"I do not know what I seem to the world, but to myself I
appear to have been like a boy playing upon the seashore and
diverting myself by now and then finding a smoother pebble or
prettier shell than ordinary, while the great ocean of truth lay
before me all undiscovered."
Sir Isaac Newton
If we are used to the ever increasing dependence on transport for our terrestrial endeavors, the colonists will find it even more crucial, for it will become the only physical link between a far off , isolated world in outer space and its home planet, the Earth.
Designing a cost efficient transportation system will not only provide a good technical solution but being able to supply eventual dwellers with frequent schedules of incoming and outgoing flights to and from the Earth will help to dispel their fears. If some day passenger flights become as commonplace and reliable as today's airline schedules the colonists will be less afraid of the remote isolation of their dwelling.
Transport requirements will be diverse and complex. It must be clearly distinguished that during the construction and development phase demand for transportation will be radically different from the requirements that will have to be met on a day to day basis when the colony is running.
During the construction and development phase some sort of transportation system will have to be designed in order to haul enormous quantities of construction materials to the libration points where the settlement will be built. These transportation materials will alternately come from the Moon, the Earth and eventually the asteroid belt.
Both during the initial stages and during the everyday running of the colonies, some supplies will have to be inevitably transported from Earth. As time progresses and the colony attains total independence, the requirements for supplies will logically diminish. However, the transportation system must be ready to resume normal operations in case of emergencies such as crop failures, etc.
At all times, colonists will arrive in the colony and some will leave the settlement temporarily or to go back to Earth. Again during initial stages passenger traffic will be intense in order to populate the settlement. Later on, it would be desirable to have frequent flights (once a week, for example) to provide for emergencies and to make settlers feel that the are really not so far from the Earth.
A modified version of the Space Shuttle could be used to put passengers into LEO
Asteroid belt : source of construction materials
Moon Base : Intermediate storage area for moon mined construction materials. Storage of emergency supplies. Passenger transport.
Low Earth Orbit Space Station : Passenger transport. Emergency source for light weight supplies.
Earth : Construction Materials. Supplies. Passenger transport.
Before actually deciding on the vehicle design and configuration, the first logical step would be to decide on an operational transportation system layout, that is, on the type of vehicles that will be needed and their specific requirements.
A heavy lift vehicle will be required to haul construction materials and heavy supplies into the settlements. This vehicle or transportation method should logically be unmanned and not necessarily use conventional propulsion. Distances will be substantial, and lift capacity important, for it will have to travel all the distance from the Earth overcoming its gravity well, or else from the Moon or the asteroids.
In all cases construction materials will be quite heavy, so boosters must be powerful enough. Speed is not necessarily a critical factor, for materials and or humans will be transported, and although distances are considerable they are not so far off.
Probably two subsystems will exist here : one to tug materials from the asteroids, where there are no launch requirements (the vehicle will drift off from the colony and push on to the asteroids, with no gravity well to be overcome, and viceversa) and another one to send materials from the Earth and the Moon, where lunch constraints are important.
This unmanned heavy lift vehicle should be cost efficient, because as it will not be designed to transport humans, multiple redundancies and extreme security measures that are common in spacecraft will not need to be engineered.
Although the heavy launch vehicle could be used to transport supplies once the colony is built, it would be a good idea to dispose of an intermediate vehicle capable of transporting supplies from Earth onto Low Earth Orbit or directly to the colony. This would ensure a more frequent replenishment of supplies rather than sporadic flights of huge cargoes. Such a scheme would add flexibility top the system.
An artist�s conception of a future heavy lift launch vehicle rolling out of the VAB.
A passenger transport vehicle should not differ much from present transport to LEO. Although this will be further analyzed subsequently, it seems plausible to have a shuttle derived system to place humans in the LEO Space Station and then push on by means of a lighter excursion vehicle to the colony.
In such a way, the Space Station can act as an intermediate point in the route and permit for initial adaptation to space. The excursion vehicle would also return passengers to the LEO Space Station where they would await incoming shuttle flights in order to return to earth.
