Space Sunday: returns and a collapse

The Hyabusa2 sample return capsule, measuring just 40 cm across, lies amidst the scrub of Woomera, southern Australia, carrying samples from asteroid 162173 Ryugu. Credit: JAXA via AP

On Saturday, December 5th (Sunday December 6th local time in Australia), Japan’s Hyabusa2 successfully returned samples gathered from the asteroid 162173 Ryugu.

It marked the culmination of a six-year mission to reach the asteroid, gather samples and then make a return to Earth – although as I mentioned in my last Space Sunday update, the return of the samples does not mark the end of the road for Hyabusa2.

Travelling at 43,190 km/h – too fast to enter orbit – the spacecraft released the 40 cm sample return capsule on the night of Friday December 4th, 2020, whilst still some 220,000 km away. With its cargo duties  discharged, Hyabusa2 performed an engine burn to start it on its way for a rendezvous with asteroid (98943) 2001 CC21 in 2026, before flying on to meet with 1998 KY26, in 2031.

With no means to slow down, the sample capsule slammed into the upper reaches of Earth’s  atmosphere at 17:28 GMT on Saturday, December 5th (the earlier  hours of Sunday December 6th in Japan and Australia). Following re-entry, that helped the capsule to slow to supersonic speeds, the capsule dropped to an altitude of 10 km before deploying its landing parachute, touching down in Australia at 17:47 GMT (04:17 a.m. local Australian time on December 6th), JAXA officials said.

Radio tracking systems deployed around the expected landing site were able to follow the capsule down allowing its landing point to be triangulated accurately so that recovery helicopters could quickly move in and retrieve the capsule and its cargo.

Following recovery, work started on capsule assessment and preparations to transfer it to the Japanese Space Agency’s (JAXA) Extraterrestrial Sample Curation Centre, a purpose-built facility designed to house and study cosmic material brought home by space missions. Here some of the samples – believed to measure just a few grams – will be studied by Japanese scientists, and some will be distributed to laboratories around the world, where scientists will study it for clues about the solar system’s early days and the rise of life on Earth.

The mission marks only the second time a dedicated sample return mission has brought samples of an extra-terrestrial body back to Earth, the first being the original Hyabusa mission, which returned samples from asteroid 25143 Itokawa in 2010. However, it will not be the last. China’s Chang’e 5 mission will shortly be on its way back to Earth with samples gathered from the Moon (see below for more), and NASA’s OSIRIS-REx will be returning samples from asteroid from 101955 Bennu in 2023.

Arecibo Collapses

When it came, it came suddenly and without warning – yet purely by chance, a drone was on hand to capture the event as it happened.

Cable break: a still from video footage recorded at the moment one of the two remaining primary cables supporting the 900-tonne receiving platform snapped, bringing about the destruction of the Arecibo radio astronomy telescope. Credit: UCF / NSF

I recently wrote about the fact that, having lost a primary and secondary support cable that were helping to keep its receiving platform aloft, the Arecibo observatory had been declared unsafe and was to be decommissioned, the replacement of the primary load-bearing cables – one of three in total – being determined to be both difficult and dangerous.

Due to the risk of the 900-tonne receiving platform collapsing onto the dish, built into a hilltop karst sinkhole, it had been hoped the telescope could be decommissioned and dismantled, possibly through the use of controlled demolition, sooner rather than later, lest further cables – including one of the two remaining primary cables – gave way.

But on December  1st, before decommissioning plans could be finalised, one of the remaining suffered a catastrophic failure, sending the receiving platform plummeting into the telescope’s 305-metre diameter dish.

The event took place shortly before 07:30 in the morning, local time – and by chance, engineers were monitoring the telescope’s cable system from the main control room and via an aerial drone positioned above the cable housings on the receiving platform when the cable failed. As a result, the entire collapse was caught on camera from two locations – although the drone had to be hastily moved away from the receiving platform as the collapse started.

Swinging towards the ground on the remaining support cables, the receiving platform disassembled as it fell, the bulk falling the 150m into the aluminium dish, the support frame swinging to smash into the the side of dish, the trailing cables also doing considerable damage. Such was the force of the failure, the mass of the platform tore away the top section of one of the support towers and brought about the complete collapse of another.

It is still not clear why the first of the primary cables failed in November. While all of the main cables have been in place since the observatory was built in the early 1960’s, the first one that broke did so at well below its rated stress point, a fact that left engineers worried that either of the two other primary cables might be a lot weaker than they were believed to be, leading to the determination to try to decommission the telescope as soon as possible.

Aftermath: a section of the Arecibo receiving platform lies atop the smashed and crushed main dish lining the base of the sinkhole. Credit: UCF / NSF

Following the collapse, both the National Science Foundation (NSF),who provided the funding for Arecibo, and the University of Central Florida, which operates the site for the NSF, entered into a formal assessment in order to determine how best to clear up the site.

