Smart Lander for Investigating
Moon (SLIM)
Results from the Moon Landing

Institute of Space andAstronautical Science
SLIM Project Team
Project Manager
Sakai Shin-ichiroToday’s report

Today, we are pleased to report on the results from the Smart
Lander for Investigating Moon (SLIM) moon landing descentoperation, that was conducted on 01/19 ~ 01/20, 2024.

1. Actual landing descent progress (to an altitude of about 50m)
2. Results from image matching and evaluation of the pinpoint
landing accuracy
3. Situation arising at an altitude of approximately 50m
4. Estimation of spacecraft behaviour after an abnormal
occurrence
5. Post-landing spacecraft operations, and images obtained withthe multi-band spectroscopic camera
6. Outlook for future operations
2

Outline of landing sequence
1. Initiate the landing descent from lunar orbit and approach the target site on the lunar surface
through autonomous navigation and guidance control, while precisely estimating the current
position using image-based navigation with the navigation cameras.
2. From above the target site, precise measurement of altitude and terrain-relative velocity conductedusing the landing radar that is integrated into the navigation guidance system.
3. Image-based obstacle detection is performed at approximately 50m above the landing site andlanding is performed autonomously, avoiding hazardous boulders and other obstacles. That is,
pinpoint landing is prioritised up to 50m above the surface, after which obstacle avoidance isprioritised for landing safety.
[Note] Spacecraft position and velocity are propagated by the onboard accelerometers and corrected
to higher accuracy by image-based navigation. Additionally, the navigation camera images are also
taken at regular intervals for use in the post-landing analysis, even when image navigation is not being
performed.

動力降下Powereddescent

Pre-landing lunar orbit.
Elliptical orbit with dimensions
approximately 15 x 600km

Altitude 15km
高度15km(basedon lunar(月半径1738km基準)
radiusof
1738km)
高度7km(対月面)
Altitude
7km(towards
Moon
surface)© JAXA

垂直降下 descent
VerticalLanding sequence
after start ofpowered descent3

Precise location information of the target landingsite
Target landing site for SLIM*1 (Mean Earth/Polar Axis System (ME))
Longitude : 25.24889 [deg] / Latitude : -13.31549 [deg] The latitude and longitude of the target landing site was*1… More precisely, the target landing site was defined via
the lunar image, and the latitude and longitude were atthese values.

previously announced to the first decimal place (except
to collaborative partners such as NASA and ISRO).
 However, the precise landing site is very important, andselected after lengthy discussions for both scientificsignificance and landing safety. This was the exact site
chosen.

(−13.3, 25.2)(−13.3, 25.2)

credit:NASA/LRO©Daichi Fujii, LRO
Credit :X @dfuji1
https://x.com/i/status/1748103951336227113

SHIOLI Crater4

Actual descent & landing[Before the start of the landing descent] Prior to the start of the powered descent, image matching navigation was performed in threeareas（1/19 23:52:43, 23:54:43, 23:56:45 JST）
 All image matching was successfully completed twice in each area, and orbit correction(guidance calculation) on the spacecraft from the results was successful. The final decision
to begin landing descent was therefore made (at around 23:59 JST).
 The main engines began to fire as planned, and the powered descent phase, the first half ofthe landing descent sequence, began (23:59:58 JST)

動力降下
Powereddescent

Pre-landing lunar orbit.
Elliptical orbit with dimensions
approximately 15 x 600km

Altitude 15km
高度15km(basedon lunar(月半径1738km基準)
radiusof
1738km)
高度7km(対月面)
Altitude
7km(towards
Moon
surface)© JAXA

