Pulsed nuclear thermal rocket

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https://en.wikipedia.org/wiki/Pulsed_nuclear_thermal_rocket

 

A sequence for a stationary-pulsed-stationary maneuver for a pulsed thermal nuclear rocket. During the stationary mode (working at constant nominal power), the fuel temperature is always constant (solid black line), and the propellant is coming cold (blue dotted lines) heated in the chamber and exhausted in the nozzle (red dotted line). When amplification in thrust or specific impulse is required, the nuclear core is "switched on" to a pulsed mode. In this mode, the fuel in continuously quenched and instantaneously heated by the pulses. Once the requirements for high thrust and specific impulse are not required, the nuclear core is "switched on" to the initial stationary mode.

 

A pulsed nuclear thermal rocket is a type of nuclear thermal rocket (NTR) concept developed at the Polytechnic University of Catalonia, Spain and presented at the 2016 AIAA/SAE/ASEE Propulsion Conference for thrust and specific impulse (I_sp) amplification in a conventional nuclear thermal rocket.

The pulsed nuclear thermal rocket is a bimodal rocket able to work in a stationary (at constant nominal power as in a conventional NTR), and as well as a pulsed mode as a TRIGA-like reactor, making possible the production of high power and an intensive neutron flux in short time intervals. In contrast to nuclear reactors where velocities of the coolant are no larger than a few meter per second and thus, typical residence time is on seconds, however, in rockets chambers with subsonic velocities of the propellant around hundreds of meters per second, residence time are around ${\displaystyle 10^{-2}s}$ to :${\displaystyle 10^{-3}s}$ and then a long power pulse translates into an important gain in energy in comparison with the stationary mode. The gained energy -by pulsing the nuclear core, can be used for thrust amplification by increasing the propellant mass flow, or using the intensive neutron flux to produce a very high specific impulse amplification – even higher than the fission-fragment rocket, where in the pulsed rocket the final propellant temperature is only limited by the radiative cooling after the pulsation. 

Statement of the concept

A rough calculation for the energy gain by using a pulsed thermal nuclear rocket in comparison with the conventional stationary mode, is as follows. The energy stored into the fuel after a pulsation, is the sensible heat stored because the fuel temperature increase. This energy may be written as

${\displaystyle E_{\text{pulse}}=c_{f}M_{f}\Delta T}$

where:

${\displaystyle E_{\text{pulse}}}$ is the sensible heat stored after pulsation,

${\displaystyle c_{f}}$ is the fuel heat capacity,

${\displaystyle M_{\text{f}}}$ is the fuel mass,

${\displaystyle \Delta T}$ is the temperature increase between pulsations.

On the other hand, the energy generated in the stationary mode, i.e., when the nuclear core operates at nominal constant power is given by

${\displaystyle E_{\text{stationary}}=\chi _{l}lt}$

where:

${\displaystyle \chi _{l}}$ is the linear power of the fuel (power per length of fuel),

${\displaystyle l}$ is the length of the fuel,

${\displaystyle t}$ is the residence time of the propellant in the chamber.

Also, for the case of cylindrical geometries for the nuclear fuel we have

${\displaystyle M_{f}=\pi R_{f}^{2}l\rho _{f}}$

and the linear power given by 

${\displaystyle \chi _{l}=4\pi \kappa _{f}(T_{f}-T_{s})}$

Where:

${\displaystyle R_{f}}$ is the radius of the cylindrical fuel,

${\displaystyle \rho _{f}}$ the fuel density,

${\displaystyle \kappa _{f}}$ the fuel thermal conductivity,

${\displaystyle T_{f}}$ is the fuel temperature at the center line,

${\displaystyle T_{s}}$ is the surface or cladding temperature.

Therefore, the energy ratio between the pulsed mode and the stationary mode, ${\displaystyle N={\frac {E_{\text{pulse}}}{E_{\text{stationary}}}}}$ yields

${\displaystyle N={\frac {c_{f}\rho _{f}R_{f}^{2}}{4\pi \kappa _{f}(T_{f}-T_{s})}}\left[{\frac {\Delta T}{t}}\right]}$

Where the term inside the bracket, ${\displaystyle \left[{\frac {\Delta T}{t}}\right]}$ is the quenching rate. 

Typical average values of the parameters for common nuclear fuels as MOX fuel or uranium dioxide are: heat capacities, thermal conductivity and densities around ${\displaystyle c_{f}\simeq 300J/(mol\cdot K)}$,${\displaystyle \kappa _{f}\simeq 6W/(K\cdot m^{2})}$ and ${\displaystyle \rho _{f}\simeq 10^{4}kg/(m^{3})}$, respectively., with radius close to ${\displaystyle R_{f}\simeq 10^{-2}m}$, and the temperature drop between the center line and the cladding on ${\displaystyle T_{f}-T_{s}=600K}$ or less (which result in linear power on ${\displaystyle \chi _{l}\simeq 45000W/m)}$. With these values the gain in energy is approximately given by:

