Can we build an interstellar starship with current technology?

Quaoar · 2021-03-02 16:25:56

As an hard SF writer, I was looking for a realistic starship for my next novel which will be set between the local stars. The ship should be about 600 ton of mass and she should be able to reach Proxima in about 16-17 years, traveling at 0.25 C.

Can we build such a ship with slightly ameliorated current technologies?

After making some rough math, I found the answer and I was quite shocked: yes we can build it using a laser sail like the mini probe of Yuri Milner, but bigger.

A 600 ton starship needs almost 880 TW of optical laser power to accelerate at 1 g.

We can image a one-micron-thick carbon-carbon sail, coated with 10 nm of molibdenum on the aft side: such a sail would weight 0.0018 kg/m2 and would have a power load of 100 MW/m2 at 2000 K. So the total sail area would be 8814000 m2, the diameter 3350 m (or a square of 2970 m of side) and the mass 15.9 ton. The sail would be furled like the sail of JAXA's IKAROS: stowed on a rolling drum like an origami, then extended and kept in shape by centrifugal force. We can image carbon nanotubes artificial muscles, embedded in the sail as stiffening ribs, that fold it again during the coasting phase of the trip.

The ship will have also four fission reactors for electrical power, a 20 T superconductive magnetic coil to shield the habitat from GCR, a passive shielding of 30 cm of water, ten one-micron-thick carbon-carbon shields for space dust, laser as point defense against debris, lidars radars and quite powerful chemical RCS rockets to dodge bigger objects.

The accelerating laser array will be build on the polar regions of Mercury: the best diode lasers have a plug to wall efficiency of 76% and we can imagine they might reach 90%. So, to have 880 TW of optical power, we need 978 TW of electrical power, that become 1632 TW due to the red shift, to keep the ship accelerating at the same rate when she reaches relativistic speeds (at 0.25 C a 216 nm laser becomes 360 nm so the beam power is at 60%).
With a constant acceleration of 1 G and 0.25 C of cruise speed, the acceleration phase ends 5765 AU away from the Sun, so the laser array needs an aperture of almost 120 km (imagine a field of lasers of 120 km of diameter) to be focused on a sail of 3350 (the lasers have 216 nm of wavelength).

The photovoltaic array will be put near the equator: at Mercury the sun power is 6600 W/m2. We can image that in a near future solar panels will become 85% efficient: so to get 1632 TW of electrical power we need a square array of panels of 1386 km of side, and we need many of these due to the rotation of the planet.

Laser and solar PP also need radiators.

All this stuff will be very expensive and difficult to build, but not impossible.

The weak point of my dream is that my spaceship needs also a laser deceleration station in the orbit of the destination star.
We can imagine three possibilities: they are built in our solar system then sent to the destination system at 0.03 C with a fission-fragment propelled spaceship. They are built in the destination system with local materials after sending robots. They are built in the destination system by intelligent aliens in communication with us.

Last edited by Quaoar (2021-03-03 18:03:46)

tahanson43206 · 2021-03-02 18:27:31

For Quaoar re new topic ...

Enjoyed your launch of this interesting new topic! Hoping it wins contributors!

Your vision covered a lot more than just these two items, but along the way I was reminded of the movie "Passengers" (which (apparently) did not have the collision avoidance system you've described) and the book series (InterstellarNet) which posits an exchange of increasingly complex messages between civilizations scattered around the neighborhood of Earth,

(th)

louis · 2021-03-02 19:20:21

I was always quite taken by the atom bomb rocket. You just have a succession of atom bombs that are periodically placed on the "engine" side of a big radiation shield. Each one accelerates the craft. I guess you could fine tune so G forces aren't too bad. Can't recall the name given to the concept. It's not Nerva. I seem to recall the atom bomb rocket could get you up to interstellar speed pretty quickly.

