May 19, 2010

Combining MHD Airbreathing and IEC Fusion Rocket Propulsion for Earth-to-Orbit Flight

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A Rocket-Based-Combined-Cycle (RBCC) propulsion system employing ducted rocket operation and MHD airbreathing to accelerate the vehicle to Mach 12 in about 4 minutes within earth’s atmosphere, and then fusion rocket propulsion to continue vehicle acceleration above the sensible atmosphere for 28 minutes until Mach 26 (orbital speed) is reached. And, here, 18 metric tons of payload can be placed in low earth orbit with a takeoff weight of only 162 tons - about the same payload and takeoff weight as that of medium size airline passenger jets.

The main MHD air breathing and IEC fusion rocket paper was presented at Space Technology and Applications International Forum (STAIF) in 2005 and was written by H. D. Froning and George Miley and Nie Luo, Yang Yang, H. Momota E. Burton. The abstract is at americanantigravity below. Froning also worked with Robert Bussard on various Fusion rocket papers which are linked to below. NASA is continuing theoretical, computational and some experimental work on MHD propulsion for space planes.
Single-State-to-Orbit (SSTO) vehicle propellant can be reduced by Magnets-Hydro-Dynamic (MHD) processes that minimize airbreathing propulsion losses and propellant consumption during atmospheric flight. Similarly additional reduction in SSTO propellant is enabled by Inertial Electrostatic Confinement (IEC) fusion, whose more energetic reactions reduce rocket propellant needs. MHD airbreathing propulsion during an SSTO vehicle’s initial atmospheric flight phase and IEC fusion propulsion during its final exo-atmospheric flight phase is therefore being explored. Accomplished work is not yet sufficient for claiming such a vehicle’s feasibility. But takeoff and propellant mass for an MHD airbreathing and IEC fusion vehicle could be as much as 25 and 40 percent less than one with ordinary airbreathing and IEC fusion; and as much as 50 and 70 percent less than SSTO takeoff and propellant mass with MHD airbreathing and chemical rocket propulsion. Thus this unusual combined cycle engine shows great promise for performance gains beyond contemporary combined-cycle airbreathing engines

Studies in Russia, Europe, and the US have shown that Magneto-Hydro-Dynamic (MHD) processes can extract electricity for vehicle and propulsion power from slowed airflow within airbreathing engines while reducing propulsive losses and propellant consumption during high-speed atmospheric flight.

H. David Froning had a 2006 AIAA paper - Combining MHD Air breathing and Aneutronic Fusion for Aerospace Plane Power and Propulsion which described MHD propulsion with Dense Plasma Focus Fusion. The AIAA paper had a bit more clarity about MHD propulsion.

Enormous amounts of electrical current are created within air breathing engines by very strong MHD (J x B) interactions within ionized and magnetized airflow at hypersonic (Mach 7 to Mach 14) flight speeds. Such current is a consequence of flow-slowing J x B interactions within airflow that is ionized to about 10^13 electrons/cm3 and subjected to magnetic fields of about 7 tesla. This current is: extracted from airflow by electrodes; conditioned to needed power and voltage within an MHD generator; and distributed to appropriate vehicle subsystems, - which, of course, include the MHD flow ionizing and magnetizing components. MHD components are located around and embedded within engine walls, and significantly increase air breathing engine mass. They include: superconducting coils-to create magnetic fields; electron beams for flow ionization; and electrodes to extract MHD-created current. Figure 1, taken from an MHD air breathing aerospace plane study for NASA by Chase, shows a typical embodiment of MHD elements, such as “saddle magnets” (built up from superconducting coils) wrapped around the airbreathing engine walls. Also shown is flow path direction and the direction of the B-field generated by the magnets.

Ionization of airflow for MHD airbreathing would be accomplished by, either utilizing the IEC fusion products themselves (positively charged alpha particles), or by electrons (within electron beams) formed from the electricity of charged fusion products. MHD slowing of airflow and MHD acceleration of combustion products to high exhaust velocity (during both airbreathing and rocket operation) will also require superconducting coils or permanent magnets in the 5 to 7 Tesla range, depending upon the airflow ionization achievable with electricity released from IEC fusion.

Aneutronic Fusion Propulsion for Earth-to-Orbit and Beyond (by Froning and Bussard 1998)

Fusion Electric Propulsion for Hypersonic flight (1993)

Other MHD Rocket Engine Work

The Effect of MHD Energy Bypass on Specific Thrust for a Supersonic Turbojet Engine (2010)

This paper describes the preliminary results of a thermodynamic cycle analysis of a supersonic turbojet engine with a magnetohydrodynamic (MHD) energy bypass system that explores a wide range of MHD enthalpy extraction parameters. Through the analysis described here, it is shown that applying a magnetic field to a flow path in the Mach 2.0 to 3.5 range can increase the specific thrust of the turbojet engine up to as much as 420 N/(kg/s) provided that the magnitude of the magnetic field is in the range of 1-5 Tesla. The MHD energy bypass can also increase the operating Mach number range for a supersonic turbojet engine into the hypersonic flight regime. In this case, the Mach number range is shown to be extended to Mach 7.0.
Space Plane Costs

Robert Bussard proposed a similar SSTO space plane. It had a payload fraction of 0.14. This is a payload of 35,000 kg delivered to orbit in each flight for 250 ton takeoff weight ship.
The MHD-IEC SSTO space plane discussed here has a payload fraction of about 0.11. Payload of 18.1 tons for 164 ton takeoff weight ship.

So if the other assumptions of development costs and number of flights per year and maintenance were matching then the costs for the MHD-IEC SSTO would be about 30% higher than the Bussard system ($66/kg instead of $51/kg for Bussard proposal in 1994 dollars). The key metrics are the flights per year and vehicle life. The Space Shuttle was also projected to fly once per week in its plan.

I think if you can get the magnetic shield (high field magnet, discussed here in April, 2010 and Nov, 2009 from a European project) to protect against the worst of the heat and plasma going through the atmosphere at Mach 10 and above then the required materials become doable and the maintenance costs come down and the ability to have high flight rates becomes possible. Just the payload fraction and lack of multiple stages probably lowers costs by 5-10 times over what we do now. The main costs savings is actually deliverying a lot of flights per year from the same vehicle (spaceplane)

Bussard's calculation from 1994 for his functionally similar SSTO space plane:
It was assumed that the vehicle manufacturing cost was $1000/kg, giving a single unit cost of $120M. Allowing a life cycle of 240 flights (for example, 24 flights per year over 10 years), the direct capital cost charges are only $ 14.29/kg delivered to LEO. Taking 0.5 of this $7.14/kg for maintenance costs adds $2.5M to the cost of each flight. The cost of propellant (H20, NH3, LH2) assumed at $1.00/kg adds another $2.72/kg for total $24.15/kg cost of payload to LEO. To account for system R&D, assume that development requires $10B for the complete engine plus vehicle operational system, and that this is allocated over 100,000 vehicle flights. This is equivalent to 200 flights (life cycle) for each of 50 vehicles, and very much less than the ca. 2E7 vehicle flights per year of the world aircraft industry. This adds about $100K per vehicle flight. Finally, allow profit generation at 100% of the direct cost of capital and operations (above). The cost additions then become $2.86/kg and another $24.15/kg, respectively. Under these assumptions the total price for payload delivery to the chosen orbit is still only $51.16/kg, about 1/200 of current rocket vehicle costs to orbit. About 47% of this is profit at a net rate of return of about 16.9% on the $120M capital cost of the vehicle. In contrast, if the system were government owned, with no profit/ROI , the delivery costs would be only $27.01/kg ($12.28/lb) to LEO

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