NASA’s OSIRIS-REx spacecraft (Origins, Spectral Interpretation, Resource Identification, Security-Regolith Explorer) will be launched on September 8, 2016 and travel to the near-Earth asteroid Bennu, to harvest a sample of surface material and return it to Earth for study.
Following a year-long period of surveying and mapping in orbit around Bennu, OSIRIS-REx will descend to the surface of Bennu, use a small vacuum-like instrument to suck up somewhere between 60 and 2000 grams of "gravel and surface material" and bring them back to Earth in the year 2023.
The Regolith material will enable scientists to learn more about the formation and evolution of the Solar System, initial stages of planet formation, and the source of organic compounds which led to the formation of life on Earth.
The following video from NASA provides a good summary of the mission -
Launch and Trajectory
The animation below shows the path that the OSIRIS-REx spacecraft will take on its journey to asteroid Bennu and back to Earth.
Instead of flying a direct trajectory to Bennu, OSIRIS-REx will conduct 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 will decrease an imperceptible amount as it imparts the kick to the spacecraft.
Approach
Around August 17, 2018, at a range of two million Kilometers, OSIRIS-REx will enter the Approach Phase. Major rendezvous burns will slow the spacecraft by 530 meters per second to achieve an approach speed of only 0.2 meters per second.
Around November 18, Dec 3 2018, OSIRIS-REx will arrive at Bennu, and will fly in tandem at a distance of 5 km.
Surveying and Mapping
Next, there will be a year-long surveying campaign, to create a high-resolution global data set containing color images, altimeter data and spectrographic data. Which will be used to help select suitable landing sites.
To identify regions on Bennu, in which the building blocks of life may be found, scientists will use OVIRS (the OSIRIS-REx Visible and Infrared Spectrometer), to measure visible and near-infrared light reflected and emitted from the asteroid, during a year long survey phase of the mission.
In the visible and infrared spectrum, minerals and other materials have unique signatures like fingerprints. These fingerprints allow scientists to identify various organic materials, as well as carbonates, silicates and absorbed water, on the surface of the asteroid. The data returned by OVIRS and OTES (OSIRIS-REx Thermal Emission Spectrometer) will actually allow scientists to make a map of the relative abundance of various materials across Bennu’s surface.
Sample Collection
When OSIRIS-REx has completed its remote-sensing campaign and sample site are selected, the mission will enter the sample acquisition phase.
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 nadir-facing side of the spacecraft which will approach the surface of the asteroid at a speed of 0.1 meters per second, touching down at the selected sampling site. Once the sampler head makes contact with the surface of Bennu, a burst of pure 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, the springs will push the spacecraft away. When sufficient material has been confirmed to be in the mechanism, 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.
The Touch-And-Go Sample Acquisition campaign lasts at least two months with two trial runs before the actual contact maneuver around July 2020.
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.
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. Touchdown in a testing range in Utah is expected at 14:52 UTC.
Key Mission Dates:
- Launch : Sept. 8, 2016 (34 day launch window)
- Earth Flyby : September 2017
- Arrival : Dec. 3, 2018
- Touch-And-Go Sample Collection : July 2020
- Asteroid Departure Maneuver : March 2021
- Sample Return to Earth : Sept. 24, 2023
Bennu
Bennu is a carbonaceous asteroid, and classified as a potentially hazardous object, with a 1 in 2700 chance of impacting Earth around the year 2135.
- Diameter = 492 - 550 m
- Mass = 6.0×1010 kg to 7.76×1010 kg
- Equatorial surface gravity = 0.000010 g (Earth = 1 g)
- Rotation period = 4.288 hours
- Orbital period around sun = 1.2 years
- Surface Temp. = min -34.6F, mean 6.8F, max 42.8F
- Earth-Bennu distance in Dec 2018 — 125 million km or 14 light-minutes.
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/...
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 processor operating at up to 200 MHz, consuming about 10 Watts of power.
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.
Miscellaneous Info.
- Mission budget approximately $800 million, excluding the launch vehicle.
- Distance to travel to Bennu: 509 million miles, relative to Earth
- Total distance traveled for mission: 4.4 billion miles round trip, relative to Earth
OSIRIS-REx Mission Progress
The project has been in planning and study phases since at least 2007. www.nasa.gov/…
Development projects were awarded in 2011.
Early Monday morning, on Aug 29, the payload fairing containing OSIRIS-REx will be rolled to the launch pad, where it will be mated to the Atlas V.
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 6 April 2016, 14,149 near-Earth asteroids are known, ranging in size from 1 meter up to 32 kilometers (1036 Ganymed). The number of near-Earth asteroids over one kilometer in diameter is estimated to be about 981, of which over 90% have been discovered.
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 (6 miles) across hit Earth 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.
Mitigatation techniques being explored include Gravity Tractor, Kinectic Impactor and Blast Deflection. More on that in a future diary.