Diagnosing Errors in Spacecraft Telemetry

Posted by on 6 November 2012 No comments

Unsurprisingly I fell into the void of work while developing software for the TechEdSat spacecraft, which explains the lack of posts on my blog.  One of the things that tends to set spacecraft software apart from regular terrestrial software is that typically you don’t get a second chance to fix things in orbit.  Sure NASA APR’s require you to have this functionality, but most small spacecraft such as TechEdSat get a waiver for the requirement as it is usually out of the scope of a CubeSat mission.

TechEdSat was deployed from the ISS with a plethora of software problems, mostly stemming from the incomplete nature of the project as we approached our delivery deadline.  An interesting one I discovered today prompted me to write this blog entry on the discovery and diagnosis of one such error.

I was decoding a packet received from JA1GDE, a HAM from Tokyo, Japan, when I discovered a small discrepancy in the timekeeping of the spacecraft.  There is only one timer on TechEdSat; the Spacecraft Elapsed Timer (or SCET), however time is stored in two locations in the beacon packet in two different formats. The SCET itself is stored as seconds elapsed in the first 8 hex ASCII characters (representing 4 bytes) after the 10 digit website header (ncasst.org).  The second storage of time is the “NON_Minutes”, which represents the time the spacecraft has spent during Nominal mode of operations in minutes, stored as 4 hex ASCII characters (2 bytes).  Due to last minute changes in the spacecraft, the processor should never enter “safe mode”, thereby resetting the “NON_Minutes” counter, so its essentially the elapsed minutes timer.  Intuitively one should think that the value of NON_Minutes should be exactly SCET/60.

Let’s look at the actual numbers:

SCETTime 8 002a9029 2789417
NON_minutes 4 b4cf 46287

In this example, the SCET shows 2,789,417 seconds and the NON_Minutes timer shows 46,287 minutes.  SCET/60 = 46,490, or a difference of 203 minutes.  I found this interesting, and made a comment to a coworker who sits next to me.  We thought about what might cause the error, and started by looking at the number and what order of magnitude it was relative to other metrics in the spacecraft.  We stumbled on an interesting relation:

The difference in time, 203 minutes, turns out to be 12,180 seconds.  This number is within 5% of (SCET/60) divided by 4.  When we realized this exactly represented a 250ms delay every time the NON_Minute timer ticked up one, we instantly realized where I had made an error:  the spacecraft main loop operates on a 4Hz cycle, for some arbitrary reason that no one can seem to remember.

delay_ms(250); // Cycle currently operates at 4Hz

The above line of code is the offender.  Because the main loop waits 250 ms at the end of every cycle, the update of the NON_Minutes timer is always 250ms late.  This time difference when compounded over the 32 days of the mission elapsed so far produces a drift in the NON_Minutes timer.

I’m taking a note of this as “lesson learned” and will not adopt a similar scheme for the spacecraft executive on my next spacecraft.

10 Years of CheeseJaguar

Posted by on 11 March 2012 No comments

As of 16 January, my username “CheeseJaguar” is at least 10 years old.  I’m a little late on the anniversary, but only recently had the inclination to go check.  I sat at least because I know I used “CheeseJaguar” before AIM as my Runescape username.  Runescape doesn’t log account creation dates, and the account seems to be deleted.

How to enable SSL encrypted google search on Chrome

Posted by on 17 January 2011 No comments

If you’re the paranoid type, you might want to use the Google Encrypted Beta.  It takes about 30 seconds to setup, and is probably well worth your time.

From Chrome, click the wrench icon in the upper left, and select “options”.  Under the basics tab, click the “Manage” button in the Search section.  Add a new entry by clicking the “Add…” button, and enter the following information:

Name: Google SSL
Keyword: google
URL:  https://encrypted.google.com/search?q=%s

Once this is done, select your “Google SSL” entry from the list, and click the “Make Default” button.  Now any Google searches made using the browser bar will default to Google’s SSL encrypted search engine.  This is useful for surfing the internet on public networks, where network sniffers may be able to intercept packets sent from your computer to Google, to see what you’re searching for.

Secure your Minecraft server with offsite backups

Posted by on 16 January 2011 No comments

Keeping incremental backups of your world folder may not be enough to prevent the loss of the your Minecraft server data. This guide will show you how to backup your entire server director to Amazon’s cloud storage solution, S3.  I chose S3 mainly because it was cheap, and had fast access speeds with redundant storage.  If you backup a 500MB world folder, you will probably spend less than $1 per month on your AWS bill.  My previous 6 bills have all been under 15 cents. S3 was also easier to use than some of the other offsite backup services I tried.

