In the morning hours of Sept. 24, a small capsule containing surface samples from asteroid 101955 Bennu will careen into Earth’s atmosphere after a seven-year journey through space. The sample capsule is the culmination of NASA’s historic Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) asteroid sample return mission, which, if the sample return on Sunday is successful, will be the first time the United States returns samples from an asteroid.
The sample return capsule (SRC) is set to land within a 14 by 58-kilometer ellipse at a Department of Defense property at the Utah Test and Training Range and Dugway Proving Ground in Utah. Touchdown of the SRC is scheduled for 8:55 AM MDT (14:55 UTC). A weather briefing on Sept. 23 forecasted low winds and dry weather on Sept. 24 at Dugway — optimal conditions for the return and recovery of the SRC.
OSIRIS-REx launched atop a United Launch Alliance Atlas V rocket on Sept. 8, 2016. Since then, OSIRIS-REx has flown past Earth, rendezvoused with asteroid 101955 Bennu, orbited the asteroid and extensively imaged/mapped its surface, collected a sample from Bennu, and made the journey back to Earth to return its sample. With its sample now barrelling toward Earth, OSIRIS-REx will fly past Earth and begin a new mission called OSIRIS-APEX, wherein OSIRIS-REx will fly out and study asteroid 99942 Apophis. The spacecraft is scheduled to arrive at the asteroid in 2029 if all goes according to plan.
Bennu is considered by many scientists to be a time capsule from the beginnings of our Solar System. The asteroid is a carbonaceous near-Earth asteroid and is classified as a B-type asteroid. Its surface is very dark and is thought to have undergone extremely little geological change during its lifetime. Bennu was specifically selected by the OSIRIS-REx team due to the availability of carbonaceous material on its surface. This material is a key element in many organic molecules that are necessary for life and is similar to matter that was present in the solar system before the formation of Earth.
The process of safely and efficiently returning and recovering the SRC is very difficult and intricate, and many things have to go right in order for OSIRIS-REx scientists to get the entire sample, which is anywhere between 400 grams and one kilogram in mass. Fortunately, asteroid sample return has been successfully performed before by the Japanese Aerospace Exploration Agency’s Hayabusa and Hayabusa2 missions, and the lessons learned from those missions are helping the OSIRIS-REx team prepare for the landing.
The return of OSIRIS-REx’s samples
Over the last several weeks, OSIRIS-REx has been regularly firing its thrusters and performing trajectory correction maneuvers to ensure that the SRC is in prime position for a successful landing back on Earth. On Sept. 17, the spacecraft performed the final trajectory correction maneuver ahead of the landing, firing its thrusters to change its velocity by three millimeters per second relative to Earth.
This final trajectory correction maneuver put the SRC on the proper trajectory for a landing within the ellipse at Dugway. The maneuver moved the SRC’s predicted landing location east by 12.5 kilometers, placing the landing spot near the center of the landing ellipse.
The landing ellipse for the SRC within the Dugway Proving Ground. (Credit: NASA/USGS/Landsat 8)
On Sunday morning, teams began monitoring weather conditions at 3:00 AM MDT (09:00 UTC) using high-altitude weather balloons, which ascend to heights of 18 kilometers and provide meteorologists with weather data needed to create accurate forecasts. Following the release of this first balloon, more weather balloons will be periodically released throughout the morning to keep weather forecasts accurate.
However, it should be noted that the deployment of these weather balloons is primarily for ground personnel assigned to retrieving the SRC following the landing. Once the SRC is released from OSIRIS-REx, teams can no longer prevent it from re-entering Earth’s atmosphere, meaning that the capsule will land at Dugway, no matter what the weather conditions are like. Ground teams need to be prepared to deal with rainy or windy weather scenarios in the event the SRC lands in such conditions.
At 4:42 AM MDT (10:42 UTC), OSIRIS-REx released the SRC from the main spacecraft. OSIRIS-REx and the SRC were around 101,389 kilometers from Earth during the moment of release. Shortly afterward, at 5:02 AM MDT (11:02 UTC), OSIRIS-REx will fire its thrusters and begin a deflection maneuver to take itself off of its collision course with both the SRC and Earth. This maneuver will see OSIRIS-REx’s velocity change by 237 kilometers per hour, allowing the spacecraft to miss Earth by 779 kilometers.
Artist’s depiction of OSIRIS-REx performing its deflection maneuver after releasing the SRC. (Credit: NASA’s Goddard Space Flight Center/CI Lab)
After a brief three-hour coast toward Earth’s atmosphere, the SRC will officially enter Earth’s atmosphere at 8:42 AM MDT (14:42 UTC) at an altitude of 132 kilometers. At this moment, the SRC will be traveling at a speed of 44,498.4 kilometers per hour. Furthermore, reentry heating will also begin, with a ball of plasma forming around the SRC.
One minute later, at 8:43 AM MDT (14:43 UTC) the SRC will experience peak reentry heating. Temperatures around the SRC will reach levels of 2,760 degrees Celsius (5,000 degrees Fahrenheit).
At 8:44 AM MDT (14:44 UTC), a drogue chute will deploy from the SRC at an altitude of 31.2 kilometers above Earth’s surface. The drogue chute will help begin the process of slowing down the SRC to the appropriate landing velocity. The SRC will continue to descend beneath the drogue chute and slow down for another six minutes.
While the SRC is under the drogue chute, the OSIRIS-REx spacecraft will make its closest approach to Earth, passing just 779 kilometers above Earth’s surface.
After slowing down for six minutes under the drogue chute, the SRC will deploy the main chute at 8:50 AM MDT (14:50 UTC) when the capsule is 1.54 kilometers above the surface. This main chute will significantly slow down the SRC, and bring its speed down to the landing speed.
The OSIRIS-REx training replica return capsule under its parachute during the final pre-landing rehearsal on Aug. 30. (Credit: NASA/Keegan Barber)
Finally, at 8:55 AM MDT (14:55 UTC), the SRC will touch down on Earth’s surface at a speed of 17.7 kilometers per hour — ending a seven-year journey around the solar system and bringing the United States’ first asteroid samples to Earth.
The SRC isn’t equipped with any GPS or tracking devices, and as such must be tracked visually using Air Force and NASA tracking cameras both on the ground and in the air. These tracking cameras will track the SRC all the way from space to the ground to ensure that ground recovery teams will be able to safely and efficiently find the capsule.
Immediately following the landing, recovery helicopters will establish the location of the SRC and fly to the landing spot. Once there, teams will hook the SRC to a long line sling and begin transferring the capsule to a temporary clean room at the Dugway Proving Ground.
After arriving at the clean room at Dugway, recovery teams will spend a day disassembling the SRC and removing the asteroid sample from the capsule. After removing the sample, teams will prepare the sample for its flight to Houston, which is planned to take off the following day. Once in Houston, scientists will begin identifying, categorizing, and working with the samples.
A significant portion of the sample will be kept in Houston for analysis and preservation, while other portions will be distributed to other scientific institutions and agencies across the world. NASA and OSIRIS-REx teams have worked with JAXA and their Hayabusa missions, and as such have experience with working with asteroid samples.
As scientists analyze the samples and begin to understand the makeup of Bennu, they will publish their results and work with other scientists, missions, and agencies to use the OSIRIS-REx data to better understand our solar system, asteroids, and our planet.
(Lead image: Artist’s impression of the SRC during peak heating. Credit: NASA’s Goddard Space Flight Center/CI Lab)
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