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Abstract and Figures

HAYABUSA is the first spacecraft ever to land on and lift off from any celestial body other than the moon. The mission, which returned asteroid samples to the Earth while overcoming various technical hurdles, ended on 2010 June 13, with the planned atmospheric re-entry. In order to safely deliver the sample return capsule, the HAYABUSA spacecraft ended its 7-year journey in a brilliant ``artificial fireball'' over the Australian desert. Spectroscopic observation was carried out in the near-ultraviolet and visible wavelengths between 3000 Å and 7500 Å at 3–20 Å resolution. Approximately 100 atomic lines such as Fe i, Mg i, Na i, Al i, Cr I, Mn i, Ni i, Ti i, Li i, Zn i, O i, and N i were identified from the spacecraft. Exotic atoms such as Cu i, Mo i, Xe i and Hg i were also detected. A strong Li i line (6708 Å) at a height of $\sim\ $55 km originated from the onboard Li-Ion batteries. The FeO molecule bands at a height of $\sim\ $63 km were probably formed in the wake of the spacecraft. The effective excitation temperature as determined from the atomic lines varied from 4500 K to 6000 K. The observed number density of Fe i was about 10 times more abundant than Mg i after the spacecraft explosion. N$_{2}^{+}$ ($1^-$) bands from a shock layer and CN violet bands from the sample return capsule's ablating heat shield were dominant molecular bands in the near-ultraviolet region of 3000–4000 Å. OH($A$–$X$) band was likely to exist around 3092 Å. A strong shock layer from the HAYABUSA spacecraft was rapidly formed at heights between 93 km and 83 km, which was confirmed by detection of N$_{2}^{+}$ ($1^-$) bands with a vibration temperature of $\sim\ $13000 K. Gray-body temperature of the capsule at a height of $\sim\ $42 km was estimated to be $\sim\ $2437 K which is matched to a theoretical prediction. The final message of the HAYABUSA spacecraft and its sample return capsule are discussed through our spectroscopy.
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arXiv:1108.5982v1 [astro-ph.EP] 30 Aug 2011
Near-Ultraviolet and Visible Spectroscopy of
HAYABUSA Spacecraft Re-entry
Shinsuke Abe
National Central University, 300 Jhongda Road, Jhongli, Taoyuan 32001, Taiwan
shinsuke.avell@gmail.com
Kazuhisa Fujita
Japan Aerospace Exploration Agency, 7-44-1 Jinidaiji-higashi-machi, Chofu, Tokyo 182-8522, Japan
fujita.kazuhisa@jaxa.jp
Yoshihiro Kakinami
Institute of Seismology and Volcanology, Hokkaido University, Kita 10 Nishi 8, Kita-ku, Sapporo
060-0810, Japan
kakinami@mail.sci.hokudai.ac.jp
Ohmi Iiyama
Osaka Science Museum, 4-2-1 Nakanoshima, Kitaku, Osaka, Osaka 530-0005, Japan
Hirohisa Kurosaki
Japan Aerospace Exploration Agency, 7-44-1 Jinidaiji-higashi-machi, Chofu, Tokyo 182-8522, Japan
Michael A. Shoemaker
Kyushu University, 744 Motooka, Nishi-ku, Fukuoka 819-0395, Japan
Yasuo Shiba and Masayoshi Ueda
Nippon Meteor Society, 43-2 Asuka Habikino Osaka 583-0842, Japan
and
Masaharu Suzuki
GOTO Inc., 4-16 Yazaki-cho, Fuchu, Tokyo 183-8530, Japan
(Received 2011 June 23; accepted 2011 August 28)
Abstract
HAYABUSA is the first spacecraft ever to land on and lift off from any celestial
body other than the moon. The mission, which returned asteroid samples to the
Earth while overcoming various technical hurdles, ended on June 13, 2010, with the
planned atmospheric re-entry. In order to safely deliver the sample return capsule,
the HAYABUSA spacecraft ended its 7-year journey in a brilliant “artificial fireball”
over the Australian desert. Spectroscopic observation was carried out in the near-
ultraviolet and visible wavelengths between 3000 and 7500 ˚
A at 3 – 20 ˚
A resolution.
Approximately 100 atomic lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I,
Zn I, O I, and N Iwere identified from the spacecraft. Exotic atoms such as Cu I, Mo I,
1
Xe Iand Hg Iwere also detected. A strong Li Iline (6708 ˚
A) at a height of 55 km
originated from the onboard Li-Ion batteries. The FeO molecule bands at a height of
63 km were probably formed in the wake of the spacecraft. The effective excitation
temperature as determined from the atomic lines varied from 4500 K to 6000 K. The
observed number density of Fe Iwas about 10 times more abundant than Mg Iafter
the spacecraft explosion. N+
2(1) bands from a shock layer and CN violet bands
from the sample return capsule’s ablating heat shield were dominant molecular bands
in the near-ultraviolet region of 3000 – 4000 ˚
A. OH(A-X) band was likely to exist
around 3092 ˚
A. A strong shock layer from the HAYABUSA spacecraft was rapidly
formed at heights between 93 km and 83 km, which was confirmed by detection of
N+
2(1) bands with a vibration temperature of 13000 K. Gray-body temperature
of the capsule at a height of 42 km was estimated to be 2437 K which is matched
to a theoretical prediction. The final message of the HAYABUSA spacecraft and its
sample return capsule are discussed through our spectroscopy.
Key words: Meteors, meteoroids – asteroid – atmospheric re-entry – spectroscopy
1. Introduction
HAYABUSA, the third engineering space mission of JAXA/ISAS (Japan Aerospace
eXploration Agency/Institute of Space and Astronautical Sciences) had several engineering
technologies to verify in space (e.g, Kawaguchi, Fujiwara & Uesugi 2008). HAYABUSA was
launched on May 9, 2003. On September 12, 2005, HAYABUSA arrived at the asteroid (25143)
Itokawa. The mission was the first to reveal that Itokawa is a rubble-pile body rather than
a single monolithic asteroid among S-class asteroids (Abe et al. 2006; Fujiwara et al. 2006).
Finally, the spacecraft performed a landing on Itokawa to collect asteroid samples in November,
2005. Due to a loss of communications, HAYABUSA started an orbit transfer to return to the
Earth in April, 2007. The round-trip travel between the Earth and Itokawa with the aid of ion
engine propulsion was the first success of its kind in the world (Kuninaka 2008).