垂直降下 descent
VerticalLanding sequence
after start ofpowered descent5

Actual descent & landing[During the powered descent phase] After the start of the powered descent, the spacecraft descended almost in line with the planned
trajectory.
 During the powered descent phase, image matching were performed twice in each of two areas,
both completed successfully. In the first area, a position correction of approximately 200m altitude/ 100m horizontal position was applied, and in the second area, a position correction of about 1km
altitude / 200m horizontal position was applied. This was immediately reflected in the planned
trajectory from the guidance recalculation.
 At the end of the powered descent phase, the spacecraft was at an altitude of approximately 6.2km
as planned, with a good horizontal position error of less than about 100m. The vertical descentphase then began.
動力降下Powereddescent

Pre-landing lunar orbit.
Elliptical orbit with dimensions
approximately 15 x 600km

Altitude 15km
高度15km(basedon lunar(月半径1738km基準)
radiusof
1738km)
高度7km(対月面)
Altitude
7km(towards
Moon
surface)© JAXA

垂直降下 descent
VerticalLanding sequence
after start ofpowered descent6

Actual descent & landing[During the vertical descent phase] After entering the vertical descent phase, altitude measurements by the landing radar weresuccessfully initiated.
 Image matching was performed twice each at an altitude of approximately 4000m and 500m, andthis was successful. The amount of horizontal position correction was about 100m and 50m,
respectively, and the resulting position correction control was also successfully implemented.
 At an altitude of 50m, image-based obstacle detection was also successfully performed, and thespacecraft autonomously identified the safest location in the image, which was then used at the
final landing target.
 Based on this information, we believe that the landing descent to an altitude to 50m was very good.
動力降下Powereddescent

Pre-landing lunar orbit.
Elliptical orbit with dimensions
approximately 15 x 600km

Altitude 15km
高度15km(basedon lunar(月半径1738km基準)
radiusof
1738km)
高度7km(対月面)
Altitude
7km(towards
Moon
surface)© JAXA

垂直降下 descent
VerticalLanding sequence
after start ofpowered descent7

Evaluation to ~50m altitude / image matching Image matching navigation was conducted twice on the spacecraft for all seven areas, and allcompleted successfully.
 For the purpose of ground support in the event of an anomaly, image matching using a morecomputationally intensive algorithm was also performed on the ground based on the images
transmitted from the spacecraft.
 All the results were consistent, and all 14 image matching navigation resulted were determined tobe accurate.

Lunar surface image

Lunar surface topographic map near the location estimatedby the onboard image navigation (CG)8

Evaluation to ~50m altitude / obstacle detection
 Obstacle detection was performed twice, both times completed successfully.
 The images used for detection were later evaluated and all the sites chosen are believed
to have been relatively safe.
 The result from the second detection was adopted for the final landing target (about
12m east-southeast from the previously set landing target)
Approximate location of landing target point
N→

E
↓

N→

E
↓
Obstacle detection #1 results（Red dots. Red box is the spacecraft footprint
including guidance errors）

Obstacle detection #2 results（Red dots. Red box is the spacecraft footprint
including guidance errors）※ images squired from the SLIM navigation camera (CAM-MZ)
9

Evaluation to ~50m altitude / toward the target
site The evaluation was conducted using

Chandrayaan-2:ISRO/SLIM:JAXA

images from Chandrayaan-2, which has
relatively high resolution and was also
used in the selection of the landing target

CV1(VLD1)
Image rangesite.
 Specifically, the task was to find featuresin the Chandrayaan-2 image in common
with the navigation camera image andidentify the area where the two images

HV2
Image range
HV1(VLD2)
Image range

overlapped.
 The right figure shows the situation at two
altitudes (CV1, HV1) and during obstacle
avoidance (HV2). The central blue dot andSequence

Assumedaltitude

Horizontal
distance fromlanding site As the altitude drops and the spacecraft

CV1(VLD1)

4km

103m

approaches the lunar surface, the centre

HV1(VLD2)

500m

42.5m

of the field of view of the navigation

HV2#1

50m

3.4m

camera gradually approaches the target

HV2#2

50m

10.2m

the red dot is the target landing site
selected prior to launch.

landing site, as a result of the navigation
guidance control.

