Can we build an interstellar starship with current technology?

Calliban · 2021-03-15 11:08:58

Relying entirely on light pressure necessitates very powerful lasers. One way of reducing the required laser power would be to use the sail as a focusing mirror for a thermal rocket. The sail itself would be aluminium coated polymer. The focus would carry a crucible made from a high temperature ceramic. Hydrogen would be fed into the crucible and would boil to generate thrust.

A variation on this concept could make use of microwaves. The mirror would focus microwaves onto a focus. Hydrogen fired into the focus would be heated into a plasma, which would transfer momentum to the sail by means of a circumferential magnetic field. The problem with this idea is the generally poor beam coherence of microwaves. This concept would only work within a few hundred thousand km of a microwave source, for a sail with diameter 100km. To achieve high final speed requires high thrust and a lot of power.

tahanson43206 · 2021-03-15 11:18:24

For Calliban re #76

Thank you for the reminder of an alternative way to use the Sun's energy to help to accelerate vessels in the Earth/Mars trade.

While the method requires use of precious mass to accelerate the vessel, there might well be a business case that justifies it. After all, the ** existing ** business case is ** entirely ** dependent upon expenditure of mass from the vessel to achieve the paltry velocity needed for a Hohmann transfer orbit.

You've pointed out that great laser power is needed for the proposed task, but a corollary is the proposition that a LOT of lasers can achieve the collective power output of one large one.

I note that this conversation is taking place in Quaoar's Intersteller topic.

I'll copy my reply into the new Interplanetary topic, which I think has a much greater near-term chance of implementation.

(th)

Quaoar · 2021-03-16 04:38:07

tahanson43206 wrote:

In a post earlier in this topic, Quaoar showed a link to a paper that reported on study of a particular concept for nuclear fission spacecraft propulsion (the "dusty" method).
The paper contained a table which contained an entry that I did not understand. Quaoar confirmed that (in his judgement) the display of data from the table was correct and not a misprint
In his reply, Quaoar confirmed that the authors were imagining a projectile to be accelerated by their system that would have an atomic weight of 10 to the 8th power. Today I continued searching for a molecule of that mass.
I'd like to comment here upon the continuing and obvious advance of the AI that Google is constantly improving to help with search.
I entered the typical crude search request and it produced no useful results (lots of results but not what I wanted).
However, I rewrote the request in normal English: Please find a molecule with an atomic weight of 10^8
This time the top citation is an offering by a PhD chemist for calculation of the atomic weight (mass) of molecules.
I'm going to paste the link and a snippet, and am asking Chemistry majors (eg, PhD in the membership) to please follow the guidelines and post examples of molecules that would have the mass defined by the authors of the paper Quaoar cited for optimum performance of the "dusty" propulsion system.
https://www.thoughtco.com/how-to-find-m … ass-608487
By Anne Marie Helmenstine, Ph.D.
Updated November 06, 2019
The molecular mass or molecular weight is the total mass of a compound. It is equal to the sum of the individual atomic masses of each atom in the molecule. It's easy to find the molecular mass of a compound with these steps:

Determine the molecular formula of the molecule.
Use the periodic table to determine the atomic mass of each element in the molecule.
Multiply each element's atomic mass by the number of atoms of that element in the molecule. This number is represented by the subscript next to the element symbol in the molecular formula.
Add these values together for each different atom in the molecule.
The total will be the molecular mass of the compound.
(th)

10^8 is not the weight in atomic unit of a molecule, but of a dust grain of uranium 238, containing 10^8/238 atoms (about 420,000). It's uncommon to express the mass of metallic dust in atomic unit, but the authors treated the grains of the dusty plasma as they were a big molecule.

