# Crowded Space: A Review on Radar Measurements for Space Debris Monitoring and Tracking
## 5 Other Countries' Radar Measurements  
Major contributions in the literature from countries outside USA and Europe are mainly sourced from Japan and Australia. Nonetheless, a few works from other nations are also noteworthy. The Middle and Upper (MU) atmosphere radar of Kyoto University is a powerful VHF (46.5 MHz) radar that has the longest history of space debris measurements in Japan [59]. The MU radar is a circular 100 m phased array composed of 475 crossed Yagi antennas, located in Shigaraki (Japan). It is capable of transmitting a RHCP signal with a peak power of 1 MW [59,60]. The features of the MU radar allow for different types of analysis on space debris, such as orbit determination using a single track [59], variation in measured RCS [60], and shape estimation [60,61]. Such characteristics guarantee a high sensitivity, enough to make the MU radar performances comparable to those of the US SSN sensors, as demonstrated by a campaign performed in 1989 [60]. The results of the latter campaign are reported in Figure 1 of [60]. In that image, the debris flux as a function of the altitude is plotted, showing a comparable amount of detections made by the MU radar with respect to the USSTRATCOM (former USSPACECOM) catalogue. Another important sensor in the Japanese debris network is the Kamisaibara Space Guard Center (KSCC) radar located in Okayama Prefecture (the western part of Japan) [62]. The KSGC radar is a S-band (3 GHz) 3 m \(\times\) 3 m active phased array enclosed in a radome, equipped with 1395 transceiver modules (TRM) capable of transmitting a linearly polarized (vertical) signal with a peak power of 70 kW [62,63]. It is designed mainly for LEO detections, with its ability to observe 1 m-sized objects at a maximum of 1350 km slant range [62,63]. The radar was employed during the 2004 fiscal year, detecting more than 500 objects. The results of the campaign are reported in Figure 23, showing the number of pieces of debris observable (and catalogued) by the KSGC radar vs. the semimajor axis of the orbit and comparing them with the total number of pieces of debris. Recent advances in the field of SSA have been made by Australia thanks to the Murchison Widefield Array (MWA). The MWA is a low-frequency (80-300 MHz) interferometer radio telescope located in the Murchison region in western Australia [64,65]. The array is organized in tiles, and each tile is a 4 \(\times\) 4 grid of dual-polarization dipole antennas with spacing of 1.1 m [64,65]. In its current status the MWA is equipped with 128 tiles, but 512 are expected as part of future plans. The peculiarity of this array is the fact that it takes advantage of a passive transmission, in the form of FM broadcast services, that  
Figure 23: Number of pieces of debris detected and catalogued vs. orbit semimajor axis for the Kamisaibara Space Guard Center (KSGC) radar 2014 campaign [62]. Reprinted from 4 th European Conference on Space Debris (ECSD), Copyright 2005, with permission from JAXA. can be reflected by objects in space [64; 65]. With this expedient, the MWA was already able to detect the International Space Station's (ISS) passage with 32 of the 128 tiles at its disposal [65]. During a recent experiment (late 2014), in the attempt to detect not only the ISS but also small satellites, the MWA was able to capture several short duration signals that under closer investigation turned out to be space debris, confirming the desired detection capability of the radar [66]. Some of the results of this campaign are reported in Figure 24, showing a total of 49 objects detected within a time interval of 19.34 min. The ability of the Ukrainian transmitter RT-70 to operate in a space debris radar scenario has briefly been discussed earlier in Section 3. The RT-70 is a 70 m dual reflector parabolic antenna located in Evaporia (Ukraine) that can operate in the frequency spectrum from VHF to X-band [67; 68]. It is able to transmit a CW signal with a peak power of about 200 kW (at 5 GHz) [67; 68].