NASA’s OSIRIS-REx spacecraft (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) is scheduled to perform its sample collection mission today around 6:12 p.m. ET, when it will swoop down on near-Earth asteroid Bennu, scoop up a sample of its surface material and stow it for return to Earth in 2023.
The spacecraft was launched on September 8, 2016. For over 2 years, the spacecraft has been in orbit around Bennu, surveying and mapping its surface and making trial runs of its final scoop-operation. Today, OSIRIS-REx will begin its slow descent around 1:45 p.m. ET and around 6:12 p.m. ET, it will use a small vacuum-like instrument to suck up somewhere between 60 and 2000 grams of "gravel and surface material" and transport it back to Earth in the year 2023.
We can follow all the action at the NASA site, on YouTube and on twitter at twitter.com/…. There will be no live video from the spacecraft, but there will be animations and minute-by-minute status updates.
The following video from NASA provides a good summary of the mission —
The Game Plan for Today
Launch and Trajectory
The animation below shows the trajectory of the OSIRIS-REx spacecraft to and from asteroid Bennu.
Instead of flying a direct trajectory to Bennu, OSIRIS-REx conducted an Earth Flyby, one year after launch, to boost its velocity, using the gravitational slingshot effect. Most deep-space missions use gravity assist from planets or moons to increase velocity instead of carrying large amounts of fuel for that purpose. Earth’s velocity decreased an imperceptible amount as it imparted the kick to the spacecraft.
Currently, Bennu is about 333 million km away from earth, near the opposite side of the Sun.
Surveying, Mapping and Rehearsals
The spacecraft arrived at Bennu on Dec 3, 2018, and has been in orbit around it since then at a distance of a few km.
Since then, OSIRIS-REX has been surveying Bennu and helped select suitable landing sites, which are safe for performing the touch-and-go operation and which harbor interesting organic material. A couple of rehearsals were conducted earlier this year, where the spacecraft went through the all the steps of the touch-and-go operation except engaging the rock collection device. The site where the touchdown operation will take place today is called Nightingale.
Sample Collection
OSIRIS-REx will use the Touch-And-Go Sample Acquisition Mechanism (TAGSAM) to collect samples from Bennu. TAGSAM is comprised of a detachable sampler head installed on an articulated arm.
TAGSAM will be extended from the spacecraft which will approach the surface of the asteroid at a speed of 0.2 meters per second. Once the sampler head makes contact with the surface of Bennu, a burst of nitrogen gas will push surface regolith into the sampler’s chamber. Regolith is the layer of loose, heterogeneous superficial material covering solid rock. Surface contact pads on the exterior of TAGSAM will also collect fine-grained material.
After a five-second contact, springs will push the spacecraft away. When sufficient material has been confirmed to be in the chamber, the sampler head will be placed in the Sample Return Capsule.
TAGSAM has three separate bottles of gas, which allows up to three sampling attempts, each lasting just a few seconds.
Unlike the Rosetta Mission to comet 67P/Churyumov–Gerasimenko, OSIRIS-REx will not land on Bennu, a difficult task under the ultra-low-gravity conditions. It will touch the asteroid for a few seconds and bounce off.
Some more insight into the difficulty of the mission -
The Return Trip
OSIRIS-REx will head back home in March 2021 when the spacecraft fires up its engines to boost itself on a course back to Earth. On September 24, 2023, OSIRIS-REx will deploy the Sample Return Capsule onto a re-entry path while itself maneuvering to fly past Earth. A parachute landing is expected at 14:52 UTC in a testing range in Utah.
Key Mission Dates:
- Launch : Sept. 8, 2016
- Earth Flyby : Sept. 2017
- Arrival : Dec. 3, 2018
- Touch-And-Go Sample Collection : 6:12 p.m. ET, Oct. 20, 2020
- Asteroid Departure Maneuver : March 2021
- Sample Return to Earth : Sept. 24, 2023
Asteroid Bennu
Bennu is a carbonaceous asteroid, and classified as a potentially hazardous object, with a 1 in 2700 chance of impacting Earth between 2175 and 2199.
- Size = 565 m × 535 m × 508 m
- Mass = 7.3×1010 kg
- Equatorial surface gravity = 0.000006 g (Earth = 1 g)
- Rotation period = 4.296 hours
- Orbital period around sun = 1.195 years
- Surface Temp. = min -34.6F, mean 6.8F, max 42.8F
- Earth-Bennu distance today — 333 million km or 18.5 light-minutes.
- Total distance traveled so far — 3.7 billion km. www.asteroidmission.org/...
- Age — over 4.5 billion years , formed in the first 10 million years of our solar system’s history.
- Bennu is likely to be rich in platinum and gold compared to the average crust on Earth — www.nasa.gov/…. Note that platinum and gold are thought to get created in neutron star mergers or perhaps in spinning supernovae (phys.org/...)
Bennu was chosen because it is a carbonaceous asteroid and is rich in volatiles — substances that boil off easily, like water. The thinking was that these are the kinds of objects that in the early days of the solar system seeded the Earth with the organics that life formed from, as well as the water needed. Bennu is expected to be a time capsule, in that it hasn't changed much over the history of the solar system and will show what materials looked like in the very early days of solar system. uanews.arizona.edu/...
From news.arizona.edu/...
Bennu is a fragment from the earliest stages of solar system formation. It escaped the fate of so many other asteroids by not becoming a piece of a planet. Earth itself formed from asteroids like Bennu; Bennu just happened to survive that process. So, Bennu is like a fossil from a time in the solar system before life or Earth even formed.