Quaoar wrote:

As an hard SF writer, I was looking for a realistic starship for my next novel which will be set between the local stars. The ship should be about 600 ton of mass and she should be able to reach Proxima in about 16-17 years, traveling at 0.25 C.
Can we build such a ship with slightly ameliorated current technologies?
After making some rough math, I found the answer and I was quite shocked: yes we can build it using a laser sail like the mini probe of Yuri Milner, but bigger.
A 600 ton starship needs almost 880 TW of optical laser power to accelerate at 1 g.
We can image a one-micron-thick carbon-carbon sail, coated with 10 nm of molibdenum on the aft side: such a sail would weight 0.0018 kg/m2 and would have a power load of 100 MW/m2 at 2000 K. So the total sail area would be 8814000 m2, the diameter 3350 m (or a square of 2970 m of side) and the mass 15.9 ton. The sail would be furled like the sail of JAXA's IKAROS: stowed on a rolling drum like an origami, then extended and kept in shape by centrifugal force. We can image carbon nanotubes artificial muscles, embedded in the sail as stiffening ribs, that fold it again during the coasting phase of the trip.
The ship will have also four fission reactors for electrical power, a 20 T superconductive magnetic coil to shield the habitat from GCR, a passive shielding of 30 cm of water, ten one-micron-thick carbon-carbon shields for space dust, laser as point defense against debris, lidars radars and quite powerful chemical RCS rockets to dodge bigger objects.

The accelerating laser array will be build on the polar regions of Mercury: the best diode lasers have a plug to wall efficiency of 76% and we can imagine they might reach 90%. So to have 880 TW of optical power we need 978 TW of electrical power, that become 1632 TW due to the red shift, to keep the ship accelerating at the same rate when she reaches relativistic speeds (at 0.25 C a 216 nm laser becomes 360 nm so the beam power is at 60%).
With a constant acceleration of 1 G and 0.25 C of cruise speed, the acceleration phase ends 5765 AU away from the Sun, so the laser array needs an aperture of almost 120 km (imagine a field of lasers of 120 km of diameter) to be focused on a sail of 3350 (the lasers have 216 nm of wavelength).
The photovoltaic array will be put near the equator: at Mercury the sun power is 6600 W/m2. We can image that in a near future solar panels will become 85% efficient: so to get 1632 TW of electrical power we need a square array of panels of 1386 km of side, and we need many of these due to the rotation of the planet.
Laser and solar PP also need radiators.
All this stuff will be very expensive and difficult to build, but not impossible.
The weak point of my dream is that my spaceship needs also a laser deceleration station in the orbit of the destination star.
We can imagine three possibilities: they are built in our solar system then sent to the destination system at 0.03 C with a fission-fragment propelled spaceship. They are built in the destination system with local materials after sending robots. They are built in the destination system by intelligent aliens in communication with us.

Void · 2021-03-02 19:46:07

You may take a look at Isaac Arthurs "Laser Highways" as well.

I am not likely to survive to the day when interstellar becomes very possible. Even probes. But I don't mind giving it a try. I don't have anything unique and special though. Just other peoples works which I read or watch.

Done.

Quaoar · 2021-03-03 07:40:58

louis wrote:

I was always quite taken by the atom bomb rocket. You just have a succession of atom bombs that are periodically placed on the "engine" side of a big radiation shield. Each one accelerates the craft. I guess you could fine tune so G forces aren't too bad. Can't recall the name given to the concept. It's not Nerva. I seem to recall the atom bomb rocket could get you up to interstellar speed pretty quickly.

The Orion drive is a very promising technology, but the original work by General Atomic gave a maximum exhaust velocity of 200 km/s, which is fantastic for interplanetary travels but too small for going interstellar.

http://ntrs.nasa.gov/archive/nasa/casi. … 085619.pdf

Excluding handweaving technologies like antimatter (we still have no idea about how to mass produce it and how to safely store it at reasonable density) or fusion (we are always ten years from doing it) at the moment the only rocket we can mount on the aft of a generation ship is a Clark-Sheldon dusty plasma fission-fragment rocket, whose exhaust velocity is about 15000 km/s. A two-stage-three-generations-starship with this rocket can reach 5% of C and travel to Proxima in almost 90 years.

http://www.rbsp.info/rbs/PDF/aiaa05.pdf

Last edited by Quaoar (2021-03-03 08:02:58)

tahanson43206 · 2021-03-03 08:27:15

For Quaoar re #5

Thank you for the reminder of the Orion drive, and the new (to me at least) link to the Clark-Sheldon design.