${\displaystyle N\simeq 6\times 10^{-3}\left[{\frac {\Delta T}{t}}\right]}$

where ${\displaystyle \left[{\frac {\Delta T}{t}}\right]}$ is given in ${\displaystyle K/s}$. Because the residence time of the propellant in the chamber is on ${\displaystyle 10^{-3}s}$ to ${\displaystyle 10^{-2}s}$ considering subsonic velocities of the propellant of hundreds of meters per second and meter chambers, then, with temperatures differences on ${\displaystyle \Delta T\simeq 10^{3}K}$ or quenching rates on ${\displaystyle \left[{\frac {\Delta T}{t}}\right]\simeq 10^{6}K/s}$ energy amplification by pulsing the core could be thousands times larger than the stationary mode. More rigorous calculations considering the transient heat transfer theory shows energy gains around hundreds or thousands times, i.e., ${\displaystyle 10^{2}\leq N\leq 10^{3}}$. 

Quenching rates on ${\displaystyle \left[{\frac {\Delta T}{t}}\right]\geq 10^{6}K/s}$ are typical in the technology for production of amorphous metal, where extremely rapid cooling in the order of ${\displaystyle 10^{6}K/s\leq \left[{\frac {\Delta T}{t}}\right]\leq 10^{7}K/s}$ are required.

Direct thrust amplification

The most direct way to harness the amplified energy by pulsing the nuclear core is by increasing the thrust via increasing the propellant mass flow. 

Increasing the thrust in the stationary mode -where power is fixed by thermodynamic constraints, is only possible by sacrificing exhaust velocity. In fact, the power is given by

${\displaystyle P={\frac {1}{2}}Fv_{\text{e}}}$

where ${\displaystyle P}$ is the power, ${\displaystyle F}$ is the thrust and ${\displaystyle v_{\text{e}}}$ the exhaust velocity. On the other hand, thrust is given by

${\displaystyle F={\dot {m}}_{\text{p}}v_{\text{e}}}$

where ${\displaystyle {\dot {m}}_{\text{p}}}$ is the propellant mass flow. Thus, if it is desired to increase the thrust, say, n-times in the stationary mode, it will be necessary to increase ${\displaystyle n^{2}}$-times the propellant mass flow, and decreasing ${\displaystyle {\frac {1}{n}}}$-times the exhaust velocity. However, if the nuclear core is pulsed, thrust may be amplified ${\displaystyle n}$-times by amplifying the power ${\displaystyle n}$-times and the propellant mass flow ${\displaystyle n}$-times and keeping constant the exhaust velocity. 

I_sp amplification

Pulsed nuclear thermal rocket unit cell concept for I_sp amplification. In this cell, hydrogen-propellant is heated by the continuous intense neutronic pulses in the propellant channels. At the same time, the unwanted energy from the fission fragments is removed by a solidary cooling channel with lithium or other liquid metal.

 

The attainment of high exhaust velocity or specific impulse (I_sp) is the first concern. The most general expression for the I_sp is given by 

${\displaystyle I_{\text{sp}}\simeq c{\sqrt {T}}}$

being ${\displaystyle c}$ a constant, and ${\displaystyle T}$ the temperature of the propellant before expansion. However, the temperature of the propellant is related directly with the energy as ${\displaystyle E\simeq kT}$, where ${\displaystyle k}$ is the Boltzmann constant. Thus,

${\displaystyle I_{\text{sp}}\simeq c'{\sqrt {E}}}$

being ${\displaystyle c'}$ a constant. 

In a conventional stationary NTR, the energy ${\displaystyle E}$ for heating the propellant is almost from the fission fragments which encompass almost the 95% of the total energy, and the faction of energy from prompt neutrons ${\displaystyle f_{\text{n}}}$ is only around 5%, and therefore, in comparison, is almost negligible. However, if the nuclear core is pulsed -as previously discussed, it is able to produce ${\displaystyle N}$ times more energy than the stationary mode, and then the fraction of prompt neutrons or ${\displaystyle f_{\text{n}}N}$ could be equal or larger than the total energy in the stationary mode; and because this neutron energy is directly transported from the fuel into the propellant as kinetic energy -unlike the energy from fission fragments which is transported as heat from the fuel into the propellant, then is not constrained by the second law of thermodynamics, meaning that there is no impediment to transport this energy from the fuel to the propellant even if the fuel is colder than the propellant, in other words, it is possible a " propellant hotter than the fuel" which is the very limit for specific impulse enhancement in classics NTRs. 

In summary, if the pulse generates ${\displaystyle N}$ times more energy than the stationary mode, the I_sp amplification is given by

${\displaystyle I_{\text{sp}}\simeq I_{\text{sp,o}}{\sqrt {f_{\text{n}}N+1}}}$

Where:

${\displaystyle I_{\text{sp}}}$ is the amplified specific impulse,

${\displaystyle I_{\text{sp,o}}}$ the specific impulse in the stationary mode,

${\displaystyle f_{\text{n}}}$ the fraction of prompt neutrons,

${\displaystyle N}$ the energy amplification by pulsing the nuclear core.

