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The SPLICE Project: Safe and Precise Landing
Technology Development and Testing
Ronald R. Sostaric
1
, John M. Carson III
2
, Samuel M. Pedrotty
3
, David K.
Rutishauser
4
, Teming Tse
5
, Joshua W. Sooknanan
6
NASA Johnson Space Center, Houston, TX, 77058
Farzin Amzajerdian
7
, Alicia Dwyer Cianciolo
8
, Christopher A. Kuhl
9
NASA Langley Research Center, Hampton, VA, 23681
J. Bryan Blair
10
NASA Goddard Space Flight Center, Greenbelt, MD, 20771
George T. Chen
11
, Po-Ting Chen
12
NASA Jet Propulsion Laboratory, Pasadena, CA, 91109
The Safe and Precise Landing—Integrated Capability Evolution (SPLICE) Project’s suite of
technologies provides a spacecraft with Precision Landing and Hazard Avoidance (PL&HA)
capabilities for conducting precise and safe landing. SPLICE has been a focal PL&HA project
since 2017 within the Space Technology Mission Directorate (STMD) Game Changing
Development (GCD) Program and has funding planned through 2024. STMD/GCD has
pursued SPLICE as a technology push to enable PL&HA capabilities for human and robotic
lander missions to the Moon, with extensibility to Mars, icy moons, ocean worlds, and other
solid-surface solar system destinations. PL&HA technologies are prioritized within NASA
Technology Roadmaps, the Artemis roadmap, and the Entry, Descent and Landing (EDL)
Systems Capability Leadership Team (SCLT) technology development plan. SPLICE has
multiple active partnerships, including funded efforts to demonstrate PL&HA technologies
on terrestrial suborbital rocket flights and planned infusion to lunar spaceflight missions. This
paper describes the SPLICE technologies in development, maturation progress, and recent
suborbital rocket flight testing.
I. Introduction
Guidance, Navigation and Control (GN&C) technologies for precision landing and hazard avoidance (PL&HA) are
enablers for future robotic science and human exploration missions to solar system destinations where hazardous
surface conditions pose a mission risk to successful and safe touchdown. These Entry, Descent and Landing (EDL)
GN&C technologies are considered high-priority capabilities within NASA space technology development roadmaps
1
SPLICE Project Manager, AIAA Senior Member.
2
STMD Technical Integration Manager for Precision Landing, AIAA Associate Fellow – Lifetime.
3
SPLICE Deputy Project Manager.
4
SPLICE Avionics Lead.
5
Hardware in the Loop Simulation Lead.
6
Six-Degree of Freedom Tendon Actuated Robot (STAR) Lead.
7
Navigation Doppler Lidar Principal Investigator.
8
ConOps Studies Lead, AIAA Senior Member.
9
SPLICE Chief Engineer.
10
Hazard Detection Lidar Principal Investigator.
11
JPL Lead for SPLICE.
12
Hazard Detection and Terrain Relative Navigation Modeling Expert.
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[1, 2], the Artemis roadmap, and the STMD EDL investment strategy to promote and enable new mission concepts to
the Moon, Mars, Icy Moons, Ocean Worlds, and beyond. The SPLICE (Safe & Precise Landing - Integrated
Capabilities Evolution) Project [3] has been established within the STMD Game Changing Development (GCD)
Program to focus on the development and maturation of a suite of PL&HA technologies, including sensors, avionics,
and algorithms.
The elements of the SPLICE project address specific PL&HA technology development needs and timelines called
out within the STMD EDL technology investment strategy. These elements also address specific mission-infusion
interests of both HEOMD and SMD, as well as provide alignment with the STMD/GCD High Performance Spaceflight
Computing (HPSC) project. Maturation and validation of the Technology Readiness Level (TRL) for the SPLICE
components is being accomplished through multiple terrestrial field tests and environmental tests at the component
and integrated-system level on the path to spaceflight infusion. The goal of the SPLICE project is to develop,
demonstrate and infuse PL&HA technologies into NASA and potential US commercial spaceflight missions, including
Commercial Lunar Payload Services (CLPS) and Artemis. The SPLICE project has planned project content from
government fiscal year 2018 through 2024. The project is the direct successor of prior NASA PL&HA projects
including ALHAT [4] (Autonomous precision Landing and Hazard Avoidance Technology) and COBALT
(CoOperative Blending of Autonomous Landing Technologies) [5]. The project continues the multi-center
partnerships across NASA field centers, including JSC, LaRC, GSFC, and JPL, as well as contributions from
Armstrong Flight Research Center (AFRC) and Marshall Spaceflight Center (MSFC).
