Can we build an interstellar starship with current technology?

Oldfart1939 · 2021-03-07 09:22:17

I guess we're playing something of a semantics game here. I was aware of the JAXA solar sail demonstrator, but I'm considering the engineering involved as well as the theoretical concepts. Building a solar sail many kilometers in diameter and thin enough to be carried to space is Engineering. I don't think we're there yet. Using a Thermonuclear propulsion unit to slow down--that's possibly doable later in this Century. After all, Fusion energy is "just 10 year away," and it has been for several decades.

Quaoar · 2021-03-07 09:39:34

tahanson43206 wrote:

For quaoar re #24 (answer to SpaceNut)
SearchTerm:SolarSail Quaoar on power from Mercury to accelerate ship at 1 go to .25 C
SearchTerm:Interstellar Quaoar series on how to send a probe to Proxima Centauri
Note that the series above includes discussion of a hybrid approach, using laser power to accelerate from the Solar System, and a form of fission propulsion to decelerate at the destination.
For Quaoar ...
Would you be willing to show the amounts of time required to reach your target velocity of .25 C and ...
the time the vessel would coast at .25 C and ...
the time the vessel would be decelerating to reach Proxima at a velocity low enough to achieve orbit?
It is possible to show graphs in this forum. Would you have any interest in learning how to do that.
(th)

Destination: Proxima Centauri
Distance: 4.2441 light years
Constant acceleration of 9.8 m/s2
Variable laser power
Vmax 0.25 C

Earth reference frame

Acceleration time: 91 days, 10 hours
Coast time: 16 years, 265 days, 0 hours
Deceleration time: 91 days, 10 hours
Total trip time: 17 years, 82 days, 28 hours

Starship reference frame

Acceleration time: 90 days 10 hours
Coast time: 16 years, 69 days, 18 hours
Deceleration time: 90 days 10 hours
Total trip time: 16 years, 250 days, 14 hours

In this simulation, I've slightly simplified the problem, assuming that departure and destination laser stations are both statites (non orbital station kept stationary by a solar sail) so acceleration is from 0 to 0.25 C and deceleration is from 0.25 C to 0.

For orbital maneuvers the starship has to angle the sail at 45° from the laser station and use the beam power to gain or lose orbital velocity. She's not a ship of low orbit, so she parks herself in the high orbit of Proxima b, not so deep in the gravity well of the planet. Then a shuttle may detach from the mothership and reaches the low orbit. At this point a three stage lander (two stage and a capsule) detaches from the shuttle, performs a deorbit maneuver, enters in the atmosphere and lands near a river or a lake (in this simulation I assumed Proxima b has an Earth like ecosystem). When the mission is finished the lander uses a compact fission reactor to produce LOX-LH2 from electrolysis and reaches the low orbiting shuttle in three stages (Proxima b is a super Earth with almost 1.3 G of surface gravity, so a SSTO is impossible).

That's a simulation. A real travel must also take account of the relative motion of the destination star to not miss the target. This is not an easy task and implies a perfect knowledge of the motion of the target star.

Last edited by Quaoar (2021-03-09 17:45:03)

SpaceNut · 2021-03-07 09:43:39

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

https://web2.ph.utexas.edu/~mwguthrie/p.solarsails.pdf
Solar Sails - A Discussion

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

https://ntrs.nasa.gov/api/citations/200 … 061088.pdf
Characterization of Space Environmental Effects on Candidate Solar Sail Material

https://edge.coherent.com/assets/pdf/La … ndbook.pdf
Understanding the Laser Basics

The issue I see for a laser system is it can not stay stationary to point towards the sail while in the influence of the sun or planets.
A tethered laser must have a power source that due to additional structure is a payload reducer.

GW Johnson · 2021-03-07 10:40:22

The Planetary Society recently flew a solar sail. It works, but the accelerations are miniscule with just sunlight. More of a whisper than electric thrusters. You can improve the effect by shining a laser on the sail, if the sail is reflective enough not to be destroyed by the beam, but across interplanetary distances, the beam spreading renders this notion rather infeasible. Too strong up close, too weak far away.

