This Week in Science (April 10 – 17)

Apr 17, 2016

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18 comments on “This Week in Science (April 10 – 17)

  • I commented on a more garbled article about this earlier:-

    https://www.richarddawkins.net/2016/04/reaching-for-the-stars-across-4-37-light-years/#li-comment-201817

    The present article is much clearer.

    Russian billionaire unveils big plan to build tiny interstellar spacecraft

    @OP- link – Instead of a futuristic propulsion system, the “nanocraft” will “leave their fuel behind,” Milner told a press conference in New York City this afternoon. The craft will have a solar sail, a few meters across and weighing a few grams. Powerful Earth-based lasers would boost the craft, which would be waiting in Earth’s orbit, with an acceleration of 60,000 g for a few minutes to reach 20% of the speed of light —fast enough to reach Alpha Centauri in 20 years.

    I am very sceptical about this!
    At 60,000g force, the structural stresses would be enormous, and with lasers beaming this amount of energy on to a small area in a short time, the heating would also be enormous!

    Milner has now launched another $100 million effort, dubbed Breakthrough Starshot, to prove the principle of sending multiple tiny craft to a star. “With light beams and a light sail and the smallest spacecraft ever created, we can launch a mission to Alpha Centauri in a generation,” U.K. physicist Stephen Hawking told the press conference. Hawking was joined on the podium by other high profile scientists backing the project, including Princeton University physicist Freeman Dyson, Massachusetts Institute of Technology in Cambridge astrophysicist Avi Loeb, and Pete Worden, former director of NASA Ames Research Center.

    This may be useful in getting people talking about new technologies, but it appears to me primarily as a publicity stunt!

    There seem to some mavericks among the line up of scientists!
    Pete Woden, now retired, had a reputation of being something of a character during his time before and at NASA, while Freeman Dyson (famed for some far-out science-fiction-like space proposals), now at the age of 92, has several years of climate change denial to his credit!

    The effort faces considerable technical challenges but Milner said it was “based on technology that is available or available in the near future.” The first challenge is in microfabrication, which he says is being driven by the cellphone industry. The project will be developing a Starchip, essentially a spacecraft on a chip, which will have cameras, photon thrusters, power supply (a radionuclide source), navigation, and communication equipment. The team estimates that today such a chip can be built weighing just 370 milligrams; by 2030 it will be down to 220 milligrams. Starchips could be mass produced for about the cost of an iPhone, Milner claims.

    I am intrigued as to how they are going to construct and power a radio transmitter, capable of sending data over inter-stellar distances within these weight limits! The other items may well be capable of miniaturisation, but this appears to be a key sticking point.

    There are nuclear isotope power sources which will power space transmitters, but the fuel required is measured in kilogrammes, not milligrams!

    https://en.wikipedia.org/wiki/Radioisotope_thermoelectric_generator#Space
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  • Alan4discussion #2

    The final section of the previous post (below), was a comment from me, and not part of the quote from the link.

    I am intrigued as to how they are going to construct and power a radio transmitter, capable of sending data over inter-stellar distances within these weight limits! The other items may well be capable of miniaturisation, but this appears to be a key sticking point.

    There are nuclear isotope power sources which will power space transmitters, but the fuel required is measured in kilogrammes, not milligrams!

    Unfortunately as it was on hold for moderation, I did not see the formatting error until after the edit time had expired.
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  • I would imagine laser comunication has everything going for it. Solid state lasers are hitting 70% efficiency and beam divergence of less than 0.3mrad. That should produce intensities (watts per steradian) to out compete even stars once pulsed and optically filtered at the reception end. (Radio conversion efficiency is 30% and beam intensity due to divergence is hundreds of times worse.)

    I think the only hope for tiny radio power generators (sources) might be beta decay materials able to generate heat and electrostatic fields to charge say graphene batteries. I see brief operation of any electronics with huge duty cycles.

    I note RTGs now migrating to stirling engines to uprate efficiency from terrible to half decent. (Unlikely to be small.)
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  • phil rimmer #4
    Apr 17, 2016 at 6:03 pm

    I think the only hope for tiny radio power generators (sources) might be beta decay materials able to generate heat and electrostatic fields to charge say graphene batteries.

    The other power issue, is recording data. With a flyby at 20% light speed, any imaging going to need to be fast, with a large memory rapidly accessed, and data transmitted before the next planet/moon/body comes into view.
    Then there are problems with heat and temperature management of space probes, – from internal heat sources, and from solar radiation at various distances from target stars.
    Chips and thermocouples can be miniaturised in solid state form, but ancillary equipment like heat-sinks variable insulation between components, and radiators operating in vacuum , will I suspect, cause problems.
    I am not sure how far lasers miniaturised along with other circuity and their power sources, could meet these constraints of time, distance, stability and targeting.

