Why does the body potential change more significantly when only the boom material is changed in a 3U + boom structure?

[shpark (SEOHYUN PARK)]

Hello,

I am using SPIS to investigate surface charging on a 3U CubeSat equipped with a boom. The boom is assumed to have dimensions of 0.01 × 0.01 × 0.2 m and to be attached to one end of the 3U satellite. To examine how the material properties of the spacecraft affect the surface charging of both the main body and the boom, I performed the following two simulations.

(1) Case 1: both the spacecraft body and the boom were set as Al2K
(2) Case 2: the spacecraft body was set as Al2K, while the boom was set as Kapton

However, even though the boom material was changed, the boom potential remained almost the same, while the body potential changed significantly. Since this was intended to represent night conditions, photoemission was assumed to be absent. The emission settings were as follows: Electron Secondary Emission = 3, Proton Secondary Emission = 0, PhotoEmission = 0.

(1) Case 1: body (Al2K) potential = -11953 V, boom (Al2K) potential = -11526 V
(2) Case 2: body (Al2K) potential = -14921 V, boom (Kapton) potential = -11392 V

According to the material properties provided in SPIS, the relevant characteristics of Al2K and Kapton are as follows.

• Al2K secondary electron emission peak energy and yield: 0.3, 0.97

• Kapton secondary electron emission peak energy and yield: 0.2, 1.9

There are three aspects that I do not understand.

(1) Why did the body potential change significantly even though only the boom material was changed?
(2) Why did the boom potential remain almost the same in Cases 1 and 2, even though the secondary electron yield of Kapton is larger than that of Al2K?
(3) In Case 2, the Kapton boom charged slightly more positively than the Al2K boom in Case 1, but why is the increase in negative charging of the body in Case 2 much larger than the difference in boom potential?

If anyone has encountered a similar case or has any idea about the cause of even one of these points, I would greatly appreciate it if you could share your thoughts. It is also possible that these results were caused by an error in our simulation setup, so I would be very grateful for any advice on possible mistakes in the simulation.

Simulation plasma conditions:

• Ambient plasma: (O+ ions) T_i = 0.2 eV, T_i = 10⁸ m^-3 / (electrons) T_e = 0.2 eV, N_e = 10⁸ m^-3

• Auroral electrons: (Thermal electrons) T_th = 11 keV, N_th = 10⁷ m^-3

• Spacecraft velocity: 7500 m/s

• Simulation time: 5 s

[frejon (Fredrik Leffe Johansson)]

Hi Seohyun, I take it the body and the boom are electronically or physically connected? So some current can flow from one surface to the other? That could allow the change of material to change the flow of currents to/from the S/C and thus the equilibrium potential of each in either direction.

Also, is this non-conductive Kapton? What is your definition of its potential then, as it probably should have a non-uniform potential distribution on the surface. I suspect what you are describing is the node ground potential, but the surfaces of the boom near the spacecraft can be at any potential and current can flow from them.

That said, I am not sure your simulation is not buggy, LEO polar is a challenging environment. If you have a significant potential at your boundary, or ions are ridiculously depleted, then this is a tell-tale sign of an unstable simulation.