Advanced Propulsion Concepts

1. Advanced Propulsion Concepts

2. High Energy-Density Chemical Fuels: 1 Form molecules with high stored energy Hydrogen + metastable Ozone (frozen, amorphous, dark blue ice) : Isp ~ 535-600 sec. Ring forms of oxygen (O4, O6,O8). Most promising: H2 + cyclic O4: ~ 565 – 635 sec. Tetrahydrogen H4, tetranitrogen N4, Cubane, C6.

3. Advanced Hydrocarbon Fuels (Higher Isp than RP-1 kerosene non-cryogenic fuel) http://std.msfc.nasa.gov/sciresearch/adv_chem_prop.html • Bi-cyclopropylidine • Octadiyne • AFRL-1 • Dimethylaminoehtylazide (DMAZ) • Quadricyclane Other nearer-term approaches (at NASA MSFC): High-pressure rocket combustion Combined-cycle pulsed detonation.

4. High Energy-Density Chemical Fuels: 2 Solids with crystalline lattice (store more energy) formed at high pressure. (e.g. diamond formed from carbon). Possible formation of metallic hydrogen (sp. Gravity 1.15), polymeric nitrogen, metallic boron. Metallic H decomposing to H2(g) can give Isp ~ 1500 - 1700 sec.

5. Lawrence Livermore National Laboratory, Public Affairs Office, Craig Savoye (SOURCE), March 21, 1996, E-mail: savoye1@llnl.govhttp://www-phys.llnl.gov/H_Div/GG/metalhydrofact.html “FACT SHEET: HYDROGEN PRODUCED IN METAL FORM FOR FIRST TIME Researchers at Lawrence Livermore National Laboratory have succeeded in achieving a long-sought goal of high-pressure physics - converting hydrogen to a metal. The likelihood that the most abundant element in the universe could be converted into metallic form at sufficient pressures was first theorized in 1935, but tangible evidence has eluded scientists in the intervening decades. "Metallization of hydrogen has been the elusive Holy Grail in high- pressure physics for many years," said Bill Nellis, one of three Livermore researchers involved in the project. "This is a significant contribution to condensed matter physics because a pressure and temperature that actually produce metallization have finally been discovered." In a paper delivered today at the American Physical Society's annual gathering in St. Louis, and published in the March 11 issue of Physical Review Letters, Livermore researchers Sam Weir, Art Mitchell, and Bill Nellis described the use of a two-stage gas gun at Livermore to create enormous shock pressure on a target containing liquid hydrogen cooled to 20 K (-420 F). By measuring the electrical conductivity, they found that metallization occurs at pressure equivalent to 1.4 million times Earth's atmospheric pressure, nine times the initial density of hydrogen, and at a temperature of 3000 K (5000 F). Because of the high temperature, the hydrogen was a liquid. The intense pressure lasted less than a microsecond. ….”

6. “Optical evidence of a new phase of hydrogen has been previously reported using an experimental approach that involves crushing microscopic-sized samples of crystalline hydrogen between diamond anvils. However, metallic character has not been established. Metallic character is most directly established by electrical conductivity measurements which are not yet possible in diamond anvil cells at these pressures. The Livermore team's results were surprising because of their methodology (shock-compression, which heats the sample), the form of hydrogen used (liquid) and the pressure needed to achieve the result (much lower than previously thought). Virtually all predictions surrounding metallic hydrogen have been made for solid hydrogen at low temperatures (near absolute zero). The Livermore team tried a different approach. They looked at hydrogen in liquid form at relatively high temperature, for which no predictions have been made. Some of the theorists who proposed the existence of metallic hydrogen also believed the substance would remain metallic after the enormous pressures required to produce it were removed, and that it might also be a superconducter. Additionally, solid metallic hydrogen is predicted to contain a large amount of energy that might be released quickly as an explosive or relatively slowly as a lightweight rocket fuel. Metallic hydrogen's light weight might also have implications for material science. The metallization events at Livermore occurred for such a brief period of time, and in such a manner, that questions about its superconducting properties and retention of metallic form following pressure removal could not be answered. "The potential uses of metallic hydrogen are fascinating to contemplate, but they are far down the road, and we've only reached the first mile post on that road," said Nellis.”

