Thursday, October 1, 2020

OSIRIS-REx - to touch and go in - 101955 Benn


Two things one can practice when needing mental peace ! ~ sit near the seashore, watch the dancing waves and think of the vastness of sea  or simply stare at the sky (with no city light refractions) and think of the vastness of the horizon.  Think of the Moon, Stars, Galaxies and more .. .. are WE alone in this Universe ? 

One can see and wonder the sky, moon and stars with a naked eye – a camera with whatever zoom may not give you that perspective ! .. then there is the telescope. The first telescope was said to be invented in 1608 in the Netherlands by an eyeglass maker named Hans Lippershey. The Orbiting Astronomical Observatory 2 was the first space telescope launched in 1968. The Milky Way is estimated to contain 100–400 billion stars  and more than 100 billion planets.

September 24 marked six years since the Indian Space Research Organisation’s (ISRO’s) Mangalyaan spacecraft – part of the Mars Orbiter Mission – entered into orbit around the red planet, making India the first Asian country to do so. Even more impressively, Mangalyaan was the country’s first interplanetary mission. Combined with the cost-effectiveness for which it is lauded, Mangalyaan is often hailed as India’s most successful space mission.   

Space exploration is the use of astronomy and space technology to explore outer space. While the exploration of space is carried out mainly by astronomers with telescopes, its physical exploration though is conducted both by unmanned robotic space probes and human spaceflight. Space exploration, like its classical form astronomy, is one of the main sources for space science. The early era of space exploration was driven by a "Space Race" between the Soviet Union and the United States. The launch of the first human-made object to orbit Earth, the Soviet Union's Sputnik 1, on 4 October 1957, and the first Moon landing by the American Apollo 11 mission on 20 July 1969 are often taken as landmarks for this initial period.  

“If God wanted man to become a spacefaring species, He would have given man a moon.” The famed rocket scientist Krafft Ehricke uttered those words in 1984. He wanted to highlight how we could use the moon as a springboard to expand human civilization into the rest of the solar system. This was more than a decade on from the last Apollo mission to the moon, and Ehricke was watching NASA and the rest of the US space program retreat from hopes of exploring more distant worlds like Mars and focus instead on Earth’s orbit. Man explored Moon, landed there and has proceeded to other planets, though human landing elsewhere has not fructified thus far, as next aim is at Mars. America is finally seeking a return to the moon with Artemis, an ambitious (and unrealistic) goal of sending astronauts by 2024. But for the White House and NASA, the mission is about more than just getting humans back on the lunar surface. The moon is also a perfect base from which to establish a follow-up program to travel to Mars. For both destinations, the goal isn’t simply to plant a flag and return to Earth—it’s to maintain a permanent presence for people to live and work.

The Red planet has had a special attraction for humanity ~ Mars is the fourth planet from the Sun and the second smallest planet in the Solar System, after Mercury. Named after the Roman god of war, it is often referred to as the "Red Planet" because the iron oxide prevalent on its surface gives it a reddish appearance. The rotational period and seasonal cycles of Mars are likewise similar to those of Earth, as is the tilt that produces the seasons.  Mars has two moons, Phobos and Deimos, which are small and irregularly shaped.

Now the World is looking forward to another  historic moment for NASA’s OSIRIS-REx mission. In just a few weeks, the robotic OSIRIS-REx spacecraft will descend to asteroid Bennu’s boulder-strewn surface, touch down for a few seconds and collect a sample of the asteroid’s rocks and dust – marking the first time NASA has grabbed pieces of an asteroid, which will be returned to Earth for study.

Asteroids are minor planets, especially of the inner Solar System. Larger asteroids have also been called planetoids. These terms have historically been applied to any astronomical object orbiting the Sun that did not resolve into a disc in a telescope and was not observed to have characteristics of an active comet such as a tail. As minor planets in the outer Solar System were discovered that were found to have volatile-rich surfaces similar to comets, these came to be distinguished from the objects found in the main asteroid belt.

101955 Bennu (provisional designation 1999 RQ36) is a carbonaceous asteroid in the Apollo group discovered by the LINEAR Project on 11 Sept 1999. It is a potentially hazardous object that is listed on the Sentry Risk Table with the second-highest cumulative rating on the Palermo Technical Impact Hazard Scale. It has a cumulative 1-in-2,700 chance of impacting Earth between 2175 and 2199. It is named after the Bennu, the ancient Egyptian mythological bird associated with the Sun, creation, and rebirth.  Bennu is the target of the OSIRIS-REx mission which is intended to return samples to Earth in 2023 for further study.  On 3rd Dec 2018, the OSIRIS-REx spacecraft arrived at Bennu after a two-year journey.  Before attempting to obtain a sample from the asteroid, it will map out Bennu's surface in detail and orbit the asteroid to calculate its mass.

OSIRIS-REx will   bring a small sample back to Earth for study. The mission launched Sept. 8, 2016, from Cape Canaveral Air Force Station. As planned, the spacecraft will return a sample to Earth in 2023. On Oct. 20, the mission will perform the first attempt of its Touch-And-Go (TAG) sample collection event. This series of maneuvers will bring the spacecraft down to site Nightingale, a rocky area 52 ft (16 m) in diameter in Bennu’s northern hemisphere, where the spacecraft’s robotic sampling arm will attempt to collect a sample. Site Nightingale was selected as the mission’s primary sample site because it holds the greatest amount of unobstructed fine-grained material, but the region is surrounded by building-sized boulders. During the sampling event, the spacecraft, which is the size of a large van, will attempt to touch down in an area that is only the size of a few parking spaces, and just a few steps away from some of these large boulders.

Because the spacecraft and Bennu are approximately 207 million miles (334 million km) from Earth during TAG, it will take about 18.5 minutes for signals to travel between them. This time lag prevents the live commanding of flight activities from the ground during the TAG event, so the spacecraft is designed to perform the entire sample collection sequence autonomously. Prior to the event’s start, the OSIRIS-REx team will uplink all of the commands to the spacecraft and then send a “GO” command to begin.  To autonomously navigate to site Nightingale, OSIRIS-REx uses the Natural Feature Tracking (NFT) navigation system. The spacecraft begins collecting navigation images about 90 minutes after orbit departure. It then compares these real-time images to an onboard image catalog, using identified surface features to make sure that it’s on the right course toward the site.  The spacecraft will autonomously abort should its trajectory vary outside of predefined limits.

To ensure that the spacecraft touches down on a safe area that avoids the region’s many boulders, the navigation system is equipped with a hazard map of site Nightingale, which delineates areas within the sample site that could potentially harm the spacecraft. If the spacecraft’s NFT system detects that it is on course to touch one of these hazardous zones, the spacecraft will autonomously wave off its approach once it reaches an altitude of 16 ft (5 m). This keeps the spacecraft safe and allows for a subsequent sample collection attempt at a future date. As the spacecraft performs each event in the sample collection sequence, it will send telemetry updates back to the OSIRIS-REx team, albeit at an extremely slow data rate. The team will monitor the telemetry during the excursion and will be able to confirm that the spacecraft has successfully touched down on Bennu’s surface soon after TAG occurs. The images and other science data collected during the event will be downlinked after the spacecraft has backed away from the asteroid and can point its larger antenna back to Earth to transmit at higher communication rates.

Sounds exciting !

With regards – S. Sampathkumar




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