※ Images from SLIM CAM-MZ superimposed10Evaluation to ~50m altitude / pinpoint landing
accuracy
 Lower right figure shows an enlarged view of the vicinity of the image for obstacle avoidance. Blue dots
indicate the centre position of the first (#1) and second (#2) image capture (blue box), which corresponds
to the horizontal position of SLIM, and its distance
Chandrayaan-2:ISRO/SLIM:JAXA
Chandrayaan-2:ISRO/SLIM:JAXA

from the target landing site is shown in the lower

HV2（obstacle detection）#2
Image range

right table.
 From the figure, it was estimated that the positional
accuracy during the obstacle detection is estimatedas about 3 ~ 4m for #1 and 10m for #2.
 As mentioned above, after this altitude, the landing
target position was reset with priority given to

SLIM footprint（incl. guidance error）
Landing site

landing safely (obstacle avoidance). Therefore the

HV2#2
HV2#1

pinpoint accuracy is estimated to be approximately

11.8m

10m or less.

Centre of safe area

 Furthermore, #2 is highly likely to have alreadydrifted eastwards due to the abnormal event
described below, and the actual pinpoint accuracy islikely to have been about 3 ~ 4 m.

HV2（obstacle detection）#1
Image range

After obstacle avoidance, landing is aimed at the centre of the safe areain the diagram. Safety is now prioritised by selecting to avoid obstacles
ahead of accurately landing at the target site (the spacecraft therefore
aimed at a site 11.8m away from the target site). Pinpoint landing
accuracy is therefore evaluated before the obstacle avoidance.

Sequence

Assumedaltitude

Horizontal
distance fromlanding site

HV2#1

50m

3.4m

HV2#2

50m

10.2m

11

Event occurrence at an altitude of approx. 50m
 The spacecraft descended smoothly to an altitude of approximately 50m, but close to this point, anabnormality occurred in the propulsion system.
 Specifically, at around 00:19:18, the total thrust generated by the two main engines suddenly
decreased to about 55%.
 Examination of the temperature behaviour after landing revealed that the –X side of the two main
engines was not exhibiting the expected temperature increase (propellent value temperature rises
due to heat soak-back).
 It is therefore likely that an abnormality occurred in the –X side main engine at this altitude.

00:19:18JST
 The brown line is the accumulated
injection time of the main engine,
and the green line is theacceleration measured by theaccelerometer, which detects theacceleration generated by the
injection of the two main engines.
 Although the injection instruction
to the main engines remained
almost constant, the total thrustgenerated as measured by theaccelerometer suddenly dropped
to about 55% after 00:19:18.
12

Event occurrence at an altitude of approx. 50m
 Two navigation camera images taken near the time of the abnormality are shown below
 Immediately after the abnormality in the main engine thrust, the navigation camera images show
spots of light and objects that had not been seen in the previous image
 Since one of these has a nozzle-like shape, it is assumed that some kind of abnormality occurred
near the main engine on the –X side at around 00:19;18, causing the nozzle to break and fall,resulting in the loss of most of the thrust generated by the main engine on the –X side

00:19:14(JST)00:19:20(JST) The blue arrow indicatesthe corresponding featurein both images
 The red arrows show spotsof light or objects not seenin the left image

13

Event occurrence at an altitude of approx. 50m
 A total of eight post-launch trajectory changes and the power descent phase have used the main
engine under higher supply pressure and higher engine load conditions, but the main engine has
not shown any signs of abnormality until just prior to this event.
 Moreover, comparison of the two main engines at the time of the incident suggests that the –X side
engine has mild combustion conditions compared to the +X side engine.
 The Project therefore believes that it is highly likely that an
external factor and not the main engine itself affected the –X
side main engine.
 The cause is still being investigated and there will be further
reports when more details are available.