7. Two-stage gas gun. Gunpowder drives piston down pump tube, compressing hydrogen gas - hydrogen breaks a rupture valve and accelerates a projectile down the second stage barrel to 7km/s (16,000 mph). Projectile generates a strong shock-wave on impact with an aluminum sample container, which is cooled to 20 degrees Kelvin (-420 F). Entering the liquid hydrogen, the shock pressure first drops, then reverberates many times between parallel sapphire anvils until the final pressure, density and temperature are reached. This reverberation produces 1/10 the temperature that would be created by a single shock to the same pressure. The temperatures achieved keep hydrogen in the form of molecules, rather than letting molecules break into atoms.

8. Because the experiments were done at higher temperatures than originally predicted, the results suggest that the metallization pressure of hydrogen is temperature-dependent.) A trigger pin in the target produces an electrical signal when it is struck by the initial shock wave; this signal is used to turn on the data recording system at the proper moment. The electrical conductivity of the hydrogen shock is then measured to determine if metallization has occurred.

9. http://physicsweb.org/articles/news/6/4/6/1 “Hydrogen metal on the horizon 10 April 2002 Scientists have long expected solid hydrogen to become a metal when it is compressed, but so far electrical conductivity has only been detected in liquid hydrogen. Now an experimental study of solid hydrogen at pressures up to 320 GPa predicts that it will become metallic at a pressure of 450 GPa – over four million times atmospheric pressure. René LeToullec and co-workers at the CEA in France also found that solid hydrogen becomes opaque – or ‘black’ – under compression (P Loubeyre et al 2002 Nature 416 613). Both the structure and electrical conduction of solid hydrogen have been intensively studied since the 1930s, when the existence of its metallic state was first proposed. Experiments conducted in the early 1990s squeezed the element to pressures of 250 GPa but failed to detect this state. More recent investigations at higher pressures have proved inconclusive, partly because the pressure cell starts to interfere with the measurements. Now the French team has succeeded in compressing hydrogen to 320 GPa, at a temperature of 100 kelvin.

10. They filled a specially designed diamond pressure cell with hydrogen, and measured its absorption of light across the spectrum as they increased the pressure. This technique – based on Raman spectroscopy – produced an absorption pattern that revealed the vibrational and rotational energy levels of the hydrogen molecules, providing information about the structure of the solid element. At 290 GPa, LeToullec and colleagues discovered that the hydrogen sample turned white, then yellow, orange and red, before becoming opaque at 320 GPa. They also established that its structure remains stable above a pressure of 160 GPa. Above 300 GPa, they found evidence for an energy bandgap – a well-known feature of semiconductors. This bandgap narrowed as the pressure rose to 320 GPa, the highest value reached in the experiment. By extrapolation, the team calculated that the bandgap would disappear at 450 GPa to become an atomic metal. The team believes that this estimate is more reliable than earlier predictions of around 620 GPa, which were based on larger extrapolations. LeToullec and colleagues now hope that their technique could be extended to study pressures in the 400 GPa range, where it could detect solid hydrogen metal for the first time. About the author Katie Pennicott is Editor of PhysicsWeb”

11. High Energy-Density Chemical Fuels: 3 Metastable Excited Molecules Metastable Helium: decays to ground state with energy release ~ 40 times that of LOX/LH2. Isp ~ 2800 - 3150 sec. possible. See “Metastable Helium” by Dr. Robert W. BassIdentification Systems DepartmentBAE SYSTEMS http://std.msfc.nasa.gov/ast/presentations/2b_bass.pdf Presentation on the feasibility of converting a gas into a “pressure-ionized plasma in the state of liquid metal that is self-cohesively self-confined yet fully ionized – a liquid metallic plasmoid (LMP).” Also can an LMP can be crystallized to “metamatter” as it cools? In the cases of helium, hydrogen, heavy hydrogen – this process will produce, respectively, crystals of metastable helium (MSH), metastable protium (MSP) or metastable deuterium (MSD). These crystals offer potentially revolutionary ways of addressing energy needs. “