I'm looking forward to following the link, but if you are willing to hive a hint of the ending of the story, does the vehicle slow as it approaches Proxima? I'm assuming it does, but your brief summary did not include that important detail.

I bring this up because (if it does) then a combination of your laser launch proposal with their slow down to dock method (assuming it works) might provide the best of both .... Your solution is terrific for the launch phase but has a problem slowing at the destination. Their design (if I understand the implications) may have the ability to slow down to arrive safely at the destination.

Taking the concept a bit further ... If a vehicle is given a massive start, and then waits until the last possible moment to begin slowing, the travel time could be reduced to the lowest possible value. A 1 G boost away from earth would presumably allow the ship itself to separate from the sail, while the sail could be collected and returned to Earth for another boost operation.

That would be a one way trip for the vessel ... it would depart with enough fuel and mass to slow at the destination, and it would set up shop there for exploration of the destination, reporting back to Earth, and potentially development of the destination if that is feasible.

PS ... would you be willing to stop in at the Solar Power topic and offer your feedback on the SPS in LEO concept?

(th)

Quaoar · 2021-03-03 09:26:54

tahanson43206 wrote:

For Quaoar re #5
Thank you for the reminder of the Orion drive, and the new (to me at least) link to the Clark-Sheldon design.
I'm looking forward to following the link, but if you are willing to hive a hint of the ending of the story, does the vehicle slow as it approaches Proxima? I'm assuming it does, but your brief summary did not include that important detail.
I bring this up because (if it does) then a combination of your laser launch proposal with their slow down to dock method (assuming it works) might provide the best of both .... Your solution is terrific for the launch phase but has a problem slowing at the destination. Their design (if I understand the implications) may have the ability to slow down to arrive safely at the destination.
Taking the concept a bit further ... If a vehicle is given a massive start, and then waits until the last possible moment to begin slowing, the travel time could be reduced to the lowest possible value. A 1 G boost away from earth would presumably allow the ship itself to separate from the sail, while the sail could be collected and returned to Earth for another boost operation.
That would be a one way trip for the vessel ... it would depart with enough fuel and mass to slow at the destination, and it would set up shop there for exploration of the destination, reporting back to Earth, and potentially development of the destination if that is feasible.
PS ... would you be willing to stop in at the Solar Power topic and offer your feedback on the SPS in LEO concept?
(th)

By the moment we are only able to accelerate at 0.25 C but not to slow down: in my novel the nearest stars have been already colonized by Clark-Sheldon ships, so the colonists communicated via radio and agreed to build laser stations in every system, creating a high-way laser network.

Last edited by Quaoar (2021-03-03 09:33:16)

tahanson43206 · 2021-03-03 10:42:40

For quaoar ... re #7

Thanks for the implied ending of the story << grin >> .... I expect to find that Clark-Sheldon ships can slow down.

However, I'm surprised by your answer, in this sense ... while your novel presumes the earlier trips by Clark-Sheldon ships, you have not (as nearly as I can tell) imagined ** those ** ships would receive a laser boost.

Since that seems eminently feasible, it would seem reasonable to me to build all the "slow down" capability you need into the vessel, and give it the needed boost when leaving Earth.

That is ** exactly ** the same scenario I've proposed for the Earth-to-Mars trip ... there is no reason (other than tradition) for the ship departing for Mars to consume ** any ** of it's mass or fuel to achieve transfer velocity. All of the needed momentum can be imparted by a pusher tug, which can then return to Earth and refuel for the next trip.