 Example of main engine related data. SLIM uses a blowdown
propulsion system, designed to gradually reduce the propellant
supply pressure. After launch, the supply pressure of both fueland oxidizer gradually decrease as propellant is consumed, andthe load on the engine also decreases (see top diagram).
 The mixing ratio (MR) of oxidizer and fuel is another importantfactor that determines the load on the engine, but the MR ofthe –X size engine is believed to be always lower than that of
the +X side engine and therefore, the load on the –X side
engine was relatively smaller than that on the +X side engine.
14

Estimation of behaviour after the abnormality
occurred
Current estimate of the spacecraft behavior after the abnormality occurred at around 00:19:18.
 The abnormality occurred while the spacecraft was hovering. One of the two main engines was lost
due to an abnormality, but the dual main engine design allowed a certain level of redundancy to
avoid a situation where a moon landing would have been impossible.
 However, a single main engine could only generate a thrust equivalent to the lunar gravity, making it
difficult to fully control the descent speed. The spacecraft continued to descent at a rate of 2 ~3m/s from around 50m.
 The two main engines were also designed to cancel each other’s lateral thrust, so the loss of one
engine on the –X side produced a horizontal velocity toward the –X side.
 At the end of hovering, the onboard navigation guidance control system detected an abnormality
and executed a mode transition. The spacecraft continued to fire the main engine while changing
the attitude to reduce lateral movement, and autonomously proceeded with the sequence towards
the landing mode sequence. During this process, LEV-1 and LEV-2 (SORA-Q) were separate at analtitude of about 5m.
 With a lateral velocity, the spacecraft landed in an almost upright standing position (at about
00:19:52). The rate of descent upon landing was about 1.4 m/s, which is slower than the specified
range (1.8 ~ 2.8 m/s). However, landing conditions such as the lateral velocity and attitude
exceeded the specified range and produced a large attitude fluctuation after landing that resulted
in a settled attitude different to expected.

15

Estimated landing site
 Relationship between the spacecraft position at the time of obstacle detection and the estimatedlanding point. The spacecraft moved east from its position during its nominal descent (about 55m
to the east *1)
Chandrayaan-2:ISRO/SLIM:JAXA

HV2（obstacle detection）#2
Image range (horizontal error approx. 10.2m)

Landing site
(estimate)

SLIM footprint（incl. guidance error）
Landing site
11.8m
Centre of safe area

*1 … Position estimated fromthe navigation data on thespacecraft. Navigation values
from the spacecraft and thelater estimated position fromthis image are generally
consistent at the time of the
obstacle detection (HV2#1)

HV2（obstacle detection）#2
Image range (horizontal error approx. 10.2m)

Sequence

Assumedaltitude

Horizontal
distance

HV2#1

50m

3.4m

HV2#2

50m

10.2m

16

Estimated landing site
 After landing, the final attitude of the spacecraft is believed to be an almost vertical
position with the main engine facing upwards and the solar panels facing west, as shown in
the figure, based on data from the spacecraft.

CG image created from the estimated landing position and attitude
Credit：JAXA / CG Production：Mitsubishi Electric Engineering Corporation

W
17

Operation immediately after landing Immediately after it was determined that the spacecraft had landed, it was confirmed that power
was not being generated from the solar cells.
 Since communication with the spacecraft had been established, the pre-arranged abnormality
response procedures were implemented in sequence.
 Operation summary (dated 01/20)
 0:20 ~ around 1:30

Data download from spacecraft, unnecessary equipment turned off,

turn off heaters etc.
 1:30 ~ around 1:50

Transition to NASA Deep Space Network (DSN) station operation due

to to end of domestic ground station visibility hours.
Implemented operations to try to reduce power consumption.
 1:50 ~ around 2:35
 2:57

Observation operation using the multi-band spectroscopic camera.

