Project Helix

Following the initial release of Project Helix on 2021.03.22, I received helpful feedback from many redditors on the various subreddits I posted to¹ ² ³ ⁴. After considering the feedback, I’d like to make this new post to share several of the updates, clarifications, modifications, and comments based on this feedback. In this post I will be highlighting a few of the general critiques along with my design response to them in an effort to move the project forward.

“The helix corridors take up a lot of space and/or are not useful.”

The corridors in Project Helix are different from typical corridors that one might encounter in their day-to-day. That is to say they perform the duties of both personnel circulation and being positive, activated space. Simply because it facilitates the circulation of passengers does not mean that it cannot be useful space that can be routinely occupied for critical functions.
In this iteration, the corridor is activated by the crew in a similar way to a community market, a pedestrian street, or a covered mall; the circulation is not merely a highway, but rather a usable space like any other. In this way, the space dedicated to the corridor is not space taken away from other purposes, it is the space used for those purposes.

“An angled corridor makes for odd shapes in the rooms.”

The initial diagram was intended more as a diagrammatic illustration of the circulation pattern for Starship. That being said, their could be geometrically non-uniform spaces if the program calls for it. This does not necessarily have to be a bad thing or even something unusual, as the cylinder form of Starship precludes uniformly orthogonal spatial organization.
In this iteration, the stepped configuration is exemplified. This allows for a more-easily perceptible positive space created by the corridor on each level. With the addition of interior design elements, the limited visibility further down the corridor can allow the space to subtly change via evolving, space-creating motifs such as colors, textures, or vegetation.

“Vertical transport is more difficult with a ramp.”

Part of the conclusion here comes from the assumptions about where the large equipment is going to be stored with respect to the "exit". Ideally, the difficult-to-transport items will be stored as close to the bottom as possible. This means the engine/skirt adjacent storage locations will be packed as much as possible. This also means that the equipment that will have to be unloaded from the pressurized section should be located as close to the exit portal as possible. Since this exit portal is located at the base of the pressurized area (as it should be), this is where the large equipment will be located. In other words, there should be little need to transport large equipment through the living spaces. While the large equipment will be located at the lowest areas, there will be supplementary equipment and supplies that will have to be unloaded as well. This is where the internal passageways come into use. Small parcels can be offloaded by hand by the crew using interior fold-down stairs along the corridors. This is another reason to have two corridors, as one can be dedicated to upwards circulation while the other can be dedicated to downwards circulation.

“The ramp/stair is too steep for cargo and people.”

The pitch of the stairs was not formally communicated in the initial concept, but the intention is to have the stairs at a reasonable rise/run ratio. Since the stair runs will follow 60 degree increments, the average pitch can be determined using the centerline radius of the stairs and the level/layer height. In this latest iteration, the stair's center radius is 3 meters and the level/layer height is 2 meters. Using the formula, we can see that the pitch is the standard 11:7 stair pitch.

As for the ramp, this is a feature that may or may not be included for similar reasons mentioned above regarding odd spaces. In any case, since the large and heavy equipment should generally be located at the base of the pressurized volume, any equipment and supplies transported via the stairs (or indeed a prospective cargo ramp) should be small enough to carry. In the event that this cannot be the case, clearance area could be added to the central service shaft such that massive items with low volume or those that are too long to easily transport by hand can be lowered down via a winch or something similar.

“What about radiation protection?”

Radiation protection will be a required component of any successful Starship design intended for Mars. At the same time, since radiation protection is an exterior perimeter condition, it is not necessary to include it in a spatial layout concept as the solution will be determined by those who are responsible for ensuring the lowest acceptable radiation exposure for the crew.

This all being said, I imagine that there is ample opportunity for radiation protection through a combination of perimeter shielding and passive shielding from interior storage and supplies. The current structural design for Starship allows for dimensional exterior trusses, in-between which radiation shielding/supplies can be located. Interior to this structural layer, a layer of equipment and supply storage could be located to further protect the crew so long as this equipment produces little to no secondary radiation⁵.

“Where to put the crew during high-G maneuvers?”