As a reality check, the beam spreading I observed with a 2-4 milliwatt helium-neon laser was from 2mm to about 6 inches beam diameter, in only 12,000 feet. This was shining one at night down the main runway at TSTC airport, Waco, Texas, 3 or 4 decades ago. The beam was still bright enough to give you a headache, so it would still have far more effect than ordinary sunlight on a solar sail. But imagine how diffuse it becomes over 12 million miles instead of 12 thousand feet. Beam spread is proportional to distance.

GW

Quaoar · 2021-03-07 10:51:40

Oldfart1939 wrote:

I guess we're playing something of a semantics game here. I was aware of the JAXA solar sail demonstrator, but I'm considering the engineering involved as well as the theoretical concepts. Building a solar sail many kilometers in diameter and thin enough to be carried to space is Engineering. I don't think we're there yet.

Sure but we can start to work on the problem, build demonstrators in scale, make simulations, then try to go bigger and bigger as we gain experience on lightsails.
Obviously the first laser sail station will be build in a optimistic future where we have avoided to nuke each other and we have succeeded in colonizing the solar system, and we have gained experience in mining asteroids for raw materials and building space habitats.

Oldfart1939 wrote:

Using a Thermonuclear propulsion unit to slow down--that's possibly doable later in this Century. After all, Fusion energy is "just 10 year away," and it has been for several decades.

At the moment we have nothing but another laser station in the destination star system to slow down from 0.25 C, and that is the weak point of my arguments. As GW posted, there is no rocket able to reach 0.25 C of deltaV.
A Clark-Sheldon dusty plasma FF-rocket has a predicted exhaust velocity of 15000 km/s, 0.05 C, so an hybrid system, with a sail for acceleration and a two stages FF-rocket for deceleration can travel at 0.1 C and reach Proxima in about 43 years.
We have never built a dusty plasma FF-rocket, but we have the knowledge and the technology to start working on the topic, as Robert Bussard did for the NTRs at the time of project Rover.

Last edited by Quaoar (2021-03-07 11:43:48)

Quaoar · 2021-03-07 11:14:32

GW Johnson wrote:

The Planetary Society recently flew a solar sail. It works, but the accelerations are miniscule with just sunlight. More of a whisper than electric thrusters. You can improve the effect by shining a laser on the sail, if the sail is reflective enough not to be destroyed by the beam, but across interplanetary distances, the beam spreading renders this notion rather infeasible. Too strong up close, too weak far away.
As a reality check, the beam spreading I observed with a 2-4 milliwatt helium-neon laser was from 2mm to about 6 inches beam diameter, in only 12,000 feet. This was shining one at night down the main runway at TSTC airport, Waco, Texas, 3 or 4 decades ago. The beam was still bright enough to give you a headache, so it would still have far more effect than ordinary sunlight on a solar sail. But imagine how diffuse it becomes over 12 million miles instead of 12 thousand feet. Beam spread is proportional to distance.
GW

The beam needs to be projected from space and to be focused on the sail: we can imagine actively cooled adaptive mirrors like those of the big telescopes (I perfectly know it will be a monstrous task to build a multi kilometer sixed space array of this devices). Gas lasers like helium-neon have worst beam quality than diode pumped solid state lasers due to the turbulence of the medium. In Earth's atmosphere the laser beam spreads a lot due to diffraction, but in space it encounters only few hydrogen atoms for cubic cm so, if the beam comes from a space laser station, I think the diffraction should be far less (I used the formulas of this old work to calculate the maximum distance at which the beam can be focused on the sail https://www.amazon.it/Laser-driven-ligh … 07Y8H8MV8) .

P.S.
Hi, GW nice to hear you. How it's going in Texas?

Last edited by Quaoar (2021-03-07 11:56:26)

SpaceNut · 2021-03-07 15:23:23

Does laser affected by gravity?

https://www.science.org.au/curious/space-time/gravity

https://www.needforscience.com/physics/ … a-quantum/

How Far Can Laser Light Travel? We explore how powerful your laser needs to be to get noticed on Mars and beyond.

https://www.physlink.com/Education/AskExperts/ae661.cfm

https://www.nasa.gov/mission_pages/ibex … uKnow.html

To have a beam unaffected means we are beyond the suns strong influences that shape how waves travel from a point due to its time space shape as caused mostly by the suns mass.

