OSIRIS-REx
OSIRIS-REx was a NASA asteroid-study and sample-return mission that visited and collected samples from 101955 Bennu, a carbonaceous near-Earth asteroid. The material, returned in September 2023, is expected to enable scientists to learn more about the formation and evolution of the Solar System, its initial stages of planet formation, and the source of organic compounds that led to the formation of life on Earth. Following the completion of the primary OSIRIS-REx mission, the spacecraft is planned to conduct a flyby of asteroid 99942 Apophis, renamed as OSIRIS-APEX.
OSIRIS-REx was launched on September 8, 2016, flew past Earth on 22 September 2017 and rendezvoused with Bennu on 3 December 2018. It spent the next two years analyzing the surface to find a suitable site from which to extract a sample. On 20 October 2020, OSIRIS-REx touched down on Bennu and successfully collected a sample. OSIRIS-REx left Bennu on 10 May 2021 and returned its sample to Earth on 24 September 2023, subsequently starting its extended mission to study 99942 Apophis, where it will arrive in April 2029.
Bennu was chosen as the target of study because it is a "time capsule" from the birth of the Solar System. Bennu has a very dark surface and is classified as a B-type asteroid, a sub-type of the carbonaceous C-type asteroids. Such asteroids are considered primitive, having undergone little geological change from their time of formation. In particular, Bennu was selected because of the availability of pristine carbonaceous material, a key element in organic molecules necessary for life as well as representative of matter from before the formation of Earth. Organic molecules, such as amino acids, have previously been found in meteorite and comet samples, indicating that some ingredients necessary for life can be naturally synthesized in outer space.
The cost of the OSIRIS-REx mission is approximately US$800 million, not including the Atlas V launch vehicle, which is about US$183.5 million. The OSIRIS-APEX extended mission costs an additional US$200 million. It is the third planetary science mission selected in the New Frontiers program, after Juno and New Horizons. The principal investigator is Dante Lauretta from the University of Arizona, having taken over in 2011 after the original PI Michael Julian Drake died four months after the mission won approval from NASA.
OSIRIS-REx was the first United States spacecraft to return samples from an asteroid. Previous asteroid returns include the Japanese probes Hayabusa, which visited 25143 Itokawa in 2010, and Hayabusa2, which visited 162173 Ryugu in June 2018.
Mission
Overall management, engineering, and navigation for the OSIRIS missions are provided by NASA Goddard Space Flight Center, while the University of Arizona Lunar and Planetary Laboratory provides principal science operations. Lockheed Martin Space Systems built the spacecraft and provides mission operations. The science team includes members from the United States, Canada, France, Germany, the United Kingdom, and Italy.After traveling for approximately two years, the spacecraft rendezvoused with asteroid 101955 Bennu in December 2018, and began 505 days of surface mapping at a distance of approximately. Results of that mapping were used by the mission team to select the site from which to take a sample of at least of material of the asteroid's surface. Then a close approach was carried out to allow extension of a robotic arm to gather the sample.
Following the successful collection of material, the sample was returned to Earth in a capsule similar to that which returned the samples of Comet 81P/Wild on the space probe Stardust. The return trip to Earth was shorter than the outbound trip. The capsule landed by parachute at the Utah Test and Training Range on 24 September 2023 and was transported to the Johnson Space Center for processing in a dedicated research facility.
Launch
The launch was on 8 September 2016 at 23:05 UTC on a United Launch Alliance from Cape Canaveral, Space Launch Complex 41. The 411 rocket configuration consists of a RD-180 powered first stage with a single AJ-60A solid fuel booster, and a Centaur upper stage. OSIRIS-REx separated from the launch vehicle 55 minutes after ignition. The launch was declared "exactly perfect" by the mission's principal investigator, with no anomalies before or during launch.Cruise phase
OSIRIS-REx entered the cruise phase shortly after separation from the launch vehicle, following successful solar panel deployment, propulsion system initiation, and establishment of a communication link with Earth. Its hyperbolic escape speed from Earth was about. On 28 December 2016, the spacecraft successfully performed its first deep space maneuver to change its velocity by using of fuel. An additional, smaller firing of its thrusters on 18 January 2017 further refined its course for an Earth gravity assist on 22 September 2017. The cruise phase lasted until its encounter with Bennu in December 2018, after which it entered its science and sample collection phase.During its cruise phase, OSIRIS-REx was used to search for a class of near-Earth objects known as Earth-Trojan asteroids as it passed through Sun–Earth Lagrange point. Between 9 and 20 February 2017, the OSIRIS-REx team used the spacecraft's MapCam camera to search for the objects, taking about 135 survey images each day for processing by scientists at the University of Arizona. The search was beneficial even though no new trojans were found, as it closely resembled the operation required as the spacecraft approached Bennu, searching for natural satellites and other potential hazards.
On 12 February 2017, while from Jupiter, the PolyCam instrument aboard OSIRIS-REx successfully imaged the giant planet and three of its moons, Callisto, Io, and Ganymede.
OSIRIS-REx flew by Earth on 22 September 2017.
