- Email: [email protected]
Results of the recent GAINS flight test
Advances in Space Research 33 (2004) 1642–1647 www.elsevier.com/locate/asr
Results of the recent GAINS flight test C.M.I.R. Girz a,*, A.E. MacDonald a, R.L. Anderson b, T. Lachenmeier c, B.D. Jamison a,d, R.S. Collander a,d, R.B. Chadwick a, R.A. Moody c, J. Cooper e, G. Ganoe f, S. Katzberg f, T. Johnson g, B. Russ g, V. Zavorotny h a
h
National Oceanic and Atmospheric Administration, Forecast Systems Laboratory, 325 Broadway, Boulder, CO 80305-3328, USA b Basic Automation, 11011 Rainbow Way, Boulder, CO 80303, USA c Global Solutions for Science and Learning, Inc., 284 NE Tralee Ct, Hillsboro, OR 97124, USA d Cooperative Institute for Research in the Atmosphere, Colorado State University, Ft. Collins, CO 80523-1375, USA e New Mexico State University Physical Science Laboratory, P.O. Box 30002, Las Cruces, NM 88003, USA f National Aeronautics and Space Administration, Langley Research Center, Mail Stop 328, Hampton, VA 23681, USA g Aerospace Innovations, 4822 George Washington Memorial Highway, Suite 200 Yorktown, VA 23692, USA National Oceanic and Atmospheric Administration, Environmental Technology Laboratory, 325 Broadway, Boulder, CO 80305-3328, USA Received 19 October 2002; accepted 2 June 2003
Abstract A demonstration flight of the Global Atmosphere-ocean IN-situ System Prototype III balloon occurred on 21 and 22 June 2002. The 18-m diameter PIII superpressure balloon carried a 147-kg payload and floated above 15 km for 10 h. This paper discusses the performance of the balloonÕs systems over the 15.5-h flight. Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Scientific ballooning; GAINS; GAINS flight test
1. Introduction The Forecast Systems Laboratory of the National Oceanic and Atmospheric Administration has been working toward a global observing system of long duration platforms called Global Atmosphere-ocean INsitu System (GAINS). The goal of the GAINS aims to provide components for a comprehensive, global, environmental measuring system. GAINS is envisioned to be part of an Earth-observing system of 400 regularly spaced platforms in the lower stratosphere that deliver environmental sondes to remote regions. The in-situ measurements of the atmosphere and ocean, and in-situ collection of air chemistry samples planned for GAINS are needed to address issues critical to global change and environmental prediction. These measurements will complement the existing surface, upper-air, and space*
Corresponding author. Tel.: +1-303-497-6830; fax: +1-303-4973329. E-mail address: [email protected] (C.M.I.R. Girz).
based observing systems, and together they can form the basis from which sound decisions can be made for the 21st century and beyond. A heterogeneous mix of superpressure balloons and remotely operated aircraft (Girz et al., 2002) maximize flexibility in targeting observations, while minimizing operational costs. Balloons that drift with the wind can populate a global network through a careful choice of float altitude. Moreover, a degree of direction control is possible if the balloon can take advantage of shear vertical wind that is floating the balloon at the altitude where the winds are most advantageous for its future location. For example, if winds at a lower altitude are more favorable for positioning the balloon to a specific point, mass can be added to the GAINS balloon by pumping external air into the internal air cell. This addition of mass increases the density of the balloon (since the outside envelope of the balloon maintains a constant volume), and the balloon sinks. The converse also pertains. The drawback is that shear direction can severely limit balloon placement for certain areas of the globe
0273-1177/$30 Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2003.06.021
C.M.I.R. Girz et al. / Advances in Space Research 33 (2004) 1642–1647
during certain seasons. On the other hand, although remotely operated aircraft can fly for days to weeks and stay on station or move to a targeted location, there is a high cost associated with these systems. Given a specified payload mass, the proposed balloon technology is a comparatively inexpensive delivery system. A number of tests (Girz et al., 2002) of the GAINS sub-systems were performed between 1998 and 2001. Flight tests qualified the environmental sensors and radios, as well as the mechanical and electronic termination components. A theoretical assessment and testing on the ground assured electromagnetic compatibility among the primary and backup transmission and termination radios. Power and instrumentation systems were qualified in an environmental chamber. Successful completion of these tests paved the way for the demonstration flight of the Prototype III (PIII) balloon on 21 and 22 June 2002. This paper presents the results of this recent GAINS flight.
2. PIII demonstration test The objectives of the demonstration test focused on the physical sub-systems of (1) the balloon vehicle, (2) onboard and environmental sensors, and (3) radio communications systems. There were additional objectives involving (4) flight support and (5) aviation safety procedures, and (6) for the additional experiments carried in the payload.