Nothing is truly stationary when it comes to the subtle effects of wind, gravity or its waves and thats not only from our sun but from all sources....

GW Johnson · 2021-03-07 17:42:03

Hi Quaoar:

We did pretty good out here on the farm in central Texas, but many of my fellow Texans did not. Statewide, the polar vortex event was pretty much a disaster. A really bad one, too.

We did as well as we did out here on the farm because we never lost power. We're on a country co-operative for our power (and another one for our water). Over the years, those have simply proven to be more reliable. But city dwellers do not have that as a choice.

It is extremely rare to see temperatures get near 0 F (-18 C) here in central Texas. Not that it doesn't happen, it is just extremely rare. When it did, it was usually a 1-3 day event. This one was 9 days below freezing without a break. It reminded me of what I experienced in Minnesota about a quarter century ago (which was 2.5 months continuously below 0 F = -18 C).

We lost some garden plants and some in the greenhouse, too. But not everything. Some of the shrubs and trees suffered damage, particularly the ones that got coated solid with re-freeze ice coming off the roof.

This event had 3 ice events embedded in it, coming after a separate system had already snowed us in before. That's 4 significant icing events (so far) in one winter. We normally see only one of those per winter here.

GW

Last edited by GW Johnson (2021-03-07 17:43:50)

Quaoar · 2021-03-08 02:53:00

GW Johnson wrote:

Hi Quaoar:
We did pretty good out here on the farm in central Texas, but many of my fellow Texans did not. Statewide, the polar vortex event was pretty much a disaster. A really bad one, too.
We did as well as we did out here on the farm because we never lost power. We're on a country co-operative for our power (and another one for our water). Over the years, those have simply proven to be more reliable. But city dwellers do not have that as a choice.
It is extremely rare to see temperatures get near 0 F (-18 C) here in central Texas. Not that it doesn't happen, it is just extremely rare. When it did, it was usually a 1-3 day event. This one was 9 days below freezing without a break. It reminded me of what I experienced in Minnesota about a quarter century ago (which was 2.5 months continuously below 0 F = -18 C).
We lost some garden plants and some in the greenhouse, too. But not everything. Some of the shrubs and trees suffered damage, particularly the ones that got coated solid with re-freeze ice coming off the roof.
This event had 3 ice events embedded in it, coming after a separate system had already snowed us in before. That's 4 significant icing events (so far) in one winter. We normally see only one of those per winter here.
GW

-18 °F is -27.8 °C!!! As I remember, we never have temperatures so low in Rome. I'm happy your farm didn't suffered heavy damage and I hope your plants can recovery as soon as possible.

Quaoar · 2021-03-08 03:53:48

SpaceNut wrote:

Does laser affected by gravity?
https://www.science.org.au/curious/space-time/gravity
https://www.needforscience.com/physics/ … a-quantum/
How Far Can Laser Light Travel? We explore how powerful your laser needs to be to get noticed on Mars and beyond.https://www.insidescience.org/sites/default/files/2020-07/laserpointerataliens_top.jpg
https://www.physlink.com/Education/AskExperts/ae661.cfm
https://solarsystem.nasa.gov/system/resources/detail_files/14745_PIA12375.jpg
To have a beam unaffected means we are beyond the suns strong influences that shape how waves travel from a point due to its time space shape as caused mostly by the suns mass.
Nothing is truly stationary when it comes to the subtle effects of wind, gravity or its waves and thats not only from our sun but from all sources....

We can calculate the gravitational redshift due to the Sun's gravity for a IR laser beam of 4.8 micron of wavelength, with this approximate formula, that is valid for distances far grater than the Scwartzschield radius (luckily, our Sun is not a black hole so it's OK):

z= GM/(c^2*R) (1)

with z=(Le-L0)/Le (for a beam going away from the celestial body)

where GM is the Sun's standard gravitational parameter (132712440018 km^3/s^2); c is the speed of light (299792.458 km/s); R is the distance of the laser station from the Sun 0.25 UA = 37399467.675 km; L0 is the initial wavelength of 4.8 micron; Le is the red-shifted wavelength we have to find; and z is an adimensional number.

the result is

z=3.95*10^-8

resolving 2 for Le we found Le=L0/(1-z)

resulting 4.80000019 micron. So a 4.8 micron laser cast from a laser station at 0.25 UA from the Sun will become 4.80000019 micron due to Sun's gravitational redshift.