Since life as we know it is made from DNA, we want to know if the building blocks of DNA are on Bennu. If the building blocks that make up DNA formed early in the solar system and were preserved in carbon-rich asteroids, then they could have been delivered to Earth, Mars, Europa, Titan and all these other places we're looking for life. It would mean the seeds of life were not unique to the Earth, so our search for life in the solar system gets more exciting.
If we don't find them on Bennu, it might mean that those life-seeding molecules had to form in Earth's early environment.
From OSIRIS-REx principal investigator at the University of Arizona -
From March 2019 — a surprising discovery that Bennu spits out particles into space!
From www.jpl.nasa.gov/… -
One of the studies found that most of these pebble-size pieces of rock, typically measuring around a quarter-inch (7 millimeters), were pulled back to Bennu under the asteroid's weak gravity after a short hop, sometimes even ricocheting back into space after colliding with the surface. Others took longer to return to the surface, remaining in orbit for a few days and up to 16 revolutions. And some were ejected with enough oomph to completely escape from the Bennu environs.
For those who want a deep-dive into the Yarkovsky and YORP effects, check out this article by the mission PI at www.planetary.org/… Bennu’s rotational speed has been increasing over time, its rotation period is decreasing by about one second every 100 years – due to the YORP effect, which is caused by heat radiation and differences in albedo on its surface. Someday, Bennu might simply fly apart!
What’s in a Name?
The name Bennu was selected from more than eight thousand student entries from dozens of countries around the world who entered a "Name That Asteroid!" contest run by the University of Arizona, The Planetary Society, and the LINEAR Project. A third-grade student named Michael Puzio, from North Carolina proposed the name in reference to the Egyptian mythological bird Bennu. To Puzio, the OSIRIS-REx spacecraft with its extended TAGSAM arm resembles the Egyptian deity, which is typically depicted as a heron.
Spacecraft Data and Comm Systems (for technology geeks)
The Command & Data System uses a radiation hardened RAD750 (PowerPC) processor operating at up to 200 MHz, consuming about 10 Watts of power. Uses the VxWorks operating system.
Many of the instruments use FPGAs with embedded soft processors, and DRAM, SRAM and EEPROM memory.
The High-Gain Antenna offers the highest data rate but only has a narrow field of view, requiring the spacecraft to be precisely pointed to Earth. The antenna is a 2.1-meter diameter dish with a dual-reflector X-Band system to achieve downlink data rates of up to 914 kbit/s.
The circular horn Medium Gain Antenna offers a larger field of view than the HGA but only achieves a fraction of its data rate. It is selected whenever the HGA can not be pointed directly to Earth for downlink of status telemetry, allowing Mission Controllers sufficient insight into the state of the spacecraft and the status of ongoing operations. The MGA will be in use for the critical Touch-and-Go sampling operation.
A pair of Low Gain Antennas, each with omni-directional coverage, provide low data rate communications via MFSK tones and carrier signal when neither the HGA or MGA can be pointed to Earth – for example during propulsive maneuvers requiring a specific spacecraft attitude to set up the appropriate thrust vector.
Power: Two solar arrays generate 1226–3000 watts, depending on the spacecraft’s distance from the Sun. Energy is stored in Li-ion batteries.
Hayabusa-2
OSIRIS-REx is not the first mission to sample an asteroid. That distinction goes to the Hayabusa mission from Japan. Its successor the Hayabusa-2 spacecraft collected samples from asteroid Ryugu last year and is scheduled to drop off its rock samples on earth on December 6. For more info, check out its twitter site and the two diaries in the References section below.
Asteroids
Asteroids are small, airless rocky worlds revolving around the sun that are too small to be called planets. There are millions of asteroids; the large majority of known asteroids orbit in the asteroid belt between the orbits of Mars and Jupiter, or are co-orbital with Jupiter (the Jupiter trojans). However, other orbital families exist with significant populations, including the near-Earth asteroids.
Trojans share an orbit with a larger planet or moon, but do not collide with it because they orbit in one of the two Lagrangian points of stability, L4 and L5, which lie 60° ahead of and behind the larger body.
As of October 2020, 24,038 near-Earth asteroids (NEA) are known, ranging in size from 1 meter up to 32 km (1036 Ganymed). The number of near-Earth asteroids over 1 km in diameter is estimated to be about 888, of which over 90% have been discovered. cneos.jpl.nasa.gov
Asteroids smaller than about 25 meters (about 82 feet) will most likely burn up as they enter the Earth's atmosphere and cause little or no damage
Every 2,000 years or so, a meteoroid the size of a football field hits Earth and causes significant damage to the area. Bennu, at 500 m diameter, falls into this category.
Only once every few million years, an object large enough to threaten Earth's civilization comes along. Impact craters on Earth, the moon and other planetary bodies are evidence of these occurrences. According to abundant geological evidence, an asteroid roughly 10 km across hit the Yucatán Peninsula in Mexico about 65 million years ago. This impact made a huge explosion and a crater about 180 km across. Debris from the explosion was thrown into the atmosphere, severely altering the climate, and leading to the extinction of roughly 3/4 of species that existed at that time, including the dinosaurs.
The NASA Asteroid Grand Challenge is a large-scale effort to detect, track, characterize, and create mitigation strategies for potentially hazardous asteroids.
Epilogue
Let’s take a few moments off the hectic political news of the day and partake in this historic mission, the first its kind for NASA and use this opportunity to learn about the origins of life and ponder over our place in the Universe. As Carl Sagan famously said, we’re made of star stuff.
See the comments section below for status updates during the mission.
At 6:12 p.m., OSIRIS-REx has a successful touchdown, collection and escape maneuver! Many years of development and 4 years of operations, planning and preparations have borne fruit.
There still remains the question of determining whether enough sample has been collected and whether another attempt will be necessary.