October 2020

RASC Calgary Centre - Current Astronomical Highlights by Don Hladiuk Follow Don on: ("astrogeo") ASTRONOMICAL HIGHLIGHTS provides information about space science events for the upcoming month. The information here is a rough transcript of information covered on the popular CBC Radio One Calgary Eyeopener segment on 1010 AM and 99.1 FM usually on the first or second Monday of each month at 7:36 AM. Don is a life member of the Royal Astronomical Society of Canada and was twice President of the Calgary Centre. Since June 1984, Don has had a regular radio column on the Eyeopener describing monthly Astronomical Highlights to southern Albertans. For additional sources of sky information see the list of links below this month's article. For information about the Calgary Centre of the RASC, please visit our web site. Interested in Astronomy? Become a member of the RASC! Click here to find out about RASC membership and RASC publications. ASTRONOMICAL HIGHLIGHTS October 2020 Broadcast Date October 5, 2020 Mars Rules the Evening Sky On October 6, Mars will be closest to Earth at only 62.7 million kilometres (3.5 minutes away) and the Red Planet will not be this close again until 2035. I encourage everyone to go out for an evening walk later in October and look towards the eastern sky after sunset. There you will see a bright orange star-like object rising above the eastern horizon. This object is our fourth planet from the sun, Mars. To the south, you will see brilliant Jupiter with fainter Saturn to its left, but Mars (on the eastern horizon) will even outshine the largest planet in our solar system. Although Mars was marginally closer in 2018, the Red Planet was much lower in our atmosphere. Mars is a small planet, only half the size of the Earth, and it is hard to see details on this terrestrial planet if you do not have good seeing conditions. During the 2020 close approach, Mars is in the constellation Pisces and will cross the sky approximately 450 degrees above the horizon (halfway up to overhead). Telescope users will have less atmosphere to peer through during this close approach and will enjoy sharper views of the Red Planet. One observing tip is to attach an orange filter (Wratten #21) to your telescope eyepiece and this will help decrease the brightness and accentuate the surface markings. These lighter and darker areas have been seen through telescopes for over a hundred years and some astronomers thought they could even see straight lines that were elaborate canal systems bringing water from the polar regions to the warmer drier equatorial Martian cities. However, after the Mariner 4 spacecraft flew past Mars in 1965 and sent back images, there were no signs of an ancient Mars civilization. We now know the darker areas are usually dust free mafic (basalt) rocks compared to the light orange areas that are more dusty regions. The orange-reddish colour is due to iron oxide (similar to rust here on Earth). When the sky is steady (less atmospheric turbulence) and the stars are not twinkling much, this is a good time to use a higher magnification eyepiece and discover the fascinating features that intrigued early astronomers in the late 1800s and early 1900s. Photo of Mars rising in the eastern sky after sunset from near Nanton, AB on August 22, 2020. Photo by: Don Hladiuk If you own or know of someone who owns a telescope, please take a look at this distant world and try to observe the polar caps, dark and light markings, and possibly even dust storms. If you do plan to look through a telescope with friends, please take proper Covid-19 prevention precautions. And if you miss this favourable viewing opportunity, you will only have to wait until February 2021, when a small armada of spacecraft from the United Arab Emirates, China, and USA arrive at Mars and send back more amazing images of the Red Planet OSIRIS-REx Sample Collection Attempt – October 20 A historic moment is on the horizon for NASA’s OSIRIS-REx mission (Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer). In October, 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. On Oct. 20, the mission will perform the first attempt of its Touch-And-Go (TAG) sample collection instrument. This series of maneuvers will bring the spacecraft down to a site named Nightingale, a rocky area 16 metres 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. During the 4.5-hour sample collection activity, the spacecraft will perform three separate maneuvers to reach the asteroid’s surface. The descent sequence begins with OSIRIS-REx firing its thrusters for an orbit departure maneuver to leave its safe-home orbit approximately 770 meters from Bennu's surface. After traveling four hours on this downward trajectory, the spacecraft performs the “Checkpoint” maneuver at an approximate altitude of 125 metres. This thruster burn adjusts OSIRIS-REx’s position and speed to descend steeply toward the surface. About 11 minutes later, the spacecraft performs the “Matchpoint” burn at an approximate altitude of 54 metres, slowing its descent and targeting a path to match the asteroid's rotation at the time of contact. The spacecraft then descends to the surface, touches down for less than sixteen seconds and fires one of its three pressurized nitrogen bottles. The gas agitates and lifts Bennu’s surface material, which is then caught in the spacecraft’s collector head. After this brief touch, OSIRIS-REx fires its thrusters to back away from Bennu’s surface and navigates to a safe distance from the asteroid. Here is a computer created image showing OSIRIS-Rex avoiding building sized boulders as it descends to the surface of asteroid Bennu to collect samples of this pristine asteroid. Photo Credit: NASA/Goddard/SVS/CI Lab After the orbit departure maneuver, the spacecraft undertakes a sequence of reconfigurations to prepare for sampling. First, OSIRIS-REx extends its robotic sampling arm – the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) – from its folded storage position out to the sample collection position. The spacecraft’s two solar panels then move into a “Y-wing” configuration over the spacecraft’s body, which positions them safely up and away from the asteroid’s surface during touch down. This configuration also places the spacecraft’s center of gravity directly over the TAGSAM collector head, which is the only part of the spacecraft that will contact Bennu’s surface during the sample collection event. Because the spacecraft and Bennu are approximately 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. As the spacecraft approaches the surface, OSIRIS-REx updates the Checkpoint and Matchpoint maneuvers based on the NFT's estimate of the spacecraft’s position and velocity. OSIRIS-REx continues to use the NFT estimates as it descends to the surface after the Matchpoint maneuver to monitor its position and descent rate. 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 5 metres. 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.

Load more