Chapter 3: Spacecraft

Here is the work-script for chapter 3

11 October  2017
3.1 Power systems
We talked about solar cells, the solar constant, the variation in illumination and batteries. Click here for animation how solar panels are deployed. Here is a link to a description of a new type of battery.
We looked at the variation of illumination and made sure that we understood every variable in the equation.

3.2 Attitude and orbit control
We then focussed on the control system for keeping the satellite in a particular orientation (attitude).
We talked about the sources of rotational torque. We leaned about earth, sun and star sensors and how an
erroneous attitude is corrected.
We then focused on the three-axis stabilization.

13 October  2017
We looked at nutation dampers. We looked at the engineering model of the RadioAstron spacecraft. We also saw the focus cabin, the flywheels,
the gas tanks and the gas jets.


18 October  2017
We covered issues related to the orbit control and compared the fuel allocations for various maneuvers 

3.3 Telemetry, tracking and command (TT&C)

We talked about the measurement of the orientation,  the environment  and the health of a satellite 
and how these measurements are transmitted.  Then we covered issues related to the tracking 
of a satellite. 
We talked about how commands are executed. 

We learned about allocated satellite bands:
                
Band         f (GHz)           usage
                (typical)
UHF         0.8 - 0.9         mobile satellite service
L               1.2 - 1.7         GPS
S               2.1 - 2.3          DSN
C               3.7 - 6.4          geostat. satellite
X               7.1 - 8.5          DSN
Ku             11  - 15           geostat. satellite
Ka              17 - 30           DSN
Q                40 - 50           intersatellite communic.
V                50 - 65           intersatellite communic.

3.4 Transponder
We learned about uplink and downlink.

20 October  2017
We interpreted the block diagram of a transponder. 

23 October  2017
We discussed the TWTA and compared it to the amplification in the magnetic field of a pulsar. We learned about solid-state power amplifiers, FETs and HEMTs. We discussed intermodulation noise, how it is generated and how it affects the spectrum.


25 October  2017
We covered three types of antennae, the wire antenna or Hertz dipole, the horn antenna and the reflector antenna. The Hertz dipole was the antenna Heinrich Hertz used to discover radio waves. Click here for a description of the dipole and how an EM wave in space pushes electrons in a dipole back and forth and generates a voltage between the two elements of a dipole and a current through them. The most famous horn antenna is the one Penzias and Wilson used to improve satellite communications and found by chance the cosmic microwave background radiation which is the strongest evidence we have for the Big Bang theory.
Small versions of the horn antenna are similar to feeds, or feed horns, which are used on satellites for a broad coverage and also in the focal area of reflector antennas.

30 October  2017
Reflector antennas are used on satellites to direct information to small areas of the Earth. Large reflector antennas are shown here and  here .
We talked about spot beam technology and the radiation pattern or beam pattern or the beam of a telescope. We also learned 
about the gain of a telescope and the degradation of the gain as a function of the rms surface variations with respect to a perfect paraboloid.
Click here for a 3-dim beam pattern of a paraboloidal antenna. Click here for figures of beam patterns as a function of gain and angle.