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internal state of the balloon (temperature and superpressure), and the state of the payload (temperature and battery voltage). Data were also gathered from a rudimentary solar power system, which was not used to supply power for any systems on the flight. 2.1.3. Radio communications Six communications systems transmitted in real time, and three provided redundant capability to terminate the flight. The objectives were to gather data from one over-the-horizon and five line-of-sight systems, and to terminate the balloon by radio command. 2.1.4. Flight support These objectives were to exercise the flight support procedures for balloon inflation, free lift weigh off, payload preparation, launch, balloon tracking from the air and on the ground, in-flight trajectory updates, descent vector calculation, and balloon recovery. 2.1.5. Aviation safety The objectives were to comply with the Federal Aviation Administration regulations on Free Balloons (FAR101) and to achieve a safe test through domestic controlled air space. 2.1.6. Additional experiments The objective was to operate the NASA/Langley Research Center experimental GPS reflection instrument on a balloon to derive wave velocity over the ocean and soil moisture over land.
2.1. Objectives of the Balloon’s sub-systems 2.2. Balloon system 2.1.1. Balloon vehicle The balloon vehicle objectives were the principal goals of the flight. Previous tests had flown the smaller (4.5-m diameter) PII vehicle for up to 5 h. Under this test, we wanted to demonstrate the integrity of the 18-m diameter PIII balloon at a nominal float altitude of 16 km for 48 h. Since this was the maiden flight of the PIII, it was important to observe the balloon achieve pressurization during ascent and under solar heating, to watch for a small depressurization during sunset and subsequent long-wave radiative cooling over night, followed by solar heating once again at sunrise on the second morning. A repetition of this cycle through the second 24-h period was desirable. Furthermore, on termination we wanted to exercise the balloon envelope recovery system (BERS), that is, the transformation on descent of the spherical balloon into a parachute. 2.1.2. Onboard and environmental sensors The balloon and payload were instrumented with several sensors to characterize the balloonÕs behavior. These sensors measured the ambient environment (temperature, pressure, and relative humidity), the
Manufactured by GSSL, Inc., of Hillsboro, OR, the 225-kg PIII balloon is a triple layer superpressure balloon. The outer envelope is a SpectraTM fabric sphere. Inside, two concentric polyurethane bladders contain helium and air. A toroidal fiberglass gondola carried the 150-kg payload containing packages from four organizations. The FSL payload included GPS for locating the system, two independent radio- and software-controlled termination methods, and environmental sensors to monitor balloon performance. The payload also contained two backup location and termination units from the Physical Science Laboratory (PSL) of New Mexico State University and from GSSL, redundant locating capability based on a design adapted from the Edge Of Space Science, Inc. (EOSS) of Denver, CO, and a GPS reflection experiment from NASA/Langley. The FSL, GSSL, PSL and EOSS line-of-sight communications transmitted GPS position on four radio frequencies at varying time intervals. Position was also determined from satellite by the Argos system. Argos receivers on the National Oceanographic and Atmospheric Administration (NOAA) series polar orbiting satellites and a
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transmitter onboard the balloon produce a location of the platform by using the Doppler effect. An amateur TV was programmed to transmit upward- and downward-pointing images intermittently during the flight to monitor the balloon, and continuously after termination to record the performance of the BERS. An onboard transponder was installed to ensure safe operation of the balloon through domestic airspace by keeping the balloon under active air traffic control. The balloon was tracked by an aircraft that recorded transmissions from the balloon and instigated termination of the flight. Mobile ground stations, positioned at the launch and recovery locations, were also capable of recording data and terminating the flight. 2.3. Launch configuration For maximum system stability, the GAINS superpressure balloons are fully inflated at launch. Helium in the innermost gas cell is filled through the EV-13 valve on the top fitting. Through a similar valve on the bottom fitting, the gas cell is filled with sufficient air to fully inflate the SpectraTM sphere. The lower valve was not under radio control for this test, and remained open to vent air as the helium bubble expanded on ascent. The upper valve was radio controlled for termination as described above. 2.4. Trajectory forecasts A suite of trajectory forecast tools has been developed which use winds from climatological soundings, radiosondes, and numerical weather prediction models. In planning for the flight, expected trajectories are computed based on climatological winds from the closest National Weather Service (NWS) station. The database contains soundings taken between 1946 and 1999. Data are averaged for each synoptic time (0000 and 1200 UTC) for every day of the year. Fig. 1 shows
trajectories for selected days in June. One constraint for the flight was that the track remain within the borders of the US; if the balloon had approached the Canadian border, it would have been terminated. The climatological trajectories for 15 and 20 June show that the bulk of the 48-h flights for these days could be completed within the US. Between 24 and 6 h before launch, trajectory forecasts are generated from numerical weather models and NWS soundings to assess the suitability of launch conditions vis-a-vis the balloon track. During the flight, trajectories are again updated from NWS soundings or weather models. Short-term (1–3 h) wind forecasts from the operational rapid update cycle (RUC) model are especially useful just before launch and termination. Collander and Girz (2004) describe these products in more detail, and discuss in particular the real-time trajectory forecasts that were made for this flight.
