Mission Possible: Cheap Access to Space

 “Up, up the long, delirious, burning blue

   I’ve topped the wind-swept heights with easy grace.
   Where never lark, or even eagle flew—
   And, while with silent, lifting mind I’ve trod
   The high untrespassed sanctity of space,
   —Put out my hand, and touched the face of God."

                                                                                  John Gillespie Magee, Jr., “High Flight,” 1941”

      --- Right this second, it runs you about $10,000 to send a pound to space. That’s about $2,500 per small pizza.

Source: Google

This is why human beings have only been to the moon’s surface half a dozen times, and it’s why our moon vehicles were paper thin in places. The fact that in 2017 we have a space travel paradigm that would’ve disappointed all the hopes of 1969 is not due to a lack of engineering or scientific genius. It’s because the cost of the way we get to space has remained stubbornly high. If we could dramatically reduce the cost, we would have better space science, better communication systems, access to off-planet resources, better ability to control our climate, and best of all, the solar system would open up for exploration and settlement.

Launching rockets is really expensive and most of the space onboard is taken up by propellant. This leaves two ways we can try to drastically lower the cost to make space access cheap: 

1. Recover the launch vehicle.
2. Use less propellant.

Vehicle recovery suddenly became a reality in 2015, which we’ll get into in the section on reusable rockets. But the basic idea is pretty simple—you can save money if you don’t junk your vehicle after one use.

Using less propellant is a little trickier, even though propellant is 80% of a spacecraft’s starting mass.

Source: Soonish

Method 1: Reusable Rockets

Reusable rockets are the best bet for cheaper spaceflight in the short term. They are traditional rockets, but rather than falling into the ocean as they do now, they fall to Earth and land after they finish the mission. This doesn’t fix the problem that the rocket only holds 4% cargo, but it potentially drives the cost way down.

There are a few difficulties with this approach, though. You have to keep extra propellant onboard for the landing phase, which lowers efficiency. You want to carry the smallest amount of extra propellant possible, but this makes the landing phase very hard.

Source: Soonish

A very serious issue is that nobody yet knows what it’ll cost to refurbish a used rocket. This thing has gone to space, man. You can’t just put a spit shine on it and put it back on the launchpad.

Method 2: Air-Breathing Rockets and Spaceplanes

Airplanes already go really high. Can’t we just have them go a bit higher so they get to space?

No. Why would you even ask that?  OH GOD!

If you want to put a satellite in orbit, the hard part is not going really high. The hard part is going really fast. That takes a lot of propellant. But using a spaceplane might allow a serious reduction. To understand why, you have to understand what propellant is.

If you refer to propellant as “fuel,” a NASA engineer will beat you with a TI-83. Propellant is actually a combination of two things: fuel and oxidizer. When you want a combustion reaction, you need three things: fuel, oxidizer, and energy. For example, when you light a campfire, the fuel is wood, the oxidizer is (you guessed it) oxygen, and the energy is a lit match.

The big problem for a spaceplane is that you need multiple types of engines to handle all the different speeds and conditions you encounter en route to space. Here’s why:

Most airplanes today use a turbofan engine. They’re a bit complicated, but the basic mechanism is simple. Fans suck air into a chamber. The air is compressed, so you have a lot of oxygen (your oxidizer!) in a small space. Fuel is injected and ignited. The result is hot compressed air that you channel out the back as you suck in more air. Now, you’ve got high-pressure air behind the engine and comparatively low pressure in front of the engine. So you go forward.

Turbofans start having trouble when you get toward the speed of sound, at about 767 miles per hour,* also known as Mach 1. At the speed of sound, the air can’t get around the plane as fast as it builds up. This creates problems if your front intake is a fan.

Method 3: Laser Ignition

Rockets basically work by firing hot stuff out the back. The hotter it fires, the more of a boost you get per volume of propellant. One way you might get things really hot would be to have a super-high-powered laser onboard to zap the fuel to extremes of heat. But this would weigh so much that it wouldn’t be worth it.

So scientists had an idea that probably left astronauts unenthusiastic: Could we fire a laser right up the rear end of a flying rocket? When we mentioned this to European Space Agency’s Michel van Pelt, he pointed out, “This may be just something to get used to. I mean, if you told people fifty, sixty years ago that you would go into orbit basically sitting on a pile of rocket fuel, basically a controlled explosion, that also probably doesn’t sound too appealing either."

You could save a lot of fuel this way. In fact, one group suggested that with a powerful enough laser, you could use zero fuel up to the first 7 miles of atmosphere. You could gain speed simply by mega heating the air under the rocket. Once you get high enough, you have to use fuel, but thanks to the added laser heat you’d still need far less.

The problem? We’re talking a huge, HUGE laser—in terms of power output, something on the order of 50,000 megawatts. That’s roughly equivalent to the combined output of fifty nuclear reactors all at once. Mind you, you only have to fire the laser for about ten minutes. But even if that weren’t an insane amount of energy, well, we don’t even know how to build a laser that powerful. The most powerful lasers that can fire continuously are U.S. military weapons, and they top out around 1 megawatt. And they only fire for about a minute.

Method 4: Space Elevators and Space Tethers

Imagine you’ve got a big rock spinning around Earth. Attached to the rock is a ribbonlike cable, about 62,000 miles long. It goes all the way down to the surface of the Earth, where specially designed elevators take cargo, travelers, and spacecraft up and down.

This idea may seem outlandish, but it’s been quite well studied (particularly by former NIAC fellow Dr. Bradley Edwards), perhaps because it would represent the ultimate solution to space travel needs. All the problems with all the other methods are fixed by a space elevator, though not without adding some new and unique challenges.

Having vehicles going up and down the cables means you can send fuel as you go. It means you don’t have to accelerate quickly. No discarded parts, no dangerous explosives, and no slamming into an unwelcoming atmosphere. You just ride to the orbit you want, picking up speed relative to Earth’s surface because the tether itself is already in orbit.

Here’s roughly what it might look like:

Source: Soonish

If you could keep cable rope away from lightning strikes, you would still need to worry about debris. There’s a lot of stuff zooming through space, so even if you can dodge the big stuff, little things might wear out the cable 

Plus, the space elevator might make for a particularly good target for terrorists. Dr. Phil Plait (astronomer and author of the blog Bad Astronomy) points out that someone coming along to snip it might not be such a remote possibility. It’s a pretty ripe target for people to want to destroy, and not everybody is nice. We have enemies.

The mechanics get a bit complex, but in short, the cable will start to whiplash back and forth, heating up in the atmosphere, until it breaks apart. Because the material is necessarily lightweight, the individual pieces probably won’t hurt anyone down on the surface.

Source: Soonish

Conclusion:

Cheap access to space means our relationship to space will change forever. It will be possible to create large space stations or even settlements in orbit. We see this as a good thing, but it could potentially put power in the hands of bad actors. One idea that originated in the Cold War was the so-called rod from God. Basically, you get a heavy hunk of metal and throw it from space at an enemy. Given its weight, height, and whatever speed bump you can give it, a simple metal rod could do as much damage as a nuclear bomb. Right now, the only people who go to space are ultra qualified super nerds—the sort of people who pass psychological tests and are willing to spend decades training for a chance to get a few months in space. If space becomes more generally populated, we could be putting ourselves in a dangerous position.

Excerpt From: Kelly Weinersmith. “Soonish.” iBooks. 

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