Last edited by Quaoar (2021-03-16 04:39:41)

Quaoar · 2021-03-16 04:55:11

Calliban wrote:

Relying entirely on light pressure necessitates very powerful lasers. One way of reducing the required laser power would be to use the sail as a focusing mirror for a thermal rocket. The sail itself would be aluminium coated polymer. The focus would carry a crucible made from a high temperature ceramic. Hydrogen would be fed into the crucible and would boil to generate thrust.
A variation on this concept could make use of microwaves. The mirror would focus microwaves onto a focus. Hydrogen fired into the focus would be heated into a plasma, which would transfer momentum to the sail by means of a circumferential magnetic field. The problem with this idea is the generally poor beam coherence of microwaves. This concept would only work within a few hundred thousand km of a microwave source, for a sail with diameter 100km. To achieve high final speed requires high thrust and a lot of power.

Conceptually it works, but it might be very hard to do the engineering: a flat sail doesn't need any rigid stiffening rib and can be kept in shape only by centrifugal force. On the contrary a kilometer-sized spherical or parabolic mirror, acting also as a nozzle for hydrogen, needs strong stiffening ribs, resulting a huge weight.
Probably it may work better to use a smaller (30-40 meters) metallic mirror with a polyethylene cylinder in the focus as propellant, surrounded by 2 or 3 superconductive coil. Then use the laser in pulse to ablate the cylinder, resulting a high Isp propulsion for interplanetary travels. It's very simple and you have not to dial to the nasty hydrogen.

Last edited by Quaoar (2021-03-16 04:59:08)

Calliban · 2021-03-16 05:06:33

Thin fibres or plates of fissile materials might work better than dust particles, as they can be constrained at each end and cross-linked for strength. Fission products penetrate about 0.01mm in matter. So the particles need to be small and fibres or plates extremely thin in order to allow most of the fission fragments to escape with most of their energy. That is why fine dust is considered.

Interestingly, it should also be possible to use a thermonuclear reactor to generate the neutrons needed to drive fission. In this case, the fuel does not need to be fissile material, but could make use of fissionable material. That means 238U or 232Th, which are both far easier to obtain and much safer to handle than 239Pu or 235U.

A probe using a fusion-fission hybrid approach could probably be launched relatively soon and could reach the nearest stars in about a century.

tahanson43206 · 2021-03-16 06:30:26

For Quaoar re #78

Thank you for your explanation of the 10^8 atomic mass of a "dusty" fission reactor particle!

SearchTerm:Dusty fission reaction particle size. See Quaoar Post 78 above.

For Quaoar re #79

Thank you for your exploration of possible designs for the mirror.

SearchTerm:Mirror for interplanetary laser driven sailing spacecraft

Note hybrid of ideas of Calliban and Quaoar evolving in the discussion immediately above.

(th)

Quaoar · 2021-03-17 15:13:25

I have found this interesting article:

https://www.nasa.gov/directorates/space … /PROCSIMA/

https://ntrs.nasa.gov/api/citations/201 … 014041.pdf

In this study the laser beam is coupled with a neutral atom beam: the neutral atom flux is confined by the electromagnetic field of the laser, which creates a potential well (like the "kagome" used to confine the ultracold BEC atoms) and the atoms act like an optic fiber avoiding the diffraction spread of the photons and increasing the maximum acceleration distance and the final speed of the spacecraft.

The study is about a kilogram sized unmanned probe, so the topic of deceleration is not discussed. For a manned spaceship with laser stations at both ends of the trip, I have some doubt about the damage produced by the neutral atom impacts during the deceleration phase.

Last edited by Quaoar (2021-04-09 11:31:49)

Mars_B4_Moon · 2021-06-08 08:31:40

Solar Sails now back in the news, Ion and Nuclear can produce speeds of 220,000 mph, another possible method for propulsion is a combo of nuclear and Hall-effect thruster, Electrostatic ion thruster, Magnetic sail, Mini-magnetospheric plasma propulsion, a Photon Rocket or something like a Plasma Rocket, in the future is possible more cosmology type exotic concepts will be used like Antimatter rocket but for now the SolarSail has been validated and proven as a possible space flight method.