3. Results of the PIII demonstration test The GAINS test was launched from Tillamook, OR, at 8:35 am local time (1535 UTC) in dead calm under a marine stratus layer. After oscillating through the cloudy layer, the balloon climbed to a maximum altitude of 17.4 km. A tracking aircraft kept the balloon within radio line of sight at all times during the 362-km long flight, and personnel on board coordinated the flight with FAA air traffic control. Two additional vehicles tracked the balloon from the ground and recovered the payload. At sunset the balloon began to accelerate downward and landed at 0003 UTC on 22 June south of The Dalles, OR. Fig. 2 shows the track of the flight. The soft landing caused no damage to the payload capsule, and minimal damage to the wheat field where it landed. The entire system was removed from the landing site and returned to Tillamook, OR, the next day. Position, balloon state, and environment data shown below were
Fig. 1. Trajectories forecast from average winds at Salem, OR, for selected days in June for a 48-h flight at 15.8 km. Wind statistics are in knots.
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Fig. 2. Track of the GAINS balloon on 21 and 22 June 2002.
recorded in the groundstations in the tracking and recovery vehicles from the real-time transmissions. 3.1. Climb out The no-wind condition at the surface made this an easy launch. However, the calm at the surface was the result of a 1.1-km deep inversion, which also produced a marine stratus cloud between 0.4 km AGL and the top of the inversion. This inversion inhibited initial ascent. The balloon took 50 m to clear the inversion (see the spike at 16.4 UTC in Fig. 3), and during that time, the balloon drifted off the coast (Fig. 2). 3.2. Float Once free of the inversion (Fig. 4), the balloon accelerated, ascending with an average velocity of 1.8 m s 1 to a maximum altitude of 17.4 km. We expected the balloonÕs internal pressure to be 40 hPa at float. But maximum internal pressure of 10 hPa occurred about an hour before maximum altitude was reached. Internal pressure
Fig. 4. Vertical trajectory in meters (dark curve) and superpressure in Nt m 2 (light curve) as the balloon climbs to float altitude. Time is in decimal hours.
dipped to 7.5 hPa, then shortly after reaching maximum altitude, superpressure dropped to 3 hPa and did not recover. The balloon floated at 16.5 km for 9 h. 3.3. Descent With solar heating waning, internal density increased and the balloon began a slow descent at )0.5 m s 1 . (Fig. 5). At 0600 UTC, the balloon appeared to selfterminate and rapidly dropped with velocities between )1.0 and )3.7 m s 1 . Several times during descent, the balloon decelerated, apparently as a result of the envelope transforming into a parachute. This especially appears to be the case in the final 2 km, when the balloon steadily decelerated from )4 m s 1 to zero. 3.4. On the ground
Fig. 3. Vertical trajectory in meters (dark curve) and vertical velocity in m s 1 (light curve) during the initial 1.5 h of the test. Time is in decimal hours.
The balloon had been tracking to the east–northeast during most of the time at float. On the basis of wind forecasts for the late-afternoon float altitude, we had
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4. Discussion
Fig. 5. Descent trajectory in meters (rectangles) and vertical velocity in m s 1 (diamonds) during descent. Time is in decimal hours, and is not rolled over past midnight. Sunset occurs at 28:00 UTC.
deployed the ground teams to Yakima, WA. As the balloon lost altitude after sunset, however, it descended into easterly then southerly winds. The aircraft team tracked the balloon to the ground, landed the plane, and then drove to the landing site to secure the balloon until the team could arrive from Yakima the next morning. At the landing site, water was observed inside the balloon. The lower valve and fitting were also coated with ice. It was estimated that the moist hangar air that filled out the sphere added up to 40 kg to the mass of the balloon. As the balloon rose, this water vapor condensed onto the inside surfaces of the gas cell. Undoubtedly some dripped out of the open lower valve before the balloon reached the freezing level at 3.5 km. However, an indeterminate amount remained inside the balloon during the entire flight. 3.5. GPS reflection experiment Hardware for the GPS reflection experiment performed well. This experimental technique has been proven for computing sea surface winds on both aircraft and balloon platforms. Given the trajectory offshore, the data include an open ocean segment. The version of the instrument flown on the GAINS balloon is a new compact version of the instrument that fits into a 20 cm 15 cm 13 cm enclosure, and a primary goal was to get flight experience for the new configuration. Of particular interest for this flight was the projected terrestrial flight track, which provided data to test the potential of computing soil moisture from the hardware. The balloonÕs track included a moist surface in western Oregon, and a very dry regime east of the Cascades. Four operating modes were tested in sequence during the flight, each mode for 30 min at a time. Of the segments recorded, 34 contained valid data. Data are currently under analysis.
