Big Endian vs Little Endian

All computers are byte addressable. For example in a 32 bit processor int is 4 bytes. There are two ways to represent this, the big endian and the little endian.


The most significant byte is stored first in the big endian. Suppose the address of the int is A. In a so-called big endian computer, the highest order byte is stored at A, and the lowest order byte is stored at address A+3. In a so-called little endian computer, address A stores the least significant byte and the most significant byte is at address A+3.


IBM, Motorola are Big endian and Intel on the other hand is little Endian. Consider the decimal integer 91,329. This is 00 01 64 C1 in hexidecimal. If this were to be stored at address A in a big endian computer, 00 would be at address A, 01 at address A+1 64 at address A+2, and C1 at address A+3. On a little endian computer, C1 would be the value at address A, 64 at address A+1, 01 at address A+2, and 00 at address A+3.


Computer networks are big endian. This means that when little endian computers are going to pass integers over the network (IP addresses for example), they need to convert them to network byte order. Likewise, when the receive integer values over the network, they need to convert them back to their own native representation.


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Subsystem -4 (CCD Subsystem) - Telescope Over the Internet

Our project uses SBIG ST – 7E CCD (765 * 510) camera to take images of the objects viewed. The CCD camera attached to the telescope eye piece is connected to the server using the parallel port. The camera is controlled using the web based server program developed by us. This program is embedded with the web interface so that the user can give the commands necessary via internet. The user can select a desired exposure time and take the image. The image can be downloaded in .ST7 format. So he will require CCDOPS software installed in his client machine to view it. This software can be downloaded for free.

CDD Fixed to the eye piece

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Subsystem 3 (Programming logic) - Telescope Over the Internet

The Login screen

The user is presented with a web interface. The interface is designed so that the user can select an object he or she wishes to view from the data base provided or manually input the celestial coordinates. He/ She is also privileged to select Sun, Moon and planets for which the ephemerides of that particular time will be automatically calculated. Initially the algorithm to convert of RA/ DEC celestial coordinates to HA/DEC Equatorial coordinates is implemented in the client side using javascript. This conversion takes the longitude, latitude of the telescope, celestial coordinates of the object to be viewed and local time as inputs and calculates the local sidereal time, from which the HA is calculated. If the user selects one of the closest objects then the ephemerides of that object for that particular time is calculated in javascript prior to the conversion algorithm

The Telescope controller screen

Resulting HA is used to check if the particular object can be viewed from the location of the telescope. If not an error message is displayed to the user saying that this object cannot be viewed as it is out of the visible sky. When the above test is passed, the current coordinates of the telescope is read from the server and resultant degrees to be turned is calculated in the serverside program which is implemented in ASP.NET/C#. This result is transmitted to the main controller through the RS232.Then the current location of the telescope is saved in the server.

Manual fine tuning is also provided if the celestial object doesn’t come within the center of field of view. User can manually rotate the telescope with a certain amount in HA/DEC to manually fine tune.

The telescope is calibrated initially to point the North and Zenith and these coordinates are defined as (0,0). The coordinate system of our telescope takes these as the reference point. After the initial turn the telescope rotation compensates for the earth rotation as well. That is, the time elapsed from the previous command to the present is calculated and HA rotation is compensated accordingly. Also for every rotation, time taken for the rotation is calculated based on the steps to be turned and it is compensated with additional steps. After the object is in the center of the field of view, the earth synchronous system compensates the earth movement and keeps the object steadily in the center.

The CCD Controller screen

Extensive testing has been done to find out the backslash in the gear system in varies positions of the telescope. This backslash has been compensated with necessary steps in the programming logic




















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Subsystem -2 (Electronic Subsystem) - Telescope over the Internet

The telescope is controlled by two motor controllers and a main controller to drive the two stepper motors attached to the telescope. The two motor controllers are attached to the main controller and the main controller is connected with the dedicated server through RS232.