Australian National University researchers light up our pathway to another planetary system in major scientific breakthrough
https://www.abc.net.au/news/2021-06-08/ … /100198228

The NASA Breakthrough Propulsion Physics Program (terminated in FY 2003 after a 6-year, $1.2-million study, because "No breakthroughs appeared imminent." but some scientific methods seemed possible?
http://www.nasa.gov/centers/glenn/techn … /warp.html

previous thread
http://newmars.com/forums/viewtopic.php?id=2438

One danger is how micrometeorites could kill them.

The Planetary Society tested a second Solar Sail after an unsucessful first mission, LightSail 2 was launched on a Falcon Heavy rocket on 25 June 2019.

Last edited by Mars_B4_Moon (2021-06-08 08:34:46)

Mars_B4_Moon · 2022-09-14 04:59:20

Citizen Scientist leads discovery of cool binary stars, nearly doubling known population

https://www.noirlab.edu/public/news/noirlab2215/

A citizen scientist has searched NSF's NOIRLab’s catalog of 4 billion celestial objects, known as NOIRLab Source Catalog DR2, to reveal brown dwarfs with companions. His intensive investigation led to the discovery of 34 ultracool dwarf binary systems, nearly doubling previously known samples.

Brown dwarfs lie somewhere between the most massive planets and the smallest stars. Lacking the mass needed to sustain nuclear reactions in their core, brown dwarfs loosely resemble cooling embers on a huge scale. Their faintness and relatively small sizes make them difficult to identify. Data from sensitive telescopes have enabled the discovery of several thousand objects but just a small subset have been identified as binaries.

To help find brown dwarfs, the astronomers of the Backyard Worlds: Planet 9 citizen science project have previously turned to a worldwide network of more than 100,000 volunteer citizen scientists who scrutinized telescope images to identify the subtle motion of brown dwarfs against background stars. Despite the abilities of machine learning and supercomputers, the human eye is still a unique resource when it comes to scouring telescope images for moving objects.

“These discoveries were made by an amateur astronomer who conquered astronomical big data,” concluded Aaron Meisner. “Modern astronomy archives contain an immense treasure trove of data and often harbor major discoveries just waiting to be noticed.”

Mars_B4_Moon · 2023-10-07 06:02:33

Different to the Solar Sail

Europa and Enceladus are the Perfect Targets for a Lightsail Mission
https://www.universetoday.com/163494/eu … l-mission/

Calliban · 2024-05-30 12:02:37

The million-year ark. Isaac Arthur discusses the feasibility of sending humans on million year journeys.
https://m.youtube.com/watch?v=25ODAzr6Bbw

Voyager 1 is moving at 17km/s and would reach proxima centauri in 70,000 years if it happened to be travelling that way. If we were blessed with infinite patience as a species, then this is scenario that we could consider using existing technology.

One option would be to travel out to the Oort cloud and find a body about 100km in diameter. We then use nuclear thermal propulsion to cancel its forward velocity, by vaporising water and using steam to produce thrust. The body would then fall towards the sun. We would use one or more planetary gravity assists to boost its speed, such that its velocity exceeds solar escape velocity. A group of humans would catch it up on the way out. Assuming we aim it roughly in the direction of a nearby star, a 10km escape speed would allow it to reach its destination on a timeframe of 1E5 - 1E6 years.

Upon reaching the icy body on its way out of the solar system, humans would set up a nuclear fusion reactor and would begin terraforming the body into an ice covered water world. They would live on and beneath the icy crust, slowly increasing their numbers, building up their infrastructure and carefully recycling everything. When they finally reach the new star, an initial population of a few thousand humans will have grown into a society of tens of millions, ready to spread across the new star system. We could crawlonise the whole galaxy in this way. But it might take a billion years.

