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The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras

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Abstract

Space missions involving humans require a better understanding of various phenomena happening in space environments. A number of experiments need to be conducted in microgravity for addressing various issues encompassing safety (primarily fire) and better understanding of fluid and material behaviour. Of the various methods used for obtaining microgravity conditions, drop towers offer ground based microgravity platform. They provide a cost effective platform for doing short duration, repeatable, high quality microgravity experiments. This paper describes key factors that influence the design of a drop tower. The salient features of 2.5 s microgravity tower set up at National Centre for Combustion Research and Development (NCCRD), IIT Madras (IITM) are discussed. Primary features of the three critical elements, namely the drop capsule, the release unit and the decelerator unit are described along with review of these elements in existing drop towers. The IITM drop tower operates in ambient atmospheric conditions to minimise the cost of operation. In order to achieve good quality microgravity levels, a dual capsule configuration is adopted. The shape of the outer capsule is arrived at by detailed transient computational fluid dynamic analysis of the drag shield under free fall condition over the drop height. A pneumatic mechanism is used for capsule release and brought to rest at the end of fall in a carefully designed decelerator unit. The decelerator unit consists of an airbag with controlled air outflow for smooth deceleration.

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Abbreviations

ASME-:

American Society of Mechanical Engineers

cDAQ -:

Compact Data Acquistion

CAS -:

Chinese Academy of Sciences

DC -:

Direct Current

DST -:

Department of Science and Technology

GoI -:

Government of India

GSM -:

Grams per Square Meter

HASTIC-:

Hokkaido Aerospace Science and Technology Incubation Center

IITM -:

Indian Institute of Technology Madras

ISRO -:

Indian Space Resesarch Organisation

LeRC -:

Lewis Research Center

NASA -:

National Aeronautics and Space Administration

NCCRD-:

National Center for Combustion Research and Development

NMLC-:

National Microgravity Laboratory China

PVC -:

Polyvinyl Chloride

SRE -:

Space capsule Recovery Experiment

ZARM-:

Zentrum für Angewandte Raumfahrttechnologie und Mikrogravitation

ZGRF -:

Zero Gravity Research Facility

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Acknowledgments

The authors acknowledge the financial support provided by the DST(GoI) to National Centre for Combustion Research and Development (NCCRD) towards the development of the microgravity drop tower facility. Further, the authors are grateful to Mr Christian Eigenbrod and Dr. Thorben Könemann of ZARM, Prof. Osamu Fujita of Hokkaido University and Prof. Satoshi Okajima of Hosei University for their valuable suggestions and to Manu N M, Arjun B J, Sabarish V N for their valuable contributions in the preliminary stages of this endeavor.

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Authors and Affiliations

  1. Department of Aerospace Engineering, Indian Institute of Technology Madras, Chennai, 600036, India

    Nikhil V.V., Abhilash Nair, Niketh P, Amit Kumar & Muruganandam T.M.

Authors
  1. Nikhil V.V.
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  2. Abhilash Nair
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  3. Niketh P
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  4. Amit Kumar
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  5. Muruganandam T.M.
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Corresponding author

Correspondence to Amit Kumar.

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Nomenclature

ad -Resultant acceleration of drag shield [m/s2] ai -Resultant acceleration of inner capsule [m/s2]adecel–Minimum ideal deceleration obtainable for a given drop height and deceleration distance [m/s2] Ap(NC)–Projected area of the airbag not in contact with the package [m2] Ap(C) –Projected area of the airbag in contact with the package [m2] A(t) –Varying airbag outlet orifice area during the deceleration [m2] CDd-Co-efficient of drag of drag shield (outer capsule) CDi -Co-efficient of drag of inner capsule Di-Aerodynamic drag experienced by inner capsule [N] Fn-Normal force exerted by the airbag on the capsule during impact g –Acceleration due to gravity [m/s2] gres,d–Residual gravity of drag shield (outer capsule) LR –Reference length in the x-direction [m] m –Mass of the falling weight on the modeled airbag [kg] Md -Mass of drag shield (outer capsule) [kg] Mi -Mass of inner capsule [kg] Pf –Final pressure [Pa] Pi–Initial pressure [Pa] ΔPbag–Pressure difference across the airbag skin [Pa] Q –Volume flow rate [m3/s] Sd-Projected area of drag shield (outer capsule) [m2] td –Deceleration time [s] T1,T2-Forces experienced by the package due to airbag [N] T∞-Temperature of gas at ambient temperature [K] TF-Temperature of gas at flame temperature [K] u -Velocity of inner capsule [m/s] UR –Reference velocity in the x-direction [m/s] U –Relative velocity between air and the falling body [m/s] v-Velocity of drag shield (outer capsule) [m/s] vi –Impact velocity [m/s] vair –Velocity of exiting air [m/s] V –Volume of pressure vessel [m3] x-Displacement [m] xd –Deceleration length [m] βi-Ballistic co-efficient of inner capsule [kg/m2] 𝜃-Angle made between the deforming airbag and the sides of the falling mass ‘m’ ρ-Density of air [kg/m3] ρ∞-Density of gas at ambient temperature [kg/m3] ρF-Density of gas at flame temperature [kg/m3] ϕ-Angle made by the airbag with gravity

This article belongs to the Topical Collection: Interdisciplinary Science Challenges for Gravity Dependent Phenomena in Physical and Biological Systems

Guest Editors: Jens Hauslage, Ruth Hemmersbach, Valentina Shevtsova

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V.V., N., Nair, A., P, N. et al. The 2.5 s Microgravity Drop Tower at National Centre for Combustion Research and Development (NCCRD), Indian Institute of Technology Madras. Microgravity Sci. Technol. 30, 663–673 (2018). https://doi.org/10.1007/s12217-018-9639-0

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