With values of ${\displaystyle N}$ between ${\displaystyle 10^{2}}$ to ${\displaystyle 10^{3}}$ and prompt neutron fractions around ${\displaystyle f_{\text{n}}\simeq {\frac {1}{20}}}$, the hypothetical ${\displaystyle I_{\text{sp}}}$ amplification attainable makes the concept specially interesting for interplanetary spaceflight. 

Advantages of the design

There are several advantages relative to conventional stationary NTR designs. Because the neutron energy is transported as kinetic energy from the fuel into the propellant, then a propellant hotter than the fuel is possible and therefore the ${\displaystyle I_{\text{sp}}}$ is not limited to the maximum temperature permissible by the fuel, i.e., its melting temperature.

The other nuclear rocket concept which allows a propellant hotter than the fuel is the fission fragment rocket. Because it directly uses the fission fragments as propellant, it can also achieve a very high specific impulse.

Other considerations

For ${\displaystyle I_{\text{sp}}}$ amplification, only the energy from prompt neutrons, and some prompt gamma energy, is used for this purpose. The rest of the energy, i.e., the almost ${\displaystyle 95\%}$ from fission fragments is unwanted energy and must be continuously evacuated by a heat removal auxiliary system using a suitable coolant. Liquid metals, and particularly lithium, can provide the fast quenching rates required. One aspect to be considered is the large amount of energy which must be evacuated as residual heat (almost 95% of the total energy). This implies a large dedicated heat transfer surface.

As regards to the mechanism for pulsing the core, the pulsed mode can be produced using a variety of configurations depending on the desired frequency of the pulsations. For instance, the use of standard control rods in a single or banked configuration with motor driving mechanism or the use of standard pneumatically operated pulsing mechanisms are suitable for generating up to 10 pulses per minute. For the production of pulses at rates up to 50 pulsations per second, the use of rotating wheels introducing alternately neutron poison and fuel or neutron poison and non-neutron poison can be considered. However, for pulsations ranking the thousands of pulses per second (kHz), optical choppers or modern wheels employing magnetic bearings allow to revolve at 10 kHz. If even faster pulsations are desired it would be necessary to make use of a new type of pulsing mechanism that does not involve mechanical motion, for example, lasers (based in the 3He polarization) as early proposed by Bowman, or proton and neutron beams. Frequencies on the order of 1 kHz to 10 kHz are likely choices.

Nuclear pulse propulsion

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https://en.wikipedia.org/wiki/Nuclear_pulse_propulsion

 

An artist's conception of the Project Orion "basic" spacecraft, powered by nuclear pulse propulsion.

 

Nuclear pulse propulsion or external pulsed plasma propulsion is a hypothetical method of spacecraft propulsion that uses nuclear explosions for thrust. It was first developed as Project Orion by DARPA, after a suggestion by Stanislaw Ulam in 1947. Newer designs using inertial confinement fusion have been the baseline for most post-Orion designs, including Project Daedalus and Project Longshot. 

Project Orion

A nuclear pulse propulsion unit. The explosive charge ablatively vaporizes the propellant, propelling it away from the charge, and simultaneously creating a plasma out of the propellant. The propellant then goes on to impact the pusher plate at the bottom of the Orion spacecraft, imparting a pulse of 'pushing' energy.

 

Project Orion was the first serious attempt to design a nuclear pulse rocket. The design effort was carried out at General Atomics in the late 1950s and early 1960s. The idea of Orion was to react small directional nuclear explosives utilizing a variant of the Teller-Ulam two-stage bomb design against a large steel pusher plate attached to the spacecraft with shock absorbers. Efficient directional explosives maximized the momentum transfer, leading to specific impulses in the range of 6,000 seconds, or about thirteen times that of the Space Shuttle main engine. With refinements a theoretical maximum of 100,000 seconds (1 MN·s/kg) might be possible. Thrusts were in the millions of tons, allowing spacecraft larger than 8×10⁶ tons to be built with 1958 materials.

The reference design was to be constructed of steel using submarine-style construction with a crew of more than 200 and a vehicle takeoff weight of several thousand tons. This low-tech single-stage reference design would reach Mars and back in four weeks from the Earth's surface (compared to 12 months for NASA's current chemically powered reference mission). The same craft could visit Saturn's moons in a seven-month mission (compared to chemically powered missions of about nine years). 

A number of engineering problems were found and solved over the course of the project, notably related to crew shielding and pusher-plate lifetime. The system appeared to be entirely workable when the project was shut down in 1965, the main reason being given that the Partial Test Ban Treaty made it illegal (however, before the treaty, the US and Soviet Union had already detonated at least nine nuclear bombs, including thermonuclear bombs, in space, i.e., at altitudes over 100 km: see high-altitude nuclear explosions). There were also ethical issues with launching such a vehicle within the Earth's magnetosphere: calculations using the now disputed linear no-threshold model of radiation damage showed that the fallout from each takeoff would kill between 1 and 10 people. In a threshold model, such extremely low levels of thinly distributed radiation would have no associated ill-effects, while under hormesis models, such tiny doses would be negligibly beneficial. With the possible use of less efficient clean nuclear bombs for achieving orbit and then more efficient higher yield dirty bombs for travel would bring down the amount of fallout caused from an Earth-based launch by a significant factor. 