The tools I will show you how to use in this tutorial were s3fs and rsync.  The software s3fs will enable you to mount an Amazon S3 bucket directly to your linux filesystem. Please note this tutorial requires a moderate knowledge of linux command line interfacing. This tutorial was written for a system using Ubuntu 10.10 Server x86, but could be modified to fit any linux operating system.

The first step is to make sure you have the required dependencies for s3fs.  If using Ubuntu, your required packages are build-essential, libcurl14-openssl-dev, libxml2-dev and libfuse-dev.  Note that this tutorial will install s3fs version 1.33, which requires FUSE 2.8.4, which is a higher version than the 2.8.1 version currently supplied in the Ubuntu repositories. To install the packages in the repositories execute the following commands as root/sudo:

apt-get install build-essential libcurl4-openssl-dev libxml2-dev

To install the latest version of FUSE (currently 2.8.5), retrieve this package from sourceforge. Once you have the package, installation is typical of what you’d expect from source.

tar -xzf fuse-2.8.5.tar.gz && rm fuse-2.8.5.tar.gz
cd fuse-2.8.5
./configure
make
make install

Now that you have the dependencies installed, it’s time to install s3fs. Again, installation will be from source, as root/sudo.

wget http://s3fs.googlecode.com/files/s3fs-1.33.tar.gz
tar -xvf s3fs-1.33.tar.gz && rm s3fs-1.33.tar.gz
cd s3fs
./configure --prefix=/usr
make
make install

You now have all the necessary tools installed to automate your offsite backups. Next we will create a directory to mount our S3 bucket to. As root:

mkdir /mnt/backup
chown your_username_here:your_username_here /mnt/backup

For the next few steps, you will need your accessKeyID and secretAccessKey from Amazon. These can be located by navigating to http://aws.amazon.com, logging in and clicking “Account” from the top menu bar, and then “Security Credentials”. The required information is listed under “Access Credentials”. Once you have this information, it would be good to create a bucket for your backup. This can be accomplished easily from the AWS Management Console.

Now we will create the backup script that will rsync files to your bucket. The way the script will work by mounting the bucket, copying files and then unmounting the bucket. Keep in mind for minecraft, you may want to back up your entire server folder as opposed to simply your world folder.  Especially if you’re using Hey0 mod, you may need to backup plugin information from stuff like iConomy. Create the following script called backup.sh

#!/bin/bash
#backup.sh - Script by CheeseJaguar
/usr/bin/s3fs yourbucketname -o accessKeyId=your_access_key_ID -o secretAccessKey=your_secret_key /mnt/backup
/usr/bin/rsync -av --delete /path/to/folder/that/you/want/backed/up /mnt/backup
/bin/umount /mnt/backup

Save the script and make sure to chmod the script so that it is executable.

chmod +x backup.sh

Now all you need to do to backup your server is run

./backup.sh

If you’d like to automate the task, add a cronjob to your crontab. As root:

crontab -e

And add the line:

0 0 * * 0 /wherever/you/saved/it/backup.sh

This example line will backup your server every Sunday at 12:00AM. The 5 characters preceding your command tell the crontab how often to execute the command. The first character tells it which minute to execute, the second character tells it which hour to execute, the third character tells it which day of the month to execute, the fourth character tells it which month to execute, and the fifth character tells it the day of the week. Asterisks indicate every minute or hour or day,etc, and you can use commas to indicate multiple times. For example, 0,15,30,45 * * * * would execute every 15 minutes. For further reading, consult the Wikipedia article on Cron.

Once you have this setup, you will be automatically backing up cheaply and securely. Now let’s say for whatever reason someone took your server and threw it out the window of a high-rise. To get your world back, simply create a script with the source and destination parameters of the previous script, but switched. Like so:

#!/bin/bash
#restore.sh - Script by CheeseJaguar
/usr/bin/s3fs yourbucketname -o accessKeyId=your_access_key_ID -o secretAccessKey=your_secret_key /mnt/backup
/usr/bin/rsync -av /mnt/backup /path/to/put/your/files/in
/bin/umount /mnt/backup

This will bring your files back to your server, like nothing had happened (since the last backup, at least).

The Folly of the Gaming Laptop

Posted by on 23 July 2010 No comments

I see it all the time.  Sometimes in Reddit’s “buildapc” section, sometimes from my google adventures and sometimes from friends.  I don’t quite understand the desire, but I think if anything it’s simply really effective marketing.   Most commonly, a kids graduate high school, they try to look for a way to continue their gaming hobby in college.  The mantra is that every college student needs a laptop, and these kids decide their laptop needs to also be powerful enough to play today’s  most demanding video games.  Usually this just means they end up overpaying for a laptop that isn’t really up to the task of gaming anyway.  This article will mainly focus on college students as that’s where I have the most experience.

