OSIRIS-REx

OSIRIS-REx launch video

Animation of OSIRIS-REx's trajectory from 9 September 2016
  OSIRIS-REx ·   101955 Bennu ·   Earth

Animation of OSIRIS-REx's trajectory around 101955 Bennu from 25 December 2018
  OSIRIS-REx ·   101955 Bennu

The launch was on 8 September 2016 at 23:05 UTC on a United Launch Alliance Atlas V 411 from Cape Canaveral, Space Launch Complex 41.[3] 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.[25] OSIRIS-REx separated from the launch vehicle 55 minutes after ignition.[2] The launch was declared "exactly perfect" by the mission's principal investigator, with no anomalies worked before or during launch.[26]

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.[26] Its hyperbolic escape speed from Earth was about 5.41 km/s (3.36 mi/s).[27] On 28 December 2016, the spacecraft successfully performed its first deep space maneuver to change its velocity by 431 m/s (1,550 km/h) using 354 kg (780 lb) of fuel.[28][29] An additional, smaller firing of its thrusters on 18 January 2017 further refined its course for an Earth gravity assist on 22 September 2017.[28] The cruise phase lasted until its encounter with Bennu in December 2018,[22] after which it entered its science and sample collection phase.[28]

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 L₄ 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,[30] as it closely resembled the operation required as the spacecraft approached Bennu, searching for natural satellites and other potential hazards.[29][31] On 12 February 2017, while 673×10^⁶ km (418×10^⁶ mi) from Jupiter, the PolyCam instrument aboard OSIRIS-REx successfully imaged the giant planet and three of its moons, Callisto, Io, and Ganymede.[32]

OSIRIS-REx flew by Earth on 22 September 2017.[33]

On 3 December 2018, NASA affirmed that OSIRIS-REx had matched the speed and orbit of Bennu at a distance of about 19 km (12 mi), effectively reaching the asteroid. OSIRIS-REx performed closer passes of the Bennu surface, initially at about 6.5 km (4.0 mi) through December to further refine the shape and orbit of Bennu. Preliminary spectroscopic surveys of the asteroid's surface by 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 presence in its parent body before Bennu split off.[34][35]

OSIRIS-REx entered orbit around Bennu on 31 December 2018 at about 1.75 km (1.09 mi) 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, surpassing the Rosetta's orbit of comet 67P/Churyumov–Gerasimenko at 7 km (4.3 mi).[13][36] At this altitude, it takes the spacecraft 62 hours to orbit Bennu.[37] At the end of this detailed survey, the spacecraft entered a closer orbit with a radius of 1 km (0.62 mi).[38]

Rehearsals were performed before the sampling event, during which the solar arrays were to be raised into a Y-shaped configuration to minimize the chance of dust accumulation during contact and provide more ground clearance in case the spacecraft tips over (up to 45°) during contact.[21] The descent was very slow to minimize thruster firings prior to contact in order to reduce the likelihood of asteroid surface contamination by unreacted hydrazine propellant. Contact with the surface of Bennu was to be detected using accelerometers, and the impact force was meant to be dissipated by a spring in the TAGSAM arm.[39]

Upon surface contact by the TAGSAM instrument, a burst of nitrogen gas was released, which was meant to blow regolith particles smaller than 2 cm (0.8 in) 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. After the timer expired, the back-away maneuver executed a safe departure from the asteroid.[21]

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 moment of inertia and determine if it was in excess of the required 60 g (2.1 oz).

Both the braking and rotation maneuvers were canceled as images of the sample container clearly showed a large excess of material was collected, a portion of which was able to escape through the container's seal due to some material jamming the mechanism open. The collected material was scheduled for immediate storage in the Sample-Return Capsule.[40][21] On 28 October 2020, the sample collector head was secured in the return capsule. Following the severance of the head from the collector arm, the arm will then be retracted into its launch configuration, and the Sample-Return Capsule lid will be closed and latched preparing to return to Earth.[41][42]

In addition to the bulk sampling mechanism, contact pads on the end of the sampling head made of tiny stainless steel loops (Velcro)[43] passively collected dust grains smaller than 1 mm.

The final four candidate sample sites

The successful October 2020 sample collection, showing OSIRIS-REx touching down on the Nightingale sample site.

Images of the TAGSAM head showing that it is full of rocks and dust collected from Bennu and that it is leaking material into space.

OSIRIS-REx successfully stows its sample of asteroid Bennu in October 2020.

