Planetary Society solar sail cubesat

[Idobox]

Let's also remember that people are actively working on graphene PV cells.

If we ever want to use things like VASIMR or other power hungry propulsion methods, we will need massive solar arrays, and they might end up looking a lot like solar sails. Even if pure solar sail propulsion never ends up being useful, the technology will be helpful.

[K^2]

That is the total with the payload.

Have you read about the payload. It's a very tiny magnetometer and a very tiny mass spectrometer. If they make up 2kg combined, I'd be surprised. Almost the entire mass of the ship is the support structure for the sails.

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Plus the solar cells... Or where you get your energy for the ion thruster?

What, for the 100W I'd need to power the 10mN ion thruster? That can be done with well under 1kg of solar panels. Or an even lighter RTG.

As I said, 32 Kg is the total weight of sunjammer, payload(several instruments, ashes, solar cells, etc) + structure-servo controls + sail.

The sail is 8kg (is not 6, I was wrong.), the structure is the same as the sail 8kg extra. Then the payload is 15 kg.

Everything I found points to the only part of considerable weight being support structure. Would you like to quote your numbers?

But even at 16kg total, ion thruster still wins.

Here explain than you need to take the double for the structure, For example if you have a sail dencity of 5g/m2, then with the support structure it will be 10g/m2.

http://trs-new.jpl.nasa.gov/dspace/bitstream/2014/18379/1/99-1857.pdf

That's for a rigid structure. Not a fold-out, like on the SunJammer. That might be the source of confusion here.

About how to calculate the deltaV of a solar sail, we cant, it will be infinite in theory.

Which is why the question is how much delta-V you need. And for any reasonable mission in the Solar System, ion thruster gives you lighter weight for the same thrust. And yes, I'm counting fuel, tanks, and payload here.

Thanks to solar sails it will be possible to sent a interstellar solar probe maybe in 50 years

Would you like to show math on that? Given the inverse square law, you end up with a rather short run up. Even if you do a two stage mission with a sun dive, you still end up with absurdly small velocity on escape.

Oh, and don't forget that once you hit heliopause, you'll be generating more drag with that thing than you do thrust. So you have to jettison or fold away the sail by then. Not that thrust is at all significant at that point anyways.

But you can do it all the time. You ever tried solar sails in ksp with the interstellar mod? I remember that the average density of that sail was really bad and even with those numbers was too easy to fall toward sun.

The trajectory calculations for solar sails takes time (even using the 2d formule), I need to see if I can find an addom for the matlab.

I wrote Mathematica code to do the trajectory in about half an hour. I was able to match it with ion thrusters down to sub-Mercurial orbit. Which is about as far as you'd want to bring any sensitive equipment anyways. But give it a shot. Maybe you'll get something different.

[AngelLestat]

Have you read about the payload. It's a very tiny magnetometer and a very tiny mass spectrometer. If they make up 2kg combined, I'd be surprised. Almost the entire mass of the ship is the support structure for the sails.

It does not said nothing about "tiny", we need to add batteries, solar cells (Im not sure if are really need it, a solar sail in theory can generate electricity just using the solar wind if some part of the sail are conductive), trasmissor, processor, ashes, etc.

The true is that we dont know nothing about the actual weight, I send a message asking, but no answer of course. That really bothers me when they dont share enoght info.

I might agree that maybe the instruments would not represent much weight, but we dont know for sure.

What, for the 100W I'd need to power the 10mN ion thruster? That can be done with well under 1kg of solar panels. Or an even lighter RTG.

??? That depends of how far are from the sun, I would said that RTG is a good option if you are far Mars orbit.

I am not very farmiliar with ion thrusters, can you give me a source where mention power consumption, xeon consumptions, total payload and deltav?

Or just thrust, I would calculate the deltav. Because the data which I read from wikipedia talks about lot of kg of xeon and 1 to 7kw.

Everything I found points to the only part of considerable weight being support structure. Would you like to quote your numbers?

I dont know what you found, because there is NONE sunjammer information about that xD

But even at 16kg total, ion thruster still wins.

