May 10, 2010

Vasimr Plasma Rocket Missions to the Moon, Mars and Jupiter

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Space exploration can greatly benefit from the high‐power electric propulsion capabilities the Variable Specific Impulse Magnetoplasma Rocket (VASIMR®) provides. [29 page pdf details missions enabled by VASIMR]

When combined with chemical rocket technologies in a flexible architecture, the VASIMR® allows new and dramatically improved mission scenarios to be considered. Employing existing state‐of‐the‐art solar cell technology, VASIMR® is able to achieve dramatic propellant mass savings to move payloads near Earth and preposition payloads for assembly near the moon, the edge of Earth’s gravitational sphere of influence, and beyond. Robotic prepositioning of assets at key locations in space allows cost and risk to be reduced for later transits between staging locations. The possibility of multi‐megawatt power levels also allows VASIMR® technology to significantly reduce the travel time and improve abort options for human interplanetary missions between staging locations near the Moon and Mars. Power levels ranging from currently available solar technologies to those requiring the future development of nuclear‐powered systems are considered.
Mission Assumptions

For missions inside the Earth’s gravitational sphere of influence (SOI), we consider VASIMR® power (P) levels ranging from 100 – 500 kW. The nominal parameters for these missions are a specific impulse, Isp, of 5,000 s with a total mass‐to‐power ratio, α = αSA + αT, of 10 kg/kW.

For robotic or cargo interplanetary missions, we consider VASIMR® power levels ranging from 1 ‐ 5 MW. The nominal parameters for these missions are a specific impulse, Isp, of 4,000 or 5,000 s with a total power efficiency of 60%, and a mass‐to‐power ratio, α (total), of 4 kg/kW.

For human interplanetary missions, we consider VASIMR® power levels ranging from 10 ‐ 200 MW. The nominal parameters for these missions are a variable specific impulse, Isp, from 3,000 to 30,000 s with a total power efficiency of 60% and a mass‐to‐power ratio, α (total), less than 4 kg/kW. A more accurate VASIMR® model, considering the power efficiency to be a function of specific impulse and power, is beyond the scope of these studies.

Prepositioning to the Edge of Earth’s Sphere of Influence

The low, but steady thrust on the spacecraft leads to a spiral orbit with increasing radius to reach the SOI (Sphere of Influence).

* for a 200 kW VASIMR® propelling a spacecraft weighing 4000 kg at LEO less than 600 kg of argon propellant is used to put a 4,000 kg spacecraft on an Earth escape trajectory.

Lunar Tug

If transit times of several months are acceptable for cargo, a reusable VASIMR® tug allows roughly twice as much payload to be delivered to the Moon as a chemical system would require for the same initial mass in low Earth orbit (IMLEO).

Cargo Delivery to Mars

* A parametric study of cargo delivery to Mars with 2 MW of power and a total specific mass of α = 4 kg/kW (power + VASIMR®) was performed using the OptiMars code with the variable Isp optimizer, for an IMLEO = 20 mT (4200 ISP). The total mass budget can be presented as 8 mT for power and propulsion plus 7 mT of propellant and 5 mT of payload. The total duration of the mission is about 3.5 months.

Mars Sample Return
The optimal level of VASIMR® power for the MSR mission is 250 kW (at 1 AU),requiring a round trip time of 3.7 years, including 140 days in low Martian orbit. The mission can be performed for specific total power, α < 21 kg / kW. Higher powers can make the mission slightly faster, but require much more propellant and much lower α. For example, 500 kW mission can be accomplished within 3.1 years but requires total α < 8 kg / kW.

Enhancing Solar Powered Capabilities to reach Jupiter

A reusable VASIMR® spacecraft can be used to “catapult” 5,000 kg robotic payloads to Jupiter using a Hohmann‐like transfer. Presently available solar power technologies with 500 kW of power and alpha of 6.4 kg/kW can launch 4 mT of payload beyond the orbit of Jupiter.

Fast Human Missions to Mars with Variable Specific Impulse

* At the 200 mega‐Watt power level, human missions to Mars in less than 39 days become conceivable with advanced VASIMR® and power technologies.
* 12‐18 MW missions arrive at Mars within 3‐4 months
* They are studying heliocentric transfer times for delivering a fixed 20 mT payload from L1 to Mars using a fixed initial mass at Earth’s gravitational sphere of influence of 600 mT, can be in the range of 55 to 60 days depending on the arrival velocity at Mars with a total oropulsion α of approximately 2 kg/kW.

A 39‐day mission to Mars with an arrival velocity 10 km/s can be achieved with total specific mass of 1.2 kg/kW. Achieving trip times of less than 90 days for these mass transfers requires the total propulsion technology, measured by α, to be less than about 2.5 kg/kW.
Using 12 MW of power and a total specific mass for the entire power and propulsion system of a challenging, but presently realizable 4 kg/kW, allows a scenario with a crewed one‐way mission time of approximately 3 months. Assuming advanced technologies that reduce the total specific mass to less than 2 kg/kW, trip times of less than 60 days will be possible with 200 MW of electrical power. One‐way trips to Mars lasting less than 39 days are even conceivable using 200 MW of power if technological advances allow the specific mass to be reduced to near or below 1 kg/kW.

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