One useful mission for this near-term technology would be to deflect an asteroid that could collide with the Earth, depicted dramatically in the 1998 film Deep Impact, even though it was a comet in that particular film. The extremely high performance would permit even a late launch to succeed, and the vehicle could effectively transfer a large amount of kinetic energy to the asteroid by simple impact, and in the event of an imminent asteroid impact a few predicted deaths from fallout would probably not be considered prohibitive. Also, an automated mission would eliminate the most problematic issues of the design: the shock absorbers.

Orion is one of very few interstellar space drives that could theoretically be constructed with available technology, as discussed in a 1968 paper, Interstellar Transport by Freeman Dyson. 

Project Daedalus

Project Daedalus was a study conducted between 1973 and 1978 by the British Interplanetary Society (BIS) to design a plausible interstellar unmanned spacecraft that could reach a nearby star within one human scientist's working lifetime or about 50 years. A dozen scientists and engineers led by Alan Bond worked on the project. At the time fusion research appeared to be making great strides, and in particular, inertial confinement fusion (ICF) appeared to be adaptable as a rocket engine. 

ICF uses small pellets of fusion fuel, typically lithium deuteride (⁶Li²H) with a small deuterium/tritium trigger at the center. The pellets are thrown into a reaction chamber where they are hit on all sides by lasers or another form of beamed energy. The heat generated by the beams explosively compresses the pellet, to the point where fusion takes place. The result is a hot plasma, and a very small "explosion" compared to the minimum size bomb that would be required to instead create the necessary amount of fission. 

For Daedalus, this process was run within a large electromagnet which formed the rocket engine. After the reaction, ignited by electron beams in this case, the magnet funnelled the hot gas to the rear for thrust. Some of the energy was diverted to run the ship's systems and engine. In order to make the system safe and energy efficient, Daedalus was to be powered by a helium-3 fuel that would have had to be collected from Jupiter. 

Medusa

Conceptual diagram of a Medusa propulsion spacecraft, showing: (A) the payload capsule, (B) the winch mechanism, (C) the optional main tether cable, (D) riser tethers, and (E) the parachute mechanism.

 

Operating sequence of the Medusa propulsion system. This diagram shows the operating sequence of a Medusa propulsion spacecraft (1) Starting at moment of explosive-pulse unit firing, (2) As the explosive pulse reaches the parachute canopy, (3) Pushes the canopy, accelerating it away from the explosion as the spacecraft plays out the main tether with the winch, generating electricity as it extends, and accelerating the spacecraft, (4) And finally winches the spacecraft forward to the canopy and uses excess electricity for other purposes.

 

The Medusa design is a type of nuclear pulse propulsion which has more in common with solar sails than with conventional rockets. It was envisioned by Johndale Solem in the 1990s and published in the Journal of the British Interplanetary Society (JBIS).

A Medusa spacecraft would deploy a large "spinnaker" sail ahead of it, attached by separate independent cables, and then launch nuclear explosives forward to detonate between itself and its sail. The sail would be accelerated by the plasma and photonic impulse, running out the tethers as when a fish flees the fisherman, and generating electricity at the "reel". The spacecraft would then use some of the generated electricity to reel itself up towards the sail, constantly smoothly accelerating as it goes.

In the original design, multiple tethers connected to multiple motor generators. The advantage over the single tether is to increase the distance between the explosion and the tethers, thus reducing damage to the tethers.

For heavy payloads, performance could be improved by taking advantage of lunar materials, for example, wrapping the explosive with lunar rock or water, likely stored previously at a stable Earth-Moon Lagrange point to be subsequently acquired by the Medusa spacecraft.

Medusa performs better than the classical Orion design because its sail intercepts more of the explosive impulse, its shock-absorber stroke is much longer, and all its major structures are in tension and hence can be quite lightweight. Medusa-type ships would be capable of a specific impulse between 50,000 and 100,000 seconds (500 to 1000 kN·s/kg).

Medusa is widely known to the public in the BBC documentary film To Mars By A-Bomb: The Secret History of Project Orion. A short film shows an artist's conception of how the Medusa spacecraft works "by throwing bombs into a sail that's ahead of it".

Project Longshot

Project Longshot was a NASA-sponsored research project carried out in conjunction with the US Naval Academy in the late 1980s. Longshot was in some ways a development of the basic Daedalus concept, in that it used magnetically funneled ICF as a rocket. The key difference was that they felt that the reaction could not power both the rocket and the systems, and instead included a 300 kW conventional nuclear reactor for running the ship. The added weight of the reactor reduced performance somewhat, but even using LiD fuel it would be able to reach Alpha Centauri, the closest solar system to our own, in 100 years (approx. velocity of 13,411 km/s, at a distance of 4.5 light years - equivalent to 4.5% of light speed). 

