Kerbal Space Program - Resurrect Jebediah Kerman

I play a lot of Kerbal Space Program. It's a lot of fun, but sometimes things go wrong, rockets go boom, and my favorite kerbal dies. Jebediah Kerman is usually the first to go, and it only takes a couple of orbits for me to miss his bad ass lack of fear.

Assuming I'm not alone in my sentimental attitude towards my kerbals, I'd like to share a unix one liner to bring your deceased kerbals back to life, so you can assign them to another ill-fated mission.

  1. Open your KSP game data files. You can either navigate from Steam, or if you're a l337 hax0r (who also bought KSP through Steam), run this command:

    $ pushd ~/Library/Application\ Support/Steam/SteamApps/common/Kerbal\ Space\ Program/saves

  2. Navigate into your save directory. Mine is named dinosaur.

    $ cd dinosaur

  3. Run this ugly one liner.

    $ cp persistent.sfs backup.sfs && cp persistent.sfs persistenttmp.sfs && \
    cat persistenttmp.sfs | sed 's/state = Dead/state = Available/g' > persistent.sfs && \
    rm persistenttmp.sfs

  4. Take your zombie Jeb on new amazing missions.

Note: This was last tested with Kerbal Space Program v0.24.2. If your version number is higher, use it at your own risk!

Double Note: Did something go wrong? Did this wreck your save file? Lucky thing it backed stuff up before editing. Replace persistent.sfs with backup.sfs to fix stuff.

Kerbal Space Program - Part model requries an Entry Purchase in R&D

Error message on a new part

Kerbal Space Program is awesome. However, it's still pre-release, so it has some confusing corners. One of them is this puzzling error message: Part model requires an Entry Purchase in R&D. You'll see this when you upgrade a save file to a new version.

It took me forever to figure out how to get access to those new parts. It turns out, you need to find the part in the research tree and unlock it explicitly. Here are the steps:

  1. From the space center, enter the research building. Space center, yay
  2. Find the new part you want in the research tree. I just clicked everywhere that I had already researched. New parts will have a price under the icon. RCS! Yay!
  3. Click on the icon for the part and then spend a few roots to unlock them. buying a new part that I've already researched

It will now be aviaible for use in the spaceplane hangar and vehicle assembly building. Now go add it to a new rocket design that will surely explode on the launch pad.

Note: This was helpful as of v0.24. If you're reading this from the distant future, it might not be relevant any more. (Also, if you're reading this from the distant future, can you send me pictures of flying cars? That'd be rad. Thanks.)

On To The Next Adventure

After 3 awesome years at Google, I'm rejoining startup-land. In a few short weeks I embark on my next adventure as a Developer Advocate at Firebase.

Yup, this means I've discovered yet another organization that wants to pay me to help you build cool stuff with APIs and technology. So, you'll continue to see me at developer events hacking on arduinos, web APIs, and wearable computers.

My Roller Derby Face Shield

Update: The newly published WFTDA rules now allow for the use of traditional non-form fitting hockey half-shields. In other words, this entry is largely obsolete. I'm publishing it anyway, just in case you want to rock a form fitting one for some reason :)

I admit it. I'm a gear junkie. If some odd-ball wheel or a new kind of knee pad comes on the market, I'll probably be first in line. A few months ago I was told that I better protect my nose when skating, or be prepared to buy a new one (and new noses are expensive!) Always looking on the bright side, this presented me with a new opportunity to geek out on gear.

Research yielded one rule and two options. The WFTDA rule 10.1.3 allows for face shields, but only if they are form fitting. Hockey style shields and cages are prohibited. This yielded two options: a custom made face shield or an off the shelf one-size-fits-all equivalent.

  • Custom face shield: This is the kind that Kobe Bryant has been seen sporting. Custom face shields are made from a cast of your actual face. Most prosthetics manufactures can hook you up with one. They offer a great fit and probably much better protection. But, they cost about $1000 D:
  • Off-the-shelf face shield: For those of us on a budget you can buy a one-size-fits-all face shield like this one. They cost between $30 and $40. They're a lot cheaper but the fit is awful and big black pads block lines of vision that are critical to roller derby.

I decided to give the off-the-shelf face shield a try. I figured that even if it was a disaster, $40 would be a drop in the bucket compared to the $1000 for a custom made one.

Initial impressions

  • Vision blocked
  • uncomfortable
  • sweat builds up under pads
  • stuck out really far

Since it was useless in its stock form I decided that there would be no harm in modding it. I hated it anyway, so even if I ruined it, there would not be a significant loss.

