Spacecoaches can be built and launched entirely using existing technologies and medium heavy launch platforms, such as the SpaceX Falcon 9 and Falcon 9 Heavy systems, unlike currently planned interplanetary missions, which are dependent on as yet built heavy lift platforms (the so-called Apollo on Steroids approach). Because of this, the first spacecoaches could be flying within a few years, and with iterative design and field upgrades, could be serviced and upgraded to improve their capabilities for many years. They will be much more like sailboats than today’s expandable ships, and will be simple, durable and upgradable.

Phase 1 : Design Competitions

We are working to organize several design competitions to further develop the spacecoach concept, and to pin down more precise numbers to use in parametric modeling (e.g. electrothermal engine performance). We envision two design competitions taking place more or less in parallel:

  1. An X-Prize style competition, the X-Plane Isp Prize, to develop candidate electrothermal engines. This is slated to begin in 2011. Austin Meyer and Laminar Research, creators of the X-Plane flight simulator, have stepped up as anchor sponsors for the competition, with more to follow. We will be announcing more details about the competition shortly.
  2. An integrated  architectural design and systems competition that solicits detailed designs from multidisciplinary teams. These designs will be vetted by space technology experts from leading companies and research institutions (details TBA later this spring).

This phase of development would span 2011-2012, and would overlap with Phase 2, as some components can be built and tested while this work is underway. By the end of Phase 1, ship designers and mission planners will be able to complete detailed designs, as well as more accurately forecast construction and operating costs.

Phase 2 : Ground Tests

Many components needed to build a spacecoach are already available off the shelf, or are in advanced stages of development. Some, such as space rated solar arrays, are available as off the shelf products. Others can be designed and realistically simulated in ground tests to simulate operation in the space environment prior to manned or robotic flight testing.

Because these ships never enter a planetary atmosphere, and never experience the types of dynamic forces and extreme heating that a conventional launch or re-entry vehicle is subjected to, their design and testing is greatly simplified. For example, electrothermal engines can be tested for performance and reliability in vacuum chambers. The empty hull design philosophy further simplifies design and testing. The ship itself is essentially a passive hull, solar powerplant, and power bus. All other systems, such as avionics, atmospheric processing (life support) units and other gear are brought on board as needed. Data from these tests can be used both to refine detailed designs.

Phase 3 : Near Earth Flight Tests

The first spacecoach would be launched into low earth orbit, and after an initial shakedown period, would be fueled with enough water for the equivalent of a Earth-Mars or Earth-Venus roundtrip (12-14 km/s delta v). The ship would execute a series of step up/step down orbit changes, while remaining close enough to Earth that the crew could escape or rendezvous with a rescue craft should a serious problem develop. These test flights would last for one to two years, long enough to simulate an interplanetary mission, and fully test all system components and processes, such as on board life support, agricultural systems, etc. The first flights would most likely be unmanned, and the systems scaled up for habitation once the platform and its systems have been validated in flight (much as Bigelow Aerospace has been doing with its unmanned flight tests for its inflatable structures).

Phase 4 : Long Range Missions

While Phase 3 is underway, additional ships could be built in low earth orbit, possibly with improvements, or the original test ship(s) could be refueled and upgraded for the next journeys. They would then proceed to more distant locations, from lunar orbit (10 km/s roundtrip) to the Martian moons (11.5 km/s round trip). The Martian moon Phobos is an especially interesting destination which we discuss in detail on this site as it will be possible to land an entire spacecoach on the surface, thus enabling the mission to include a lot of interesting geological science (e.g. excavate the surface to research its composition and the availability of useful materials that could be utilized by future missions).

One of the key benefits of the spacecoach system is that these systems are not designed for a specific destination. They will be highly reusable so a single ship could travel to many destinations during a mission or series of round trip missions, while they can be upgraded as they are refueled after each trip.

The first generation ships should be able to reach many interesting destinations, including:

  • Lunar orbit (delta V ~ 9.6 km/s roundtrip)
  • Martian moons Deimos and Phobos (delta V ~ 11.4 km/s roundtrip)
  • Venutian orbit (delta V ~ 14 km/s roundtrip)
  • Near Earth Objects (delta V ~ 10 km/s roundtrip, varies with target object)

Long Term System Evolution

Spacecoaches should last for many years, with lifespans comparable to the Mir space station or ISS, which is expected to last for 15-20 years (and possibly much longer if they are designed so that every module is replaceable). Instead of relying on infrequent technology breakthroughs, the system is improved by making incremental refinements to key components, such as:

  • Improving engines to operate at incrementally higher specific impulse and efficiency with each generation. (First generation MET engines should run at 900 seconds, while Hall Effect thrusters, if they can be adapted for water, can reach up to 3000 seconds, with dramatically better fuel efficiency).
  • Replacing current generation solar arrays with lighter arrays that generate more power per kilogram of mass. This will enable ships to travel further from the Sun, or to accelerate more quickly to shorten trip times. Spacecoaches will benefit from the billions of dollars currently being invested in terrestrial solar power systems, thin film photovoltaic materials in particular.
  • Structural materials. The use of advanced composite materials or inflatable structures made from high strength fabrics will enable designers to further reduce the empty weight of the ship, savings that can be used to increase payload capacity, range, or a combination of both.
  • Should a low gravity site such as Phobos or Ceres have readily accessible water ice, this will enable ships to refuel at these destinations. Water mining operations would also be able to extract and deliver water to rendezvous points or destinations where it is scarce (e.g. Earth orbit, Venus orbit). The ability to use in situ refueling will reduce mission costs dramatically, by a factor of 5-10 fold (for return refueling) to 100 fold or more (when water is backhauled to low earth orbit to fuel outgoing ships so that no water need be launched from Earth to low earth orbit).

