STRATOSPHERIC BALLOON BASES IN THE WORLD

Hyderabad is the capital of the Indian state of Andhra Pradesh. Situated on the Deccan Plateau, at the heart of the subcontinent it has an average elevation of about 500 metres above sea level. Most of the area has a rocky terrain but there is a lot of cultivation in the surrounding zones with paddy fields and other crops growing. Is one of the most developed cities with the fifth largest metropolitan area in the country. Also is known for its ancient history, multilingual culture and rich architecture representing a meeting point for North and South India.

Several factors contributed from the very beginning to transform Hyderabad in the true capital of the scientific ballooning in India. Almost three diferent places served as balloon launch sites along the years mainly due to the advantages offered by his location. As widely known, Equatorial regions have great atractive for scientists in many branches of science, specially in regard of some key atmospheric and physical processes occuring in those regions. Sadly, less than a fifth part of the equator is occupied by land, a large part of which is impenetrable jungle or inaccessible desert areas. Thus there are few places available from where would be possible to carry out in situ atmospheric studies involving balloons, due to the fact that in some cases (when are flown experiments to collect samples or when expensive equipment is involved) recovery of the instrumentation is imperative.

In this regard, the region around Hyderabad offers a reasonably clear land area, at least 300 to 400 miles in width, with road networks, communications, and other important factors necessary for balloon flight operations. Aditionally, the area has special conditions -a low atmospheric gamma and X-ray radiation level- which along the closeness with the geomagnetic equator already mentioned, give to this zone a special attractive too for researchers who wish to conduct studies on cosmic radiation and X-ray astronomy.

India's atmospheric exploration and cosmic ray studies programes were the main boosters of the birth of ballooning activity. It was back in the decade of 1940 when Dr. Homi J.Bhabha from the Tata Institute of Fundamental Research (TIFR) became a pioneer in the field, sending scientific equipment to altitudes of 25-30 km using clusters of up to 60 hydrogen filled rubber balloons. The aim of these early experiences was to study the secondary cosmic radiation through the use of emulsion plates to record the track left by these particles interacting with our atmosphere.

Over the years the evolution in complexity of the experiments forced to increase the payload's size which became progressively larger and heavier. Thus, in March 1956, another pioneer in the ballooning arena, Prof. Bernard Peters from TIFR started a research program for the manufacture of plastic balloons able to transport these bigger payloads to near 35 km of altitude. The effort was under direction of Prof. M. G. K. Menon, with the technical guidance of Prof. G. S. Gokhale. As a result of the work they had done, the first successful polyethylene balloon flight took place in April 1959 from the Osmania University Campus in Hyderabad, a place that would become the main balloon launch site in the decade that followed.

In 1960 the lack of data on Equatorial regions led to several agencies and universities from the U.S. to search for a place from where launch balloons to allow those studies. Soon, after a careful study and after ruling out other possibilities (for example launch the balloons from ships in open sea), diplomatical meetings and arrangements were made to conduct a joint balloon launch campaign at Hyderabad in 1961. The expedition had the sponsorship of the Air Force Cambridge Research Laboratory (AFCRL) and the support from TIFR and the local balloon group, as part of the cooperative effort.

The launch operations were carried out from two diffrent places. Begumpet Aerodrome, located approximately one mile northwest of Secunderabad (twin city of Hyderabad), was selected as the launching site for the U.S. balloons because of the large paved area needed for the dynamic launch technique used by the contractor (General Mills). Also, since many of the payloads were stratospheric dust collectors, it was advisable to avoid surface contamination generated by vehicles moving around unpaved areas. Headquarters, working areas, and communications center were located in the "Lahore Hut", and at the recreation hall of the Indian Air Force distant one-half mile from the Aerodrome.

Unlike the U.S. operations, the Indians launched their balloons using the stationary method, so they choose as launch pad the cricket field at Osmania University. Their headquarters, communications center, office and temporary laboratories, as well as living quarters, were situated in the Hostel at the University.

Balloon flight activities of the program began on 2 February 1961 with the successful launching of an Indian cosmic-ray counter telescope. A second flight, three days later, was attended by India's Prime Minister Jawaharlal Nehru. Operations were then suspended for more than three weeks because of unpredicted high westerly winds at floating altitude. In all, 40 large polyethylene balloons were launched during the Program (24 from U.S. and 16 from India), with a great record of success.