On June 13, 2010, the HAYABUSA spacecraft returned to the Earth with the re-entry
capsule containing asteroid samples. The sample return capsule was separated at 10:51 UT,
which was just 3 hours before the atmospheric re-entry. Due to the failure of all bi-propellant
thrusters for orbital maneuvering, the HAYABUSA spacecraft could not escape from its Earth
collision course. Though Japan had several successful experiences with re-entry capsule tests
(e.g., RFT-2 (1992), OREX (1994), EXPRESS (1995), HYFREX (1996), and USERS (2003)),
the HAYABUSA sample return capsule was the first Japanese re-entry opportunity that entered
the Earth’s atmosphere directly from an interplanetary transfer orbit with a velocity over 12
km/s. The HAYABUSA sample return capsule and the spacecraft entered the atmosphere at
2
Table 1. Specifications of spectroscopic and imaging cameras.
Name Color Lens Spectrograph FOV (H ×V) Pixels Frame rate
VIS-HDTV Color 80mm/f5.6 300 /mm25×171920 ×1080 30 fps
UV-II B/W 30mm/f1.2 600 /mm23×13720 ×480 29.97 (NTSC)
NCR-550aColor 4.6 – 60 mm 90– 8diagonal 800 ×412 29.97 (NTSC)
Nikon D300sColor 18 – 200mm 10×71280 ×720 24 fps
WAT-100N∗∗ B/W 25mm/f0.95 15×11768 ×494 29.97 (NTSC)
Spectrum resolution = 12˚
A (1st order), 6˚
A (2nd order) & 3˚
A (3rd order).
Spectrum resolution = 20˚
A.
Video data was published on the JAXA digital archive; http://jda.jaxa.jp
∗∗ Video data is used for the trajectory estimation of fragmented HAYABUSA (Shoemaker et al. 2011).
13:51 UT. The HAYABUSA spacecraft disintegrated in the atmosphere, and the capsule flew
nominally and landed approximately 500 m from its targeted landing point.
Spectroscopy of the HAYABUSA re-entry was a golden opportunity to understand (i)
the atmospheric influence upon Earth impactors such as meteors, meteorites and meter-sized
mini-asteroids, because for such natural bodies the original material, mass, and shape are all
unknown (e.g., Ceplecha et al. 1996; Abe 2009); for HAYABUSA, not only these parameters
but also the re-entry trajectory were under perfect control, (ii) the hypervelocity impact of large
objects that are difficult to reproduce in laboratory experiments, and (iii) the flight environment
of re-entry capsules for the utilization of future Japanese sample return missions.
2. Observation and data reduction
A ground observation team consisting of 16 members was organized by JAXA (Fujita
et al. 2011a). Triangulation observations were coordinated between GOS3 station at Tarcoola
(134.55858 E, –30.699114 S, 0.152 km altitude) and GOS4 station at Coober Pedy (134.71819
E, –29.03392 S, 0.224 km altitude) in southern Australia (figure 1). The National Astronomical
Observatory of Japan (NAOJ) also made a HAYABUSA observing expedition at Coober Pedy
(see Watanabe et al. 2011).
Spectroscopy was carried out using two spectrograph systems: a VISual HDTV camera
(VIS-HDTV) and an UltraViolet Image-Intensified TV camera (UV-II). An EOS 5D MarkII
with lens (f=80mm, f/5.6) was applied to the VIS-HDTV system equipped with a transmission
grating (300 grooves per mm, blazed at 6100 ˚
A). The UV-II system consisted of a UV lens
(f=30mm, f/1.2), a UV image intensifier (φ18-mm photo-cathode: S20), two relay lenses
(f=50mm, f/1.4), and a SONY HDTV Handycam. The UV-II system was equipped with a
reflection grating (600 grooves per mm, blazed at 3300 ˚
A). The VIS-HDTV camera obtained
the 0th, 1st, and 2nd order spectra in 4000 – 7000 ˚
A , and the UV-II camera observed the 1st
3
128˚
128˚
130˚
130˚
132˚
132˚
134˚
134˚
136˚
136˚
138˚
138˚
140˚
140˚
−36˚ −36˚
−34˚ −34˚
−32˚ −32˚
−30˚ −30˚
−28˚ −28˚
−26˚ −26˚
0 100
km
AUSTRALIA
Woomera
GOS3 (Tarcoola)
GOS4 (Coober Pedy)
Adelaide
113.2 km
66.9 km
33.2 km
99.4 84.5 62.7
54.9 40.0
Fig. 1. HAYABUSA tra jectory and observation stations in Australia. The HAYABUSA re-entry has
flown over and landed on the Woomera Prohibited Area (WPA) where unauthorized people have no
admittance. GOS sites were located on the border of the WPA. A thick black line shows the trajectory
of sample return capsule in which white dots indicate the heights of beginning (113.2 km), maximum
brightness (66.9 km) and the end (33.2 km) detected by our cameras. Several heights at which the spectra
were analyzed are indicated by the X marks.
4
Table 2. Beginning and terminating of light detected by each camera and corresponding trajectory of HAYABUSA and the
capsule.
Time HeightVelocityEvent Cameras
UT km kms1(SPectrum or IMage)
13:51:50.1 113.21 12.05 Beginning WAT-100N (IM)
13:51:53.5 106.17 12.06 Beginning NCR-550a (IM)
13:51:54.3 104.53 12.06 Beginning UV-II (SP)
13:51:57.8 97.46 12.06 Beginning D300s (IM)
13:52:03.9 85.47 12.07 Beginning VIS-HDTV (SP)
13:52:12.9 68.63 11.95 Explosion all
13:52:13.6 67.38 11.90 Explosion all
13:52:13.9 66.85 11.88 Maximum all
13:52:17.1 61.39 11.57 Explosion all
13:52:17.2 61.22 11.55 Explosion all
13:52:19.5 57.53 11.18 Explosion all
13:52:19.9 56.90 11.10 Explosion all
13:52:22.7 52.79 10.44 Ending VIS-HDTV (SP)
13:52:40.2 36.81 3.38 Ending UV-II (SP)
13:52:42.1 35.98 2.94 Ending D300s (IM)
13:52:47.4 34.09 2.08 Ending NCR550a (IM)
13:52:50.6 33.17 1.74 Ending WAT-100N (IM)
The trajectory of HAYABUSA and the capsule was obtained by our observation (Boroviˇcka et al. 2011).
The velocity relative to the Earth’s center is given (the velocity relative to the surface is about 0.37 km/s
lower because of Earth’s rotation).
order spectrum in 3000 – 7500 ˚
A (figure 2). A part of the 2nd order spectrum of the VIS-
HDTV was overlapped with the 3rd order spectrum. The specifications of the spectroscopic
and imaging cameras are summarized in table 1.