Arrival and survey
On 3 December 2018, NASA confirmed that OSIRIS-REx had matched the speed and orbit of Bennu at a distance of about, effectively reaching the asteroid. OSIRIS-REx performed closer passes of the Bennu surface, initially at about through December to further refine the shape and orbit of Bennu. Preliminary spectroscopic surveys of the asteroid's surface by the OSIRIS-REx spacecraft detected the presence of hydrated minerals in the form of clay. While researchers suspect that Bennu was too small to host water, the hydroxyl groups may have come from water present in its parent body before Bennu split off.OSIRIS-REx entered orbit around Bennu on 31 December 2018 at about to start its extensive remote mapping and sensing campaign for the selection of a sample site. This is the closest distance that any spacecraft has orbited a celestial object, closer than the Rosetta orbit of comet 67P/Churyumov–Gerasimenko at. At this altitude, it took the spacecraft 62 hours to orbit Bennu. At the end of its detailed survey, the spacecraft entered a closer orbit with a radius of.
Sample acquisition
Procedure
Rehearsals were performed before sampling, during which the solar arrays were raised into a Y-shaped configuration to minimize the chance of dust accumulation during contact and provide more ground clearance in case the spacecraft tipped over during contact. The descent was very slow, minimizing thruster firings prior to contact to reduce the likelihood of asteroid surface contamination by unreacted hydrazine propellant. On 20 October 2020, contact with the surface of Bennu was detected using accelerometers, and the impact force was dissipated by a spring in the TAGSAM arm.Upon surface contact by the TAGSAM instrument, a burst of nitrogen gas was released to blow regolith particles smaller than into the sampler head at the end of the robotic arm. A five-second timer limited the collection time to mitigate the chance of a collision, and the probe then executed a back-away maneuver to depart safely.
The plan was then for OSIRIS-REx to perform a braking maneuver a few days later to halt the drift away from the asteroid in case it was necessary to return for another sampling attempt. It would then take images of the TAGSAM head to verify a sample had been acquired. If a sample was acquired, the spacecraft would rotate about the short axis of the sample arm to determine sample mass by measuring momentum of inertia and determine if it was in excess of the required.
Both the braking and rotation maneuvers were canceled when images of the sample container clearly showed a large excess of material was collected, some of which was able to escape through the container's seal because some material had jammed the mechanism open. The collected material was scheduled for immediate storage in the Sample-Return Capsule. On 28 October 2020, the sample collector head was secured in the return capsule. Following the separation of the head from the collector arm, the arm was retracted into its launch configuration, and the Sample-Return Capsule lid was closed and latched preparing to return to Earth.
In addition to the bulk sampling mechanism, contact pads on the end of the sampling head made of tiny stainless steel loops passively collected dust grains smaller than.
Operations
NASA selected the final four candidate sample sites in August 2019, named Nightingale, Kingfisher, Osprey, and Sandpiper. On 12 December 2019, they announced that Nightingale had been selected as the primary sample site and Osprey was selected as the backup site. Both were within craters, with Nightingale near Bennu's north pole while Osprey was near the equator.NASA planned to perform the first sampling in late August 2020; NASA's originally planned Touch-and-Go sample collection was scheduled for 25 August 2020, but was rescheduled for 20 October 2020, at 22:13 UTC. On 15 April 2020, the first sample collection rehearsal was successfully performed at the Nightingale sample site. The exercise took OSIRIS-REx as close as from the surface before performing a back-away burn. A second rehearsal was successfully completed on 11 August 2020, bringing OSIRIS-REx down to from the surface. This was the final rehearsal before the sample collection scheduled for 20 October 2020, at 22:13 UTC.
At 22:13 UTC, on October 20, 2020, OSIRIS-REx successfully touched down on Bennu at a distance of from Earth. NASA confirmed via images taken during sampling that the sampler had made contact. The spacecraft touched down within of the target location. A sample of the asteroid which was estimated to weigh at least was collected by OSIRIS-REx following the touch down. After imaging the TAGSAM head, NASA concluded that there were rocks wedged in the mylar flap meant to keep the sample inside, causing the sample to slowly escape into space. In order to prevent further loss of the sample through the flaps, NASA canceled the previously planned spinning maneuver meant to determine the mass of the sample as well as a navigational braking maneuver, and decided to stow the sample on 27 October 2020 rather than 2 November 2020 as originally planned, which was completed successfully. The collector head was observed hovering over the Sample Return Capsule after the TAGSAM arm moved it into the proper position for capture, and the collector head was later secured onto the capture ring in the SRC.
When the head was seated into the Sample-Return Capsule's capture ring on 28 October 2020, the spacecraft performed a "backout check", which commanded the TAGSAM arm to back out of the capsule. This maneuver is designed to tug on the collector head and ensure that the latches – which keep the collector head in place – are well secured. Following the test, the mission team received telemetry confirming that the head was properly secured in the Sample-Return Capsule. Thereafter, on 28 October 2020, two mechanical parts on the TAGSAM arm were disconnected – these are the tube that carried the nitrogen gas to the TAGSAM head during sample collection and the TAGSAM arm itself. Over the next several hours, the mission team commanded the spacecraft to cut the tube that stirred up the sample through the TAGSAM head during sample collection, and separate the collector head from the TAGSAM arm. Once the team confirmed these activities were done, it commanded the spacecraft on 28 October 2020, to close and seal the Sample-Return Capsule, the final step of the sample stowage process of Bennu's samples. To seal the SRC, the spacecraft closed the lid and then secured two internal latches. On inspecting images, it was observed that a few particles had escaped from the collector head during the stowage procedure, but it was confirmed that no particles would hinder the stowage process, since the team was confident that a plentiful amount of material remained inside of the head, more than the needed, that is,. The sample of Bennu was safely stored and ready for its journey to Earth. With the collector head secure inside the SRC, pieces of the sample would no longer be lost.