Our main "pipeline to space" service is based around a High Altitude Platform airship vehicle, which will operate at an altitude of approximately 70,000 ft. This will serve as a launch and landing strip for an autonomous suborbital space plane which will weigh about 30 tons at takeoff. This will achieve a suborbital velocity of about 4.5 km/s and deliver about 4 tons of fuel and cargo to the second phase vehicle. The phase two vehicle will decelerate from orbit using an aerobrake surface, rendezvous with the first stage vehicle at its suborbital apogee, and then accelerate to a suborbital velocity of about 6.5 km/s, where it will deliver about 2 tons of fuel and cargo to the third phase vehicle. The phase three vehicle will be similar to the phase two vehicle but lighter still. It will also decelerate using aerobrake and rendezvous with the stage two vehicle, and then accelerate to full orbital velocity of about 7.8 km/s. Once in orbit it will transfer the cargo of about 1 ton to a yet lighter orbital transfer vehicle which will deliver it to its first destination in space, normally either a space station or a fuel depot.
Once the first stage vehicle has finished its rendezvous transfer manoeuvre, it will aerobrake back to a wheeled landing on the High Altitude Platform. The other vehicles will be stationed in orbit and be refurbished when necessary in workshop facilities attached to a space station. The principal behind this pipeline system is that all vehicles involved are specifically designed and optimised for the task they do and the environment in which they operate. This makes them more efficient and enables them to operate with less relative stress and to achieve a high degree of reusability.
The challenge of this approach is to carry out the rendezvous and transfer manoeuvres reliably. Three such manoeuvres must be executed for each load of the order of 1 ton that is delivered to space. Given the low cost of this system, even if only one in every two attempts successfully delivered a cargo to orbit, the method would still be very cheap. However, in the first instance it is intended to aim for at a failure rate of only one flight in 1000 attempts. A missed rendezvous would result in a failsafe procedure whereby all craft would simply return to there previous positions to try again, the only real penalty would be the cost of the fuel involved.
Rocket fuel is not normally considered a major expense in space flight operations, but at about $3000 per ton for rocket fuel grade liquid hydrogen, this would be an important factor in a system that has few other expenses and which uses about 5 tons per flight. This will reduced significantly by manufacturing the liquid hydrogen fuel on a large support airship at lower altitude. The hydrogen fuel and the cargo for each flight will be brought up to the HAP by a transfer airship. The liquid oxygen fuel for each flight will weigh about 20 tons. This will be manufactured by a separate HAP vehicle which will operate in tandem with the main launch HAP. The L02 fuel required for each flight will be transferred to the launch HAP via an umbilical connection shortly before the flight commences.
All cargo transferred to space by this pipeline will either be prepared as part of the pipeline infrastructure itself in the case of common liquid cargoes such as LOX or LCH, or in the case of solid goods, they can be brought to a support airship at the base of the pipeline by transport airships from their place of origin. Hence every phase of the pipeline will be not only very efficient, but environmentally friendly. All rocket operations will involve small craft operating at a minimum altitude of about 70,000ft and usually in a region remote from any population centres. A single HAP platform and associated craft can easily put 20 tons per day into LEO. Allowing for refurbishment, it can conservatively put about 5000 tons per year to LEO. A fleet of 200 such pipeline systems, could then lift 1,000,000 tons per year to LEO - of basic materials and small goods that can be accommodated within a 1 ton cargo limit.
At least 70 percent of all materials required for a developing space economy can be lifted to LEO in this fashion, and with the increasing use of simple and powerful additive manufacturing methods that can be used in orbit, this figure could rise substantially. In any case, as can be seen in the subsequent section on IST ground launch systems, having cheap rocket fuel available in orbit will substantially reduce the cost of lifting bulkier cargoes to LEO by appropriately designed reusable shuttle craft.