Along the campaign were very remarkable the differences between both programmes: while the Indian balloons, carrying telemetering cosmic-ray counters or nuclear emulsion packages, were tracked only by optic and radio theodolites, due to the higher costs of aerial operations, the American ones following the methods used in the United States for their operations, were in full control of the balloons in flight until recovery, using a Beechcraft Bonanza plane hired in India for tracking purposes.

Five years after, during the International Quiet Sun Year (IQSY) was carried out at Hyderabad a second cooperative campaign. This time the sponsorship was from the National Science Fundation from United States and the launches were carried out between March and April of 1965, under management of the National Center for Atmospheric Research, and TIFR. This time all the operations for both sides were consolidated at Osmania University. During the campaign a total of 17 flights were performed involving the participation of scientists from India, United States, as well from Australia, Great Britain and Ireland.

After two decades at Osmania and more than 170 flights made there, time arrived in mid sixties to start thinking about the growing and consolidation of a national scientific balloon program. The next logical step was of course to build a dedicated launch base.

After careful consideration, decision was taken to create the National Balloon Facility (NBF). It was established on a open terrain of 25 hectares belonging to TIFR and located in a then rural, low populated area east of Secunderabad. By December 1969 was operative with the first launch of a balloon acomplished succesfully. The initial isolation of the launch facility, changed radically over the years as the zone experimented a sudden grow with the consolidation in the nineties decade of the Cherlapally Industrial Development Area as well several population settlements. Today the base is sorrounded by the Cherlapally Central Jail in the east, the North Kamala Nagar village in the west and the big facility of Electronics Company of India Ltd. in the south. Below these lines we can see a satellite image of the zone and the facility location. The big circle is the launch pad.

The base is under the overall management of the so called Balloon Facility Board composed by staff members from TIFR and the Indian Space Research Organisation (ISRO). Is divided into four departments: Electronics, Mechanical, Balloon Production and Administration.

The main constructions on the site include administrative buildings, laboratory blocks, storages areas for vehicles and hidrogen cylinders and a small hostel with 32 rooms to be used by the scientific staff participating of the launch campaigns. All these buildings are connected each other through internal small paved roads. On regard support instrumentation, the base counts with two low temperature chambers, one vaccum chamber, and a Liquid Nitrogen cooled low temperature chamber used to test in near space conditions the payloads to be flown. For calibration of pointing systems of the gondolas, outside the integration area is located a non-magnetic frame. All the electrical power needed for the operation of the entire facility is generated through a 11 KV 250 KVA main sub-station counting also with a stand-by 200 KVA back-up diesel generator used in case of a main electrical failure.

The launch pad is a circle of unpaved terrain measuring near 300 M of diameter with merging slopes of 80 meters around it. The current launch capability of the station is for balloons of up to 700,000 m3 of volume and gross loads of about 3000 kg. To reach these numbers was necessary to design and built a new mobile launch spool system (used to hold the gas bubble of the balloon during inflation). The launch vehicle (image at left - clisk to enlarge) is an old 25 Ton. Leyland truck with the addition of a launch arm to hold the payload at the moment of the launch and a protective structure to prevent the vehicle to tip over his side. The launch arm was entirelly made new recently to better manage the progressive increase in the size and weight of the gondolas being launched.

While the use of the truck would lead to conclude that the main launch technique is the so called "dynamic", as a matter of fact during layout and launch, several portions of the long flight train used on each mission are maintained floating several meters above the terrain by small auxiliary balloons, thus avoiding to drag the instruments over the ground and resulting in some sort of "mixed" launch method.

In regards of telemetry and telecommand (TM & TC) infrastructure, in the beginning the TIFR Balloon Facility used a system operating in the VHF band. However, over the years it turned to be somewhat problematic as tended to cause considerable interference in many sensitive payloads and often suffered of signal fading. Aditionally a limited coverage range and troubles to physically manage the non aerodynamic on-board antenna at launch, lead in recent years to take decision to switch to a S-Band system. After several upgrades made by the Control Instrumentation Group today the S-band system can handle data transfer rates in flight of up to 1 Mbs.