In the case of your proposed journey to Proxima, a hybrid solution would bring the future you are "seeing" into being a whole lot sooner.

As a follow up ... others have proposed slowing a laser powered ship. I'm reminded of the work of Dr. Robert Forward. As I remember, the plan called for a double reflector design ... energy from Earth would impact a reflector, which would send the photons back to the arriving vehicle, whose smaller mirror would accept the slowing momentum.

A serious problem with that proposal and with all of the similar ones I have seen is that they depend upon accuracy of beam pointing over interstellar distances and many years that I think is unreasonable.

The hybrid solution which I infer from your description of the laser boost launch idea is NOT dependent upon laser energy after departure from Earth. If you are so inspired, please compute the distance needed to give a vessel 1 g of acceleration until it reaches velocity that would put it at Proxima in 100 years (including slowing)

It is ** that ** distance the laser facility on Mercury would have to cover, not the far greater distance Dr. Forward was considering.

(th)

Quaoar · 2021-03-03 17:38:20

tahanson43206 wrote:

For quaoar ... re #7
Thanks for the implied ending of the story << grin >> .... I expect to find that Clark-Sheldon ships can slow down.
However, I'm surprised by your answer, in this sense ... while your novel presumes the earlier trips by Clark-Sheldon ships, you have not (as nearly as I can tell) imagined ** those ** ships would receive a laser boost.
Since that seems eminently feasible, it would seem reasonable to me to build all the "slow down" capability you need into the vessel, and give it the needed boost when leaving Earth.
That is ** exactly ** the same scenario I've proposed for the Earth-to-Mars trip ... there is no reason (other than tradition) for the ship departing for Mars to consume ** any ** of it's mass or fuel to achieve transfer velocity. All of the needed momentum can be imparted by a pusher tug, which can then return to Earth and refuel for the next trip.
In the case of your proposed journey to Proxima, a hybrid solution would bring the future you are "seeing" into being a whole lot sooner.

Yes, it's feasible to build an hybrid spaceship with a laser sail for acceleration and a two stages Clark-Sheldon rocket for deceleration: in this case we will have a maximum speed of 0.1 C, that's very exiting and can reach Proxima in about 43 years. But in my novel, during the Age of Diaspora there was no laser stations. They will be built some centuries later in the Age of Reconnection.

tahanson43206 wrote:

As a follow up ... others have proposed slowing a laser powered ship. I'm reminded of the work of Dr. Robert Forward. As I remember, the plan called for a double reflector design ... energy from Earth would impact a reflector, which would send the photons back to the arriving vehicle, whose smaller mirror would accept the slowing momentum.
A serious problem with that proposal and with all of the similar ones I have seen is that they depend upon accuracy of beam pointing over interstellar distances and many years that I think is unreasonable.
The hybrid solution which I infer from your description of the laser boost launch idea is NOT dependent upon laser energy after departure from Earth. If you are so inspired, please compute the distance needed to give a vessel 1 g of acceleration until it reaches velocity that would put it at Proxima in 100 years (including slowing)
It is ** that ** distance the laser facility on Mercury would have to cover, not the far greater distance Dr. Forward was considering.
(th)

The problem with this approach is that you need a 5200 km wide laser array of 216 nm of wavelenght to focus on a 3.35 km wide sail at 4.2 LY. 5200 km is quite less than the diameter of Mars which is 6800 km. It's very impractical with a big manned starship, but it may work with a voyager-sized probe.

Last edited by Quaoar (2021-03-03 17:59:20)

Quaoar · 2021-03-03 18:10:04

Void wrote:

You may take a look at Isaac Arthurs "Laser Highways" as well.
I am not likely to survive to the day when interstellar becomes very possible. .

Me too. I'm 57, but I hope my son and my daughter will be still alive that day.

tahanson43206 · 2021-03-03 18:11:47

For Quaoar re #9 and topic in general

First, thank you for considering my hybrid suggestion ...

I hesitate to risk imposing upon your generosity ....