Objectives for the onboard sensors, radio communications, and flight support were met. Data from the onboard sensors that were transmitted through the radio communications systems have been shown in the previous Section 3. Not shown are the 14 position reports from Argos made between shortly after launch at 1612 UTC on 21 June and while the balloon was being secured on the ground at 0844 UTC on 22 June. Space limitations do not permit discussion of the additional parameters that were measured. Airspace safety objectives were also successfully met. Although the balloonÕs aircraft transponder failed, air safety was never an issue due to coordination with air traffic control and position reporting by personnel on the aircraft. This was especially important at launch and during the first hour of the test. At 9:00 am that morning, approximately 20 military aircraft were running training sessions just offshore from Tillamook, causing concern during the slow initial ascent. Three circumstances contributed to the slow ascent. The hangar air used to fill out the balloon was colder than the atmosphere into which the balloon was launched; we estimate a 4–6 °C difference. Second, because the system was significantly over its weight budget, the balloon was launched with minimal free lift. Consequently, there was little lift to accelerate through the cloud. Third, while the balloon was bobbing in the warm cloud layer, the envelope picked up moisture. This additional mass further depressed the balloonÕs free lift. The internal gases eventually came to equilibrium with the ambient air, and presumably, some of the excess external moisture was lost at altitude through sublimation. Balloon performance objectives summarized in Table 1 show that several objectives, such as ascent rate, descent rate, and float altitude, were completely met; however, the objectives related to balloon integrity (time at float, superpressure, and day–night altitude changes) were only partially met. It is more difficult to explain why the balloon did not pressurize. As Fig. 4 shows, pressurization stopped suddenly just as float altitude was reached. If the helium cell experienced a rupture at that time, the loss of mass
Table 1 Target and achieved values of balloon performance measures Parameter Ascent rate Float altitude Time at float Descent rate Superpressure Day–night altitude change
Target
Achieved 1
2.5 m s 16.5 km 48 h <3.8 m s 1 40 hPa 160–330 m
2.0–3.0 m s 1 15.5–17.4 km 15 h 32 min 4.1–2.5 m s 1 10 hPa Descended to surface
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would accelerate the balloon; this, however, was not seen. Vertical velocity actually slowed from 2.3 m s 1 just before maximum superpressure to 1.8 m s 1 immediately after. A final analysis of balloon performance will be completed in the future.
bers, and awaits confirmation of these results with testing at altitude. With the successes of the PIII demonstration test and the advances in developing a pump, GAINS is right on track.
5. Summary
Acknowledgements
The maiden flight of the 60-ft diameter GAINS Prototype III (PIII) balloon on 21 June 2002 met several development objectives including launching the PIII balloon, floating it at altitude for >8 h, transforming the balloon envelope into a deceleration device, achieving a safe descent rate, tracking the balloon from an aircraft, forecasting balloon trajectory before launch, updating balloon landing position during flight, and recovering the balloon and payload. The two critical technologies for the GAINS sheardirected balloon are the superpressure balloon vehicle and the pump for controlling density. This flight indicates the feasibility of a superpressure balloon of the WindStar design to pressurize at altitude, and thus is a first step in confirming the possibility of superpressure balloons of this design. Since development of the GAINS pump began two years ago, an experimental pump has been qualified in two environmental cham-
The PHI demonstration flight benefited from the advice and support of a number of individuals in the years leading up to this point. The GAINS team gratefully acknowledges the contributions of the following persons: V. Lally, A. Bedard, B. Johnson, D. Latsch, N. Abshire, S. Nahmen, M. Shannahan, C. Bliss, and B. Keppler. Thanks to N. Fullerton for a careful editorial review.
References Collander, R.S., Girz, C.M.I.R. Evaluation of balloon trajectory forecast routines for GAINS, Adv. Space Res., 2004 (doi:10.1016/ j.asr.2003.05.016). Girz, C.M.I.R., MacDonald, A.E., Caracena, F., Anderson, R.L., Lachenmeier, T., Jamison, B.D., Collander, R.S., Weatherhead, E.C. GAINS – a global observing system. Adv. Space Res. 30, 1342–1348, 2002.
