I’m doing some science research before starting seriously on my next book. My first book is Entering Space: Creating a Space Faring Civilisation by Robert Zubrin, published in 1999.
The first thing I learned was that the biggest obstacle to space travel is gravity.
Current-day rockets ... can deliver about one percent of their take-off mass to orbit - - most (about 90 percent) of the remaining mass is propellant.
The heavier the payload, the more fuel you need, but the fuel weight adds to the payload and needs a bigger rocket to hold it, which weighs more, etc etc. Hence the search for a more efficient engine and /or fuel. The book talks about methods of propulsion in a later chapter.
This is not the only reason for the decline in space projects. The author goes on to explain the relationship between the US government and the engineering and aerospace industries which means they are protected from foreign competition and can effectively charge what they like. This caused space exploration to stagnate and become almost unaffordable. There is no incentive to reduce costs or to innovate.
Another major factor in launch costs is the fact that almost all existing launch vehicles are partly or wholly expendable.
Of all the methods of transportation known to human history, only launch vehicles are descended from ammunition. When John Glenn travelled to orbit in 1962, he rode atop an Atlas rocket. The Atlas was an ICBM directly derived from the German army's V-2, which itself was simply a replacement for the Paris Gun and other long-range artillery forbidden Germany by the victors of World War I.
Because launch systems are expendable there is no need for landing gear, a deceleration system, or a re-entry thermal protection system. That reduces the weight and makes things simpler all round. They also don't need servicing or maintenance. The author says that the Space Shuttle ground support team is virtually a standing army with an annual cost (in 1999) of $5 billion per year.
Ann Marie Thomas is the author of four medieval history books, a surprisingly cheerful poetry collection about her 2010 stroke, and the science fiction series Flight of the Kestrel. Book one, Intruders, is out now. Follow her at http://eepurl.com/bbOsyz