The Sheep in Wolf’s Clothing

I’m going to analyze one specific laptop, out of the dozens of good options for a “gaming” laptop, the Alienware M17x.  The stock configuration of this laptop is as follows:

  • Intel i5-520M 2.93GHz Dual Core Processor
  • ATI 5870 Mobility
  • 17 Inch 1440×900 Display
  • 2x2GB DDR3 Memory
  • 250GB 7200RPM HDD
  • Combo Drive
  • 802.11n Wireless Support

Total price? $1,799.99.  If you were unaware, that’s a lot of money for the spec’s you get.  Most people try and justify the cost of the gaming laptop saying that they need a laptop for college.  Do you need an $1800 laptop for college? Definitely not.

My Advice

My recommendation for all college students and all parents of college students is to not spend more than $500 on a laptop.  Why? Because no college student needs to lug around a 12 pound laptop to their classes every day.  The ideal laptop for a college students in my mind is the Dell Mini-10v. It’s small but not too small, it’s got a 92% size keyboard and 9.5 hours of battery life all for just $299.  It packs plenty of punch for taking notes in the classroom or working on a powerpoint in the library.  You can even use DropBox to synchronize your school work on the go.  What it can’t do?  It likely can’t watch YouTube videos full screen and it can’t play any 3D games.  Bummer?  Not really.  Cause if you were just about to spend $1800 on a laptop and you only spent $300 on this guy, how much do you have leftover?  For those of you playing at home, $1500!  $1500 will build you a monster of a computer!

The M17x Desktop Equivalent

So if you wanted the same exact power of an M17x, but in desktop form, how much would you have to pay? $740.  That’s a markup of over $1000 just so you (or your son/daughter) can carry around a mini-super computer.

Same (if not more) performance for $740, at the cost of decreased mobility and a more space taken up at your desk.  Add the price of a $300 netbook to this computer and you’re still left with $700 in your budget.

What to do with the leftover $700

I’ve been a university student for 3 years now, and I know all the little lies people tell themselves about why they need what.  ”I need a powerful laptop so I can do CAD”, “I need to be able to compile programs”.  ”I’m going to be writing a lot of papers so I need a nice laptop.” “I want to be able to take notes on my laptop in class.”  There is merit to all these arguments, however there is no reason a desktop can’t be used.  In fact, I find that most people are less productive doing work outside of their room anyway.  The reality is that my girlfriend has gone through 4 years of college as a Pre-Vet Biology (Systems Physiology) major with a $400 Dell desktop, and her GPA is excellent.   In addition, I find that it’s simply easier to take notes by hand for pretty much any class.  A lot of note taking involves drawing diagrams, and doing so may be difficult to do quickly on a laptop.

So What to do with the leftover $700 to optimize yourself for your university studies?

  • RAID 1 Hard drives: RAID 1 provides data backup in case of a hard drive failure.  If you loose all of your papers and homework, you will be sorely upset.  Trust me.  All you have to do is buy a second hard drive of the same make and model and configure them for RAID.
  • Buy two monitors.  Dual monitor setups can be extremely helpful for multitasking, and especially helpful for students who are doing video editing, CAD, graphic design.
  • Invest in a good pair of headphones.  You don’t need noise cancelling, noise “muffling” will do just fine, I’ve got a pair of Sennheiser HD-280 Pro’s and they are great for blocking out noise and focusing on work.
  • Upgrade: 5770 not enough for you?  Why not upgrade to a GTX 480 if you need the power (you’d also need a better power supply).  Need a quad core? Probably not but if think you do then the i5 750 is a great processor.

The choice is ultimately yours.  If you think you need to spend $1800 on a laptop then go ahead, but you’ll most likely be wasting a lot of money.  My parents spent $2200 on my MacBook Pro when I started school, and I was very thankful.  My laptop could play video games, use CAD better than most laptops, and it was pretty fast at day to day tasks.  However, my laptop was too heavy even at 6 pounds, so I rarely brought it to class with me.  My campus is one of the smaller college campuses and it was still a half mile walk each way to some of my classes.   When I did bring it to class, I found it was more of a distraction.  I found myself mostly using it at my desk in my room.  Not to mention when it came time for an upgrade, I could upgrade the RAM and the hard drive but nothing else.  Desktops are fully upgradeable.  There are plenty of genuine reasons why you might need a powerful laptop, but be sure when you go for that gaming laptop that you think the extra $1000 is worth it.