Results of the recent GAINS flight test C.M.I.R. Girz a,*, A.E. MacDonald a, R.L. Anderson b, T. Lachenmeier c, B.D. Jamison a,d, R.S. Collander a,d, R.B. Chadwick a, R.A. Moody c, J. Cooper e, G. Ganoe f, S. Katzberg f, T. Johnson g, B. Russ g, V. Zavorotny h a
h
National Oceanic and Atmospheric Administration, Forecast Systems Laboratory, 325 Broadway, Boulder, CO 80305-3328, USA b Basic Automation, 11011 Rainbow Way, Boulder, CO 80303, USA c Global Solutions for Science and Learning, Inc., 284 NE Tralee Ct, Hillsboro, OR 97124, USA d Cooperative Institute for Research in the Atmosphere, Colorado State University, Ft. Collins, CO 80523-1375, USA e New Mexico State University Physical Science Laboratory, P.O. Box 30002, Las Cruces, NM 88003, USA f National Aeronautics and Space Administration, Langley Research Center, Mail Stop 328, Hampton, VA 23681, USA g Aerospace Innovations, 4822 George Washington Memorial Highway, Suite 200 Yorktown, VA 23692, USA National Oceanic and Atmospheric Administration, Environmental Technology Laboratory, 325 Broadway, Boulder, CO 80305-3328, USA Received 19 October 2002; accepted 2 June 2003
Abstract A demonstration flight of the Global Atmosphere-ocean IN-situ System Prototype III balloon occurred on 21 and 22 June 2002. The 18-m diameter PIII superpressure balloon carried a 147-kg payload and floated above 15 km for 10 h. This paper discusses the performance of the balloonÕs systems over the 15.5-h flight. Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. Keywords: Scientific ballooning; GAINS; GAINS flight test
1. Introduction The Forecast Systems Laboratory of the National Oceanic and Atmospheric Administration has been working toward a global observing system of long duration platforms called Global Atmosphere-ocean INsitu System (GAINS). The goal of the GAINS aims to provide components for a comprehensive, global, environmental measuring system. GAINS is envisioned to be part of an Earth-observing system of 400 regularly spaced platforms in the lower stratosphere that deliver environmental sondes to remote regions. The in-situ measurements of the atmosphere and ocean, and in-situ collection of air chemistry samples planned for GAINS are needed to address issues critical to global change and environmental prediction. These measurements will complement the existing surface, upper-air, and space*
Corresponding author. Tel.: +1-303-497-6830; fax: +1-303-4973329. E-mail address: [email protected] (C.M.I.R. Girz).
based observing systems, and together they can form the basis from which sound decisions can be made for the 21st century and beyond. A heterogeneous mix of superpressure balloons and remotely operated aircraft (Girz et al., 2002) maximize flexibility in targeting observations, while minimizing operational costs. Balloons that drift with the wind can populate a global network through a careful choice of float altitude. Moreover, a degree of direction control is possible if the balloon can take advantage of shear vertical wind that is floating the balloon at the altitude where the winds are most advantageous for its future location. For example, if winds at a lower altitude are more favorable for positioning the balloon to a specific point, mass can be added to the GAINS balloon by pumping external air into the internal air cell. This addition of mass increases the density of the balloon (since the outside envelope of the balloon maintains a constant volume), and the balloon sinks. The converse also pertains. The drawback is that shear direction can severely limit balloon placement for certain areas of the globe
0273-1177/$30 Ó 2004 COSPAR. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.asr.2003.06.021
C.M.I.R. Girz et al. / Advances in Space Research 33 (2004) 1642–1647
during certain seasons. On the other hand, although remotely operated aircraft can fly for days to weeks and stay on station or move to a targeted location, there is a high cost associated with these systems. Given a specified payload mass, the proposed balloon technology is a comparatively inexpensive delivery system. A number of tests (Girz et al., 2002) of the GAINS sub-systems were performed between 1998 and 2001. Flight tests qualified the environmental sensors and radios, as well as the mechanical and electronic termination components. A theoretical assessment and testing on the ground assured electromagnetic compatibility among the primary and backup transmission and termination radios. Power and instrumentation systems were qualified in an environmental chamber. Successful completion of these tests paved the way for the demonstration flight of the Prototype III (PIII) balloon on 21 and 22 June 2002. This paper presents the results of this recent GAINS flight.
2. PIII demonstration test The objectives of the demonstration test focused on the physical sub-systems of (1) the balloon vehicle, (2) onboard and environmental sensors, and (3) radio communications systems. There were additional objectives involving (4) flight support and (5) aviation safety procedures, and (6) for the additional experiments carried in the payload.
