MARS NUCLEAR SORTIE? It's hard to tell from this article what the actual specifics of the mission concept are, but it looks to me like the Bush Administration may be floating a trial balloon. In this case, it covers two different issues: nuclear power in space, and a manned mission to Mars.

Space nuclear power will be required for any manned undertaking beyond Earth orbit (including a return to the Moon), so the development of space-capable reactors for power generation is not just a good idea it is a sine qua non. Of course, that assumes that what is planned is a nuclear-electric drive rather than nuclear thermal (NERVA, Timberwind) or nuclear pulse (Orion) system.

Nuclear-electric will provide by far the most long-term benefit, in that it will result in a multi-purpose nuclear power system that can provide both propulsion and spacecraft power. Plus, being a low-thrust/very-high-impulse (~30 times the ISP of an SSME) system, electric propulsion would keep the spacecraft under constant acceleration, minimizing the effects of microgravity on the crew and making the design of the spacecraft internal systems much simpler. Then there is the technical readiness level of the concept -- the electric propulsion portion of nuclear-electric has already been tested at small scales on Deep Space 1, so the development required should be straightforward. Compare this with nuclear thermal or nuclear pulse, which have only been ground tested and only as general concepts, not flight-like hardware.

(Well, so far as we know, anyway.)

Nuclear thermal, when I last read up on the concept, is likely to be extremely heavy. These rockets would have high-thrust/high-impulse (2-5 times the ISP of an SSME), which require the ejection of large amounts of reaction mass in a very short interval. To accomplish this, the reactor (which would take the place of the thrust chamber on a liquid-fueled rocket) would have to run very hot. Which means it is putting out a great deal of radiation in the process, and that a heavy shield of some sort is required between the engine and the crew. In addition, there is the weight penalty of the large, high-pressure thrust chamber in which the core is contained, and the feedlines and valves and other fluid management hardware required to deliver the working fluid to the core at the required rate. Plus there are the impacts on the rest of the spacecraft, namely the need to carry a separate power-generation system and the need to design everything for prolonged periods of microgravity. The Timberwind particle-bed reactor concept might offer some improvements over the old NERVA approach, but it's hard to see NTR overcoming these inherent disadvantages to the spacecraft system taken as a whole.

As for nuclear pulse: while it may be feasible in the long term, I really don't see NASA overcoming the technical and PR/political hurdles on that concept by 2010. The anti-nuke crowd is going to have a hard time with nuclear reactors as it is, why actually hand them an easy propaganda target? The public can be swayed by reason on the issue of nuclear power reactors in space, but the idea of "nuclear bombs in orbit" is easy to propagandize and is bound to have some emotional resonance that will lead to public discomfort if not opposition to such a project.

So, my hope for this (such as I am actually investing any hope in something coming from it) is that Prometheus will be a straightforward nuclear-electric design. That is, a new space nuclear power system large enough to power a large, no-frills electric drive.

Unfortunately, given NASA's penchant for "complexifying" straightforward projects until they become bloated monsters that do little more than gobble up budget and produce a few token bits of useless hardware, I am expecting something a bit more baroque. I'm guessing that, even if the more sensible nuclear-electric concept is chosen, the Agency will see the project as an opportunity to throw a bone to every team at every NASA center, and we will end up with a push to build VASIMR or some other overly-ambitious advanced propulsion system. Rather than taking small steps and getting results, there will be a push to do everything all at once that will end up doing nothing in the end.

So, what's the solution? If the project is to succeed, there needs to be a very clear articulation of what the project is, what it is to accomplish, and who is to make the decisions.

• Defining up-front what the project is, in terms of the technologies to be developed new vs. used off-the-shelf, will give the project manager some leverage in fending off attempts to shoehorn-in various pet concepts that benefit the project itself less than they benefit a certain center or Congressional district.
  
• Spelling out what the project is to accomplish is also a means of imposing discipline on the Agency, the Congress, and the contractors. By establishing a clear and limited scope for the project -- developing a new class of space nuclear power and propulsion systems, and demonstrating them by sending humans to (or at least around) Mars -- NASA can limit the amount of "mission creep" that inevitably complicates its projects and wrecks cost and schedule plans: "No, we don't need a Venus fly-by...No, we don't need to land on Phobos first...No, we don't need to build a space dock at L-1, or fuel depots on the lunar surface..." Focus the project on a few specific goals. But, while this sort of focus limits the project scope, it need not result in another "mule" or "flags-and-footprints" program -- it all depends on what the chosen goals are.
  
• Rather than pitting one NASA center against another for intramural political reasons, or splitting the work among contractors and districts for the primary purpose of buying Congressional support, NASA should take this project as an opportunity to change how it manages its efforts. It should provide clear guidance on who makes the decisions for the progam, what criteria will be used for allocating the work among centers and contractors, and who has the final say in project-related decisions. And by "who", I really mean one, specific person: someone high enough up to make decisions that can't be overruled on a whim by any of several dozen Under-Administrators and Deputy-Assistants, and someone who is close enough to the technology to make intelligent decisions and involved enough with the project team to track day-to-day progress. Perhaps a special ad-hoc project manager, who bypasses the bureaucracy to report directly to the Administrator.
  

Time will tell, I suppose. I am a little suspicious of the claim that the President will announce the project in the State of the Union speech, though...it's entirely likely that he will be dealing with more immediate subjects then, such as a declaration of hostilities agains Iraq.

Posted by T.L. James on January 18, 2003 12:19 PM