A number of NASA scientists and directors met with Congress this week to discuss the future of NASA’s planetary science division and the various shortcomings and issues that must be resolved in order for the organization to make meaningful progress with long-term exploratory goals. Key to many of these goals is NASA’s long-term Space Shuttle replacement, the Space Launch System (or the Senate Launch System, if you believe the critics.)

The SLS is designed to debut as in a Block 1 configuration that can lift up to 70 metric tons to low-Earth orbit (LEO). This early configuration wouldn’t match the Saturn V, but it would make the SLS the heaviest lift system slated for near-term deployment (Elon Musk’s Falcon Heavy will be able to lift an estimated 53 metric tons to LEO). The Block 1 variant would use recycled RS-25D engines recycled from the Space Shuttle. Blocks 1 and 1b will also use five-segment rocket boosters based on the four-segment boosters from the original Space Shuttle — these designs were adapted to save costs compared to building new engines from scratch.

Paging through the prepared remarks at the Tuesday hearing, it’s obvious that NASA is bullish about its plans for further planetary science, with talk of a mission to Europa, a second New Horizons mission to Pluto, and further unmanned investigation of Mars, leading to a manned mission at some point in the future. Similarly, evaluated on paper, the SLS offers massive performance. If the Block 2 design hits its performance target, it’ll be capable of boosting up to roughly 45 megatons (MT) to Mars. The Falcon Heavy, in contrast, is expected to top out at around 13.2MT. On the surface, this is a straight win for SLS, at least for certain mission profiles. In reality, things are a great deal more complicated. The diagram to the right compares the SLS against the Saturn V and Space Shuttle, but there’s more to the story than how the NASA rocket compares to its predecessors.

There are two basic problems with the SLS. First, there’s the question of what mission NASA should pursue with its new super-heavy rocket. To date, Congress has balked at actually approving any significant missions for the rocket. Both the GOP and the Democratic party love NASA’s work when it comes to doling out high-paying and prestigious jobs in the aerospace industry, but the GOP has balked at approving missions  that might actually result in the government looking good.

To be fair to the Republicans, however, the White House has also slashed NASA’s planetary science budget multiple years in a row — despite the fact that NASA accounts for 0.45% of the federal budget to begin with. Cost concerns are also why NASA doesn’t plan to deploy the Block 2 configuration of the SLS until 2030 at the earliest, 10-11 years after the first flight is supposed to take place.

Limited funding has plagued the SLS since inception and limited some of NASA’s choices, such as reusing old Shuttle technology to cut expenses. A government audit last year found that NASA needed $400 million in funding to meet its timetable for SLS deployment. Meanwhile, other voices have pointed out that the SLS is so expensive, with an estimated cost of $12 billion, that NASA can’t afford to spend much money developing the payloads that the rocket would carry.

It may be necessary to fund payload development after rocket development, which means our expensive shiny Saturn V successor could spend months or years on the ground, not doing much of anything. NASA notoriously overestimated how often the Space Shuttle would launch, but given the cost and complexity of the SLS, it seems unlikely that NASA could afford to launch more than once per year. Some estimates have concluded that the final situation could be much worse, with no more than one launch every four years.

Do we want to explore space or not?

There’s a fundamental question that the United States needs to answer about its own goals for the space program. Whether or not we turn to companies like SpaceX to provide low-cost commercial launches, the SLS is designed to do a job that even the upcoming Falcon Heavy can’t do — namely, to launch payloads, including crewed capsules, farther and faster than any previous rocket. SpaceX is currently working on its own next-generation Raptor engine, but it may not be ready for commercial use before at least Block I of the SLS — which means that at least initially, the SLS would have an advantage over the Falcon Heavy in terms of maximum payload.

Artist’s conception of the Falcon Heavy

I’m not going to take a position on whether SpaceX or NASA is the better organization to fund for space travel. I will say I think there’s a great deal of room for collaboration between the two organizations, particularly given NASA’s decades of experience in training astronauts and its unrivaled expertise in planetary exploration. Mars, Europa, Titan, Pluto — every location we visit in the solar system has surprised us in some fashion and, in the process, taught us more about what to expect in other planetary systems.

All too often, funding NASA is positioned as a false comparison in which one incredibly expensive thing (say, the military budget or Medicare) is positioned against NASA’s budget in an either/or comparison. In reality, you could triple or quadruple NASA’s budget and still lose it in the background noise from other federal programs. We can probe the oceans of Europa, the methane seas of Titan, or the cryovolcanos of Enceladus — but only if we agree on a vision that will take us there.

The issue at hand is bigger than the SLS or SpaceX’s Raptor. It’s a question of what we want our priorities to be. Without a long-term commitment to space exploration that survives new administrations and shifts between Democrats and Republicans in Congress, we’re always going to be stuck trying to justify expensive programs that take decades to complete. Throwing money at a problem doesn’t fix everything, but when it comes to rocket design and engine testing, it can enable an awful lot of progress in a shorter period of time.