Battery disconnected from power system by command, and spacecraft power

was turned off.
 The above operation allowed retrieval of all the technical data and image data recorded on thespacecraft during the landing descent.
 Battery disconnection was a measure to avoid the permanent loss of the spacecraft due to overdischarge. Since SLIM can operate once power generated from the solar cells exceeds the required
level, it is expected to operations will resume once the generated power is restored in the future.
The remaining battery charge (SOC) when the battery relay is off was about 12%.
18

Observation with the multi-band spectroscopic
camera Observations with the multi-band spectroscopic camera (MBC) were conducted
for approximately 45 minutes after landing. Implementation details:
 Single-band imaging with launch lock (exposure time determined by theauto-exposure) Launch lock release Scan imaging
 To prevent the temperature of the spacecraft transmitter from exceeding theguaranteed operating temperature, instead of capturing 333 image in 35 minutes,
the scan was terminated after 15 minutes. 257 of the 333 images were therefore
taken and downloaded.

 In the above operation, the launch lock for the movable mirror was successfully
released and the movable mirror operated normally. The auto-exposure function
and single band imaging also worked as expected.
 In addition, from the images obtained by the image scan shown on the next page,
observation candidate targets were identified that are expected to yield
scientific results in more detailed observations.
19

Observation with the multi-band spectroscopic
cameraImage mosaic obtained by joining the 257 images from the scan imaging
Image capture
range of one
image shot

Originally, the rightside of the image
should have beenin the upward
direction.
White areas arewithout data
because the scan
was terminated at
the half-way point.
Indicate
candidateobservation
sites
JAXA, RITSUMEIKAN UNIVERSITY, THE UNIVERSITY OF AIZU

20

Observation with the multi-band spectroscopic
cameraSimulation image

Landscape simulation
based on DTM of
KAGUYA TC

CAM-PX:JAXA
MBC:JAXA, RITSUMEIKAN UNIVERSITY, THE UNIVERSITY
OF AIZU

Navigation camera (CAM-PX) matching with multi-band spectroscopic camera (MBC) scan images.
Slightly whitish are in the upper right is the CAM-PX image

21

Prospects for future return operations
 Based on the results of operations conducted immediately after landing, thespacecraft is currently expected to resume operations once power generationfrom the solar cells is restored, although there is a risk of equipment failure due
to high temperatures.
 From the estimate of the post-landing attitude, it is believed that once the Sun
is shining on the solar cells facing west, i.e. in the evening on the lunar surface,power generation may be restored and the spacecraft operations resumed.
 Current estimates suggest that resumption of spacecraft operations can occur
by 02/01, when the Sun sets. The spacecraft will be automatically activated by
the power generation. In parallel, communication with the spacecraft is
attempted to be established for a few hours every day since landing.
 After communication is established and operations become possible, theobservation operation with the multi-band spectroscopic camera will be
immediately resumed, and scientific observations with spectral imaging in 10
bands will be conducted in order of priority for the observation candidates
selected based on the acquired scan images.

22Summary (results from moon landing descent
1/2)
 SLIM successfully conducted the landing descent operation until an altitude of about 50m, justprior to performing obstacle avoidance.
 In particular, all 14 image-matching navigation steps, including the navigation results, wereconducted normally.
 The appropriate point to evaluating the pinpoint landing accuracy of SLIM is just before obstacle
avoidance. The result of that evaluation indicate a pinpoint landing accuracy of less than 10m, andprobably about 3~4m.
 At an altitude of approximately 50m, an abnormality occurred which resulted in the loss of one of
the two main engines.
 Due to having a level of redundancy, SLIM did not suffer a catastrophic failure that would prevent
landing, but continued a slow descent and moved gradually to the east. The ultra-small rovers(LEV-1 and LEV-2 (SORA-Q)) were successfully separated at an altitude of about 5m and delivered
to the Moon’s surface. The spacecraft landed at a descent rate lower than the specified range.
However, as landing conditions aside from the descent rate were outside the specified range, thespacecraft settled at a different attitude than expected.
 The landing location is estimated to be about 55m east of the landing target. The attitude after
stabilization is considered to have the solar panels facing west, and the Sun was positioned to theeast at the time of landing, resulting in a loss of power generation by the solar cells.
23