The tracking observations at GOS3 were carried out by S. Abe using co-aligned dual
imaging cameras (Nikon D300s and WAT-100N) and the UV-II spectrograph which were
mounted on the same hydraulic tripod. Tracking was performed while watching a video mon-
itor taken by WAT-100N (WATEC Inc.). The high-sensitivity television camera, NCR-550a
(NEC Corp. & GOTO Inc.), equipped with three 1/2 type EM-CCD (Electron Multiplying
CCD) image sensors, was also used to observe the zoomed color TV operated by O. Iiyama. At
GOS4, the VIS-HDTV spectroscopy was achieved by Y. Kakinami adopting the same tracking
method. Meanwhile, 6×7 photographic cameras using a fish-eye lens with a rotating shut-
ter were operated simultaneously at GOS3 by S. Abe and at GOS4 by Y. Kakinami and Y.
Shiba. In this paper, the most reliable trajectory (time, height, and velocity) determined by
5
0.0
0.2
0.4
0.6
0.8
1.0
3000 4000 5000 6000 7000 8000
Efficiency
Wavelength (Å)
VIS (1st order)
VIS (2nd order)
UV (1st order)
Fig. 2. Efficiency curves of the VIS-HDTV and UV-II spectroscopic cameras. The 1st order spectra are
normalized 1.0 at their maximum. The efficiency of the 2nd order of the VIS-HDTV is relative to its 1st
order spectrum. The maximum efficiency of the UV-II and the VIS-HDTV’s 1st and 2nd orders are 4440,
5804, and 5160 ˚
A, respectively.
our photographic observation is referred (Boroviˇcka et al. 2011). Note that the trajectories
derived from different cameras (Shoemaker et al. 2011; Ueda et al. 2011) were comparable
to our result and the JAXA prediction. Tracking the capsule was difficult because although
there were predictions for the time and point in the sky when the objects would first appear,
the capsule moved faster and tracking became more difficult later in flight. In order to track
the fast moving HAYABUSA trajectory smoothly, observers were sufficiently trained by using
an imitation moving laser pointer on the planetarium dome that was arranged by M. Suzuki.
These instrument pointing exercises allowed successful tracking of the HAYABUSA emissions
(Abe 2010).
Background and stars were removed by subtracting a median frame shortly before or
after the spectrum. After flat-fielding and averaging of the HAYABUSA spectrum, the wave-
length was examined carefully using well-known strong atomic lines such as Mg I(5178 ˚
A) and
Na I(5893 ˚
A). The pixels were converted to wavelengths with a simple linear function. After
6
more known lines were identified, the wavelength was precisely determined again with regard
to the synthetic atomic lines that were convolved by the spectrum resolution (Boroviˇcka 1993).
On the other, spectra of Venus and Canopus (αCar) were used to calculate the efficiency curves
for the VIS-HDTV and UV-II cameras, respectively (figure 2). Table 2 gives trajectories of the
HAYABUSA spacecraft (H >50 km) and the capsule (H<50 km) compared with detections
by our imaging and spectroscopic cameras. The VIS-HDTV spectroscopy was aimed at the
HAYABUSA spacecraft (50<H<85 km), whereas the UV-II spectroscopy was intended to ob-
serve the faint spectrum at the beginning height (H>80 km) and the capsule spectrum near
the terminal height (H<50 km). Here, we selected some of the best data among a series of
spectrum (see figure 12 in Fujita et al. 2011a).
3. Results
3.1. VIS-HDTV spectrum in 4000 – 7000 ˚
A
Figure 3 shows the VIS-HDTV spectra of the HAYABUSA spacecraft at heights of 84.5,
62.7, and 54.9 km. The estimated absolute magnitude at each height were –7, –12, and –8,
respectively. Note that the absolute magnitude is defined as the magnitude an object would have
as if placed at the observer’s zenith at a height of 100 km. Corresponding color images taken
with the NCR-550a and the Nikon D300s were compared. These spectra were not calibrated
by the sensitivity curve so that they could be compared with the color as seen by an average
human eye as well as with the color images. Identified atoms were indicated on the top of
each emission. After the spectral response calibration, the 1st and the 2nd order spectra were
obtained (figure 4). Most of the 1st order spectra of the VIS-HDTV and the UV-II during the
explosion phase were saturated in their intensities. The 2nd order spectra of the VIS-HDTV,
fortunately, were free from saturation and were worthy of close inspection. The absolute flux
was estimated using the unsaturated 2nd order spectrum when the maximum magnitude of –
12.6 was reached at a height of 66.9 km (Boroviˇcka et al. 2011). Identified atoms and molecules
using the VIS-HDTV are summarized in table 6.
At a height of 84.5 km, Mg I(5173 and 5184 ˚
A) and Na I(5890 and 5896 ˚
A) emissions
were dominant. During the explosion phase, numerous strong emissions were seen in the visible
spectrum. Some exotic lines were detected, such as Cu I(5700 and 5782 ˚
A), Mo I(5506 and
5533 ˚
A), Xe I(4624 and 4671 ˚
A), and Hg I(4358 and 5461 ˚
A), which typically could not be
seen in a natural meteor spectrum. Note that the “duralumin” of HAYABUSA’s structure
contains Al, Cu, Mg, and Mn. MoS2(molybdenum disulfide) was used as a lubricant in many
places of the spacecraft. HAYABUSA’s propulsion system operated by accelerating ionized Xe
(xenon gas) through a strong electric field, and expelling it at high speed. Of the total 66 kg
of xenon gas that was carried on HAYABUSA, there remained about 10 kg at the time of the
Earth return. Xe Iat 4671 ˚
A was clearly seen in the spectrum (H=62.7 km) after the main
7
Fig. 3. Visible spectrum of HAYABUSA spacecraft compared with color images taken by the NCR-550a
(NEC Corp. & GOTO Inc.) forming a background and the Nikon D300s in a rectangular box. Identified
atomic lines are indicated atop each emission. ’?’ marks are unknown (unidentified) lines. A color spec-
trum as seen by an average human eye is shown (Nick Spiker; http://www.repairfaq.org/sam/repspec/).
explosion, and disappeared at a lower height (H=54.9 km). The strong Li Ilines (6104 and
6708 ˚
A) at a height of 54.9 km were detected from the spectrum of the HAYABUSA spacecraft.
It is most likely that the observed Li Iemissions originated from the Li-Ion batteries consisting
of 11 prismatic cells with 6.3 kg total mass onboard the HAYABUSA spacecraft. A series
of strong Zn Ilines (4680, 4722, and 4811 ˚
A) were detected that was probably originated from
the spacecraft. Similar Zn Ilines have been seen in a “paint” spectrum of the NASA Stardust
capsule due to paint that was applied to the surface of the capsule (Abe et al. 2007a; Jenniskens
2010a).