You still need to make that case

That's for a rigid structure. Not a fold-out, like on the SunJammer. That might be the source of confusion here.

There is no confusion, the weight of the structure is 2 times the weight of the sail.

It said clearly in the last table.

"The mass of the sail (including all sail hardware carried by the sailcraft after the sail is deployed except for control)

is - 122.6 kg for a total areal density of 1 dm2"

You had the spacecraft sail parts, and the deployment parts.

The deployment parts (the same as sunjammer) are detached from the sail after this is fully deploy it.

There is also papers/patents which explain methods to reduce the structure weight of the solar sails. But none of those are in use in the current solar sails.

Which is why the question is how much delta-V you need. And for any reasonable mission in the Solar System, ion thruster gives you lighter weight for the same thrust. And yes, I'm counting fuel, tanks, and payload here.

Maybe you are right, but I would like to elaborate this case to compare if you find time later.

Would you like to show math on that? Given the inverse square law, you end up with a rather short run up. Even if you do a two stage mission with a sun dive, you still end up with absurdly small velocity on escape.

Yeah, you reach the 95% of the speed in just 15 minutes. I guess was Zubrin the guy who first calculated something similar but with worst materials.

Then Adam Crowl update the numbers using Carbon Nanotube new densities with quarter wave method to make the surface refractive.

http://crowlspace.com/?p=1882

http://crowlspace.com/?p=1585

http://crowlspace.com/?p=1580

It uses a gravity assist of jupiter to make the sundive.

I found a Solar Sail calculator, but it does not take into account your initial speed or the CTN quarter wave material example.

http://www.georgedishman.f2s.com/solar/Calculator.html

Oh, and don't forget that once you hit heliopause, you'll be generating more drag with that thing than you do thrust. So you have to jettison or fold away the sail by then. Not that thrust is at all significant at that point anyways.

No, the drag is not an issue, your sail is so thin that any atom or molecule that hit the sail, only slow the sail atom that you miss.

It makes a microscopic hole, the momentum is not absorbed by the spacecraft.

The stronger magnetic fields by other hand, might be a real issue in case your sail is made of a conductive layer as CNT.

I wrote Mathematica code to do the trajectory in about half an hour. I was able to match it with ion thrusters down to sub-Mercurial orbit. Which is about as far as you'd want to bring any sensitive equipment anyways. But give it a shot. Maybe you'll get something different.

What formule do you use?

I dont use the Mathematica since 10 years, and I never was very good at it. If I need something I just download the function already scripted

Edited July 4, 2014 by AngelLestat

[K^2]

There is no confusion, the weight of the structure is 2 times the weight of the sail.

And the fact that this is a completely different mission, with completely different sail design doesn't bother you at all?

It does not said nothing about "tiny"

Oh, but it does. If you go to the pages of universities that were responsible for the equipment, you'll note that they were trying to make them absolutely tiny.

You still need to make that case

There are a whole bunch of ion drive designs. You can take a look at the Wikipedia page for a start. It's all going to depend on what's more important for the task. But limitations for modern drive are up to about 50km/s of specific impulse and up to about 1mN/kg of specific thrust. You can compute everything else from that.

They are all rather efficient (except for electrostatics) in 70-80% ranges. You can easily compute specific power from that as well.

So lets take SunJammer's actual mission. Travel to L1 from Earth after being launched on escape trajectory. It can only brake at 70% efficiency, so that puts it at 7.6mN of total thrust. That can be matched with less than 8kg of hardware. With a 16kg payload, that would still leave you with 8kg for the propellant. Even if we consider that ion thrusters don't scale great, and we happen to use only 20km/s one, that still gives you 5km/s of delta-V for this particular mission. While the entire mission to L1 is going to be done in under 2km/s. That's less than 3kg of propellant, putting total mass in under 27kg.

Now, for the actual sun dive, yeah, if I take 16-to-16 mass, I'd have to scale down on ion drive's thrust and settle for a much slower dive. But as I pointed out, we're nowhere near that on the actual SunJammer.

What formule do you use?

Equations of motion in polar coordinates with gravity and thrust thrown in. Then I simply get Mathematica to NDSolve.

[Everten P.]

