Celestial Heist
OSIRIS-REx’s Journey from Bennu to Earth
In the grand tapestry of space exploration, NASA’s OSIRIS-REx mission is a testament to human ingenuity and our unquenchable thirst for knowledge about the cosmos. Launched on September 8, 2016, this pioneering mission aimed to study and eventually collect samples from an asteroid, 101955 Bennu. Named after the ancient Egyptian god of the afterlife, Osiris, and the acronym for Origins, Spectral Interpretation, Resource Identification, Security, Regolith Explorer, OSIRIS-REx represents a monumental step towards understanding the origins of our solar system.
The Target: 101955 Bennu
Bennu, a near-Earth asteroid, was chosen as the mission’s target due to its intriguing characteristics. Measuring approximately 500 meters in diameter, Bennu is a remnant from the early solar system, offering a snapshot of the materials present during the formation of celestial bodies over 4.5 billion years ago. Its dark, carbon-rich surface hints at a composition rich in organic compounds, which may have played a crucial role in the emergence of life on Earth.
OSIRIS-REx started on a two-year journey to rendezvous with Bennu. Along the way, the spacecraft performed a gravity assist maneuver around Earth and executed a flyby of asteroid 3122 Florence, providing valuable calibration data for its instruments.
In December 2018, OSIRIS-REx reached its destination and began an extensive survey of Bennu’s surface. This phase involved detailed mapping of the asteroid’s topography and identifying potential sample collection sites.
Given Bennu’s rough terrain, the OSIRIS-REx team took additional time to assess possible sample collection areas. They looked for flat surfaces between multiple rugged boulders. They also looked for regions with fine grains that the spacecraft could smoothly ingest on the surface. Through their own computations and a public mapping campaign, the mission team identified more than 50 sites, later boiling those down to 16 and then to the final four candidates. The spacecraft then spent a month examining each of the four sites and sending home images so scientists could further evaluate them.
The mission team selected “Nightingale,” located in a northern crater that is 140 meters wide. The reasoning behind this was that the crater was considered relatively young, and the Regolith, or rocks and dust, was freshly exposed. This means the site would likely allow for a fresh sample of the asteroid, giving the team insight into Bennu’s history.
On October 20, 2020, OSIRIS-REx executed a balletic touchdown on Bennu, its robotic arm delicately caressing the asteroid’s surface to procure a cosmic treasure. However, a minor hiccup with the sampler head raised a few heartbeats at NASA, but their confidence held firm. The result? We got our samples.
Before departing Bennu, OSIRIS-REx performed one last flyby of the sample site so scientists could see how the spacecraft’s contact with Bennu’s surface altered it. They saw something unanticipated: Even though the spacecraft barely touched the surface, it left a sizeable crater and scattered many rocks. Scientists ran numerous computer simulations to understand how this could have happened, given they had predicted the spacecraft would leave only a small divot on the surface. That’s when they understood that the particles making up Bennu’s exterior must be loosely packed and lightly bound to each other, which means they act more like a fluid than a solid. Had it not fired its thrusters to back away instantly after grabbing a sample, OSIRIS-REx would have sunk into Bennu.
The OSIRIS-REx mission was not just about cosmic capers; it’s a scientific symphony orchestrated in the depths of space with multiple instruments working in perfect harmony. The mission module was equipped with cutting-edge technology to help us better understand the asteroid. Let’s check out the remarkable tools that made this mission a cosmic masterpiece.
The OSIRIS-REx Camera Suite (OCAMS) consists of three powerful imaging instruments that work in unison to capture the essence of Bennu:
1. PolyCam: A telescope that captured breathtaking images, each one revealing more detail as the spacecraft drew nearer to the asteroid.
2. MapCam: A camera that looked for other small things near Bennu and checked if any gases were coming out. At the same time, it drew pictures of Bennu using four different channels.
3. SamCam: The diligent documentarian of the sample acquisition process, SamCam ensured every moment was recorded.
Complementing OCAMS, a suite of other cutting-edge instruments contributed to our cosmic heist:
At the heart of our celestial heist was the Touch-And-Go Sample Acquisition Mechanism (TAGSAM). TAGSAM enabled not one but up to three precise sampling attempts, guaranteeing a sample of at least 60 grams.
