15 mar 98  INEEL, mod 30 mar 1999  A Zuppero
ROUGH DRAFT  Working Paper


Moon Ice For LEO to GEO Transfers

(to take communication satellites from low earth orbit to geosynchronous orbit)


Lunar ice could mean a fast, cell phone internet connection.



** The INEEL
The Idaho National Engineering and Environmental Laboratory  (INEEL)is a United States Department of Energy national laboratory located in Idaho Falls, Idaho.  Since the early 1950's this laboratory was key to the development of the exceptionally reliable and safe nuclear reactors used to power the United States Navy's nuclear submarine fleet. The reactors heat water into steam, which powers the submarine.

Scientists and engineers at the INEEL found a simple and relatively inexpensive way to remove water ice from the lunar surface and place it into orbit around earth. This engineering discovery would provide several orders of magnitude larger quantities of propellant than all known affordable alternative schemes.
 
 

 

Water would be used as the propellant in nuclear-heated steam rockets. Such a rocket would haul rocket fuel payloads, such as ice, from the surface of the moon into orbit. Solar-heated steam rockets would take the ice to an orbit out of the moon's gravity and then into an orbit that just grazes the atmosphere of the Earth. The orbit of the ice would slowly decay. The result would be ice in orbit around Earth. Delivering this rocket fuel or propellant to Low Earth Orbit could dramatically lower the cost of space transportation. Rockets from Earth could rendezvous with the ice and use it for rocket propellant.
 
 
Lunar_Ice_Rocket INEEL engineers and scientists published the details of this scheme at the Joint Propulsion Conference in Seattle, June 1997. It used lunar south pole ice as the resource. 
A follow-up publication "Lunar South Pole Space Water Extraction and Trucking System" details a lunar south pole space water truck, which was presented at the 6th International Conference and Exposition on Engineering, Construction, and Operations in Space, 26-30 April 1998.
 Systems analysis revealed that using the lunar water directly seemed to result in a dramatic drop in complexity, and especially a dramatic drop in the hardware needed on the lunar surface. This architecture is sketched below.

The architecture would use solar powered steam rocket propulsion for all the steps beyond the low lunar orbit. The solar options permits us to keep the nuclear system trapped in a deep gravity well in deep space. These are discussed below.

A program to develop the steam rocket at the INEEL is described.

Generating electricity in space handicaps all known alternatives.
A bottleneck step, launching ice from the surface of the moon to low lunar orbit, strongly favors a nuclear-heated steam rocket. All other known options require orders of magnitude more support and processing hardware to achieve the same results. Generating electricity in space causes the problem.

Generating electricity in space requires hardware that weighs about 1000 times more than that of the steam scheme. This means alternatives cost 1000 times more.

NASA and others suggested that one could use electrolysis to split the water, which would give hydrogen and oxygen gasses. These would then be refrigerated and condensed into the same cryogenic liquid rocket fuels used by the Shuttle. This approach requires that all the energy be supplied by electricity. This alternative would therefore cost about 1000 times more than the steam scheme.

The INEEL scheme DOES NOT use electricity as the energy source.



Architecture for Lunar Water for LEO to GEO Transfers

The objective is to fuel a propulsion system that takes payloads to GEO once they are delivered to LEO. Communication satellites operate at GEO (geosynchronous orbit). Rockets take payloads to LEO (low earth orbit). The propellant or fuel would be water obtained from the North or South poles of the moon.
A small nuclear heater melts ice at the forever dark North or South pole of the moon. A condenser collects the water vapor, providing pure water. A nuclear-heated steam rocket launches water or ice from the moon poles and delivers it to low lunar orbit.
A solar-heated steam rocket transfers payloads from low lunar orbit to an earth transfer orbit.
 The ice payload, covered by a low mass heat shield, grazes the earth's atmosphere and looses a small amount of velocity. This lowers its apogee. It grazes the earth's atmosphere repeatedly until its orbit is a nearly circular, low earth orbit. A Mars probe is using its solar panels as an incremental aerobrake to achieve just this kind of result.
Small solar-heated steam rockets take payloads from LEO to GEO, using water propellant.   A systems analysis may show that splitting the water and using the resulting gasses directly in a chemical rocket may reduce costs. It may even show that splitting water at LEO is reduces costs. The availability of massive (1,000 ton units) of water ice at LEO would offer a new degree of freedom in commercial space operations.

   (click for hi res image)
Solar thermal rockets are similar to nuclear heated rockets. Inflateable mirrors focus the sun on a heat exchanger.

Using water to take payloads from LEO to GEO uniquely provides a path for cash flow, to pay for such space resource utilization schemes.

