This past December, NASA’s most recent interplanetary mission arrived at its destination. The OSIRIS-REx spacecraft arrived at Bennu, a tiny near Earth asteroid, to eventually take a sample and bring it back to Earth. With this mission, we hope to unlock the secrets to how life formed here on Earth through studying the unique composition of Bennu.
I had a chance to talk with an engineer working on this mission, a old labmate and friend of mine Samantha Rieger. Samm works for NASA Goddard as well… I’ll let her tell you. Let’s get to it!
Marielle: What is your job title?
Samm: Aerospace Engineer or Maneuver Design/Mission Design Analyst
M: What does a Mission Design Analyst do?
S: The main part of my job is to tell the spacecraft where to go. We have Optical Navigation (using pictures of the asteroid taken by the spacecraft) and Orbit Determination (using radar (same thing used by cops to get your car speed)) to determine exactly where the asteroid is. My job is to take that information and determine how much we need to fire the thrusters to get the spacecraft where it needs to go around the asteroid.
Also, because we didn’t really know much about the asteroid (mass, density, shape) until we got to the asteroid in December, my job has also been to update the path we take around the asteroid since the spacecraft will move around the asteroid differently depending on i the asteroid is bigger or smaller than we expected.
M: What is your average day?
S: My average day is usually spending the morning working on planning future parts of the mission or coding tools that help us with the analysis we need to do. When the optical navigation and orbit determination teams are done telling us where the spacecraft is and predicting where it is going, another maneuver design teammate and I will design the next maneuver (how long to thrust and where to point the thrusters). Then we will analyze how this will change the orbit. We then give this solution to the spacecraft team who will write up our solution in computer code that the spacecraft will understand. This code is uplinked to the spacecraft for execution the next day.
M: How did you originally get involved with OSIRIS-REx?
S: I originally started working on OSIRIS-REx as an intern at Lockheed Martin. I enjoyed the work I did so much, I decided to go to graduate school so I could learn more about how to fly a spacecraft to other planets, moons, asteroid and comets. In graduate school I received a fellowship where NASA paid for my education in exchange for me to do research for them and work at a NASA center 10 weeks of the year. Because my research was on asteroids and my previous experience on OSIRIS-REx, I collaborated with NASA Goddard Space Flight Center on asteroid research that would benefit OSIRIS-REx. I started looking into the chances of whether natural satellites (rocks or debris) that could be in orbit around Bennu. I was offered a job at NASA Goddard when I finished grad school and they offered me the job I currently have now.
M: Did you always want to work for NASA?
S: Haha, no. I actually wanted to work for Lockheed Martin because of my internships there and I wanted to work on real space missions. But through graduate school, I found I really enjoyed going to research conferences and engaging with a larger community of people who did similar work to me. NASA was able to give me the best of both worlds where I am able to do research but work on real interplanetary missions. But at the same time, I always knew I wanted to work on space missions to other planets, so whether it was NASA or a contractor at NASA, I always knew I wanted to be involved in space missions like this.
M: What has been your favorite mission milestone and what are you most looking forward to?
S: So far, my favorite mission milestone was called orbit-A. Orbit A is special because it is the smallest orbit a spacecraft has ever gone into, as close as 1.5 km (~mile) in orbit, around the smallest object a spacecraft has ever been able to orbit around. Bennu is ~0.5 km (.3 miles) in diameter. It is in a special frozen orbit along the terminator plane (where the daylight side of the asteroid meets the night side). This frozen orbit balances SRP and the gravity of the asteroid.*
*Side note from me Marielle. SRP is solar radiation pressure. This is the name we give for how the Sun’s light pushes an object (yes light can push an object). So what Samm is talking about here is a special orbit where the gravity and SRP effects are in perfect harmony so that the orbit won’t change. Okay back to Samm!
The video below shows Preliminary survey and Orbit A. Because the gravity is so low, we can change the direction of the orbit early easy will a very small amount of thrust from the spacecraft. You can’t do orbits like this around planets or moons.
I am most looking forward to Reconn, which is the part of the mission where we are getting really close to the asteroid (225 m above the surface) to take pictures of the possible sites for the TAG, the sampling portion of the mission. This is because it’s a part of the mission I am helping design and figure out, so it will be cool to see how it ends up. I know my answer should probably be TAG, when we get the sample, but it will be bittersweet for me, because after that OSIRIS-REx will be heading home and there won’t be much left for us engineers to do!
M: What is your favorite image released from the mission?
S: The composite image that shows Bennu with particles rupturing off the surface. This is super exciting when we first discovered this was happening, since it was the first time anyone has ever captured such an event for an asteroid and it is kind of related to by graduate research on natural satellites around Bennu.
I also let you all ask Samm some questions. Thanks for submitting!
Follower: How many samples will be taken back to Earth?
S: Nominally one, we are capable of doing 3 attempts to make sure we get the minimum sample amount, which is 60 g. We are capable of collecting up to 2 kg.
F: What specifically can we learn about the returned sample other than its age?
S: We also want to look at the molecular structure of the sample. OSIRIS-REx went to Bennu because it is a carbon-rich asteroid and therefore may have organic molecules. Organic molecules are what make up all living things on Earth. So Bennu is like a time capsule to show us what organic molecules may exist before there is life. This can help us better figure out how our solar system went from a bunch of floating space rocks to one space rock, Earth, having a bunch of life.
A huge thank you to Samm for taking the time to chat with us during a busy time in the mission schedule. You can reach out to her with any questions you may have on her instagram.