Modding phase 1: depadding and reshaping

I had seen a face plate once before. During the second jam of my first scrimmage I met Feisty Irish on the jammer line. Not only did she kick my ass but she also did so with a shiny piece of plastic in front of her face. I didn't remember any ugly black pads, so I emailed her.

She replied indicating that she was using the same off-the-shelf face shield that I chose, but without the black foam pads.

I carefully peeled the pads off. My vision was improved but the fit was not. The fit went from awful to unbearable. I knew there was only one thing that could save me: a heat gun. If in doubt add energy, right?

Polycarbonate, the material that these masks are made from, is very strong at room temperature, but when you warm it up it becomes quite malleable. Unfortunately, the temperature at which it's easily workable is quite close to where it begins to break down. If I warmed and shaped the mask enough I hoped for an improved fit. Here are the steps I followed to reshape it.

  1. Remove the foam pads and straps. They melt at a much lower temperature and it'd really ruin your day if they caught on fire.
  2. Place the mask against your face and select a part to reshape. Focus on places where the mask is flat or curving on only one axis.
  3. Hold the mask with tongs or a protected hand (oven mits work great). It's going to get hot.
  4. Turn your heat gun to its lowest setting. Point the heat gun at the part that you would like to reshape. Hold it about 3cm from the surface and move it in small circles. Focus the heat on the spot you would like to bend, but be sure to warm the surrounding area too. We want a smooth change rather than an abrupt crease.
  5. After what seems like an eternity but is probably under a minute you will start to see the spot that you are heating change. Edges will start to round out a bit, the reflectivity of the surface will change slightly and the shield may begin to bend from gravity. Stop heating the mask.
  6. Are you still heating it? do you see bubbles starting to form? Stop right away!
  7. The shield is a lot hotter than you think. With your protected hands carefully bend the heated suface to the desired shape.
  8. Let the mask air cool. After a few minutes when it is cool enough to put near your face, go back to step 2 and repeat.

Some importnat things to note:

  • Did you get a ton of bubbles? This is bad news. The polycarbonate is a lot weaker now.
  • Fewer heat cycles are better. As you heat and cool the shield it becomes weaker. My hope is that the improved fit is worth the decrease in strength.
  • Make SURE it's cool before you put it near your face. It's hard to tell how hot it is, and plastic burns hurt a lot.

I ruined one shield with this technique, but the second one turned out great! The fit was acceptable and it sat close enough to my face to leave most of my vision relatively unimpeded.

Modding phase 2: grinding and drilling

Spring arrived. The rink I practice at began to warm up with the longer days. Sweat and fog began to build up beneath my face shield. My vision was once again blocked, by my own vapors of athleticism. Around this time I also switched to a hockey style helmet. The hockey helmet covered more of my head and provided less room for my face shield. Something had to be done.

In addition to being heat shapable, polycarbonate is also quite machinable. High speed tools work better, so I grabbed my trusty dremel and went to work.

First, I used a coarse grinding wheel to grind away parts of my mask that prevented it from fitting under my helmet, or were otherwise not helpful. I removed 7mm from the top, narrowed the part that covered the bridge of my nose by 5mm on each side, and removed a whopping 1cm from the tip of the nose (who are these people and why are their noses so long?) This obviously weakens the shield, but it was worth it for the improved visibility and air flow.

I wasn't ready to put away the dremel yet, though. I swapped the grinder out for a drill bit and drilled dozens of small 2mm holes. I placed them just under 1cm apart across the portions of the shield that cover my cheeks and forehead.

Later that night I took it for a spin. Not only was the fogging problem resolved, but it felt much cooler and the portions of the shield that bore holes became more flexible. This improved the fit even further.

Modding phase 3: helmet mounting

All this time I wore the shield under my helmet using the strap harness provided. Getting the straps tight enough yet tolerably comfortable was a continuous challenge. This is when I noticed that my hockey helmet had screws in all the perfect places.

I cut the elastic harness into 5 strips of varying length and used the mounting screws to secure my shield to the helmet. This only works because my helmet fits extremely well. My helmet shifts less than the harness that came with the shield making this an improvement.

Wrapping it up

So has my adventure into face shield hacking been worth it? Yup! I've taken many a wild arm to the face and every time the bearer of that wild arm has been damaged more than I have :)

Inline Skate Wheels for Roller Derby

Before the rotten fruit and beer bottles come flying let me clear one thing up: I am not writing about the use of inline skates in flat track roller derby. I agree that would be blasphemy. Instead I'm here to discuss the crazy idea of screwing inline skate wheels to your favorite quad skates. Yes, I skate with inline wheels on my quad skates.

