudes, and superpressure balloons at the remaining locations.
4. CONCLUDING REMARKS GAINS continues to make progress with the balloon vehicle. Development and testing has begun on the next critical element, namely a pump to control balloon altitude. For flights longer than 48 hours, battery weight becomes an issue. Development of a solar system to meet the GAINS power needs is essential.
5.
ACKNOWLEDGMENTS
Fig. 2. GPS altitude trace for the 18 May 2000 test flight.
Fig. 3. Flight track for the 18 May 2000 test flight.
Fig. 6. Integration of the electronic packages into the torus for the 48-h flight.
Fig. 4. Vertical velocity trace for the 18 May 2000 test flight.
Fig. 7. PIII torus suspended during the radio distance check.
Fig. 5. The GAINS PIII, 60-ft diameter balloon inflated in the GSSL small balloon facility in Tillamook, OR.
