HIGH ENERGY ASTROPHYSICS WITH RUBBER BALLOONS

Sandip K. Chakrabarti(1,2)

, Debashis Bhowmick(2)

, Ritabrata Sarkar(2)

, Sushanta Mondal(2)

, Arnab Sen(2)

(1)S.N. Bose National National Centre for Basic Sciences, JD Block, Salt Lake, Kolkata, INDIA,

Email:chakraba@bose.res.in (2)

Indian Center for Space Physics, 43 Chalantika, Garia Station Rd., Kolkata 700084, INDIA, Email:

debashis@csp.res.in; ritabrata@csp.res.in;sushanta@csp.res.in;arnab@csp.res.in

ABSTRACT

Rubber balloons are being used to obtain weather

related parameters, such as wind velocity, pressure and

temperature profiles. They are also excellent tools for

initiation in balloon borne experiments in colleges and

universities. With the advent of miniaturization, it is

now possible to have light weight X-ray detectors and

gamma-rays detectors which can be flown to space

using these small inexpensive balloons. We describe

here the efforts of Indian Centre for Space Physics to

carry out scientific experiments in this direction.

1. INTRODUCTION

With the miniaturization of the detectors in X-rays and

gamma rays, it has become possible to imagine that

space science could be done using latex balloons which

can fly as high as 33-42km. There are several

advantages of using weather balloons as opposed to

conventional large sized balloons. A mission with a

weather balloon is most certainly less expensive (by a

factor of say 100 or so). It is possible to launch them in

a matter of hour’s notice. Thus solar flares or

flares/outbursts in black hole binaries can be picked up

easily. There is no need to have a canonical launching

pad of ‘facility’ for small balloons and indeed they can

be launched from anywhere (including boats) as long as

predicted trajectories ensure that they may be recovered

at desirable places. Long term planning (often running

to decades) are not required and errors made in a

mission is easily corrected in the next mission.

Of course, there are disadvantages. Due to severe

weight restrictions limited to a few kilograms, it is

hardly possible to have large gyroscopes for

stabilization and accurate pointing. Similarly large

ballasts are not possible to be loaded. Large area

proportional counters must be replaced by small area

solid state detectors, for instance. Instead of pointed

observations, we may have to have observations in

survey mode (all sky monitoring) or ‘hit or miss’ mode

where a particular object may be observed in every few

seconds. Innovative imaging may have to be done so

that all the bright sources may be images and their

variabilities studied. However, ‘serious’ science can still

be done with appropriate approach. In future, we plan to

use with zero pressure plastic balloons to have longer

flight time without a need for ballasts.

With these goals in mind, Indian Centre for Space

Physics (ICSP) has been carrying out small weather

balloon missions named Dignity (D) for the last three

years. So far, fourteen un-tethered missions have been

launched (D-1 to D14) in which two were lost, and

several tethered missions were used to test indigenously

made ejection system, photography, radio

communication with the payload from ground,

telemetry, on board storage etc. Although we have been

successful only to carry out real measurements of

cosmic rays by Geiger Counters while ascend and

descend, judging from the GEANT4 simulation results

of various detectors which we have built and are going

to complete in near future, we are certain that significant

scientific goals could be achieved using these low cost

balloon missions.

2. INITIAL TESTS WITH VIDEO CAMERAS

Figure 1 shows an example of the trajectory [1] of the

balloon from lift-off till landing. Here the ground

communication with the payload was tested and real

time trajectory could be seen on a Google map. Two

video cameras, one scanning the horizon and the other

pointing to the earth were functioning till about 80

minutes after lift-off. Heath parameters inside the

payload was also computed and transmitted back.

Figure 1. Real time GPS data at the ascending and

descending phases of the D8 mission when the payload

was recovered about 130km away.

_________________________________________________ Proc. ‘20th ESA Symposium on European Rocket and Balloon Programmes and Related Research’ Hyère, France, 22–26 May 2011 (ESA SP-700, October 2011)

Figure 2. Stratospheric clouds just below the camera

(left) at about a height of 22km while blue Earth and

tropospheric clouds are seen below.

Figure 3. Details of a cloud in a video frame pointing to

the ground in D10 Mission.

Figure 4. Reconstruction of the cloudy Earth by

stitching several frames from D10 Mission.

