Verification of operation plan and power balance

Power system

The solar cells (GaAs multi-junction cells) are pasted on the five panels of top and side. The connections of cells are 8 series (18.64V), and 4 parallels (1780mA) on side panels or 2 parallels (890mA) on top panel. The power generation when the panel is straight to solar direction is 33.2 W in side panels and 16.6 W in top panel. The average total power generation in sunshine calculated by numerical analysis is 41.1 W when the satellite is spinning in 2 deg/s, or 47.6 W when the bottom panel is controlled to the earth direction with 0.2-deg/s spin motion of the axis straight to earth center.

The battery unit consists of 9 series NiMH battery cells, and the total spec. is 10.8 V and 3.7 AH. In the logic circuits for charge and discharge control, the battery voltage in any temperature and current is measured and converted to the voltage (T.C.BAT-V) in specific temperature and current. When the T.C.BAT-V reaches more than 13.13 V, the charge is stopped. When it reaches less than 10.55 V, the power saving mode is started and the almost instruments are switched off. It is estimated that the battery state of charge is kept in 13 % to 87 %.

In electrical tests, the solar power (SCP-P), the battery power (BAT-P) and the bus power (BUS-P) are measured, and the loss of conversion is determined. When the bus instruments are using 25 W, it was confirmed that the value of BUS-P was 87% of SCP-P or 95.5 % of BAT-P.

Verification of power balance using satellite simulator

Developing a satellite simulator program, the change history of power parameters are estimated. This program is a server-type software running on general PC, and it includes the math models of orbit, attitude, solar cell, battery, control algorithm of battery charge and discharge, loss of power conversion, and consuming power of bus or mission instruments. The program can realize the command codes and send telemetry codes just like a satellite. It can be operated from the QL software for RISING-2 with the same procedure of electrical tests. The merits of simulator are that it can generate detail logs every 0.1 seconds and run in several-time time speed. The analysis of power budgets can be verified faster than using real satellite hardware.

  • Detail results are shown in: Y.Sakamoto, et al., "Development Status and Operation Plan of 50-kg Microsatellite RISING-2 for Earth Observations by Multi-Spectrum Instruments," The 28th International Symposium on Space Technology and Science, June, 2011, Paper No.2011-f-25.

Science observation modes

The observation modes are defined as follows. The each mode is executed in 15-min observation mode. The consuming power is the sum of the sensor instruments and the handling unit (SHU).

  • Mode-1. sprite mode (using LSI-N,W, VLFR), 7.8 W, only in eclipse
  • Mode-2. lightning mode (using WFC, VLFR), 7.6 W, only in eclipse
  • Mode-3. LSI-N mode for cumulonimbus, ground and sea surface, 5.4 W
  • Mode-4. WFC mode for aurora, ground and sea surface, 5.7 W
  • Mode-5. BOL mode for cumulonimbus, ground and sea surface, 13.3 W
  • Mode-6. RGB telescope mode (using HPC-R,G,B) for cumulonimbus, ground surface, moon and planets, 7.5 W
  • Mode-7. multi-spectrum telescope mode (using HPC-M, LTCF) for cumulonimbus, ground surface, moon and planets, 5.9 W

(C) The Space Robotics Lab (Space Exploration Lab), Tohoku University
Last-modified: 2011-06-16 (Thu) 08:33:07 (2804d)