Over on Charles Stoss’s blog there Is an interesting post by H Harold Page on the Traveller RPG some of the commenters on that post mentioned the use of planetoid accelerated to some appreciable fraction of c as a planet killer weapon.
Interested by this I dug out my old traveller books and ran the numbers on what it would cost to produce such a weapon using the Traveller ship design rules.
On idea was you find a suitable planetoid in the ort cloud and build it into a weapon in place – how you avoid the systems defences whilst you build such a planet killer is another matter as typically you would have SDB (system defence boats in the ort cloud).
I have designed a PS (Planetoid Strike) 10kT using book 5 for two scenarios one where the platinoid is built in system and one where it has some Jump (FTL) capability allowing the weapon to be built at a distance and move to the target system (though it would need supporting tankers if it had to make more than three jumps)
The ship is based on the Mistel concept from WW2 with a second jump capable star ship being used to control the ship on the final run and separating at the last moment to jump away with the crew.
Option 1 No FTL
This option is where the ship is built in secret in the ort cloud and sortied directly from the target system assuming a month of acceleration at 6g you get close to 0.3 c. A second-hand type S is used to control the final run in and to allow the skeleton crew to escape (I have assumed 10% of the normal crew is require for a one-way trip. This ship costs 4715 Mcr.
|Name||A Lot of Gravitas|
|Crew||10||24||0.125||Skeleton Crew @ 10 %|
|Mistel||0||20||Second Hand type S|
Option 2 FTL
This option is where the ship is built in another system with minimal jump capability 3x Jump 1 in the case a second-hand type A I used to remove the crew I have assumed 20% of the standard crew in this case to cover the extra requirements for FTL. This option can sortie from up to 3 jump ones away or from further way provided tankers are available to refuel.
The ship would jump into the target systems ort cloud and start accelerating for a month which should get you to around .3c
This option Costs 5535 Mcr
|Name||Even More Gravitas|
|Fuel (j)||0||3000||0||Enough for 3x Jump 1|
|Crew||20||48||0.125||Skeleton @ 20%|
|Mistel||0||40||Second Hand type A|
Note that this is built using the average tech level in the imperium and build time using high guard is from 24-60 Months for a ship of this size building the ship in the target system would presumably take longer as there would be no local ship yard.
Neither of the ship have any armament at all, apart from those on the type S or Type A A system that had any relatively modern defences would easily detect and engage this sort of attack. With a cost for 4 to 5 Billion Credits for a single use weapon that only works against much lower tech I don’t think this is a viable weapon.