This scheme again provides the greater flexibility and a gravity rationale. Most of the energy is consumed in actually placing the person in Low Earth Orbit, so transit between the Space Station and the colony would be both fast and economical. Although the Space Station can hardly be considered Earth, it is closer to home than the Space Settlement, and an easy transit to it will help in the already expressed idea of making the colonists feel less isolated.
This system would also double up as transport for lightweight emergency supplies (medicines, etc.)
It is obvious that al of these vehicles should be very carefully engineered so as to provide maximum security.
If an object is to be hurled out into space, a tremendous force must be supplied for it to go up and escape the Earth's atmosphere and venture into outer space.
Newton's third law, known as the principle of action and reaction, states that whenever a force is applied onto a certain object, that object will react with a force that is of equal magnitude and opposite direction to the first force. That is, if we apply a force we will receive the same force on us. If we pull a cart, our body will need to overcome the reaction of the cart that pulls back from us and thus move it.
That same reaction can be used to produce a movement. If we go ice-skating and we exert a force on a wall, the reaction of the wall will move us back.
A rocket is a device which uses this reaction to hurl itself upwards. The rocket chamber is filled with propellants, that is, elements that produce some sort of a reaction which results in an enormous pressure exerted on the air below. In turn, this air reacts with that same pressure on the rocket producing the necessary thrust that will result in lift-off and flight.
A possible design for an excursion vehicle.
A good example of the above process is constituted by chemical propulsion. In it, fuel burns in the presence of an oxidizer (there is no oxygen in space) to produce a violent exothermic reaction.
All rockets launched so far have used chemical propulsion. Some propellants provide more specific impulse than others, but no technological breakthroughs are expected in this specific type of propulsion.
In chemical propulsion, both solid and liquid propellants can be used. Liquid propellants have a higher specific impulse (the amount of impulse that is obtained per pound of fuel) but are more dangerous to handle, for they must be pressurized and cooled. Typical liquid propellants are liquid hydrogen and liquid oxygen.
Solid propellants are easier to handle, but their specific impulse is lower and generally, once ignited, they have to be consumed. (Shuttle instructors usually say : "Once the SRBs are lit, you have two options : you launch, or you launch")
The nuclear rocket engine is twice as efficient as the conventional chemical propulsion energy. This engine, which was under development in the U.S. in the 1960s and 1970s, uses liquid hydrogen, which is converted to gas and heated by means of a nuclear fission reactor to very high temperatures. The hydrogen does not burn but simply passes through a rocket nozzle at high pressure and velocity. It is designed for use in space rather than for launching from earth into space.
Ion engines have also been proposed for space flight. Their source of fuel would be an easily ionizing substance, such as cesium metal, to supply ions, or charged particles. A generator or solar batteries would produce an electric field that would repulse the ions strongly enough to eject them from the engine, thereby generating thrust. Such engines would produce very little thrust, but they should be able to operate for long periods in interstellar flight
This deep space transportation method, originally suggested by Tsiokolsky, utilizes solar flux to propel a spacecraft by means of a solar sail. The solar wind is a stream of charged particles, mostly high velocity electrons and protons, emanating from the solar corona.
The lightsail makes use of the solar photon flux for propulsion. While photons have no rest mass, they do have mass in motion, and thus momentum. Upon collision with the reflective sail material the photon will be reflected and thus apply a force to the sail. The size of the total force on the body of the craft will thus be proportional to the sail's area.
The applied force can be directed by tilting the sail with respect to the incoming photon flux, which will change the direction of the acceleration applied and thus the spacecraft's orbit.
A solarsail spacecraft design
With the exception of the Delta Clipper test flights, and of course the Space Shuttle, that is partially reusable, no other rocket that has gone into space has been completely reusable.
Following the idea of disposing of its mass as it used, rockets have staged and discarded their parts as the propellant for that stage is consumed.
