I just realized that I started this a few weeks ago and never finished it. Not sure I have the gumption to do so now, but I might as well publish what I’ve done.

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These SLS apologia are so tiresome. I’ve been too busy to respond to them, but maybe I will fisk this one. My comments in italics:

The release of Space Policy Directive 1 in December 2017 redirected the U.S. civil space program to pursue a sustainable program of exploration with a near-term emphasis of returning humans to the moon. Since then, the related details indicate an aggressive schedule to initiate lunar activities, and a desire for much of the architecture between here and the moon to be reusable. Reusability has been partially implemented before, but recent SpaceX and Blue Origin booster landings have reignited hopes that reusability can change the economics of space activity simply by switching from expendable to reusable launch vehicles.

[Caption: The intertank that will be flown on Exploration Mission-1 as part of NASA’s Space Launch System heavy-lift rocket has completed its avionics functional testing at the Michoud Assembly Center in New Orleans. The avionics, shown here inside the intertank structure, guide the vehicle and direct its power during flight.]

Note that the picture and caption have nothing to do with the point about reusability or expendability. They are simply tech porn for people who get off on giant rockets.

Aggressive schedules and reusability are well understood and directly relate to space exploration. However, sustainability has subtle but important implications in the space exploration domain. Sustainability is the ability to maintain competency levels and the delicate balance for all supporting elements of a program over a long-term program in an affordable manner.

This is certainly not how I would define “sustainability.” I would define it as the ability of a program to be sustained, financially and (in the case of a government program) politically. And we also have different definitions of “affordable.” If you’re of the Apollo mindset, “affordable” means at a low-enough cost, combined with the political benefits of distributing taxpayer funds to the politically important zip codes, that budgets can be maintained year on year, from one Congress and administration to the next. I have a different definition. I view affordability as the ability to financially enable large-scale space activity, both government and private. But large-scale space activity is the opposite of the Apollo mindset, to which too many remain in thrall.

For space exploration, this balance is hard to achieve as these programs are expensive and funding-constrained. Especially in large-scale programs such as those involved in human space exploration, budget constraints can drive short-term decisions that result in atrophy of knowledge and expertise, needed equipment, and processes that are part of the program life cycle, leading to limited or no retained capacity. Such decisions are sometimes unavoidable, but will ultimately undermine programs long-term.

As I’ve noted over the years, there are hidden assumptions in this paragraph. The first is that the purpose of human civil spaceflight is “exploration.” This is a fiction that goes back to Apollo, and it creates a false mindset that allows the kinds of programmatic insanity represented by programs such as SLS/Orion. But in fact, the purpose of human spaceflight in the sixties was to defeat the Soviet Union in a peaceful battle in the Cold War, since then, the purpose has been to maintain the jobs base created by Apollo and supported by those in Congress who (with rare exceptions) insinuate themselves onto the committees in Congress that control space spending in order to steer taxpayer funding to their states and districts. Actual accomplishments in space, let alone in “exploring” it, have always played third or fourth fiddle. SLS/Orion, which have spent billions for many years, with little to show for it, are ideal to meet this need, with no need to actually accomplish anything.

Absent more specifics about what kinds of “short-term decisions” he is describing, I can’t really comment on that. I would note that in fact the entire op-ed is short on specifics, which of course makes it harder to throw rocks at it.

Despite the challenges associated with sustainability, great strides have been made in human spaceflight since the first mission of NASA’s Mercury program in 1961. This November, the U.S. space program will soon achieve a milestone of 18 years of continuous human presence in space on the International Space Station (ISS). That accomplishment has been built from the lessons learned through NASA’s Gemini, Apollo, space shuttle and ISS programs, but there is still need for improvement. As the U.S. space program now looks to the challenges of long-duration exploration beyond low Earth orbit, sustainability concerns need to drive the early decision making.

Ignoring the continual repetition of the E word, who can argue with that? It’s motherhood. But none of his actual arguments, to the limited degree they exist, follow from it.

As with any space exploration endeavor, returning astronauts to the moon and onto Mars all starts with the rocket. Human space exploration to the moon and beyond requires a super heavy-lift rocket.

As usual, an assertion with no actual basis or argument, and in the face of NASA’s own internal studies that put the lie to it. And not just heavy lift, but SUPER heavy lift. Maybe even SUPER DUPER heavy lift. You know, in Bill “Ballast” Nelson’s technical term, a “big monster rocket.”

The Saturn 5 rocket, designed by Wernher von Braun and the brightest minds working at NASA and industry, remains to this day the world’s most powerful rocket ever launched.

Note again the argument from authority and hero worship, meant to impress people who don’t understand the history, programmatics, or technical issues. Note also the repetition of the word “powerful,” the mantra of SLS supporters, as though “power” per se is a useful metric of the utility of a rocket, and all others (e.g., cost, or reliability, or frequency of flight) can be ignored.