Could you develop your "Voyager sized probe" idea a bit more? If humans (ie, you) were to design a space probe with the mass that Voyager had, using modern technology, ** and ** if humans (ie, you) were to to plan to boost the ship using lasers at Mercury, ** and ** if the ship were designed to slow down to go into orbit at Proxima, what would that system look like?

Such a vessel could (presumably) operate under conditions that humans would find difficult, and (if properly designed) such a probe could (presumably) return useful information from the destination solar system.

In reflecting a bit more, I think that it might be a good idea to increase the mass of your (hypothetical) probe slightly, to accommodate a power supply able to operate reliably for a couple of hundred years. That would allow commands from Earth to (hopefully) direct activities of the probe after arrival at the destination.

***
Would you be willing to comment upon the SPS in LEO concept, in the Solar Power topic?

(th)

SpaceNut · 2021-03-03 20:45:16

Sail boats use vector sail push to change direction and speed which can not be done with a straight outward path...slowing down would use that same back and throw motion of tacking to allow the approaching solar wind to slow the vehicle down...

Quaoar · 2021-03-04 05:27:54

tahanson43206 wrote:

For Quaoar re #9 and topic in general
First, thank you for considering my hybrid suggestion ...
I hesitate to risk imposing upon your generosity ....
Could you develop your "Voyager sized probe" idea a bit more? If humans (ie, you) were to design a space probe with the mass that Voyager had, using modern technology, ** and ** if humans (ie, you) were to to plan to boost the ship using lasers at Mercury, ** and ** if the ship were designed to slow down to go into orbit at Proxima, what would that system look like?
Such a vessel could (presumably) operate under conditions that humans would find difficult, and (if properly designed) such a probe could (presumably) return useful information from the destination solar system.
In reflecting a bit more, I think that it might be a good idea to increase the mass of your (hypothetical) probe slightly, to accommodate a power supply able to operate reliably for a couple of hundred years. That would allow commands from Earth to (hopefully) direct activities of the probe after arrival at the destination.
***
Would you be willing to comment upon the SPS in LEO concept, in the Solar Power topic?
(th)

I have many doubts about the feasibility of a two stage laser sail probe able to decelerate in the destination system. First of all, the deceleration takes place at 4 LY from Earth, so if the beam is misaligned it would be impossible for the AI in control to call the laser guys and tell them to move the beam, because it will take 8 years.
Even if the alignment is perfect, at 0.25 C the beam arrive at 60% of its power due to relativistic red shift. At this point, the big sail of stage 1 has to change its shape from flat to concave, to focus the beam on the smaller sail of stage 2. But stage 1 still continues to accelerate in opposite direction of stage 2, further decreasing the power of the beam.
I think it's more practical a laser sail for acceleration and a Clark-Sheldon stage for deceleration. We can imagine a five stages probe: a laser-sail stage able to reach 0.2 C and four Clark-Sheldon deceleration stages with a 800 kg probe as payload.

Last edited by Quaoar (2021-03-04 05:56:29)

tahanson43206 · 2021-03-04 07:40:16

For Quaoar re topic development ...

I think it's more practical a laser sail for acceleration and a Clark-Sheldon stage for deceleration. We can imagine a five stages probe: a laser-sail stage able to reach 0.2 C and four Clark-Sheldon deceleration stages with a 800 kg probe as payload.

Thank you for your response to the probe inquiry ....

The ideas you are developing here could become a project ... The details will evolve as our (human) understanding of the Universe improves, and as we (humans) demonstrate capability. This undertaking (probe to Proxima) is similar in scope to construction of the Great Cathedrals in Europe in centuries past.

It will take several generations to bring it to pass, but it all starts with a single visionary who can create the momentum. You are ideally suited for this task because you are already an experienced writer.

If you are willing to continue along these lines, this forum may be a helpful venue for polishing your ideas before you submit an article to a major journal.