NASA selected the final four candidate sample sites in August 2019, named Nightingale, Kingfisher, Osprey, and Sandpiper.[44] On 12 December 2019, they announced that Nightingale had been selected as the primary sample site and Osprey was selected as the backup site.[45] Both located within craters, Nightingale is near Bennu's north pole while Osprey is near the equator.[46]

NASA's initial plans were to perform the first sampling in late August 2020;[47] NASA's originally planned Touch-and-Go (TAG) sample collection event was scheduled for 25 August 2020, but was rescheduled for 20 October 2020, at 22:13 UTC.[48][49] 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 65 m (213 ft) from the surface before performing a back-away burn.[50][51] A second rehearsal was successfully completed on 11 August 2020, bringing OSIRIS-REx down to 40 m (130 ft) from the surface. This was the final rehearsal before the sample collection scheduled to take place on 20 October 2020, at 22:13 UTC.[52][53]

On 20 October 2020 at 22:13 UTC, OSIRIS-REx successfully touched down on Bennu.[54] NASA confirmed via images taken during sampling that the sampler had made contact. The spacecraft touched down within 92 cm (36 in) of the target location.[55][56] After imaging the TAGSAM head, NASA concluded that there are rocks wedged in the mylar flap that is meant to keep the sample in, causing the sample to slowly escape into space.[57] In order to prevent further loss of the sample through the flaps, NASA canceled the previously-planned spinning maneuver 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 was originally planned, which was completed successfully. It was seen that the collector head hovering over the SRC after the TAGSAM arm moved it into the proper position for capture and later the collector head secured onto the capture ring in the Sample Return Capsule.[57]

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 is properly secured in the Sample-Return Capsule. Thereafter, on 28 October 2020, two mechanical parts on the TAGSAM arm must first be 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.[58] To seal the SRC, the spacecraft closes the lid and then secures two internal latches. Additionally, 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 remains inside of the head, being more than the needed amount, 60 g (2.1 oz), that is, between 60 g (2.1 oz) and 2,000 g (71 oz). Now, the sample of Bennu is safely stored and ready for its journey to Earth. Now that the collector head is secure inside the SRC, pieces of the sample will no longer be lost.[59]

Artist's rendition of the Sample Return Capsule returning to Earth in 2023.

The OSIRIS-REx team is now preparing the spacecraft for the next phase of the mission, the return cruise to Earth.[60][61] The departure window opens in March 2021 for OSIRIS-REx to begin its voyage home on 10 May 2021. On 24 September 2023, the OSIRIS-REx return capsule is scheduled to re-enter Earth's atmosphere and land under a parachute at the Air Force's Utah Test and Training Range.[62] The sample would be curated at NASA's Astromaterials Research and Exploration Science Directorate (ARES) and at Japan's Extraterrestrial Sample Curation Center.[62][63] The sample material from the asteroid would be distributed to requesting organisations worldwide by ARES.[64]

Imaging camera suite

The OSIRIS-REx Camera Suite (OCAMS) consists of the PolyCam, the MapCam, and the SamCam.[75] Together, they acquire information on asteroid Bennu by providing global mapping, sample site reconnaissance and characterization, high-resolution imaging, and records of the sample acquisition.[77]

• PolyCam, an 20 cm (7.9 in) telescope, acquired visible-light images with increasingly higher resolution on approach the asteroid and high-resolution surface images from orbit.
• MapCam searches for satellites and outgassing plumes. It maps the asteroid in four blue, green, red and near infrared channels, and informs the model of Bennu's shape and provides high resolution imaging of the potential sample sites.
• SamCam continuously documents the sample acquisitions.

OVIRS

The OSIRIS-REx Visible and IR Spectrometer (OVIRS) is a spectrometer which maps minerals and organic substances on the asteroid's surface.[75] It provides full-disc asteroid spectral data at 20 m resolution. It maps blue to near-infrared, 400–4300 nm, with a spectral resolution of 7.5–22 nm.[78] This data will be used in concert with OTES spectra to guide sample-site selection. The spectral ranges and resolving powers are sufficient to provide surface maps of carbonates, silicates, sulfates, oxides, adsorbed water and a wide range of organic compounds.

OTES

The OSIRIS-REx Thermal Emission Spectrometer (OTES) provides thermal emission spectral maps and local spectral information of candidate sample sites in the thermal infrared channel covering 4–50 µm, again to map mineral and organic substances.[75] The wavelength range, spectral resolution, and radiometric performance are sufficient to resolve and identify silicates, carbonates, sulfates, phosphates, oxides, and hydroxide minerals. OTES is also used to measure the total thermal emission from Bennu in support of the requirement to measure emitted radiation globally.