    The overall mass looks ridiculously small for establishing high power low divergence laser beams over interstellar distances.
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  • Operating at 350K surface temperature an iPhone 6S Plus would need to generate 16W or so of heat with 3K surroundings. Graphene gets the heat out OK and makes things isothermal and everything can work well at 350K. One might get up to 3W out of a Beta emitter generator dissipating 16W total.
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  • phil rimmer #6
    Apr 17, 2016 at 7:38 pm

    Operating at 350K surface temperature an iPhone 6S Plus would need to generate 16W or so of heat with 3K surroundings. Graphene gets the heat out OK and makes things isothermal and everything can work well at 350K. One might get up to 3W out of a Beta emitter generator dissipating 16W total.

    I think you are more up to date on the details of the physics than I am, so for now I’ll raise the questions which I see as problematic.

    Stability of probes is usually maintained by 3 axis flywheels, or attitude thrusters. These involve mass! Spin can also be used, but is not much use alone when aiming signals, and is problematic at all but the lowest rates in conjunction with solar sails.

    A light weight solar sail structure, does not look compatible with the stresses of an acceleration of 60,000 g for a few minutes.

    Solar sails are affected by the solar wind and photons from stars, although this may be beneficially manageable.

    I raised the issue potential rises and falls in temperature, from of pulses of heat from the probes’ functions and variable levels of solar radiation, in maintaining the heat balance within the systems and circuits.
    It may be possible to use solar sails as sun shades, but the sail effect would then affect the course.

    The high velocity of the flybys, means that targeting of bodies to be studied within star systems and acquisition of data, will be on very tight times scales. (All planetary probes within the Solar System have required course corrections) Random high-speed passages through a star systems are unlikely to pass near anything of interest. Probes need sensors, analysis and feed-back to make powered course adjustments.

    I also have reservations about siting propulsion lasers on Earth, and sending the beam through the atmosphere. (Even with adjustments from adaptive optics.)
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  • I know of electronics surviving 30,000g experienced by some ordnance and the new 3D printing of electronics promises flip-chips solidly embedded in ceramic filled matrices.

    Using Colossal Carbon Tube (specced for space elevator use.) six threads of 2mm diameter will yield at 120tons. 30 tons is needed for a half kilo payload. Three loops create the simplest form to support a graphene mesh sail.

    I think you have exactly the main problem- managing the flyby. This might be why swarms of things pushed at the same time may have more success. Using the outward stellar flux you are falling towards for tacking and braking would indeed be nice.

    Additional thermal load could be managed by managing both surface albedo and orientation. Electrochromic type materials exist (though not on the Bugatti Veyron sadly) and an orientable iPhone shape is about perfect to handle an inbound but directional radiation flux.

    I agree that space born lasers are the way to go, though this might not be happy making for lots of us especially if it is controlled from a hollowed out volcano.
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  • Just to expand on this comment:

    A light weight solar sail structure, does not look compatible with the stresses of an acceleration of 60,000 g for a few minutes.

    Early experiments with gun launched projectiles to orbital heights involved high g-forces.

    http://www-spof.gsfc.nasa.gov/stargaze/Smartlet.htm

    HARP, for High Altitude Research Project, was a study of the upper atmosphere by instruments shot from a cannon. The project was conducted in the 1960s by scientists of the McGill University in Montreal

    To reduce air resistance, the 200-lb Martlet vehicle was given a smaller diameter than 16 inches, with wooden blocks filling the space between it and the barrel. Because the payload and attachments were about 10 times lighter than the regular 16-inch shell, the acceleration was much larger, about 25,000 g: electric circuits had to be encased in plastic to resist the great forces.

    Edit; This comment seems to have crossed with your post above Phil.
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  • My company twenty years ago along with TRW and Loughborough University were involved in a government funded programme to put electronics directly into a plastic injection mould tool. We were achieving 5,000g numbers with no effort. A discussion I had (which I can’t detail) about a power delivery system for a gun launched missile invoked a 30,000g spec for some monitoring electronics already extant. (I declined the work.)
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  • phil rimmer #8
    Apr 18, 2016 at 10:04 am

    Using Colossal Carbon Tube (specced for space elevator use.) six threads of 2mm diameter will yield at 120tons. 30 tons is needed for a half kilo payload. Three loops create the simplest form to support a graphene mesh sail.

