## Bias

“Wald applied his statistical skills in World War II to the problem of bomber losses to enemy fire. A study had been made of the damage to returning aircraft and it had been proposed that armor be added to those areas that showed the most damage. Wald’s unique insight was that the holes from flak and bullets on the bombers that did return represented the areas where they were able to take damage. The data showed that there were similar patches on each returning bomber where there was no damage from enemy fire, leading Wald to conclude that these patches were the weak spots that led to the loss of a plane if hit, and that must be reinforced.”

– http://en.wikipedia.org/wiki/Abraham_Wald

## Uncoordinated

I was mucking about in javascript, simulating geostationary satellites orbiting around the earth. Then I started thinking about simulating moon missions – ie. properly simulating the thrust of (say) the Saturn 5 rocket at various stages of the launch, how the fuel mass decreased and so resulted in increasing acceleration at fixed thrust. There’s plenty of data available about when they lit engines and started roll programmes for the Apollo missions.

Anyhow, this lead me to realise that I’m too earth-centric in my coordinate systems. I need to know where the moon was in 1969 when Apollo 11 took off. Actually, I’m wasn’t even sure which coordinate system you’d measure that in. WGS84, used by GPS sysems, ain’t so much use if you’re flying to the moon! The ICRF is what you need.

It also made me think about a location-a-pedia. Ie. something which tells you where objects were at a certain time. Where was the moon at the instant when Apollo 11 took off? Where was it when Apollo 11 landed? Perhaps for flying sims, you might have historical data about where different commercial flights were at different times. For space sims, you need to know where the objects of the solar system were. Newton’s laws will tell you how they move, but you need a starting point.

(Update: Omg, it’s 2013 and I just used a telnet interface to an online system).

Maybe in 20 years, all objects will be reporting their coordinates (in some galactic coordinate system) to a central database. That way, if you lose your keys, you’d have an easy way to find them. Even if you were on Mars.