The greatest high-G maneuvers for the crew of Starship will be during the takeoff from Earth. These forces will be in the axial direction, meaning that all locations on Starship will be experiencing roughly the same acceleration as far as the crew is concerned. When the Starship is undergoing the "belly-flop" maneuver, the acceleration will again be from the same direction for the whole ship, albeit from the perpendicular direction to the aforementioned Earth takeoff (and different on the interior with respect to the radial distance from the Starship's "belly"). The only circumstance that will lead to significantly dynamic G-forces seems to be the flip-to-upright maneuver upon landing.

The securing of crew during the maneuvers is of utmost importance, especially during the descent to Mars after a six-month journey in null gravity. The ability of the crew-securing seats to function adequately with respect to the direction of acceleration is not a problem unique to Project Helix however, as any configuration will have to design around the changing direction of acceleration. This will likely necessitate the invention of a seat system that is able to dynamically change direction based on the predominant direction of acceleration.

This being said, the location that would be easiest on the crew as far and dynamic G-forces go would be Starship's center of mass. This translates to the lower decks and the Starship core. This is in part why the crew quarters were located in the lower section of Starship, and it is also why the new version has the crew quarters located exclusively along the central column.

“What about leaks/decompression due to impacts?”

There is no significant difference in puncture risk between the Helix design concept and "conventional" layouts. The main argument here was regarding the ability of compartments to be sealed-off with hatches in the event that a compartment decompression was necessary. There is nothing preventing an iteration of the Helix concept from including periodic hatches if deemed necessary.

More importantly, the risk of a decompressive puncture for starship is exceedingly unlikely. Firstly, there is a lower risk for impact on route to Mars than there is in LEO, due to the comparatively increased risk of impact from orbital debris. Since there is no orbital debris on route to Mars, only micro/meteoroids are a danger, and the risk of these impacting is unlikely. Even in the unlikely event of an impact, there will be a roughly 40cm distance between the Starship exterior and the pressurized surface of the interior. This would almost certainly ensure that the energy is adequately dissipated before impacting the pressurized layer. With adequate pressure sensor buildout, the compartmentalized exterior layer should allow any leak to be found and patched quickly in the further unlikely event of a penetration.

“Passengers can't egress in space, so redundant passageways are not important.”

There is a subtle but important difference between exiting and egress. Exiting is a form of egress, but egress really just means getting to safety. In this sense, there are a few situations I can think of that would benefit from being able to egress. Let's say a fire occurs and blocks one of the passages; a second way around the ship would be very prudent. The same goes for a shift in cargo or the main opening becoming otherwise blocked. This sort of egress does not involve exiting the vessel, but it does provide the crew a way to move to a safer area of the ship from a hazardous area they might otherwise be trapped in.

Aside from egress, having two passages also provides higher circulation throughput both during transit and after arriving at the destination. On Mars, one corridor can be designated for ascending while the other can be designated for descending.

“Gravity agnostic design is irrelevant because the Starship will be tethered to another and spun to simulate gravity.”

While the tethered solution is interesting, it is by no means confirmed for each and every trip, let alone the first ones. To be clear, the Helix concept does assume the need for a layout version that works in microgravity. It is likely that this will always be needed to some extent for purely orbital trips and for trips to the moon and back.

“It won't work with that many people.”

The initial Helix proposal attempted to approach the 100 person target initially pitched by Elon Musk in the press briefings for the Starship Mars mission. At the time I designed the initial concept, anything less than attempting this target seemed to be lowering the goal post as it were. In any case, it is now my opinion that the target crew count should indeed be dropped considerably in order to both increase comfort and simplify logistics. This latest iteration of the Helix concept proposes crew compliments in the range of 12-36.

For example, an important consideration in space travel that is nearly universally overlooked is the necessity of toilets and other hygiene apparatus. The 2018 International Building Code (IBC) specifies that the minimum toilet count for an R-2 occupancy (that which seems to be the closest programmatically to Starship) is 1 toilet per 10 individuals. Taken in combination with the consideration that the use of space toilets may take anywhere from 2-4x as much time to use and subsequently clean as gravity-bound toilets, that the occupants can't exactly just "go outside" in an emergency, and that space toilets can be rendered out-of-commission at any time, the recommended toilet count may be at least as many as 1 toilet per 5 individuals. For 100 people, there may have to be at least 20 toilets. A lower crew compliment would lower the burden of this requirement.

Project Helix - v.2 Update