Useful Links for Building A Computer

Posted by on 19 July 2010 No comments

There are several websites I use frequently for researching and purchasing computer parts.  Some are obvious and well  known, and some you may have missed.  I hope you’ll find these links helpful, there is a lot of information out there and not a lot of it is helpful.

Google

http://www.google.com

Google is a pretty obvious resource.  I feel like I shouldn’t even have to mention it, but then again I often see people with questions that google can answer very quickly.  Knowing how to use google isn’t terribly difficult but you do know how to phrase search terms.  When comparing two purchase options, it’s often helpful to search “Option A vs Option B”, as chances are you’re not the first to have thought of such a mystery.

Newegg

http://www.newegg.com

One of the most popular websites out there for buying computer parts, Newegg will always be my favorite simply because of the way you can filter out different products when searching for something.  Once you have an idea of what motherboard or processor you want, it becomes very easy to search for exactly what time of memory you need, or what size case, etc.  I’ve spent hours just surfing Newegg and looking at different combinations and reading reviews on different products.  While Newegg may not be the best place to start, it’s definitely the best place to finalize your build.  Newegg is also awesome for their Shell Shocker deals, which I subscribe to on

Amazon

http://www.amazon.com

Amazon is not often the first choice for some computer building enthusiasts, but I’ve grown pretty fond of it.  If you’re an Amazon Prime account holder, you can get Prime Eligible items to your doorstep in 2 days, and next day for only $3.99 per item.   Amazon’s prime eligible selection is not as large as you may need, but you’ll probably find that most popular hardware is prime eligible.  Furthermore, if you live in California like me Newegg has sales tax, while Amazon doesn’t.

eXtreme Power Supply Calculator

http://extreme.outervision.com/psucalculatorlite.jsp

When choosing power supply size, it takes a lot of research to be able to find the exact power requirements of most items.  Often finding the TDP (Thermal Design Power) rating of most devices is difficult for anything besides CPU’s.  This handy calculator will let you know if your power supply will be able to manage your upgrade, or just tell you what size you need to buy for your new computer.  Don’t take the results as gospel however, for example if you get a result of 630W you should probably buy something more than a 650W PSU. In engineering we use what’s called a factor of safety, and I tend to prefer to use a factor of safety of at least 1.2 when buying power supplies.  Basically a FoS of 1.2 on a 600W requirement would mean you buy at least a 720W PSU. (600 * 1.2).

Reddit

http://www.reddit.com/r/buildapc

Even I’ve stopped by this awesome little reddit for advice on building a new computer.  It never hurts to ask questions when considering a new build.  There are a lot of knowledgeable people that post there, just remember to take all advice with a grain of salt.

AnandTech

http://www.anandtech.com/

AnandTech is in my opinion the best place to get information about hardware.  I used to be fond of Tom’s Hardware, but recently I’ve become very disenfranchised with that site.  AnandTech has very in-depth reviews and has a plethora of benchmarks when they review new hardware.  Their benchmark charts can make comparison shopping much easier.

Passmark CPU Benchmarks

http://www.cpubenchmark.net/high_end_cpus.html

Is one CPU “better” than another? It’s often hard to tell.  Often different processors be better suited for different tasks, however the theoretical processing power any given processor is useful when making decisions. Synthetic benchmarks should never be used to say “Processor A is better than Processor B, but can often show you how much better a certain $200 processor is than a certain $100 processor.

These aren’t the only websites I use, but the ones that I think you may find the most helpful in starting out your research.  There are many good forums out there which have a lot of advice, and Google is a great place to find those forums.  Of course, don’t forget you can always just ask me for advice.

How to Build a Computer: Beta

Posted by on 15 July 2010 No comments

If you look to the top of this webpage you’ll notice there is a new tab titled “Request Computer Build Advice.”  This is a new service I’m rolling out free of charge.  Building computers is something that I enjoy, so I don’t mind taking 10-20 minutes out of my day to help someone put together a computer they will enjoy for the next 3-5 years.  While I can’t offer any sort of guarantee or warranty, I will hope to offer some good advice that you can take into consideration when building your computer.

The service rolled out yesterday, and from a simple post to the BuildaPC reddit I received over 170 visitors yesterday! That’s awesome, especially since my monthly unique visitor rate was about ~100.  I’ve added a donate button to the bottom of the page, feel free to give a dollar or so if you’d like.  All money donated will be reinvested in the blog (hosting, advertising, etc.) and is mostly a safeguard in case for some reason my site gets swarmed by a lot of traffic and I have to foot a large bandwidth bill.