Last edited by Quaoar (2021-03-09 15:13:12)

tahanson43206 · 2021-03-08 07:44:35

For Quaoar re #35 above ...

In trying to follow your presentation, I note that the result quoted is different by only .00000019 micron ... The start was 4.8 micron wavelength, and the value you derived was that plus the small shift of 19 to the minus 8 (if I counted digits correctly).

In other words, not much! Am I missing a digit somewhere?

(th)

SpaceNut · 2021-03-08 17:59:08

Inside of mercury's orbit is risking it to solar storms and heat damage as its not going to stay stationary as its got to move in order to stop from falling towards the sun.
The laser then can be blocked as its targeting must be moved to keep the beam on target and it will spread out as distance from the sun gets greater not to mention the sun will block it while its orbiting for periods of time as well.
You need to be out beyond Pluto to get a beam that is not shifted and dispersed by the suns gravity...
The sun is the strongest laser I know and even its beam drops with distance....

tahanson43206 · 2021-03-08 19:04:07

For Quaoar re SpaceNut's post #37

Do I understand correctly that you are proposing to install the laser system on the surface of Mercury?

If that is correct, it would address the issue raised by SpaceNut, of the installation falling into the Sun.

In the next issue raised by SpaceNut ... How long would the acceleration be needed?

In your earlier post you provided velocity values, but if you provided times for acceleration and deceleration I missed it.

If I understand your post correctly, you have addressed SpaceNut's point about needing to go all the way out to Pluto by explaining that the effects of gravity on the beam are minimal (ie, vanishingly small) and the issue of dispersion raised by GW Johnson you address by giving the relatively uncluttered environment of space itself (in the vicinity of Mercury) as a reason to expect the cohesion of the laser beam to hold up for the distances involved in acceleration

The first probe needs to include the deceleration component you've described, because there won't be a laser at the receiving solar system.

***
Going back to SpaceNut's points ... pointing the laser at the receding starship/mirror while moving wth Mercury in it's orbit will require some clever engineering.

Do you have some preliminary thoughts about how you would design that feature of the system?

(th)

SpaceNut · 2021-03-08 19:47:50

Mercury orbits the Sun at an average distance (semi-major axis) of 0.387 AU (57,909,050 km; 35,983,015 mi) so a laser station of 0.25 Au is inside the orbit of mercury and is not on mercury's surface at all....

Red shift is what happens to the lights color as something is receding which is shining as well while blue shift is approaching..

edit
https://solarscience.msfc.nasa.gov/SolarWind.shtml

As predicted and measured by the voyagers
https://www.sciencedaily.com/releases/2 … 102033.htm

However, when New Horizons traveled beyond Pluto, between 33 and 42 AU, the solar wind measured 6-7% slower than at the 1 AU distance, confirming the effect.

https://www.discovermagazine.com/the-sc … from-pluto

Pluto's orbit is also highly elliptical, stretching from 4.4 billion km to just over 7.3 billion km from the Sun. Doing the math again, that means the Sun goes from being 0.0012 to 0.0004 as bright as it is from Earth: a range of roughly 150 to 450 times as bright as the Moon from Earth. That's a change in brightness by a factor of three!

tahanson43206 · 2021-03-08 21:14:28

For SpaceNut ... it is good that you are checking the figures posted by contributors to the topic as we go along.

I went back to the top of the topic, to see if the location of the laser station had been specified...

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).

I trust that Quaoar will not be offended by close reading of his posts, just as others who contribute can expect feedback in the event of a typo or some other departure from what is needed.

For Quaoar ... It seems that SpaceNut has identified a difference in the possible distance of the station from the Sun.

And while you're looking at that, could you add a thought or two more about where the station would be located? Is there a location on Mercury where the starship could receive constant thrust from Mercury for as long as acceleration is needed?

The quote above suggests the polar region ... would it make sense to install a laser station at ** both ** poles? Is there a characteristic of the movement of Mercury that would make that beneficial? Is Proxima Centauri in the Solar Plane or away from it, so the beam could be held on the ship for as long as necessary without interruption?