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internal state of the balloon (temperature and superpressure), and the state of the payload (temperature and battery voltage). Data were also gathered from a rudimentary solar power system, which was not used to supply power for any systems on the flight. 2.1.3. Radio communications Six communications systems transmitted in real time, and three provided redundant capability to terminate the flight. The objectives were to gather data from one over-the-horizon and five line-of-sight systems, and to terminate the balloon by radio command. 2.1.4. Flight support These objectives were to exercise the flight support procedures for balloon inflation, free lift weigh off, payload preparation, launch, balloon tracking from the air and on the ground, in-flight trajectory updates, descent vector calculation, and balloon recovery. 2.1.5. Aviation safety The objectives were to comply with the Federal Aviation Administration regulations on Free Balloons (FAR101) and to achieve a safe test through domestic controlled air space. 2.1.6. Additional experiments The objective was to operate the NASA/Langley Research Center experimental GPS reflection instrument on a balloon to derive wave velocity over the ocean and soil moisture over land.
2.1. Objectives of the Balloon’s sub-systems 2.2. Balloon system 2.1.1. Balloon vehicle The balloon vehicle objectives were the principal goals of the flight. Previous tests had flown the smaller (4.5-m diameter) PII vehicle for up to 5 h. Under this test, we wanted to demonstrate the integrity of the 18-m diameter PIII balloon at a nominal float altitude of 16 km for 48 h. Since this was the maiden flight of the PIII, it was important to observe the balloon achieve pressurization during ascent and under solar heating, to watch for a small depressurization during sunset and subsequent long-wave radiative cooling over night, followed by solar heating once again at sunrise on the second morning. A repetition of this cycle through the second 24-h period was desirable. Furthermore, on termination we wanted to exercise the balloon envelope recovery system (BERS), that is, the transformation on descent of the spherical balloon into a parachute. 2.1.2. Onboard and environmental sensors The balloon and payload were instrumented with several sensors to characterize the balloonÕs behavior. These sensors measured the ambient environment (temperature, pressure, and relative humidity), the
Manufactured by GSSL, Inc., of Hillsboro, OR, the 225-kg PIII balloon is a triple layer superpressure balloon. The outer envelope is a SpectraTM fabric sphere. Inside, two concentric polyurethane bladders contain helium and air. A toroidal fiberglass gondola carried the 150-kg payload containing packages from four organizations. The FSL payload included GPS for locating the system, two independent radio- and software-controlled termination methods, and environmental sensors to monitor balloon performance. The payload also contained two backup location and termination units from the Physical Science Laboratory (PSL) of New Mexico State University and from GSSL, redundant locating capability based on a design adapted from the Edge Of Space Science, Inc. (EOSS) of Denver, CO, and a GPS reflection experiment from NASA/Langley. The FSL, GSSL, PSL and EOSS line-of-sight communications transmitted GPS position on four radio frequencies at varying time intervals. Position was also determined from satellite by the Argos system. Argos receivers on the National Oceanographic and Atmospheric Administration (NOAA) series polar orbiting satellites and a
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transmitter onboard the balloon produce a location of the platform by using the Doppler effect. An amateur TV was programmed to transmit upward- and downward-pointing images intermittently during the flight to monitor the balloon, and continuously after termination to record the performance of the BERS. An onboard transponder was installed to ensure safe operation of the balloon through domestic airspace by keeping the balloon under active air traffic control. The balloon was tracked by an aircraft that recorded transmissions from the balloon and instigated termination of the flight. Mobile ground stations, positioned at the launch and recovery locations, were also capable of recording data and terminating the flight. 2.3. Launch configuration For maximum system stability, the GAINS superpressure balloons are fully inflated at launch. Helium in the innermost gas cell is filled through the EV-13 valve on the top fitting. Through a similar valve on the bottom fitting, the gas cell is filled with sufficient air to fully inflate the SpectraTM sphere. The lower valve was not under radio control for this test, and remained open to vent air as the helium bubble expanded on ascent. The upper valve was radio controlled for termination as described above. 2.4. Trajectory forecasts A suite of trajectory forecast tools has been developed which use winds from climatological soundings, radiosondes, and numerical weather prediction models. In planning for the flight, expected trajectories are computed based on climatological winds from the closest National Weather Service (NWS) station. The database contains soundings taken between 1946 and 1999. Data are averaged for each synoptic time (0000 and 1200 UTC) for every day of the year. Fig. 1 shows
trajectories for selected days in June. One constraint for the flight was that the track remain within the borders of the US; if the balloon had approached the Canadian border, it would have been terminated. The climatological trajectories for 15 and 20 June show that the bulk of the 48-h flights for these days could be completed within the US. Between 24 and 6 h before launch, trajectory forecasts are generated from numerical weather models and NWS soundings to assess the suitability of launch conditions vis-a-vis the balloon track. During the flight, trajectories are again updated from NWS soundings or weather models. Short-term (1–3 h) wind forecasts from the operational rapid update cycle (RUC) model are especially useful just before launch and termination. Collander and Girz (2004) describe these products in more detail, and discuss in particular the real-time trajectory forecasts that were made for this flight.