Antimatter-catalyzed nuclear pulse propulsion

In the mid-1990s research at the Pennsylvania State University led to the concept of using antimatter to catalyze nuclear reactions. In short, antiprotons would react inside the nucleus of uranium, causing a release of energy that breaks the nucleus apart as in conventional nuclear reactions. Even a small number of such reactions can start the chain reaction that would otherwise require a much larger volume of fuel to sustain. Whereas the "normal" critical mass for plutonium is about 11.8 kilograms (for a sphere at standard density), with antimatter catalyzed reactions this could be well under one gram. 

Several rocket designs using this reaction were proposed, some which would use all-fission reactions for interplanetary missions, and others using fission-fusion (effectively a very small version of Orion's bombs) for interstellar missions. 

MSNW magneto-inertial fusion driven rocket

MSNW magneto-inertial fusion driven rocket

Concept graphic of a fusion-driven rocket powered spacecraft arriving at Mars
Designer	MSNW LLC
Application	Interplanetary
Status	Theoretical
Performance
Specific impulse	1,606 s to 5,722 s (depending on fusion gain)
Burn time	1 day to 90 days (10 days optimal with gain of 40)
References
References
Notes	Fuel: Deuterium-tritium cryogenic pellet Propellent: Lithium or aluminum Power requirements: 100 kW to 1,000 kW

NASA funded MSNW LLC and the University of Washington in 2011 to study and develop a fusion rocket through the NASA Innovative Advanced Concepts NIAC Program.

The rocket uses a form of magneto-inertial fusion to produce a direct thrust fusion rocket. Powerful magnetic fields cause large metal rings (likely made of lithium, where a set for one pulse has a total mass of 365 grams) to collapse around the deuterium-tritium plasma, compressing it to a fusion state. Energy from these fusion reactions heats and ionizes the shell of metal formed by the crushed rings. The hot, ionized metal is shot out of a magnetic rocket nozzle at a high speed (up to 30 km/s). Repeating this process roughly every minute would propel the spacecraft. The fusion reaction is not self-sustaining and requires electrical energy to induce fusion. With electrical requirements estimated to be between 100 kW to 1,000 kW (300 kW average), spacecraft designs incorporate solar panels to produce the electrical energy needed for the fusion engine.

This approach uses Foil Liner Compression to create a fusion reaction of the proper energy scale to be used for space propulsion. The proof of concept experiment in Redmond, Washington, will use aluminum liners for compression. However, the actual rocket design will run with lithium liners.

The performance characteristics of the engine are highly dependent on the Fusion energy gain factor achieved by the reactor. Gains are expected to be between a factor of 20 and 200, with an estimated average of 40. With higher fusions gains comes higher exhaust velocity, higher specific impulse and lower electrical power requirements. The table below summarizes different performance characteristics for a theoretical 90-day Mars transfer at gains of 20, 40 and 200.

FDR parameters for 90 Mars transfer burn

Total gain	Gain 20	Gain 40	Gain 200
Liner mass (kg)	0.365	0.365	0.365
Specific impulse (s)	1,606	2,435	5,722
Mass fraction	0.33	0.47	0.68
Specific mass (kg/kW)	0.8	0.53	0.23
Mass propellant (kg)	110,000	59,000	20,000
Mass initial (kg)	184,000	130,000	90,000
Electrical power required (kW)	1,019	546	188

By April 2013, MSNW had demonstrated subcomponents of the systems: heating deuterium plasma up to fusion temperatures and have concentrated the magnetic fields needed to create fusion. They planned to put the two technologies together for a test before the end of 2013.

They could later be scaled up in power and plan to add the necessary fusion fuel (deuterium) by the end (Sept 2014) of the NIAC Study.

Breakthrough Starshot

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/Breakthrough_Starshot

 

On 24 August 2016, ESO hosted a press conference to discuss the announcement of exoplanet Proxima b at its headquarters in Germany. In this picture, Pete Worden giving a speech.

 

Breakthrough Starshot is a research and engineering project by the Breakthrough Initiatives to develop a proof-of-concept fleet of light sail spacecraft named StarChip, to be capable of making the journey to the Alpha Centauri star system 4.37 light-years away. It was founded in 2016 by Yuri Milner, Stephen Hawking, and Mark Zuckerberg.

A flyby mission has been proposed to Proxima Centauri b, an Earth-sized exoplanet in the habitable zone of its host star, Proxima Centauri, in the Alpha Centauri system. At a speed between 15% and 20% of the speed of light, it would take between twenty and thirty years to complete the journey, and approximately four years for a return message from the starship to Earth. 

The conceptual principles to enable this interstellar travel project were described in "A Roadmap to Interstellar Flight", by Philip Lubin of UC Santa Barbara. Sending the lightweight spacecraft involves a multi-kilometer phased array of beam-steerable lasers with a combined coherent power output of up to 100 GW.

