This article is from the 2015 NESC Technical Update.
For NASA to embark on missions to asteroids, Mars, and beyond, three extremely complex systems must work together in an exceptionally intricate harmony: the new heavy-lift rocket that will launch the astronauts beyond Earth’s orbit — the Space Launch System (SLS); the crew vehicle that will carry those astronauts — Orion Multi-Purpose Crew Vehicle (MPCV); and the infrastructure and personnel who will facilitate that launch — Ground Systems Development and Operations (GSDO).
Today, each of these systems is being designed, built, and tested individually. But NASA needs to fully understand how these three systems will work together once they are integrated, long before lift-off from a launch pad. That means visualizing how these systems will interact, anticipating any potential issues, and finding ways to resolve them.
To aid in that effort, the NESC put together a multi-Center team, who since early 2012 has been developing independent models and simulations of the Orion spacecraft’s end-to-end journey from launch to splash-down, and the critical events that must happen along the way. Jill Prince, Manager of the NESC Integration Office, has been leading this assessment and explains the work required to undertake this modeling and simulation effort and what the team has accomplished so far.
Why is independent modeling and simulation (M&S) so important when it comes to integrating complex flight systems?
The key word here is complex. With a complex flight system, sometimes you can identify issues, or failure modes, once systems are integrated that you wouldn’t necessarily catch on a subsystem level or during individual component testing. One way to identify those issues is with modeling and simulation — putting everything into one simulation to find things you wouldn’t find otherwise. There, we look for areas of risk and try to reduce or mitigate those risks where we can.
What were the major steps the NESC had to take to bring all of these independent systems together into one M&S tool?
We already had an M&S framework to get started — the Program to Optimize Simulated Trajectories (POST), which has been used for other flight projects across all mission directorates. But because this complex system incorporates elements from across the Agency and industry, we had to find simulation experts from relevant Centers and bring them on board. Modeling and simulation is my background, so I knew some great people to get us started. But who wasn’t as familiar to me were the experts doing the in-line work within Exploration Systems Development (ESD). Developing those relationships was really important before we could move forward.
What will independent M&S do for the SLS/Orion MPCV/GSDO Program? What do we ultimately hope to gain from this effort?
We’re hoping to have an independent simulation, and the experts to use it, at the ready. That way, if a technical risk comes up within the life span of SLS, Orion MPCV, and GSDO, we can corroborate, verify, or mitigate that risk with a mature, verified, and validated independent model. Also, by working independently, we can look for additional risks that may not have been identified or characterized yet. That way we can stay ahead of the game.
Are there key areas where we are focusing our M&S efforts? What have we learned?
We’ve developed a nominal, high fidelity simulation that’s allowed us to provide an independent assessment of several key events in the SLS timeline. And we’ve run the nominal simulation against the SLS simulation and verified those results.
Building on that, we’ve looked at several clearance events on the timeline. We’ve delivered a lift-off proximity analysis of SLS and its separation from the GSDO systems, an SLS booster separation analysis to determine if the boosters would come close to recontacting the core vehicle as it ascends, and we also simulated the separation of the service module panels to look for potential recontact. And we’ve looked at separation of the ICPS, the interim cryogenic propulsion stage, from the core, and separation of the launch abort system. Those are the events we’ve focused on so far, but we’re continually adding events to take a closer look at their details.
We’ve also put together an end-to-end, 3 degree-of-freedom capability that allows us to model the entire trajectory from SLS lift-off to splashdown of the Orion crew module. This lets us find potential efficiencies that we might not have found in a piece-meal look. We were able to run several trade studies, for example, optimizing the day of launch and time of day for best mass performance. As we build the capability, we learn more about our framework, what it is capable of, and the limits to its flexibility.
How important is it to see an animated visual of these simulations?
We’re using EVE, Exploration Visualization Environment, which is critical to getting everyone on the same page. The animation makes more sense to the many different people working on this program. That animation is critical to my understanding, the engineers, and the stakeholders. It’s easier to understand where something can go wrong if you can see it.
What’s the next step for the M&S team?
We’ll continue to update the simulation to be current with the program’s simulations. Soon we’ll be switching out a component of the vehicle as missions change and seeing what effects that will have, and doing some additional trade studies as we look at Exploration Mission-2 and beyond. There’s no shortage of work.
Because our analysis has been helpful for ESD, they’ve continued to ask for more, and we’re so appreciative of the easy transfer of data between the programs and the NESC. I think the relationship we’ve built is strong and we’ll continue to work on that relationship because we all know there’s a great return on investment here.
What will you take away from this assessment?
Respecting the complexity of this program while figuring out how to reduce it to a simpler form for easier understanding has been really interesting. It’s a whole new knowledge pool that I didn’t have. And there’s always a new challenge, and we’re always adding new people to the skill mix and growing the expertise across the Agency. That’s been very exciting for me.