I think for humans to be prepared to undertake journeys of tens to hundreds of thousands of years, they would need to view their ark ship as a home and worthwhile destination in its own right. When we talk about colonising Mars, we tend to view Mars as being a more or less permanent location for habitation, that we are prepared to invest effort into, building a new world. We do this without expecting Mars to take us anywhere else. Likewise, most of us are content here on Earth, without any expectation of leaving. The humans that colonise an Oort cloud body thrown onto an interstellar trajectory, would have to see it in the same way. It would be their world, to build and maintain. Colonising a new star is something their distant descendants would be doing. They would need to be content living on their terraformed water world for the entirety of their lives.

See also: Crawlinising the galaxy.
https://m.youtube.com/watch?v=FpXwyDWDww8

Last edited by Calliban (2024-05-30 13:15:56)

Calliban · 2024-05-31 00:28:27

Hmm. I have looked at the possibility of using TNOs as interstellar slow boats before. It seems like a good idea until one looks into the energy requirements of altering the trajectory of a 100km diameter ice and rock ball. Changing velocity by just 1km/s, requires the energy equivelent of 3 million tonnes of uranium.

I reach the same conclusion as last time. If we can find rogue objects that are already detached from the sun's gravity well, then hitching a ride on them might work as an interstellar colonisation strategy. But the case collapses if we need to alter their velocity by more than a few tens of m/s.

The strategy therefore depends upon finding rogue objects that nature has already provided. In a future colonised solar system, a group of colonists may need to wait for centuries for an icy wanderer to pass through our solar system with the right size, course and speed. Using a fusion drive, they would then intercept it and set up whatever they need for a new branch of humanity on its surface. It would gradually be transformed into a new home over centuries, able to sustain an independant group of humans for millenia. Some stars have velocities measured in hundreds of km/s relative to the sun. So finding a rogue ice world with similar velocity is entirely plausible. At 300km/s, it would be travelling at 0.1% C. The solar system orbits the centre of our galaxy at 1/1300 C. So this is about galactic orbital speed at our distance from the galactic core.

It would take 10,000 years to travel 10 light-years at 0.001C. Ten thousand years is roughly recorded human history. And a wandering dwarf planet would be a new world to conquer, with a world of resources. If human society could survive on such a body for a million years, it would travel 1000ly. Nurmerous close approaches to other star systems are possible in that time. Isaac Arthur speculates that people living in future advanced civilisations could have effectively infinite lifespans, by regenerating their DNA or by uploading their consciousness onto super computers. A 10,000 year journey might be entirely acceptable to people in that position, especially if they are passing the time in comfortable cities with plenty to entertain them.

Last edited by Calliban (2024-05-31 00:53:02)

Void · 2024-06-01 13:55:09

You may like this Calliban: https://www.bing.com/videos/riverview/r … &FORM=VIRE "Fraser Cain, Utube, Interstellar Travel Without Breaking Physics with Andrew Higgins"

It is long and interesting.

I might add the idea of transformers, and also intelligent fetus in an egg.

Transformers is just like the movie, the mass has a configuration suitable to get a propulsion needed, and then to reorganize the matter into a cruse configuration and then finally the arrival configuration.

Intelligent Fetus in an egg, is quite strange, and if I decide to go into it, I may annoy some people as I would need to reveal things about humans, that they don't want to know or admit. So, it is dangerous.

The basic idea would be a humanoid of a small size that is in a gestation configuration all the way but may be periodically conscious and "Wired" to a configuration of other intelligent entities, and perhaps also having the ability to interact with robots that periodically become active as may be useful. Being in an "Egg", or "Womb", there then has to be a Parent/Mother, which does not have to be intelligent on its own but may have a computer intelligence running it. So, an extended body with organs that can maintain itself and the Fetus biologically.
Not aging or being able to repair the effects of aging. The Fetus when awake could live in a virtual world with other aware entities.

This would be to minimize life support needed, and so then facilitate the transfer of humanoid process to a distant location.

I may continue with this in another topic which I will name in a bit.

Done

OK, I will do something here: https://newmars.com/forums/viewtopic.ph … 06#p223906

Done

Last edited by Void (2024-06-01 17:29:55)

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#76 2021-03-15 11:08:58

Re: Can we build an interstellar starship with current technology?

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