By Gary Michael Church
The recent crash of the Virgin Galactic “spaceship one” has identified a need to clarify for the public what the term “spaceship” is all about. When a vehicle that cannot even achieve Low Earth Orbit (LEO) is called a spaceship it should be explained such a label is at best a misrepresentation. The first part of space-ship is the space through which the ship ostensibly travels. Space by one definition begins at an altitude of 62 miles. Any conveyance that carries human beings to other planets requires a different measure to be taken seriously. That mark may most logically be set at 22,236 miles above the Earth. A complete 165,000 mile circle around the Earth’s equator at this altitude is known as GEO, or Geostationary Equatorial Orbit. An object in this orbit hovers over a single spot on the surface of the Earth and this is where the present junkyard of mostly dead communication satellites and associated hardware reside. It is at this altitude where a “ship” can most easily begin a voyage to the nearest heavenly body, the Moon. LEO does not really qualify as “space” considering this domain is far below the Van Allen radiation belts that soak up most of the harmful radiation coming from solar storms.
This is an important distinction because interplanetary travel beyond the Moon will most likely never begin in LEO or for that matter even GEO due to nuclear safety concerns. The reason deep space travel will begin from the vicinity of the Moon is the magnetic field, or magnetosphere, surrounding the Earth and extending out almost to the Moon. Any true spaceship capable of carrying human beings on journeys to the outer solar system would necessarily be nuclear propelled in order to accomplish such missions within psychological time limitations of well under a decade. The necessity for nuclear energy arises due to the very large mass of shielding required to protect space travelers from a certain form of Galactic Cosmic Radiation (GCR) that permeates deep space. Chemical rocket propellants and any form of electric ion propulsion are incapable of pushing such a mass of shielding around the solar system in a timely manner. Presently and for the foreseeable future the only practical nuclear propulsion system for a spaceship capable of multi-year missions uses atomic bombs or, more efficiently, H-bombs. This system, known as Nuclear Pulse Propulsion, cannot be “lit” anywhere within the magnetosphere because the radioactive fallout would eventually funnel down into the Earth’s atmosphere.
The minimum effective GCR shielding for a small capsule is about 400 tons. The psychological requirements for living space mean a larger spaceship and the thousands of tons of shielding required are most efficiently acquired from the Moon. Water derived from lunar ice is the most utilitarian form of shielding and can also be used as fuel in mission scenarios to icy bodies such as Ceres and the moons of the gas giants. The bombs used in pulse propulsion systems superheat any hydrogen rich material, such as water, into a cloud of plasma that pushes the spaceship in steps, or pulses, to the extreme speeds required. A spaceship can thus cut down on the fuel mass it must carry by burning its water shield to slow down upon approaching an icy body and after landing quickly convert the local ice back into shielding as well as fuel for the return journey. Upon return the spaceship can again burn its radiation shielding as it slows down near the Earth’s Moon. Due to the availability of ice, and the ability to land even a large spaceship on low gravity icy bodies, Mars is not the best first destination for a human deep space mission. The best candidate is Ceres and then moving on to the several moons of the gas giants that may have living subsurface oceans. The only place to acquire shielding, assemble, test, and launch such nuclear missions, is our own Moon.
Exactly what the first spaceship carrying humans to the outer solar system will look like depends on the best all-around engineering solution. There are several variations, from a “soft spaceship” that resembles in some ways a jellyfish with a parachute-type pulse engine, to a “hard spaceship” that is constructed of more massive solid components. A limited capability parachute spacecraft could possibly even be assembled in an elliptic high Earth orbit and avoid some of the contamination problems but such a vehicle would be extremely small, the risks high, with nowhere near the capabilities a larger version utilizing lunar resources would have. The minimum mass of GCR shielding would be quite expensive to bring up from Earth instead of acquired on the Moon. It would not qualify as a proper spaceship. Unless some form of suspended animation was perfected allowing for a much smaller crew compartment, this smaller non-spaceship would be so limited in range and endurance it would have no place to go. The temptation to “go cheap” has been found to be a worthless dead end and revealed the path to human deep space travel as very inflexible. There is no smaller, cheaper, flexible path. These limitations leave the Moon as the first stop, the gateway to the solar system, and only destination for beginning any realistic program of space exploration.