The continuum spectral profile around 6000 ˚
A at a height of 62.7 km is very similar to
published laboratory measurements of the “orange bands” of FeO which have been detected by
Jenniskens (2000) and Abe et al. (2005a) in Leonid meteor persistent trains. FeO is the most
common molecule observed in the spectrum of bright and relatively slow fireballs (Ceplecha
8
0
100
200
300
400
4200 4400 4600 4800 5000 5200 5400 5600 5800 6000 6200 6400 6600 6800 7000
Flux (10−9 W m−2 nm−1)
Wavelength (Å)
2nd order
H=62.7km (13:52:16.3 UT)
H=54.9km (13:52:21.2 UT)
FeO (Jenniskens, 2000)
0
20
40
60 1st order
H=84.5km (13:52:04.4 UT)
H=54.9km (13:52:21.2 UT)
Fig. 4. The VIS-HDTV spectra of the HAYABUSA spacecraft in the 1st (upper panel) and in the 2nd
(lower panel) order after spectral sensitivity calibration. The 2nd order spectrum was not obtained for
H=84.5 km due to its faintness, while the 1st order spectrum was mostly saturated for H=62.7 km. The
spectral match with the laboratory spectrum of the FeO orange bands (Jenniskens 2000) is superposed.
Since the 3rd order is clearly mixed with the 2nd order spectrum below 6600 ˚
A , the 3rd order spectrum
is omitted.
1971; Boroviˇcka 1993). The FeO can be formed during the cooling phase when the temperature
drops to 2500 – 2000 K (Berezhnoy & Boroviˇcka 2010), thus it may be emitted in the wake of
the HAYABUSA spacecraft. Recently, FeO has been discovered in a terrestrial night airglow
spectrum observed with the Odin spacecraft (Evans et al. 2010).
3.2. UV-II spectrum in 3000 – 4000 ˚
A
Figure 5 shows a series of the UV-II spectra for the spacecraft-capsule mixed at heights
between 99.4 km – 82.9 km and for the capsule at heights between 44.7 km – 39.6 km before
spectral sensitivity calibration. N+
2(1) at 3908 ˚
A was a significant band head during the
beginning phase, and during the later phase the near-ultraviolet region was filled with N+
2(1)
bands whose band heads were 3880 and 3533 ˚
A. Figure 6 shows the UV-II spectra at heights of
92.5 km and 82.9 km after sensitivity calibration. A scaled 3rd order spectrum obtained using
9
Table 3. Identification of atoms and molecules in 3000 – 4000 ˚
A. Identified atoms here were based on the spacecraft-capsule
mixed spectrum at a height of 82.9 km (13:52:05 UT), while molecular bands resulted from the spacecraft-capsule mixed
spectra at a height of 92.5 km (13:52:00 UT), 82.9 km (13:52:05 UT), and 62.7 km (13:52:16 UT). Identified atoms and
synthetic molecular spectra are shown in the UV-II spectrum (figure 6). The precision of the temperature estimation is
about ±500 K.
Identified line
Band head Temperature Molecule
Wavelength (˚
A) Tv=Tr(K)
3092 2000 OH system (A2Σ+X2Π)
3294 4000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3560 4000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3908 4000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3292 13000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3533 13000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3880 13000 N+
2(1) system (B2Σ+
uX2Σ+
g)
3585 13000 CN violet system (B2Σ+X2Σ+)
3849 13000 CN violet system (B2Σ+X2Σ+)
Identified line
Wavelength (˚
A) Element multiplet Wavelength (˚
A) Element multiplet
3020 Fe I9 3434 Ni I19
3021 Fe I9 3441 Fe I6
3091 Mg I5 3441 Fe I6
3092 Fe I28 3444 Fe I6
3093 Al I3 3446 Ni I20
3093 Al I3 3648 Fe I23
3134 Ni I25 3687 Fe I21
3226 Fe I155 3944 Al I1
3233 Ni I7 3962 Al I1
3415 Ni I19 3969 Fe I43
3424 Ni I20
10
0
50
100
150
200
250
300
3000 4000 5000 6000 7000 8000 9000 10000
Relative Intensity (a.u.)
Wavelength (Å)
N2+(1−)
CN
Fe I
N2+(1−)
Fe I + Ni I
N2+(1−)
OH
Altitude (UT)
99.4km (13:51:56.8)
96.5km (13:51:58.3)
94.5km (13:51:59.3)
92.5km (13:52:00.3)
82.9km (13:52:05.3)
44.7km (13:52:29.4)
42.7km (13:52:31.4)
41.8km (13:52:32.4)
Fig. 5. A time series of the UV-II spectra of HAYABUSA spacecraft (dotted lines) and the re-entry
capsule (solid lines) before spectral sensitivity calibration. The saturation in intensity reaches near 250 in
this figure. Some important molecular and atomic species below 4000 ˚
A are indicated atop each emissions.
the VIS-HDTV is superposed on this figure. The model spectrum of N+
2(1) (B2Σ+
uX2Σ+
g)
system with four bands heads (3300, 3500, 3900 and 4200 ˚
A) caused by different vibrational
states were carried out varying the temperatures from 1000 K to 20000 K using the SPRADIAN
numerical code (Fujita & Abe 1997). Assuming that a rotation temperature equals to a vibra-
tion temperature, N+
2(1) bands convolved by the spectral resolution (20 ˚
A) were examined
(figure 6). The CN violet bands (B2Σ+X2Σ+) and a possible contribution of OH band
(A2Σ+X2Π) were also demonstrated in the same way. N+
2molecules were originated from
the atmospheric gas. CN molecules were produced by a chemical product of ablated carbon
atoms from the heat shield of the capsule and atmospheric nitrogen molecules. Both N+
2and
CN molecules were generated in the shock layer of the body. The derived temperatures of
N+
2(1) bands at heights of 92.5 km and 82.9 km were 4000 K and 13000 K, respectively.
Though most of CN bands were buried under strong N+
2(1) bands, a clear CN band head at
3533 ˚
A was detected which is explained by the vibration temperature of 13000 K. The other
emission features consisted mainly of Fe I, Mg I, Al Iand Ni I. Table 3 gives the identification
11
0
100
200
300
400
500
600
700
800
900
3000 3200 3400 3600 3800 4000 4200 4400
Relative Intensity (a.u.)
