I spent five days the week of July 27 in the audience at meetings of the NASA Advisory Council (NAC). I forgot how much I love committee meetings. They were public meetings in Pasadena, California, so it was easy for me to attend, and with good Internet in the rooms I could multitask during those occasional times when my mind wandered or got bored. However, let me not be too facetious: The discussions were good and informative.

NASA faces many big issues, some about where we are and some about where we are going. The big one that I was especially interested in came across as a theme in many discussions: the tension between those who want a plan and those who want a flexible path for NASA’s human spaceflight program.

I state that as an either-or more starkly than it really is. One can have a plan that is flexible, and one can be on a flexible path that is well-planned. But there is a qualitative difference, and those urging a plan want prescriptive specifications: launch dates, payload specifications, vehicle assumptions, technology milestones, trajectories, crew size, precursor missions and more. With such a plan they contend progress can be measured and cost estimated. What they don’t say is that it gives them (and everyone else) a target they can shoot at and forces either planning an unsustainable program leading to slipped milestones and chaotic changing goal posts (e.g. Constellation) or planning a conservative one that disappoints everyone by its lack of excitement and ambition (more orbiting of Earth with no destination).

NASA officials, to their credit, and despite catcalls from the outside, are not rushing into a plan — instead they are developing what they call an “evolvable Mars campaign.” I think of it as a concatenated organization of programs working toward the goal of humans on Mars. The programs are conducted, as recommended in several leadership studies of the past decade and most notably by the Augustine committee on human spaceflight, on a “go-as-you-pay” approach. As Congress attacks the NASA technology program or holds up the transition to commercial crew, NASA has to go slower because that’s how they pay. As Congress adds money for the Space Launch System, they can go faster — to the extent that concatenated programs can function out of synchronization.

The evolvable Mars campaign has already identified a huge issue, which the NAC agreed needs a lot more attention and analysis: the transition from the low Earth orbit human program to that in cislunar space that prepares astronauts and their support cargo for the journey to Mars.

This is most starkly brought forward by planning for the end of the International Space Station (or at least NASA’s role in it) and freeing up funds for the new cislunar developments in what NASA now calls the “proving ground” leading to Earth independence for future astronauts on interplanetary flight.

Previous human spaceflight program transitions (Apollo to shuttle, shuttle to Constellation) have been characterized by long flight gaps — gaps filled by Russia, which no one in the United States really liked. NASA is trying to plan the next transition to cislunar space without such a gap and without such a program disruption. That is going to be difficult: As several NAC members noted, “The U.S. cannot afford two human space programs.” NASA has to try to make it one program. Agency officials said they are starting to do that as they redirect space station utilization for the goal of long-duration human spaceflight to Mars.

The flexible path accommodating such steps gives me the hope that despite the critics’ hand-wringing over the lack of a clear plan, we in the United States are for the first time making progress toward the human Mars goal.

NASA’s evolvable Mars campaign is not a plan, but it is already orchestrating different parts of the agency toward the Mars goal in a way that no previous program (or plan) did.

The Asteroid Redirect Mission (ARM) was formulated before the evolvable Mars campaign, but it creates a key initial steppingstone for humans beyond the moon. The Asteroid Redirect Crew Mission, proposed for 2025 at just about the time of the nominal end of the ISS program, fits well in the transition from ISS to cislunar, and serves as a potential gap-filler for human spaceflight during that time. NASA would extend the range of astronaut flights in the same time period as human flight development is finishing up on the ISS.

The SLS/Orion/ARM (robotic retrieval and then a crewed mission or missions) is a sustainable program even while ISS is operating. Afterward we can take the further “evolvable” steps in and then beyond cislunar space into the solar system.

The Jet Propulsion Laboratory study of evolving that flight capability to reach one of Mars’ moons before taking on the expensive development of the Mars landing suggests a sustainable program can exist within current budget constraints.

One can wish for greater specificity in a plan for reaching Mars, but as deep as I am into this subject I cannot say whether the longer-duration (for example, six to 12 months) missions in the proving ground should be in the distant retrograde lunar orbit, on a six- or 12-month Earth resonant orbit, to a near-Earth asteroid on a native orbit, or to a sun-Earth Lagrangian point. A premature plan specifying which is a bad idea; a better one is the flexible path built as we go, with evolvable technologies and sustainable costs.

The flexible path accommodating such steps gives me the hope that despite the critics’ hand-wringing over the lack of a clear plan, we in the United States are for the first time making progress toward the human Mars goal. It’s true that reaching that goal is, like it always has been, 25-30 years in the future. But we are building the rocket, developing the crew capsule, planning first missions for humans beyond the moon, creating the support infrastructure with solar electric propulsion for the cargo and the first in-situ propellant experiment planned for flight to Mars, and perhaps most significantly have all parts of NASA — human exploration, science, robotic missions, space technology and (not unimportantly) communications (public engagement) — playing together. That could be enabling — if only the Congress is open to the ideas.

NAC is apparently taking the action item to look carefully at the evolvable Mars campaign with an eye to helping NASA ease the transition away from humans in low Earth orbit. It’s not going to be easy, but watching NAC members try did boost my morale while another part of me was sorely tested from sitting in five days of committee meetings.

Louis Friedman is executive director emeritus of the Planetary Society. His book “Human Spaceflight: From Mars to the Stars” is scheduled for publication this fall. He can be reached at louisdfriedman.com.