    Any ideas on how such a graphene structure would respond to being on the hot end of the suggested multiple tight laser beams in vacuum?
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  • phil rimmer #13
    Apr 18, 2016 at 12:04 pm

    This is much more interesting than I thought.

    A very interesting link

    @link: – 27 May 2015
    Spacecraft built from graphene could run on nothing but sunlight

    The team placed pieces of graphene sponge in a vacuum and shot them with lasers of different wavelength and intensity. They were able to push sponge pieces upwards by as much as 40 centimetres. They even got the graphene to move by focusing ordinary sunlight on it with a lens.

    But how was this movement happening? One explanation is that the material acts like a solar sail. Photons can transfer momentum to an object and propel it forwards, and in the vacuum of space this tiny effect can build up enough thrust to move a spacecraft. Just last week, the Planetary Society in Pasadena, California, launched a small solar sail to test the technology. But the forces the team saw were too large to come from photons alone.

    The team also ruled out the idea that the laser vaporises some of the graphene and makes it spit out carbon atoms.

    Instead, they think the graphene absorbs laser energy and builds up a charge of electrons. Eventually it can’t hold any more, and extra electrons are released, pushing the sponge in the opposite direction. Although it’s not clear why the electrons don’t fly off randomly, the team was able to confirm a current flowing away from the graphene as it was exposed to a laser, suggesting this hypothesis is correct (arxiv.org/abs/1505.04254).

    Graphene sponge could be used to make a light-powered propulsion system for spacecraft that would beat solar sails. “While the propulsion force is still smaller than conventional chemical rockets, it is already several orders larger than that from light pressure,” they write.

    “The best possible rocket is one that doesn’t need any fuel,” says Paulo Lozano of the Massachusetts Institute of Technology. He thinks a graphene-powered spacecraft is an interesting idea, but losing electrons would mean the craft builds up a positive charge that would need to be neutralised, or it could cause damage.

    Phil #8 :- Additional thermal load could be managed by managing both surface albedo and orientation. Electrochromic type materials exist.

    If we think of the Yarkovsky effect or something similar, using irregular/angled surfaces, angled sails, or surfaces with variable albedo on the probes, perhaps some steering could be achieved while in the initial laser beam, or in sunlight at a destination planetary system.
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  • Phil @#8 -I agree that space born lasers are the way to go,

    If I was planning laser powered inter-stellar space probes, I would have nuclear or fusion powered booster lasers, previously sited in the Kuiper Belt and Oort Cloud. – Possibly with the lasers for the initial launch from Earth orbit, sited on the Moon.
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  • My default for space based activities is Lagrange 4 and 5. Thats where I put the rare-earth asteroid processing plant and the first colonies Philo4 and Philo5. They are low cost access, perfect insolation 24/7, gravitationally stable with low to zero debris momenta for any created or captured.

    It seems to me useful to roll this into asteroid deflection testing. (Comets being volatile should be a cinch.)

    Yarkovsky, absolutely.

    If there was a way to turn on and off the photonic effects of a graphene coating maybe by putting discontinuities with shorting link at 200nm to 2,000nm geometries (well within the scope of e-beam lithography) quite complex vectoring might be achieved. Phased array beam stearing may be possible?

    There are a plethora of possibilities.

    This is fun. The last time I designed a space ship was when I was 7. I had a gunpowder one, a nuclear one (well it had a box with a radiation symbol on) and even an ion thruster one. (My dad told me about an ion thruster in the states and said how it worked like valves with a hole in the anode. It had a grid connected to the accelerator pedal. In truth, that was probably him.)
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  • phil rimmer #17
    Apr 18, 2016 at 2:43 pm

    My default for space based activities is Lagrange 4 and 5. Thats where I put the rare-earth asteroid processing plant and the first colonies

    I found this rather neat diagram when I was posting earlier about the James Webb Telescope.
    There will probably be a long queue for positions there!

    http://jwst.nasa.gov/orbit.html

    To have the sunshield be effective protection (it gives the telescope the equivalent of SPF one million sunscreen) against the light and heat of the Sun/Earth/Moon, these bodies all have to be located in the same direction.

    This is why the telescope will be out at the second Lagrange point.

    The first Sun-Earth Lagrange point, L1, is 1.5 million km from the Earth towards the Sun, and there have been many solar observatories located here, including DSCOVR, WIND, SOHO, and ACE.

    There have been other satellites out at Sun-Earth L2, where JWST will be, including WMAP, Herschel, and Planck.
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