Laser propulsion system - is it possible to tack?

[Catastrophe]

PA
Have you any info please on the mechanics/equipment necessary for ion thrusters?
This in terms of power/weight ratio.

Cat

 

[Particle Article]

I am new to the field 8D,
but I imagine there are many resources on the net
usually the fuel is xenon
here are some leads-
Ion thruster - Wikipedia
Electrically powered spacecraft propulsion - Wikipedia
NASA - Ion Propulsion | NASA
Silent and Simple Ion Engine Powers a Plane with No Moving Parts - Scientific American

with lasers we can dramatically apply more wattage,
and burn fuel faster,
perhaps meaning more thrust

ion and plasma thrusters are very similar, I understand that plasma is the most recent

sorry no, I don't know power/weight ratios for these techs
I can understand Newtons and Watts though

 

[Catastrophe]

"sorry no, I don't know power/weight ratios for these techs"

That was the point of my question. Can a method produce significantly more thrust than the power needed to move its own fuel/mechanism?

Cat

 

[Particle Article]

"On the other hand, the entire ion propulsion in DS1 can produce 92 mN of force which is "roughly" equivalent to the pulling power of a large beetle, like a cockroach, and DS1 weighs 489.5 kg. This is much less than 1 lbf/lb!"

source:
Could ion propulsion work on Earth or does it work only in space? (northwestern.edu)

DS 1 craft further:
NASA - Deep Space 1 Ion Propulsion System Operation Sequence and Status

the xenon used for that mission was 72kg, we can assume the craft had around 77.5kg xenon tank
the 72kg provided 16,246 hours of thrust

 

[Catastrophe]

PA
Sorry, you lost me here. Is the xenon system viable or not? First para seems to say no.

Cat

 

[Particle Article]

viable regarding what objective Cat?

DS-1 mission objectives were all accomplished
many satellites use ion thrusters to maneuver

the thrust is:-
92 millinewtons (0.33 ozf) thrust at maximal power (2,100 W on DS1)
and the craft weighs 489.5 kg

edit- oh I see, in regards to this thread, to power such a unit with a laser
it's very low thrust, but it's the existing technology. I'll try and put the figures together for the time to Mars
cheers!

edit- at a speed that this machine is capable of 56,000 kmh,
it would take 189.6875 days to travel to Mars
254,940,000 km away

 

[Catastrophe]

viable regarding what objective Cat?

DS-1 mission objectives were all accomplished
many satellites use ion thrusters to maneuver

the thrust is:-
92 millinewtons (0.33 ozf) thrust at maximal power (2,100 W on DS1)
and the craft weighs 489.5 kg

edit- oh I see, in regards to this thread, to power such a unit with a laser
it's very low thrust, but it's the existing technology. I'll try and put the figures together for the time to Mars
cheers!

Many thanks, Cat

 

[Catastrophe]

Things are getting fanciful You need to see this (from Lightsails):

There is a very good article in Astronomy May 2021, entitled Breakthrough Starshot: A Voyage to the Stars.

Essential reading for anyone who thinks that this is a practical means of space travel.

"A necessary requirement for the Breakthrough Starshot mission is keeping the mass of each sail-equipped Starchip to just a few tenths of an ounce (a few grams). . . . . . . likewise the solar sail itself, which is expected to span up to around 13 feet (4 metres), will need to weigh in at less than 0.035 oz (1 gram). It will also need to be extremely thin, as otherwise the sail would absorb far too much heat and be vaporized by the barrage of laser light . . . . . . "
the barrage of laser light to drive a few grams??
"Mass is the bane of accelerating objects to great speeds. To significantly increase the velocity of a heavy object takes a tremendous amount of energy. So, if the goal is to reach a distant star in a reasonable amount of time, say within a generation, a spacecraft must be extremely tiny and, therefore, robotic. Plus, it still requires an insanely energetic boost to get up to speed."
" . . . propelling a lightsail-equipped nanocraft, or Starchip, would require hundreds of individual lasers ,spanning roughly 200 acres (1 square kilometer). The array would also need access to enough energy to fire a coherent 100 gigawatt laser beam for several minutes during each . . . launch.
That's roughly the amount of power generated by all the nuclear power plants in the U.S. in a given year."

Another problem occurred to me, which is not mentioned. 200 acres of individual lasers surely would not be very manoeuvrable. Would it be able to follow said Starchip, even for a few minutes (as the Earth turns)? Also, would it not be usable only at a fixed latitude - that at which it was built?

Not to mention stopping when it gets there!

Cat

 

[YetAnotherBob]

I've seen reports and articles that propose using high thrust light sails. Those reports generally ignore the absorbed light. Thermodynamics has defeated a great many wonderful designs in the past and it appears to be continuing the trend.

Breakthrough Starshot is planning on it's star wisps, basically a single IC chip with a meter square thin aluminum sail, intercepting the laser light from a large number of industrial strength lasers on Earth and attached to a field of telescopes to then focus on the 'ship' for several hours each day.

The focusing effort is beyond any technology we can produce for distances beyond the orbit of the Moon. This is done at megawatt levels too. If even a thousandth of the signal is absorbed, it's Bye-Bye Wisp. Chips don't dissipate kilowatts of heat non-destructively.

It's beyond present day technology, but not that far beyond. It should be doable in a decade or so. Still, it isn't really a very useful star-ship. The plan is to launch several thousand of these in the hope that one may make it to the target star and send back some observations.