General

The project was announced on 12 April 2016 in an event held in New York City by physicist and venture capitalist Yuri Milner, together with cosmologist Stephen Hawking, who was serving as board member of the initiatives. Other board members include Facebook CEO Mark Zuckerberg. The project has an initial funding of US$100 million to initialize research. Milner places the final mission cost at $5–10 billion, and estimates the first craft could launch by around 2036. Pete Worden is the project's executive director and Professor Avi Loeb (Harvard University) chairs the Advisory Board for the project.

Leaders

Management and Advisory Committee

• Pete Worden, Executive Director, Breakthrough Starshot; former Director of NASA Ames Research Center
• Avi Loeb, Chairman, Breakthrough Starshot Advisory Committee; Harvard University
• Jim Benford, Microwave Sciences
• Steven Chu, Nobel Prize winner, Stanford University
• Bruce Draine, Princeton University
• Ann Druyan, Cosmos Studios
• Freeman Dyson, Princeton Institute of Advanced Study
• Lou Friedman, Planetary Society, JPL
• Robert Fugate, Arctelum, LLC, New Mexico Tech
• Giancarlo Genta, Polytechnic University of Turin
• Olivier Guyon, University of Arizona
• Mae Jemison, 100 Year Starship
• Joan Johnson-Freese, US Naval War College
• Pete Klupar, Director of Engineering, Breakthrough Starshot; former Director of Engineering, NASA Ames Research Center
• Jeff Kuhn, University of Hawaii Institute for Astronomy
• Geoff Landis, SA Glenn Research Center
• Kelvin Long, Journal of the British Interplanetary Society
• Greg Matloff, New York City College of Technology
• Claire Max, University of California, Santa Cruz
• Kaya Nobuyuki, Kobe University
• Kevin Parkin, Parkin Research
• Mason Peck, Cornell University
• Saul Perlmutter, Nobel Prize winner, Breakthrough Prize winner, UC Berkeley and Lawrence Berkeley National Laboratory
• Martin Rees, Astronomer Royal
• Roald Sagdeev, University of Maryland
• Ed Turner, Princeton University, NAOJ
  

Objectives

The Breakthrough Starshot program aims to demonstrate a proof-of-concept for ultra-fast, light-driven nano-spacecraft, and lay the foundations for a first launch to Alpha Centauri within the next generation. Secondary goals are: Solar System exploration and detection of Earth-crossing asteroids. The spacecraft would make a flyby of, and, possibly photograph any Earth-like worlds that might exist in the system. 

Target planet

In August 2016, the European Southern Observatory (ESO) announced the detection of a planet orbiting the third star in the Alpha Centauri system, Proxima Centauri. The planet, called Proxima Centauri b, is orbiting within the habitable zone of its star, and it could be a potential target for one of the projects of Breakthrough Initiatives. 

In January 2017, Breakthrough Initiatives and the European Southern Observatory entered a collaboration to search for habitable planets in the nearby star system, Alpha Centauri. The agreement involves Breakthrough Initiatives providing funding for an upgrade to the VISIR (VLT Imager and Spectrometer for mid-Infrared) instrument on ESO's Very Large Telescope (VLT) in Chile. This upgrade will greatly increase the likelihood of planet detection in the system. 

Concept

A solar sail concept

 

The Starshot concept envisions launching a "mothership" carrying about a thousand tiny spacecraft (on the scale of centimeters) to a high-altitude Earth orbit and then deploying them. A phased array of ground-based lasers would then focus a light beam on the crafts' sails to accelerate them one by one to the target speed within 10 minutes, with an average acceleration on the order of 100 km/s² (10,000  ɡ), and an illumination energy on the order of 1 TJ delivered to each sail. A preliminary sail model is suggested to have a surface area of 4 m × 4 m. An October 2017 presentation of the Starshot system model examines circular sails and finds that the beam director capital cost is minimized by having a sail diameter of 5 meters.

Earth-size planet Proxima Centauri b was discovered in 2016 orbiting within the Alpha Centauri system habitable zones, compelling the Breakthrough Starshot to try to aim its spacecraft within 1 astronomical unit (150 million kilometers or 93 million miles) of it. From this distance, a craft's cameras could potentially capture an image of high enough quality to resolve surface features.

The fleet would have about 1000 spacecraft, and each one (dubbed a StarChip), would be a very small centimeter-sized vehicle weighing a few grams. They would be propelled by a square-kilometre array of 10 kW ground-based lasers with a combined output of up to 100 GW. A swarm of about 1000 units would compensate for the losses caused by interstellar dust collisions en route to the target. In a detailed study in 2016 Thiem Hoang and coworkers found that mitigating the collisions with dust, hydrogen and galactic cosmic rays may not be quite as severe an engineering problem as first thought.

Technical challenges

Light propulsion requires enormous power: a laser with a gigawatt of power (approximately the output of a large nuclear plant) would provide only a few newtons of thrust. The spaceship will compensate for the low thrust by having a mass of only a few grams. The camera, computer, communications laser, a plutonium power source, and the solar sail must be miniaturized to fit within a mass limit. All components must be engineered to endure extreme acceleration, cold, vacuum, and protons. The spacecraft will have to survive collisions with space dust; Starshot expects each square centimeter of frontal cross-section to collide at high speed with about a thousand particles of size at least 0.1 μm. Focusing a set of lasers totaling one hundred gigawatts onto the solar sail will be difficult due to atmospheric turbulence, so there is the suggestion to use space-based laser infrastructure. According to The Economist, at least a dozen off-the-shelf technologies will need to improve by orders of magnitude.