Sorry but it's not badass enough

[NERVAfan]

"Only practical method of interstellar voyage"? PUH-leeeze. I would prefer Orion with all its craziness.

I think they're really talking about unmanned interstellar missions. Supposedly if you use a really light sail and a very close sun flyby you can get to Alpha Centauri in a thousand years or so. Still impractically long IMO, but way better than 70 or 80 thousand with chemical propulsion.

If you use a giant laser in space close to the sun (for maximum solar power) you could get them going really fast.

I actually do think nuclear pulse propulsion is better since I think really light flimsy solar sails are likely to get shredded by interstellar dust impacts at really high speeds. If you use an Orion type thing, you can bring massive heavy shielding. And it's actually not particularly crazy at all if built in space.

(Actually, statistically, the real hazards of an Orion launch even from the ground would probably not be nearly as bad as your average big coal power plant. In the original Orion days they IIRC calculated 0.1-1 excess deaths per launch, but a) we could do better now, especially if the launch site was prepared right and if you don't buy the linear-no-threshold model of radiation risk, it might not affect health at all. The effects of really low radiation doses are not well known and it's debated whether they are actually harmful. The linear-no-threshold model which is used for official calculations is a conservative assumption, not necessarily right.

It's completely politically unfeasible, yes, and there would probably be EMP problems as it passed through the ionosphere, but it's really not the environmental nightmare one would at first expect.)

You can get what, 10μN of thrust from square meter under optimal conditions?

Not if you use a sun flyby. That's about right at Earth's distance from the sun. But IKAROS, at Venus' distance from the sun, got about twice that. And if you do a really close sun flyby, that can skyrocket.

And you wouldn't be able to go much thinner than 0.01mm for foil

IKAROS is already 7.5 micrometers (0.0075mm). I don't see why future materials science, or simply less margin once we've tried them out a few times and know more about how they work in practice, couldn't reduce that.

Edited July 7, 2014 by NERVAfan
finished incomplete sentence; second quote

[AngelLestat]

And the fact that this is a completely different mission, with completely different sail design doesn't bother you at all?

No, because is something that I read it before, but I dont remember where. I know that the average mass structure its 2 times the sheet sail mass. And it can be lower. Of course I can not be sure on sunjammer because I dont have that info.

Oh, but it does. If you go to the pages of universities that were responsible for the equipment, you'll note that they were trying to make them absolutely tiny.

I already saw them before when I wrote my previous post, I was searching the mass of those instruments. But it does not mention either. Also we can expect low weight design components for anything that its made for space.

There are a whole bunch of ion drive designs. You can take a look at the Wikipedia page for a start. It's all going to depend on what's more important for the task. But limitations for modern drive are up to about 50km/s of specific impulse and up to about 1mN/kg of specific thrust. You can compute everything else from that.

Ok, Lets take the Dawn Mission example (is the spacecraft launched with the most advance ion thruster that I could find)

http://dawn.jpl.nasa.gov/mission/Dawn_overview.pdf

http://nssdc.gsfc.nasa.gov/nmc/spacecraftDisplay.do?id=2007-043A

It has 450 kg Xenon, 3 Ion engines with 3200-1900 ISP, they need 3 kw, for that reason PV need to be

Dry mass 747.1 kg

fueled launch mass of 1217kg

But is not easy to divide all the components needed for the mission from the components needed for propulsion.

For example it has

Mechanical/structure 108 kg (gymbals, tanks, etc)

Ion Engines 129 kg

Electrical power system 204 kg (I dont know what porcentage we would need to cut in case we dont use ion engines, this include the solar cells)

In the manual it said that their delta V is 10 km/s

If we made the math with 3100 ISP it give us 13 km/s (of course is not always 3100)

The max thrust is 0.092 N.

So what sail dimensions we need to get something similar?

This is a tricky questions, because it depends on the time which took to the ion engines to achieve that speed and the travel time.

We need 9 times the sunjammer area to provide the same max thrust.

