+Wednesday’s theme will be science, a subject that excites me as much as history on Monday and language on Tuesday. Here’s the first installment of Wednesday Wonders — all about science.
Last week, NASA managed something pretty incredible. They managed to bring the Voyager 2 probe back online after a system glitch forced it to shut down. Basically, the craft was supposed to do a 360° roll in order to test its magnetometer.
When the maneuver didn’t happen (or right before it was going to), two separate, energy-intensive systems wound up running at the same time and the probe went into emergency shut-down to conserve energy, turning off all of its scientific instruments, in effect causing data transmission back to home to go silent.
The twin Voyager probes are already amazing enough. They were launched in 1977, with Voyager 2 actually lifting off sixteen days earlier. The reason for the backwards order at the start of the mission is that Voyager 1 was actually going to “get there first” as it were.
It was an ambitious project, taking advantage of planetary placement to use various gravitational slingshot maneuvers to allow the probes to visit all of the outer planets — Jupiter and Saturn for both probes, and Uranus and Neptune as well for Voyager 2.
Not included: Pluto, which was still considered a planet at the time. It was in a totally different part of the solar system. Also, by the time the probes got there in 1989, Pluto’s eccentric orbit had actually brought it closer to the Sun than Neptune a decade earlier, a place where it would remain until February 11, 1999. While NASA could have maneuvered Voyager 2 to visit Pluto, there was one small hitch. The necessary trajectory would have slammed it right into Neptune.
Space and force
Navigating space is a tricky thing, as it’s a very big place, and things don’t work like they do down on a solid planet. On Earth, we’re able to maneuver, whether on foot, in a wheeled vehicle, or an aircraft, because of friction and gravity. Friction and gravity conspire to hold you or your car down to the Earth. In the air, they conspire to create a sort of tug of war with the force of lift to keep a plane up there.
When you take a step forward, friction keeps your back foot in place, and the friction allows you to use your newly planted front foot to move ahead. Note that this is why it’s so hard to walk on ice. It’s a low-friction surface.
The same principle works with cars (which also don’t do well on ice) with the treads on the tires gripping the road to pull you forward or stop you when you hit the brakes — which also work with friction.
Turning a car works the same way, but with one important trick that was discovered early on. If both wheels on opposite sides are on the same axle, turning the wheels does not result in a smooth turn of the vehicle. The axles need to be independent for one simple reason. The outside wheel has to travel farther to make the same turn, meaning that it has to spin faster.
Faster spin, lower friction, vehicle turns. While the idea of a differential gear doing the same thing in other mechanisms dates back to the 1st century BCE, the idea of doing it in wheeled vehicles wasn’t patented until 1827. I won’t explain it in full here because others have done a better job, but suffice it to say that a differential is designed to transfer power from the engine to the wheels at a relative rate dependent upon which way they’re aimed in a very simple and elegant way.
Above the Earth, think of the air as the surface of the road and an airplane’s wings as the wheels. The differential action is provided by flaps which block airflow and slow the wing. So… if you want to turn right, you slow down the right wing by lifting the flaps, essentially accelerating the left wing around the plane, and vice versa for a left turn.
In space, no one can feel you turn
When it comes to space, throw out everything in the last six paragraphs, because you don’t get any kind of friction to use, and gravity only comes into play in certain situations. Bookmark for later, though, that gravity did play a really big part in navigating the Voyager probes.
So, because no friction, sorry, but dog-fights in space are not possible. Hell, spacecraft don’t even need wings at all. The only reason that the Space Shuttle had them was because it had to land in an atmosphere, and even then they were stubby and weird, and even NASA engineers dubbed the thing a flying brick.
Without friction, constant acceleration is not necessary. One push starts you moving, and you’ll just keep going until you get a push in the opposite direction or you slam into something — which is just a really big push in the opposite direction with more disastrous results.
Hell, this is Newton’s first law of motion in action. “Every object persists in its state of rest or uniform motion — in a straight line unless it is compelled to change that state by forces impressed on it.” Push an object out in the vacuum of space, and it will keep on going straight until such point that another force is impressed upon it.
Want to turn right or left? Then you need to fire some sort of thruster in the direction opposite to the one you want to turn — booster on the right to turn left, or on the left to turn right. Want to slow down? Then you need to fire that thruster forward.
Fun fact: there’s no such thing as deceleration. There’s only acceleration in the other direction.
Also, if you keep that rear thruster going, your craft is going to keep on accelerating, and over time, this can really add up. For example, Voyager 2 is currently traveling at 15.4 kilometers (9.57 miles) per second — meaning that for it to take a trip from L.A. to New York would take five minutes.
Far and away
At the moment, though, this probe is 11.5 billion miles away, which is as long as four million trips between L.A. and New York. It’s also just over 17 light hours away, meaning that a message to and response from takes one day and ten hours.
And you thought your S.O. was blowing you off when it took them twenty minutes to reply to your text. Please!
But consider that challenge. Not only is the target so far away, but NASA is aiming at an antenna only 3.66 meters (12 feet) in diameter, and one that’s moving away so fast. Now, granted, we’re not talking “dead on target” here because radio waves can spread out and be much bigger than the target. Still… it is an impressive feat.
The more impressive part, though? We’re talking about technology that is over forty years old and still functioning and, in fact, providing valuable data and going beyond its design specs. Can you point to one piece of tech that you own and still use that’s anywhere near that old? Hell, you’re probably not anywhere near that old, but did your parents or grandparents leave you any tech from the late 70s that you still use? Probably not unless you’re one of those people still inexplicably into vinyl (why?)
But NASA has a track record of making its stuff last well beyond its shelf-life. None of the Mars rovers were supposed to keep on going like they have, for example, but Opportunity, intended to only last 90 days, kept on going for fifteen years, and the NASA Mars probes that actually made it all seem to last longer than intended.
In the case of Voyager, the big limit is its power supply, provided by plutonium-238 in the form of plutonium oxide. The natural decay of this highly radioactive element generates heat, which is then used to drive a bi-metallic thermoelectric generator. At the beginning, it provided 470 Watts of 30 volt DC power, but as of 1997 this had fallen to 335 Watts.
It’s interesting to note NASA’s estimates from over 20 years ago: “As power continues to decrease, power loads on the spacecraft must also decrease. Current estimates (1998) are that increasingly limited instrument operations can be carried out at least until 2020. [Emphasis added].”
Nerds get it done.
Never underestimate the ability of highly motivated engineers to find workarounds, though, and we’ve probably got at least another five years in Voyager 2, if not more. How do they do it? The same way that you conserve your phone’s battery when you forgot your charger and you hit 15%: power save mode. By selectively turning stuff off — exactly the same way your phone’s power-saver mode does it by shutting down apps, going into dark mode, turning off fingerprint and face-scan recognition, and so on. All of the essential features are still there. Only the bells and whistles are gone.
And still, the durability of NASA stuff astounds. Even when they’ve turned off the heaters for various detectors, plunging them into very sub-zero temperatures, they have often continued to function way beyond the conditions they were designed and tested for.
NASA keeps getting better. Nineteen years after the Voyagers, New Horizons was launched, and it managed to reach Pluto’s orbit and famously photograph that not-a-planet object only 9½ years after lift-off — and with Pluto farther out — as opposed to Voyager’s 12 years.
Upward and onward, and that isn’t even touching upon the utter value of every bit of information that every one of these probes sends us. We may leave this planet in such bad shape that space will be the only way to save the human race, and NASA is paving the way in figuring out how to do that.
Pretty cool, huh?