3. Results of the PIII demonstration test The GAINS test was launched from Tillamook, OR, at 8:35 am local time (1535 UTC) in dead calm under a marine stratus layer. After oscillating through the cloudy layer, the balloon climbed to a maximum altitude of 17.4 km. A tracking aircraft kept the balloon within radio line of sight at all times during the 362-km long flight, and personnel on board coordinated the flight with FAA air traffic control. Two additional vehicles tracked the balloon from the ground and recovered the payload. At sunset the balloon began to accelerate downward and landed at 0003 UTC on 22 June south of The Dalles, OR. Fig. 2 shows the track of the flight. The soft landing caused no damage to the payload capsule, and minimal damage to the wheat field where it landed. The entire system was removed from the landing site and returned to Tillamook, OR, the next day. Position, balloon state, and environment data shown below were
Fig. 1. Trajectories forecast from average winds at Salem, OR, for selected days in June for a 48-h flight at 15.8 km. Wind statistics are in knots.
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Fig. 2. Track of the GAINS balloon on 21 and 22 June 2002.
recorded in the groundstations in the tracking and recovery vehicles from the real-time transmissions. 3.1. Climb out The no-wind condition at the surface made this an easy launch. However, the calm at the surface was the result of a 1.1-km deep inversion, which also produced a marine stratus cloud between 0.4 km AGL and the top of the inversion. This inversion inhibited initial ascent. The balloon took 50 m to clear the inversion (see the spike at 16.4 UTC in Fig. 3), and during that time, the balloon drifted off the coast (Fig. 2). 3.2. Float Once free of the inversion (Fig. 4), the balloon accelerated, ascending with an average velocity of 1.8 m s 1 to a maximum altitude of 17.4 km. We expected the balloonÕs internal pressure to be 40 hPa at float. But maximum internal pressure of 10 hPa occurred about an hour before maximum altitude was reached. Internal pressure
Fig. 4. Vertical trajectory in meters (dark curve) and superpressure in Nt m 2 (light curve) as the balloon climbs to float altitude. Time is in decimal hours.
dipped to 7.5 hPa, then shortly after reaching maximum altitude, superpressure dropped to 3 hPa and did not recover. The balloon floated at 16.5 km for 9 h. 3.3. Descent With solar heating waning, internal density increased and the balloon began a slow descent at )0.5 m s 1 . (Fig. 5). At 0600 UTC, the balloon appeared to selfterminate and rapidly dropped with velocities between )1.0 and )3.7 m s 1 . Several times during descent, the balloon decelerated, apparently as a result of the envelope transforming into a parachute. This especially appears to be the case in the final 2 km, when the balloon steadily decelerated from )4 m s 1 to zero. 3.4. On the ground
Fig. 3. Vertical trajectory in meters (dark curve) and vertical velocity in m s 1 (light curve) during the initial 1.5 h of the test. Time is in decimal hours.
The balloon had been tracking to the east–northeast during most of the time at float. On the basis of wind forecasts for the late-afternoon float altitude, we had
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4. Discussion
Fig. 5. Descent trajectory in meters (rectangles) and vertical velocity in m s 1 (diamonds) during descent. Time is in decimal hours, and is not rolled over past midnight. Sunset occurs at 28:00 UTC.
deployed the ground teams to Yakima, WA. As the balloon lost altitude after sunset, however, it descended into easterly then southerly winds. The aircraft team tracked the balloon to the ground, landed the plane, and then drove to the landing site to secure the balloon until the team could arrive from Yakima the next morning. At the landing site, water was observed inside the balloon. The lower valve and fitting were also coated with ice. It was estimated that the moist hangar air that filled out the sphere added up to 40 kg to the mass of the balloon. As the balloon rose, this water vapor condensed onto the inside surfaces of the gas cell. Undoubtedly some dripped out of the open lower valve before the balloon reached the freezing level at 3.5 km. However, an indeterminate amount remained inside the balloon during the entire flight. 3.5. GPS reflection experiment Hardware for the GPS reflection experiment performed well. This experimental technique has been proven for computing sea surface winds on both aircraft and balloon platforms. Given the trajectory offshore, the data include an open ocean segment. The version of the instrument flown on the GAINS balloon is a new compact version of the instrument that fits into a 20 cm 15 cm 13 cm enclosure, and a primary goal was to get flight experience for the new configuration. Of particular interest for this flight was the projected terrestrial flight track, which provided data to test the potential of computing soil moisture from the hardware. The balloonÕs track included a moist surface in western Oregon, and a very dry regime east of the Cascades. Four operating modes were tested in sequence during the flight, each mode for 30 min at a time. Of the segments recorded, 34 contained valid data. Data are currently under analysis.
