Its been 50 years since Willy Ley and Wernher vonBraun completed their
book EXPLORATION OF MARS - and not much as been done but talk since
then.

That book, along with Disney's work, and the Collier articles five
years earlier, and the Mars Project in 1953 introduced the concepts of
interplanetary travel to the public a year before Sputnik.

The back of the book has an appendix and works out the payload weights
and other details of the launchers, engines, and interplanetary travel.

I'm sure if vonBraun were alive today and asked why we haven't been to
Mars yet, he would say, we lacked the will to do it.

http://history.msfc.nasa.gov/vonbrau...y_article.html
http://homepage.mac.com/srogers4/roc...etro/vonbraun/
http://home.flash.net/~aajiv/bd/colliers.html

Is that the real reason why we haven't done this yet?

Maybe, maybe not. Here's another answer;

http://www.spacedaily.com/news/rocketscience-03zzf.html

You can get an updated version of one of these reports by von Braun at
Amazon

http://www.amazon.com/gp/product/025...Fencoding=UTF8

Csomic radiation is a problem with a long-duration journey. We could
however house the piloted modules within tanks of water and propellant
used for the mission to afford some protection. Also, MEMS
(micro-machine technology) appears capable of creating millions of tiny
life support systems operating in parallel to maintain air and water
quality for the crew. Such systems have very high reliability at the
system level, if common mode failures can be avoided. So maintenance
need not be an issue.

Modifying the Shuttle's external tank so that it becomes a flyback
booster, and taking this booster and propelling it with five SSME class
LOX/LH engines at its base and arranging six boosters to operate in a
particular cross-feed arrangement - can quickly get us (for about $6.4
billion) a 500 metric ton to orbit RLV.

This vehicle would be developed as a launcher for a light-weight Solar
Power Satellite - and a fleet of five would have a launch rate of 1 per
week. The Inflatable SPS would have a GW useful power - and beam
energy anywhere on the Earth visible to it. But, it could also do
double duty as a launcher for a Mars expedition.

The Mars Ship would use this updated External Tank / flyback booster as
a basic airframe for interplanetary flight - just as the SIVB was used
to create SKYLAB,and would provide a low-cost path to long-duration
missions. A fully functioning long-duration system could be put into a
single modified External Tank airframe - and six additional external
tanks could cluster around it - carrying needed propellants and
providing sheilding - each tank propelled by a cluster of five RL10
derived engines operating at high expansion at 461 seconds

Off-gassing of cryogenics would provide cooling of the long-duration
mission module, and would also provide hydrogen and oxygen to power
fuel cells on board the module. Water produced would be potable and
consumed by the crew, and run cryogenic refrigerators to return the
bulk of the off-gassing propellants to their long term storage tanks.
Hydrogen would also be used to scrub the air aboard the module,
producing hydro-carbons, the hydro-carbons and dirty water would be
evaporated into space to provide a secondary level of cooling.

The 725 tonne ET would be pared down to 500 tonne systems for placement
on orbit,and seven flights of the Nova Class RLV would be sufficient to
place a 3,500 tonne system on orbit. The long-duration module with
crew and provisions mass 250 tonnes, and itself carries 250 tonnes of
propellant. Development of this system, and construction of three
flight vehicles is expected to cost $1.5 billion.

Three ships - totalling 10,500 tonnes on orbit would be assembled over
21 weeks and a total of 18 people would be sent to Mars aboard these
ships.

Four of the 500 tonne tanks would be consumed during Trans Mars
Injection. Two would remain throughout the flight. The tanks would be
retained for sheilding during interplanetary transit and for use of the
propellant ullage as fuel cell power..

At Mars the two full tanks along with the mission module would separate
and aerobrake at mars. The four empty tanks would also be recovered at
mars. Once in Mars orbit they would rejoin and continue their mission.
The fleet would dock at Diemos - using it for sheilding while at Mars.
Using the empty tanks as the beginning of a mars orbiting base.

There would be an expedition to Phobos, as well as to the Mars surface
after observation from orbit aboard 3 tonne landing ships - carrying
1.5 tonnes of payload, and 10 tonnes of propellant - propelled by RL10
engine, built into the base of each of the empty propellant tanks.-
capable of drawing propellant from the other propellant tanks. A total
of four landers - Mars SSTO is easier to achieve than on Earth - each
powered by an RL10 - provide a capacity to land in many locations
around Mars and return to orbit. There are 20 tonnes of deployable
payloads within each mission module, 500 kg each - 40 total, that are
deployed during descent of each of these stages. There is sufficient
spare propellant for 2 trips to the surface and back per lander. 8 per
mission module. A total of 24 landings for the fleet and 120 unpiloted
daughter landers - The crew is based on the surface of Diemos during
their waiting to return. Including a number of visits to Phobos.

At the right time in the synodic period the two large propellant tanks
for each vessel send each now 150 tonne mission module back to Earth -
three total. And the empty tanks are used as before, and all three
tanks from each vehicle enter the Earth's atmosphere separately and
land on Earth to be recovered and reused.

The 12 mars landers, 12 External Tank based systems mounted on Diemos
as a long -term base, along with 120 unmanned landers and 6 manned
landing sites on the surface of Mars (landings occur in pairs) remain
in the mars system.

During the next exploration cycle two years following on - less
hardware, and more propellant and consumables are brought along, so
more landings can occur. Two of the four spare propellant tnaks can be
guided to the surface and used as a base there, while two of the tanks
can be used on Phobos to start a base there. Additional 'landers' can
be modified for inter-moon transport.