StarChip

StarChip is the name used by Breakthrough Initiatives for a very small, centimeter-sized, gram-scale, interstellar spacecraft envisioned for the Breakthrough Starshot program, a proposed mission to propel a fleet of a thousand StarChips on a journey to the Alpha Centauri star system, the nearest extrasolar stars, about 4.37 light-years from Earth. The journey may include a flyby of Proxima Centauri b, an Earth-sized exoplanet that is in the habitable zone of its host star. The ultra-light StarChip robotic nanocraft, fitted with lightsails, are planned to travel at speeds of 20% and 15% of the speed of light, taking between 20 and 30 years to reach the star system, respectively, and about 4 years to notify Earth of a successful arrival. The conceptual principles to enable practical interstellar travel were described in "A Roadmap to Interstellar Flight", by Philip Lubin of UC Santa Barbara, who is an advisor for the Starshot project. 

In July 2017, scientists announced that precursors to StarChip, named Sprites, were successfully launched and flown through Polar Satellite Launch Vehicle by ISRO from Satish Dhawan Space Centre. Sprites will also be flown on the KickSat-2 mission scheduled for November 2018. 

Components

Each StarChip nanocraft is expected to carry miniaturized cameras, navigation gear, communication equipment, photon thrusters and a power supply. In addition, each nanocraft would be fitted with a meter-scale lightsail, made of lightweight materials, with a gram-scale mass.

Cameras

Four sub-gram scale digital cameras, each with a minimum 2-megapixels resolution, are envisioned.

Processors

Four sub-gram scale processors are planned.

Photon thrusters

Four sub-gram scale photon thrusters, each minimally capable of performing at a 1W diode laser level, are planned.

Battery

A 150 mg atomic battery, powered by plutonium-238 or americium-241, is planned.

Protective coating

A coating, possibly made of beryllium copper, is planned to protect the nanocraft from dust collisions and atomic particle erosion.

Lightsail

The lightsail is envisioned to be no larger than 4 by 4 meters (13 by 13 feet), possibly of composite graphene-based material. The material would have to be very thin and be able to reflect the laser beam while absorbing only a small fraction of the incident energy, or it will vaporize the sail.

Other potential destinations

The table below lists possible target stars for similar photogravitational assist travel. The travel times are for the spacecraft to travel to the star and then enter orbit around the star (using photon pressure in maneuvers similar to aerobraking).

Name	Travel time (yr)	Distance (ly)	Luminosity (L☉)
Proxima Centauri	121	4.2	0.00005
α Centauri A	101.25	4.36	1.52
α Centauri B	147.58	4.36	0.50
Sirius A	68.90	8.58	24.20
Procyon A	154.06	11.44	6.94
Vega	167.39	25.02	50.05
Altair	176.67	16.69	10.70
Fomalhaut A	221.33	25.13	16.67
Denebola	325.56	35.78	14.66
Castor A	341.35	50.98	49.85
Epsilon Eridani	363.35	10.50	0.50

• Successive assists at α Cen A and B could allow travel times to 75 yr to both stars.
• Lightsail has a nominal mass-to-surface ratio (σ_nom) of 8.6×10⁻⁴ gram m⁻² for a nominal graphene-class sail.
• Area of the Lightsail, about 10⁵ m² = (316 m)²
• Velocity up to 37,300 km s⁻¹ (12.5% c)
  

Other applications

The German physicist Claudius Gros has proposed that the technology of the Breakthrough Starshot initiative may be utilized in a second step to establish a biosphere of unicellular microbes on otherwise only transiently habitable exoplanets. A Genesis probe would travel at lower speeds, about 0.3% of the speed of light. It could hence be decelerated using a magnetic sail.

National Space Society

From Wikipedia, the free encyclopedia

https://en.wikipedia.org/wiki/National_Space_Society

 

National Space Society

Founded	1987
Type	Space advocacy, 501(c)3 Education
Location	Washington, D.C., United States
Area served	Worldwide
Website	nss.org

The National Space Society (NSS) is an American international nonprofit 501(c)(3) educational and scientific organization specializing in space advocacy. It is a member of the Independent Charities of America and an annual participant in the Combined Federal Campaign. The society's vision is: "People living and working in thriving communities beyond the Earth, and the use of the vast resources of space for the dramatic betterment of humanity."

The society supports human spaceflight and robotic spaceflight, by both the public (e.g., NASA, Russian Federal Space Agency and Japan Aerospace Exploration Agency) and private sector (e.g., Ansari X Prize, Transformational Space, Scaled Composites, etc.) organizations.

History

The society was established in the United States on March 28, 1987 by the merger of the National Space Institute, founded in 1974 by Dr. Wernher von Braun, and the L5 Society, founded in 1975 based on the concepts of Dr. Gerard K. O'Neill.