The onboard segment of the TM & TC system is located in the flight gondola and consists of two sub assemblies: the onboard telecommand system and the onboard telemetry system. The onboard transmitter have a power output of 1 watt and a line of sight maximum range of 350 km. For such cases in what the signal is loss or is remarkably noisy, the system counts with a small telemetry storage system based in a single board computer card (a 300 MHz Intel processor with 256 MB RAM) capable to write up to 8 GB of data in a flash memory module. The flight train is formed by a passive radar reflector, a pair of GPS units, a medium wave radio beacon, a GPS radiosonde with independent transmission, a medium wave radio direction finder and a command programmable timer for separation of the payload from the balloon. All the integrated package weights 18 kgs. For astronomy payloads that made use of stellar orientation systems is available a short range telemetry link between the load-line control package and the main payload, to allow onboard data exchange without the need of TM & TC hardware duplication.

The ground station (which allows the reception of both scientific data and TM & TC information) is composed by a steerable 3.8 m dish antenna (image at right - click to enlarge) connected to a preamplifier and a receiver. Telemetry signals from on-board transmitter are passed to the main demodulator and to the receiver to generate signals for auto tracking operation of the dish orientation system. After filtering and demodulation of the signal, the decoded information can be accessed by end users on the NBF Ethernet network, or can be displayed in real time on a workstation or can be recorded on a permanent storage media for post-flight analysis. To send commands to the payload, they can be entered in a dedicated computer, formated and then sent bit by bit, in serial form, to the transmitter for modulation, then amplified by a 50W Solid State Power Amplifier before being fed to the dish antenna, to be sent to the balloon.

The best surface wind conditions to perform balloon launches are from mid-October to mid-April each year. Balloon launches are not conducted during pre-monsoon and monsoon period (May to September) and during the time frame comprised between January and mid-Februry. In the later case this is due to the presence of strong tropospheric westerly jets and associated wind shears that can damage the balloons at launch.

The NBF is located 11 kms east of the Begumpet Airport which until the inauguration in march of 2008 of the new air terminal south of the city, concentrated all the aerial operations for the region. This possed severe restrictions over the operations. Since the airport's main air corridor passed right over the base and the balloons not carried any radar transponder (merely passive reflectors) the India's Directorate General of Civil Aviation (DGCA) confined to a limited area all balloon operations bellow 15 Km both during ascent or descent phases. Also the allowed flying corridor covers an area bounded by the DGCA to avoid the balloons flying over densely populated areas or closer to the coast line. Finally as the base is sourrounded by the Air Force flying areas in the northern sector, whenever they conduct night exercises, launchings are forbbiden too. All this restricts the real operating range of the base to 364 km to the East, 396 km to the North, 486 km to the West and 392 km to the South.

Due to the high costs of aerial recovery operations, historically, all the balloon flights launched at NBF were followed by ground teams instead of being tracked and pursued by airplanes. A typical rescue mission develope as follows: to ensure that the rescue team reaches the payload impact point as quickly as possible, an advance recovery party is sent in a jeep to follow the balloon immediately after it reaches its ceiling altitude. They keep in constant communication with the NBF, being continuously briefed about the trajectory of the balloon.

The advance team tries to follow the balloon path and in most cases is able to reach the payload impact point within a couple of hours of the touchdown. In all the flights, as an additional measure, monetary reward tags are attached to the payload train to encourage the finders to preserve the equipment with the assistance of local police until the arrival of the advanced party. Once in the impact site they take care of the instruments and await the arrival of the Main Recovery Team. They are well prepared and equiped to handle the difficult situations that often arose with the local population.

The main recovery team leaves the base station after the termination of flight in a truck capable of accommodating the main payload and the flight train accessories. They proceed to the projected payload impact point obtained from the GPS/Radar Data, or the actual impact point in case the touchdown message is received at the NBF before they leave the base. They also keeps a close communication with NBF for fresh inputs regarding the payload landing area. In case no information is available, the advance team and the main recovery team conduct searches in the estimated area of the payload landing till is found and recovered.