SPLICE is in the process of maturing multiple avionics, sensor, and GN&C capabilities that together comprise an
integrated descent and landing subsystem. The major technologies include Navigation Doppler Lidar (NDL) for
velocimetry and ranging, Descent and Landing Computer (DLC) for high-speed processing of PL&HA algorithms,
Hazard Detection Lidar (HDL) for performing real-time safe site assessments, and advanced PL&HA GN&C
algorithms. The performance of these technologies is being assessed through a combination of performance
simulations, hardware-in-the-loop (HWIL) testing, and field testing.
II. Mission Concept Analyses and Requirements
SPLICE is conducting modeling and Concept of Operations (ConOps) analyses of multiple candidate mission EDL
architectures for robotic and human landings on the Moon, Mars, and other solar system bodies. The analyses use
multiple reference landers, combinations of GN&C and PL&HA sensors, and different EDL trajectories. These
analyses are used to assess the applicability of existing PL&HA technologies to near-term missions, and to identify
capability gaps that require future NASA investments into next-generation PL&HA technologies. The ConOps studies
are key to driving future mission architectures and EDL and PL&HA technology investments.
The SPLICE ConOps studies primarily utilize two toolsets: Linear Covariance (LinCov) [6] analyses and Program
to Optimize Simulated Trajectories II (POST2) [7, 8]. LinCov is a powerful tool for conducting rapid architectural
trade studies of sensor selection, quality, and phasing during EDL to determine design points to consider in higher-
fidelity, computationally expensive Monte Carlo simulations. POST2 is a high-fidelity, six-degree-of-freedom (6-
DOF) simulation tool for conducting detailed analyses of atmospheric ascent and entry flight. These tools are used in
complementary ways to provide a thorough approach to EDL mission studies, and their independent results provide
valuable cross comparisons and validation of performance against anticipated mission requirements. LinCov is well-
suited to quickly analyze a large combination of sensors and sensor performance, the results of which are used to
select a subset of cases for more detailed analyses within POST2 simulations.
Figure 1 provides a notional descent and landing ConOps highlighting representative PL&HA phases and the
sensor systems during each of the phases. The sensing capabilities under evaluation in the studies include Terrain
Relative Navigation (TRN), Hazard Detection (HD), Hazard Relative Navigation (HRN), Navigation Doppler Lidar
(NDL) and/or optical velocimetry for velocity, and NDL or other altimeters for ranging. TRN uses a passive optical
camera and a reconnaissance map to determine a global navigation state. HD utilizes an optical sensor to determine
landing hazards and safe landing sites from either a camera image or a lidar-generated map: SPLICE technologies are
focused on active lidar-based HD. HRN utilizes the lidar-generated map from HD to perform a subsequent TRN-like
function. The final, or Terminal Phase, culminates in soft landing in a safe location on the planetary surface.
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Fig. 1 Notional PL&HA ConOps.
III. Project Technologies
The SPLICE project is advancing the maturity and mission readiness of multiple technologies/subsystems that
comprise an integrated PL&HA system, including the following items.
A. Navigation Doppler Lidar Subsystem
The NDL provides ultra-precise and direct velocity measurements, as well as range measurements [9-11]. NDL
measurements are used in a lander GN&C subsystem to minimize navigation error in velocity and position (minimize
the landing ellipse) and to tightly control vertical and lateral velocities during terminal descent to ensure a soft and/or
well-controlled touchdown. The NDL Engineering Test Unit (ETU), shown in Figure 2, consists of an electronics
chassis and an optical head housing three fiber-coupled telescopes. The telescopes can be separated for packaging
advantages with spacecraft design and integration.
The NDL ETU is designed to achieve line-of-sight velocity and range performance of +/-215 m/s and 7+ km
(lunar), respectively, with accuracies on the order of 2 cm/s and 2 m, respectively. The Size, Weight, and Power
(SWaP) for the NDL ETU are as follows: chassis size 37 cm x 25 cm x 18 cm, chassis mass 10.9 kg, optic head mass
~2 kg (customizable), power 77 W (avg.). NDL has been in development at NASA LaRC for more than a decade and
has been matured to TRL 6 through a combination of testing: including static range tests, dynamic range testing [12],
suborbital rocket tests, and environmental testing.
Fig. 2 NDL ETU electronics chassis illustration (left), as-built (center), and example optical head (right).
