He joined the NASA Jet Propulsion Laboratory in 1999 and rose through the ranks to become the leader of the team that designed the Mars Rover robot that landed on the red planet. Over the years, his responsibilities have involved flight projects, flight projects review boards, mission formulation, technology tasks, technical writing and proposals. He also served as a reviewer for NASA Science Mission Directorate technology proposals and NASA Office of Education proposals. Other engagements at NASA are 2003 – Mars Exploration Rover, 2007 – Phoenix Mars Lander and Mars Science Laboratory which is scheduled for launch in 2011 and will be NASA's third generation of rover to explore Mars. Among his roles at the In Sight Mars Mission were Product Delivery Manager and Chief for the Instrument Deployment System, a technical group lead in the Robotic Manipulation & Sampling group at NASA Jet Propulsion Laboratory, California Institute of Technology, where he has been since 1999. His technical research interests include on planetary rovers and its operations, system of systems, manipulation, multiple mobile robots, mechatronics, reconfigurable robots, audjustable autonomy and man-machine interaction. Closely linked to these are various areas in robotics systems and engineering: Space Robotics Systems, Flight Systems Integration & Test, Planetary Rover Operations, System of Systems Design, Distributed Mobile Robotics, System Architectures, Dynamic Modeling, Control Systems design for Aerospace and Mechatronics Systems and Contract Technical Management. He has more than 95 publications to his credit. He was a Research Scholar at the Institute for Complex Engineered Systems at the Carnegie Mellon University in Pittsburgh where he was instrumental in the design and implementation of a system of All Terrain Vehicles for distributed tactical surveillance for the Defense Advanced Research Projects Agency. In an interview with the BBC, Ashitey Trebi-Ollennu noted that he had started a project in his home country of Ghana to make Science Technology Engineering and Mathematics more likable and fun. He worked on the Phoenix that found water on Mars. The InSight mission successfully landed on the red planet on Monday 26 November 2018. As per the New York Times, the spacecraft was expected to study the Mars' underworld, listening for marsquakes and seeking clues about the dusty world's formation. In 2011 Ashitey founded the Ghana Robotics Academy Foundation, a nonprofit volunteer organization dedicated to motivating and inspiring young Ghanaians in science, technology and engineering. His foundation won the Google RISE Award 2013. Commenting on his job, he noted, "The brilliant thing about my job is that, it is not a circumscribed routine, there are different challenges everyday. Believe me, it is a lot of fun. NASA is also a great organization that cares about its people and their personal development, need I say more?”
Sir Monty Finniston Achievement Medal "For outstanding technical contribution to any field of engineering from the Institution of Engineering and Technology, Europe's largest professional society for engineers;" "For outstanding technical contribution to the NASA's Mars Exploration Rovers mission”
Outstanding Engineer Award, from IEEE Region 6 from MER "For outstanding leadership in the analysis and resolution of the IDD unstow anomaly on Opportunity Rover"
Ollennu's team awards include:
NASA Group Achievement Award-Mars Exploration Rover Avionics Team, 25 May 25, 2004
NASA Group Achievement Award-Mars Exploration Rover Flight System, Management and Engineering Team, 25 May 2004
NASA Group Achievement Award-Mars Exploration Rover Project Operations Team, 25 May 2004