ECSS-E-ST-35 and E-ST-35-01 cover all electric propulsion systems used on spacecraft including those discussed here. That standard gives top-level requirements including performance, interfaces, operation, quality and verification.
The requirements described in the present Standard cover:
• Design requirements arising from the interaction of the spacecraft with the plasma and electric and magnetic fields outside the spacecraft, including those generated by neutralizers, and presented in 11.2. These requirements are related both to the effect of the plasma environment on the operation of the EP system and the effect of the EP system on other spacecraft systems through its interaction with the environment.
• Validation requirements on ESD validation of electric propulsion systems, covered in 11.3. This addresses both the method of validation and specific aspects to be validated.
¾
Validation is achieved mainly
through ground testing and computer modelling. Both of these approaches have
limitations, and it is important to give careful consideration to using
complementary experimental and computer simulations to provide confidence in
different aspects of a design.
For systems with flight heritage, in-flight performance monitoring can provide
further validation.
o Ground testing is covered in 11.3.1. The ground testing of EP systems involves vacuum chambers. To minimize wall effects on beam characteristics, chambers are large compared to the size of the thruster and the vacuum quality is continuously monitored. However, the accuracy of the measurements suffers from the physical limitations imposed by the chamber. For example, chambers usually have a higher background plasma density than the one found in orbit and usually do not show the full effect of beam space-charge, since the beam is neutralized by impact with the chamber wall or target. Similarly, there is usually increased sputtering in the chamber because of the higher plasma density.
o Computer modelling is covered in 11.3.2. Computer modelling of the EP system and its spacecraft plasma interaction is the most complete way to get a deep insight into the behaviour of a thruster on a spacecraft. However, computer simulations generally involve simplifications and approximations which make simulations practical within limited resources.
o In-flight monitoring is covered in 11.3.3.
¾ Requirements on particular aspects of ESD validation are covered in 11.3.4 (spacecraft neutralization), and 11.3.5 (beam neutralization).
There are a number of other environmental interactions of EP systems that are addressed by designers that are not covered here, e.g.
• Neutralizers as sources of EMC interference. (ECSS-E-ST-20-07 applies).
• Ion thrusters and neutralizers and the emitted beams as sources of optical and UV light and thermal radiation.
• EP plasma beams interfering with reception and transmission of radio communications.