Last month I finally got up close and personal with the OSIRIS-REx spacecraft. I am now making regular visits to the Lockheed Martin Space Systems facility in Littleton, Colorado, where OSIRIS-REx is under construction. However, during most of these visits, I only get to see the spacecraft from the viewing gallery on the third floor, where I can look down on the vehicle and see the technicians at work. This last visit was different – I actually suited up in full clean room gear and inspected the spacecraft at close range. I can’t fully describe the thrill of seeing over a decade of hard work by hundreds of people come to life in front of my eyes.
I was joined on the tour by Kevin Walsh, Lead Regolith Scientist for OSIRIS-REx. Kevin and I were at Lockheed Martin for a “Technical Interchange Meeting” or TIM. This TIM focused on the details of our plans to understand the response of the asteroid surface to our Touch-and-Go sampling event. A key topic of discussion at this meeting is the compression of the sampling arm, part of the TAGSAM device, after contact is made with Bennu. The design of TAGSAM includes a constant-force spring, which is supposed to hold the TAGSAM head against the asteroid surface with a constant force as the spacecraft decelerates. As the name implies, the constant-force spring maintains a uniform force as it compresses over the entire stroke length of 30 centimeters.
However, in addition to the spring, TAGSAM contains a harness – a bundle of cables that deliver power to the wrist motor and transmit data from the sensors on the arm. This harness adds additional force during TAGSAM compression. Furthermore, the harness acts more like a kx-type spring, so named because the force increases as the harness wires get compressed. This behavior turns out to be good news for our efforts to understand the nature of the regolith on Bennu. By performing detailed measurements of the force profile on the ground, we will be able to use TAGSAM as a crude penetrometer to probe the cohesive forces that hold the regolith grains together. Not only will TAGSAM collect a large bulk sample of the regolith – it will also provide valuable scientific data about the geomechanical properties of regolith in the microgravity environment. The very act of collecting a sample becomes a science experiment in and of itself!
One of the more interesting test setups for TAGSAM is the BAB or the Big Aerial Balloon. This equipment includes a giant helium-filled balloon attached to the TAGSAM arm. The BAB is used to offload the gravitational acceleration at the surface of the Earth. This configuration allows the team to test the full range of motion for TAGSAM, without concern about deflection of the arm due to gravity. The ingenuity of the Lockheed Martin team in solving these kinds of problems never fails to amaze me.
I am particularly grateful to Ben Bryan from Lockheed Martin for leading this first-class tour. Ben manages the activities on the ATLO floor for OSIRIS-REx. Not only does he make sure that all the work is performed according to the tight requirements for the spacecraft, but he genuinely cares about the scientific success of the mission. It is because of his efforts, and that of the other dedicated team members across the project, that OSIRIS-REx will safely bring back those valuable samples from Bennu.