Today, NASA, Russia, China, and even new entrants SpaceX and Blue Origin, have reached the same conclusion as von Braun regarding the need for a super heavy-lift rocket. NASA is now nearing completion of such a vehicle, the Space Launch System (SLS). The SLS is even more capable than the Apollo-era Saturn 5 and the space shuttle, which was used to build the International Space Station. The SLS is the only rocket that can provide the needed lift and support the need dates for the deep space exploration missions, but is it sustainable?

Again, an assertion without an argument. And a misleading statement, because it implies that SpaceX and Blue Origin are building a heavy-lift vehicle because it is needed for “deep-space exploration missions.” But SpaceX and Blue Origin are not in fact interested in “deep-space exploration.” They are interested in developing and settling space. NASA thinks, or at least claims, it needs a big vehicle because it is afraid of orbital assembly. SpaceX and Blue Origin want big vehicles because they want to move a metric buttload of stuff into space, with thousands and millions of people living there.

I would also note that the continual invocation of von Braun’s name probably has him rolling in his grave. He was an advocate for fleets of reusable vehicles and space assembly. The only reason he took the route of the “super heavy-lift rocket” (gee, it’s almost as though the catch phrases are poll tested among the bubbas) is because he had the charge of getting a man to the moon and back in a decade, and that was the only way to do that. And note, that because he chose that route of necessity, it turned out to be unsustainable once the race had been won and there was no longer a need for such a vehicle.

Like the Apollo Saturn 5 launch vehicle, the SLS is expendable, and some may argue that a reusable launch vehicle would offer a more sustainable solution. While reusability appears to offer advantages, reusability also includes performance penalties when compared to an expendable rocket. A reusable rocket requires additional systems including thermal protection, flight stabilization, and the considerable fuel reserves needed to maneuver and land. Mission payload weight must then be sacrificed to offset the additional vehicle weight, and these penalties only increase as a rocket travels farther from Earth. To match SLS lift performance, a reusable rocket would need to be even larger and in the end become more complex and costly. The other option is to break the in-space exploration payloads into smaller pieces, but doing so adds further complexity, weight, cost to the payloads and increases risk to the program. Statistically, more launches and higher complexity increases the overall mission failure risk.

Note the lack of quantification of the argument. Yes, all those tradeoffs are true, but despite them, SpaceX has already flown a partially-reusable vehicle with payload equivalent to SLS block 1, whose first flight has now slipped beyond 2020. And it flies at a small fraction of the theoretical marginal cost of an SLS slight, let alone the amortized cost per flight, which will never be less than a couple billion (much more if one amortizes the insane development costs).

Then there is the issue of flight rate.

Yes, there is that issue.

Before starting SLS development, NASA anticipated the SLS flight rate would be as low as one flight per year. Under these conditions, sustainability necessitates streamlined production for affordability, a steady level of activity to maintain critical skills over the life cycle of the rocket for reliability, a stable industrial base, and the ability to incorporate product improvements as needed. NASA selected an expendable rocket architecture as the best design to meet their mission objectives and overall sustainability needs.

Like the original expectations for space shuttle, there are proposals for large reusable launch vehicles with a life expectancy of up to 100 flights. However, a reusable vehicle used at a low flight rate is counterproductive to sustainability. The combination of reusability and low flight rates creates production gaps between builds, discontinuities in workforce and loss of critical skills. The production gaps also pose additional challenges to attracting and maintaining a healthy supply chain. During the space shuttle program, suppliers were unable to provide parts later in the program due to loss of tooling, technology or processes that became obsolete due to the long gaps since their original production. This occurred because these processes and tooling were not needed each time the vehicle was reflown. These programmatic and industrial base factors are often overlooked, but essential for sustainability. A low but constant production rate of building one rocket a year, such as the SLS, serves to maintain key critical skills, keeps the industrial base supply chain active, and offers opportunities to fix problems, on-ramp new technologies or block improvements.

There are also additional costs and risks associated with reusability which should be taken into consideration. Successful reusability is built upon a detailed understanding of system degradation over the useful life. This requires additional analysis and design efforts, use of more expensive materials to endure the rigors of use, and an on-going test program to demonstrate and validate the design and manufacturing processes. If a significant change is made to an element or system of the rocket, then the test-experience clock for that is reset to zero. There are the additional recovery and refurbishment infrastructure and personnel costs to factor in as well. The bottom line is launch vehicle reusability comes at a cost and is not always the best solution for every scenario. Alternatively, it is important to look at opportunities for in-space hardware reuse, such as satellites, propulsion systems and habitats that operate in more benign environments than launch vehicles, and therefore do not have the extensive reuse overhead.

For human space exploration to be affordable, sustainable and therefore to succeed, every possible advantage to reduce cost must be studied and understood. New ideas for efficiencies must be solicited, explored and demonstrated to reach realistic and reliable solutions. Deep space exploration is a highly complex endeavor involving complex trade-offs in cost and risk.

Von Braun and the team that led the successful Apollo missions had it right. Although a lot has changed since the 1960s, the laws of physics and the architecture to conduct successful crewed missions to the moon remains unchanged. NASA is on the right track to support President Trump’s goal of returning astronauts to the moon in the early 2020s and preparing for even more ambitious missions to Mars. The Space Launch System is the right rocket for this mission.