He is correct that missile components can go to 4 decimal precision, with the exception of engines which are now restricted to 1 decimal precision.
You have some tech that is hurting you.
Your warhead tech is really eating into the available msp for a size 1 missile. With the new engine designs being limited to single decimal this needs to be at least "Fusion-boosted Fission Warhead: Strength: 5 x MSP" which let's you have a .2msp 1pt warhead. This leads to being able to use a .7msp engine and still have .1msp for agility and fuel.
For defensive launchers stay away from reduced size tech, with the exception of box launchers in some applications. Your defense launchers need the maximum ROF you can get. Your missile reload tech is also hurting you in this. Jump this to "reload rate 3" and you have a 10second cycle for size 1 missiles. (rate 6 gets you the highest rate for size 1 of 5 seconds)
The spec's that Nathan posted will work, but in my opinion leave something on the table. It's nothing dramatic, just a difference in approach.
To modify his spec's to my approach it would look like this:
Warhead: .3334msp for 1pt
Engine stays the same: .5msp/X3.5 modifier for 1.05 propulsion pts
Agility: .1409msp for 5pts of agility giving a maneuver rating of 15
Fuel: .0257msp giving 64.25liters of fuel for a range of 11,966,509km
The agility is lower because of how the program handles rounding. I've detailed this in a different thread.
http://aurora2.pentarch.org/index.php/topic,5444.msg56064.html#msg56064Personally I'd change to:
Warhead stays the same
Engine: .6msp for 1.26 propulsion pts giving a missile speed of 25,200kps
Agility : .047msp for 2pts of agility giving a maneuver rating of 12
Fuel: .0196msp for 49liters of fuel for a range of 10,336,445km
The hit chances of my suggestion are a little worse:
1000 km/s Target: 302.4%
3000 km/s Target: 100.8%
5000 km/s Target: 60.5%
10000 km/s Target: 30.2%
30000 km/s Target: 10.1%
50000 km/s Target: 6.0%
This is driven by my preference for the fastest practical speed in my defensive missile. Your mileage may very.