Unfortunately, the forum format (posts that flow under the bridge never to be seen again) (except when SpaceNut brings them back) does not lend itself to the fixed structure needed for polishing an idea. I understand that SpaceNut has asked the Mars Society for help, but so far nothing has happened.

By any chance, do you have resources available where you could set up shop to work on your idea in a public way?

GW Johnson is an example of a member who has created an independent repository of his writings... You can see his work at his exrocketman Wordpress blog.

***
Have you any thoughts about the SPS in LEO topic?

Italy would be a beneficiary of the system, if it is brought into existence.

(th)

Quaoar · 2021-03-04 14:46:08

tahanson43206 wrote:

By any chance, do you have resources available where you could set up shop to work on your idea in a public way?
GW Johnson is an example of a member who has created an independent repository of his writings... You can see his work at his exrocketman Wordpress blog.

There is a big difference: GW is an experienced aerospace engineer and a rocket scientist, while I'm a SF writer: I can do some rough math using formulas, but I've no idea how to really do things.

tahanson43206 wrote:

Have you any thoughts about the SPS in LEO topic?
Italy would be a beneficiary of the system, if it is brought into existence.
(th)

I like SPS and I use it for my laser stations: I've make a little upgrade so my starships can now reach 0.3 C (above this speed, realtivistic red-shift become prohibitive for laser power and the ship needs meters thick shields to stop neutral hydrogen atoms).
A 300 ton starship with 2 people and 150 ton of cargo, with a 2400 meters and 8 ton sail, requires a 370 km wide solar array (in an orbit where solar radiation is 10 KW/m2) to produce 816 TW of electric power for a 250 km wide laser array.

There are two unintended consequences:

1) a 300 ton starship flying at 0.3 C can be easily turned in a weapon of mass destruction: 300 ton at 0.3 C become 314.4855, giving a kinetic energy of about 1.3 Yj (1.3 x 10^21 joule!!!) which can crush a planet in case of collision.

2) A 350 km wide orbital laser station with a 250 km wide laser array of 734.5 TW of optical power is also a weapon of mass destruction (it's impossible not to think to Darth Vader's Death Star). It can also be used in mode-lock (burst of short pulses) to vaporize an erratic starship on a collision course with a planet.

Last edited by Quaoar (2021-03-04 15:00:32)

tahanson43206 · 2021-03-04 15:24:33

For Quaoar re #15 ...

Thank you for considering SPS.

Your cautions about the use of laser systems strong enough to accelerate a star ship seem well thought out. I would put them in the category of atomic energy on Earth .... it needs to be carefully managed and kept away from persons who might be tempted to use them for evil purposes.

On the positive side, such a system should be quite useful for regular service inside the Solar System.

For one thing, it can boost intra-Solar-System transport which is intended for outward movement.

For another, it can provide welcome bursts of useful power to human (or automated) "customers" out-system ....

This kind of system needs to be funded and managed as a Solar System resource.

It would be practical if humans achieve sufficient maturity to forego the kinds of evil-doing they are still engaged in all over the planet today.

Edit#1: I finally scheduled some time to look at the paper on "dusty" fission rocket design.

This is a (to me) very interesting paper from 2005, which describes the evolution of a concept through several versions. The "current" one seeks to address the problem of heating of the fuel by reducing the size of individual components/particles to nano size.

In light of the need for small size, I am pretty sure there is an error in Table 2 Rigidity of various fission fragments.

In the line for "Dust" the Atomic weight is given as 10 to the 8th.

I'm pretty sure the intention was to publish as 10 to the ** minus ** 8th.

However, I'm certainly open to being corrected if ** I ** am in error.

My reasoning is that the progression of atomic weight is from 140 through 95 and 4 to the bottom row for dust.

In addition, the rest of the values in the "Dust" row are all negative powers of 10, except for Tesla-meters, which is published as .001 instead of 10 to -3.

That aside, I'm finding the article quite interesting, and hope other forum members will take a look at it.

At this point (only having reached page 4 of 7) I am not sure how the paper will turn out, but am looking forward to the journey.