(th)

SpaceNut · 2021-03-08 22:14:21

Our nearest star system, Alpha Centauri, is 4.4 light-years away and physicists believes probes can make the interstellar trip in just 20 years on the wind from the sun at 60 million meters a second, seems fanciful. You need to boost the power of the light source to brighter than the Sun and shrink the mass of the spacecraft.
Now making an array of high powered lasers that are spread out point like a cone towards the sail means more force striking the same target even if they do get weaker with distance there is still more of them to push the sail.
Of course the issue is that the lasers will need to stay focused on the light sail for the entire boosting phase with a target size that is shrinking with every passing kilometer that the sail moves away from the laser.

https://www.space.com/29950-lasers-powe … craft.html

https://www.space.com/40512-breatkthrou … ology.html

So large nuclear powered stationary lasers point to a common target out past the influence of the suns solar winds could get to speed if we do not burn a hole into it....

tahanson43206 · 2021-03-09 07:18:47

For Quaoar re SpaceNut #41

It seems SpaceNut is giving you some backing in this post ... The details about multiple lasers and nuclear power are interesting and I'll be interested in how you might expand upon them. I would have thought there is no need for separate nuclear power for these systems, since the fusion reactor is ** right there ** to provide all the power you need, but perhaps there is something I'm missing.

Could SpaceNut's suggestion of laser's spread out be implemented on just Mercury, or would the project require other locations?

For steering, I would expect feedback from the probe would be helpful. It would be able to report back the amount of power received at any moment, and any useful beam steering information it can glean from observing the flux at various points in the mirror.

In fact (come to think of it) ... this ** is ** a mirror, so the mirror itself may be capable of providing direct and immediate feedback, by reflecting some of the photons back to the laser site.

On the "ground" the laser guidance mechanism will still have to deduce the likely target location when the photons arrive days or eventually weeks later.

This will put "kentucky windage" and "tennessee elevation" into practice in a big way!

(th)

Quaoar · 2021-03-09 15:19:12

tahanson43206 wrote:

For Quaoar re #35 above ...
In trying to follow your presentation, I note that the result quoted is different by only .00000019 micron ... The start was 4.8 micron wavelength, and the value you derived was that plus the small shift of 19 to the minus 8 (if I counted digits correctly).
In other words, not much! Am I missing a digit somewhere?
(th)

I've approximate z: the real value is 3.9482514879433695243028286559985*10^-8 so it's possible to have some wrong decimal

Quaoar · 2021-03-09 15:22:30

SpaceNut wrote:

Mercury orbits the Sun at an average distance (semi-major axis) of 0.387 AU (57,909,050 km; 35,983,015 mi) so a laser station of 0.25 Au is inside the orbit of mercury and is not on mercury's surface at all....
Red shift is what happens to the lights color as something is receding which is shining as well while blue shift is approaching..
edit
https://solarscience.msfc.nasa.gov/SolarWind.shtml
As predicted and measured by the voyagers
https://www.sciencedaily.com/releases/2 … 102033.htm
However, when New Horizons traveled beyond Pluto, between 33 and 42 AU, the solar wind measured 6-7% slower than at the 1 AU distance, confirming the effect.
https://www.discovermagazine.com/the-sc … from-pluto
Pluto's orbit is also highly elliptical, stretching from 4.4 billion km to just over 7.3 billion km from the Sun. Doing the math again, that means the Sun goes from being 0.0012 to 0.0004 as bright as it is from Earth: a range of roughly 150 to 450 times as bright as the Moon from Earth. That's a change in brightness by a factor of three!

Sure I put it more inside to spare panels surface. Maybe the best station to propel a sail-ship is not an orbital station but a statite, with a solar sail to keep it aligned with the ship course.

