High-Altitude Ballooning Program

High-Altitude Ballooning Program: Why and How Margarita Safonova and Jayant Murthy and IIA Research Team: Joice Mathew, Mayuresh Sarpotdar, Ambily Suresh, K. Nirmal, A. G. Sreejith, Binukumar Nair

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Introduction

Why do we do astronomy? The most spectacular show on Earth, free for all and available every night is the night sky. Humanity has been fascinated with it since time immemorial, and much of our technological advances are driven by the insatiable desire to know what is out there? where do we live and where are we going? The dawn of space exploration began with the pioneering works of Konstantin Tziolkovski and barely 50 years later we successfully launched the artificial satellite Sputnik 1 to Earth’s orbit. And the era of space astronomy started as even this tiny satellite — about the size of a ball — contained a scientific instrument: a barometric switch, designed to change the duration of the radio signal if the pressure inside fell due to the meteor puncture of the hull – the low-orbital environment was not known in the sense of how safe was it to launch anything into low-Earth orbit. In addition, the decay of Sputnik’s orbit in the atmosphere enabled a reconstruction of the atmospheric density at those altitudes. Radio signals from Sputnik 1 allowed a study of the upper layers of the ionosphere, because all that was known before was only the reflections of radio waves from the low layers. And with the next successful mission Sputnik 3, its cosmic ray detectors indicated extreme levels of enhanced radiation, which concluded in the discovery of the Van Allen radiation belts by the American Explorer-1, all just within a year of the first ever launch. Now, we have an extensive space exploration program, our satellites even ventured out of the Solar System, and visited most of the planets within. But, access to space remains a risky and very expensive business. The cost of putting just 1 kg into orbit, including insurance costs for launch failures, comes to 15,000 euros, by some estimates. The Indian ASTROSAT mission, launched in 2015, cost approximately US$6 mln, and NASA UV telescope GALEX, US$150 mln. Once launched, the retrieval are impossible and repairs are barely possible; with one exception being for the Hubble Space Telescope that was launched in 1990 with cumulative costs estimated to be about US$10 billion (it was repaired by a human team in space walks several times, last in 2009). Though development of nano and CubeSats considerably reduced the costs involved, these satellites have yet to show the scientific potential, and are still irretrievable after the launch. What could be the alternatives?

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High-Altitude Balloon Platform

Near space is the region of Earth’s atmosphere that lies between 20 km and 100 km above sea level, encompassing the stratosphere, mesosphere, and the lower thermosphere; the area above 99% of the atmosphere, above the ozone layer and most of the turbulence. Ozone layer prevents ultraviolet (UV) light reaching the ground, and atmospheric turbulence distorts the optical images of the astronomical sources. Telescopic platforms at 1

high altitudes have significant advantages over operations from the ground enabling observations at forbidden wavelengths with diffraction-limited imaging without the use of adaptive optics. A UV telescope (200–400 nm) in the stratosphere with apertures of just 6 inch in diameter given sufficient pointing stability/accuracy and a 1K×1K CCD array could provide wide-field images with sharpness better than 1 arcsecond approaching the diffraction limit [1], similar to that of space observatories but at a much lower cost. Floating zero-pressure balloons can provide continuous observations varying from a few hours to few days. The lower cost and the flexibility in launch timings and flight duration make high-altitude balloon experiments a wonderful test-bed for space technologies (Section 3). Small telescopes/cameras on board balloons or sounding rockets are attractive because they are much cheaper and yet can yield substantial scientific output; the first UV spectrum of a quasar was obtained during a short rocket flight [2]. Stratoscope I and II, flown in the 1950s and 1960s by Princeton University at heights of over 32 kilometers, were essentially precursors to the Hubble Space Telescope; the first – a 30-cm solar telescope – obtained sharp pictures of the solar corona; and a second one with the 90-cm mirror made several photographs of planets with a resolution close to a tenth of an arcsecond [3]. There is a surge of interest in flying balloons to the edge of near space in recent years, largely due to the major reduction in costs of all the involved components, from inexpensive latex balloons to easily available lightweight, compact, and simple in operation microelectromechanical (MEM) devices. The same availability allows also to apply this to the scientific objectives, to do serious science at low cost. We have initiated a HighAltitude Ballooning (HAB) program at Indian Institute of Astrophysics (IIA), Bangalore, in the year 2011 [4] with the primary purpose of developing and flying low-cost scientific payloads on a balloon-borne platform; an endeavor to enable carrying out scientific space experiments and observations at costs accessible to university departments.

