IEEE - Aerospace and Electronic Systems - May 2022 - 32

Hayabusa2 Re-Entry Capsule Tracking by Marine Radars
25. For reference, the minimum speed of a commercial
marine radar is 24 r/min. Figure 2 shows a comparison of
the noise floor level of this marine radar and a commercial
product as well as the improvement in sensitivity by
decreasing the antenna rotation speed.
The second modification was to tilt the antenna by
Figure 2.
Noise floor level of the marine radar used in the recovery operation
(blue) and a commercial product (black).
inserting an attachment between it and the transceiver unit
(see Figure 3). This modification was made in order to detect
the I/M at higher altitudes and to reduce the number of
ground reflected waves. In addition, the repetition frequency
and the pulsewidth were maximized within the limits of
marine radar regulations in Japan. This was done to improve
sensitivity, but it also increased heat generation inside the
transceiver unit. Therefore, the air-cooling mechanism of
the transceiver unit was strengthened. Other specifications
were the same as commercial marine radars.
Figure 4 shows the measurement results of the signalto-noise
power ratio (SNR) to the received power [15].
The SNR V0 required to identify the target is5 dB in (3)
[18]. However, Pf of 0.9 and false detection probability
(Pd)of 105. From Figure 4, the received power required
to identify the target was assumed to be128.4 dBm
V0 ¼5log10M
þ 6:2 þ
4:54
p
Figure 3.
Outline and photograph of the marine radar.
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Mþ 0:44
log10 Aþ 0:12ABþ 1:7BðÞ
(3)
where
A ¼ lnð0:62=PfÞ, B ¼ lnPd lnð1PdÞ.
PRELIMINARY TEST OF DETECTION PERFORMANCE
The detection performance of the marine radar was confirmed
by the preliminary tests at the Uchinoura Space
Center (USC) in February 2019 and at the Woomera Prohibited
Area (WPA) in December 2019. The USC is a
rocket launching area in Japan and is equipped with precision
radar for rocket tracking. The WPA is a land-based
test range covering more than 127,000 km2 in Australia
and was the planned landing area for the SRC following
the previous Hayabusa mission [3], [7].
In the USC test, the target with a known RCS was
Figure 4.
Measurement results of the SNR to the received power.
In this operation, Ndmin > 20 was determined with reference
to the international standard for marine radars (IEC
62388), and v was set to 1 r/min. However, Vcp was set to
6 m/s based on the previous Hayabusa mission [7], Lcp
was set to the parachute deploying altitude (10 km), and
the Pf was set to 0.9. At this time, M¼ 400, and Ndmin ¼
32
tracked to confirm the detection performance. The target
was suspended from a balloon and released. The balloon
ascended with the target to an altitude of 10 km or more
from the ground, and the precision radar tracked the target
together with the marine radar (see Figure 5). The target was
a Styrofoam sphere with a diameter of 0.45 m covered with
aluminum film. This RCS was calculated to be 0.159 m2 in
(4) [19]. This value was set based on the report of the previous
Hayabusa mission [7]
s ¼ pa2
where s is RCS (m2) and a is the radius of target (m).
IEEE A&E SYSTEMS MAGAZINE
MAY 2022
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IEEE - Aerospace and Electronic Systems - May 2022

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