Figure 2 shows the pictures of the stratospheric clouds

taken at a low latitude (~25 degree north). The

translucent cloud was seen just below the camera at

around a height of 22km. In Figure 3, we show a

snapshot from a height of 22 km and in Figure 4 we

show two swaths of the cloudy earth in one of the

Missions (D10) [2].

In Figure 5 we show the panoramic views obtained from

the video frames taken by the D8 payload when it was

launched inside the belt of totality 45 minutes before the

total solar eclipse started on 22nd of July, 2009 [1]. The

views shown at various stages of the eclipse is first of

its kind giving details of how the shadow of the moon

moved in and moved out.

Figure 5. 360 degree panoramic view from D8

payload. From top to bottom: 250s before totality; 150s

before totality; 50s before totality; during totality (1);

during totality (2) and when the totality at the site is

over. Note that the shadow moves in from south west in

the second panel and moved to north-east in the final

(bottom) panel.

3. STUDIES OF COSMIC RAYS

This is the first real scientific instrument that was sent.

Before that X-rays plates were sent (D3) to see how

much they were fogged and whether imaging could be

done with plates also. We also sent a rat and brought

back safely [1].

For the cosmic ray studies we used a Geiger Muller

(GM) counter with on board storage plus GPS/telemetry

and radio communication system. The Counter was very

small (two inches long and about two centimetres in

diameter) operating at 400 volts. Figure 6 shows [3] the

GM counter payload onboard D10 mission. In D10,

D12, D13 and D14 GM counters were sent, though the

results from the D13 is more complete as the data came

from the liftoff to landing. Figure 7 shows the

counts/minutes as a function of the time since liftoff.

Figure 6. ICSP GMC payload for D10 Mission.

Figure 7. Rate of cosmic ray counts per minute plotted

against time in minutes after liftoff in D13 Mission. The

peaks of particles at ~15km are observed while going up

and coming down by parachute. The burst occurs at

33km. There is some noise after the burst and before

opening of the parachute.

The classic curves obtained by the GM shows a count of

about 250 per minute at a height of 15-16 kilometers

while going and coming back. We also obtained about

50 counts per minute at 33km where the curve is

flattened for about 10 minutes. These are clearly

primary rays and we plan to fly more payloads to

determine their compositions.

Figure 8. Our X-ray Detector (XRD) payload

undergoing text and evaluation. It consists of Si-PIN

diode

4. FUTURE MISSIONS

Figure 8 shows the actual payload (700gms) constructed

by our team with Si-PIN photo diode [1, 4]. The pre-

amplifier and post-amplifier assembly have been tested

already. In Fig. 9 we show its shape used for GEANT4

simulations.

Figure 9. The computer made XRD payload of ICSP

which was used for GEANT5 simulation.

Fig. 10 and Fig. 11 show the spectra of calibrating

materials which were obtained from XRD. In Fig. 10,

Eu152 was used and in Fig. 11 Ba133 was used. We

also used sources like Cs and Am. We made a

calibration curve from these standard spectra (Fig. 12)

which will be used for spectral study of solar flares.

Figure 10. Eu152 spectrum using our XRD

In Figures 13-15, we show the GEANT4 simulation

results of the possibility to detect a Solar M class flare

by XRD using the configuration shown in Fig. 9 [4]. In

Fig. 13 we show how the incoming M-class flare

spectrum is absorbed by the atmosphere at different

heights. ranging from 32 to 42km. In Fig. 14, we show

how the Si-PIN detector would actually see it at

different heights. In Fig. 15, we show the same results

for CdTe detector in XRD. It is quite clear that without

Figure 11. Ba133 spectrum using our XRD.

Figure 12. Channel Energy calibration of our XRD.

increasing the size of the detector we can detect better if

we reach at least a height of 42km. Second, the soft

photons below about 15 keV are absorbed by the

residual atmosphere above 42km. Third, there are

secondary particles generated inside the detector at

lower energies and those have to be taken care of while

data analysis is carried out. We have done a similar

analysis with X-class flare. We find that we will be able

to detect the X-class flare (also see, [5-6]).

In Figure 16-18, we present similar results for a typical

Gamma Ray Burst (GRB) [4]. Figure 16 shows the data

after it is partly absorbed through the atmosphere of

different heights. Figures 17 and 18 show the GEANT4

simulated results obtained using SiPIN and CdTe

detectors onboard XRD. It is clear that in both of these

cases we can get significant photons only in the range of

15-80keV or so. Thus we need to either go even higher

or increase the surface area of the detectors.

