SpaceX LaunchDecember 21, 2015
For people intrigued by giant things that blast off into space, tonight (or tomorrow, possibly) is a tense time. SpaceX is returning to flight after a six months hiatus following the rocket that exploded a minute into flight in June. Not only that, this will be their first attempt at landing the rocket back on land, and if it's a successful landing, it will be a historic day -- the first commercial rocket to lob something into orbit, and then return and land on land.
There is quite a bit of anxiety in the air.
People like me realize that, while not likely, the primary mission could be a failure, either due to the rocket exploding, or due to some secondary malfunction. Even if that succeeds, there's still quite a bit of anxiety about the landing. We all want, very badly, for the landing to be a success. And if all of that wasn't enough, there's anxiety about whether the rocket will launch tonight. Anything, such as the weather, or a technical glitch, or even something else, could postpone the launch. Even if it is postponed until tomorrow, it might be postponed again, even into January.
Anxiety, and lots of it.
The anxiety about the rocket exploding is higher than it would normally be for a return-to-flight, because SpaceX, for the first time ever, is flying a modified rocket. Not only is the rocket modified, but they are for the first time ever trying a launch with a super-super-cooled variety of fuel. Anyone with an inclination of an engineer will see changes like that as an invitation for unknown things to happen. And unknown things in the world of rockets, where everything has to happen 99.9% right (or kaboom) brings with it anxiety.
Another contributor to the anxiety is that there is an atmosphere of expectation around the landing being a success. Well, expectation is perhaps a bit strong. But consider that back in June, my internal feeling for a successful landing was still around 40%... I thought it more likely that the rocket would again crash into the drone ship and go kaboom. (but also knew that it could very well work) Today, however, my internal sense is about an 80% likelihood for successful landing. And anytime you start to feel that something is likely, but not certain, you start to feel anxious, because you've told your internal self "I expect it will work, but it might not". Isn't that the very definition of anxiety? (kind of?) No one likes their expectations dashed.
On that 80% figure -- why am I feeling more confident? Well, SpaceX has had 6 months to think long and hard about the landing. That's actually quite a bit of time to tweak things, testing things, etc. Secondly, it's on land, giving them a much wider margin for error, and when you're doing something this insanely difficult, a 50% or 100% or 200% wider margin for error is huge in terms of odds of success. Just imagine the rocket, at the last minute, computing "oh crap, trying to land within 40 feet of the intended target would require aggressive tilting that brings with it low odds of success... oh, but hey, my landing area is way bigger, so forget landing within 30 feet of my target, I'll just go with 100 feet from my target". Even if the rocket were to miss the concrete and land on the packed gravel, the odds of it staying upright are probably decent. Finally, I'm going on SpaceX's posture. They (Elon) are being so bold to invite people to watch the landing from the causeway, and my understanding is that, unlike the low-probability barge landings, they'll be live-streaming the landing. I suspect they wouldn't be live streaming it if the odds of success were still below 50%. I imagine their internal sense is that the odds are > 80%. Ok, one final thought on the odds of successful landing -- they have *already* numerous times successfully done soft touchdowns, they just happened to be on the water, rather than on the barge or land. That indicates that bringing the rocket down to a soft vertical landing is pretty "easy" at this point, and the real challenge is trying to get it within 30 feet, especially if that target is moving somewhat (the barge). Perhaps one of the big unknown variables is how far from the pad SpaceX has programmed their rocket to considering an acceptable landing spot. ie. If landing within 150 feet of the target is deemed low probability by the rocket in the final seconds, will it make a compromise and accept a landing spot that is perhaps 200 feet away from center? If they have that much flexibility, I might think the odds of success to be as high as 85-90% for the landing.
Right, so lots of anxiety floating around.
I'm going to get pessimistic for a moment: Part of me expects the odds of mission failure to be much higher than people might think. The reason for that is mainly around the modifications that SpaceX has made around fuel densification, etc. It is also due to the fact that SpaceX failed three times in a row when they were building the Falcon 1. What's the point? The point is that it is somewhat in SpaceX's DNA to fail spectacularly. They are pushing the envelope, and they're pushing it hard. And when you're doing things at the very edge of what's possible, rapidly iterating and experimenting, watch out -- kaboom is going to be more likely than as compared to the guys who are taking the slow conservative approach. I actually think SpaceX is going about things the right way, so long as they don't get
too carried away with their aggressive envelope pushing. Flying this fuel densified version of their rocket on return to flight -- is that too aggressive or is it reasonable? My gut is telling me it might be a bit too aggressive. If they're successful tonight with it, and successful the next few flights with it, then they will have gotten away with it. I truly hope that's the case. But if the primary mission fails, it is going to be an almost impossibly difficult blow to SpaceX and to Elon Musk. I do worry about his emotional state. Interviews he's given make it apparent just how difficult it was for the rocket to explode in June. What would a second consecutive mission failure do to his psyche?