The motor movement commands carrying degrees by which the two motors have to be turned from the current location are sent from the server through the RS232 protocol to the main controller. The main controller board calculates the steps for each motor and sends the appropriate motor commands to both individual motors.

The two motors are driven sequentially. The time taken to turn is also calculated and compensated while delivering the degrees by which the telescope needs to be turned and this will be explained in detail in subsystem 3




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Subsystem -1 (Mechanical subsystem) - Telescope over the Internet

The telescope is rotated about two axes, HA (Hour Angle) and DEC (Declination). A Bipolar stepper motor is used for the HA axis and a unipolar stepper used for the DEC axis. Both the motors have been supported with a good, high torque supportable gear system which gives the telescope an overall resolution of 1.8 arcsec in DEC and 10.3 arcsec in HA.

After the construction of the gear system, the gear ratios of the DEC and HA axes are 2520 and 3600 respectively.

The telescope is mounted in an equatorial mount. Thus the telescope has been mounted with an inclination of 6° 40’  with the vertical axis and the initial position of the telescope has been calibrated to point the North Pole. This eliminates the need for both axes to be rotated to track the viewing object continuously. Our system has been coupled with a clock drive which allows us to rotate the telescope compensating the earth’s rotation for continuous tracking. Also equatorial mount eliminates the rotation of the objects against their focal point and thus enables clear and smooth imaging

HA Motor and gear System

Declination Motor and part of the gear system

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Architectural Over View of the system - Telescope over the Internet

The basic architecture of the project is given above. Telescope over the internet system is divided into four subsystems.

 Subsystem 1 (Mechanical Subsystem)

Subsystem 2 (Electronic Subsystem)

 Subsystem 3 (Programming logic)

 Subsystem 4 (CCD controller)

Components of the project

  8” Schmidt Cassegran 2110 mm optical telescope

  SBIG ST – 7E CCD  (765 * 510)

  Unipolar and Bipolar stepper motors with supporting gear system

  Earth synchronous system

  L298 – heat sink fixed Motor control boards

  Main controller board

  Dedicated server

  Power system unit

Telescope Over the Internet - Introduction

Telescope over the Internet was a product developed as a final year project for BSc Engineering Course of University of Moratuwa, Faculty of Engineering, for the Electronic and Telecommunication Engineering Department, by group No 14 from the batch of 2005/2006

An Introduction about this project is provided below

Telescope over the Internet is novel in the aspect that it will be the first telescope in Sri Lanka which can be accessed by the general public over the internet. The system involves automation of a manual 8” Schmidt Cassegran 2110 mm telescope into a fully automated telescope which can be controlled through the internet to focus at the celestial bodies and download pictures using the SBIG ST – 7E CCD camera attached to it. The user will be able to enter the celestial coordinates of any celestial object in our web interface and download real-time CCD images over the internet.

High resolution stepper motors and gear systems give the telescope a resolution of 1.8 arcsec. Users can either enter the celestial coordinates of the objects they wish to observe or they can select any object from our database for which the ephemerides will be automatically calculated. Celestial to equatorial conversion algorithm has been implemented in the client side and the resultant equatorial coordinates are passed to the local dedicated server located at the telescope site. The server runs two simultaneous programs

(1) Telescope Controller

(2) CCD controller

 The server side Telescope Controller program extracts the last focused coordinates of the telescope, compensates for earth synchronous motors and calculates the angle for both axes to turn further. This result is passed to the main controller board in the telescope. After processing the motor movement commands are sent to both the motor controller boards.

After the telescope movement completes, the user establishes connection to our local ST7 CCD camera through our server side CCD controller program, sets exposure time and downloads the image to his machine.

User also has the privilege of manual fine tuning the telescope to bring the object within the center of field of view. Earth synchronous motors (The third motor set) fixed to the HA axis, compensates for the earth movement, so that an object remains within the field of view despite earth’s rotation.

Web based control of a telescope and CCD camera with high precision is the key part of this project.


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