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Fig. 9.10 Internal arrangement of the Skylon SSTO spaceplane concept (courtesy Reaction Engines Limited)

Fig. 9.11 There is no real up or down in free-fall, in orbit, or between planets. These astronauts are enjoying a few moments of free-fall inside NASA's converted KC-135 (courtesy NASA)

while the spaceplane must carry a large proportion of it inside the fuselage as well. The body of the spaceplane may have a bulged appearance, so that it can contain enough propellant for it to reach orbital speed. This is a good thing, of course, because the same design attribute which is required to enable SSTO spaceflight also makes the advanced spaceplane the perfect space tanker, which is needed for the Lunar tourist economy.

But what about tourist accommodations? Spaceliners bound for the Moon will be outfitted with a large number of viewports, lounges, sleeping areas with "bunk-bags," and zero-G restrooms. Unlike today's International Space Station, which appears on NASA television to have an untidy, jumbled interior, the spaceliners of the future will arrange their cabins so that there is a "visual up" and a "visual down." There will be decks, bulkheads, and overheads, as in any ship. On the deck will be neatly arranged tables and chairs, on the bulkheads will be port holes and paintings, and in the overhead will be recessed lighting. There may be shelves of books on some walls, with special arrangements to keep them in place. And there will be flat-panel display screens, firmly anchored to the bulkheads, with a definite "up" and "down." If some passengers wish to float upside down during the zero-G flight to the Moon or in orbit, they will be free to do so (Fig. 9.11). But for the psychological well-being of all passengers, the accommodations will be made to appear as normal as practical. Above all, the jumbled appearance so characteristic of the interior of government spaceships will be avoided.

What will the cockpit look like? The pilots' stations will look very much like those you would find in any airliner, and many of the controls would be familiar to any pilot. The control yoke will be replaced with a control stick, similar to those found in jet fighters. This will be done for the practical reason of attitude control in space. In flight, aircraft have three mutually perpendicular axes of motion: pitch, yaw, and roll. Pulling back on the stick pitches the nose up, and pushing forward pitches the nose down. Moving the stick to the left rolls the wings counterclockwise, and moving it to the right rolls the wings clockwise, as seen from the pilot's station. Yaw control in the atmosphere is normally accomplished by means of foot pedals, but in space, a twist of the stick will accomplish this function, because the hand is far more dexterous than the foot. Therefore, although the spaceplane will be equipped with foot pedals for yaw control in the atmosphere, this function will be accomplished by a control stick twist while in space. There will be a switch on the instrument panel or pilot's console that will enable or disable attitude control thrusters. At heights above 100,000 ft or 20 miles, this switch will be turned on so that the spaceplane will not lose control due to lack of sufficient aerodynamic forces operating on the conventional control surfaces.

Radar altimeter will be one instrument common to all spaceplanes, especially those outfitted for Lunar flight. Conventional aircraft rely on barometric air pressure to indicate altitude. But because there is no air on the Moon, the only way to accurately determine altitude above the ground is by radar.

The advanced Lunar spaceplane of the future will be equipped with ventral thrusters to enable landing in the manner of a Harrier jump-jet. This maneuver may be termed vertical landing in a horizontal attitude, or VLHA. The same acronym refers to vertical liftoff in a horizontal attitude. Lunar-landing spaceplanes will all be VLHA vehicles. A level landing pad cleared of all debris will be necessary before this is attempted. Unlike the DC-X, there will be no danger of the Lunar spaceplane tipping over on the Moon, for the same reason that airplanes are not plagued by this problem on Earth. Spaceplanes of the future will have VLHA capability on the Moon long before they develop this ability on Earth. The reason, of course, is that the Moon has only one sixth the gravitational acceleration of Earth, and so only one sixth the thrust is required to land or lift off.

Eventually, ultra-advanced spaceplanes will appear, with the ability to perform VLHA on Earth as well as on the Moon. This capability will actually increase the safety of these craft, because they will have a much smaller probability of crashing in bad weather on Earth. They will simply "hover" their way to a precise radar-controlled landing on any planet. These kinds of craft will likely not appear for many years, but they will appear eventually.

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