Defense Intelligence Reference Document Laser Lightcraft Nanosatellites

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• ri = 1: this is the conversion efficiency of laser rocket propellant-thrust-jet KE into
vehicle KE, in which the propellant/laser is designed so that the rocket thrust-jet
velocity is equal to the vehicle velocity throughout the mission, i.e., the laser
rocket has variable lsp "" 100 seconds at beginning of mission to 1000 seconds at
end of mission;
• up = 0.5: u is efficiency of laser energy absorption and p is efficiency of
conversion of propellant internal energy into thrust-jet KE;
• y = 0.7: this is the atmospheric transmission efficiency;
• Eiaser = 750 MJ.
These numbers multiplied together give a vehicle KE = 262. 5 MJ in LEO. If the effective
change in velocity (Av) required to get to LEO is 10 km/sec (8 km/sec orbital velocity +
1 km/sec for gravity+ 1 km/sec for drag loss), then 1 kg in LEO has 50 MJ of energy
investment and a 5.25 kg payload in LEO has 262.5 MJ of energy investment.
The 60 kg/sec mass flow requirement of the 3: 1 N2/C02 lasing gases means that a
mass flow of 15 kg/sec of CO2 and 45 kg/sec of N2 is required. For the 300 seconds of
thrust we will therefore need 4.5 tons of CO2 and 13.5 tons of N2 gases (we are
neglecting the tiny amount of H2) to launch a payload to LEO. Liquid CO2 costs $100
per ton and liquid N2 costs $154 per ton. The total lasing gas cost is therefore $450 for
the liquid CO2 and $2,079 for the liquid N2. Adding these two gas fuel costs to the $104
cost of the required electrical energy gives a total of $2,633 to launch a 5.25 kg
payload to LEO. This result represents a cost of $501 per kg of payload (or $228 per
pound) launched to LEO, which is 44 times lower than the oft-quoted standard space
launch industry cost of $10,000 per pound for conventional chemical propulsion rockets
systems.
However, this cost figure needs to be slightly adjusted to account for other factors. If
we use the N2/C02 gases at a temperature of 217 Kin the laser, then we will have to
boil the liquid CO2 and the liquid N2 with additional heating of the gaseous N2. Boiling
4.5 tons of liquid CO2 at 217 K requires 1,175 MJ of energy, boiling 13.5 tons of liquid
N2 at 77 K requires 2,683 MJ of energy, and heating the 13.5 tons of gaseous N2 from
77 K to 217 K requires 1,890 MJ of energy. Therefore, the additional energy required
to prepare the laser gases is 5,748 MJ (= 1,175 MJ + 2,683 MJ + 1,890 MJ), which
represents an additional electricity cost of $160. Adding this additional energy cost to
the previous total of $2,633 gives a final total cost of $2,793 to launch a 5.25 kg
payload to LEO. This new final result represents a cost of $532 per kg of payload (or
$241 per pound) launched to LEO, which is 41 times lower than the space launch
industry cost of $10,000 per pound for conventional chemical propulsion rockets. Note
that this final cost estimate excludes the operations, life-cycle, and maintenance costs
that are listed in Table 1, which were based on the use of a bulk solid-state laser.
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