Targeting Bennu – OSIRIS-REx launched yesterday !

One of the most important missions for NASA has begun yesterday at 23:05 GMT on SLC-41 at Cape Canaveral. Atlas V rocket delivered to orbit Origins, Spectral Interpretation, Resource Identification and Security-Regolith Explorer (OSIRIS-REx).

OSIRIS-REx is first in NASA history sample return mission to asteroid. It will be third in the world after successful Japanese Hayabusa and Hayabusa 2 mission which was targeting to S-type asteroid 25143 Itokawa asteroid in June 2010 with return of the samples on November. Second mission was Hayabusa 2 with  C type asteroid 162173 Ryugu as objective; JAXA planned return of the samples for 2020. For NASA asteroid sample return mission is something new, but still this mission was developed under less expensive program (comparing to Mars program missions like InSight) New Frontiers. Along with New Horizons (Pluto) and Juno (Jupiter), OSIRIS-REx with asteroid Bennu as target for exploration, will surely improve our knowledge about space and asteroids. It is worth to remind that next mission under New Frontiers will be probably announced this year and will be started in 2024, just one year after samples gathered by OSIRIS-REx will return to Earth.


On picture above: Artist's view of OSIRIS-REx approaching to Bennu.

Launch of the Atlas V in 411 configuration was scheduled for yesterday for 23:05 GMT. Weather was described for 80% for go and after finishing fueling rocket and upper stage at 22:47 GMT everything was ready for final "go" command. At 22:59 GMT command was given and countdown procedure entered into final phase. Atlas V (411) with four meter wide (12 m in length) payload fairing, single SRB booster and single RL-10A engine in Centaur upper stage was ready for its fifth flight (in this specific configuration and for 65th flight in Atlas V history). After arming safety system of the rocket at 23:03 GMT, fuel tanks of the Atlas V were already pressurized. At 23:05 rocket started to lift off and SRB solid fueled with HTPB AJ-60A engine and RD-180 fueled with LOX/RP-1 begun to provide full thrust. At T+57" rocket reached speed of 1 Ma and was already on correct azimuth of 89°. Point of maximum dynamic pressure was reached at T+70" and at T+1'33" SRB was shut down to be jettisoned at T+2'19". First stage, Common Booster Core, was cut off at T+4'6" and stopped providing over 4100 kN of thrust. Long for 32.46 m CBC was jettisoned eight seconds later. AtT+4'24" Centaur upper stage ignited its RL-10A engine, which started to provide 99 kN of thrust burning 20 tons of LH2/LOX propellant. Nine seconds later payload fairing was split and jettisoned. OSIRIS-REx was getting close to beginning of its lasting 7 years mission. First burn of Centaur was finished at T+12'41" and after 3 minutes 19 seconds of ballistic flight, parking orbit was reached. After next 19 minutes of tests and checking parameters, Centaur reoriented itself and ignited engine at T+37'27" for the second time. After 13 minutes, at T+44'12" RL-10A was cut off and OSIRIS-REx reached interplanetary orbit to be deployed at T+59'11". At 00:15 GMT today OSIRIS-REx deployed solar arrays and sent first report on its state to confirm, that everything works as it was planned. OSIRIS-REx started its mission to Bennu with touch down planned for July 2020 after almost two years of rendezvous and returning samples to landing zone in Utah (Utah Test and Training Range) in September 24, 2023 after departing Bennu in 2021.

OSIRIS-REx is one of most important missions covered by New Frontiers. Bennu, asteroid spotted for the first time in 1999, is B class object with irregular shape and diameter in widest point at 246 m. Estimated weight of Bennu is around 77600000 tons and it is passing through space with speed of around 100000 km/h. Unfortunately orbit of asteroid (with orbital period of 437 days and 4.29 h full rotation) is crossing orbit of Earth.  Between 2169 and 2199 probability of collision with Earth will increase to 0,071%, what is low value but caused, that NASA decided to focus on Bennu N. In spite the fact that Bennu orbit was not well evaluated, it was possible to predict that it will pass Earth from 300000 km in closest point. If it would hit Earth, it would generate around 1400 MT and create crater with diameter of 5 km. Gathering data on its composition, research on its orbit and parameters will help to evaluate precisely orbit of Bennu. Samples delivered to Earth will be also analyzed if there is any organic material and will also give information about Yarkovsky effect (force which makes asteroid spinning caused by thermal photons). Material will also give information on composition of carbonaceous asteroids.


On picture above: OSIRIS-REx during integration.

Launched yesterday OSIRIS-REx was manufactured by Lockheed Martin (just like Juno). Spacecraft weighs 2110 kg (860 kg dry) and is cubical in shape with 3.15 m x 2.4 m x 2.4 m dimensions. Span of solar arrays is 6.2 m after deploying; they are able to provide from 1.2 up to 3 kW of power for onboard instruments and scientific payload depending on distance from the Sun. Spacecraft is also utilizing two Li-ion onboard batteries with capacity of 30 Ah each. For attitude control and navigation spacecraft is equipped with two startrackers, two  Inertial Measurement Units, sun sensor; for navigation during approach to Bennu OSIRIS-REx will utilize cameras (TAGCAMS) and Light Detection And Ranging device (LIDAR) for optical 3D orientation. Touch And Go Camera System (TAGCAMS) is based on 3 C50 cameras combined with digital video recorder. Communication with Earth is provided via NASA Deep Space Network; spacecraft is equipped with four antennas: single high gain, two low gain and single medium gain antenna. High gain antenna with 2.1 m dish is providing downlink with speed of 914 kbit/s on X band. They are combined with Small Deep Space Transponder (SDST) with Traveling Wave Tube Amplifier. Propulsion of OSIRIS-REx is based on hydrazine thrusters (with central propellant tank compressed with helium). Four Aerojet Rocketdyne MR-107S thrusters are main propulsion used also for deep space maneuver. Single MR-107S is able to provide 275 N of thrust with peek trust up to 360 N and 85 N in lowest level (thrusters are throttable). Spacecraft has also six medium thrusters (MR-106L) for pitch and yaw control, each with thrust at 22 N and sixteen low thrust motors for precision maneuvers utilized during collecting samples from Bennu (MR-111G with 4.5 N of thrust). Scientific payload consists of following instruments: OSIRIS-REx Laser Altimeter (OLA) and mentioned above LIDAR will serve for creating topographic map of Bennu and help in touch down maneuver. OVIRS (OSIRIS-REx Visible and IR Spectrometer), which is basically a spectrometer, will help in selecting place for taking sample material along with thermal spectrometer (OSIRIS-REx Thermal Emission Spectrometer-OTER). REXIS (Regolith X-ray Imaging Spectrometer), an X ray spectrometer, will create X ray images of solar wind affecting on regolith on Bennu. Most important device of OSIRIS-REx is TAGSAM (Touch-And-Go Sample Acquisition Mechanism) - sampler with deployable 3.35 m robotic arm equipped with grasper for collecting regolith samples. It has three hermetic containers filled with nitrogen for storing 180 g of material (grasper will also collect around of 20 g of fine regolith). Samples will be deployed during passing Earth in 2023 in special capsule with Thermal Protection System based on Phenolic-Impregnated Carbon Ablator (PICA). It is also known as SRC and it is similar to capsule used in Stardust space probe. It has 81 cm in diameter and 51 cm in height. It is equipped with gravity sensors and avionics powered by onboard battery. It uses single drag parachute deployed on altitude of 31 km for speed reducing and after releasing it, main parachute is deployed on altitude of 3 km. After landing UHF beacon is started to transmit radio signal for at least 20 hours for recovery teams.