Landing on any planetary body is a hazardous prospect. NASA has been continuously working on finding ways to make the landing safer. The success of any space mission on a planetary body depends on a safe touchdown. Only then can the exploration begin.
Towards this end, NASA is developing and testing a set of high-accuracy landing and hazard-avoidance technologies. The technologies are being developed under project SPLICE – Safe and Precise Landing-Integrated Capabilities Evolution.
NASA is running this project within its Space Technology Mission Directorate. It is expected to be a game-changer for future space missions to Moon and Mars, and other planets as well. With this technology in place, a spacecraft will be able to avoid threats like huge boulders, craters, and locate safe landing zones.
SPLICE comprises four main sub-systems: terrain relative navigation, navigation Doppler lidar, descent and landing computer, and a hazard detection lidar
Let’s try to understand in brief how each of these subsystems functions and what purpose do they serve.
Terrain Relative Navigation
The terrain relative navigation system gets activated by the SPLICE computer during the descent several miles above the surface of the planetary body. The cameras onboard take real-time photographs of the surface at an impressive rate of 10 pictures per second.
These pictures are compared with satellite images of the landing area and also a database of known landmarks. With the help of this comparison, computer algorithms approximate the location of the aircraft and send this information to the guidance and control computer.
This determines the flight path to the landing surface and also is responsible for its execution. Thus step by step the spacecraft nears the touchdown point. This relative navigation goes on until the spacecraft is situated around four miles above the surface.
Navigation Doppler lidar
After that, the Doppler lidar comes into play and helps with the navigation process. The on-board SPLICE computer activates the navigation Doppler lidar as soon as the spacecraft has reached the mid-point of the descent.
Doppler lidar complements the terrain relative navigation by measuring parameters like the velocity of the spacecraft, its direction and the distance from the ground. Lidar which stands for light detection and ranging works similar to radar but uses laser waves instead of radio waves.
The required parameters are calculated from the wavelength and travel time of the beams reflected back from the landing surface. Calculations are done at a rapid speed of 20 times per second for each of the three laser beams and then the generated information is once again passed onto the guidance computer.
Descent and Landing computer
Now, all of the data gathered from the navigation units is fed into the descent and landing computer. This computer powerhouse uses its onboard algorithms to generate pathways for a precise and safe landing.
The descent and landing computer’s primary task is to make sure that individual SPLICE units operate smoothly in unison. It is also the unit that has to interact continuously with the other systems on any given spacecraft.
This powerful computing unit prevents SPLICE technologies from overloading the primary flight computer.
Hazard detection lidar
Although NASA hasn’t provided any details on this, it is expected to use a mechanism similar to the navigation Doppler lidar. With the potential hazards, detected adjustments can be made by the landing computer in the descent pathway.
The accuracy of data gathered from Doppler Lidar may vary depending on the surface of the planetary body. It works very well on Earth. Although, on a less reflective surface like that of the Moon the measurements may vary due to weaker beams being reflected back.
NASA has an upcoming mission that will use a Blue Origin New Shepard rocket and three SPLICE subsystems will undergo their first integrated test flight on it. In the fourth subsystem, the hazard-detection lidar will be tested in the future through flight and ground tests.