ROCSAT-1 (Republic of China Satellite-1)
February 10, 2025
What is ROCSAT-1?
ROCSAT-1, later renamed FORMOSAT-1, was the first satellite mission carried out by Taiwan’s National Space Organization (NSPO). Taiwan partnered with several US organizations to develop the capability to produce and operate high-reliability satellite systems. Through a collaboration with TRW (later Northrop Grumman), UTD provided the lonospheric Plasma and Electrodynamics Instrument (IPIE) and partnered with NSPO to develop and carry out the mission science investigation. ROCSAT-1 operated successfully on-orbit from 1999 to 2004, starting at an altitude of 600 km and an orbit inclination of 35°.
Mission Objectives
A wide range of technical objectives included a comprehensive examination of the charged particle motions in the low and middle latitude regions during a time when the levels of solar activity were high. The propagation and scattering of radio waves as they pass through the ionosphere is directly dependent on the refractive index of the medium, which is determined by the charged particle density distribution in space and time. This spatial and temporal distribution of charged particles is dependent on their motion, the fundamental parameter that the IPEI is designed to measure. Continuous operations of the payload allowed seasonal, longitudinal and local time variations in the particle motion to be observed for the first time at altitudes near 600 km, thus providing the foundation for specification and prediction models of the charged particle density distribution.
Launch and Operation
The ROCSAT-1 satellite was launched from Cape Canaveral on January 27, 1999 using an Athena launch vehicle. The satellite was released into a 600 km circular orbit with a 35° inclination. It provided over five years of continuous operations across all latitudes between +35° and -35° for all longitudes and local times during a period of high solar activity. Satellite operations were conducted by the National Space Program Office in Taiwan, where a specially designed ground station was used to command the spacecraft and receive the downlink science data.
Planar Plasma Sensors
Planar plasma sensors, such as the lon Trap, lon Drift Meter, and Retarding Potential Analyzer, use a series of fine mesh grids to create potential fields to affect the motion of ions and electrons that enter the sensor aperture. Grids are typically constructed of woven gold- plated tungsten wire with diameter as small as 0.001 inch,comparable to the diameter of human hair. Fine wire is used to allow most of the particles to pass through the screen orgrid.
A spacecraft in low Earth orbit moves at speeds of around 7,000 m/s, so the neutral particles, ions and electrons that enter the sensor are moving at this high relative speed. Positively charged ions can be slowed down or repelled by a positive potential field, and negatively charged electrons react in a similar way to negative fields. If the kinetic energy of a given particle is greater than the grid potential energy (1⁄2 m2 >q), it passes through and reaches the collector, otherwise it is repelled.
The energy distribution of the plasma is determined by measuring the collected current at a range of grid potentials. The shape of this distribution is used to determine ion velocity, composition and temperature. Specific species of ions may be excluded by setting the potential energy above the average kinetic energy of the species. This principle is used to exclude H+ ions from lon Drift Meter.
The ROCSAT-1 IPIE
- SenPot: Detects the local plasma potential used to set sensor bias
- Ion Trap: High-frequency ion density measurement
- lon Drift Meter A and B: Simultaneous horizontal and vertical ion drift measurement
- Retarding Potential Analyzer: Ion ram velocity, composition and temperature
ROCSAT-1 Discoveries
The IPEI project, through collaboration between the National Central University and the University of Texas at Dallas, produced a unique data set that was utilized by groups at each institution in addition to being distributed for use by the world community of
scientists.
Notable achievements were:
- Provided data for the first space comprehensive empirical model of the vertical motions of the plasma in the topside ionosphere at low and middle latitudes [Fejer et al., 2008]
- Revealed the simultaneous presence of storm time influences in the vertical plasma motions in the middle latitude ionosphere. [Huang et al., 2008]
- Revealed an altitude variation in the superrotation of the topside ionosphere at the equator [Pacheco et al., 2011]
References
Fejer, B. G., Jensen, J. W., & Shin-Yi, S. (2008). Quiet time equatorial F region vertical plasma drift model derived from ROCSAT-1 observations. Journal of Geophysical Research, 113,A05304. https://doi.org/10.1029/2007JA012801
Huang, C. M., Chen, M. Q., and Su, S. Y. (2008), Plasma drift observations associated with intense magnetic storms by the IPEI on board ROCSAT-1, J. Geophys. Res., 113, A11301, doi: 10.1029/2008JA013405.
Pacheco, E. E., Heelis, R. A, & Su, S.-Y. (2011). Superrotation of the ionosphere and quiet time zonal ion drifts at low and middle latitudes observed by Republic of China Satellite-1 (ROCSAT-1). Journal of Geophysical Research, 116(A11), A11329. https://doi.org/10.1029/2011JA016786