Last edited by Quaoar (2021-03-09 16:28:00)

Quaoar · 2021-03-09 15:36:22

SpaceNut wrote:

Our nearest star system, Alpha Centauri, is 4.4 light-years away and physicists believes probes can make the interstellar trip in just 20 years on the wind from the sun at 60 million meters a second, seems fanciful. You need to boost the power of the light source to brighter than the Sun and shrink the mass of the spacecraft.
Now making an array of high powered lasers that are spread out point like a cone towards the sail means more force striking the same target even if they do get weaker with distance there is still more of them to push the sail.
Of course the issue is that the lasers will need to stay focused on the light sail for the entire boosting phase with a target size that is shrinking with every passing kilometer that the sail moves away from the laser.
https://www.space.com/29950-lasers-powe … craft.html
https://www.space.com/40512-breatkthrou … ology.html
So large nuclear powered stationary lasers point to a common target out past the influence of the suns solar winds could get to speed if we do not burn a hole into it....

An small unmanned probe has far fewer problems than a big manned spaceship: it can be busted at thousands of gee, without crushing the crew, so all the acceleration phase takes place near the laser beam source: a gram-sized probe, busted with an initial acceleration of 5000 G, reaches 0.25 C just in 32 minutes in at 0.52 UA from the laser.

Viceversa, a manned 10,000 ton sail-ship, with a 14 km wide, 260 ton C-C sail, with a 15 PWo 12 micron IR laser array, has an initial acceleration of 9.8 m/s2 and reaches 0.25 C in 111 days at 2601 UA from the laser station, so she needs a 1100 km wide laser array, to focus a redshifted 15.49 micron beam on her sail at that distance*

I see no need of nuclear powered lasers in space, where sunlight is abundant and ever present: why not a high efficient diode pumped-solid state laser powered by an array of solar panel or alternatively a solar pumped-solid state laser, which doesn't need to convert solar energy in electricity?

*in these days I perfected my spaghetti-code and now I can simulate real sails with non complete reflectivity: during the simulations, I discovered that the tungsten coating doesn't work very well when the sail reaches its exercise temperature. So I eliminate it and make an uncoated graphite-fiber-reinforced-graphite sail, that become almost 0.95 reflective over 3000 K in the mid-infrared spectrum, resulting a lighter and more efficient sail.
I also write a code for the integration by parts, so now I can calculate the time and the final distance of the acceleration phase at constant power output, with an acceleration that decreases progressively due to relativistic doppler effect, while the sail increases its reflectivity with the increment of the light wavelength.

Last edited by Quaoar (2021-03-09 17:31:39)

SpaceNut · 2021-03-09 19:50:17

I was wondering if we could use the in a configuration that is like a tunnel in which the ship sets in the center a just ahead of the many lasers that would push it to speed. The corner lasers would be a multi type point unit with ability to push the unit ahead of it as well as push the ship which is in the center of them.

Another concept I was thinking was to have a parabolic sail that is also pointed at by multiple lasers but it connects to a fixed laser assembly on the ship facing aft. The dish would scooped up particles and focus them back towards the ship. The laser would be unfocused onto the dish but via reflection the particles would be heated and reflected back out a center hole in the dish.

This is missing the center exit hole but ahead of the reciever is the nuclear power and laser assembly to make it work like a star trek deflector dish...picking up the incoming particles and accelerating them aft as it heads towards its target destination...

Quaoar · 2021-03-10 03:42:32

SpaceNut wrote:

I was wondering if we could use the in a configuration that is like a tunnel in which the ship sets in the center a just ahead of the many lasers that would push it to speed. The corner lasers would be a multi type point unit with ability to push the unit ahead of it as well as push the ship which is in the center of them.
https://i.pinimg.com/originals/8b/d6/54 … c7f33f.jpg
Another concept I was thinking was to have a parabolic sail that is also pointed at by multiple lasers but it connects to a fixed laser assembly on the ship facing aft. The dish would scooped up particles and focus them back towards the ship. The laser would be unfocused onto the dish but via reflection the particles would be heated and reflected back out a center hole in the dish.
http://www.see.murdoch.edu.au/resources … age007.jpg
This is missing the center exit hole but ahead of the reciever is the nuclear power and laser assembly to make it work like a star trek deflector dish...picking up the incoming particles and accelerating them aft as it heads towards its target destination...

For particles do you mean space neutral hydrogen atoms?

Terraformer · 2021-03-10 08:19:58

Re. the deceleration phase, what are the objections to using a magnetic sail to slow down? Not enough drag from the solar wind at the destination?