Wavelength (Å)
... VIS (3rd order)
Al I+Fe I
Fe I
Fe I
Fe I + Ni I
Fe I + Ni I
Ni I Mg I + Fe I + Al I
H=92.5km (13:52:00.3 UT)
H=82.9km (13:52:05.3 UT)
H=62.7km (13:52:16.3 UT)
N2+(1−) ; Tv,r = 4000K
N2+(1−) ; Tv,r = 13000K
CN ; Tv,r = 13000K
OH ; Tv,r = 2000K
Fig. 6. Selected UV-II spectra of HAYABUSA spacecraft after sensitivity calibration compared. The
scaled 3rd order of the VIS-HDTV spectrum without sensitivity calibration is shown in the 3400 – 3600
˚
A range. N+
2(1) bands from a shock layer and CN violet bands from an ablating heat shield of a
sample return capsule are dominant molecular bands. OH(A-X) band is likely to exist around 3092 ˚
A,
but blended with atomic lines. Assuming that a rotation temperature equals to a vibration temperature,
the model spectrum of N+
2(1), CN, and OH(A-X) systems are superposed.
Table 4. Gray-body temperature of the sample return capsule.
Time Height Velocity Temperature
UT km kms1K
13:52:31.35 42.69 6.35 2482 ±11
13:52:32.35 41.81 5.88 2437 ±14
13:52:32.99 41.28 5.58 2395 ±15
of atoms and molecules in the range between 3000 – 4000 ˚
A.
12
1
10
100
1000
4000 4500 5000 5500 6000 6500 7000 7500
Relative Intensity (a.u.)
Wavelength (Å)
H=41.8km, V=5.9km/s (13:52:32.35 UT)
Gray−body temperature = 2437 ± 14 K
Fig. 7. The gray body spectra of the sample return capsule at a height of 42 km. Near-ultraviolet
region below 4500 ˚
A is affected by atom and molecule emissions. Thus, Plank’s formula was applied to
the range between 4500 – 7000 ˚
A as shown.
3.3. Gray-body spectrum of the capsule
A black-body is an idealized object with a perfect absorber and emitter of radiation
whose emissivity is larger than 0.99. An object which has lower emissivity such as a re-entry
capsule is often referred to as a gray-body. The capsule spectrum was well separated from
HAYABUSA’s fragments below 45 km in height while N+
2(1) and CN bands were still strong
in the near-ultraviolet region (figure 5). After sensitivity calibration, the gray-body temperature
in the wavelengths between 4500 – 6500 (7000) ˚
A was estimated employing Planck’s formula.
The gray-body temperatures of 2482 ±11 K, 2437 ±14 K, and 2395 ±15 K were measured
at heights of 42.7 km, 41.8 km, and 41.2 km, respectively (table 4; figure 4).
13
Table 5. Derived excitation temperature of radiating gas, the column density and the intensities of identified main neutral
atoms. The precision of the temperature estimation is about ±500 K, and that of other parameters is within a factor of 2–3.
Height (km) 84.51 62.72 54.94 54.94
Spectrum order 1st 2nd 1st 2nd
T (K) 6000 6000 4500 4500
Mg I1.0E+0 1.0E+0 1.0E+0 1.0E+0
Fe I6.0E-1 1.0E+1 9.0E+0 9.0E+0
Mn I 2.0E-1 3.0E-1 3.0E-1
Ti I<1.0E-3 2.0E-2 2.0E-2 2.0E-2
Na I1.2E-2 1.8E-2 1.0E-3 7.0E-4
Cr I1.2E-2 4.0E-2 4.0E-2 4.0E-2
Li I – 3.2E-3 –
Ni I<1.0E+1 1.0E+1 <1.0E+0 5.0E+0
4. Discussion
4.1. VIS-HDTV spectrum in 4000 – 7000 ˚
A
When the surface temperature of HAYABUSA reached about 2000 K, occurring at a
height around 100 km, the spacecraft material started to sublimate from the surface and was
surrounded by evaporated vapors. Excited states of atoms of these vapors were gradually de-
excited by radiation. HAYABUSA luminosity consisted mostly of radiation of discrete emission
spectral lines belonging under the most part to metals and mainly to iron. Ablation particles
injected into the flow also emitted radiation as a continuum spectrum due to their temperature.
Thus, observed atomic spectrum was mixed with thermal continuum and molecular bands.
Subtracting these background, excitation temperature and element intensities were estimated
under the assumption of a local thermal equilibrium (LTE) condition. Table 5 gives the derived
physical quantities.
The excitation temperature was estimated using Fe Iand Mg Ilines around the 5000
– 5500 ˚
Awavelength range. The derived excitation temperatures were 6000 K at heights of
84.5 km and 62.7 km, and 4500 K at a height of 54.9 km. These excitation temperatures are
comparable to a normal meteor temperature, 5000 K (e.g, Boroviˇcka 1993; Ceplecha et al.
1996; Trigo-Rodriguez et al. 2003) and the excitation temperature range between 5000 K – 6000
K caused by a large bolide (Boroviˇcka et al. 1998). Although the ratio of Fe I/Mg Iwas 0.6 at a
height of 84.5 km, the ratio increased to 10 below a height of 62.7 km. Since HAYABUSA was
made with much more Fe than Mg, it is likely that iron was conspicuously evaporated during
the explosion phase.
Detected Ti Ilines seem to originate from fuel and gas tanks, and also bolts with nuts
14
that were made of Ti-6Al-4V. H Iline (4861 ˚
A) is possibly present, presumably as a result of the
dissociation of N2H4which was used as thruster fuel, meaning that some of the thrusting fuel
remained at re-entry. All other elements (Ni, Cr, and Mn) were probably used for constructing
the HAYABUSA spacecraft. Though Hg Iwas identified as the most probable element to
explain the presence of lines at 4358 and 5461 ˚
A, details are proprietary information that were
not available to the authors. The detected Na I, especially at heights of 62.7 km and 54.9 km,
is not likely to have originated from the atmosphere; although Earth’s atmosphere contains
natural sodium known as the sodium layer at a height of 80 – 105 km which originated from
meteoroids, this sodium is more rare at these low altitudes. Therefore, sodium must have
originated from material ablated by the HAYABUSA spacecraft or its capsule. Sodium was
also detected by the Stardust capsule at altitudes of 54 – 48 km (Stenbaek-Nielsen & Jenniskens
2010).
OIand N Iare most likely atmospheric lines, or a part of O Iand N Iarising from the
fuel oxidizer, N2O4. O I, N I, H I, and Xe Iare of high excitation atoms which require either high
temperature or a large amount of atoms to be detected. Therefore, these atoms are thought
to be excited by the shock layer. On the other hand, typical lines of the high temperature
components as seen in the meteor plasma such as Mg II (4481 ˚
A) and Fe II (e.g., 4583, 4923,
and 5018 ˚
A) have not been detected in HAYABUSA spectra. The one explanation for the
absence of Mg II and Fe II is that the emissions of O I, N I, H I, and Xe Iarise promptly from
the shock layer in the gas–gas phase, while the ablation of solid Mg and Fe should transform
into a gas phase that takes more time than gas–gas transformation because of the low velocity
(10 km/s) compared with typical meteors (40 km/s).
