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In the 1970s America faced increasingly worse energy shortages. It’s main source of petroleum had ground to a halt thanks to the international crisis in Iran and the Middle East, and nuclear had been ruled out after two high-profile nuclear meltdowns.

NASA pitched series of 60 gigantic geosynchronous platforms orbiting the planet, beaming down refined energy for the world's use. It was called the Solar Power System and would be comprised of a global network of gigantic photovoltaic arrays. And they were huge, with two long solar panel structures 5 km long by 4 km wide, or 3.1 miles by 2.4 miles - for a total of 11.73 kilometers long, 7.2 miles in imperial unites, and weighing the small amount of 10.42 million kilograms or 22.97 million pounds.

By being in orbit, weather, dust and day and night cycles would be eliminated, allowing 24/7 constant energy production. The electricity generated would be sent down via microwaves to a thin receiving mesh, that could be built anywhere, even over oceans.

"The SPS is an attractive, challenging, worthy project, which the aerospace community is well prepared and able to address," physicist Robert G. Jahn wrote in support of the project.

But the problem was – how would NASA even get these into orbit. So far, they had only launched the 77-metric-ton (85-U.S.-ton) Skylab into low-earth orbit using a huge Saturn 5 rockets left over from the apollo moon mission. The new solar powerplants weighed 100 times more than even the modern international space station above us today, and rockets wouldn’t cut it - it would need over 1,000 saturn 5 launches to get even one SPS into orbit - let alone 60. So NASA turned to Boeing for the solution.

The Space Freighter was Boeing’s pitch to solve the earth to orbit problem of the SPS program. As its name may infer, it was a rocket system slash space plane that would act like a lorry for space station componets for assembly in orbit. Each mission would have had a payload of around 424,000 kilograms or 934,000 pounds.

For the goal of two SPSs a year, this system would have required a stunning 240 space launched a year – or a turn around every 36 hours. Wommentating on the plans later in 1981, NASA made a very interesting observation.

"The magnitude and sustained nature of this advanced space transportation program concept requires long-term routine operations somewhat analogous to commercial airline/airfreight operations,".

Rockwell came up with this, the Airbreather/Rocket-Powered, Horizontal Takeoff Tridelta Flying Wing, Single-Stage-To-Orbit Transportation System, or dubbed today as "the Rockwell International Starraker. It was a space plane that was 103 meters (310 feet) long with a wing span of about 93 meters (280 feet), and would have carried a maximum of 89.2 metric tons (196,600 lbs) of cargo into low earth orbit around 300 nautical miles above the equator - or 555 kilometers. Overall this would have allowed firms to get payloads into orbit for a cost of $15 per pound ($55 per pound in 2010 dollars). In metric, this is $25 USD per kilograph.

For comparisons sake, Elon musk with his space x rockets costs around $2,720 per kilogram into orbit. So clearly, this dream of low-cost orbit delivery is totally insane.

thanks to its vast tri-delta wing blendered design, there was a great deal of internal volume for not only cargo but fuel as well. The cargo deck was modeled after the C-5 galaxy, 20 feet high and 20 feet wide, in a square shape, and 141 feet long. Thats 6 meters by 6 meters, bt 42.9 meters for those living outside the US.

The craft would have two engine systems, the first was conventional jet engines, specifically hydrogen fueled high bypass supersonic turbofan/air-turbo-exchanger/ramjet engines, each with 140,000 lbf of thrust. Then the space plane also had three hydrogen fuelled rocket engines, each with 1.06 million lbf of thrust and an ISP of 455 seconds - enough to get it into a high orbit.

Here is where it gets crazy, the aircraft would then rise to an altittude of 45,000 feet, before diving directly down to 37,000 feet to build up speed and break the sound barrier, then it would angle upwards to reach 95,000 feet, or 29 km before activating its rocket engines - hitting speeds up to Mach 7.2 .

In terms of the SPS program we outlined before, this would mean than 1100 flights would have been required each year

Yet- why was never built?

In the end, the star raker never really came close to development. it was a change in political power in the United States to the Reagan administration, and the price of oil plummeting that made this expensive enegy concept, the SPS, seem foolish.

Without a need for a launch craft, the whole concept unraveled. Work did continue on other projects, but thats a video for another day.