Some planets have their thick layers of gas arranged in permanent, orderly bands with turbulent, curlicue edges circling their respective gas giant. But Earth’s atmosphere is layered like an onion, an active one, pulsing in and out every day, sorted more in the vertical dimension. We live in the lowest, densest part, the troposphere, where every rain storm, every blizzard, and every type of cloud formation save one mostly originate and reside. The next layer, the stratosphere, acts as an invisible lid on the troposphere. But you see its effects when a thunderstorm builds and then flattens out abruptly at the top, giving it that angry, anvil look.
The next layer up is the mesosphere. This the realm of ghostly, noctilucent clouds, sometimes lit by exotic high-altitude denizens in the form of red sprites and blue jets. The mesosphere is alien, so thin it stops behaving like the air we are familiar with. This is where X-15s fly and millions of meteors die, most of the latter smaller than an apple seed, streaking through rarefied gas thinner than the atmosphere on Mars and colder than Antarctica in mid-winter. Then we come to the thermosphere, so thin that that’s where we start calling it space.
To get in the lowest stable orbit that lasts several revolutions, a rocket has to loft a spacecraft through all those lower layers, up to an altitude of at least 100 miles or more, plus leave it moving sideways relative to the surface at almost 5 miles/sec (7.8 km/s) or about 18,000 miles per hour. That takes considerable power, and for years now we’ve been buying rocket engines to do that from—of all places—the former Soviet Union. Let’s talk about all that below.
A few years ago I asked Richard Garriott what he thought when he first looked out a Soyuz portal from low Earth orbit, or LEO. He said, “You know it's funny, the first thing I thought was, Wow! We're awful close! … Consider that on the scale of a classroom globe, LEO is about as high off the surface of that globe as a nickel is thick. Not much room for error there.”
That’s the thing about LEO, it’s low. It’s also safely below and protected by magnetic and radiation belts. It’s where most satellites orbit, where the International Space Station sits, and where every manned space mission to date has occurred, aside from a handful of Apollo missions that went to the moon.
There are higher Earth orbits, of course. The next bogey that’s useful to discuss in terms of cost and power is called geostationary orbit. That’s where a satellite takes exactly one day to make one orbit. So, if its over the equator, it stays right above the same spot on the Earth.
To get from LEO to GEO, most spacecraft go through a transitional path called geostationary transfer orbit, or GTO. Since most rockets are not launched from the equator, this is how both the altitude and inclination of the original LEO are changed. GTO is a big oval with one end kissing LEO and the other touching GEO. With two or three judicious burns on the far end, the spacecraft can round that orbit into official GEO and move it over the equator.
After that, translunar injection is an interesting orbit. This is where a spacecraft boosts enough to break free of the Earth and falls around the backside of the moon. Once the moon is rounded, TLI can be tweaked into the lunar free return trajectory, a sort of lopsided figure eight that cycles an object from close to the Earth to the moon continuously. It only takes a little more fuel to turn TLI into an interplanetary orbit where the spacecraft is now orbiting the sun, like a planet, instead of orbiting the Earth or the moon.
An interplanetary orbit near the Earth can be most efficiently changed into a higher orbit that touches Mars’ orbit, or any other outer object in orbit around the sun, using a Hohmann transfer. It’s just a version of the burns that get a vehicle from LEO to GTO to GEO. The duration typically quoted for getting to Mars during an ideal window using a transfer range is between 180 and 250 days, if timed during the very best launch windows that only occur about every two to three years. The fastest we’ve ever made it was Mariner 7 in 131 days starting on March 27, 1969.
Right now, the most exciting development in launch vehicles has been from SpaceX. Their Falcon 9 can put in 50,000 lbs. in LEO and almost 20,000 lbs. in GTO. The Falcon Heavy, now in late development, will more than double those figures. One of the main things holding us back from just using Falcons going forward is production: SpaceX is making them as fast as they can and expanding their production to make more, but that will take time to complete.
Which brings us back to LEO and a sticky political vs. technology issue: There’s another type of really useful low Earth path called a polar orbit. As the name suggest, this orbit circles the poles, while the Earth or object under study rotates beneath, giving the sat a close up view of every section of the planet over time. When we put a typical spacecraft in orbit, we usually fire it off in the same direction as the Earth rotates, east to west, to take advantage of the “free ride.” This provides almost 1000 mph of sideways velocity for free when launching from Kennedy Space Center. But that doesn’t help boost into a circumpolar orbit, because it’s in too different a direction.
The best engine and vehicle widely available to achieve that pole to pole orbit is called an RD-180 and it goes into an Atlas V made by United Launch Alliance, mostly by Lockheed. Through a series of convoluted acquisitions, the company that makes the 180 is the Russian-owned NPO Energomas (this is for unmanned launches, and it is in addition to the reported $70 to 80 million we’re paying Russia to put each U.S. astronaut into space). And circumpolar orbits are ideal for spy and recon sats:
“What were we thinking? It’s clear now that relying on Russia for rocket engines was a policy based on hope, not good judgment,” said Michael V. Hayden, a four-star Air Force general who headed the National Security Agency and the Central Intelligence Agency before his retirement in 2009.
There are two problems with this reliance on Russian technology. First, Mr. Putin could decide tomorrow to stop providing the heavy-lift engines. Second, the company that produces the RD-180 is owned by several of Mr. Putin’s cronies.
So first of all, Russia is charging every last dime and then some they can squeeze out of us for both manned and unmanned launches. Second, Putin could decide for strategic or tactical reasons to limit those capabilities any time he wants.
Which puts the U.S. in a real bind, and so a series of bills and proclamations have been bouncing around Congress over this for the last several years—and that discussion may heat up quite a bit in the next few weeks. We’ll go into those arcane, convoluted details when the time comes here on Daily Kos.
But the way things are going, it’ll probably be sooner rather than later.