Improved Solar Arrays

As solar arrays are improved to deliver more power per kilogram of mass, ships will be able to travel beyond Mars to the Asteroid Belt, and possibly to the Jovian system. As power density increases, Ceres, Juno and the Asteroid Belt will become accessible, even without substantially upgrading the engines. Ceres is an especially interesting destination because of the large amounts of water ice it contains.

Second Generation Electrothermal Engines

The first generation engines, most likely MET type engines, will run at about 900 seconds specific impulse, and will enable spacecoaches to travel economically to Lunar orbit, the Martian system, Venus (possibly Ceres and the Asteroid Belt). To go further, to Mercury traveling inward, or to the outer planets, the high delta V requirement drives water costs up. Even marginal improvements to engine efficiency, for example increasing specific impulse to 1200-1500 seconds (on the low end for Hall Effect engines), will reduce propellant costs 3 to 10 fold. If engines can be improved to run at 3000 seconds (Hall Effect thrusters are already there with inert gases), these costs decrease 50-100 fold for missions to high delta V destinations (Mercury, Jupiter and Saturn).

In Situ Resource Utilization

There are many sites throughout the solar system where water ice exists, either on the open surface or just beneath the surface soil. A large reservoir of water ice will be straightforward to mine, and will enable ships to extract water at their destination or points in en route, and thus reduce or eliminate the amount of water that needs to be launched from Earth to low earth orbit, and also makes high delta V missions easier by breaking them into several legs versus one long inbound or outbound trip that requires a full fuel load. Among the sites known to harbor water ice are:

  • Moon : permanently shadowed areas in lunar craters at the moon’s south pole
  • Mars : polar surface ice, subsurface ice elsewhere (unknown if Phobos or Deimos contain usable amounts of subsurface ice, something the upcoming Phobos-Grunt mission will investigate)
  • Mercury : permanently shadowed areas in polar craters
  • Ceres : thought to contain vast amounts of water ice, equivalent to all of the fresh water on Earth. The NASA DAWN mission will visit Ceres and will provide more detailed data about water resources there.
  • Jupiter and Saturn : the moons of Jupiter and Saturn contain large amounts of water ice. Small, low gravity moons will be especially attractive sites to mine water from due to the ease with which a large ship can land on these sites. In the future, missions to these systems will probably involve side trips to these sites on the way to and from larger moons closer in to the parent planet. This greatly reduces the delta V required on any one leg of the trip, further reducing cost.

In situ refueling has the potential to further reduce mission costs, by a factor of 5 to 10 fold in the case of return refueling (water for the outbound trip from Earth is still launched to LEO), and by 50-1000 fold if water is backhauled to LEO to fuel outgoing ships. In the latter case, only the hull, payload and crew are launched to earth orbit, while water is delivered inward from other sites. Ceres is an especially interesting candidate as an industrial water mining site as it is located mid-way between Earth and the outer planets.

Nuclear Power

Nuclear electric powerplants, combined with high specific impulse engines such as Hall Effect Thrusters, will enable spacecoaches to travel to the outer planets on fast trajectories that reduce trip times from years to about a year in each direction (comparable to a Mars mission). Nuclear powerplants are well understood, but have been politically unpalatable for space exploration (scientists thoroughly explored nuclear rockets, and ground tested them in the 1960s NERVA program, which proved nuclear power was viable for spacecraft propulsion).

Spacecoaches equipped with nuclear electric powerplants need not pose a threat to Earth, as they could be restricted so that they never approach closer than lunar orbit or another rendezvous point that insures they never return to Earth orbit once they are fueled and activated. Nuclear reactors have safely powered naval aircraft carriers and submarines for decades, suggesting that it should be possible to achieve similar results with spacecraft.

Should this type of program be reconstituted in the future, the spacecoach platform will enable humans to travel freely all the way to the outer planets, and do so with trip times that are comparable to a Mars mission or extended stay on ISS. This may or may not happen for many years, but in any case, solar electric spacecoaches should be able to reach destinations throughout much of the inner solar system within a few years of their initial operation, and then be upgraded over time from there.


Even with modest backing, we should be able to complete the design competitions and develop highly detailed, technically feasible system designs within 2-3 years. While the project will require more extensive support to proceed beyond ground testing to actual flight tests, it should be clear whether the system is technically and economically feasible with current materials within a short period of time and at minimal expense. If so, the decision to proceed to unmanned and then manned flight tests should be a straightforward one, especially if private operators play a key role in the development of key system elements, as they tend to be less risk averse, and willing to improvise during the development process.

The bottom line .. it is mostly a matter of will, and if the concept proves to be viable in stage 1 and 2, it should be possible to reach Phobos within a decade. Recall that the Apollo program was developed from a much more limited technology base within ten years, while this platform uses existing technologies that are already in flight or well developed from a technical perspective. While it won’t be easy, and there will surely be unforeseen issues, the technical challenges for this project are far less daunting than reaching earth orbit was in the 1950s and 1960s. We can treat getting to earth orbit as a solved problem by renting space on SpaceX and other platforms, and thus focus entirely on the task of traveling from earth orbit to and from other destinations.

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