Who are you? Are you insane?

Jentropy, and yes I am.

Anyway, I guess I should tell you a bit about myself and how I skate: you know, for context. I spend most of my time jamming for the Peninsula Roller Girls. I may not be the fastest skater, but I'm very agile. Unlike the rest of my life, where I focus on being well rounded, in derby I focus on improving what I do best.

How did you end up here?

clean wheels

Why inline skate wheels? Shortly after I started jamming I tried slim wheels: Radar Diamonds. They were awesome. Slimmer wheels are more agile, lighter, result in fewer wheel bumps and conserve energy with their lower rolling resistance. The scientist in me had to know, though, if slim is awesome is slimmer more awesome? To find out which width works best for me I must keep going slimmer until I discover problems[1].

And yes, I am a wheel junkie.

Get to the point already. Are they awesome?

For me? Hell yeah!

The Pros

  • They're ridiculously agile: I find that I can pop onto my toe stops and pop off very easily. Juking/side stepping is also much easier for some reason. The wheels connect to the ground quickly, but they also let go fast.
  • They're much lighter: I never expected a few ounces to make such a big difference.
  • Short bursts of speed: Since they make getting on and off of ones toe stops easier, short bursts of acceleration become more accessible. I find I use them a lot more on inline wheels.

The Cons

  • No hubs: All of the inline wheels that I can find which fit under my skates are the 'aggressive' style. This means that they do not have much of a hub. This makes them a lot squishier than typical quad skate wheels of the same durometer. For this reason they seem to drain my energy reserves faster.
  • Rolling ankles: They're really skinny! The wheels I currently favor have a 18mm footprint. This means sometimes when I come down my center of pressure (where I'm pushing down) falls outside of my wheel base. When this happens my ankle starts to roll. So far I've been able to react quickly and avoid injury, but only time will tell if I can retrain myself.

Wheel Reviews

The wheels I stole from my partner's children's inline skates

stolen wheels

The first inline skate wheels I tried were the ones off of my girlfriend's inline skates. These were marked with 'Bauer' on the side. They were of unknown specification, but normal skate bearings fit. I estimate that they were 75a hardness and 60mm tall. They were also just too wide so I had to McGyver my axel nuts to keep them on.

During my first experiment, at Wumpskate[2], my eyes lit up. I jumped out on to the surface and noticed that I could run around as if I were in sneakers. I skated around a bit and found junking, jumping and stops all very quick. The rolling resistance, however, was pretty bad. I didn't have any reference for speed, but I felt sluggish in the straight line.

Just the same I took them for a spin at my next scrimmage practice. They were very fast off of the jammer line, and I was able to shuffle through the pack with ease, but I was unable to score any points. They were sooooo slow! They were as fun as they were useless at derby. As the other jammer zoomed past me I realized my experiment had failed... or had it?

Yak 96a 62mm aggressive

attempt 2

Not ready to give up I scoured the web for inline wheels to try. My search led me to Amazon and to these Yak wheels.

Upon receiving them I tried them out at the next available alternative skating event: Rainbow Skate[3]. They had the same burst of speed potential as the mystery wheels, but they did not feel like skating through mud! I've kept them on ever since. They've been to derby practice, around my office and even outside. Here's what I've learned about them.

  • They're 96a durometer but skate more like a 92a. I blame the lack of a harder hub.
  • I can finally power slide / hockey stop! Whee!
  • Landing big jumps (e.g. jumping the apex) is a lot easier.
  • They fit almost entirely under my skate which makes wheel bumping nearly impossible.
  • I get a lot lower when I'm turning during a sprint. My chest is almost at my front knee. I have no idea why.
  • They seem to handle a variety of surfaces better. They even work OK outdoors!
  • But, I'm a lot slower than my 96a Radar Diamonds in the longer sprints. This has changed my strategy a bit. When I'm not the lead jammer I'll favor a sprint and hit instead of attempting to nonviolent pass.


If you like slim or super slim wheels, you may want to try out inline wheels.

If you're not ready to try them out yet, keep an eye on my blog. As I try more inline wheels I'll post my thoughts here.

Footnotes on a blog entry? neeerd!

Yes I realize that there is a risk of finding a local minimum with this experiment technique. If you can come up with a cost effective method of conducting this experiment (say without buying every wheel size imaginable) feel free to contact me.
I'm kind of a little bit goth, at least sometimes.
Yeah, I'm also gay. Is that a problem? Grr!