Edit#1 ... after thinking about the table for a while, and considering the entire paper is about nano sized "dust" particles, I'm leaning toward the possibility the authors did ** not ** omit a minus sign, and were in fact thinking of a collection of baryons that would total up to 10 to the 8th power.

While (obviously) larger than an individual atom, or even a molecule, this is still a very ** small ** collection of matter.

I'd appreciate another forum contributor taking a look at that table, to see if the 10^8 collection of baryons idea makes sense.

(th)

Quaoar · 2021-03-05 14:14:28

tahanson43206 wrote:

For Quaoar re #15 ...
Thank you for considering SPS.
Your cautions about the use of laser systems strong enough to accelerate a star ship seem well thought out. I would put them in the category of atomic energy on Earth .... it needs to be carefully managed and kept away from persons who might be tempted to use them for evil purposes.

Huge laser stations needs hug amount of money so they will be likely built by a strong and centralized government: some kind of Wittfogel's hydraulic empire.

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

I don't like autocratic states, but in case of relativistic sail-ships, a centralized empire might be the lesser evil: consider a laser station with a 327 km wide photovoltaic array, orbiting near a star, able to produce 909 TWe, powering a 818 TWo laser: this station can accelerate a 300 ton spaceship to 0.3 C, under the constant acceleration of 1 g, and that is OK, but the same station can also accelerate a 10 ton sailing torpedo (8 ton of sail and 2 ton of stuff) to 0.9 C, resulting a completely unstoppable planet killer, able to deliver 1.16 Yj on the target. 0.9 C is too close to C to be detected by a radar and destroyed with a laser shot, so there is no defense and in case of cold war between star systems, whoever delivers the first shot wins.

tahanson43206 wrote:

On the positive side, such a system should be quite useful for regular service inside the Solar System.
For one thing, it can boost intra-Solar-System transport which is intended for outward movement.
For another, it can provide welcome bursts of useful power to human (or automated) "customers" out-system ....
This kind of system needs to be funded and managed as a Solar System resource.
It would be practical if humans achieve sufficient maturity to forego the kinds of evil-doing they are still engaged in all over the planet today.

Sure: laser stations can also be used to accelerate interplanetary sailing-ship: in this case the requirements are far less challenging.
Accelerations of about 0.1 m/s2 are good for interplanetary travel outside the gravitational wells (i.e. Lagrange Zone): a 300 ton spaceship needs only 4.5 TW of optical power and a 80-kg-250-meter-wide sail.

tahanson43206 wrote:

Edit#1: I finally scheduled some time to look at the paper on "dusty" fission rocket design.
This is a (to me) very interesting paper from 2005, which describes the evolution of a concept through several versions. The "current" one seeks to address the problem of heating of the fuel by reducing the size of individual components/particles to nano size.
In light of the need for small size, I am pretty sure there is an error in Table 2 Rigidity of various fission fragments.
In the line for "Dust" the Atomic weight is given as 10 to the 8th.
I'm pretty sure the intention was to publish as 10 to the ** minus ** 8th.
However, I'm certainly open to being corrected if ** I ** am in error.
My reasoning is that the progression of atomic weight is from 140 through 95 and 4 to the bottom row for dust.

I'm not an expert, but I think 10^8 might be quite correct because the weight is not given in kg but in atomic units: it only means that a dust gran weights 10^8 times a hydrogen atom, which is likely because it contains many uranium atoms.

Last edited by Quaoar (2021-03-05 17:35:40)

Oldfart1939 · 2021-03-05 15:46:18

The question was "Can we build an Interstellar Starship with current technology?

Short answer: No.

Long answer: No.

tahanson43206 · 2021-03-05 16:13:28

For Oldfart1939 re #18

Your reply reminds me of Arthur C Clarke's famous quotation....

While I surmise you are not a "professor", you are someone who would be in the the very small set of human beings who are "distinguished elderly professors".

Paraphrasing, Clarke said if such a person says something can be done, they are almost certainly right.

