26 to meet the power constraints for this mission. Power had been originally determined using values from an  FPGA- based digital  contr oller used on another project. A second reason is that a grassroots cost estimate  resulted in a significantly  lower cost for the an alog design over the FPGA design. Once the project was  awarded, the product design lead, the primary author of this paper, had tremendous concern about lack of  flexibility and resulting excessive risk of  the baselined MCE approach. While there were perceiv ed benefits  in terms of power and cost for the baseline choice, subsequent analysis found that power could be met with  an FPGA -based  design, and further review  found that manpower beyond what was baselined would be  required to develop  the seemingly  simple discrete electronics. The project ultimately agreed  to change the  plan and develop an FPGA -based MCE .  

As a lesson learned, it became apparent near the end of th is project how important this decision was.  If the  MCE  was not FPGA -based, it would have lacked the flexibility to correct position sensor issues as well as  assist with system identification when in TVAC . Without the FPGA -based MCE , some crucial specifications   would not have been met  thus negatively  impact ing the science.  

As a rule, i t is of critical importance that  the design architecture be correct from the beginning. With today’s  schedule and budget constraints, it is very difficult to change course when problems arise. Thus, diligence   must be exercised to get it right the first time because there is typically  not time for an additional iteration.  Sound arguments and p erseverance are necessary ingredient s to gain project approval if  it becomes  necessary to change the path forward to that with th e lowest practical risk.  

Conclusion  

The L’Ralph SMS team had the benefit of leveraging the previous ATLAS BSM development. The SMS at  first was thought to be a straightforward task since compared to the BSM,  it appeared to be less challenging.  The SMS would be  a single axis system rather than a dual axis system,  utilize off-the-shelf flex pivots  rather  than require development of a custom flexure, would have a similar DPSS and a similar MCE, and was  specified to have about seven  times coarser resolution than the BSM. Yet, the requirements were quite  different resulting in a n SMM that looks very different from the BSM, and a new set of development  challenges came about. The team was highly motivated, enjoyed the challenges, and gained a new set of  lessons learned that we are sharing with the aerospace mechanisms community  via this paper. T he team  can be proud of the SMM final product,  which support s an incredible mission that will advance our  knowledge  of planet formation.  Figure 15 and Figure 16  are views  of the flight  SMM.   

Acknowledgements  

Michael G. Edick ***, Theodore J. Hadjimichael*, William M. Hansell **, Douglas B. Leviton ****, David W.  McClaeb* , Joseph C. McMann*****, Armando Morell**, Matthew  A. Owens ***, Gary L. Sheridan** , and  Patrick L. Thompson* .   ____________________________   * NASA Goddard Space Flight Center, Greenbelt, MD                ** ATA Aerospace , LLC , Greenbelt, MD   *** Florez Engineering, LLC , Laurel, MD   **** Leviton Metrology Solutions, Inc., Boulder, CO   ***** Northrop Grumman Corp. , Greenbelt, MD