Civil Engineering Reference
In-Depth Information
Table 2.2 Small Sat preliminary mission requirements
Mission Related Orbit:
668 km at 98.085
o
inclination
Design life:
5 years
Communication relay:
Ground station in Egypt
Coverage:
Local area of Egypt
Payload Instrument:
Multi band earth imager
Size:
0.45 m diameter by 1.1 m length
Weight:
45 kg mass
Power:
100 watts when operating
Resolution:
2.5 m
Nadir viewing with a half angle of 2
o
Payload instantaneous field of view:
o
Payload field of regard:
half angle of 80
from Nadir
o
Pointing accuracy:
±0.25
Position knowledge:
±1km
Launch Vehicle: Dnepr
Small Sat allowable mass band (includes
launch vehicle adapter):
200-300 kg
Spacecraft Derived Requirements Control:
3-axis (because of off-nadir viewing)
Payload duty cycle:
Approximately 12 min per orbit
Programmatic considerations:
Low cost with minimal development
2.4 Launch Vehicle Selection
At present, the following methods of orbital injection for small satellites are
employed in world practice:
1. Single (solitary) launching with the help of a small launch vehicle
2. Series (group) launching of several satellites with the help of one launch
vehicle:
- Launching as the additional payload together with the main satellite
- Series launching of the satellites of the same class, ''cluster launch''
3. Separation from the main satellite, ''baggy back''
In the process of selection, it should be taken into account that the small
satellite under development will function on a circular sun-synchronous orbit with
altitude of 668 km and mass band of 200-300 kg. Therefore, satellite launching
from the main satellite is not acceptable, as the disadvantages related to the latter
can affect the launching latency (waiting) time. In addition, the orbit of the main
satellite specifies the small satellite orbit. Single launching by using small launch
vehicle, like Pegasus, is also not accepted, because costs of the launching services
are thoroughly included in the satellite launching costs.
The best way to minimize launch costs is using a launch vehicle which deals
with series launching. The most famous launchers in this category are Arian 4,
Arian 5, Delta 2, Delta 4, Taurus, and Dnepr. Using Delta 2, Delta 4, and Taurus
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