Objectives for the onboard sensors, radio communications, and flight support were met. Data from the onboard sensors that were transmitted through the radio communications systems have been shown in the previous Section 3. Not shown are the 14 position reports from Argos made between shortly after launch at 1612 UTC on 21 June and while the balloon was being secured on the ground at 0844 UTC on 22 June. Space limitations do not permit discussion of the additional parameters that were measured. Airspace safety objectives were also successfully met. Although the balloonÕs aircraft transponder failed, air safety was never an issue due to coordination with air traffic control and position reporting by personnel on the aircraft. This was especially important at launch and during the first hour of the test. At 9:00 am that morning, approximately 20 military aircraft were running training sessions just offshore from Tillamook, causing concern during the slow initial ascent. Three circumstances contributed to the slow ascent. The hangar air used to fill out the balloon was colder than the atmosphere into which the balloon was launched; we estimate a 4–6 °C difference. Second, because the system was significantly over its weight budget, the balloon was launched with minimal free lift. Consequently, there was little lift to accelerate through the cloud. Third, while the balloon was bobbing in the warm cloud layer, the envelope picked up moisture. This additional mass further depressed the balloonÕs free lift. The internal gases eventually came to equilibrium with the ambient air, and presumably, some of the excess external moisture was lost at altitude through sublimation. Balloon performance objectives summarized in Table 1 show that several objectives, such as ascent rate, descent rate, and float altitude, were completely met; however, the objectives related to balloon integrity (time at float, superpressure, and day–night altitude changes) were only partially met. It is more difficult to explain why the balloon did not pressurize. As Fig. 4 shows, pressurization stopped suddenly just as float altitude was reached. If the helium cell experienced a rupture at that time, the loss of mass
Table 1 Target and achieved values of balloon performance measures Parameter Ascent rate Float altitude Time at float Descent rate Superpressure Day–night altitude change
Target
Achieved 1
2.5 m s 16.5 km 48 h <3.8 m s 1 40 hPa 160–330 m
2.0–3.0 m s 1 15.5–17.4 km 15 h 32 min 4.1–2.5 m s 1 10 hPa Descended to surface
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would accelerate the balloon; this, however, was not seen. Vertical velocity actually slowed from 2.3 m s 1 just before maximum superpressure to 1.8 m s 1 immediately after. A final analysis of balloon performance will be completed in the future.
bers, and awaits confirmation of these results with testing at altitude. With the successes of the PIII demonstration test and the advances in developing a pump, GAINS is right on track.
5. Summary
Acknowledgements
The maiden flight of the 60-ft diameter GAINS Prototype III (PIII) balloon on 21 June 2002 met several development objectives including launching the PIII balloon, floating it at altitude for >8 h, transforming the balloon envelope into a deceleration device, achieving a safe descent rate, tracking the balloon from an aircraft, forecasting balloon trajectory before launch, updating balloon landing position during flight, and recovering the balloon and payload. The two critical technologies for the GAINS sheardirected balloon are the superpressure balloon vehicle and the pump for controlling density. This flight indicates the feasibility of a superpressure balloon of the WindStar design to pressurize at altitude, and thus is a first step in confirming the possibility of superpressure balloons of this design. Since development of the GAINS pump began two years ago, an experimental pump has been qualified in two environmental cham-
The PHI demonstration flight benefited from the advice and support of a number of individuals in the years leading up to this point. The GAINS team gratefully acknowledges the contributions of the following persons: V. Lally, A. Bedard, B. Johnson, D. Latsch, N. Abshire, S. Nahmen, M. Shannahan, C. Bliss, and B. Keppler. Thanks to N. Fullerton for a careful editorial review.
References Collander, R.S., Girz, C.M.I.R. Evaluation of balloon trajectory forecast routines for GAINS, Adv. Space Res., 2004 (doi:10.1016/ j.asr.2003.05.016). Girz, C.M.I.R., MacDonald, A.E., Caracena, F., Anderson, R.L., Lachenmeier, T., Jamison, B.D., Collander, R.S., Weatherhead, E.C. GAINS – a global observing system. Adv. Space Res. 30, 1342–1348, 2002.