Speaking of traffic, I purchased a Reddit sponsored link for $20.  We’ll see how it works out, the link should run Monday and will take people to the “How to Build a Computer” page if clicked.

The New Nvidia GTX 460

Posted by on 14 July 2010 No comments

After the failure that was the GTX 465, Nvidia has decided to release a new budget card for the market that specifically takes swipes at ATI’s 5770 and 5830.  Both Nvidia and ATI are competing for the $200 range graphics card, which is a much more popular price point than the $300 and $400 cards that enthusiasts tend to buy.  So has Nvidia succeeded with the GTX 460?

The GTX 460 is the newest edition of Nvidia’s Fermi family of GPU’s.  While the 465, 470 and 480 are based on the GF100 GPU, the 460 is based off a new GPU titled “INSERT GF-WHATEVER HERE”.  Two flavors of the card will be offered, one with 768MB video memory and one with 1GB for $30 more.

The 460 is showing improved frame rates over the 5770 and the 5830, making it an excellent choice for a budget gaming computer.  Unfortunately, the 460 is still a member of the Fermi family, and as such requires two 6-pin PCI-E power connectors from your power supply.  While this means that those with older power supplies will be unable to upgrade to the newer GTX 460 without a new power supply, most new power supplies should have the required cables to fulfill your card’s thirst for electrons.  On the subject, I would also strongly discourage people from using power supply adapters as older PSU’s without the necessary connectors may also not have the necessary amperage to run high-end video cards.

In the end, the 460 is a very competitive introduction to the market, and Nvidia will most likely see increased market share in the $200 video card market.  However, expect to see price drops on the 5770 and 5830, as well as the 5850 and 5870 in the near future to make ATI more competitive with Nvidia.

My new i7 Build

Posted by on 14 July 2010 No comments

I decided that I needed a new computer for playing video games.  Also I probably needed a better CAD/CFD machine, but mostly for video games.

Intended Hardware:

CPU: Core i7 930
Cooler: Corsair H50
RAM: Corsair XMS3 2x2GB DDR3 1600
Motherboard: EVGA SLI 3X
HDD: Western Digital 1TB Caviar Black
Optical Drive: ASUS 24x Combo
Video: EVGA GTX 470
PSU: Corsair 750W TX
Case: Antec 902

Total cost: $1250

So far I’ve purchased the case, processor and motherboard.  Here is a picture of them sitting on my desk.

Mobo, Processor and Case

I’m waiting on my next paycheck to buy the rest of the parts, but I can’t wait! I’ll post updates as my build progresses.  I’ll also be using this as an opportunity to show people how building a computer works.  I’m also open to questions about building a computer, so feel free to ask.  I can’t wait to get started!

Free Amazon Prime for Students

Posted by on 13 July 2010 No comments

Last night Amazon debuted a free service to all students with a .edu email address: free Amazon Prime for one year. I was ecstatic to hear this, because I have always preferred to use Amazon whenever possible to order computer parts online. Sure, Newegg has the best information, is the best way to search, sort and filter, but Newegg often just can’t compete with Amazon’s pricing. I’m one of those unlucky people who live in California (or New Jersey), and we have to pay sales tax on everything we buy on Newegg. Not Amazon.

My new computer (upcoming post, stay tuned) will cost an estimated $1200. At a tax rate of 8.25% that’s an extra $100! So parts on Amazon basically have to be more than an 8% markup from Newegg prices for them to be more expensive. Furthermore there is the issue of shipping. Amazon has free shipping on all orders greater than $25, and the shipping while not the fastest is not bad. Amazon’s free shipping is 5-9 business days, as opposed to select items on Newegg, which ship free in 2 business days. For this reason, sometimes I would buy from Amazon and sometimes I would buy from Newegg. If I was in a hurry and didn’t want to wait 2 weeks, maybe I’d spend a couple more bucks and order from Newegg. Now I have an Amazon Prime account, and I can get anything Prime-eligible to my door the next day for $3.99, or the day after for free.

The selection of Prime-eligible computer parts isn’t amazing, but most mainstream components are Prime-eligible. But seriously, $3.99 per item next day shipping for any student is amazing. As long as you place your order by 6:30pm EST, your order will arrive the very next day. For $3.99. If you haven’t noticed, this makes me ecstatic. I hate having to wait 2 weeks for something I spent so much money on to arrive.

Amazon is a very interesting company, and I hope to see them continue to thrive.