The society has an elected volunteer Board of Directors and a Board of Governors. The chairman of the Board of Governors is United States Air Force Colonel Karlton Johnson (retired). The chairman of the Board of Directors is Kirby Ikin. 

The National Space Society was awarded the "Five-Star Best in America" award by the Independent Charities of America organization in 2005.

In 2014, the National Space Society launched the Enterprise In Space program. In order to ignite interest in space and science, technology, engineering, art and math (STEAM) education, Enterprise In Space plans to design, build, and launch a 3D-printed spacecraft into Earth orbit carrying 100+ experiments from K to postgraduate student teams. The orbiter is planned to be returned to Earth with the experiments for the student teams to analyze. 

Ad Astra

The Society publishes a magazine Ad Astra, which appears quarterly in print and electronic form. 

International Space Development Conference

The society hosts an annual International Space Development Conference (ISDC) held in major cities throughout the United States, often during or close to the Memorial Day weekend.

NSS Chapters network

Locations and "sphere of operation" of current NSS chapters in the United States (image courtesy of NSS)

 

As listed in each quarterly issue of Ad Astra, a large number of NSS chapters exist around the world. The chapters may serve a local area such as a school, city or town, or have a topical or special interest focus, such as a rocketry or astronomy club, or educational/community outreach program. Chapters are the peripheral organs of the society by organizing events, communicating with the public on the merits and benefits of space exploration, and working to educate political leaders.

Location of current NSS chapters in Australia (image courtesy of NSS)

National Space Society of Australia

A strong contingent of chapters is located in Australia. Prior to the NSI-L5 merger, the L5 Society had been developing chapters around the world, and in Australia, three chapters had been established. The 'Southern Cross L5 Society' was formed in 1979, with groups in Sydney, Adelaide (in 1984) and Brisbane (in 1986). It was decided in late 1989 to create the National Space Society of Australia (NSSA) which could act as an umbrella organization.

Similar efforts have taken hold in Brazil, Canada and Mexico, as well as European countries that have a strong aerospace presence. including France, Germany, and the Netherlands.

Awards

The society administers a number of awards. These are typically presented during the annual International Space Development Conference that NSS hosts. These awards are in recognition of individual volunteer effort, awards for NSS chapter work, the "Space Pioneer" award, and two significant awards which are presented in alternate years. 

Robert A. Heinlein Memorial Award

The Robert A. Heinlein Memorial Award, is given in even-numbered years (2004, 2006, etc.) to "honor those individuals who have made significant, lifetime contributions to the creation of a free spacefaring civilization. 

Heinlein Award Winners:

• 2018 - Dr. Freeman Dyson
• 2016 - Dr. Jerry Pournelle
• 2014 - Elon Musk
• 2012 - Dr. Stephen Hawking
• 2010 - Dr. Peter Diamandis
• 2008 - Burt Rutan
• 2006 - Brigadier General Charles E. "Chuck" Yeager
• 2004 - Capt. James Lovell
• 2002 - Robert Zubrin
• 2000 - Neil Armstrong
• 1998 - Dr. Carl Sagan
• 1996 - Dr. Buzz Aldrin
• 1994 - Dr. Robert H. Goddard
• 1992 - Gene Roddenberry
• 1990 - Dr. Wernher von Braun
• 1988 - Sir Arthur C. Clarke
• 1986 - Dr. Gerard K. O'Neill
  

NSS Von Braun Award

The NSS Von Braun Award is given in odd-numbered years (1993, 1995, etc.) "to recognize excellence in management of and leadership for a space-related project where the project is significant and successful and the manager has the loyalty of a strong team that he or she has created." Awardees include:

Von Braun Award Winners:

• 2019 - Tory Bruno
• 2017 - Prof. Johann-Dietrich Wörner
• 2015 - Mars Curiosity Rover project Team
• 2013 - Dr. A.P.J. Abdul Kalam
• 2011 - JAXA Hayabusa Team
• 2009 - Elon Musk
• 2007 - Steven W. Squyres
• 2005 - Burt Rutan
• 2001 - Donna Shirley
• 1999 - Robert C. Seamans, Jr.
• 1997 - George Mueller
• 1995 - Max Hunter
• 1993 - Dr. Ernst Stuhlinger

Other scholarships and award activities

Other scholarships and award activities NSS provides or assists with include the following awards:

• The Space Pioneer Awards
• The NSS-ISU scholarship, worth $12,000, to the International Space University. Application deadline is December 31 of each year, for study during the following year. The 2005 recipient was Robert Guinness of St. Louis;
• EURISY international youth science fiction writing competition (NSS provided US support in 2005), and;
• Permission to Dream space adventure for students, teachers and parents from the Space Frontier Foundation which is partly sponsored by NSS.
  

Affiliations

The National Space Society is an alliance organization of the Meade 4M Community, the Coalition for Space Exploration, in support of the educational initiatives and outreach of NSS, and a founding executive member of the Alliance for Space Development.