This is highly efficient from the point of view of propulsion, but very inefficient in terms of costs, for the rockets can only be used once. The Apollo spacecraft and the Saturn V booster were perhaps the epitome of propulsion efficiency, shedding their parts and finally reentering the Earth in a tiny capsule.
On the other hand, the Single Stage to Orbit (SSTO) concept, consists in a single reusable spacecraft that launches vertically and lands by aerobraking. The Delta Clipper, who has undergone successful test flights and is now awaiting further development, has demonstrated the feasibility of this concept.
SSTO rockets should carry huge quantities of propellants in order to make the round trip. However, the concept of ISMU (Indigenous Space Materials Utilization), could help it materialization.
If propellants are mined from the Moon or other likely sources the rocket would only need to carry enough propellant to make the one way trip and then be refurbished in space. The Moon, for example, is abundant in oxygen, trapped in the mineral ilmenite (FeTiO6). Ilmenite processing would not only yield oxygen but also titanium, a lightweight but highly resistant metal for construction.
This subsystem is the critical issue in transport, for the other vehicles should only be more efficient versions of current technology. Heavy Lift capacity will ultimately make possible the transportation of construction materials to the settlement, which is a capability that cannot be achieved with current rockets
Materials from the Earth and the Moon: An essential characteristic of this subsystem is its capacity to lift off vertically heavily loaded with construction materials and heavy supplies, overcoming a deep gravity well.
Launching a rocket from the Earth implies that strict security measures must be enforced. Nuclear propulsion is very promising, but concerns on safety of nuclear engines have stagnated the development of this propulsion method.
In order to be realistic, chemical propulsion is chosen for the heavy lift launch vehicle. Because oxygen will have to be produced for the space colony and at an eventual lunar base, the ISMU concept will have to be put into practice, thus potentially increasing the weight to lift ratio of the rocket.
Reusable SSTO rockets constitute a more rational option than disposable rockets, so they will be ultimately preferred even if they are not current technology.
The asteroid freighter : In order to obtain construction and other materials from the asteroids, as no launch capabilities are required , non conventional propulsion would be used. Solar sails are economical, but offer limited speed, which would not be a problem with adequate planning. Nuclear engines could also be developed in space, where risks of an accident's effects are lower.
Mass driver : A very well known source of electromagnetic propulsion is the mass driver. A coil is wrapped around a meal bucket that has further coils. When a current (for example converted from the Sun's energy) is driven around the external coil, it induces a magnetic field that accelerate the bucket. If the bucket contains a payload, it could be accelerated to very high speeds. The mass driver has been tested, but it is not yet ready to be used as a standard device.
The main problem with using a mass driver is that in some way or other, the free bucket must be caught or stopped at the construction site, that is, violently decelerated from its speed to rest.
A more advanced version of a shuttle based vehicle could be used to put passengers into LEO in the Space Station. This vehicle should also be able, as it was said, to transport light emergency supplies in the same way it would do to service the Space Station.
The excursion vehicle should be a completely new design, for it need to have no launch capability, moving from one point in orbit to the libration point. Conventional chemical propulsion could be used by taking advantage of the oxygen extracted from ilmenite at the potential MoonBase.
�Mankind will not remain on Earth forever, but in its quest
for light and space will at first timidly penetrate beyond the
confines of the atmosphere, and later will conquer for itself all
the space near the Sun.� -
Konstantin E. Tsiolkovsky
�And then, the Earth being small, mankind will migrate into
space, and will cross the airless Saharas which separate planet
from planet and sun from sun. The Earth will become a Holy Land
which will be visited by pilgrims from all the quarters of the
Universe. Finally, men will master the forces of Nature; they will
become themselves architects of systems, manufacturers of worlds.�
-
Winwood Reade
Comments and suggestions : [email protected]
NAS contact: Al Globus
|
Curator: Al Globus If you find any errors on this page contact Al Globus. |
 |
This site was hosted by the NASA Ames Research Center from 1994-2018 and is now hosted by:
