Can Low Earth Orbit be developed faster by dropping our old approach to building space stations?

Starship launches are estimated by SpaceX to cost less than $2M per launch (ref. IAC presentation 2017, min 25:00). This could represent a dramatic decrease compared to today’s launch costs and in fact, Starship, once completed, will be the most cost-effective rocket in existence even while being the largest (it has a 150 ton to orbit capacity which is more than the launch capacity of Saturn V — the rocket which launched humanity to the Moon).

What if we could use SpaceX infrastructure to assemble a spaceport in years from now rather than the decades a traditional approach would take? The International Space Station (ISS) cost more than $150B to construct and took over ten years to complete. Such expense, and timelines, hinder the development of Low Earth Orbit. Why not revolutionise our approach by moving towards new ways of building in space and fully leverage the advances in design, materials, as well as software & hardware that have enabled the massive growth the sector has seen in many in recent years?

Here’s how. Rather than launching self-contained station capsules as was the case using the Shuttle to build the ISS, the upper stage of SpaceX’s Starship could be used as a building block of the spaceport. Its interior happens to be perfectly designed as a living space under artificial gravity. Using the rocket itself as infrastructure will be far more efficient than launching separate capsules enclosed in rockets or spaceplanes. And doing so will save years of design time; Starships are built for long-term space missions — they are built to remain pressurised in space for years on end. Why not use them to live in?

Once in space, the Starship upper stages (they will be called ‘habs’ from now on) are connected in a circular fashion and then spun to create gravity. Spinning stations to create artificial gravity is a well known technique that has been the cornerstone of many space station designs, and at one point seriously evaluated for the ISS. The design below sets the outer diameter of the rotating segment at 200m, which at 1.9 rotations per minute, will create an artificial gravity of 0.8g for the occupants (ie. four fifth’s of Earth’s gravity). The above specs are deemed as safe to humans by most space architects (ref. Spin-Calc, Creating artificial gravity will make it much safer as well as more pleasant for humans to remain in space for extended periods of time.

The connection of the habs is done through pressurised gantries to create a ring. Orientated inwards when spun, the different levels inside the Starships will act as floors. The spinning itself will be achieved by the gimballed Raptor engines on Starship’s upper-stage or secondary thrusters otherwise used to orientate it. With so many thrusters available, it will be easy to maintain a spin as well as to manoeuvre the station as a whole (eg. to maintain orbit or avoid debris). The tension created by the angular momentum will be carried by steel cabling connecting each hab to the central docking platform along with a boarding tunnel and maintenance shaft.

The question now arises as to whom will pay for such a construction? The premise that it should be funded by governments is false as it risks us following old ideas and approaches, which will likely explode the price of the station. The first spaceport should therefore be privately funded (as is SpaceX), for example, a luxury hotel. The business model is broken down below to show how it will make financial sense. A lot of assumptions have been made as to the cost of infrastructure (incl. Starship uppers stages), but considering the number of test Starships SpaceX has launched (and exploded) to date with limited funds, it would be surprising if the costs end up being an order of magnitude higher.

Business model for a luxury hotel in orbit using SpaceX infrastructure

The below is a back-of-the-envelope calculation which will surely change, but gives us a starting point.

Let’s assume fifty guests every two weeks paying $350K each. The assumption of 50 people is based on the number of people that can be launched in one go onboard a Starship. The price-tag of $350K is assumed because even though it’s a lot, there will be more than enough global demand for a two-week holiday in space at that price point. As a result, revenue generated by the hotel could be upwards of $35M per month (two launches per month equals 100 guests x $350K) or $420M per year. Net income will come to roughly $180M per year after launch costs. It’s worth noting that revenue potential changes drastically based on ticket price, and the number of stays (based on the number suites onboard) assumed each month.

But, in short, if the spaceport cost $3.0B or less, it would pay for itself in less than 20 years which is a reasonable return on investment for any large-scale terrestrial project of a similar magnitude, let alone one based in space.

Now let’s breakdown the potential costs:

  • Eight modules (Starship upper stages) will cost $80M to launch altogether (ie. eight launches at €10M each, assuming SpaceX will want to make a profit).
  • Assuming a cost of $60M per upper-stage, the total price of eight habs will equal approx. $480M. Remember, we don’t have to pay for the Starship lower stage as it’s fully re-usable — it would essentially be bundled into the launch cost
  • The connecting gantries (x8) using x16 launches ($160M) and at a cost to build of $120M for each segment, will come to $1.12B
  • Let’s assume the central docking structure requires four launches and $150M to build ie. $190M
  • And a Zero G recreation hab (a must for a space hotel!) will cost approx. $60M plus $10M for the launch or $70M

In total, these costs come to $1.94B. Add roughly 25% for additional expenses (eg. retrofitting the habs, the solar tiles, cabling, control software and project management), and the grand total comes to $2.5B. We need also to assume an operational cost to cover staffing, branding, terrestrial operations and service launches — $50M per year seems reasonable.

Assuming the operational cost and revenue potential together, net income is €130M year, meaning the hotel will indeed pay for itself in under twenty years. The calculation does not take into account additional revenue that may be generated through docking or refuelling services.

Other design elements

Assuming fifty guests, no more than three habs will be required for accommodation, which frees up five for other uses. At the same time, a central docking area under microgravity could house a recreational hab, as well as fuel re-supply services for transiting spacecraft. The latter would represent as secondary source of revenue for the hotel. Here is list of other considerations (which could be applied to all use-cases) in designing the hotel;

  • Habs dedicated to indoor farming could provide oxygen and food, partly reducing the load on the spaceport’s life-support system
  • A boarding platform could be gimballed such that it would not rotate with the station, making it easier to dock. Passengers would simply pull themselves into the rotating part once inside.
  • A Zero G recreational hub could attach in the middle, again not part of the rotating segment.
  • The whole station could be covered with solar tiles (similar to those used on the Dragon spacecraft), removing the need for a cumbersome solar array.
  • The spaceport could also serve as a fuel re-supply station for interplanetary trips, reducing mission risk. Again, SpaceX infrastructure could be used here. Starship upper stages converted to fuel tankers are already being designed, and could simply be attached to the station and periodically refilled as needed.

As alluded to, there are other use-cases for a spaceport design similar to the above. These include;

  1. Space infrastructure for companies pursuing R&D or other space-based operations eg. debris removal or mining
  2. Research facilities for governments
  3. Research facilities for universities

Easily 4–5 versions of the spaceport could be built to meet demand if costs can be kept under control. In fact, at such a low price, they could even be sold outright; a company or country could have its own for just $2.5BN!

In short, using SpaceX’s low-cost infrastructure, massive and cost-effective spaceports could be assembled relatively cheaply and quickly, with the potential to transform Low Earth Orbit into a hive of activity and commerce in a matter of years rather than decades. These stations could also serve as important re-supply bases for missions to Mars or the Moon. And notably, they would be able to replicate gravity, making working and living in space much less demanding on the human body, and long-duration stays a matter of course.

Old approaches to constructing infrastructure in space can and should be abandoned. There is no reason we cannot transform our approach to space, and radically reduce the costs associated with developing it. The benefits space exploration will bring to our economy will be enormous; an explosion in revenues from space tourism, numerous technological breakthroughs spun-out to applications on Earth, the mining of precious metals and a source of inspiration for yet another generation of scientists & engineers.

However, without action, an idea remains just that, an idea. If you know someone who could be relavent to making the above a reality, go ahead and share this article with them!

Founder of Skytree, a company committed to finding technological solutions to climate change. Physicist. Ex-ESA engineer. Current scuba-diver.