The Mars Helicopter, visible in lower center of the image, was attached to the belly of NASA’s Perseverance rover at Kennedy Space Center on April 6, 2020. The helicopter will be deployed onto the Martian surface about two-and-a-half months after Perseverance lands. Credit: NASA/JPL-Caltech
The Mars 2020 launch window opens on Wednesday, July 30, 2020. First Mode team members have contributed to Mars expeditions dating back to Pathfinder in the 1990’s and up to the impending launch of Perseverance. As we lead up to the launch, our team reflects on the work that goes into building rovers that can traverse the surface of Mars. Check out other posts by Peter Illsley and Mallory Lefland for more insights!
SOME ASSEMBLY REQUIRED – DOCUMENTATION IN MARS ROVER DESIGN
By Spencer Anunsen, Senior Mechanical Engineer
We have all been victims of poorly written assembly instructions. Whether they’ve been for shelving, toys or electronics, putting things together can be painful. Many people aren’t aware that assembly instructions also exist for Mars rovers, and not following these instructions and procedures can risk injury and millions of dollars.
When building the Mars 2020 rover Perseverance, the Jet Propulsion Laboratory’s (JPL) unique requirements on their products led to unique requirements on their assembly procedures. In 2018, First Mode was selected to help document the critical integration of components into and onto the rover chassis. The process of creating and running assembly procedures is the final link in the integration chain that gets the rover ready for testing, for launch, and for arrival on the Martian surface.
Perseverance carries much of its design heritage from the 2011 Curiosity rover, but fundamental changes in mission and lessons learned from Curiosity mean that this rover’s design diverged in significant ways. This resulted in new assembly orders, new hardware to be installed, and new requirements for planetary protection. These planetary protection rules ensure that Earth life doesn’t contaminate the Martian environment where Perseverance will cache samples for future return to Earth.
In addition, the purpose-built spacecraft that JPL makes are nearly always one or two of a kind. A testbed copy remains on Earth and spare hardware is built, but each rover is hand-assembled and fundamentally unique. All of these elements combine to mean that JPL’s product has a set of unique characteristics that drive to some of the most strict and complete assembly procedures and documentation requirements in the world.
A Culture of Following Through
It’s human nature to find shortcuts. In design, Bill Gates famously sent the lazy person to find the easy way to do the hard job. Yet, once a course is set and documentation plans agreed, being lazy has consequences.
For example, engineers and technicians assembling the NOAA N-Prime satellite began a routine operation to rotate the satellite from vertical to horizontal when, at 13 degrees of tilt, the satellite fell to the floor causing over $100M in damage.
The Mishap Investigation Board (MIB) found that the operations team failed to ensure that the 24 bolts needed to secure the spacecraft to its turnover fixture were properly installed. The Responsible Test Engineer relied on previous paperwork indicating that the fasteners were installed and overlooked or misinterpreted an instruction to “assure” the proper configuration. The MIB found many contributing factors to the accident, but principal among them was a consistent lack of discipline in following procedures that “evolved from complacent attitudes toward routine spacecraft handling, poor communication and coordination among operations team, and poorly written or modified procedures.”
Once a project and customer agree on levels of documentation and risk, actions taken at the lowest level to evade rigor may introduce risks that can’t be quantified or accepted. Engineers who should be able to trust — but must verify what others have signed off on as true — may lose the trust that is so necessary to multidisciplinary design.
Determining What to Do
First Mode engineers have unique experience in the design and integration of Perseverance’s precursor Curiosity, allowing the team to work directly with JPL engineers for both the integrated hardware and the software for Perseverance. We drafted the steps a technician implemented, identified hazardous operations, relevant JPL and industry standards, and provided recommendations for workmanship-critical operations like epoxy and thermal interface material applications. That process illuminated fit and installation issues with enough time to make modifications and successfully get the rover ready for launch. At the end of the process, JPL engineers had integration procedures approved and ready for use.
Documentation of What Happened
With the rover driving around Mars, there is no crew on-site to troubleshoot and figure out what went wrong. Is a connector loose? Did a bolt back out in the vibration of launch because a technician forgot to torque it? Lessons learned in sixty years of spaceflight have driven JPL to strict documentation of each action on flight hardware. Take off a cover plate? Write it down. Clean out the threaded holes? Write it down. Put the plate back on, put washers on bolts and lubricate threads with threadlocker, install bolts and torque? Write down what lot of bolts and washers and threadlocker, which torque wrench you used, what you set it to and when it needs to be calibrated. Take pictures of completed work, all witnessed and signed off by Quality Assurance Engineers.
That level of documentation gives JPL the pedigree of hardware so that when a problem arises, there is a history of sequence of assembly, de-integration, and reassembly that is required when building a prototype spacecraft that has to work the first time.
Project managers, engineers, customers and stakeholders accept risk and accept cost when choosing the level of detail they require when planning and running assembly and test activities. Maintaining a culture to follow through with the plan once established and getting buy-in for any proposed changes ensures that risks and costs can be weighed and assessed, and that trust is maintained between engineers, technicians, managers and customers.
Seeing the Perseverance rover reach the launch pad as the end result of the procedures authored by the First Mode team is uniquely rewarding. The First Mode culture of solving the hardest problems through engineering rigor and innovation, built on a foundation of trust and delivering it right the first time, played a key role in our ability to support NASA’s largest, heaviest, most sophisticated vehicle ever sent to the Red Planet.
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