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Objectives

The science goals include studies of the phenomena occurring in the upper atmosphere in the ultraviolet (UV) range, of airglow and zodiacal light, and spectroscopic UV observations of extended astronomical objects such as, for example, comets, using the spectrograph in the near-UV window from 200 to 400 nm; the range that has been yet largely unexplored by the balloon (or the UV) community. This window includes the lines from several key players in atmospheric chemistry such as S02 , O3 , BrO, HCHO and allows to observe a strong OH signal (308 nm) in astronomical sources (also C2 , CS, CO2+ ). Balloon-borne instruments are a comparatively cheap and rapid method of measuring in situ profiles of ozone and other trace gases [5] in the upper troposphere and stratosphere. We have developed a number of payloads which operate in the near-ultraviolet (NUV), but we are limited to weights under 6 kg for regulatory reasons which constrains our payload size. Our first experiments were of atmospheric lines [6] where the pointing stability is less important, but we plan to observe astronomical sources for which a pointing mechanism is required. We are also planning on performing high-altitude astrobiological experiments, such as for example survival of microbes in upper atmosphere [7], or collection of stratospheric samples to study the air/dust composition, especially in view of the recent claims of detection of extra-terrestrial cells in stratosphere [8]. Despite the importance of this topic to astrobiology (stratospheric values of gas pressure, temperature, humidity and radiation are very similar to the surface of Mars), stratospheric microbial diversity/survival remains largely unexplored [10], probably due to significant difficulties in the access and in ensuring the absence of ground-mid-atmospheric contaminations.

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4

Essentials

Figure 1: The balloon set-up flight train.

4.1

Permissions necessary to carry out the launches

Approvals from different airport and defence agencies are necessary to perform free-flying balloon experiments. These permissions have to be requested at least 8 to 12 months before the beginning of the program. Launches are only allowed after obtaining all the required No-Objection Certificates (NOCs), and we can carry out the flights only on a certain local non-flying days, currently on Sundays.

4.2

Balloons

The overall structure of the HAB system is presented in Fig. 1: balloon(s) on the top, parachute(s) between the balloon and the payload, and the payload(s) at the bottom. Many types of balloons are used for high-altitude balloon experiments depending on the weight of the payload, scientific objectives and the scale of the program. Latex balloons, also known as sounding or weather balloons, are designed to reach 35–40 km and burst, after which a parachute is deployed to safely carry the payload back to Earth. They are low-cost, easily available and, since they usually do not exceed volumes of 3 m3 on the ground, are easy and inexpensive to launch. More sophisticated balloons, the socalled zero-pressure thin plastic balloons, are used by NASA’s Balloon Program, National Scientific Balloon Facility, USA [10], or Tata Institute of Fundamental Research (TIFR) National Balloon Facility, Hyderabad, India [11] which can carry payloads of several tonnes to altitudes of 50 km and float for several hours. But because they require special manufacturing and specially designed launch towers, they are very expensive. Since our aim was to develop a low-cost balloon program affordable to universities and colleges in India, we decided to use latex balloons as they are cheap, small and readily available. We use 1.2 and 2-kg balloons from Pawan Exports, Pune, India.

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4.3

Gas for the balloon filling

Helium as an inert gas is considered the safest for filling the balloons, however, because it is expensive and due to scarcity of pure helium in the world [12], we use much cheaper commercial hydrogen. The price of a 10 m3 helium cylinder is Rs. 17,000 as compared to Rs. 800 for a 7 m3 commercial hydrogen cylinder. We buy gas for each launch from Sri Vinayaka Gas Agency, Bangalore, India.

4.4

Parachutes

Parachutes used in high-altitude ballooning are usually made out of ripstop nylon. We use parachutes of two different sizes, 7 and 8 foot diameter that have lift capacity of 4.0 – 4.9 kg and 5.4 – 6.8 kg, respectively. In some flights, we connect these parachutes serially.

4.5

Flight Termination Unit (FTU)

Balloons drift off if winds are high during the flight. To restrict the drift to another state or territory, we have designed two independent FTUs for the balloon system. One system is based on a timer circuit and placed below the parachute, and the other – Arduino-based system with a GPS – is placed inside the main payload box. The FTU uses a thermal knife to cut the load line between the balloon and the parachute: the nichrome wire wound across the load line which heats when the current is passed through it and melts the nylon load line, severing the payload from the balloon.

