v0.2 - 25-04-2020
Asteroid and Comet landings
Missions to land on asteroids and or comets are special for the ability to land on low-gravity planets. These bodies have no atmosphere, making them somewhat comparable to landings on Earth's moon. The very low gravity of an asteroid means that the mission has to land very slowly, otherwise bounding might be a problem. This was seen in ESA's Philae mission which was to fire harpoons into the surface of the comet
67P/Churyumov–Gerasimenko. Besides the harpoon, Philea was to fire a downward thruster to lessen the bouncing of the lander. Unfortunately, both the thruster and harpoon did not work as expected, leading to multiple bounces. Other landers to have landed on asteroids are the Minerva landers, part of the JAXA Hayabusa missions. These were small landers and rovers that investigated the asteroids Itokawa and Rygugu.
Rosetta and the Philae Lander
Operator: ESA
Target: Comet lander
Landing date: 2004
Status: Completed
The European Space Agency’s (ESA) Rosetta mission, launched on March 2, 2004, was a groundbreaking endeavor aimed at studying the comet 67P/Churyumov-Gerasimenko. The mission’s primary objective was to gain insights into the early solar system by analyzing the comet’s nucleus and its environment. After a decade-long journey through space, Rosetta successfully entered the comet’s orbit on August 6, 2014. However, the mission’s most notable achievement was the deployment of the Philae lander, which made history by performing the first-ever landing on a comet’s surface.
Philae, a 100-kilogram lander, was designed by a European consortium led by the German Aerospace Research Institute (DLR). The lander was equipped with a suite of scientific instruments intended to conduct in-situ analysis of the comet’s surface. The design of Philae was both innovative and robust, featuring a box-shaped structure with three legs for landing stability. The lander’s body was constructed using a carbon fiber baseplate and a polygonal sandwich construction, which provided strength while keeping the weight minimal.
Philae’s instruments were housed beneath a hood covered with solar cells, which were intended to power the lander by converting sunlight into electricity. The lander carried nine scientific instruments, including a drilling system to collect subsurface samples, a camera system for capturing high-resolution images, and various spectrometers and analyzers to study the comet’s composition. An antenna was also included to transmit data back to Earth via the Rosetta orbiter.
On November 12, 2014, Philae was released from the Rosetta orbiter and began its descent towards the comet’s surface. The landing, however, did not go as smoothly as planned. Upon touchdown, Philae’s anchoring harpoons failed to fire, causing the lander to bounce twice before coming to rest in a shadowed region of the comet2. This unexpected location limited the lander’s ability to recharge its batteries using solar power, significantly shortening its operational lifespan.
Despite these challenges, Philae managed to conduct a series of scientific experiments during its initial 60-hour battery life. The lander successfully drilled into the comet’s surface, analyzed samples, and sent valuable data back to Earth. Among its key findings, Philae detected organic molecules, providing crucial insights into the building blocks of life and the early solar system.
Philae’s performance, although hindered by its precarious position, was a testament to the resilience and ingenuity of the mission team. The data collected by Philae, combined with observations from the Rosetta orbiter, has significantly advanced our understanding of comets and their role in the solar system’s formation. [225, 226]
Render of Philae on the comet
Hayabusa
Operator: JAXA
Target: Asteroid Sample Return
Landing date: May 2025
Status: In development
The Japan Aerospace Exploration Agency (JAXA) has made significant strides in space exploration with its Hayabusa missions, focusing on asteroids to uncover the mysteries of our solar system. Both Hayabusa 1 and Hayabusa 2 missions have provided invaluable insights into the composition and history of asteroids, which are considered the building blocks of planets. These pages describe mainly the importance of the missions, the earth side EDL of both missions can be found here.
Hayabusa 1 Mission
Launched in 2003, Hayabusa 1 was the first mission to successfully return samples from an asteroid to Earth. The target was asteroid Itokawa, a small, stony (S-type) asteroid. The mission faced numerous challenges, including a malfunctioning sampling mechanism and communication issues. Despite these hurdles, Hayabusa 1 managed to collect tiny particles from Itokawa and return them to Earth in 20101. These samples revealed that S-type asteroids are composed of materials similar to those found in meteorites, providing clues about the early solar system’s conditions.
Hayabusa 2 Mission
Building on the success of its predecessor, Hayabusa 2 was launched in 2014 with the goal of exploring asteroid Ryugu, a carbonaceous (C-type) asteroid. C-type asteroids are rich in organic materials and water, making them prime candidates for studying the origins of life and water on Earth. Hayabusa 2 arrived at Ryugu in 2018 and conducted multiple touchdowns to collect samples, including subsurface material exposed by an artificial crater created by the spacecraft.
The samples from Ryugu, which returned to Earth in 2020, have already provided groundbreaking insights. Initial analyses have detected organic compounds and water, supporting the theory that asteroids may have delivered these essential ingredients for life to Earth3. The mission also demonstrated advanced space exploration technologies, such as precise landing and sample collection techniques, which will be crucial for future missions.
Tianwen-2
Operator: CNSA
Target: Asteroid Sample Return
Landing date: May 2025
Status: In development
Tianwen-2, also known as Zhang He, is the second flagship mission of China’s ambitious Tianwen program to demonstrate its interplanetary science capabilities. After successfully completing the first goal of soft-landing a probe and rover on the surface of Mars by Tianwen-1, the CNSA aims to perform a sample return mission. The Tianwen-2 probe is planned to launch in May 2025, heading towards the Kamo’oalewa near-Earth asteroid. The vehicle is designed to make use of both a touch-and-go manoeuvre, as well as a so-called anchor-and-attach approach using drills integrated into the four landing legs. These two approaches are chosen to maximise the likelihood of successfully collecting a sample. [220][221]
A paper from 2019 also mentions the use of a nano-lander and nano-orbiter that will be used explore the Kamo’oalewa asteroid, particularly after using an explosive to expose the underlying surface layers and thereby allowing us to get a better understanding of its internal composition. [220]
Tianwen-2 is scheduled to head back to Earth in order to deliver the collected regolith sample using a reentry capsule. The probe will thereafter continue its journey to study another asteroid, 311P/PanSTARRS.