If they say that something "can't" be done, they are almost certainly wrong.

I am supportive of Quaoar's premise because (to this point at any rate) he has made what looks to me like a reasonable case for a hybrid starship(probe) launch that would employ laser beams from the Solar System to gain outward momentum, and an interesting looking fission derived mechanism to slow down.

Taking into account that Quaoar claims to be a science fiction writer, and NOT a scientist or engineer, I give him a lot of credit for doing the research he's reported so far, and hope he will continue developing his ideas in greater detail.

(th)

GW Johnson · 2021-03-05 18:12:51

This whole argument depends upon what you really mean by "starship". There are 5 probes out there right now that are going into interstellar space: the two Pioneer probes, the two Voyager probes, and the New Horizons probe that recently passed by Pluto. They are interstellar travelers in point of fact; does that not make them "starships" by definition?

It simply gets down to how long you want to wait before the "starship" gets there. None of the 5 probes is actually headed to Alpha Centauri, which is around 10^13 km away. (Most destinations are much, much further.) Relative to the sun, these probe velocities far from the sun are on the order of 10 km/s max, due to gravity boosts at the major planets, which is then crudely near 3x10^8 km/year. The travel time over about 4 light years to Alpha Centauri, is thus on the order of 3x10^4-3x10^5 years. The other destinations, it takes longer still.

That's with chemical propulsion, using things like Atlas-5 and Delta-4 Heavy, and taking advantage of gravity assists at the major planets, or it would be around 10 times slower. But 10^5+ years is just too long for most folks to consider.

Higher performance propulsion shortens the time by raising speeds far from the sun, but that also reduces the effectiveness of major-planet gravity boosts (smaller percentage effect). So you cannot use that effect.

If your Isp is about 10,000 s (very large-mass nuclear explosion drive, or "Project Orion" atomic explosion drive, ship), your exhaust velocity is on the order of 100 km/s. For a single stage design, with a mass ratio near 7.39, your expected max available delta-vee is then near 200 km/s.

You need half of that to slow down at arrival, so this thing has essentially only duplicated something like 10 times the effective speed of the chemical propulsion result, except without any gravity boost effects. You are still looking at 100 km/s ~ 3x10^9 km/yr flight speed, for a flight time of around 3x10^3 years to a destination 4 light years away. Except that you can actually "slow down and arrive", which those gravity-boosted probes cannot. 3000 years. That's still an impractically-long flight time. But lots better than 100 thousand years.

For 10^6 Isp (there are no available technologies that can do this), exhaust velocity is on the order of 10,000 km/s ~ 3x10^11 km/year. Again for single stage, near mass ratio 7.39, and slowing down to arrive, your travel speed is near that same 3x10^11 km/yr at that same 4 light-year destination distance. That's what gets you there to Alpha Centauri in around 30 years.

That's the math with rocket propulsion, guys. We really do need "warp drive". Whatever that really turns out to be.

GW

Last edited by GW Johnson (2021-03-05 18:14:34)

SpaceNut · 2021-03-05 20:14:49

The Star Trek warp drive is made of antimatter and energy to cause the speed to change. Its a far off future for when we can control the combination for sure.

The trials of solar sails are still in the infancy and its unknown as to just how much payload can be moved for a give sail size and distance from the source that propels the ship.
Of course solar wind in moving the heavier part of the equation in the particle from the sun that the striking the sail and its that atom which gives it more energy into the sail for motion.

Lasers over distance continue to spread and would need to be continually refocused to keep the beam not only on target but concentrated to force the sail speed to keep increase as a beam that is spread or diffusing will cause the speed to drop.

So what is the solar wind, can it be created, are there sufficient particles in space to cause energy to be transferred to a sail if a simulated wind could be only a short distance from the ship to keep it moving....

article not quite what I would think would be a source for the warp drive content
scientists-announce-a-physical-warp-drive-is-now-possible-seriously

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Can we build an interstellar starship with current technology?

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