An overview of the ‘Aryabhata’ project

Aryabhata, India’s first satellite, was successfully launched into a nearearth orbit on 19 April 1975, from a USSR Cosmodrome. The primary objective ofAryabhata was to establish the indigenous capability in satellite technology.Aryabhata, weighing 358 kg, was quasispherical in shape, and had body-mounted solar cells and Ni-Cd chemical batteries as primary power sources. Other features of the spacecraft include power control systems, passive thermal control system, PCM/FM/PM telemetry system transmitting data at 256 bits/s in real time and 2560 bits/s in the stored mode, PDM/AM/AM telecommand system, cold gas spin stabilisation system with nutation damper and a number of sensors. The satellite also included three scientific experiments—one on x-ray astronomy, the second for observing solar neutrons and gamma rays and the third on aeronomy. The present paper gives an overview of the basic features of the satellite, associated ground stations and a brief account of the fabrication, testing and (in-orbit) performance of the satellite. Results of some of the technological experiments carried out inAryabhata are also briefly described.     

The attitude control system of the satellite for earth observation ‘ Bhaskara ’

The satellite for earth observation (Bhaskara) launched on 7 June 1979 has two TV cameras and a passive microwave radiometer for earth resources survey and meteorological studies respectively. As it had to be a minimally modified version of the earlier spin-stabilised satelliteAryabhata, it is configured as a spin-stabilised satellite, with a spin rate of between 6 to 11 rev/min and a spin axis perpendicular to the orbital plane within 3°. The cold gas system ofAryabhata was modified to provide a low and controlled thrust for spin-up and spin-axis orientation operations. Two horizon-crossing sensors are used for automatic spin-axis control and attitude determination on ground. This paper presents a report on the system evolution, design, simulation and on-orbit performance ofBhaskara.     

The thermal control system

This paper presents the design, analysis and performance of the thermal control system ofAryabhata. A passive thermal control system, using flat absorber-AK-512 black paint for the outer surface of the satellite and a combination of solar reflector-AK-512 white paint and mechanical polishing for the inner surfaces, was employed to maintain the temperature of all the electronics subsystems onboard the satellite within the specified limits of 0°C and 40°C during the operational life of the satellite. The in-flight temperature data obtained from sixteen temperature sensors onboard the satellite was compared with the theoretically predicted temperature values and the agreement was good for all electronic subsystems housed within the framework of the satellite. The observed deviations in temperature for the tape recorder, proportional counter package and gas bottles of the spin-up system are attributed to the assumptions made for the mathematical model. It has been found that by improving these approximations, the deviations could be reduced to negligible values.     

The communication system

The paper discusses the salient features of system design considerations for both uplink and downlink, subsystem details and the in-orbit performance of the communication system forAryabhata.     

The stabilisation system

The attitude stabilisation ofAryabhata was accomplished by spinning it about its axis of maximum moment of inertia. The spin stabilisation ensures satisfactory thermal control, uniform power generation through the body mounted solar panels and the scan capability for the scientific payloads. To bring down the nutation of the spinning spacecraft to a value well within the specified limits, a fluidin-tube damper was also provided. The design philosophy, specifications, details and the dynamics of such a system are presented in this paper along with the qualification and performance evaluation tests of the components and subsystems. Also, the in-orbit performance of the stabisation system is discussed.     

Orbit computations

Orbital information forAryabhata was computed and made available for telemetry and tracking schedules and for mission analysis. Taking an available statevector once in a week from USSR, the orbital computations were made for the first four months using a numerical integration procedure. During the later period of the mission, an analytical method was adopted to reduce the computer time.Aryabhata, in a near circular orbit at 600 km and having an inclination of 50.68°, experienced a constant atmospheric drag due to which the semi-major axis decayed by about 0.5 km in one year. The nodal regression rate, due to asphericity of the earth, was almost constant at 4.632°/day. The inclination remained constant throughout the year.     

The telemetry system

This paper describes the telemetry system employed inAryabhata. The telemetry link provides a means for monitoring diagnostic and other parameters for efficient and controlled operation of the satellite besides transmitting data pertaining to the three scientific experiments. The design specifications and details, qualification tests and in-orbit performance of the telemetry system are also described in this paper.     

The power system

The paper describes, in detail, the power system forAryabhata. The various elements of the power system-solar array, storage battery and the power conditioners and control units-are covered. The in-orbit performance of the power system is dealt with, highlighting the probable reasons for the failure of one of the bus-lines of the power system.     

The telecommand system

The telecommand system plays an important role in the success of any satellite mission. This paper provides insights into the design, development and evolution of theAryabhata telecommand system. The paper includes detailed specifications and performance of both the ground and onboard segments of the telecommand system.     

Antenna systems for the “Aryabhata’ mission

The onboard and ground antenna system employed in theAryabhata mission for telemetry and telecommand operations are described. The onboard antenna system common to telemetry and telecommand frequencies consists of four monopoles fed in turnstile configuration and generates a near isotropic pattern with worst dips of the order of −10 dB over approximately 0.2% of the total radiation sphere area. The ground antenna system consists of a high gain (16 dB) telecommand antenna and a telemetry array of eight medium gain Yagis (gain 22 dB).     

