Saturday, February 19, 2011

Nautilus-X update

I sent an email to Mark L. Holderman of NASA-JSC, asking him to respond to my last post about the Nautilus-X. Here is his response:
Hello Ed,
Thank-you for taking the time to look at Nautilus and to post the presentation on your site. [I have attached a slightly updated version; there has been some file corruption from multiple downloads]

I apologize for not responding sooner, but for some I/T reason a great many emails have been directed to the Server SPAM file; I now check it regularly.

A great deal of "detail" information is not contained in the presentation. This was by design; it was crafted to be an oral presentation with much of the technical content addressed by the speaker, who directly answers audience questions and can therefore better engage the particular interest(s) of various groups. What you have viewed is the Concept "Sales" package - it attempts to paint a picture that folks might want to find out more about. So questions, observations, critiques, no matter on what subject - and as long as they are more-or-less civil in tone, are all welcomed. If a dialog results, well then --- yahoo!

Your questions about thermal considerations are spot on. While in LEO [construction phase],the classic basting roll maneuver would likely be employed. But transit to L1, and at L1 require a different solution. Most folks don't notice the lack of thermal rejection capability in the Concept images; they are usually taken aback at the general (size) and odd structural manifestation that good engineering details are not usually assessed. Thermal load/rejection and management at L1 will be different than at LEO, will be different than during a CIS-Lunar route [repeated], and definitely different than for an inner Solar System junket[trek...I wanted to avoid that term]. So yes, Thermal management is a major technical consideration that has a couple of nifty solutions that are being pursued. One of the inflatables will have a decidedly green element associated with it....[think Silent Running w/ Bruce Dern]. It is a partial thermal shunt, not the complete solution. Radiators will still be required, along with some new Variable Conducting Heat-Pipes that the old Hughes Aircraft Corporation had utilized.

The "Winnebago" section is new-think applied to the design success of the Apollo LEM. The Lunar Excursion Module is THE most successful spacecraft ever built. Purely and completely a space-craft that journeys in the Space environment. I purposefully exclude ISS, as it is essentially a static platform. Many of its design factors were constrained by the method of its construction --- Orbiter delivery with on-orbit assembly. The OV payload bay is incredible, but it does have both constraints and strong limitations [I am from the SSP]. With that understood, Nautilus design knowingly departed from ortho/iso-grid cylinder construction to embrace the lessons learned from the Grumman "flat-panel" LEM. Load path negotiation was a nightmare back then, and early NASTRAN was an indication of a trend, not even remotely considered an absolute.

The addition of what is called the "exo-truss" to the entire vehicle, for managing and transmitting the Propulsion Pod(s) thrust(and Isp), will give Nautilus sufficient structural integrity. We also hope for hefty a natural frequency so that the Centrifuge can become a positive input into the overall GN&C design.

I hope this helps answer of few of your questions. If nothing else, it is hoped that Nautilus-X is utilized as a development tool/mechanism for good System(s) engineering design and produces some decent axioms for large, long-duration spacecraft design. But it is something of a nifty Concept....

Warm regards,
--- mark

First of all, thanks to Mark for shedding a little more light on this concept. The updated powerpoint (linked above) contains a few more pictures of the Nautilus-X from different angles.

Slide 32 is particularly interesting - an orthogonal view of the "underside" of the craft. It is clear from this slide that the single biggest section is that "Winnebago" at the nose. No other segment even comes close in size - everything else could probably be launched on currently- or near-term-available rockets, but that Winnebago would need something much bigger than we have right now.

I understand they are eager to use the flat panels, drawing from the Lunar Excursion Modules as an inspiration. The slide-out concept might even work just fine. That heavy lift requirement for just that one element is the problem.

If one were to imaginarily slide that command deck back and the big airlock forward, it is easy to see that this one piece could be broken up into three pieces with no slide-outs, each of which could fit on existing rockets.