4.2. UV-II spectrum in 3000 – 4000 ˚
A
The vibration temperature of molecular N+
2(1) was dramatically changed from 4000 K
at a height of 92.5 km to 13000 K at a height of 82.9 km (table 3; figure 6). The observed spectra
are a superposition of the post shock plasma radiation which is mixed with a shock layer heating
and downward plasma. Thus, it is logical to understand that the high temperature region was
induced by a shock layer of the HAYABUSA spacecraft which rapidly grew between 92.5 km
and 82.9 km in height. The molecular band of N+
2(1) was also observed in the spectrum of the
Stardust re-entry capsule with a rotational temperature of 15000 K at heights between 71.5 km
and 62 km (Winter & Trumble 2011). Interestingly, at a height of 84 km, N+
2(1) was detected
with a vibration temperature of 10000 K from a –4 magnitude bright fireball of the Leonid
meteor shower whose entry velocity was 72 km/s (Abe et al. 2005b). The flux of the spacecraft
at a height of 62.7 km (–12 absolute magnitude) was about 1600 times brighter than that of
the capsule’s flux (–4 absolute magnitude at the maximum). Therefore, the N+
2(1) bands
originated from the spacecraft was much stronger than CN bands originated from the capsule
in which C was the major erosion product of the Carbon-Phenol heat shield of the capsule as
15
seen by the Stardust capsule (Jenniskens 2010a; Winter & Trumble 2011). Clear C Ilines were
also observed in the near-infrared spectrum (around 1 µm wavelength) of the Stardust reentry
capsule (Taylor & Jenniskens 2010). Note that the vibrational and rotational temperatures of
CN violet bands were measured to be 8000 ±1000 K in the Stardust capsule at a height of 60
km (Jenniskens 2010b). C–N coupling occurs at a higher excited state than a ground state, and
then vibration-rotation temperature approaches to the translational temperature. For instance,
the estimated translation temperature in the shock layer of the capsule was 11000–13000 K.
Hence, the vibration-rotation temperature of 13000 K for N+
2(1) and CN is reasonable.
Bright fireballs sometimes leave a self-luminous long-lasting plasma at altitudes of about
80–90 km that is called ’persistent trains’. It is generally believed that the luminosity of
persistent trains is fueled by reactions involving O3and atomic O, efficiently catalyzed by metals
from the freshly ablated meteoroids (e.g., Jenniskens 2000; Abe et al. 2005a). A persistent train
was observed at heights between 92 km and to 82 km for about 3 minutes(Yamamoto et al.
2011). It is reasonable to suppose that sufficient metals were supplied by the ablation of the
spacecraft at these heights.
It is important to understand how meteoroids and meteors supply the Earth with space
matter including organics and water (e.g., Abe et al. 2007b). Meteors represent a unique
chemical pathway towards prebiotic compounds on the early Earth and a significant fraction of
organic matter is expected to survive. Thus, the investigations of OH(A-X) in the HAYABUSA
spectrum is of particular interest. The most likely mechanism for emitting OH(A-X) band in
the meteor is caused by the dissociation of water or mineral water in the meteoroid. Our
possible detection of OH(A-X) band indicates an Earthly origin caused by the dissociation of
water in the upper atmosphere. However, due to blending with other atomic lines such as Mg I,
Fe I, and Al I, further spectroscopy with higher resolution and sensitivity around 3090 ˚
A will
be needed for further confirmation.
4.3. Gray-body spectrum of the capsule
A continuum consisting of a gray-body emission of the capsule at near-ultraviolet and
visible wavelengths was examined. A continuum radiation of the capsule obtained at a height
of 42 km was that of a gray-body at a fitted temperature employing Planck’s formula. Our
derived temperature from an excellent UV-II data set was 2437 ±14 K at a height of 41.8 km
(figure 7). The surface temperature of 2525 K ±50 K at a height of 41.1 km was estimated
based on radiative equilibrium Computational Fluid Dynamics (CFD) (Fujita et al. 2003). Our
observed temperature agrees qualitatively with the CFD model prediction. The gray-body
temperature observed from NAOJ’s team at Coober Pedy resulted in 2400 ±300 K at a
height of 40.5 km (Ohnishi et al. 2011) which is comparable with our result. Note that
dynamical pressure at a height around 40 km was the maximum 64 kPa (Yamada & Abe
2006). At the GOS3 site, a strong sequence of sonic booms was detected at 13:55:21 UT using
16
a video recorder’s microphone which was observed at Tarcoola by Y. Akita and his colleagues.
A sonic boom is the sound associated with a shock wave created by the supersonic flight of
the capsule. According to this time delay, the shock wave generation point was estimated at
a height around 40 km. Considering these fluid conditions, further analysis will be made in a
forthcoming paper (e.g., Fujita et al. 2011b).
5. Conclusion
At 13:51:50 UT on June 13, 2010, the HAYABUSA spacecraft appeared as planned in the
dark sky over the Australian desert, along with the faint dot of the capsule. The HAYABUSA
spacecraft was flying behind the capsule, roughly 1 km above as if he must protect his tiger cub.
While the spacecraft burst into many fragments, as if falling into the Milky Way, the capsule
became an independent bright fireball wearing an ablative heat shield as its thermal protection
system (TPS), as if demonstrating its will to overcome adversity. The planned atmospheric
re-entry was perfectly completed. The HAYABUSA spacecraft ended his journey in a brilliant
flash of light that provided us a treasure trove of “artificial fireball” data, which has never been
observed in a scientific way. Atomic lines such as Fe I, Mg I, Na I, Al I, Cr I, Mn I, Ni I, Ti I, Li I,
Zn I, O I, and N Iwere identified. The excitation temperature ranging from 4500 K to 6000 K
was estimated using Fe Iand Mg Iwithin the 5000 – 5500 ˚
A wavelength region, which is similar
to a common excitation temperature of meteors and bolides. The identification of emission lines
may be inadequate and contain some unknown lines. Exotic atoms such as CuI, Mo I, Xe I,
and Hg Iwere also identified. The explosion of the spacecraft injected a large amount of iron
which increased the density of Fe I. The surprising strong red line during the last flash of the
spacecraft was well explained by a Li Iline (6708 ˚
A) that was probably caused by explosions of
the onboard Li-Ion batteries. A clearly detected FeO band at a height of 63 km is similar to
a common bolide spectrum which is likely to emit in the wake, where the radiation is emitted
just behind the body. The alteration in the hot plasma temperature of N+
2(1) bands (from
4000 K to 13000 K) appears to be the strongest proof that an intense shock layer around the
HAYABUSA spacecraft was rapidly formed at heights between 93 km and 83 km. The gray-
body temperatures ranging from 2482 K to 2395 K were measured at heights between 42.7
km and 41.2 km that can be explained by the CFD model prediction. Further investigation
is required to understand the performance of the TPS. Our experiences will be instructive in
observing the planned HAYABUSA-II Earth return mission.