An experiment to detect energetic neutrons and gamma rays from the sun

A payload for the detection and measurement of high energy neutrons and gamma rays from the sun was flown onboard the first Indian satelliteAryabhata. The payload system for this neutron-gamma experiment was designed for detecting energetic neutrons in the energy range 10–500 MeV and gamma rays in the energy range 0.2–20 MeV. The details of the design of the payload, various tests carried out on it as well as the preliminary in-orbit performance are presented.     

The structure

The design, analysis and testing methods of theAryabhata satellite structure are briefly presented. The general requirements and constraints which formed the basis of the design of the structure are explained. The theoretical and experimental studies conducted to evaluate the structural behaviour under various environmental loads expected during ground operations and during flight are also described. The salient features of the fabrication procedures and the details of physical parameters are presented. Finally the evaluation of the structure is made on the basis of the results of ground tests and the flight performance.     

A statistical analysis of weight and cost parameters of spacecraft with special reference to ‘Aryabhata’

The available data on the weights of several NASA and ESRO spacecraft have been statistically analysed using the regression analysis technique and empirical relationships of the type W_T = AW{kx/β} have been established, where W_T is the total weight of the spacecraft, W_x is the weight of one of its chosen subsystems andA and β are constants for the chosen subsystem. It is found that the weight data ofAryabhata show a fairly good fit with these empirical relationships. Further, using an established statistically derived relationship for NASA satellites, involving the cost of a spacecraft and its weight parameters, it is found that the cost ofAryabhata is much lower than that of other NASA satellites of comparable weight. The implications of these results are briefly discussed.     

The x-ray astronomy experiment

One of the scientific experiments onboardAryabhata was designed to detect and measure celestial x-rays in the energy range 2.5–155.0 keV. The payload systems comprising proportional counter and scintillation counter, telescopes were intended for observations in the pointed and scan modes respectively for investigating the emission properties of celestial x-ray sources. The paper presents the details of these telescopes, their inflight performance as well as the nature of the data obtained during the first few orbits.     

Electromagnetic metamaterials

This paper proposes a review of electromagnetic metamaterials based on the idea that these are composite materials, their properties depending of the type and dimensions of the structural elements as well as the dimensions of unit cell. From the multitude of structural elements, only few that could present negative permittivity and negative or very high permeability in the range of radio and microwave frequency were chosen. The method of determination for the constitutive parameters (μ_eff and ?_eff) of metamaterials based on the S parameters or transmission and reflection coefficients is presented. Moreover, some applications of metamaterials are described, the attention being focused on perfect lenses and novel structures, namely conical Swiss rolls, electromagnetic cloaks and sensors for nondestructive evaluation of materials. Given that the spatial resolution of these sensors can be substantially improved in comparison to classical sensors, the metamaterial lenses are used for the manipulation of evanescent waves.     

Monitoring of resin flow in the resin transfer molding (RTM) process using point-voltage sensors

Multiple point-voltage sensors were used to monitor the mold filling stage of the resin transfer molding (RTM) process. Both lineal- and point-voltage sensors are electrical circuits in which the two poles of the sensor are closed when liquid thermoset resin arrives at the sensor location in the mold cavity. The electrical conductance of the liquid resin causes an increase in the output voltage, V_sens of the circuit. Although the gradually varying in situ data of a lineal sensor is more informative than a point-voltage sensor, lineal-voltage sensors might mislead the user if the resin covers the wires at multiple sections, or if the resin covers the wires starting from an unexpected section. Two kinds of sensors were developed: a set of similar, wrapped and compact lineal-voltage sensors acting as point-voltage sensors; and a point-voltage sensor with voltage amplification. Without this amplification, the increase in V_sens might be difficult to detect if the resin system has a low electrical conductivity and there is noise in the DAQ system. The accuracy and reliability of the new sensor system was verified by comparing the in situ sensor data with the visually recorded resin flow.     

The aeronomy experiment

The experiments described here were flown onAryabhata and were mainly designed to study the global distribution of suprathermal electrons, ionosphere-magnetosphere coupling, theF-region anomaly and the hydrogen geocorona. The experiments consisted of a retarding potential analyser and two ultraviolet ion chambers. The former was designed for the measurement of the flux of suprathermal electrons in the earth’s atmosphere while the latter was for measuring the intensity of the resonantly scattered hydrogen Lyman alpha (1216 Å) and photoelectronically excited OI (1304 Å) emissions.     

Spin decay of ‘Aryabhata’

The spin decay ofAryabhata due to eddy current losses in the earth’s magnetic field is analysed in this paper. The satellite is idealised as a conducting spherical shell while the earth’s field is taken to be equivalent to that of a magnetic dipole. The results of this simplified analysis match quite well with the actual observations.