B. Descent and Landing Computer
The DLC [13] is a stand-alone EDL GN&C computer designed to offload the computationally expensive
processing of PL&HA algorithms from the flight critical functions running on the primary flight computer. It utilizes
an FPGA plus ARM-based processors with a scalable architecture as a surrogate for the in-development High-
Performance Space Computer (HPSC) capability. The DLC interfaces with multiple sensors in the SPLICE suite,
including NDL, HDL, IMU, and camera. The DLC is designed, built and assembled at NASA JSC.
The first flight version of the DLC has been built and implemented as an Engineering Development Unit (EDU),
suitable for terrestrial suborbital flight and short duration vacuum exposure. The DLC EDU is shown in Figure 4. This
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unit includes the quad core A53’s, and FPGA, 4 GB RAM, and 960 GB data storage. Its mass is 6 kg, size 22 x 25 x
17 cm, and uses 28 V with 60 W peak power. It has been environmentally tested for vibration, shock, thermal, and
EMI. Design work has begun on the full spaceflight follow-on ETU version, with initial build anticipated in 2023.
Fig. 4 DLC Engineering Development Unit (EDU)
C. Hazard Detection Lidar Subsystem
Hazard Detection Lidar (HDL) is a scan-array lidar system developed at NASA GSFC that couples an optical
beam steering mechanism with a small detector array to generate a precise three-dimensional terrain map within
seconds. HDL consists of an electronics/photonics box along with a fiber coupled optical head. The optical head
includes a telescope and two spinning Risley prisms that are controlled to a specified scan pattern to maximize over-
sampling of ground pixels to eliminate mapping gaps. When operating from a 500-meter range and a near-vertical
descent, the HDL generates a 100-meter-diameter circular map in 2 seconds with a 5-cm ground sample distance and
a range precision of 1 cm (1-sigma). The HDL can be operated at multiple ranges during descent for use in other
PL&HA functions such as early site evaluation and map updates to TRN. The surface data can also provide high-
resolution maps and intensity images to inform mission science and plan ground operations.
Fig. 5 NASA HDL in-dev optical head (left) and electronics/photonics box (right)
An initial lab unit version of the HDL was demonstrated in static rooftop testing in 2019 in which the signal to
noise was scaled to replicate lunar lander conditions at 500 m range. Figure 6 shows images generated from the lidar
return signal intensity (Left) and the lidar range measurements (Right). The lidar data is range gated by color to
visually show contrast in range. Currently, a flight-like version of the HDL sensor is being tested in both static and
dynamic conditions.
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Fig. 6 HDL Rooftop Test Results: Intensity (left), Range (right)
D. Flight Software Prototyping and PL&HA Algorithms Development
Safe and precise landing requires complex algorithms and high-performance computing to fuse sensor data and
plan intelligent maneuvers that are subsequently executed with the vehicle propulsion system. The SPLICE project is
investing in new and novel methods for onboard HD for safe site identification, terrain relative sensor fusion for
improved navigation, and 6-DOF guidance. In addition, SPLICE is leveraging existing NASA and US Government
investments into TRN algorithms and FSW development.
1. Core Flight Software Development
The SPLICE project is developing algorithms as applications in core Flight System (cFS) framework. cFS is
developed at GSFC and has been used for a number of past NASA projects, including LADEE, Morpheus, Seeker,
and Mighty Eagle [15]. cFS uses a layered architecture which creates a development environment to support rapid
development of flight software through modular applications and platform independence. It supports the goal of
streamlining maturation of software and infusion to flight.
2. Dual-Quaternion Guidance (DQG) Development
SPLICE is developing a descent and landing guidance algorithm capable of incorporating 6-DOF constraints into
the guidance solution [16-18]. The algorithm development began as a research effort through a Co-operative
Agreement with the University of Washington. Through a rapid prototyping and coding process, the SPLICE team
has deployed a flight code version of DQG on the DLC for test benchmarking.
The DQG algorithm uses convex optimization methods to solve the constrained 6-DOF guidance problem.
Inclusion of attitude constraints into the guidance solution allows for a powerful capability useful for descent and
landing to incorporate constraints such as vehicle tip-over or sensor pointing. Follow-on work is planned to fully
assess implementation for mission applications in combination with existing heritage powered guidance approaches.
3. Terrain Relative Navigation (TRN) Development
TRN provides a powerful onboard navigation capability using passive optical camera images collected in flight.
