Space Transportation - mmmt_transportation.pdf - Moon Society

As flights are short, the reconfiguration of seat backs and postures or the closing off of clumsy cramped
crawl-space passageways and gimballing of pods are bound to be distracting, cumbersome, and annoying. Mere
annoyance could change to trouble fraught with danger if a seat resists reconfiguration or a pod decides not to
gimbal. It is curious that NASA which shrinks from tests of artificial gravity because of the engineering challenges,
embraces a configuration which almost mandates one contrived Rube Goldberg accommodation or another. But there
is a history of this, witness the Shuttle tile thermal protection system which is just as unnecessarily contrived (and
expensive), mandated by an unnecessary choice of reentry attitude and angle.
In contrast, the VTOL, vertical take off and land, and HOTOL, horizontal take off and land, offer one simple
unchanging configuration throughout both legs of the flight. “KISS,” i.e. “keep it simple, stupid!” Fans of VTOL, the
Delta Clipper’s way of doing things, point out that a Clipper-configured craft could land on the Moon and take off
again whereas a VentureStar-patterned craft could not.
VTOL would give us CATS and CATL (Cheap Access To Luna) in one craft. That is tempting. But is it the best
route. Could their be cheaper craft specialized for LEO (Low Earth Orbit) to Luna runs just as VentureStar is best
specialized for ground based shuttle operations to space on a thick atmosphere world? We must explore and test all
the options. Only then can we have confidence in our choices. “God and Heinlein decreed that rockets should take off
and land on their tails!” Maybe. Maybe not. I see problems with VentureStar’s mixed mode operation. But it may just
work.
By 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 throwaway 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
Given enough traffic following a given route into space, it should be feasible to orbit automated or remote
control “tankers” that they could tap robotically or by teleoperation. Such a tanker could be sent up full, to be replaced
and deorbit when empty. In time, permanent refueling stations parked in handy orbits, could “purchase” unneeded
residual fuels and oxidizers from some vehicles to “sell” to others needing to refill or top off their tanks.
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 refueling 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.
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