The biggest obstacle to human space exploration and colonisation of the solar system are not the distances involved, but rather our hard-to-escape imprisonment - Earth gravity well. Conventional way using only chemical rockets has surely achieved a lot in the past, but it still doesnt allow practical space colonisation. Present-day launch costs are very high — $10,000 to $25,000 per kilogram from Earth to low Earth orbit (LEO). Thats after 100 years of chemical rocket development - clearly we need far more cost-effective ways if we ever want to settle space. So, what are the best options?
A launch loop or Lofstrom loop is a design for a belt-based maglev orbital launch system that would be around 2000 km long and maintained at an altitude of up to 80 km (50 mi). Vehicles weighing 5 metric tons would be electromagnetically accelerated on top of the cable which forms an acceleration track, from which they would be projected into Earth orbit or even beyond.
The published cost estimates for a working launch loop are significantly lower than a space elevator, with a greater launch capacity, lower payload costs and similar or greater payload masses; and unlike the space elevator no new materials need to be developed. The structure would constantly need around 200 MW of power to keep it in place.
The system is designed to be suitable for launching humans for space tourism, space exploration and space colonization with a maximum of 3g acceleration.
Lofstrom estimates that an initial loop costing roughly $10 billion with a 1 year payback could launch 40,000 metric tons per year, and cut launch costs to $300/kg, or for $30 billion, with a larger power generation capacity, the loop would be capable of launching 6 million metric tons per year, and given a 5 year payback period, the costs for accessing space with a launch loop could be as low as $3/kg.
http://launchloop.com/LaunchLoop?action=AttachFile&do=view&target=launchloop.pdf - Original Launch Loop paper
In contrast to a space gun, a mass driver can have a length of hundreds of kilometers and therefore achieve acceleration without excessive g forces to the passengers. It can be constructed as a very long and mainly horizontally aligned launch track for spacelaunch, targeted upwards at the end, partly by bending of the track upwards and partly by Earth's curvature in the other direction.
Natural elevations, such as mountains, may facilitate the construction of the distant, upwardly targeted part. The higher up the track terminates, the less resistance from the atmosphere the launched object will receive.
By being mainly located slightly above, on or beneath the ground, a mass driver may be easier to maintain compared with many other structures of non-rocket spacelaunch. If not underground then it still needs to be housed in a pipe that is constantly vacuum pumped in order to reduce drag.
In order to be able to launch humans and delicate instruments, it would need to be several hundreds of kilometres long. For rugged objects, with magnetic assistance, a significantly smaller, circular, track may suffice.
A mass driver on Earth would be a compromise system. A mass driver would accelerate a payload up to some high speed which is not high enough for orbit. It would then release the payload, which completes the launch with rockets. This would drastically reduce the amount of velocity needed to be provided by rockets to reach orbit, since most fuel is needed for the initial phase of conventional rocket launch. On Earth, a mass driver design could possibly use well-tested maglev components.
Another promising method could be beam-powered propulsion, when powerful laser is aimed at the craft which can concentrate this energy to combust a propellant or even the air, producing thrust.
A lightcraft is a vehicle currently under development that uses an external pulsed source of laser or maser energy to provide power for producing thrust (beam-powered propulsion).
The laser shines on a parabolic reflector on the underside of the vehicle that concentrates the light to produce a region of extremely high temperature. The air in this region is heated and expands violently, producing thrust with each pulse of laser light. In space, a lightcraft would need to provide this gas itself from onboard tanks or from an ablative solid. By leaving the vehicle's power source on the ground and by using ambient atmosphere as reaction mass for much of its ascent, a lightcraft would be capable of delivering a very large percentage of its launch mass to orbit. It could also potentially be very cheap to manufacture.
Early in the morning of 2 October 2000 at the High Energy Laser Systems Test Facility (HELSTF), Lightcraft Technologies, Inc. (LTI) with the help of Franklin B. Mead of the U.S. Air Force Research Laboratory and Leik Myrabo set a new world's altitude record of 233 feet (71 m) for its 4.8 inch (12.2 cm) diameter, 1.8 ounce, laser-boosted rocket in a flight lasting 12.7 seconds. Although much of the 8:35 am flight was spent hovering at 230+ feet, the Lightcraft earned a world record for the longest ever laser-powered free flight and the greatest "air time" (i.e., launch-to-landing/recovery) from a light-propelled object. This is comparable to Robert Goddard's first test flight of his rocket design. Increasing the laser power to 100 kilowatts will enable flights up to a 30-kilometer altitude. Their goal is to accelerate a one-kilogram microsatellite into low Earth orbit using a custom-built, one megawatt ground-based laser. Such a system would use just about 20 dollars' worth of electricity, placing launch costs per kilogram to many times less than current launch costs (which are measured in thousands of dollars).
Myrabo's "lightcraft" design is a reflective funnel-shaped craft that channels heat from the laser, towards the center, using a reflective parabolic surface causing the laser to literally explode the air underneath it, generating lift. Reflective surfaces in the craft focus the beam into a ring, where it heats air to a temperature nearly five times hotter than the surface of the sun, causing the air to expand explosively for thrust.
I have not included presently unrealistic methods which require some new technology breakthrough, like antigravity or high tensile strenght materials. Even without them, we are still able to make Earth to LEO trip more practical and cost-effective.
The estimated cost of the Launch Loop concept does not exceed 30 billion dollars, electromagnetic catapults would be far less costly, but offer not so promising launch costs (still far less than current method). Compare that to estimated Iraq War cost - $100 to $200 billion, or even with NASA and ESA budgets, its not that high cost for the benefits it could bring.
For 200 billion, we could already have 5 Launch Loops or many more EM catapults running, driving the launch costs to few dollars per kilogram or even less. Shouldnt we concentrate on this rather than "big dumb booster" approach aka Constellation? It does not have the promise for vastly reducing launch costs.. What do you think?