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G-Hab
An illustration showing one concept for the G-Hab Hotel that could provide a partial gravity environment for researchers and tourists. (credit: B. Brodbeck)

The G-Hab hotel


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Nearly a half-century has passed since the earliest rotational artificial gravity testing was performed, such as at the Rockwell Rotational Test Facility and the NASA Langley Rotating Space Station Simulator. Periodically over the decades since then a few experiments have taken place, and proposals have been made for government-sponsored rotating artificial gravity test facilities, both on the ground and in orbit.1,2 And yet no such project has been started since those early government programs.

With the new space age developing, now is the time to set us firmly on the path to healthy long-term deep space habitation, and do so profitably.

Today we’re evidently at the dawn of a new age of human spaceflight, one fueled increasingly with private funds, seeking, of course, profits. Suborbital space tourism will likely take flight within just a couple years, provided by private firms such as Blue Origin and Virgin Galactic. While NASA will launch its new heavy-lift Space Launch System and its Orion crew vehicle in the coming years, private firms such as SpaceX and Boeing will orbit crewed spacecraft even sooner, likely to be followed by Blue Origin and Sierra Nevada Corp. Several firms are cost-sharing with NASA, via its NextSTEP program, the prototyping of zero-g habitat modules for cislunar space and new environmental control and life support systems (ECLSS) to develop “habitats and the systems to keep astronauts safe as they live and work in deep space for long periods of time”.3

But where are the proposed rotating artificial gravity systems? Unfortunately, it appears we will continue indefinitely with only zero-g habitation and experimentation facilities for our space personnel. Do we have to wait another half-century for us to solidify humanity’s spacefaring quest with artificial gravity habitats and spacecraft better able to preserve the health of astronauts? With the new space age developing, now is the time to set us firmly on the path to healthy long-term deep space habitation, and do so profitably.

The G-Hab Hotel would be a privately funded, owned, and operated low Earth orbit (LEO) hotel with artificial gravity. Guests—that is, paying lodgers—would include space tourists and institutional, governmental, and corporate researchers and scientists. It may eventually include high-orbit space workers on furlough or cislunar transfer layovers. Research activities would be focused on human biomedical factors and adaptations to the use of a rotational habitat at 0.5g (50 percent gravity) along with zero-g activities. A more limited operational crew, including a medical officer, would be resident.

Attached to one end of the hotel, the artificial gravity segment consists of a 25-meter-radius toroid centrifuge spinning at 4 rpm to provide 0.5g. Two opposing tubular spokes radiating from that hub, with ladders and maybe folding chair lifts inside, give access to and from the non-rotating zero-g segment of the hotel. Several features could utilize elements from the NASA Nautilus-X design, such as an external counter-rotating torque-offset flywheel, Hoberman circumferential stabilizing ring, and spin startup/control thrusters on the CF exterior.4 Other than electrical power-sharing across the hub, both the zero-g and 0.5g areas of the hotel would have independent ECLSS.

Multiple modules, perhaps Bigelow’s B330 or similar designs, with external docking ports could be attached laterally to the central spinal module(s) to form the basics of the zero-g segment. Additionally, a guest lounge with viewing cupola, remote manipulator system (RMS), EVA airlock, communications gear, deployed solar and radiator panels, and other necessities would be attached here.

Partial artificial gravity most importantly improves crew and guest health. The system will mitigate the negative effects of zero-g on human health and productivity, both in-space and after Earth return.

In the centrifugal section, over 150 meters of torus tube (circumferential) length would be available for use. The torus tube of the CF might be something like 3.5 meters in cross-section. Enough cross-sectional space should be available to allow a through path, and on at least one, if not both sides of the path, 1.5 meters or more width of usable space along the torus length. If a personal berth were, say, 4.5 meters in length—room for individualized sleep and relaxation, privacy, personal hygiene, communications, and stowage— then 34 berth spaces can occupy one side. Amenities include partial-g toilets and body-wash/shower-stations.

Of course, fewer than 34 crew and guest berths might be accommodated, depending also on whether one or both sides of the torus were to be used, so that space is given for the ECLSS, a medical and bio-sciences testing area, partial-g exercise space and equipment, and access spokes, perhaps even a hydroponics section or space for other science research equipment.

The zero-g hotel segment modules host the various crew-operated equipment, logistics and communications management activities, including docking controls, RMS operation, and EVAs, bulk supplies, etc. These modules also provide for guest-related activities such as dining, exercise and education, bio-medical testing, and, of course, Earth and space viewing and photography from a cupola with stunning views.

Partial artificial gravity most importantly improves crew and guest health. The system will mitigate the negative effects of zero-g on human health and productivity, both in-space and after Earth return. These zero-g health negatives are well known and documented, especially in comparison to the far more positive effects on human health of providing rotational artificial gravity. Indeed, part of the hotel’s purpose will be to study and help determine the extent and range of health effects and benefits. This will include human responses to repeated transitions into and out of partial-g as well as including potential increases in crew and guest productivity. Small vertebrate animal (e.g., mice) testing could also take place at the facility comparing zero-g versus artificial gravity effects over multiple generations.

The cost of such governmental funded human-factors research will be greatly reduced as funding and development of the in-space facility is made privately, with the expectation that the sponsored researchers will be paying guests during their programs at the hotel. No doubt the habitat is itself a major attractive feature of the hotel for all types of guests, providing improved rest, privacy, personal comfort, and general interest amenities.

Increases in length of stay for crew and guests can be expected in some if not most cases. This improves guest revenue quality and decreases crew costs, in particular due to decreases in the high transport costs vis-à-vis the Earth’s surface relative to the time and cost of lodging. Once a guest considers the cost of transport cost versus the lodging cost, if the latter is significantly lower, likely longer stays will be reserved, helping to stabilize and grow revenues.

Undoubtedly, a number of the tourist guests, being space development enthusiasts, will wish to participate at some level in the biomedical studies during their space vacations, thus contributing in their own way to humanity’s permanent expansion across the solar system. The G-Hab Hotel provides a wider non-astronaut population for such studies.

Over time, due to the health and cost benefits, the hotel may attract other types of guests. Perhaps workers at cislunar zero-g facilities will lodge at the hotel for a gravity remediation furlough, rather than traveling to and from Earth, in between deployments at the work facilities. Fewer crewed direct Earth-to-high-orbit and direct Earth-to-cislunar launches and trips will be needed, as purely orbital transfer craft from the hotel could complete those journeys, potentially lowering Earth launch costs and broadening the launch market.

The G-Hab hotel is intended to be profitable, forming the basis for additional space business and investment expansion, in addition to the artificial gravity benefits noted.

In the end, and perhaps most importantly, the G-Hab Hotel sets space industry on the developmental path towards healthier deep space exploration, such as for human interplanetary journeys (Mars, etc.); longer-term, larger-scale orbital habitats; and eventually multi-generational free-space habitation. This is a huge step initially, but the experience gained will be used for improving succeeding and enlarged centrifugal habitat projects. And finally, it demonstrates to the world that long-term space habitation and settlement are a definite human future to be enjoyed by many.

The G-Hab hotel is intended to be profitable, forming the basis for additional space business and investment expansion, in addition to the artificial gravity benefits noted, including its direct study. As a private enterprise, it would largely be independent of shifting and politicized governmental priorities, would decrease development time and cost, and lowers the costs of human oriented governmental space research programs.

Being as I am not an expert in this field any financial estimates I make are not even up to the level of a SWAG (scientific wild-a** guess). Nevertheless, the following may spark serious consideration of the concept, or at the least make for an interesting read and perhaps discussion. And since I am not competent to estimate the cost of developing and implementing such a facility, we’ll start with the revenue guesstimate first and then back into what level of cost might be supported.

The following revenue figures are based on weekly guest lodging fees exclusive of transportation to and from the G-Hab Hotel. Four different levels of implemented guest berths (6, 12, 18, 24) are considered in the table, along with four levels of weekly lodging fees ($0.5, $1.0, $3.0, and $5.0 million), and a 77 percent occupancy rate (40 of 52 weeks). Next, the present values (PVs) of the above ten-year revenue streams are calculated based on a 4 percent annual discount rate, the annual revenue amounts (assumed to be level) minus $200 million in annual operating costs.

revenue table

The PV is the amount of funds in current (discounted) dollars that the net annual revenues yield over ten years, basically telling us how much we can afford to invest now for that future revenue. The negative PV values mean the project costs more in today’s dollars than it brings in over the future years.

Assuming, for example, the project cost estimate is $10 billion, then, per the PVs, in order to be profitable, we would minimally need 12 guest berths at a $5-million weekly lodging fee, or 18 guest berths at a $3-million weekly lodging fee, to be profitable. Above those levels of berths and lodging fees, the allowable project costs and/or the revenues are significantly higher.

As of today, there have only been seven tourists who visited the ISS, including one who made two trips, for a total of eight trips. These eight trips averaged 11.75 days and cost an estimated $15.6 million per week, including transportation. That’s a very small number of people who have paid large sums for such trips, although it was limited by ISS administration at times.5 The portion of that $15.6-million figure that was spent for transportation is unknown, although at $5 million a week for lodging, then obviously more than $10 million remains for transport. The number of suborbital trips that have been booked by Virgin Galactic is about 700, at $200,000 to $250,000 each.6 But then those are trips providing only five minutes in space, which may be constraining the number.

In the projections above, 18 guest berths are occupied a total of 720 weeks per year. If half of those are tourist guests, that would entail 9 berths with 360 total weeks of occupation per year. If those tourists stayed on average two weeks, then 180 tourist guests would be required per year. At a lodging fee of $6 million (twice $3 million a week), plus $10M transportation cost, each trip would cost $16M. Would such a market exist?

Additionally, a similar number of weeks of researcher guests would be required, although the average length of stay would probably be much longer.

Obviously, cost of reaching low Earth orbit is a critical factor. Perhaps it’s the most important factor, impacting not just the costs of construction and operations, but also the lodging and transportation rates and the size of the guest market, ultimately greatly impacting profitability. Hopefully the arrival of reusability will present greatly reduced costs.

Besides design alternatives, a number of other factors would have to be analyzed and run in a preliminary feasibility analysis that might be accomplished for several million dollars or less.

Laying the foundation in the near term for healthy habitation in various Earth and cislunar orbits, as well as for interplanetary journeys and other planetary orbits, has long-term benefits that seriously outweigh those of a few crewed “flags and footprints” excursions to the closest planets.

Innovative design approaches may even be taken to step out the cost and investment risk, such as constructing an inner ring first. A 12.5-meter-radius centrifugal section rotating at 4 rpm yields about 0.28g, which happens to be in between lunar and Martian gravity. This circumferential torus tube length would be 78.5 meters, allowing for up to maybe 10 berths plus adequate length for ECLSS and other equipment.

Later, the spokes could be extended and an outer 25-meter-radius 0.5g ring added. Extendable spokes, instead of intersecting centered on the inside diameter centerline of the torus, could be offset to one side of the inner torus for an overlapping half-tube-width interface. This would make the spoke tubes more readily extendable past the inner torus to the outer 0.5g torus.

Now is the time to begin the private development of a G-Hab Hotel prospect, with preliminary studies covering potential markets, engineering, financial capitalization and return, innovative approaches, and overall feasibility. Laying the foundation in the near term for healthy habitation in various Earth and cislunar orbits, as well as for interplanetary journeys and other planetary orbits, has long-term benefits that seriously outweigh those of a few crewed “flags and footprints” excursions to the closest planets. The step-wise propagation of human activity into space on this basis would seem to be much more logical and vastly more economically productive.

Endnotes

  1. Diamandis, Peter H., Reconsidering Artificial Gravity for Twenty-First Century Space Habitats. SSI/AIAA Space Manufacturing volume 6: Nonterrestrial Resources, Biosciences and Space Engineering; 1987.
  2. Hudson, Gary C., Why G-Lab?. G-Lab 2017 Slides and Script, Silicon Valley Space Center/AIAA-SF TechTalk; February, 2017.
  3. NextSTEP Partners Develop Ground Prototypes to Expand our Knowledge of Deep Space Habitats. NASA NextSTEP-2 Selections News Release; August 9, 2016.
  4. Holderman, Mark L., Nautilus-X: Multi-Mission Space Exploration Vehicle. NASA Technology Applications Assessment Team, FISO Telecon presentation; January 26, 2011. (Holderman_1-26-11.ppt)
  5. Space tourism; List of flown space tourists. Wikipedia; 2017.
  6. Space tourism; Sub-orbital space tourism. Wikipedia; 2017.

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