It might seem at first blush that developing and building a ground system for the upcoming Landsat 9 mission would be less complicated than past missions, particularly since L9 is often characterized as a repeat of Landsat 8.
Far from it, say USGS EROS Landsat Development Manager Brian Sauer and USGS L9 Ground System Manager Steve Zahn.
While an independent panel at the L9 Ground System Preliminary Design Review (PDR) this March in Sioux Falls, SD, offered high praise for the science, system engineering rigor, and technical excellence that have been part of the USGS EROS ground system development efforts so far, getting to that result was anything but routine, Sauer and Zahn say.
The NASA-assigned Goddard Standing Review Team (GSRT) noted several programmatic concerns in its Requests for Action (RFA) after the March review. A staffing question has arisen after several members of the L9 team left USGS employment in recent months. Another RFA indicated a desire for answers about a funding reserve for the ground system that was below the suggested amount.
USGS is addressing those issues, Sauer said afterward, noting in particular with staffing that “we are currently working with EROS and USGS management on actions to mitigate this risk.”
With the Landsat 9 Mission Critical Design Review coming April 17-20 at Goddard Space Flight Center, it’s worth noting that similarities between the two missions have been beneficial. That is especially true of the Landsat 8 heritage system capability within the ground system elements, including the Ground Network Element (GNE), Data Processing and Archive (DPAS), and the Landsat Multi-satellite Operations Center (LMOC).
For example, with so much heritage available from L8’s GNE—which operates the network of ground stations that receive data from the spacecraft—the ground system development team came into the March review far enough ahead of the game to meet many requirements for the next step after the PDR, the Critical Design Review. The same is true with the DPAS, which ingests, archives, processes, distributes, and safeguards data from Landsat missions. The real complexity comes with the LMOC, which requires changes not only for Landsat 9, but also for the Landsat 8 and 9 missions to be able to operate out of the same mission operations center.
That said, “We’re taking advantage of the heritage from GNE, DPAS and LMOC, allowing ourselves to do all of the work we’re trying to get done in a slightly more compressed time frame … than it took us for (Landsat 8),” Zahn said.
The question then becomes, if Landsat 9’s ground system shares so many commonalities with Landsat 8, is there really a need to spend time and money on extensive reviews again? For several reasons, Sauer and Zahn say, the answer is “yes.”
Zahn said NASA historically follows strong engineering project management processes. Any large development like this needs to go through the entire life cycle, with a completely documented systems engineering management plan, he said. These reviews—“milestone gates,” he called them—are an important part of that life cycle.
“We shouldn’t just not do them because we have heritage,” Zahn said. “But we are taking advantage of the fact that we have heritage to allow us to be most effective with all the resources and with all the time we’re allowed to get everything done.”
Orbital ATK has mission readiness tests in its contract to build the L9 spacecraft that it is required to run, Sauer said. The USGS team needs to ensure its system is developed, tested, and functional so it can support and participate in those readiness tests. Among other things, Sauer said, it has to ensure that it meets NASA’s criteria for that testing—something the reviews show it has been doing.
And the reality is, L9 is not exactly a carbon copy of L8, the two men say. The Landsat 9 spacecraft is part of an Orbital ATK product line that has evolved and changed since the launch of L8 in February 2013. Components onboard the spacecraft have gone through updates. The procedures for managing them are different. Ultimately, these changes will affect the operational products that command the L9 satellite.
“When you look underneath the hood, and look at the tools and the mechanics and the components that make up the spacecraft, it’s different,” Zahn said. “There’s enough differences to still make it complex, but enough heritage on there that still makes it a lot easier for us to do a lot of things.”
There are other new wrinkles that add to the complexity of the L9 mission as well. Roughly 8 or 9 months ago, the decision was made to add Level-2 processing to the ground system. That means atmospheric corrections will be applied to the data to better support land surface change studies.
While Level-2 processing has required significant engineering for the L9 ground system, EROS isn’t a novice at this. It has been doing Level-2 products for five years, and the algorithms have matured significantly over that time, Sauer and Zahn say. It’s simply time now to put that level of processing into an operational system, Sauer said. “And doing Level-2 product development will not impact or delay our ability to deliver the Landsat 9 ground system to NASA,” Zahn added.
Again, the other significant change with the coming of L9 is the move to the LMOC, which will combine mission operations for L8 and L9 into a single building and architecture—a move that will result in appreciable operations costs in the future. A big part of the ongoing development reviews is putting together an understanding and a plan for how L8 operations will transition into the new LMOC after L9 is flying and its mission operations are under way, Sauer and Zahn say.
“The complexity is testing Landsat 8 into this when the priority right now is the Landsat 9 ground system,” Sauer said. “When you transition to a new end system, you don’t just flip a switch. You go through a lot of steps in requirements verification and validation to get there. It’s more difficult to prepare the L8 system for transition while Landsat 9 is performing mission readiness for launch, early orbit, and commissioning, then moving L8 to the LMOC shortly following mission transition to the USGS.”
In the end, the ultimate goal in all of this work is the science that will be enabled by L9, its ground system, and the continuation of the Sustainable Land Imaging program. To ensure the continuation of that quality science, neither NASA with its development of the spacecraft and launch segments, nor the USGS with its development of the ground and mission operations systems, can afford to cut corners, Zahn and Sauer say.
That’s why heritage alone isn’t enough to build a ground system, nor to ensure its success for mission readiness tests when it comes to integration with the spacecraft, to launch, and to early orbit and commissioning, Sauer said. “All these pieces need to fit together, everything from acquisitions of data all the way to downlinking data and processing data and preparing it for science operations,” he said. “It takes process and procedures and rigorous reviews. The reason we do all that is for the science.”