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Showing posts from November, 2010

GAGA-1: CoCom limit for GPS

One problem for high-altitude balloon projects is the CoCom limit on how high and how fast a GPS will operate. To prevent GPS modules from being used in very fast moving weapons (such as ballistic missiles) GPS receivers are not allowed to operate at:

1. Higher than 60,000 feet

2. When traveling faster than 1,000 knots

The second restriction doesn't matter for GAGA-1, but the first does. GAGA-1 will have a maximum altitude (balloon dependent) of more like 100,000 feet.

Different manufacturers implement the CoCom limit in different ways: some use an AND rule (>60,000 ft and >1,000 knots) and others use an OR rule (>60,000 ft or >1,000 knots). For high-altitude ballooning it's ideal if the GPS uses AND. Unfortunately, this information is shrouded mostly in mystery and it's only through actual flights and testing that people have managed to determine which GPS receivers are AND and which are OR.

For GAGA-1 I have two GPS units: one in the Recovery Computer and on…

GAGA-1: Capsule insulation and antenna mounting

A bit of physical stuff on GAGA-1 this weekend after the Recovery Computer software last time. I'd previously painted the capsule for high visibility, but hadn't started cutting it or sticking on parts. After the successful test of the Recovery Computer it's time to put some bits on the box!


The three antennae visible on the box (as with the other components) are hot glued in place. I pierced holes in the box using a long metal skewer and a chop stick.

Here's a close up of the top of the capsule.


The top two antennae are for the two GPS modules (one in the Flight Computer and the other in the Recovery Computer). The long thin antenna is for the GSM connection that's part of the Recovery Computer.

The other two parts are a small red straw and a large black straw. The small red straw is simply there to allow the pressure to equalize between the inside and the outside of the capsule. Since the pressure is very low in the stratosphere it would be dangerous to send th…

Notes on Kryptos Part 4

Copy of message I sent to the Kryptos group on Yahoo! for anyone whose working on Kryptos but not in that group.

Given Elonka's notes mentioning that K4 uses a cipher system not known to anyone else I decided to investigate other possible ways of attacking K4. Specifically, I wondered if the BERLIN crib might not be as simple as NYVTT turning letter for letter into BERLIN.

First I assume that this is something that's breakable by hand as was the rest of Kryptos and thus would simply be based on MOD 26 arithmetic of letters and might involve transposition of characters.

So I went to see if there's a word that could be permuted to create some permutation of BERLIN from NYVTT. There is: it is SILENT

NYVTT
ENTSIL
-----
RLINBE

More strikingly this works if you are sliding SILENT from the start of K4, it falls in just the right position to make BERLIN

OBKRUOXOGHULBSOLIFBBWFLRVQQPRNGKSSOTWTQSJQSSEKZZWATJKLUDIAWINFBNYPVTTMZFPKWGDKZXTJCDIGKUHUAUEKCAR
SILENTSILENTSILENTSILENTSILENTSILENTSIL…

A proper Dr.

I wrote in my bio for The Geek Atlas that (speaking about myself in the third person) "Because he has a doctorate in computer security he's deeply suspicious of people who insist on being called Dr.". I am very suspicious of people who shove their PhD in your face, or who insist on being called Dr. In fact, like a British surgeon, I would much prefer to be called Mr. (which I suppose is a form of snobbery) mostly because it's what I've done after my doctorate that I'm most proud of.

Which brings me to the case of "Dr." Gillian McKeith. I only became aware of her because of the wonderful Ben Goldacre who has taken her to task about her qualifications and claims.

In an old article Goldacre talks about McKeith's qualifications and her legal threats against people who criticize her. He makes the very good point that it's easy to validate real credentials (e.g. if you want to check that I've really got a DPhil from Oxford you just need to c…

GAGA-1 Recovery Computer Ground Test

Today was the first live test of the GAGA-1 Recovery Computer and it, at least initially, didn't go well. The result is much improved, fully working, code in the repository. This is why I'm obsessed with actual testing of the components of GAGA-1.

First the good news: the module ran on 4 AA batteries for 9 hours without showing any problems caused by power. For over 3 hours the module was getting GPS location information and sending SMS messages. This is very reassuring.

Here's the module sitting on the kitchen table ready to go:


Here's the commit message for the code changes:

Significant changes based on live testing of the code on the Telit GM862-GPS module:

1. The module does not support floating point and so the gps2.get() function has been modified to only use integer arithmetic and thus not do conversion of latitude and longitude. This leaves most of the returned elements as strings. Except altitude which is needed for comparisons.

2. The main loop is wrapped i…

I guess Hacker News doesn't do meta very well

(which is ironic for something written in a Lisp variant)

Recently, I've grown tired of stories about the TSA on Hacker News.

So I posted and item saying that I was taking a break (the title was "Au revoir Hacker News") with text saying that I was fed up with the TSA stories (and in particular the Ron Paul story in the top slot) and that I was going to take a temporary break. It ended saying I'd see everyone in the New Year once things had blown over.

It was at this link but it was nuked by someone. Not made [dead], simply expunged by a moderator.

Feels a bit uncalled for to me, I'd have been happy for the community to shoot me down.

(Actually it is [dead] so it was the community that killed it off)

I guess I'll be back in the New Year.

The things make got right (and how to make it better)

make is much maligned because people mistake its terse syntax and pickiness about whitespace for signs of being an anachronism. But make's terseness is what makes make fit for purpose, and people who design 'improvements' rarely seem to understand the fundamental zen nature of make.

Here are some things make does well:

1. make's key use is in the expression of dependencies. make has a compact, syntactic cruft-free way of expressing a dependency between a file and other files.

2. Since make is so dependent on handling lists of dependencies it has built-in list processing functionality.

3. Second to dependency management is the need to execute shell commands. make's syntax for including dependencies in shell commands is small which prevents the eye from being distracted from the commands themselves.

4. make is a macro-language not a programming language. The state of a build is determined by the dependency structure and the 'up to dateness' of files. There…

GAGA-1 Recovery Computer

Finally, got some time to work on the GAGA-1 Recovery Computer that uses a combination of a GPS and a GSM module to send position updates via SMS to a cell phone. The complete code is now in the repository in the gaga-1/recovery/ folder.

The recovery computer itself is a Telit GM862-GPS module mounted on a board that supplies power from four AA batteries. It has two external antennas: one for GPS and one for GSM access. Here's a shot of the computer before installation in the capsule (clearly the cables are going to have to be shortened and the power supply cleaned up before the real flight). The GPS antenna is square and the GSM is the long thin bar.


The GM862-GPS has an integrated Python interpreter so the control software is a set of Python modules that handle getting GPS information (and sundry information like temperature and voltage) and sending SMS messages at appropriate times. Here's the key piece of code for the recovery computer:

# The recovery computer runs thro…

The most common objection to my 'releasing scientific code' post

Is...

And why dismiss so casually the argument that running the code used to generate a paper's result provides no actual independent verification of that result? How does running the same buggy code and getting the same buggy result help anyone?

Or as expressed at RealClimate:

First, the practical scientific issues. Consider, for example, the production of key observational climate data sets. While replicability is a vital component of the enterprise, this is not the same thing as simply repetition. It is independent replication that counts far more towards acceptance of a result than merely demonstrating that given the same assumptions, the same input, and the same code, somebody can get the same result. It is far better to have two independent ice core isotope records from Summit in Greenland than it is to see the code used in the mass spectrometer in one of them. Similarly, it is better to have two (or three or four) independent analyses of the surface temperature station data sh…