TRN is a relatively mature capability for Earth [19, 20] and is anticipated to be demonstrated at Mars on the Mars
2020 mission [21]. Lunar versions of TRN are also in development [22]. SPLICE is partnering with the Charles Stark
Draper Laboratory to incorporate TRN into the set of PL&HA technologies tested in the SPLICE suite, with the
eventual goal of lunar infusion. Research into new methods of fusing TRN-type measurements into the navigation
filter is ongoing [23-25].
4. Hazard Detection and Safe Site Identification
Identification of safe landing sites is accomplished with an HD algorithm that analyzes the DEM to determine
candidate surface sites with high probability for safe landing (i.e., acceptable slopes and roughness). The algorithm
considers lander geometry, hazard tolerances, touchdown orientations, and lidar and navigation uncertainty in the
determination of a safety probability for each candidate location within the generated terrain map. The identified safe
landing sites are then utilized within higher-level GN&C logic to plan and execute a hazard avoidance divert to
accomplish a safe and precise landing. The HD phase of PL&HA is time critical, so the HD algorithm must process
the DEM and identify safe landing sites rapidly in real time. The SPLICE HD algorithm work is evolving techniques
developed at NASA JPL during the former ALHAT project [26].
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IV. Testing Capabilities
Component-level and integrated system-level tests are critical to the PL&HA TRL maturation process. The
SPLICE project is conducting numerous component-level tests in lab, ground, and airborne test facilities to evaluate
component technology performance. System-level testing is a challenge, however, as the intended operational
environment for PL&HA technologies is within a spacecraft GN&C subsystem performing an EDL trajectory profile.
To accomplish integrated system-level tests, SPLICE is primarily leveraging two types of testbeds, a HWIL simulation
and suborbital rockets.
E. Laboratory HWIL Simulation
The SPLICE HWIL simulation testbed (Figure 7) at NASA JSC has been implemented for use in the development,
performance testing, and validation of PL&HA subsystems and flight software, as well as for future playback and
analysis of field test data. The HWIL testbed provides a low-cost method for system level development and validation
prior to incurring the higher costs of field/flight testing or spaceflight mission infusion. The HWIL testbed incorporates
physical avionics, sensor hardware, ground consoles, and a 6- DOF high-fidelity simulation. The simulation is
developed using the JSC Trick framework, which integrates 6-DOF dynamic body models, environment models, and
sensor and actuator models. The HWIL testbed is being used in the development and performance testing of the DLC
EDU architecture, which executes flight software within the NASA cFS framework. The HWIL simulation testbed
and the cFS-based flight software together provide the SPLICE project with capabilities that support future DLC
migration to the HPSC flight processor, as well as validation of PL&HA technologies in simulated flight-like
environments to advance TRL and mitigate risk in future spaceflight applications.
Fig. 7 Pictures of the SPLICE hardware-in-the-loop simulation testbed.
A 6-DOF robotic capability, called the Six degree of freedom Tendon Actuated Robot (STAR), is being added to
the HWIL facilities. STAR will allow for subscale HWIL testing of algorithms during certain landing flight phases.
The planned capability is shown in Figure 8.
The STAR system provides a capability to perform subscale indoor trajectory testing supporting SPLICE. The
robot features full 6-DOF motion capability. The STAR laboratory is intended to reproduce lunar approach trajectories
across subscale terrain. The terrain mock-ups are reconfigurable and span the floor of the laboratory, approximately
10 x 7m. The STAR is providing the ability to rapidly develop and test terrain-relative as well as hazard-relative
navigation algorithms at low cost.
The STAR utilizes cable actuation to achieve full 6-DOF motion within a 7 x 10 x 7m structure, with a rotational
capability of +/- 10 degrees in x, y, and z axes. The system is capable of carrying a 50 kg payload, achieving an
acceleration of 1 m/s2 and a velocity of 2 m/s. The interface to the robot is a Trick compatible API, providing the
capability for simulation-in-the-loop operation. The system also features an OptiTrack system, which provides
position and orientation feedback of the end-effector with mm-level accuracy.
The robot is comprised of eight high power servo driven winches arranged at the vertices of a 7 x 10 x 7m
rectangular prism. The winches use proximal load sensing to actively measure the tension within the tendons. The
tendons all actuate a single end-effector within the workspace of the robot. The tendons are comprised of a synthetic
light-weight, low stretch rope. The parallel nature of the robot technology inherently provides high stiffness, when
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compared to serially arranged manipulators. The combination of parallel robot technology, a stiff tendon, and a large
tension capability allow the robot to have precise and accurate 6-DOF motion within the workspace.
