The Space Review by Ari Allyn-Feuer Monday, April 17, 2017
From the beginning, the “Journey to Mars” program architecture as a whole, and the design and execution of the Space Launch System and Orion programs in particular, have been dogged by controversy stemming from a sense held by many that there was no one at the wheel. No concrete goal or plan governing the consequential long-term decisions being made as the program advanced. Now, with many of these decisions made, and major program elements committed, NASA has unveiled an exploration architecture which doesn’t square with these commitments.
The SLS was designed ostensibly with the purpose of facilitating Mars exploration, but without any public and articulated plan for what this would mean.
As a result, it accomplishes little exploration despite very large expense and initial mass in low Earth orbit (IMLEO) over a long period of time, and endangers astronaut safety unnecessarily. However, a “revisioning” of the same architecture, which plays to the strengths of the key technologies involved (SLS, Orion, and electric propulsion), can resolve these issues, and at this early stage in the process could be undertaken with little disruption.
NASA has a rocket and a plan, but are they right for each other?
The SLS was designed ostensibly with the purpose of facilitating Mars exploration, but without any public and articulated plan for what this would mean. Why was the SLS designed with no commitment to achieve a particular flight rate that would be required for an articulated program? Why were there four versions of the same launcher, some flown as few as once? Why 70, 100, and 130 tons to LEO, and not other numbers? Why did the Orion capsule have provisions for six, and not a different number? Why 21 days and not longer or shorter? Why was Orion designed to reenter from lunar orbit and not a Mars-origin interplanetary trajectory? What, in sum, was the plan, and how were the major elements of program hardware designed against the plan?
It’s not clear that these program elements were designed against a specific plan, but designed they have been, and now, an exploration plan must be designed against them. The SLS has many disadvantages: high ongoing maintenance cost, high cost per launch, low flight rate, and very large sacrifices of payload when launching into higher energy orbits. The SLS also requires very heavy sacrifices in cargo mass and volume when cargo is co-manifested with a crewed Orion spacecraft. But the SLS has advantages as well: very large payload mass to LEO as well as a very large monolithic cargo fairing. Any plan should be formulated to take maximal advantage of these strengths, and not to tread on these weaknesses.
Now, in an extremely welcome gesture, NASA has at last described an articulated plan for using the SLS in crewed Mars exploration. It recently published a manifest of 12 SLS launches with their destinations, cargoes, approximate launch dates, and mass budgets, leading from here to a crewed Mars mission in the early 2030s, at approximately the 2033 launch window. This mission would not be a Mars landing, but a Mars orbit mission, possibly with a Phobos and/or Deimos landing included.
Ultimately I will critique this plan and argue that it makes no sense and does not square with the design decisions made in the development of SLS and Orion. But first, it will serve to talk about the plan, and mention its many positive points. First, it’s specific. It is a real thing we can understand and analyze and discuss. Second, it is workable. Although it relies on all the pieces to work, there is nothing insane or undoable there. It could happen. And third, it’s not set in stone yet. None of the key pieces of cargo in the manifest, other than the SLS and Orion themselves, have yet been specified in such a way that they can’t change. If it’s decided that modifications to the architecture would improve it—and I will argue that they would—these changes can and should be adopted, and these improvements realized.
With this in mind, I will proceed to describe the current plan, and then critique it.
More:
http://www.thespacereview.com/article/3220/1