A recent improvement on this area is the development of a real-time tracking system based on the Google-earth platform which process the information fed by the balloon onboard GPS receiver and shows the trajectory plotted over a high resolution digitalized map. This new system is of great help for the flight director to choose the right time and place to terminate the mission, making more efficient the recovery process and reducing the payload search time.

A known flaw of the wind pattern at equatorial latitudes is the absence of a long turnaround period with low velocity winds, which is a common feature on high altitude circulation scheme on mid-latitudes launch sites. Over Hyderabad the stratospheric winds during March are moderate and longer float durations of 8 to 10 hours may be possible, but in early April, stratospheric easterlies strengthen in speed thus reducing the possible float duation by a few hours. In change during December, the occasionally westerlies appear to be more predominant at higher altitudes, so float durations of 8 to 10 hours may be possible only during the second half of November for altitudes in the range of 29 km to 35 km, and for altitudes of 36.0 km and above during the first half of December.

To allow the realization of longer float periods, two possibilities were at some time under study. The first one was to conduct launch operations from the city of Port Blair, located in the Andaman and Nicobar Islands in the Bay of Bengal, about 1400 km from the east coast of India. In the latest years several surveys were conducted in the islands and as a result were located almost two places with enough open space to perform the launches near the local airport at Port Blair. According to the estimations, after launch the balloons will drift in the upper easterly wind for more than 40 hours until termination over the continent. The main setback of this project is the amount of logistics support needed to move the launch operations to the new base, and the long range of the communication link needed. On regard this last point is being studied the possibility to establish a ship-based relay station to extend the range of the TM & TC link during the flight. The second option considered was to conduct the launches from Hyderabad with a westward flight path and recovery in the eastern part of middle east. Althought this option had the advantage of using the already established base to launch the balloons, the plan was soon dismissed due to the fact that it needed international collaboration and support for overflight and recovery operations in other countries.

Recently NBF showed interest in a third option: to perform long duration circumpolar flights in the austral summer from the Indian Antarctic Station of Maitri. The enterprise will imposse to the program a series of challenges in areas as balloon fabrication, communications, control of instrumentation, payload design and international cooperation. Among the several objectives to be completed are under study:

• The design and fabrication of a test balloon with integrated flexible solar panels on the top plate, which can be deployed while being inflated allowing the obtention of additional power while reducing the gross load on the balloon.
• The implementation of a larger on-board data storage system based on flash memory units which can be fabricated at very economical cost and also requires low power to operate.
• To adapt to the balloon gondola an Iridium based two-way communication system, now being used routinely in satellite missions, for monitoring the health of the experiment during the out-of-range periods.
• To develope an automatic ballast dispenser, mandatory to maintain a constant level of flight for weeks.

According to plans, once a regular program of launches in Antarctica could be established, India will offer to the United States to create a network of two down-range Telemetry stations, by using cooperativelly the facilities at McMurdo and Maitri. As the two bases are located in opossites sides of the white continent, this will allow to make massive data dumps to download stored data whenever the balloons passes close to any of the stations.

One of the unique features of the NBF, is the presence of a full-fledged balloon manufacturing unit inside the base. As often described in the specialized literature the Indian balloons were back in the 60's constructed of polyethylene tinted with controlled amounts of carbon black. This was a very smart solution to increase their absorption of solar radiation, resulting in very high ascent rates and warmer film temperatures at the critical path of breaking the colder equatorial tropopause.

A continued effort for research and develope balloon materials led to the creation of a balloon grade film called "ANTRIX" which has better low temperature characteristics at Tropopause in comparation with other leading balloon films such as "Astro E2" and "SF-372". A number of flights with balloons made out of this film have been successful to transport up to 1200 kg payloads in the stratosphere. Also the load tapes that reinforce the balloon envelope are manufactured at the facility with 3 different breaking strength ratings, to cover the entire load tape requirement for the Indian balloons.

Recently to meet the growing demand from scientists in X-ray Astronomy and other fields which desire to carry out flights to 42 km with near 1 Ton of equipment, the balloon production building has been extended by 27 Metres to accommodate the 178 Metre long Balloon Work Table. Now balloons of up to 740,000 m3 of volume can be fabricated at the facility, representing an increase of near 70% in comparation with the largest balloons fabricated earlier at NBF.