On solar electric propulsion system application possibility for low-orbit small spacecraft

Аuthors

Marakhtanov M. K.¹, Pil'nikov A. V.^2*

1. Bauman Moscow State Technical University, MSTU, 5, bldg. 1, 2-nd Baumanskaya str., Moscow, 105005, Russia
2. Central Research Institute of Machine Building, TSNIIMash, 4, Pionerskaya str., Korolev, Moscow region, 141070, Russia

*e-mail: corp@tsniimash.ru

Abstract

A comprehensive material on operation of spacecraft with solar electric propulsion systems is accumulated by now. The latter are designed for spacecraft correction on both geostationary and circular low earth orbits.

At the same time, there is a tendency to developing of small spacecraft of various purposes, such as scientific, communication, Earth remote probing, navigation, hydro-meteorological etc. operating on low circular orbits with the height within the rage of 180–280 km. Such spacecraft are relatively cheap and possess the mass of 10 to 500 kg. However, such indicator as minimum orbit height, its relationship with the spacecraft weight and size, as well as parameters of its engine unit remain undetermined. System analysis and experimental data on spacecraft with solar electric propulsion systems, operating at the height of 140–280 km are practically inaccessible.

The paper considers the problem of small spacecraft transition fr om a higher circular orbit to a lower one. As far as the Earth atmosphere gradually transfers to vacuum, the aerodynamic drag force grows while a spacecraft descent. We suggest surmounting this force through the electric jet engine thrust power. It is obvious that while the spacecraft descent the aerodynamic drag grows, and such parameters as thrust power and electric jet engine power should be increased continuously. At large the problem becomes dynamical. Besides, the main cause of the orbit height limiting will be the drag force of the solar battery. Thus, the minimum orbit height h_min below which the spacecraft, equipped with the solar electric jet engine cannot exist, is limited by the spacecraft drag force due to the solar battery. At the lower altitude the battery's drag force will be greater than the electric rocket engine thrust force.

For the spacecraft motion analysis, we assumed that the solar battery takes the shape of an autonomous panel with rotation angle control to the sun radiation direction. The power flux density or the solar radiation at the Earth orbit is Q = 1400 W/m² (solar constant). The efficiency of photoelectric transducers based on a three-stage gallium arsenide (GaAs) equals to η_SB= 0.22. The solar battery specific power is α = 308 W/m². If the solar battery plane is oriented normally to the orbital movement velocity vector the drag factor equals to C_SB = 2.15, and if it is oriented along this vector it equals C_SB = 0.15.

If an ion thruster is used as an electric jet engine its specific impulse is assumed as Ι_SP = 4500 s, and its efficiency equals to η_T= 0.7. In case of plasma engine of the SPT type I_SP = 1700 s and η_T= 0.55 correspondingly.

The lower limits of the orbit altitude h_min = 200 for the solar electric jet system with the ion engine, and h_min = 180 km with plasma engine of the SPT type were established by the results of the performed analysis. The upper lim it of the altitudes descending from which requires continuous build-up of the electric jet system solar battery area to overcome the atmospheric aerodynamic drag is the altitude of h_max = 260 km.

The paper demonstrates that for a spacecraft continuous exploitation at the latitude of 180–260 km application of solar electric jet engine and atmospheric gas as a working agent is possible. Application of high- frequency ion engine of 4.4–5 kW is expedient for the propulsion installation such kind. With the specified power and solar battery weight, the weight of electric jet propulsion installation will be no less than 90–100 kg, and the total minimum weight of the spacecraft will be no less than 500–600 kg.

Keywords:

small spacecraft, minimal circular orbit height, electric propulsion system, solar cell array

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