4.6

Payloads

The heart of the controlling system is a Single Board Computer (SBC). For this purpose, we use the Raspberry Pi (RPi) SBC developed inhouse [13] that interacts with different sensors and records data (temperature, attitude, etc.) and images at regular intervals throughout the flight on SD card. It also keeps a record of housekeeping files to verify the performance of the sensors. Small size (85.6 × 56.5 mm) and low power consumption (5 V, 1 A) of an SBC makes it a suitable candidate for a flight computer. Depending on the scientific and technical objectives of every flight, the payloads differ (Fig. 2). Some of the equipment is always present, such as camera, data sensors and tracking devices. Other equipment may be a telescope, spectrograph, pointing and stabilization platform, special sensors such as a Geiger counter, or an astrobiological set-up [14].

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Experiences

Our launch site is the CREST campus of the Indian Institute of Astrophysics, with coordinates 13.1131 N, 77.8113 E, and 960 m altitude. We have carried out more than 20 launches since 2011: tethered, testing, and free-floating [15]. Many times we have reached altitudes of more than 30 km, though the usual is about 25 – 27 km (Fig. 3a). One or two days before the launch we calculate the balloon flight path using the Cambridge University Spaceflight Landing Predictor (http://predict.habhub.org/) together with our own codes written in MATLAB and IDL. We calculate the atmospheric parameters from ATMOSPHERE3, which is an atmospheric model of how the pressure, temperature, density etc. vary over a wide range of altitudes. The balloon information to use in the simulations is provided by the manufacturer. All our codes with explanations and how-torun instructions are available on our website: www.iiapballoongroup.wix.com/blue. Our experience show that our predictions for the balloon/payload path are generally correct and the payloads are always found close to the predicted locations (Fig. 3b). 4

We monitor the temperatures inside and outside the payload box in order to control the working of electronics: at low temperatures the batteries drain very fast. In Fig. 3c, atmospheric temperature inversion is clearly seen, while the conditions inside the payload box remain operational. Change of altitude with time is recorded by the GPS onboard (Fig. 3d). Latex balloons usually do not float, they reach maximum altitude and burst, after which the parachute is deployed and the payload comes down. Alternatively, we set the FTU to terminate the flight after it reaches certain altitude (or a certain time elapses). We observed the scattered solar UV spectrum on three flights. One of our objectives is to detect the airglow lines and to establish the altitude dependence of the strength of the trace gases lines, such as ozone (Fig. 4). We also take photographs of the Earth and space from the stratosphere, as well as monitoring the balloons and parachutes from the camera facing upwards (Fig. 5).

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Space Spin-offs

Our balloon experience has been invaluable as training and verification for our current space activities. We now have several payloads that are either ready for space flight or are planned for future flights. The first of these is LUCI – Lunar Ultraviolet Cosmic Imager – which is planned to go to the Moon in early 2019 (Fig. 6a and b). This telescope will be the first Lunar Observatory from India and will look for supernovae and other flashes of light (transients in the UV) from the sky [16]. We have developed a space camera designed to act as a star sensor [17] for small satellites (Fig. 6c), and are developing an ultraviolet camera to scan the sky in collaboration with PES University as part of the PISAT program [18]. The near-UV wide-field telescope is built ready to fly on a CubeSat – the WiFi (Fig. 6d) [19]. Our program is one of the few experimental space programs in the country and we are training students for the growth of space astronomy.

References [1]

Fesen, R., and Brown, Y. A method for establishing a long duration, stratospheric platform for astronomical research. Experimental Astronomy, 39, 475, (2015).

[2]

Davidsen A. F., Hartig G. F. and Fastie W. G. Ultraviolet spectrum of quasi-stellar object 3C273. Nature 269: 203, (1977).

(a) Basic Stamp 2 MC board, Satguide tracker, Canon Ixus (b) Gimbal with a telescope, (c) UBEX – Ultraviolet Bal115 HS camera. loon Experiment for astroUV Spectrograph. nomical observations.

Figure 2: Examples of different payloads.

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(b) June 2014 flight. Top: Predicted path of the balloon travel. Bottom: Actual path travelled by (a) Altitudes reached on seven flights between the balloon. March 2013 and October 2014.

(c) Variation of external (black curve) and internal (red curve) temperature in degrees Celsius during the October 2014 flight. The launch time (d) Flight altitude profile on June 2014 flight. corresponds to 0.5 hrs in the graph.

Figure 3: Various examples of data obtained from the balloon flights.

Figure 4: June 2014 flight. Left: Variation in UV atmospheric spectra with altitude. Right: Observed ozone Slant Column Density (SCD), i.e. the trace gas absorption of the spectrum with respect to the solar reference spectrum. [3]

Nayak, A., Sreejith, A. G., Safonova, M. and Murthy, J., High-altitude ballooning programme at the Indian Institute of Astrophysics, Current Science, 104, 708, (2013).

