When last we talked with Eric Sahr, he was at the beginning of an adventure deep into space. It was just over two years ago in 2016, when NASA launched the Osiris-REx Sample Return Mission.
At that time, the 2008 Fountain Hills High School graduate was doing post graduate studies at the University of Arizona and had obtained a job on the Osiris REx mission with the project’s science operations. This is a job that controls cameras and other instruments at the direction of the mission scientists.
In the roughly two-plus years since the launch, Osiris-REx has raced hundreds of thousands of miles through space to locate the asteroid Bennu, an orbiting rock with a radius of less than a quarter mile.
During that time Sahr has graduated and gone to work for Arizona-based KinetX Aerospace of Tempe and is working in Simi Valley, Calif. at the company’s Space Navigation and Flight Dynamics operations. His current role is that of an optical Navigation Engineer on the mission.
After arriving at its destination, Bennu, earlier this year the spacecraft performed its primary mission, the Touch-and-Go (TAG) sample acquisition event on Oct. 20.
“Watching the spacecraft go in for TAG was an extremely tense period,” Sahr said. “It took about four hours from when we departed orbit to when the spacecraft touched down.
“For me personally, it was the culmination of over seven years of work, and now the spacecraft is executing the plan and there's nothing you can do to intervene if things start to go wrong. As events unfolded, I found myself mentally going through many different things I had worked on throughout the years, searching for anything I might've missed that would improve our chances of success. However, things went about as perfectly as they could have.”
Sending and receiving signals across the expanse of space also created a bit of an edge to the mission.
“We were experiencing the TAG sequence in real-time, but delayed by about 18 minutes” Sahr said. “The reason for that is the spacecraft is so far from the Earth, it takes the radio signals that long to reach us while traveling at the speed of light. There’s a certain tension knowing that as you receive that data, you are late by 18 minutes and whatever happened in space has already happened.
“Also, while we were getting telemetry in real-time, we were not getting any images, and it would be several hours before we could visually confirm that we had made contact with the surface as we expected.”
They also discovered it is possible to have too much of a good thing, even as things were going well for the mission. In this case the “too much” proved to be the sample that was picked up.
“The design of the Sample Acquisition Mechanism was such that it should've closed after the sampling attempt. However, we got so much sample that it had become wedged open, with larger rocks preventing it from closing,” Sahr said. “This allowed for smaller rocks to begin to float out as we moved the sampling mechanism after the attempt.
“The entire team immediately had to spring into action to save our sample, requiring urgent work through nights and weekends once we realized what was happening.
“We had a plan after TAG to assess whether we had successfully acquired enough sample, but we aggressively moved up the timeline upon realizing the sample was leaking out. Normally, we spend considerable time planning every move with the spacecraft and doing considerable analysis on alternatives and ‘what-if’ scenarios. It was exciting to do this kind of work urgently, knowing that the faster we got the sample stowed, the more of it we could save for the scientists.”
Now that the sample is stowed and the Osiris-REx craft is no longer orbiting Bennu, mission personnel are preparing for the return. Sahr said he will likely be working on other missions once the spacecraft departs the vicinity of the asteroid.
Osiris-REx will begin its journey back to Earth in March 2021 and will fly its return trip of two and one-half years. It is scheduled to arrive in September 2023.
“At that time, the Sample Return Capsule containing our sample will jettison from the spacecraft and land under parachutes at the Utah Test and Training Range a few hours later,” Sahr said. “The sample will then be carefully catalogued by curators at the NASA Astromaterial Acquisition and Curation Office. After every piece is catalogued, it will finally be available for study to scientists on our mission and around the world.
“However, a large portion of the sample is reserved for future study – so schoolchildren learning about this mission may potentially be able to study this sample far into the future with techniques and tools that don't even exist yet.”