At the moment a manned Mars mission would be too expensive. The same amount of money could get a much larger project off the ground, for example my ARMXER Orbital Skyhook Infrastructure. I'm working on a new buildup timeline and I have the preliminaries nailed down pretty well -- although I think I'll start using revision levels and release dates on my website documents. To build an ARMXER Orbital Skyhook Infrastructure goes something like this:

0. Build all the components for a 1450-tonne hub and 1-tonne-cargo-rated tether. The time and cost for this stage is unknown and assumed to be zero for convenience sake.

1. Spend 10 years launching the components on Delta IV heavy-lift rockets, at a rate of 5-6 launches per year and cost of about $1 billion annually. Hub components are assembled by astronauts at the ISS. Concurrent with Hub component launches a series of ground-based powerplants and microwave transmitters are built, to provide 340 MW of usable power to a spacecraft orbiting at 2000 km altitude on the same groundtrace. Upon completion the Hub boosts itself to 2000 km orbit using its magsail and power beamed from the surface. Time elapsed is 10 years.

2. Spend 5 years operating the small Skyhook, working out the bugs, smoothing out the logistics. The 1-tonne payloads should consist of nothing but mirror & antenna components for a Solar Concentrator Beam Power Satellite and components for a 60,000-tonne Skyhook Hub and 40-tonne-cargo-rated tether. After 5 years solar components launched should be upwards of 24,431 tonnes, enough solar mirrors to provide 340 MW of usable power to the Skyhook. Total additional Hub components launched should be 58,550 tonnes, for a grand total of 82,981 tonnes. The small Skyhook is put on standby. Ground-based powerplants are diverted for civilian uses. No additional ground-based powerplant infrastructure will be required. Time elapsed is 15 years.

3. A single full-scale Skyhook with 340 MW of solar power should now be in service. This Skyhook is rated for 40-tonnes per launch, but is limited intially to 1-tonne per launch by the solar power available. Of the 17,265 launches annually, half are allocated to human passengers, and half are allocated to additional solar power components. The first fleets of private spacecraft are small, rated for perhaps 5 passengers and short durations in space. These 1-tonne spacecraft are conducive to privatization and small commercial startups, carrying 43,162 people on short journeys into space every year. Time elapsed is 16 years.

4. The solar powerplant components which are launched all year long are assembled and brought online once annually, gradually increasing the power available for launch. More solar powerplant components can be launched in the same amount of time, and with a 50-50 split of launch capacity with human passengers, spacecraft can also be built larger, to carry more people with each launch. This process slowly compounds itself year after year. After 29 years have elapsed we are still operating a single full-scale Skyhook, but its solar powerplant is generating so much power that it can now handle a full 40-tonnes per launch. There is still a 50-50 split between passengers and powerplant components (we want to keep growing), even so the Skyhook carries more than 1.6 million people into space every year. The MIPCC-equipped rendezvous aircraft as well as the human-carrying spacecraft have reached the design-point 180-passenger configuration and do not need to be scaled up further, only increased in number. We launch the Hub components for a 2nd full-scale Skyhook. Time elapsed is 28 years.

5. We now have two Skyhooks operating, carrying a 50-50 split of passengers and powerplant components on 34,530 launches annually. It does not take long for the powerplant capacity to come online and the skyhooks to reach maximum capacity again. After just two years, human passengers exceed 3.4 million annually, and we launch Hub components for a 3rd Skyhook. Time elapsed is 30 years.

6. We now have three Skyhooks operating with a 50-50 split of passengers and powerplant components. After two years we are again at maximum capacity, human passengers exceed 5 million annually, and we launch components for a 4th and 5th Skyhook. Time elapsed is 32 years.

7. We now have five Skyhooks operating with a 50-50 split. After 2 years we are again at maximum capacity, with 8.6 million passengers, and so we launch components to add a 2nd tether to each of the five Skyhook Hubs, effectively doubling the launch frequency of each. It is equivalent to say that there are now 10 Skyhooks. Time elapsed is 34 years.

8. We now have 10 Skyhooks operating with a 50-50 split. After 2 years we are again at maximum capacity, with over 17.2 million passengers annually. We now add two more tethers to each Hub, doubling their launch frequency. We now have five Hubs, each with four tethers in a starfish geometry. This is equivalent to 20 Skyhooks. Time elapsed is 36 years.

9. We now have 20 Skyhooks operating with a 50-50 split. After 3 years we are at maximum capacity, with over 30 million passengers annually. We can stop launching powerplant components, which would double passenger launch capacity to 60 million annually (1 percent of world's population), or we can continue launching cargo at the same rate. Cargo can consist of alternative types, either added powerplant components, or perhaps SpaceDock habitats. Another alternative is Lunar Underground infrastructure components. Speculation stops here for now. Time elapsed is 39 years.

(I'll have this on my website within a couple days.)