Based on the performance of Mini-TES in the dusty surface environment of Mars, OTES was designed to be resilient to extreme dust contamination on the optical elements.

The Regolith X-ray Imaging Spectrometer (REXIS) will provide an X-ray spectroscopy map of Bennu to map element abundances.[75] REXIS is a collaborative development by four groups within Massachusetts Institute of Technology (MIT) and Harvard University, with the potential to involve more than 100 students throughout the process. REXIS is based on flight heritage hardware, thereby minimizing elements of technical risk, schedule risk, and cost risk.

REXIS is a coded aperture soft X-ray (0.3–7.5 keV) telescope that images X-ray fluorescence line emission produced by the absorption of solar X-rays and the solar wind with elements in the regolith of Bennu leading to local X-ray emissions. Images are formed with 21 arcminute resolution (4.3 m spatial resolution at a distance of 700 m). Imaging is achieved by correlating the detected X-ray image with a 64 x 64 element random mask (1.536 mm pixels). REXIS will store each X-ray event data in order to maximize the data storage usage and to minimize the risk. The pixels will be addressed in 64 x 64 bins and the 0.3–7.5 keV range will be covered by five broad bands and 11 narrow line bands. A 24 seconds resolution time tag will be interleaved with the event data to account for Bennu rotation. Images will be reconstructed on the ground after downlink of the event list. Images are formed simultaneously in 16 energy bands centered on the dominant lines of abundant surface elements from O-K (0.5 keV) to Fe-Kß (7 keV) as well the representative continuum. During orbital phase 5B, a 21-day orbit 700 m from the surface of Bennu, a total of at least 133 events/asteroid pixel/energy band are expected under 2 keV; enough to obtain significant constraints on element abundances at scales larger than 10 m.

On 11 November 2019, university students and researchers involved in the mission accidentally discovered X-ray burst from a black hole name MAXI J0637-430 locate 30,000 light-years away, during observing the asteroid with REXIS.[79]

The OSIRIS-REx Laser Altimeter (OLA) is a scanning and lidar instrument that will provide high resolution topographical information throughout the mission.[75] The information received by OLA creates global topographic maps of Bennu, local maps of candidate sample sites, ranging in support of other instruments, and support navigation and gravity analyses.

OLA scans the surface of Bennu at specific intervals to rapidly map the entire surface of the asteroid to achieve its primary objective of producing local and global topographic maps. The data collected by OLA will also be used to develop a control network relative to the center of mass of the asteroid and to enhance and refine gravitational studies of Bennu.

OLA has a single common receiver and two complementary transmitter assemblies that enhance the resolution of the information brought back. OLA's high-energy laser transmitter is used for ranging and mapping from 1 to 7.5 km (0.62 to 4.66 mi). The low-energy transmitter is used for ranging and imaging from 0.5 to 1 km (0.31 to 0.62 mi). The repetition rate of these transmitters sets the data acquisition rate of OLA. Laser pulses from both the low and high energy transmitters are directed onto a movable scanning mirror, which is co-aligned with the field of view of the receiver telescope limiting the effects of background solar radiation. Each pulse provides target range, azimuth, elevation, received intensity and a time-tag.

OLA was funded by the Canadian Space Agency (CSA) and was built by MDA at Brampton, Ontario, Canada.[80] OLA was delivered for integration with the spacecraft on 17 November 2015.[81] The lead instrument scientist of OLA is Michael Daly from York University.[82]

TAGSAM arm test before launch

The sample-return system, called Touch-And-Go Sample Acquisition Mechanism (TAGSAM), consists of a sampler head with an articulated 3.35 m (11.0 ft) arm.[2][75] An on-board nitrogen source will support up to three separate sampling attempts for a minimum total amount of 60 g (2.1 oz) of sample. The surface contact pads will also collect fine-grained material.

Highlights of the TAGSAM instrument and technique include:

• Relative approach velocity of 10 cm/s (3.9 in/s)[83]
• Contact within 25 m (82 ft) of selected location
• OCAMS documents sampling at 1 Hz
• Collect samples in less than five seconds, direct nitrogen (N₂) annular jet fluidizes regolith, surface-contact pad captures surface sample
• Verify bulk sample collection via spacecraft inertia change; surface sample by imaging sampler head
• Sampler head stored in sample-return capsule and returned to Earth