Figure 13. The typical X-ray flare data after absorption

by atmosphere (Solar M class) at different heights.

Figure 14. The simulation of the same flare when

observed through the SiPIN detector of XRD.

Figure 15. The simulation of the same flare when

detected through the CdTe detector of XRD.

Figure 16. Example of a typical GRB spectrum

absorbed by atmosphere at different heights.

Figure 17. GEANT4 simulation of the same GRB

observed by our SiPIN detector.

Figure 18. GEANT4 simulation of the same GRB

observed by our CdTe detector.

5. FUTURE PAYLOADS

So far, we discussed about the XRDs fabricated by us.

We are also assembling commercially available solid

state X-ray detectors.

It is clear from our GEANT4 simulations that we need

to have a larger area detector to gather more photons at

lower energy, since our height limit is around 40km. For

this reason we are preparing detectors with larger

photon gathering capabilities, such as Photo-multiplier

tubes with NaI or CsI scintillators and CZT detectors.

For charge particles we want to use plastic scintillators

as well.

For imaging, we are in a position to send a payload

using CMOS detector with masks, such as Coded

Aperture masks (CAMs) or Fresnel Zone Plates as used

in our earlier RT-2 payloads on-board CORONAS-

PHOTON satellite [6-8].

For test and evaluation inside the laboratory, we have

assembled a climate chamber capable to going up to -40

degree Celsius and one millibar. Figure 19 shows the

climate chamber used for testing and evaluating our

payload.

Figure 18. Climate chamber to test and evaluate the

small payloads before flying.

6. SUMMARY AND CONCLUDING REMARKS

There is a niche in the subject where smaller weather

balloons may be used to achieve serious scientific goals.

We have made a professional approach to this issue and

constructed prototype instruments. We have carried out

the GEANT4 simulations for estimation of the

backgrounds and found that due to atmospheric

absorption we cannot capture the soft X-rays up to

about 15keV, but from 15 keV to 50-80keV we can

have statistically significant X-rays coming from solar

flares, black hole systems and gamma ray bursts. We

are in the process of launching our XRD payload and

hope fully will improve upon the instruments from the

results obtained.

In future we are planning to launch CZT and CMOS

detectors both for spectral and imaging studies. We

have also found that photo-multiplier tubes together

with appropriate scintillators one could obtain

statistically significant number of photons in 20-80keV

energy ranges,

We have already developed the basic necessary systems

in house: These include ejection system, radio tracking

with GPS and successful recovery by predicting the

landing location using the velocity data in the ascending

phase. So we are now ready to conduct these scientific

experiments.

7. ACKNOWLEDGMENTS

We acknowledge the members of the balloon

inflation/electronics team: H. Ray, U Sardar, R.C. Das

and recovery/logistics team members: S. Ray, S.

Mondal and S. Chakrabarti.

8. REFERENCES

1. Chakrabarti, S.K. (2010) Annual Report of Indian

Centre for Space Physics, 10

2. Chakrabarti, S.K. (2011) Annual Report of the Indian

Centre for Space Physics, 11

3. Chakrabarti, S.K., Bhowmick, D., Sarkar, R.,

Mondal, S., Sen, A., Ray, S. , Chakrabarti, S. (2011),

Measurements of Cosmic rays near Kolkata using a

weather balloon, EPL (Submitted)

4. Sarkar, R. , Chakrabarti, S.K. Bhowmick, D.,

Mondal, S., Sen, A. (2011), Simulation and laboratory

test results of a weather balloon borne X-ray detector,

Exp. Astron. (Submitted)

5. Sarkar, R. and Chakrabarti, S.K. (2010) Feasibility of

Spectro-Photometry in X-rays (SPHINX) from the

Moon, Exp. Astron. 28, 61-68

6. Sarkar, R., Mandal, S., Debnath, D., Kotoch, T.,

Nandi, A., Rao, A.R., Chakrabarti, S.K. (2011)

Instruments of RT-2 experiment on board CORONAS-

PHOTON and their test and evaluation: Background

simulations using GEANT-4 toolkit, 29, 85-107

7. Chakrabarti, S.K., Palit, S., Debnath, D., Nandi, A.,

Yadav, V., Sarkar, R. (2009), Fresnel Zone Plate

Telescopes for X-ray Imaging I: Experiments with

a quasi-parallel beam, Exp. Astronomy, 24, 109

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