Perhaps the three failures of Falcon 1, and the insane pressure of 2008, will be useful experience for Elon... now that his organizations are much, much larger, knowing how to chart such difficult waters may be a huge asset.
But let's hope my pessimism is unfounded. We're all hoping for a big party tonight. (or tomorrow)
MemoryDecember 12, 2015
Something that I think I've noticed about myself -- or perhaps it's due to my steadily increasing age -- is that my memory is a significant limiting factor to my ability to learn.
I suppose the first point is this: When I was 23, I imagined myself as someone who would continue learning, and really enjoying learning, for decades to come. But at some point in my 20s I realized that I was forgetting faster than I was learning. I had made some quizzes for myself for courses in my 4th year of university, and 10 years later I tried taking a quiz. I wasn't able to answer even a single question. The vocabulary was now unfamiliar, the concepts too fuzzy to recall.
But now I've noticed the trend occurs more quickly. This year I took a sabbatical and spent time studying grammar and probability. This week someone was talking about "MAP", "Maximum a Priori", which was a term I recall from the probability course, but I couldn't remember the concept itself. I found that somewhat bewildering -- a whole chunk of the course was on that topic, and I couldn't bring it to mind.
This year I was strongly chastised at work for doing something that (apparently) had been mentioned not to do on a mailing list at least a couple of times over the last 4 years. Do I remember? Not in the slightest.
No one has perfect memory, but I'm starting to suspect that this may be one of my personal weaknesses. It will be interesting to see how that changes over the coming years.
And I'm wondering if this struggle with remembering has been making "higher learning" more difficult for me. Knowledge is like a tree -- you learn the basics, and then branch out from there. But if the tree below you is evaporating at too fast a rate, it makes it hard to build new branches, because you're forgetting the lower level concepts you need to make the new information sensible.
On the positive side, I think I've been making some good progress when it comes to tools that help store and recall information. I use a system of hierarchical notebooks (somewhat akin to the web) to create trees of projects, tasks, and sub-tasks, which is helpful in the future to be able to "re-trace" the structure of what was going on, and even drill down to the details. This dove-tails nicely with a natural language system I use at work for associating linguistics with things -- I can type "todo" and get my TODO notebook. I can type "meetings" and get my meetings notebook. I can type "probability" and get a root notebook to then branch off various areas of probability that I've been learning about. It's been working quite nicely and, as is not unusual, I wonder how many people out there would benefit quite a bit from having this synergy of hierarchical notebooks + the ability to associate them with NLP "commands" for very quick access.
Fuzziness: Discrete VS Continuous / Digital VS Analog / ApproximationNovember 30, 2015
I remember a few years ago that I was feeling excited about injecting a degree of uncertainty into computation. The point was that while we often create systems that only act if they are certain about their inputs, a world of new possibilities opens up if you are willing to act when you're almost but not completely sure about something.
I gave the example of Google search -- it will often say "assuming you meant ...", and the addition of those smarts is incredibly useful.
Sometimes I think of these systems as "95% systems" -- systems that are willing to treat things as tentatively true if it's >= 95% likely that they're true, and if it is later determined that a false assumption was made, then you go back and fix that assumption.
Recently my mind has been resonating on that theme again. This time the perspective is slightly different -- it is the realization that in math, there are things we call "discrete" -- such as integers, prime numbers, etc, and there are things we call "continuous" -- such as the function y = x^2.
The realization is that the "fuzziness" of "95% systems" is really the introduction of continuity / continuous functions into the realm of computation, and furthermore, neural networks and probabilistic modelling are the primary examples of continuity in computing today. They have opened up a whole new world of possibilities, solving all sorts of problems that discrete systems struggled with.
Another way of looking at this dichotomy is the digital/analog divide.
An intuition/bias that I've had for a number of years is that good things come when you figure out how to property synergize discrete and continuous systems. The point is that neither system of reasoning is the slam dunk answer to intelligence, but rather each of them is more or less useful depending on the domain.
My vague guess is that the intelligent systems of the future will harness both discrete and continuous models in powerful ways, and that those intelligent systems will excel at having those two systems play nicely with one another. Well, more than that -- that those systems will employ a kind of "resonant synergy" that will achieve something far more mind bending than an attempt that used only one of the approaches could achieve.
One last analogy I'll throw in is the notion of "approximate algorithms": There are many problems in computer science for which it is impossible to calculate an exact solution. For example, the famous "travelling salesman" problem... rather than computing the optimal solution, we focus on computing solutions that are likely to be really close to the optimal solution, and to do it in what might be a trillion times faster than trying to get the very best solution. These approximate algorithms I think are yet another example of "fuzziness", and how it can be such an important and exciting area of development.
older >>
