You will need thrusters to position the big satellite in the first place (or the parts if it is assembled on site), and to counteract the Moon and Sun's tidal forces. If you can handle those, light pressure will be a small issue.

> I think a large problem is going to be space debris -

Nope. If you can build giant solar arrays in GEO, you can build small ones and attach ion thrusters to them. See the Dawn mission at Ceres and the Asteroid Redirect Mission NASA is proposing for examples. These space tugs can putter around and collect loose space debris. That however does not eliminate natural meteoroids. So your power satellite will need a maintenance program, or just accept a small amount of degradation as stuff hits it.

Solar arrays are thin, so most debris will just punch a small hole.

> The biggest unknown is the microwave link to send power to Earth.

We actually have tons of data about this, from all the GEO communications satellites, and rain fade that happens sometimes.

> The next-biggest unknown is availability of construction materials.

I was one of the people who worked on this issue while at Boeing. We found that 98% of the materials for a solar power satellite can be obtained from the Moon. A higher percentage are available if you use the Moon + Near Earth Asteroids. We didn't do the numbers for the NEO case back in the 1980's, since we had only discovered ~150 back then vs 12,500 today, and ion thrusters were not fully developed until about the year 2000. A modern study would account for both sources of materials.

We solved that problem early in the Solar Power Satellite studies at Boeing. The microwave transmitter in orbit is a phased array. The reference signal to adjust the phase is a transmitter in the center of the rectenna on the ground, powered by the rectenna. If the beam wanders off target, no reference signal, and the beam is no longer focused.

Hi Maury,

* Spectrolab rates their space solar panels for 20 years at GEO: http://www.spectrolab.com/Data.... Since they don't need to withstand weather, they can be much lighter than ground-mounted panels. 13 W/kg for a typical ground panel (not counting mounting and tracker) vs 177 W/kg for the space ones. That has implications for the energy payback time if you manufacture the panels in space.

* Your comparison of operating hours neglects that in space you have 36% higher insolation, because there is no atmospheric absorption. Therefore it takes fewer cells to produce the same output. Also the Nevada desert is an excellent location on Earth. The average location on Earth gets considerably worse hours of sunlight. Since we can't transmit power all over the Earth, cherry-picking a good location is unfair.

SpaceX couldn't get an export license then. Rockets fall under the "International Traffic in Arms Regulations" (ITAR) and need a license to export. We even had to follow those rules for the Space Station modules being built by Boeing. That's despite it being an international station occupied by lots of foreigners, Russians even.

> It does seem that the ULA has been mostly sitting on their laurels sucking at the government teat for a long while now.

Let me explain how this works. At the start of the Sea Launch program, which Boeing was a partner of, and I was working on, our program manager was an ex-Air Force officer who was a launch director from Vandenberg (where the Air Force launches polar satellites). He was a smart and competent guy, but the main reason Boeing hired him is *he knew all the right players on the Air Force side*. Another manager of mine was a former Marines officer who had done helicopter procurement.

When the people who make the buying decisions already know you, because they used to work with you, you have a much better chance than someone they never met before and have no idea how good they are, if they will get along, etc. This "revolving door" works in the other direction too, where someone in industry then goes to work in government, in the same field. The problem is you often can't find anyone else who is qualified to oversee such contracts.

> And no effective way to store it for use at night and the evenings.

I guess you haven't heard of solar thermal with storage. You concentrate sunlight with curved troughs or steerable mirrors. This is used to heat a storage material such as thermal oil or rocks. In the off-hours you use the heat to boil water, and the steam runs through a tubine-generator set like in conventional fossil plants. There haven't been a lot of thermal storage units built yet *because we don't need them yet*. For example, the 400 MW Ivanpah solar thermal plant is on the same power line as Hoover Dam. The dam serves as storage by not using water when Ivanpah is running, and saving it for night-time. Eventually you run out of existing storage capacity, and need to add more, but we are not there yet in most places.

Several reasons:

* Curiosity has almost twice the landed weight of the Viking Landers
* Rocket thrusters firing at ground level would contaminate the soil, which they wanted to analyze
* Curiosity is a rover. You either are carrying dead weight from the propulsion system, or need a roll-off ramp
* Curiosity's wheels and suspension allowed landing on rougher ground by landing on them directly. Rocket thrusters might have damaged the wheels by throwing rocks around

Elon Musk wants to build a Mars Colony too, but he has a rocket factory (SpaceX), and several other businesses that can earn lots of money *and* supply hardware for Mars: Tesla (electric cars on Earth, electric rovers on Mars), Solar City (home roofs, and soon high efficiency cells for Earth and Mars), and the Gigafactory (batteries for vehicles *and* nighttime backup for solar panels). So his plan is a lot more feasbile than Mars One's.

The real question is where is Mars One going to get the $6 billion they estimate for their project? If they have that money, they can hire the right aerospace companies and engineers to build real hardware. But without it, they just have pretty pictures on a website, and aren't going anywhere.

And as someone who helped build the Space Station, and written a book on Space Systems Engineering ( http://en.wikibooks.org/wiki/S... ), Mars One isn't being innovative *enough* to really bring down costs.

Our supposedly omnipotent spy agency should be able to track down where these posts are coming from. Their silence on this matter is deafening.

Sounds like someone failed to do a proper "systems engineering" job in the first place. Part of that job is identifying system interfaces between the parts early, then controlling the interface. In computer terms, the PCI specification is the interface between the PCI slot and the PCI card that goes in the slot. You have to control that specification so the parts will work together. A rocket and the launch site it uses are just bigger and more complicated interfaces.

Then the answer is not to send the hardware to empty buildings, but to install a GPS tracking device in the shipping container, and see where it goes off-course. Bonus points if you can track it all the way to the NSA modification warehouse, but at least if you know where it got diverted, you can figure out *how* it gets diverted. I suspect the truck drivers are in on it, but without tracking data, that is just a theory.

The head of the Mars Society is Robert Zubrin, who is a well qualified and inventive aerospace engineer. I assume the rest of their work at least involves doing the relevant math.

The Mars One project's problem isn't wanting to go to Mars, it's the missing step two in their plan:

(1) Raise around a million dollars from crowdsourcing, tee shirt sales, and application fees
(2) ???
(3) Finish $6 billion worth of space hardware and launch it.

Elon Musk/SpaceX also want to go to Mars, but they have actual rockets and customers, and his other businesses (Tesla and Solar City) both stand to make a lot of money, and are useful to the original goal. You will need electric rovers, batteries for power storage, and solar panels on Mars. It helps if you have companies that already make that stuff. So I rate the SpaceX Mars program way higher on the probability scale.

Hey, uninformed person, these drones have lithium batteries, and sunlight is more powerful at high altitude due to less atmospheric absorption. So it can fly for years or until something breaks.