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Earth Simulator

The Earth's simulator is an Earth globe that provides:

  • a geometrically-scaled appearance of the Earth (with a diameter of 130 cm) visible from the satellite board;
  • the kinematics of the satellite's motion on the sub-satellite track along the equatorial orbit, either in real time or using reasonable scaling (acceleration, deceleration of time) conditions for surveying certain surface areas. The kinematics are the same as shooting the actual earth's surface by remote sensing satellites (time, orbital parameters, coordinates of the point, coordinates of the region);
  • the conditions for communication with the “ground” (ground telemetry stations - GTSs) via a telemetry and telecommand radio link. When the ground station is in zone of geometric radio visibility of the board, the LEDs of the corresponding “ground station” are switched on;
  • the conditions for transferring data “to the ground” via a high-speed communication channel when a ground station is in zone of geometric radio visibility of the spacecraft.

The satellite “travels in a near-earth orbit,” and in fact hangs on a thread in a simulated “geomagnetic” field (inside the current frame) and rotates in a horizontal plane - either freely or under the action of an on-board control system programmed by user - at the same time as the Earth globe in front of it rotates. This simulates the movement of the spacecraft along the equatorial orbit. The part of the globe's surface near the globe's equator that is required for taking photos eventually appears in front of the suspended device. The task of the satellite control system is to orient and stabilize the satellite on the thread by this time, direct the camera's field of view with the necessary accuracy to the area of interest, take photos, and transmit the data to the user “on Earth” by orienting the photodiode pointer to the required “ground” receiving station.

The globe is controlled via the PC USB port. The PC tasks include controlling the rotation of the globe, the network of GTSs (on the globe's surface), and “ground” centers for receiving high-speed information. These centers are located on the surface of the “Earth” in previously known, fixed, and unchanging geographical points in time.

The conditions for communicating with the “Earth” via the telemetry and telecommand radio link are simulated by calculating when a particular GTS on the surface of the globe is in the zone of geometric radio visibility of the board suspended from the thread, and then issuing the appropriate command to turn on and off the radio receiver of this ground station. After switching on, the ground station is by default in the receive data (telemetry) mode.

The conditions for transferring data from the spacecraft to the Earth (a photodetector on the surface of the globe) via a “high-speed communication channel” (in our case, Wi-Fi) are simulated by using a photodiode illumination on the transmitter while maintaining connection with a given area on the surface of the rotating globe (receiver). The fact that the photodiode is illuminated on the surface of the globe for a predetermined time interval is a sign of the normal orientation of the “board” to the “Earth.” The data from the board is then transmitted via the usual Wi-Fi channel while the transmitter highlights the required marker.

The main characteristics of the globe:

  • diameter 130 cm,
  • mass of the entire simulator (globe and drive with control system inside) 40 kg,
  • mass of the globe 20 kg, globe material - durable fiberglass,
  • good contrast of globe cover,
  • a map with a view of the Earth from space and a grid of parallels and meridians,
  • vertical axis of rotation of the globe,
  • the speed of globe rotation can be PC controlled fluently or stepwise from 0 to 1 rpm; the maximum error in maintaining the rotation speed is not more than +/-2%; during the competition, the rotation speed will be set to 0.2 rpm,
  • all drives, electronics and other are located inside the globe,
  • the globe is connected to a 220V power outlet and to the USB port of the controlling PC

Characteristics of the globe control system:

  • uniaxial electric drive
  • driver for gear and driver management card
  • connection to a computer via USB
  • control system for “ground” telemetry stations and a photodiode for detecting the light

All the geometric parameters of the globe, the kinematic parameters of its rotation, the satellite gimbal, and the onboard payload capabilities (field of view, exposure time, light conditions, data transmission speed) used in the model for obtaining special information are coordinated with the dynamic on-board control system capabilities of the satellite model (speed, accuracy, number of degrees of freedom, time of continuous operation).

The task list formulated for working groups to solve using the stand should be created keeping the possibilities and limitations of the “stand + model” system in mind. The list should take into account known, well-defined, clearly-stated restrictions. These restrictions, however, should not influence the “physicality” of the phenomena and principles underlying the theory and practice of controlling a real satellite in a near-earth orbit.

The “stand + model” system should also allow for the variation of initial conditions during the experiment, thereby providing users with different versions of tasks of the same complexity and the choice of several alternative ways to solve the said task.

en/sim_earth.txt · Last modified: 2020/03/25 16:28 (external edit)