In the morning hours of Sept. 24, a small capsule containing surface samples from asteroid 101955 Bennu careened into Earth’s atmosphere after a seven-year journey through space. The landing of this sample capsule is the culmination of NASA’s historic Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer (OSIRIS-REx) asteroid sample return mission, which is now the first American mission to return samples from an asteroid.
The sample return capsule (SRC) landed 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 occurred at 8:52 AM MDT (14:52 UTC) — three minutes earlier than planned. Low winds and dry weather was present at Dugway during the landing — 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, made the journey back to Earth, and now returned its sample. As the SRC was streaking through Earth’s atmosphere, OSIRIS-REx performed a flyby of Earth and began 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 was very difficult and intricate, and many things had 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 helped the OSIRIS-REx teams with landing operations.
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.
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 were periodically released throughout the morning to keep weather forecasts accurate.
However, it should be noted that the deployment of these weather balloons was primarily for ground personnel assigned to retrieving the SRC following the landing. Once the SRC was released from OSIRIS-REx, teams could no longer prevent it from re-entering Earth’s atmosphere, meaning that the capsule would land at Dugway, no matter what the weather conditions were like. Ground teams needed to be prepared to deal with rainy or windy weather scenarios in the event the SRC landed in such conditions. Fortunately, conditions at Dugway were perfect for the landing.
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 fired its thrusters and began a deflection maneuver to take itself off of its collision course with both the SRC and Earth. This maneuver saw OSIRIS-REx’s velocity change by 237 kilometers per hour, allowing the spacecraft to miss Earth by 779 kilometers.
After a brief three-hour coast toward Earth’s atmosphere, the SRC officially entered Earth’s atmosphere at 8:42 AM MDT (14:42 UTC) at an altitude of 132 kilometers. At this moment, the SRC was traveling at a speed of 44,498.4 kilometers per hour. Furthermore, reentry heating also began at this point, with a ball of plasma forming around the SRC.
One minute later, at 8:43 AM MDT (14:43 UTC) the SRC experienced peak reentry heating. Temperatures around the SRC reached levels of 2,760 degrees Celsius (5,000 degrees Fahrenheit).
At 8:44 AM MDT (14:44 UTC), a drogue chute deployed from the SRC at an altitude of 31.2 kilometers above Earth’s surface. The drogue chute provided the SRC with stability during its descent and began the process of slowing down the SRC to the appropriate landing velocity. The SRC continued to descend beneath the drogue chute and slow down for another six minutes.
While the SRC was under the drogue chute, the OSIRIS-REx spacecraft made 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 deployed the main chute at 8:50 AM MDT (14:50 UTC). This main chute significantly slowed the SRC, and brought its speed down to the landing speed. During the landing, the main chute deployed higher than originally anticipated, meaning the SRC likely drifted a bit off course and landed farther away from the original landing location. Nonetheless, teams had a visual on the SRC the entire time and were able to locate the capsule.
Finally, at 8:52 AM MDT (14:52 UTC), the SRC touched down on Earth’s surface at a speed of 17.7 kilometers per hour — ending a seven-year and 3.6 billion mile 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 needed to be tracked visually using Air Force and NASA tracking cameras both on the ground and in the air. These tracking cameras tracked the SRC all the way from space to the ground to ensure that ground recovery teams would be able to safely and efficiently find the capsule.
Immediately following the landing, recovery helicopters established the location of the SRC and flew to the landing spot. Once there, teams secured the area, took a sample of the local environment, and hooked the SRC to a long line sling to transfer 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. Once removed from the capsule, teams will prepare the sample for its flight to Houston, which is planned to take off the following day. When the sample arrives 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: The SRC on the ground in Utah after its return to Earth. Credit: NASA/Keegan Barber)