12. High Energy-Density Chemical Fuels: 3 Energetic Free Radicals: H+(g) + H-(g) Isp~3730 – 4190 sec.

13. Fusion energy - electricity vs. propulsion http://std.msfc.nasa.gov/sciresearch/adv_plas_prop.html Department of Energy is funding a fusion power research: . “The technical priorities for applying fusion energy for space propulsion are somewhat different, even though the science and engineering underpinning both applications share much overlap and synergism. For space propulsion, a low mass for the propulsion system is the primary requirement. Cost of energy as high as tens of dollars per kW-hr may be acceptable for space propulsion. Fusion reactions for propulsion can be operated in open-cycle, whereas closed cycle operation is preferred for electrical power generation. Several viable fusion options exist, especially those involving pulsed operations. So, it may be possible to find quicker, less expensive R & D pathways to the realization of fusion for propulsion than for electrical power generation.”

14. Advanced Plasma Propulsion http://std.msfc.nasa.gov/sciresearch/adv_plas_prop.html Near term: High-power, high-efficiency plasma rockets to work with solar electric and nuclear electric power sources to get ISP up to 10,000s. Plasma thruster efficiencies > 50% sought.

15. Inertial electrostatic confinement http://std.msfc.nasa.gov/sciresearch/IEC_Webpage.pdf Technique to create spherical plasma with radial ion flow. http://std.msfc.nasa.gov/sciresearch/IEC_Webpage.pdf

16. Daedalus http://www.grc.nasa.gov/WWW/PAO/images/warp/warp12.gif

17. Solar Thermal Propulsion •  Like nuclear thrusters, but use solar energy either directly or indirectly to heat a working fluid (typically hydrogen). Isp ~ 600 - 900s. • LEO to GEO in 10 to 30 days. Inflatable mirrors with turntable attachment for mirror-steering (Air Force concept; NASA Marshall RC )

18. Nuclear Fusion Rockets Magnetic Confinement Systems Ionized plasma of fusion atoms collects in a magnetic “bottle”, where it heats and compresses to the point where fusion starts. Inertial Confinement Systems Small pellet of frozen fusion fuel is confined in a hollow sphere (gold? Uranium?), compressed and heated from all directions by laser beams, elementary particles, or hypervelocity pellets. Breakeven energy release not demonstrated (or announced…) so far. Primary or secondary reactions produce uncharged neutrons which carry away energy and pose radiation hazard.

19. Solar Sails Photon Sails (Solar Sails) – work by reflecting photons from the Sun MagSails – work by creating a magnectic field that diverts the solar wind (high speed particles like protons and electrons) These have lower imparted momentum, from the lower-velocity solar wind, but the system can be lighter Solar Sails: Sail material is very thin metal-coated mylar ~ 5 microns thick; 5 – 20 g/cm2. “STATITE”: Hovering spacecraft, with solar force balancing gravity. Deployment problem: air drag > solar force at LEO. FN Tip Controllers

20. = Solar Flux at 1 A.U. = 1360 W/m2 = 1 A.U. = Distance from Sun to Earth = current distance from Sun to Earth is pressure. e is emissivity = 1 for black body and 0 for reflector. c is Speed of light in vacuum These pressures and forces are very low (~ 4 E-6 N/m2). Hence sails have to be very large and have very small mass.

21. Note that while the acceleration is low, the fact that the sail is propellant-less means that the Acceleration can continue indefinitely and thus the sail can reach very high speeds. Steering: Adjusting the angle q allows the sail to speed up or slow down with respect to the Sun. There is a “Solar Simulator” at http://www.ec-lille.fr/~u3p/Glenans/apjava.html Other sail materials: Carbon – high temperature (laser push?) Silverized carbon (highly reflective, but heavier) Sails with adjustable polarization for thrust variation / steering. FN FN

22. Magnetic “Sails” MagSails – work by creating a magnetic field that diverts the solar wind (high speed particles like protons and electrons) These have lower imparted momentum, from the lower-velocity solar wind, but the system can be lighter MiniMagnetospheric Plasma Propulsion Mechanism similar to aerodynamic lift (not drag). Can move “upwind” at a fairly steep angle

