Getting closer

In recent months, two of my hobbies have been amateur telescopy and spectating at orbital rocket launches. Conceptually, these are kin; one brings the universe closer to us, and the other brings us closer to the universe. But experientially, they don’t share much. One is silent, rigid, and tests your patience, the other is an explosion of matter and emotions, gone before you can grasp it.

If there’s anything I’m optimizing for at a launch, it is to “be there”. Everyone knows that rockets go up, just as everyone knows that babies are born. But it is something different to be there. You can watch a live stream of a launch, just as you can watch the superbowl on TV. But even though you see what happens at the same time as everyone else, it is something different to be there.

I don’t know how or why, but some part of the mind knows, and cares deeply, about the distinction between knowing and experiencing. So after I saw my first launch I thought, how can I get closer? How can I increase the intensity of my experience? During that first launch I had used binoculars, and they helped me resolve significantly more detail. So… why not watch a launch through a telescope?

Now, let’s just be clear that this is a ridiculous idea. Finding a still object in the night sky is a tricky endeavor. If it’s really bright like the Mars or Vega you can point and shoot, but for most cases you want a “finder” scope, a smaller, low magnification scope that’s aligned with the big one. It’s far easier to find an object at lower magnification where you can see lots of surrounding context, and then switch to a higher magnification for detail, than to start at higher magnification and only be able to see a few nearby stars for orientation. Furthermore, if the object is moving, it’s tricky to keep up. Most things in the night sky don’t seem to move, but everything has an apparent motion of at least at the rate that the earth rotates. The highest magnification my equipment gets is ~500x, and at that rate the earth takes it out of the viewing field in maybe 15 seconds. I’ve caught planes in the scope before, and it was pretty cool, but you definitely had to be on your toes to keep up with it. Obviously a rocket goes faster than a plane.

Nevertheless, I’m at a place in my life where it’s good for me to practice the virtue of empiricism. So I dragged the gear all the way to Vandenberg and set it up in broad daylight. I was with three other friends and we’re watching a Falcon 9 take up a batch of Iridium satellites. (You can see the original webcast for this launch here). From the closest public viewing spot on Ocean Ave, you can’t actually see the launch facility. Though it’s only 3.5 miles away, the Air Force had an understandable desire that their base not be easily visible, so there’s a hill in the way, just high enough to cover it all. So I couldn’t just point the scope at the rocket on the pad, wait for liftoff, and track it from there. I’d have to catch it in the air.

While we wait, I put in the eyepiece. Normally during an astronomy session, I start looking at something with the lower-magnification eyepieces and work my way up. In this case, my moving target gives me no time to switch them out. I want to see the rocket at the highest magnification I can, but that will also make it harder to find and track in the scope. So I pick an eyepiece in the middle, with a 10mm focal length, giving me 65x magnification. I make sure it’s focused, using the one distant building we can see.

As an aside, I was also curious as to whether the exhaust flames could be seen through the solar viewing glasses we all bought for the eclipse of August 2017. The exhaust has the extraordinary brightness quality of the sun, while being obviously not as bright (otherwise viewing launches would be a discouraged act).

At the exact prescribed time, we see the column of flames rise over the hill, and I grab the eclipse glasses. It takes a second for my eyes to adjust to the darkness (because the launch is during the day) but indeed I can see the flames through the glasses. This puts a very high lower bound on their brightness; much brighter than a lightbulb.

As soon as that’s established, I run over to the scope. With the rocket rising fast, I crouch behind it and slew it to where I think the rocket will be by the time I stand up and get my eye in the eyepiece. Bingo. It’s early enough in the burn that the vehicle still subtends a very large angle in the sky, and its brightness also leaves a halo to follow. But it’s still moving, so I immediately have to get my bearings and start to guide the scope upwards.

Screenshot from 2018-07-15 22-00-29
The Falcon 9 during ascent. The exhaust plume spreads out as the atmospheric pressure drops, making the nozzle effectively underexpanded.

The detail is beautiful. I can see the bulb of the payload fairings, I can see the landing legs, I can see the grid fins. If it were rotated correctly, I’m sure I could read the SpaceX logo. I follow its steady rise, up and up and up. I wish I had a camera where my eye is. I lose it for a second, but I follow its orange halo back. Since rockets always end up going away from you, the fuselage tips over and becomes increasingly foreshortened. And since the atmospheric pressure around the rocket is decreasing as it gains altitude, the flames start to fan out. The Falcon 9 has eight engines in a circle and one in the center, making a pattern of flames that ends up looking something like a flower. This pattern is very clear through the scope. The flames spread wider, and consequently get dimmer. After a couple minutes, the flames cut out. There’s no announcer at this viewing spot, so I yell out “main engine cut off!” in case anyone is interested. I see the long white blur split in two, and the pieces drift apart. “Stage separation!” At 50 miles up, the pieces are really tiny, but still discernible. I see flames again. “Second stage ignition!”

Now there are two objects in my view. One of them, carrying the payload, is accelerating toward space under 210,000 pounds of thrust. The other, a charred and spent 16-story machine, is in freefall. I have about four seconds before one of them goes out of view. The booster is landing in the ocean; there’ll be no boost-back burn, but there will be an entry burn to slow it down. The second stage is small and only getting smaller. I decide to let it go.

To my surprise, I see some angular puffs of white come from the top of the first stage. They’re so rapid and dim that they seem more like a light blinking than a rocket engine. I later learn that these are cold nitrogen thrusters, pressurized cans of gas used to make very slow but precise changes to the rocket’s orientation. (You can see these in the webcast starting here.) They appear sporadically, clearly the result of real-time calculations of the rocket’s current position.

Though the booster is now falling to the ground, it’s still travelling away from me and toward the deep pacific ocean. The sheer distance between us gives the sky the chance to obscure it with the blueness of Rayleigh scattering. I lose sight of the now infinitesimal machine.

After almost three minutes of continuous viewing, I step away from the scope and look up for the first time. There’s a fantastic contrail extending to the southeast, and it casts its own shadow in the mist of the upper atmosphere. Besides that, it’s over. There is nothing more to see. Even the crackle has faded. I look around at my friends, realizing that they had a completely different experience than me. That… was awesome. But also… it felt pretty similar to just watching a webcast. It actually felt less like “being there”. After some reflection, I concluded that the fact that I couldn’t easily switch between looking through the scope and looking at the sky, like one can with binoculars, was a critical factor. I could only use one eye. I couldn’t place what I was seeing in my surrounding context; I couldn’t connect it with the sounds I was hearing; I couldn’t see all the people around me reacting. It was worth doing, but I’m very glad I tried it during my second launch viewing. I’ll have to find some other way to get closer.

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