So I'm trying to work out what would be required to move a realistic weighted asteroid using KSP.
Firstly I've determined that the ION engines are vastly overpowered and use a miniscule amount of power.
From what I can find with google:
Engine: :mass :thrust :power : propellant use
PB-ION engine 250Kg 2,000N 8.729 E (1) 0.0485Kg/s
SMART-1 29Kg .068N 1200W 0.01611Kg/h
NEXT(2)
? .236N 6900W
200 Kw VASIMIR(3) 1200Kg 5N 200Kw 5000isp
Mw VASIMIR(4) 1200Kg
1000KW 2000isp
(1) Power requirement of kerbal technology can be determined by analysis of solar panel output, a Gigantor has an area of approx 14 square meters and produces 18 E/s, with 30% efficiency this comes out to 60 E/s solar output at one KAU(kerbin astronomical unit), This becomes 216,000 E per hour, If we assume that Kerbin receives the same amount of light as Earth which gets approx 1366 Watts (per hour) then approx 11.295 E are worth 1 watt. Therefore a OX-stat produces 238 watts(an unreasonably high number) and a Gigantor produces 5.7 Kilowatts (a realistic number, but considering the calculation was based on this panel then It should definitely be)
(2) I couldn't find data on the mass or the fuel use of the NEXT, however the ISP was around 4200seconds which matches the PB-ION and a simple calculation would tell me the actual fuel usage
(3) An actual working test engine, However using solar panels for this kind of engine is considered unfeasible in real life, AD astra assumes a capability of producing working space capable nuclear reactors in the range of 1 kilogram per watt in order to run this kind of engine, however the soviet TOPAZ reactor had a weight of 100 kilos per watt, NASA were hoping on producing a 65 kilo per watt reactor for Prometheus and Robert Zubrin who seriously doubts the capabilities of VASIMIR, assumes a best case estimate of 20 kilograms per watt being possible. Note that solar panels can easily achieve 2 kilograms per kilowatt using current technology, but they're very expensive, I'm assuming however that mass production for an asteroid capture mission would reduce costs untill they're far below that of a nuclear reactor, also the development time for said reactor might be rather high compared to merely producing panels. Also note that a gigantor weighs 61 kilograms per kilowatt. Finally a note on RTGs(Radioisotope
Thermoelectric Generators) the RTG recently sent to mars on a rover weighs 45 kilograms and produces 110 watts, which is 409 kilos per watt, And the PB-NUK produces 239 watts and weighs 80 kg which equates to 334.7 kilos per watt
(4) The data I can find for the megawatt VASIMIR is terribly conflicting and doesn't match up with the observed capabilities of the 200 KW VASIMIR, particularly annoying is the paper titled"The VASIMR Engine: Project Status and
Recent Accomplishments" which lists the 1 MW engine as having a total weight 1.2 MT. Which either means 1200 Tonnes or 1.2 Metric tons. Considering the 200KW test engine weighed this much it might be reasonable that a newer model weighs 20% as much due to attention being paid to actually lightening the design, once again i couldn't find any data on the actual power output, but i would have to assume it is 5 times the 200KW model.
What do I make of all this? Firstly the PB-ION is 3411 lighter than a Smart-1 engine, and 2000 times lighter than a VASIMIR engine. It also only requires 2.7 KW electricity but for that thrust level should actually require 35,000-80,000 KW, propellant use hasn't yet been taken into consideration, but a 2000N rocket should use 0.131 kg/s propellant which is 2.7 times as much fuel (actually not too far off reality) Add to this the fact that Kerbal asteroids are 2% the weight of real asteroids and then you have a small problem.
I shall have to produce a rebalanced ION engine perhaps:
PB-ION engine 10,000 kg 100N 1764 kW 5536 E/s 0.00658kg xenon per second.
Note: Weighs 40 times as much as the stock ION, or double what a hypothetical VASIMIR would, produces 1/20th as much power, requires 634 times as much power or 307 Gigantor panels, and requires 1/7th as much xenon.
I'm going to need that part welding mod so my computer doesn't melt from the solar panels alone.