23. Tethers Tethers are long, thin “ropes” in Space that can be used to speed up or slow down Spacecraft without propellant (Momentum exchange). Types: Gravity-gradient (vertically) stabilized : “Bridge to Space” Rotating (Rotavator) Electrodynamic. G-G tether. Center of Mass Describes Orbit Please download “Fundamentals of Tether Momentum Exchange” from http://std.msfc.nasa.gov/sciresearch/mxer.pdf

24. Forces on a Tether The bottom tip of the tether moves moves at This is slower than the circular satellite velocity at that distance: Thus the tip of the tether wants to “fall” downward, placing the bottom of the tether in tension: Similarly, the top of the tether is moving faster than the local circular-orbit velocity, and thus the top is also in tension.

25. Using a Tether Payload is captured at the bottom, and travels up the tether to the center of mass, and then outward along the upper tether. A rule of thumb is that the increase is apogee is ~ 7 times the tether length. Thus the payload can increase its velocity without propellant. Of course, the center of mass of the tether drops during the process. This can be raised back by reversing the process: capturing a fast satellite and releasing it slower, or by using a propulsion system on the tether. Using a large tether center of mass helps: (Humble Fig. 11.17)

26. Terminator Tether http://science.nasa.gov/headlines/y2000/ast09jun_1.htm

27. Rotating Tether • Advantages: • Low capture speed • Higher release speed • Shorter tethers “Rotavator” http://science.nasa.gov/headlines/y2000/ast09jun_1.htm

28. Electrodynamic Tethers If the tether is also a conductor, we can apply power to it and use the Earth’s magnetic field to raise and lower the tether. http://science.nasa.gov/headlines/images/tethers/EDT.jpg http://science.nasa.gov/headlines/y2000/ast09jun_1.htm

29. Voltage vs. time prediction for a tether “Pre-mission prediction of the voltage generated across the tether over time. The SETS and DCORE experiments will make detailed measurements of tether-generated potential. “ liftoff.msfc.nasa.gov/shuttle/ sts-75/tss-1r/exp/sets.html

30. Tether Boost for ISS http://astp.msfc.nasa.gov/proseds/future.html

31. Space Elevator http://www.affordablespaceflight.com/SEf04.jpg

32. Other Advanced Concepts • Interstellar Ramjet (Bussard Ramjet) Fusion from interstellar hydrogen • Daedalus (pulsed nuclear fusion; inertial confinement) • Beamed Energy • Pulsed Detonation

33. Bussard Ramjet http://www.grc.nasa.gov/WWW/PAO/images/warp/warp12.gif

34. Antimatter propulsion http://std.msfc.nasa.gov/sciresearch/nuclear_prop.html “Highest energy release per unit mass of any reaction known in physics. When a paticle and antiparticle come in close contact, they annihilate each other through a series of interactions with the ultimate result that their rest mass is converted entirely into energy. Antimatter stores energy at very high density. Approximately 42 milligrams of antiprotons (about 0.6 cubic centimeters in the form of antihydrogen) have energy content equal to the 750,000 kilograms of fuel and oxidizer stored in the Space Shuttle External Tank. “

35. Laser Lightcraft http://std.msfc.nasa.gov/sciresearch/propellant_prop.html • “ ground-based laser for propulsion to deliver small, multi-user payloads to low-Earth orbit for $100 per pound within six years of beginning full-scale development. • Applications: • High-resolution imaging • Replacement for sounding rockets for micro-payloads • Secure communications • Global positioning • Remote sensing • Near-Earth space environment research • Laser Lightcraft system consists of an all-azimuth, launch-on-demand, 5-pound spacecraft and a 2 MW pulsed, ground-based laser which will provide the power to launch the spacecraft. During launch, the spacecraft initially operates in air-breathing mode and then transitions to rocket mode at approximately Mach 5 and an altitude of 30 kilometers. • Subscale prototypes have been propelled to 125 feet altitude during testing at the Army's White Sands Missile Range.” Note: See research by Prof. L. Myrabo at R.P.I.