Fig. 8 STAR Planned Capability
F. Field Testing
Suborbital rockets provide a valuable capability for integrated testing and maturation of EDL and PL&HA
technologies. Multiple suborbital rockets have been leveraged within the NASA PL&HA community during past
efforts, including ALHAT, ADAPT, and COBALT [27-30]. These testbeds provide terrestrial, moderate-cost
capabilities to evaluate PL&HA technologies (in open-loop or closed-loop configurations) within a vehicle GN&C
subsystem performing dynamically relevant powered descent and landing. This additional test capability provides
further risk reduction and systems-level TRL maturation prior to the PL&HA technologies being infused into a high-
cost spaceflight mission.
SPLICE has partnered with STMD Flight Opportunities Program to conduct a suborbital flight test of a lunar TRN
capability being developed at the Charles Stark Draper Laboratory based on prior US Government funded work. The
flight was completed in Fall 2019 on Masten Xodiac flight test vehicle [31]. The flight resulted in the successful
demonstration of the TRN at low altitude (<1 km).
A more recent test of SPLICE technology was completed on a Blue Origin New Shepard rocket. The effort was
funded via a Tipping Point agreement jointly funded by STMD Game Changing Program and Flight Opportunities,
called the Blue Origin Deorbit Descent and Landing Tipping Point (BODDL-TP). The flight test included a NDL
ETU, DLC EDU, Inertial Measurement Unit (IMU), and camera. The algorithms tested on the DLC include the
SPLICE navigation filter, TRN, and DQG. An environmental test program was completed to qualify the hardware
prior to flight [32].
The Blue Origin New Shepard vehicle is a 60 ft long reusable rocket comprised of a propulsion module (PM) and
a crew capsule (CC). The PM and CC are attached at launch and separate during ascent, ascending to about 100 km
altitude before descending. On descent, the PM uses aerodynamic surfaces to guide its return towards the nearby
landing pad and reignites its main engine for braking and vertical landing. The CC uses parachutes to softly land.
The SPLICE payload was integrated into the PM. The sensor heads, including the NDL optical head, IMU, and
TRN camera, were placed in an external location with visibility downward and away from the vehicle. The external
area was covered from airflow with a material that allowed transmission in the visible and infrared wavelengths. The
DLC and NDL chassis were mounted internally.
The primary SPLICE objectives for the test were data collection and demonstration of the hardware in the
suborbital flight environment, which included brief vacuum exposure, significant vibration, and thermal variation.
Secondary objectives were to demonstrate the real-time capability of the PL&HA algorithms (including navigation
filter, TRN, and DQG) in an operational analog environment for lunar landing.
The flight test, designated NS-13 by Blue Origin, was completed on Oct 13, 2020, at the West Texas Launch Site
(WTLS). The NDL, DLC, IMU, and camera operated throughout the duration of flight and collected a complete data
set. The data set will be extremely valuable for future development of these technologies. Initial analysis showed that
the real-time objectives of the PL&HA algorithms were not achieved due to an incorrect time referencing assumption
and invalid NDL measurements being ingested into the navigation filter. A more thorough analysis of the data,
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including the addition of playback capability in order to fully leverage the collected data set, will be completed and
reported in the future. A software update is planned in preparation for a second flight in 2021 of the same hardware.
V. Conclusion
The SPLICE Project is continuing to develop a set of avionics, sensors, algorithms, and software technology for
Precision Landing and Hazard Avoidance for future planetary destinations. These technologies directly infuse into
NASA missions as individual technologies or as an integrated system. A second flight of the NDL and DLC including
onboard software and algorithms is anticipated in 2021 on Blue Origin’s New Shepard rocket. Two lunar robotic
infusion flights of the NDL are expected in 2021, on the Intuitive Machines Nova-C and Astrobotic Peregrine
missions.
Future HDA development and testing is ongoing within SPLICE. A field test of the standalone HDL is expected
in early 2021, and an integrated suborbital rocket demo with HDL and DLC is expected in 2023. These development
and demonstration activities support a maturation of SPLICE to a full set of spaceflight technologies in 2024 for a
lunar demonstration mission, with eventual infusion to human lunar missions and Mars missions expected in the
future.
Acknowledgments
A large number of individuals have contributed to SPLICE team accomplishments past and present, and their hard
work and contributions toward solutions to PL&HA challenges is deeply appreciated.
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