Space travel. The mere idea fosters images of technical ability without limit. Yet, it’s been over 30 years since we’ve placed people on the Moon. Certainly, we’ve got probes and satellites all about but a couple of people in low-Earth orbit is the best we now achieve with putting ourselves into the picture.
Further, satellites crash back into Earth and probes run out of energy to operate. As well, people need to be transferred to and from the space station. Maintaining our existing capabilities requires constant rocket launches. Rockets rely upon energy from fuel. This energy mostly originates with petroleum.
Can we continue our space adventure without petroleum. Let’s balance the energies. The Saturn 5 rocket placed people on the Moon. It used 702 611 kilograms of liquid hydrogen. With an energy density of 143 MJ/kg, the fuel contains nearly 1e14 joules of energy. For one flight!
Switch-grass is now touted as an ethanol source. However, the energy from 10 000 hectares of switch-grass is equivalent to one rocket launch. Assume we have a 50% efficiency energy transfer from ethanol to liquid hydrogen, then we need 20 000 hectares of switch-blade to make enough liquid hydrogen for one flight of the Saturn C5.
However, we also need liquid oxygen to oxidise the fuel. Separating and chilling oxygen requires about 1179 hectares worth of the switch-blade’s energy. Assume Saturn’s remaining material, over 100 tonnes worth, had the energy demand of the primitive forging of iron. This needs energy and charcoal of the equivalent of about 10 hectares of typical temperate forest. This isn’t a lot but it took hundreds of years for this patch of mature forest to contain enough energy to meld the iron.
If we wanted 4 launches a year, we’d need energy from about 100 000 hectares; about the area of Rhode Island. But this energy is a simple estimate of the material. No consideration is made for infrastructure or workforce. The Apollo program had a material to non-material ratio of about 1:130. If this stayed the same, then four annual spaceflights comparable to the Saturn 5 requires the energy of 13 million hectares, close to the area of Louisiana.
Of course, to continually maintain this launch rate, we’d need this area every year and have to wait for harvested areas to rejuvenate. This could amount to over hundreds of millions of hectares; close to the area of the continental USA. Will humankind have the desire to commit such a vast area of vegetation so a spaceport can send a few people out to learn more of our existence? If not, where does humanity’s future lie?
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