Also, I'm now wondering what the Isp limits of ablative sails are. Mind, targeting issues (you're talking about vaporising it into a very hot plasma and then directing that with a magnetic nozzle) probably make it a non starter.

Still, I don't think you should give up on Orion just get. Fusion bombs + magnetic nozzles could potentially get 0.08c exhaust velocity? Enough if you pile them on to reach 0.2c, if you can use a magsail to decelerate...

tahanson43206 · 2021-03-10 08:45:11

For Terraformer re #48

Your idea may have merit .... do you need assistance finding the physics to support it?

My first impression would be that it would need to be quite large, and it would only work with charged particles, so it might work best close to the destination star. But if the vehicle is moving at .25 C, and it is many tons of mass, it will need to encounter a corresponding quantity of charged matter to achieve velocity reduction.

***
For Quaoar .... The region of which Italy is today identified has a remarkable history of birthing and supporting global explorers.

It is entirely imaginable that the architect of an interstellar probe might come from Italy.

This would be a global enterprise, consuming significant resources and lasting several generations.

It could begin with a speech to the United Nations by the Ambassador from Italy, whose speech might be crafted by a gifted writer with a vision of the future that is notable even in the context of the NewMars forum.

(th)

tahanson43206 · 2021-03-10 09:13:13

For Quaoar ... this post is reserved for a SearchTerm to point to your recent post with specific calculations about the time it would take to boost a spacecraft to .25 C for a trip to Proxima Centauri.

SearchTerm:111 days to boost an interstellar vessel (or a probe for that matter) to .25 C after departure from the Solar system.
SearchTerm:laser boost time required at 1 G acceleration
SearchTerm:Interstellar probe given laser boost from Earth and using rocket equation to slow at destination
SearchTerm:probe
SearchTerm:quaoar Interstellar probe or ship to Proxima Centauri

http://newmars.com/forums/viewtopic.php … 64#p177464

Post #45 above

Further work welcome ... At this point (to the best of my recollection) this forum archive does not contain details about pointing that would be needed to send a probe to Alpha Centauri. Using Quaoar's vision as a starting point, the probe would need to arrive at wherever Proxima Centauri is going to be when the probe gets there, taking acceleration, coast and deceleration into account.

The laser propulsion system only needs to deliver power for 111 days. It will be done while Mercury is moving in orbit around the Sun.

Per Google, the orbit of Mercury takes 87.97 (88) days, so the laser propulsion system must operate for more than one orbit.

If someone with an astronomical inclination is willing to add to this topic, I'm curious to know where Proxima Centauri is with respect to the plane of the elliptic of the Solar System. If the destination is NOT in the plane, then pointing steadily and without interruption should be possible.

The proposal (of Quaoar) would permit feedback from the vessel during boost. At the end of the boost phase, the vessel would be traveling at .25 C

Assuming steady operation of the boost system, it should be possible compute the distance of the probe at the end of the boost phase, and thus the time required for light from the probe to return to the propulsion system on Mercury.

I expect the light time will be measured in days, but am looking forward with great interest to seeing the actual figure. It is ** that ** time delay that will influence how the beam pointing apparatus orients itself during the final stages of the boost.

Edit#1: This forum is (somewhat cautiously) talking about creating a course of study leading to Certification as a Journeyman Spacecraft Navigator for the Earth/Mars trade. The vision of Quaoar will require a bit more capability than a Journeyman Spacecraft Navigator might be expected to possess.

Edit#2: For Quaoar ... this is a big ask ... is there a chance pushing a ship the size of the one you've imagined for 111 days would affect the orbit of Mercury?

That force would be (in effect) a steady shove on the rim of a gyroscope ... it ** should ** cause a noticeable effect, depending upon the angle at which the beam must be pointed to sustain delivery of photons to the mirror.

In the case of a smaller unmanned probe, the effect may not be noticeable, but it would certainly be present.

A reviewing committee at the UN (or anywhere) is going to ask that question, so now is a good time to address it.

Edit#3: Here is a link to a set of short biographies of Great Italian Explorers

https://www.lifeinitaly.com/history/her … explorers/

There are familiar names (to me at least) in the article, but there are many names that are new to me.

The article and the biographies support my thesis that the logical place to find a proposal to launch an interstellar probe is Italy.

(th)

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