Tagging Asteroid Bennu

Although 2020 has seen a lot of shutdowns here on Earth, there are some exciting space missions that remain an enthusiastic “go.” In particular, this year features a milestone for one the most exciting space exploration missions yet: NASA’s OSIRIS-REx. The OSIRIS-REx spacecraft will use its TAGSAM instrument to collect a sample from the surface of the asteroid Bennu — the smallest object that any spacecraft in human history has orbited. Bennu holds answers to some of our biggest questions about our solar system and where we came from. And since Bennu is classified as a near-Earth asteroid, studying it closely can help scientists refine long-term risk assessments about whether objects like Bennu threaten life on Earth.

Never before has a space mission attempted something as precise as traveling to and from an asteroid to bring back samples. This daring plan has presented the mission teams at NASA, Lockheed Martin, and University of Arizona major challenges such as:

• The need to respond quickly to the uncertain environment around an asteroid, and the challenging orbital mechanics and attitude dynamics involved.
• The surface mapping of an unusual object in deep space.
• Rapidly responding to the evolving mission design to meet the science requirements.

Figure 1: A particle ejection event from the surface of Bennu, a previously unknown phenomena for carbonaceous asteroids discovered by the OSIRIS-REx mission.

Seems like a lot. How can this be done?

More than anything, the teams on OSIRIS-REx have to be prepared to expect the unexpected. To do that, this mission incorporates several key attributes of digital mission engineering, including:

• High-fidelity mission design. The mission teams created a design reference mission (DRM) that connects all aspects of the mission and enables each team – Ground, Mission, Design, or Spacecraft Design – to prove that OSIRIS-REx could be successful at every phase. The DRM is critical to connecting individual observations back to OSIRIS-REx’s high-level requirements, demonstrating that the teams have built a mission that can succeed.
• Monte Carlo simulations of critical mission events. These simulations determined that the OSIRIS-REx spacecraft was ready for the journey down to Bennu’s surface to collect a sample. High levels of rigor are applied to these crucial phases of the mission so that the spacecraft can succeed in the uncertain environment that Bennu creates.
• The touch-and-go (TAG) design and error analysis is all based on an automated MATLAB simulation that uses Systems Tool Kit (STK) as its targeter and propagator. The simulation determined the unique sequence of nominal orbit departure, Checkpoint, and Matchpoint maneuvers that will deliver the spacecraft to the TAG site. Then, a Monte Carlo analysis is performed to understand the expected trajectory dispersions associated with this case. During the Monte Carlo sequence, perturbations are applied to the initial state, maneuvers, and force models.
• The STK scenario that is created for the nominal trajectory will also be used for visualization on the mission website on the day of TAG (October 20, 2020).
• The flexibility to work seamlessly within the organization and with its partners. Each team had to share its outputs to be compatible and easily integrated with third-party software tools.

Figure 2: Multiple views of the OSIRIS-REx's planned descent to asteroid Bennu’s surface on October 20, 2020, rendered in STK.

Learn more about how AGI and our partner, Phoenix Integration, supported the OSIRIS-REx teams in solving some of these challenges during our virtual Digital Engineering Forum on December 1, 2020. We are honored to have been included in OSIRIS-REx and we can’t wait for the exciting moment on October 20 when the spacecraft will “TAG” Bennu and inspire the world.