Easy access to GEO means faster wireless internet connections.


Steam rockets use water propellant
A steam rocket is a rocket with water vapor exhaust. The Shuttle main engines burn LOX and Liquid Hydrogen LH2 to produce steam exhaust.
A nuclear or solar heated steam rocket delivers heat to a heat exchanger to generate steam. Some of the steam can be used to energize a turbo-pump to increase the heat exchanger pressure, which increases performance.



Exceptional Simplicity

The nuclear-heated option provides an exceptionally simple architecture. A relatively small nuclear heater provides enough energy to heat shovel plates to cut through the extremely cold, 80 Kelvin permafrost. A small nuclear electric generator would provide 100 Kilowatts for headlights, computers and communications. It would weigh several tons mass and shed 3 Megawatts of "waste" heat. A small nuclear heater (3 Megawatts) provides the heat (3.5 megajoules per kilogram) needed to vaporize the ice (27,000 tons per year) to room temperature vapor. A condenser collects the pure water.

The nuclear-heated steam rocket then uses the water as propellant to launch payloads to low lunar orbit.
 
 
In sharp contrast, splitting the water requires a complex and heavy architecture. This is a chemical propulsion option, using electrolysis. The chemical option requires that all the energy stored in the LOX and LH2 rocket fuels originate first as electricity. Electric generators in space are severely handicapped because they have neither convective nor conductive nor phase-change heat sinks. Space is a thermos jar. Masses per unit energy are typically 10,000 times greater than the purely thermal processes of the steam rocket option.

Compressing and refrigerating the gaseous oxygen and hydrogen to make them liquid cryofuels also takes compressors and heat sinks. The refrigerator for the LH2 requires more electricity than splitting water, and is not very efficient because LH2 is at 22 Kelvin.

The chemical option is complex and requires massive hardware to deliver comparable payloads to LLO.

The only advantage of the chemical option is that it uses about 3 times less water than the nuclear option.


Minimum Thrust Is Required
Launching from the Lunar surface requires at least sufficient thrust to overcome the crushing gravity of the moon. Lunar gravity is only 6 times lower than that of Earth. (Comet gravity is 100,000 times lower.) A parametric analysis showed that the minimum specific power (power per rocket engine mass) must exceed about 150 megawatts per ton engine, or the rocket will not lift of the lunar surface. If the specific impulse is too low (less than about 120 seconds) or too high (greater than about 1000 seconds) the required specific power increases sharply.
 
A LOX/LH2 rocket (RL-10) can achieve about 1300 megawatts per ton engine.

A nuclear heated steam rocket to develop this specific power needs to provide a mixed mean outlet steam temperature into the nozzle of about 1100 Kelvin. This is half the temperature of the NERVA rocket (> 2500 Kelvin) demonstrated during the late 1960's. The specific power density in the core is something between 1 and 3 megawatts per liter of reactor core. The specific power is less than that of NERVA (3 megawatts per liter).



END of Document

Technical Details and Background
 
 
 
An INEEL scientist first proposed using ice from space at the First International Conference on Near-Earth Asteroids, June 1991. Another paper presented at the World Space Conference, 1992, detailed how steam rockets heated by nuclear reactors would use water ice taken from a little known and accessible comet formation in the space between Mars and Jupiter to transport tens of thousands of tons of payload. The payload would have been more water ice, or possibly the hydrocarbons found on comets. The destination was an orbit around Earth itself.

Unlimited Mass Changed Meaning of the Rocket Equation

A thermal rocket can deliver its heat to however large or small a propellant mass that is convenient. This permits the thermal rocket to choose its specific impulse. However, the thermal rocket has only a limited amount of energy to deliver. In every case known, it will deliver as much energy as it can for as long as it can. This contrasts a chemical rocket, where the energy in the fuel is directly proportional to how much fuel is in the tank.
 
 
 
Thermal rockets use a slightly different form for the rocket equation. The rocket equation gives the change in velocity a rocket will experience after all the propellant is exhausted. The energy available and the chosen specific velocity determine how much propellant mass is used. The specific velocity, V, is the product of specific impulse, Isp, and gravity at earth surface, 9.8 m/s/s.
 
 
The consequence is that increasing the specific impulse beyond an optimum value will make the rocket go slower or deliver a smaller payload. For the ideal case, the optimum specific velocity (rocket exhaust velocity) is about 2/3 the mission delta-V.

This does NOT minimize the amount of propellant used. The optimum specific velocity results in the propellant requirement of about 4 times the payload. The assumption is that

Near Earth Asteroids (NEA's) and comets have 1E8 to 1E15 tons mass, with near zero gravity. So if one docks with a nearly zero gravity object in the space near earth, one has access to "nearly unlimited mass." The moon has almost to much gravity to qualify as a zero-gravity object.