The collapse brings to an end 57 years of almost continuous operations for this most iconic radio observatory. In its time, the main dish was used for both radar and radio astronomy, as well as taking part in the Search for Extraterrestrial Intelligence (SETI); it was also frequently used by NASA to help in the detection of near-Earth objects (NEOs).

Most importantly, Arecibo was the most powerful radio telescope in the world that could be used in planetary astronomy. As such, its loss a significant hole in our ability to analyse planets and exoplanets via radio means.

Due to the cost of developing a replacement, it is going to be hard to replace; while NASA has what is possibly the second most powerful radio telescope that could be used for planetary astronomy in the in Goldstone telescope located in California, the primary mission for that dish is deep-space communications with ongoing missions as a part of NASA’s Deep Space Network. As such, its ability to carry out planetary research activities is limited.

However, while the destruction of the main dish signals an end for the iconic telescope, Arecibo as a whole is not finished. As well as being home to the now destroyed radio astronomy dish, the facility also operates a 12-m radio telescope intended for very-long-baseline interferometry (VLBI), and a LIDAR system, both of which are continuing their missions and studies.

China’s Chang’e 5 Prepares for Return to Earth with Lunar Samples

Launched on November 23rd on what was to be a mission of up to 23 days in length, China’s Chang’e 5 (“Heavenly Princess 5”) mission will shortly be commencing its trip back to Earth, having successfully collected samples from the surface on the Moon.

The mission is the third such lunar mission China has sent to the surface of the Moon, with the Chang’e 4 lander and rover still operating on the Moon’s far side. However, Chang’e 5 is perhaps the most technically complex mission the Moon China has yet undertaken, comprising four individual elements: an orbiter (propulsion / power) and a sample return capsule, both of which remained in orbit around the Moon, and a lunar lander and a sample ascender designed to gather the samples.

The Chang’e 5 craft. Credit: CNSA

Following launch, the mission entered orbit around the Moon on Saturday, November 28th, some 400 km above the lunar surface. Then, on Monday, November 30th, the lander / ascender elements separated from the orbital components and descended to make a successful landing at Mons Rümker in Oceanus Procellarum (Ocean of Storms).

A large, elevated volcanic mound 70 km in diameter that features a strong spectroscopic signature of basaltic lunar mare material, the landing zone is a prime example of “young” lunar material around 1.21 billion years old, thus providing a strong contrast with the 4.4 to 3.1 billion-year-old samples gathered by the Apollo missions.

Following touchdown, the lander deployed a drilling mechanism that allowed it to gather pristine samples of the “young” Moon rock,untainted by solar radiation, and deliver them safely to a special container on the ascent module. At the same time, the lander carried out a visual survey of its surroundings using panoramic cameras, mapped conditioned below the surface under it with ground-penetrating radar, and carried out an analysis of the surface material beneath it to determine its mineral and water content.

A camera on the Chang’e 5 lander captures the moment the ascender lift-off, carrying the gathered samples to a rendezvous with the orbital components of the mission. Credit: CNSA/CLEP

Due to the need to complete surface operations during the 336-hour lunar “day” – neither the lander nor the ascender are equipped with the necessary heater circuits to survive the cold lunar night -,  and with samples successful gathered on the first set of operations, the ascender craft blasted off from the lander at 15:00 GMT on Thursday, December 4th, to commence what was regarded as the most complex part of the mission: a fully automated lunar orbit rendezvous and docking.

This was achieved by the ascender reaching orbit and then it and the orbital components of the mission carrying out a series of manoeuvres over a 2-day period that allowed them to close to a point where a microwave radio link could be established between them, allowing one to be guided towards the other with an accuracy of 0.1%.

In terms of the space tasks that humans have performed so far, only the Apollo program missions have completed the rendezvous and docking in lunar orbit. However uncrewed rendezvous and docking have never been done before. It will be the historic first, and it will be very difficult and requires a flight control accuracy of less than 5 centimetres during the approach of the two vehicles.

Peng Jing, deputy chief designer of the Chang’e 5 probe

Rendezvous came at 21:42 GMT on December 5th (05:42 on December 6th, Beijing time), with one vehicle using a claw to grab a horizontal bar on the other. Once grasped, the bar was then used to draw to two craft together, the sample container held within the ascender directly aligned with a receptacle on the sample return capsule.

With docking complete, a mechanism on the ascender transferred the sample container to the sample return capsule, allowing a cover one the latter to be rotated into pace and sealed over the container to protect it during its descent back to Earth at the end of the mission. With the transfer completed, the ascender was jettisoned.

The orbital components of Chang’e 5 will remain in orbit around the Moon for around another week, until the optimal Earth-return window opens to allow the vehicle deliver the sample return capsule for a landing in Dorbod Banner, Inner Mongolia, on or around December 16th.

As well as being a full sample return mission in its own right, Chang’e 5 is also seen by the Chinese as a vital means of testing capabilities they will need during their own ambitions to establish a human presence on the Moon – something with which the upcoming Chang’e 6 sample return mission will also assist.