Summary (results from moon landing descent
2/2)
 After landing, communication with the spacecraft was established, but power
generation from the solar cells could not be confirmed. Therefore, in
accordance with the abnormality situation response procedure, data including
images during the landing descent were acquired, scan imaging was initiatedwith the multi-band spectroscopic camera, and the battery disconnected fromthe power supply on command in order to maintain spacecraft functionality. This
causes SLIM to power off.
 As the Sun moves to the west, power generation from the solar cells is expected
to gradually recover and operations resume. After resumption of operations,scientific observations will be conducted in 10 bands using the multi-band
spectroscopic camera, and candidate observation sites have already been
selected based on the scan imaging results.

24

Summary（results & issues）
 Although detailed data evaluation needs to be continued, it is believed that SLIM was able todemonstrate the landing technology for all the planned engineering test items, with the exceptionof the two-step landing dynamics.
 In particular, the demonstration of the image matching technology and pinpoint landing accuracyof less than 10m (perhaps 3~4m) has been achieved is a major accomplishment for future lunar
and planetary exploration.
 Regarding the lunar activities after landing, the operation of LEV-1 and LEV-2 (SORA-Q) on the
lunar surface, after successful separation from the SLIM lander and delivery to the surface, hasbeen confirmed, and these were successfully delivered to the Moon’s surface. Scanning imaging
was performed with the multi-band spectroscopic camera, and the integrity of the equipment
confirmed. If observational operation can be resumed in the future, further scientific results canbe expected.

 On the other hand, it is necessary to conduct a detailed study on the abnormal events that
occurred before and after the obstacle detection to identify the causes and clarify issues andcountermeasures for the future.
 The engineering technology developed for SLIM, including the two-step landing dynamics that
could not be demonstrated this time, will be organised and prepared for transfer to future
missions.
 The results of future operations and studies are intended to be announced in a timely manner.

25

Summary（results & issues）
Engineering test target items
Minimum
success

status

Evaluation etc.

Develop image-matching navigation, which isessential for high-precision landing, and combine
this with other navigation systems to result in anavigation error of about 100m.

Achieved

All 14 image matching runs conducted on orbit werecompleted successfully. Based on the landing accuracy
obtained, the navigation accuracy was evaluated to beless than 10m.

Provide a simple shock-absorbing mechanism forsoft-landings

Under
investigationRealise a compact, lightweight, high-performancechemical propulsion system.

UnderinvestigationAchieved

A compact and lightweight computer and power supply
system were developed and installed. Both instrument
functioned normally from launch to post-landing,contributing to the success of the pinpoint landing.

Achieved

The landing guidance rules worked well before andafter the obstacle detection, demonstrating theperformance of the pinpoint landing. The obstacle
detection results were also confirmed to be valid.

A high-precision landing (accuracy of 100m) on
the Moon’s surface performed by a spacecraft
equipped with these technologies, and results
verified.

Achieved

Based on evaluations near obstacle detection, pinpoint
landing accuracy was less than about 10m (perhaps
3~4m). Even after the subsequent events, thespacecraft is estimated to have landed about 55mfrom the target landing site.

Spacecraft remained functional after landing.

Achieved

After landing, the spacecraft continued to operate,and data obtained during the landing descent was
reproduced and received on the ground.

After reaching the Moon’s surface, the mission
continued for a period until sunset.

Ongoing

Once power generation from the solar cells is resumed,
observation operations are planned with the multiband spectroscopic camera for a period of time.

Weight reduction of the core elements of thespacecraft, including the computer and power
supply system.

FullsuccessExtra
success

Realise autonomous landing guidance rules that
can take into account navigation guidance errors
while detecting obstacles.

※ The overview of Project objectives were quoted in the press kit and other descriptive
documents, but given in more detail in this report for the purpose of comparison.

26

From the era of “Landing where we can”
to “Landing where we want”

Thankyou for your support
Image credit throughout this document is JAXA (unless otherwise stated)