However, energy is not free. And peak power is definitely not free. This situation favors all propulsion processes that use heat alone, and strongly dis-favors processes that require electricity.

The unexpected result of the thermal-rocket equation is that the optimum favors steam rockets for lower delta-V missions. "Lower delta V" means under about 4000 m/s. INEEL scientists published architectures for such missions,  (click here for architecture image) which included going to Mars from a high earth orbit, going to the outer edge of the asteroid belt from a high earth orbit, for delivering payloads from Low Lunar Orbit to GEO, or for going from LEO to GEO.

Further, water has a uniquely low (7 mm Hg) vapor pressure just above its melting point. This permits tankage fractions under 1%. Extracting water from space ice requires only a room temperature thermal process.
 
 These engineering factors make water even more desirable. For example, missions to return massive payloads back to Earth orbit from the Jupiter family comet formation, with delta-V as high as 6500 m/s, become highly competitive compared to chemical or other propulsion options.
 




Technical Program Considerations

The critical path is the nuclear heater with sufficient power per mass to achieve launch from the lunar surface.

INEEL scientists and engineers determined that the current state of the art of water cooled nuclear systems strongly suggests the required system can be constructed. The 4 engineering options  identified for nuclear fuel elements are:


Technical Elements
A program to develop the nuclear fuels and a high-peak power nuclear reactor would have the following elements:

Technical Discussion

Minimum required performance characteristics for a nuclear steam rocket to ferry water from the lunar surface to low lunar orbit have been identified in terms of the power-to-weight ratio. Power-to-weight ratios and power densities in excess of the required value have been demonstrated (NERVA) for devices using hydrogen as the coolant/propellant. Power densities in excess of those believed to support the needed power-to-weight ratios are achieved in aluminum clad U-Al(sub x) plate fuels (such as ATR) operating with relatively low temperature water.

The current experience base is not adequate to project how mundane (or how exotic) an approach might be required to achieve an adequate power density and power-to-weight ratio in a reactor utilizing approximately 1100 K steam as the coolant and propellant. Concept definition and evaluation work is required to estimate what performance can be achieved.

Four concepts have been identified for preliminary evaluations. The first draws heavily on the existing reactor technology base. The fourth offers exceptionally high performance potential but also represents the greatest technology development effort.

Serial evaluation of the concepts is proposed. Evaluation of the first may yield performance estimates that suggest moving immediately to the fourth concept. Evaluation of the first may also indicate adequate performance is achievable with the first and suggest moving immediately to Phase II for Concept Development and Evaluation.
 

Nuclear-heated Steam Rocket Program

Given the above background, the opportunities are ripe for the INEEL to get in at the start on a development that could have a significant influence on the future of space travel and exploration. The following are ideas for a skeleton program plan at the INEEL for the design of a nuclear reactor that could power a steam rocket.

Issues related to he development of a nuclear reactor for use in a steam rocket

Clearly there are many issues that have to be addressed in the development of a nuclear steam rocket. At the top level of conceptual design efforts, these issues should include: reactor design/performance including fuel element design,
fuel configuration,
cooling system,
safety systems
rocket nozzle including design,
configuration,
performance
materials performance (stress, strain, corrosion, temperature, neutronics, etc. effects on strength) investigations including fuel cladding,
cooling system,
nozzle,
related support structure
The elements of a program necessary to produce a conceptual design will include the tasks needed to address the above issues. These elements include:
  Reactor physics, fuel design and performance - to obtain the (expected) required power to system mass ratio, it is likely that new ideas (e.g. core, fuel, fuel containment, etc.) must be developed and tested. Core designs featuring these new ideas and different fuel types must be considered, developed, analyzed analytically, and eventually tested. Experienced reactor physics and fuel performance analysts will have to design the fuel and core configurations and adapt these to considered reactor designs. It is expected that current generation analysis codes (such as FRAPT-4, sn and shielding calculations) along with traditional hand calculations will be required to accomplish this task.