Acknowledgements. We are thankful to all of the ISAS/JAXA personnel who organized
and participated in the recovery operations, especially Jun-ichiro Kawaguchi, Hitoshi Kuninaka,
Tetsuya Yamada, Makoto Yoshikawa, Masanao Abe, and Hajime Yano. We are also grateful
to all of the JAXA ground observation team members at JAXA, NAOJ, Kochi University of
Technology, Kanazawa University, and Nagoya University who assisted in observing at GOS3
17
and GOS4 stations. GOTO Inc. and NEC Corp. kindly provided a newly developed high-
sensitive EMCCD camera (NCR-550a). Noboru Ebizuka (Nagoya University) designed the
UV-II spectroscopic camera with the aid of SHOWA Industry Co., Ltd in Japan. Yuichiro
Akita kindly provided recording data of the sonic boom observed at Tarcoola. We express
many thanks to Jiˇı Boroviˇcka (Ondˇrejov observatory) for constructive comments and kind
advice. Synthetic spectrum was carried out in part on the general-purpose PC farm at the
Center for Computational Astrophysics (CfCA) of NAOJ. Shinsuke Abe is supported by JAXA
and the National Science Council of Taiwan (NSC 97-2112-M-008-014-MY3, NSC 100-2112-M-
008-014-MY2). Welcome Back Home “Okaerinasai” HAYABUSA!
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19
Table 6. Identification of atoms and molecules in 4200 – 6800 ˚
A. All atoms except Li Iin the table were analyzed from the
spacecraft spectrum at a height of 62.7 km (13:52:16 UT). Li Ilines resulted from the spacecraft spectrum at a height of 54.9
km (13:52:21 UT). Identified atoms are indicated in the visual spectrum (figure 3). The values for intensities were measured
in relative units.
Observed line Identified line
Wavelength (˚
A) Intensity Wavelength (˚
A) Element multiplet
4234 10.9 4234 Fe I152
4236 11.0 4236 Fe I52
4256 12.2 4254 Cr I1
4262 29.3 4261 Fe I152
4282 24.7 4272 Fe I42
24.7 4275 Cr I1
24.7 4290 Cr I1
4300 19.5 4308 Fe I42
4358 6.1 4358 Hg I1
4388 5.1 4384 Fe I41
4408 2.0 4405 Fe I41
4414 2.0 4415 Fe I41
4434 3.4 ? –
4466 2.8 4467 Fe I350
4502 1.6 ? –
4538 13.8 4533 Ti I42
4558 19.2 ? –
4575 8.6 ? –
4618 1.8 4617 Ti I4
4622 1.6 4624 Xe I1
4656 14.6 4651 Cu I1
4670 10.2 4671 Xe I1
4684 16.0 4680 Zn I1
4704 7.3 4705 Cu I1
4724 4.0 4722 Zn I1
4540 1.7 ? –
4760 2.6 4754 Mn I16
4762 2.2 4762 Mn I21
4782 1.6 4783 Mn I16
4811 3.6 4811 Zn I1
4822 4.3 4824 Mn I16
4846 12.0 ? –
20
Table 6. (Continued.)
Observed line Identified line
Wavelength (˚
A) Intensity Wavelength (˚
A) Element multiplet
4868 9.3 4861 H I20
4872 9.0 4872 Fe I318
4898 7.0 4891 Fe I318
4912 6.4 ? –
4932 9.2 ? –
4958 4.3 4957 Fe I318
4982 6.1 4982 Ti I38
4992 4.7 4991 Ti I38
5014 6.4 5014 Ti I38
5040 8.6 ? –
5081 5.8 5081 Ni I4
5016 9.4 5106 Cu I1
5125 2.7 ? –
5146 3.2 5147 Ti I1
5170 8.2 5167 Mg I2
8.2 5167 Fe I37
8.2 5173 Mg I2
5184 7.8 5184 Mg I2
5208 7.4 5205 Cr I7
7.4 5205 Fe I1
7.4 5206 Cr I7
7.4 5208 Cr I7
5246 4.6 ? –
5268 10.2 5270 Fe I15
5296 11.3 5293 Cu I1
5326 13.8 5328 Fe I15
13.8 5331 O I12
5344 12.2 ? –
5370 11.1 5371 Fe I15
5378 3.5 5383 Fe I1146
5394 8.5 5393 Fe I553
5397 4.0 5397 Fe I15
5407 12.6 5404 Fe I1165
12.6 5406 Fe I15
5429 10.0 5430 Fe I15
21
Table 6. (Continued.)
Observed line Identified line
Wavelength (˚
A) Intensity Wavelength (˚
A) Element multiplet
5448 7.6 5447 Fe I15
5460 8.9 5456 Fe I15
8.9 5461 Hg I1
5488 3.6 ? –
5510 6.7 5506 Mo I1
5534 15.5 5533 Mo I1
5702 32.5 5700 Cu I1
5784 39.8 5782 Cu I1
5856 21.0 ? –
5870 4.9 ? –
5896 40.2 5890 Na I1
40.2 5896 Na I1
6104 2.2 6104 Li I2
6152 10.0 6156 O I10
6702 4.7 6708 Li I1
5500-6100 FeO –
22

Supplementary resource (1)

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Conference Paper
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Acoustic/infrasonic/seismic waves were observed during the re-entry of the Japanese asteroid explorer ``HAYABUSA'' at 6 ground sites in Woomera, Australia, on 2010 June 13. Overpressure values of infrasound waves were detected at 3 ground sites in a range from 1.3 Pa, 1.0 Pa, and 0.7 Pa with each distance of 36.9 km, 54.9 km, and 67.8 km, respectively, apart from the SRC trajectory. Seismic waveforms through air-to-ground coupling processes were also detected at 6 sites, showing a one-to-one correspondence to infrasound waves at all simultaneous observation sites. Audible sound up to 1 kHz was recorded at one site with a distance of 67.8 km. The mother spacecraft was fragmented from 75 km down to 38 km with a few explosive enhancements of emissions. A persistent train of HAYABUSA re-entry was confirmed at an altitude range of between 92 km down to 82 km for about 3 minutes. Light curves of 136 fragmented parts of the spacecraft were analyzed in detail based on video observations taken at multiple ground sites, being classified into three types of fragmentations, i.e., melting, explosive, and re-fragmented types. In a comparison between infrasonic waves and video-image analyses, regarding the generation of sonic-boom type shock waves by hypersonically moving artificial meteors, both the sample return capsule and fragmented parts of the mother spacecraft, at an altitude of 40 ± 1 km were confirmed with a one-to-one correspondence with each other.