The OSIRIS-REx Visible and IR Spectrometer (OVIRS) helped us understand Bennu’s surface by mapping minerals and organic substances with an astonishing 20-meter resolution.
Complementing OVIRS, the OSIRIS-REx Thermal Emission Spectrometer (OTES) extended the investigation into the thermal infrared spectrum, analyzing minerals via their thermal fingerprints.
To better help us understand the cosmic elements of Bennu, the Regolith X-ray Imaging Spectrometer (REXIS), a collaboration between MIT and Harvard University, helped us uncover Bennu’s elemental composition via X-ray spectroscopy.
After the meticulous process of sample collection, the Sample Return Capsule came into action, ensuring the precious material was securely stored for its journey back to Earth. This capsule, built with state-of-the-art materials and technology, safeguarded the sample from the harsh space conditions. With every step meticulously planned, the OSIRIS-REx mission set the stage for a historic return, promising to reveal insights from the dawn of our solar system.
The return capsule’s structure consisted of a graphite-epoxy material covered with a Thermal Protection System using NASA’s PICA heat shield technology — aka Phenolic-Impregnated Carbon Ablator.
PICA is a lightweight material designed to withstand high temperatures and mechanical stress. This technology was developed at NASA’s Ames Research Center and is currently in its third generation after undergoing gradual improvements.
The back shell of the SRC was also covered with thermal protection material. Its Thermal Protection System consists of cork-based material known as SLA 561V, originally developed for the Viking missions to Mars in the 1970s. It was used on several missions, including the Mars Pathfinder, Genesis, and MER rover missions. Within the backshell, the parachute mechanism was also present with secure attach points to the capsule.
The Sample Canister was an aluminum enclosure mounted on an equipment deck sandwiched between the backshell and heat shield. The overall performance of the SRC aimed to maintain the sample at a temperature below 75°C to avoid pyrolysis, which means the thermochemical decomposition of organic material at higher temperatures.
The capsule was also equipped with a UHF (Ultra high frequency) radio locator powered by multiple lithium sulfur dioxide batteries that would have lasted for about 20 hrs, providing sufficient time for locating the SRC even in extreme weather conditions.
So, the OSIRIS-REx spacecraft gracefully bid farewell to its cosmic companion, releasing the capsule containing a piece of asteroid Bennu. This celestial pod hurtled through space for four suspenseful hours before piercing Earth’s atmosphere over California, later founding its earthly abode in Utah. The recovery team, deployed via helicopters and trucks, positioned themselves at the edge of the landing ellipse, ready to retrieve the cosmic relic upon its arrival.
At 8:22 pm IST, after a staggering 3.86-billion-mile journey, the OSIRIS-REx sample capsule made its triumphant touchdown at the Utah Test and Training Range. This historic moment marked the first-ever sample return of its kind, promising to unveil secrets from the dawn of our solar system.
The mission’s first post-landing act was to transfer the capsule from the range to a temporary clean room, resting under a nitrogen purge, safeguarding it from earthly contaminants. The team ensured the precious cosmic relic remained pristine with the utmost care. As some team members prepared the sample for its journey to the clean room, others meticulously cataloged potential contaminants in the air and on the ground.
As the OSIRIS-REx capsule found its sanctuary in the temporary clean room, preparations began for its voyage to NASA Johnson Space Center. Applause and congratulations echoed through the mission control center, honoring the team members who had played pivotal roles in this cosmic triumph. Now, let’s see what the analysis of the sample results in.
With the celestial sample safely nestled on Earth, OSIRIS-REx transitioned into a new phase — OSIRIS-APEX (APophis EXplorer). This extended mission set its sights on a new cosmic target — the near-Earth asteroid 99942 Apophis. Scheduled for an incredibly close encounter with Earth on April 13, 2029, OSIRIS-APEX would be there around Apophis for about 18 months. Using its thrusters, the spacecraft would stir up Apophis’s surface, allowing us to study its hidden depths.
The OSIRIS-REx mission has etched its mark on the canvas of space exploration, offering us an invaluable chance to glimpse into the early solar system. This mission has redefined the boundaries of our cosmic aspirations, from the nail-biting decision to release the capsule to the triumphant touchdown and the transition to OSIRIS-APEX. With OSIRIS-APEX, we eagerly anticipate even more groundbreaking discoveries on the horizon.
