Moon Miners' Manifesto

#99 October 1996

Orbit to Orbit Transfers

Peter Kokh

Presently, rockets must carry along all the fuel, and any extra stages, needed to get a payload in its intended final orbit. A payload brought up by the Shuttle destined for a higher orbit than the Shuttle can reach, must carry along a throw-away pre-fueled kick motor to do the trick. Imagine how expensive it would be to fly to another city if we had to pay the freight for bringing along our own taxi (and its fuel) to get us from the arrival airport to our hotel or other destination! Carrying that fuel to orbit means either less allowable payload or a bigger and more expensive booster than would be needed if (a) the vehicle could be refueled upon reaching low Earth orbit, or (b) it was possible to "hire" a kick motor once in low Earth orbit to do the job.

Refueling in low Earth Orbit

A 1988/'89 Space Studies Institute study outlined how such an orbiting cryogenic fuel depot, using spent Shuttle External Tanks, could be set up phase by phase. Most of the liquid Hydrogen and liquid Oxygen needed would be "scavenged" from residual amounts left in other ETs reaching orbit.

There are two logical orbital locations in either case (tankers used serially, permanent filling stations): in the International Space Station yards, and in low equatorial orbit. The latter would be far more useful, being more reachable, with less fuel, from most locations, and at maximum window frequency. An equatorial filing station alone makes sense for payloads bound for geosynchronous Clarke orbit or beyond, for the Moon, Mars, or elsewhere in the ecliptic-hugging Solar System. Building a refuelling station in Alpha Town for vehicles and payloads intended for deep space would be a lot like putting a gateway for Europe-bound Americans in Patagonia.

Kick Motor "Tugs for Hire" - Orbitug Inc.

While the former might be agency operated, heaven forbid, the later is a prime entrepreneurial commercial opportunity. Tugs could be launch company owned and operated (Lockheed Martin, McDonnell Douglas, Boeing North American, Arianespace, Energiya, etc.), or time-share pool operated, or perhaps leased by independent operators. Of the major contractors, Arianespace, able to launch from a 6xN site in French Guiana, has a big advantage.

Legislation to insure the commercial option may no longer be needed but was proposed more than a decade ago in the "Space Cabotage Act." Cabotage means the "coastal" trade in cargo, after John Cabot, the British explorer of the North American Coast (c. 1497). "Coastal' is appropriate as Earth's true "space coast" is not Brevard County, Florida but LEO to GEO orbitspace.

Tug fees would of course reflect weight and delta v required for the orbital transfer. But they would also reflect whether the payload to be boosted was delivered to the tug home base (filing station) or whether the tug had to go fetch it in some other orbit first. Tug return to base fuel expenditures would also have to be paid by the shipper. Now if these fees in total are appreciably lower than the alternative cost of bringing along a one-use throwaway pre-fueled kick motor, we have a viable entrepreneurial space business opportunity.

Tug services would be "by appointment" and reservation only, at least until traffic grew large enough to attract speculative operators, able to "earn a living" through payloads of opportunity.

Nor does the opportunity exist just for traditional chemical rockets. Tether operated momentum boosters, possibly solar powered, could easily carve out a number of high traffic niches

Manned tugs would be useful for carrying replacement parts to already orbiting satellites needing repair. If this service can be profitably provided in a timely fashion at less cost to the satellite owner than the procurement and launching of a replacement satellite, we have another prime commercial opportunity. Such a manned tug would be a natural complement to a commercially owned and operated station or industrial park facility in equatorial orbit, serving as home "port".

Refueling prices could come down once made on Luna fuels are available in quantity and quality. We are talking about lunar liquid oxygen, silane (SiH4, a methane analog and hydrogen "extender"), and possibly powdered aluminum or liquid hydrogen aluminum slurry fuels.

Each of these "enhanced CATS" scenarios wait on a steady growth in traffic to become economically viable. For low Earth orbit is only"halfway to anywhere in the Solar System" [Robert A. Heinlein]. Orbital Filing Stations and Tugs for Hire may be where we will find our CATS price-reducing solutions in this theater of operations. MMM

Contents of this issue of Moon Miners' Manifesto