Thermal and heat transfer analysis - Thermal, heat transfer, and fluid flow analysis will have to be conducted for every specific reactor core configuration and balance of system. Questions to be addressed in these analyses include how efficiently core energy generation is transferred to the cooling medium and how reactor operating conditions and environment influence the thermal and thermal hydraulic conditions at the nozzle entrance. In essence, hand calculations along with analysis using current reactor design and performance codes (such as RELAP5) will be used to examine the performance and behavior of the reactor and system for a wide variety of steady-state and transient operating conditions. Given the plausibility of new fuel designs, literature will have to be searched to find appropriate correlations to support this analysis. Clearly, these calculations will be iterative in nature as the design concepts continue to develop. Thermal analysis must also be conducted to estimate the performance of the nozzle attached to the reactor. Through a combination of hand calculations and computational fluid dynamics analysis, a map of the nozzle performance (e.g. ISP) as a function of thermal-hydraulic conditions (e.g. temperature, quality, flowrate, void fraction, pressure) at the nozzle entrance will be generated. This map will be generally useful in that the results should be independent of the reactor concept for the most part.

Mechanical Design - Mechanical design will be conducted for each configuration proposed. This task essentially determines what the various reactor components are and how the components fit together to compose a working system. Details of component equipment pieces (such as pumps), piping system design and layout, packaging, control system, and so forth will be defined in this task.

Mechanical/Stress Analysis - As with any design, analysis must be conducted to address the performance of the materials and components of the system to ensure that they are not unnecessarily overloaded or over stressed during the design life of the system. Many factors must be considered including the fuel, fuel cladding, fuel support structure, piping, piping support system, nozzle, and so forth.

It is expected that each of the above tasks will require 1 FTE to examine two configurations. Thus 8 capable FTEs will be required to develop and analyze the four potential concepts.

Other tasks supporting the above will be required. These tasks include:

Requirements Development - A requirements document will need to be development.  This document will
address primarily top-level requirements for now which will be refined as time goes on.  Assumptions with regard to cost, schedule, reliability, performance capability, etc. will have to be factored in and shown. Potential mission scenarios will have to be documented.  Methods for evaluating design tradeoffs will have to be developed.  Interfaces with man and potential NASA launch vehicles will have to be addressed.

Safety  - We will need to develop a Safety Program Plan similar to that for the Multi-Megawatt Space Reactor Program.  This Plan should address the top-level safety requirements, how safety will be managed and control within the program, who will have what safety responsibilities, what safety documents will have to be generated, and what safety milestones and schedules have to be met. Safety interface requirements with humans and potential NASA launch
vehicles will have to be defined.  A Safety Plan for the Concept Development Project should also be developed which relates the overall Safety Program Plan to specific design concepts and lays out safety
requirements for each.  Real work, as Bruce describes it, would involve developing potential safety approaches for each concept and performing preliminary fault tree analyses, failure modes and effects analyses,
criticality analyses, etc. on the preliminary design concepts.

Function and Operations - As mentioned above, detailed requirements for all aspects of the project must be developed and maintained. This includes functional and operational specifications, safety requirements, disposal requirements, and so forth.

Materials Testing - New materials or derivatives of existing materials may have to be developed to support the mechanical and operational requirements and needs of the concept design. Materials for cladding, nozzle, piping system, etc. will need to be examined in high temperature, corrosive steam environments similar to that expected during reactor operations to determine material performance. The INEEL Supercritical Water Oxidation Loop may well be capable of doing coupon testing required to support these needs.

Mission Development - Mission profiles and plans will likely be developed by other participating agencies. However, the INEEL must remain closely involved in these developments. First, it must be ensured that mission profiles fit within the assumed/established requirements for the reactor designs being considered. Second, the INEEL needs to remain in the decision making process associated with the profile developments to ensure that the best interests of the INEEL can be realized and future prospects can be capitalized on.
 

It is expected that with the exception of the Materials Testing, each of the above tasks will require 1 FTE to support all the design configurations contemplated. Materials Testing will require 4 FTEs to support all the concepts. Thus 8 capable FTEs will be required to develop and analyze the four potential concepts.

Based on the above discussions and preliminary task definitions, 16 FTEs for 1.5 years would be necessary to effect the conceptual reactor design(s).
 
 





principal author:  anthony zuppero
nuclear and reactor physics: bruce schnitzler
thermal hydraulics, engineering analysis and experimetal programs: tom larson
nuclear propulsion and power, reactor concepts and DOE HQ interface: ralph bennett
safety, functional and operational requirements: john rice

strategic: don yurman
systems: dave nipper, lyn parlier
extraneous elements deleted because they are obvious to all:

Project Management - A capable project manager will be required to coordinate and ensure the project goals are accomplished within schedule and budget limitations and that a team environment is maintained.

Chief Scientist - A visionary will be required to help expose the project, define the limits, ensure a broad support base for it, lead the project in the directions consistent with the best interests of those involved, and protect the project. It is expected that the Chief Scientist would help develop beneficial collaborations with appropriate entities (such as NASA, other Labs, commercial entities, etc.) and help develop and maintain the funding base.