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The HAYABUSA spacecraft re-entered the Earth's atmosphere on 2010 June 13 UT, together with the capsule for the sample return. This was the first trial of the re-entry experiment as a Japanese interplanetary spacecraft. We undertook an expedition to South Australia for ground-based observations, and succeeded in obtaining valuable data of various phenomena occurring at this re-entry. Our data were widely used not only for scientific analysis, but also for outreach purposes. This paper provides an overview of our expedition.
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Thermal radiation of the heatshield and the emission of the postshock layer around the Stardust capsule, during its reentry, were detected by a NASA-led observation campaign aboard NASA's DC-8 airborne observatory involving teams from several nations. The German sur experiment used a conventional spectrometer, in a Czerny-Turner configuration (300 mm focal length and a 600 lines/mm grating), fed by fiber optics, to cover a wavelength range from 324 to 456 nm with a pixel resolution of 0.08 nm. The reentering spacecraft was tracked manually using a camera with a view angle of 20 deg, and light from the capsule was collected using a small mirror telescope with a view angle of only 0.45 deg. Data were gathered with a measurement frequency of 5 Hz in a 30-s time interval around the point of maximum heating until the capsule left the field of view. The emission of carbon nitride (as a major ablation product), N(2)(+) and different atoms were monitored successfully during that time. Because of the nature of the experimental setup, spatial resolution of the radiation field was not possible. Therefore, all measured values represent an integration of radiation from the visible part of the glowing heatshield, and from the plasma in the postshock region. Further, due to challenges in tracking, not every spectrum gathered contained data. The measured spectra can be split up into two parts: 1) continuum spectra, which represent a superposition of the heatshield radiation and the continuum radiation of particles due to microspallation in the plasma, and 2) line spectra from the plasma in the shock layer. Planck temperatures (interpreted as the surface temperatures of the Stardust heatshield) were determined assuming either a constant surface temperature, or a temperature distribution deduced from numerical simulation. The constant surface temperatures are in good agreement with numerical simulations, but the peak values at the stagnation point are significantly lower than those in the numerical simulation if a temperature distribution over the surface is assumed. Emission bands of carbon nitride and N(2)(+) were tracked along the visible trajectory and compared with a spectral simulation with satisfying agreement. Values for the integrated radiation of the transitions of interest for these species were extracted from this comparison.
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2=nm=sr. Absolute calibration errors add to these values a systematic uncertainty of about 20%. The capsule’s heat shield consistedofaphenol-impregnatedcarbonablator.Hence,theintensityofthecarbon-atomlineemissionisameasure oftheablationrateduringdescent,butitalsodependsonthedetailsofcarbon-atomablationandtheexcitationinthe shock layer.
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During the 2006 Stardust Sample Return Capsule entry observing campaign, the highest spectral resolution data gathered onboard NASA's DC-8 Airborne Laboratory was measured with a fixed-mounted slitless cooled charge. coupled-device spectrograph, called ASTRO. Spectra were recorded around the time of peak heating similar to 09 : 57 : 33 Coordinated Universal Time (UTC) on 15 January. The data covered three 0.8-second time intervals centered on 09:57:32.5, 34.4 and 36.3 s (+/- 0.5 s) UTC, when the capsule was at an altitude of 60 and 210 km from the spectrometer. The observed spectrum was a composite of first-, second-, and third-order emissions. The first-order spectrum contained only continuum emission. Second-order emissions included the 615 nm atomic line of oxygen: third-order emissions included the CN violet 0-0 band, the isoelectric N(2)(+) band, and two Ca(+) atomic lines. The Ca(+) lines had an instrumental full-width at half-maximum of 0.15 +/- 0.01 nm. The CN violet band contour measured vibrational and rotational excitation temperatures of T(v) = T(r) = 8, 000 +/- 1, 000 K, if self-absorption is neglected.
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An unidentified pseudo-continuum in the 600 nm region is observed in the upper mesosphere with the limb-scanning OSIRIS imaging spectrograph on-board the Odin spacecraft. Averages of low latitude spectra at a series of tangent limb altitudes from 75 to 105 km are assembled and matched with synthetic spectra of the known night airglow emission band systems to isolate the underlying airglow continuum. The upper limit of the NO + O --> NO2* air afterglow continuum component in the observed 600 nm pseudo-continuum is estimated to be 5% at low latitudes. The spectral profile of the unidentified 600 nm residual airglow continuum is very similar to published laboratory measurements of the `orange bands' of FeO. The volume emission rate altitude profile of this 600 nm airglow continuum, derived from averaged limb radiance profiles, is very similar in shape and in altitude to the concurrently observed Na vertical profile suggesting related source mechanisms.
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Spectroscopic observations of the 2006 Stardust Sample Return Capsule entry are presented, obtained by means of a slitless miniature echelle spectrograph onboard NASA's DC-8 airborne laboratory. The data cover the wavelength range from 336 to 880 nm, at 0.14-0.9 nm resolution, and were obtained during the time interval when radiative heating was most important. The data contain a broadband continuum, presumably from the hot heat-shield surface, shock-layer air plasma emissions of N, O, and N(2)(+), and atomic hydrogen and CN molecular band emission from the ablating heat-shield material, a form of phenol-impregnated carbon ablator. Early in flight, there were also atomic line emissions of Zn, K, Ca(+), and Na, presumably from a white Z-93P paint applied to the top of the phenol-impregnated carbon ablator. At each moment along the trajectory, the whole spectrum was recorded simultaneously, but broken into smaller segments. Key issues addressed in the data reduction and calibration are described. The interpretation of these data was given elsewhere.
Forebody and aftbody radiative heating rates of the MUSES-C asteroid sample return capsule have been assessed along the reentry trajectory from an engineering standpoint. Nonequilibrium hypersonic flows around the capsule with ablation of the thermal protection system involved were determined by CFD calculations, while the radiative heat transfer was computed by the radiation code SPRADIAN in a non-coupled manner with the flow analysis. In order to take into account much uncertainty in the thermal relaxation, chemical reaction, and ablation models used in the flow analysis, parametric studies were performed by changing these models to obtain the conservative estimation of the radiative environments. The radiative heat flux was found to be considerably affected by the ablation model, especially in the aftbody region of the capsule.