[4]

Wanjek, C. The Ultimate Mountaintop – Astronomy Aboard Stratospheric Balloons,

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Figure 5: Photos from our camera in stratosphere.

(a) LUCI telescope on Team Indus lunar lander.

(b) Team Indus mission to send observatory to the Moon.

(c) Star sensor and camera for orbital flights.

(d) WiFi telescope on the CubeSat.

Figure 6: Instruments developed for space flight. Sky & Telescope Magazine, September 2000. [5]

Okano, S., Okabayashi, M. and Gernandt, H. Observations of ozone profiles in the upper stratosphere using a UV sensor on board a lightweight high-altitude balloon. Memoirs of NIPR Spec. Issue, 51, 225, (1996).

[6]

Sreejith, A. G., Mathew, J., Sarpotdar, M., Nirmal, K., Suresh, A., Prakash, A., Safonova, M. & Murthy, J. Measurement of limb radiance and Trace Gases in UV

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over Tropical region by Balloon-Borne Instruments – Flight Validation and Initial Results. 2016, Atmos. Meas. Tech. Discuss., doi:10.5194/amt-2016-98, (2016). [7]

Smith, D. J. Microbes in the Upper Atmosphere and Unique Opportunities for Astrobiology Research. Astrobiology, 13, 981, (2013).

[8]

Narlikar, J. V., Lloyd, D., Wickramasinghe, N. C., et al. A Balloon Experiment to detect Microorganisms in the Outer Space. Astrophysics and Space Science, 285: 555-562, (2003).

[9]

Smith, D.J., Griffin, D. W., Schuerger, A. C. Stratospheric microbiology at 20 km over the Pacific Ocean. Aerobiologia, 26: 35-46, (2010).

[10] Smith Jr., I. S. The NASA balloon program: an overview. Advances in Space Research, 30: 1087-1094, (2002). [11] Vasudevan R., Sreenivasan S., Suneel K. B. and Kulkarni P. M. Report on the Activities of National Balloon Facility, Hyderabad. 39th COSPAR Scientific Assembly, 39, 2061, (2012). [12] Nuttall W.J., Clarke R.H. and Glowacki B. A. Resources: Stop squandering helium. Nature, 485, 7400: 573575, (2012). [13] Sreejith A.G., Mathew J., Sarpotdar M., Mohan R., Nayak A., Safonova M. and Murthy Jayant. A Raspberry Pi-Based Attitude Sensor. Journal of Astronomical Instrumentation, 3, 1440006: 1-10, (2014). [14] Prakash A., Safonova M., Murthy J., Kumble S., Mathew J., Sreejith A.G., Sarpotdar M., Nirmal K., Ambily S., Chakravortty D. and Rangarajan A., Collection of Stratospheric Samples using Balloon-Borne Payload System, 41st COSPAR Scientific Assembly, abstract ID #19527, 30 July–7 August, Istanbul, Turkey, (2016). [15] Safonova, M., Nayak, A., Sreejith, A. G., Mathew, J., Sarpotdar, M., Ambily, S., Nirmal, K., Talnikar, S., Hadigal, S, Prakash. A. and Murthy, J., An Overview of High-Altitude Balloon Experiments at the Indian Institute of Astrophysics. Astron. & Astroph. Trans., 29, (2016). [16] Safonova, M., Mathew, J., Mohan, R., Sreejith, A. G., Murthy, Jayant, Brosch, N., Kappelmann, N., Sharma, A., Narayan, R. Prospect for UV observations from the Moon. Astrophysics and Space Science, 353, 329, (2014); Prospect for UV observations from the Moon. II. Instrumental design of an ultraviolet imager LUCI. Astrophysics and Space Science, 362, 37 (2017). [17] Sarpotdar, M., Mathew, J., Sreejith, A. G., Nirmal, K., Ambily, S., Prakash, A., Safonova, M. and Murthy, Jayant. A software package for evaluating the performance of a star sensor operation. Experimental Astronomy, 43, 99, (2017). [18] Ambily, S., Sarpotdar, M., Mathew, J., Sreejith, A. G., Nirmal, K., Prakash, A., Safonova, M. and Murthy, Jayant. Development of Data Acquisition Methods for an FPGA-Based Photon Counting Detector. Journal of Astronomical Instrumentation, 6, 1750002, (2017). [19] Mathew, J., Ambily, S., Prakash, A., Sarpotdar, M., Nirmal, K.; Sreejith, A. G., Safonova, M., Murthy, Jayant and Brosch, N. Wide-field Ultraviolet Imager for Astronomical Transient Studies. Experimental Astronomy, doi: 10.1007/s10686-018-95754, (2018).

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