150
A. V. Bogatiy et al.
At the same time, pulsed plasma thrusters have their own advantages. In APPT,
the thrust and power consumption are controlled by changing the frequency of the
pulses at constant discharge energy. As a result, their specific characteristics, such as
specific impulse and thrust efficiency, are independent of power consumption. At the
same time, for stationary electric propulsion, this dependence does not take place:
with a decrease in power consumption, the specific characteristics of the thruster are
decreasing, too. When the power of the electric propulsion system is below a certain
threshold, the pulsed plasma thrusters will be superior to stationary ones in basic
characteristics. Besides, the pulsed plasma thrusters have a number of additional
advantages:
• Simplicity of design and electrical circuit and lack of expensive materials, which
leads to a low cost of the electric propulsion system as a whole.
• Low weight and ease of control of PPU having one channel only for converting low
onboard voltage to high (or two identical channels in the case of dual redundancy).
• Simplicity and reliability of the solid propellant storage and feed system, which
does not have pipelines, valves, or other fittings.
• Cheap and non-deficient propellant, which is usually a fluoroplast-4 (Teflon).
• Constant operation readiness and extremely precise value of the thrust pulse,
which is explained by the accuracy of defining the small magnitude of impulse
bit.
• Monoblock design of the electric propulsion system, which does not require
separate slots for PPU and PSFS to be provided for in SSC design.
The overall dimensions of the available domestic APPT with a power consumption
of about 100 W make it possible to store enough propellant to provide a total pulse
of up to 15–30 kN s. Based on this fact, it is possible to determine the predominant
field of application of APPT-based electric propulsion system—the maintenance of
small spacecraft with a power of supply system of up to 100 W and with an active
lifetime in a range from 1 to 10 years in low Earth orbits with altitudes of 400 km to
700 km.
In addition, it is necessary to take into account the possibility of APPT using as
a part of the precise attitude control systems of SSC for remote-sensing and other
purposes. Table 11.3 shows the characteristics of APPT-based electric propulsion
Table. 11.3 Comparative
characteristics of electric
propulsion systems based on
low-power APPT designed
for SSC attitude control
EPS
EO-1
APPT-120
Power consumption, W
60
60
Average thrust, mN
0.86
0.90
Total EPS mass with propellant store, kg 4.05
3.0
Total pulse, kN s
0.46
0.7
Impulse bit, mN s
0.86
0.45
Specific impulse, m/s
10,400 7,160
Effective specific impulse, N s/kg
93
233
A. V. Bogatiy et al.
At the same time, pulsed plasma thrusters have their own advantages. In APPT,
the thrust and power consumption are controlled by changing the frequency of the
pulses at constant discharge energy. As a result, their specific characteristics, such as
specific impulse and thrust efficiency, are independent of power consumption. At the
same time, for stationary electric propulsion, this dependence does not take place:
with a decrease in power consumption, the specific characteristics of the thruster are
decreasing, too. When the power of the electric propulsion system is below a certain
threshold, the pulsed plasma thrusters will be superior to stationary ones in basic
characteristics. Besides, the pulsed plasma thrusters have a number of additional
advantages:
• Simplicity of design and electrical circuit and lack of expensive materials, which
leads to a low cost of the electric propulsion system as a whole.
• Low weight and ease of control of PPU having one channel only for converting low
onboard voltage to high (or two identical channels in the case of dual redundancy).
• Simplicity and reliability of the solid propellant storage and feed system, which
does not have pipelines, valves, or other fittings.
• Cheap and non-deficient propellant, which is usually a fluoroplast-4 (Teflon).
• Constant operation readiness and extremely precise value of the thrust pulse,
which is explained by the accuracy of defining the small magnitude of impulse
bit.
• Monoblock design of the electric propulsion system, which does not require
separate slots for PPU and PSFS to be provided for in SSC design.
The overall dimensions of the available domestic APPT with a power consumption
of about 100 W make it possible to store enough propellant to provide a total pulse
of up to 15–30 kN s. Based on this fact, it is possible to determine the predominant
field of application of APPT-based electric propulsion system—the maintenance of
small spacecraft with a power of supply system of up to 100 W and with an active
lifetime in a range from 1 to 10 years in low Earth orbits with altitudes of 400 km to
700 km.
In addition, it is necessary to take into account the possibility of APPT using as
a part of the precise attitude control systems of SSC for remote-sensing and other
purposes. Table 11.3 shows the characteristics of APPT-based electric propulsion
Table. 11.3 Comparative
characteristics of electric
propulsion systems based on
low-power APPT designed
for SSC attitude control
EPS
EO-1
APPT-120
Power consumption, W
60
60
Average thrust, mN
0.86
0.90
Total EPS mass with propellant store, kg 4.05
3.0
Total pulse, kN s
0.46
0.7
Impulse bit, mN s
0.86
0.45
Specific impulse, m/s
10,400 7,160
Effective specific impulse, N s/kg
93
233