Personally, I believe that the desired 20% of light speed will not be realized because of atmospheric dispersion. Still, I'd be quite willing to settle for five to fifteen percent of C for the first probes. I also wouldn't expect to get much information back either. After all, a complete satellite with a mass of less than a gram simply doesn't have much room for actual instrumentation. not much room for transmitters either. And at light years range, it will be quite hard to pick out any signal at all from the noise of the nearby star.

A far better plan would be to place the lasers up in orbit and then use diffraction limited optics to send the beam. Feed the whole thing with solar panels, and you could send off a star wisp every few hours.

Though I also wonder somewhat just how much acceleration these systems will be able to withstand. To reach 20% of C in a day requires an awful lot of acceleration. Not as much as a bullet, but for much longer than the time a bullet spends in the barrel of a gun. Bullets deform quite a lot when fired off. Silicon chips don't do deformation gracefully.

Ah well. I'm probably overthinking this. I do tend to look at the niggling details and try to work things out. This project though is intended to stretch the limits of technology. Yes, it is beyond what is possible today. Maybe what is possible over the next ten years as well. But maybe not.

I hope there are things I don't envision that will come into play.

I hope it, but I don't expect to see it.

Tacking with a light sail is a completely different problem. I've addressed it before. Yes, it is possible in a somewhat limited sense. I don't believe the Breakthrough Starshot designs should be expected to tack with the light until they are close to the target star. Some use of this may be needed close to Earth too. Tacking using a light sail decreases the thrust as the cosign of the angle, so it falls off to zero at some angles, and generally you average only around one over the square root of two of your direct thrust. Not optimum. Unfortunately, it isn't possible to use the light sail as a wing, as racing sailboats do on Earth to actually tack faster than the wind. Light sails don't allow for this.

Sorry, no Faster-Than-Light here.

It's actually a problem for the project physicists to tackle. I'm sure they are up to the challenge.

 

[Clovis]

Ion propulsion, a tiny pulse that pushes a spaceship a bit at a time, but it's consistent . Over the vastness of space that's significant. Interstellar or even in our own solar system we could reach near light speed. The problem is slowing down, that would require rockets. It's already been used to send a probe to Jupiter. And it worked .

 

[Clovis]

Gravity on our ships , that's why you see a centrifugal portion spinning around the space ships . Artificial gravity. Something like this. And this ship also used ion propulsion.

View: https://youtu.be/nzJse7kfEnk

 

[Clovis]

You don't think SciFi predicts the future ? Remember your old flip phones.
MRI machines

 

[IG2007]

You don't think SciFi predicts the future ? Remember your old flip phones.
MRI machines

I don't think HG Wells' Time Machine will ever become true... Or, will it?

 

[Catastrophe]

I don't think HG Wells' Time Machine will ever become true... Or, will it?

Not if he sits on a bicycle and pedals

 

[Clovis]

Maybe it already has. We wouldn't know about it anyway. Time travel can be a very complex subject even if it's only messages sent from the future into the past. Or vice versa, which wouldn't be very useful because the future already knows.

 

[Clovis]

The past is gone it cannot be brought back . The present becomes the past as soon as it arrives. There is only the future. Oppenheimer.

 

[Clovis]

All kinds of differant scenarios , and paradoxes. You go back to the time before your father met your mother. You get into an argument with your. Father and end up killing him. What then happens to you? Will you no longer exist? Rule of thumb, if go back in time and come across yourself, you cannot even touch yourself . Same matter cannot occupy the same time and space. In any kind of parallel in time.
But that's only a theory, this is how complicated it can become.

 

[Clovis]

In fact it's all only theory's. Einstein was big on this so was Stephen
Hawking. Hawking explained it in his book The Universe in a nut shell.
He disagreed with Einstein on many occasions. Carl Sagan was another one. I saw him speaking at Texas Tech University when I was going to school there. A very smart man.

 

[Catastrophe]

One way to avoid time paradoxes is to postulate that you must arrive in an alternate universe. Cat
That is, in one in which you do not exist e.g., your parents never met.

 

[Clovis]

Sagan had his own theories on time and space. He was big on the possibilities of worm holes, and the bending of time and space.
And how black holes could possibly play a big role in all of this.
The movie Interstellar used a lot of Sagans theories in its production.

 

[Clovis]

One way to avoid time paradoxes is to postulate that you must arrive in an alternate universe. Cat
That is, in one in which you do not exist e.g., your parents never met.

Interesting, so now your talking about Dimensions. And the possibility of a Fifth.

 

[Catastrophe]

"Interesting, so now your talking about Dimensions. And the possibility of a Fifth."

No. I am talking alternate universes. which, I have to say, I consider unlikely and probably the worst sort of SF. However, there are probably 57 varieties, some worse than others.

My take is simply alternatives in this Universe. End of.

Cat

 

[Clovis]

Two dimensional is interesting, if you look at it like a sheet of paper. You see one side and another side, but when turned sideways it doesn't exist, it has no depth.

 

[Catastrophe]

"Two dimensional is interesting, if you look at it like a sheet of paper. You see one side and another side, but when turned sideways it doesn't exist, it has no depth."

Clovis, what about a Moebius strip? You know, half a turn and gum the ends together.'
Just follow along the surface - there is only one, however much you think there are two.

Cat

 

[Clovis]

"Interesting, so now your talking about Dimensions. And the possibility of a Fifth."

No. I am talking alternate universes. which, I have to say, I consider unlikely and probably the worst sort of SF. However, there are probably 57 varieties, some worse than others.

My take is simply alternatives in this Universe. End of.

Cat

I think it's unlikely also.