The Russians are shuttling astronauts to the International Space Station (ISS)
while the USA’s Space Shuttle Program is under review. Unfortunately, the
Russian Space Agency (RKA) has fallen upon hard times itself and so must place
the following restrictions on its mission. Your task is to plan a series of
steps that will get all four astronauts to the ISS.
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The RKA has only one shuttle but can use it many times for this mission.
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The RKA’s shuttle can carry only two astronauts at a time (a driver and a
passenger.)
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The shuttle has no auto-pilot and so must have a driver for each part of the
mission.
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The RKA has only 14 units of fuel allocated for this mission.
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Contrary to any physical explanation, the shuttle must consume one unit of fuel
for each unit of weight of the HEAVIEST of the two astronauts. Thus if a 5 unit
astronaut and a 4 unit astronaut travel then the trip will take 5 units of
fuel.
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Inexplicably, rule 5 also applies to return trips. However, you will most
likely send only one astronaut back with the shuttle each trip so his/her
weight will determine the fuel consumed.
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The four astronauts weigh 1, 2, 5, and 7 units and their names are 1, 2, 5, and
7 respectively ;)
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