The Global Positioning System (GPS) satellite signals provide not only traditional radionavigation service but inexpensive and convenient radio beacons for signal propagation studies on ionosphere and atmosphere. This thesis describes the development and testing of a specialized GPS sensor which measures, plots and records real-time high-resolution L1 (1575.42MHz) GPS signal strength at a data rate of up to 10Hz. The instrument is based on an open architecture GPS receiver development kit that can be modified and rebuilt. The signal strength is defined as mean-square signal strength in the thesis. The coarse/acquisition code (C/A-code) correlation is applied and the raw correlation data from a GPS correlator chip is obtained to calculate the signal strength. The gain variation of the automatic gain control (AGC) in the GPS signal link is considered, and a model is designed and implemented in data post-processing to reduce the AGC distortion to GPS signal strength measurements. Speed limitation of 1,000 knots and height limitation of 60,000 feet are removed so that it can track spacecraft such as low earth orbit (LEO) satellite. Four testing plans are developed and conducted to test the GPS signal strength sensor. A GPS simulator is used and the testing results prove that the space-borne sensor is fully operational and the signal strength resolution can be smaller than 0.05dB. Additionally, a COM-port-to-TCP/IP GPS simulation remote control gateway is designed and implemented for the senor and the GPS simulator to conduct formation flying. A graphic user interface (GUI) program is also built to retrieve data from a commercial high-performance space-borne GPS receiver for comparison. A Red Hat Linux signal strength sensor based on the National Aeronautics and Space Administration (NASA) PiVoT GPS receiver is achieved by modifications. The NASA PiVoT sensor, working together with the former signal strength sensor and the commercial space-borne GPS receiver, will strengthen our academic research strength in the studies on the ionospheric and atmospheric effects and irregularities which cause GPS signal degradation and scintillations.