I agree completely with doing the ISS demo of the centrifuge. We might get lucky with that size centrifuge and find the right amount of spin to reduce or eliminate bone loss without making astronauts dizzy. If it turns out we need a bigger centrifuge, then we've found that out early on. If not, then that's a big hurdle out of the way.

I agree with the external truss framework. It makes lots of sense. The one weak point is at the centrifuge. All thrust loads have to be transmitted through those bearings. I could see having a central truss through the centrifuge taking the load off the bearings, but having that centrifuge located coaxial with the main thrust axis in between the Winnebago and the rest of the ship gives me the willies. It might be better located right at the nose of the craft. Having two centrifuges rotating perpendicular to the centerline might even be better. It isn't clear whether the centrifuge is rotating during any boosting operations; if not, that might simplify the loading during boost.

"Silent Running w/ Bruce Dern" - oh, boy. Bruce Dern also gives me the willies. Kidding aside, I think that having lots of plants and hydroponic food and so forth will go a long way towards improving the life support system of space vessels. Hydroponic gardens are already extensively used by submarine crews around the world, and will surely be useful in long-duration space flight. Just having green growing things around will provide a psychological boost to the astronauts, but their primary use would be to help replenish the oxygen supply and to provide food. I'm all for it.

The more I look at the solar panel arrangement, the more convinced I am that the booms should be longer, and that there should be Canfield joints between the booms and the solar panels. The mechanism is far less complicated than the SARJ used on the ISS, and would allow a full hemisphere of aiming for each solar panel.

Saturday, February 12, 2011

NASA designs an actual spaceship

The Nautilus-X MMSEV is the closest NASA has come to a design for an honest-to-goodness spaceship in decades. There has already been extensive discussion over at Selenian Boondocks and Hobbyspace, and this is probably a couple weeks late on the subject. However, this is an idea that has considerable merit and deserves further study. So, I uploaded the Holderman powerpoint to Google Docs, and here it is:

If you click on the "open in new window" button, then you can view it in full screen.

There is a lot that I like about this design - in fact, much of it looks like items on my list of technological stepping stones to space. For one thing, it is modular. Yes yes absolutely yes. Several launches are required to put it together, all of which could be done with existing vehicles (with one exception which I'll get to later). It includes a centrifuge, which might mitigate some of the bone loss effects of microgravity. It includes inflatable modules. Above all it is a spaceship - its environment is space, it has no landing gear or reentry heat shield.

Now, there are some things I don't like about the Nautilus-X.

That big core section would require a single launch, probably on something heavier than anything in stock today. It has RV-style slide-outs for the command deck and a large airlock. Worst of all, it has flat walls - probably due to the slide-outs. The flat walls and slide-outs are brand-new technology that introduce unnecessary failure modes and complexity. This could be redone as two pieces with curved walls: the radiation mitigation chamber is one piece, the airlock and command deck are another, set "sideways" to make a T shape. These two smaller pieces could then probably be launched on existing launch vehicles.

The centrifuge radius is an educated guess. We don't know the minimum gee required to reduce or eliminate bone loss. That particular centrifuge would produce no more than a few percent of a gee (i.e. about lunar gravity at 4RPM by my estimate) before problems due to high angular velocity start to occur. If a few percent gee is enough to slow or stop bone loss, great! If not, then this centrifuge would be an added layer of complexity for limited benefit. There would be benefits, no doubt, particularly for things like eating and ablutions, but the primarily-intended benefit would be missing. The bearings on the centrifuge - allowing nearly frictionless rotation while not allowing atmosphere to escape - are going to be a novel engineering challenge.

The MMSEV is intended for very long duration missions, up to two years. Unlike satellites in low earth orbit, which spend half their time in Earth's shadow, the MMSEV would be out in cislunar space or interplanetary space constantly being exposed to the sun. The entire craft would have to do a slow "barbecue roll" to avoid overheating one side, most likely along its long axis in the opposite direction of the centrifuge. Canfield joints at the end of the beams holding the big solar panels would allow them to continuously track the sun during the barbecue roll.

It's a good start.

Update Mark Holderman responds.