Solid Lithium Propellant Solar Thermal Rocket
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Solution Overview
Problem
The use of hydrogen as a propellant in solar thermal rockets is impractical for long-duration missions due to boil-off, high mass and cost of cryogenic refrigeration, and the need for heavy, oversized tanks, which limits mission longevity and increases launch costs.
Innovation Solution
A solar thermal rocket system using solid lithium as a propellant, where lithium is melted using thermal energy from light to produce lithium vapor for propulsion, eliminating the need for cryogenic refrigeration and allowing for a more compact and lightweight design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If hydrogen is used as propellant in solar thermal rockets, then high specific impulse is achieved, but the propellant boils away due to lack of cryogenic refrigeration, limiting mission duration
Solution Approach 1:
The patent changes the propellant from hydrogen (which requires cryogenic temperatures to prevent boil-off) to lithium (which remains solid at ambient temperatures). This parameter change in the propellant's physical state and thermal properties eliminates the need for cryogenic refrigeration and prevents boil-off, enabling long-duration missions while maintaining high specific impulse through lithium vapor generation at elevated temperatures.
2Use of energy by moving object
If hydrogen is used as propellant, then high specific impulse is achieved, but heavy cryogenic refrigeration systems are required, increasing mass and cost
Solution Approach 1:
The patent extracts and eliminates the heavy cryogenic refrigeration system by selecting lithium as the propellant. Since lithium remains solid at ambient temperatures and only requires heating (not cooling) to vaporize, the complex and heavy cryogenic refrigeration infrastructure is completely removed from the system, significantly reducing overall mass while maintaining propulsion effectiveness.
Solution Approach 2:
The patent changes the thermal management parameter from requiring cryogenic cooling (for hydrogen) to requiring only ambient or elevated temperature heating (for lithium). This fundamental parameter change in the propellant's thermal behavior eliminates the need for heavy cryogenic refrigeration systems, reducing vehicle mass.
3Use of energy by moving object
If hydrogen is used as propellant, then high specific impulse is achieved, but specialized heavy tanks and alloys are required, increasing cost and mass
Solution Approach 1:
The patent changes the propellant from hydrogen to lithium, which fundamentally alters the material compatibility requirements. Lithium's properties allow use of standard, off-the-shelf metal tanks and components rather than requiring specialized heavy alloys and complex manufacturing processes, significantly simplifying production and reducing costs.
4Duration of action of moving object
If solid lithium propellant is used, then long-duration missions are enabled without boil-off, but the propellant must be melted and vaporized, requiring thermal energy input
Solution Approach 1:
The patent employs a periodic thermal cycling process where the solar thermal rocket system cycles between heating the lithium propellant to vaporize it for propulsion and allowing it to cool and solidify during non-propulsion phases. This periodic action enables continuous operation over long durations by repeatedly melting and vaporizing the lithium, utilizing the sun's thermal energy to sustain propulsion without requiring the propellant to remain in a transient state.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The use of solid lithium propellant enables long-duration missions without boil-off issues, reduces system mass and cost, and provides a safer and more efficient propulsion system with improved thrust-to-weight ratios and reduced launch risks, while maintaining comparable overall system mass to hydrogen systems.
Implementation Method 1
an optical absorber operable to transform optical energy into thermal energy
Implementation Method 2
a heat exchanger operable to transfer thermal energy from said optical absorber to said quantity of solid propellant
Implementation Method 3
utilizing a portion of the thermal energy to melt solid propellant containing lithium within a propellant tank
Implementation Method 4
pumping the liquefied lithium through a heat exchanger to generate boiling lithium
Implementation Method 5
A pump is installed on the vehicle along with a heat conduit, said pump operable to pump the liquefied portion of the solid propellant into said heat exchanger
Implementation Method 6
an engine operable to utilize lithium vapor from the boiled lithium to propel said vehicle
Data Source
Figure 1~2
Figure 3
AI summary
A vehicle is disclosed that includes a propellant tank, an optical absorber operable to transform optical energy into thermal energy, a quantity of solid lithium within the propellant tank, a heat exchanger, and an engine. The heat exchanger is operable to transfer thermal energy from the optical absorber to the quantity of solid lithium to liquefy at least a portion of the solid lithium, and further operable to boil the liquefied portion of the solid lithium. The engine is operable to utilize lithium vapor from the boiled lithium to propel the vehicle.