If we took a conservative value about sail + structure mass from sunjammer would be 18kg. So with only 162 kg of sail, you can achieve similar thrust than 450 + 129 + 100 +20 = 700 kg (estimate mass of dawn propulsion system)

You can take lower values for sail due to distance, add different issues, or things, but the case remains. Solar sails are very usefull, more if we pass from the 15g/m2 to 2g/m2.

So lets take SunJammer's actual mission. Travel to L1 from Earth after being launched on escape trajectory. It can only brake at 70% efficiency, so that puts it at 7.6mN of total thrust. That can be matched with less than 8kg of hardware. With a 16kg payload, that would still leave you with 8kg for the propellant. Even if we consider that ion thrusters don't scale great, and we happen to use only 20km/s one, that still gives you 5km/s of delta-V for this particular mission. While the entire mission to L1 is going to be done in under 2km/s. That's less than 3kg of propellant, putting total mass in under 27kg.

I dont see any description of how you did the math and where all those numbers come from. I hope I have made ​​a more clear example.

Equations of motion in polar coordinates with gravity and thrust thrown in. Then I simply get Mathematica to NDSolve.

Ok that approach seems correct, but how do you calculate the thrust vector? Because in solar sails you always had the prograde and retrograde components plus the radial out commponent.

Also the best way to made a sundive with solar sails is not a spiral toward the sun, first you gain altitud at the same time you slow your orbit speed, then you fall.

Sorry but it's not badass enough

Sorry, but things in space are measure it taking into account how usefull they are. But from the "like" point. I found Solar Sails beautiful and inspiring.

In our early years Sails gave us the medium to cross oceans. Now hundreds of years later, we are in the shore of a new ocean, and sails come back to save us one more time.

I think they're really talking about unmanned interstellar missions. Supposedly if you use a really light sail and a very close sun flyby you can get to Alpha Centauri in a thousand years or so. Still impractically long IMO, but way better than 70 or 80 thousand with chemical propulsion.

He knows that, he was mentioning the use of solar sails at 1AU average.

I actually do think nuclear pulse propulsion is better since I think really light flimsy solar sails are likely to get shredded by interstellar dust impacts at really high speeds. If you use an Orion type thing, you can bring massive heavy shielding. And it's actually not particularly crazy at all if built in space.

They are not, in fact solar sails is the propulssion system that less damage would receive from the interstellar medium at high or low speeds.

The sail does not need shield as I explain some post earlier, the mass of your spacecraft is highly reduced because you dont need any proppelent, so if you have a manned vehicle, only that part needs to be shielded, but if you take any fusion or (wherever proppelent technology) you would find that the spacecraft area in risk increase exponentially.

Edited July 8, 2014 by AngelLestat

[NERVAfan]

They are not, in fact solar sails is the propulssion system that less damage would receive from the interstellar medium at high or low speeds.

Why? I mean, an Orion is already built to stand up to nukes...

(OK, not direct impacts, there is some distance between the explosion and the pusher plate. Still I would think an Orion coasting 'plate first' would be a lot less damaged by interstellar dust than a sail.)

Unless you're saying that the sail would be full of holes but not enough to really affect its performance as a sail? Maybe. I wonder if it would stay 'deployed'/keep its shape under really energetic impacts though.

the mass of your spacecraft is highly reduced because you dont need any proppelent, so if you have a manned vehicle, only that part needs to be shielded, but if you take any fusion or (wherever proppelent technology) you would find that the spacecraft area in risk increase exponentially.

Once you're talking manned interstellar missions, probably decades of closed ecological system... that's a really big sail. If you're building in space anyway, with established space industry (and you might need to for a ridiculously big sail), what's the problem with a nuclear pulse engine? There won't be much area at risk because you'll have a really thick layer of ice and/or asteroid for shielding. The ship might be a billion tons or more but there's a LOT of deuterium in the outer Solar System, so who cares?

EDIT: I think sails with close sun passes might make a lot of sense for interstellar precursor missions, flybys of distant KBOs etc. Maybe even interstellar probes if they can survive the dust impacts. But I think for manned missions you need fusion.

Edited July 8, 2014 by NERVAfan
added "a sail" (incomplete sentence)

[christok]

Unless you're saying that the sail would be full of holes but not enough to really affect its performance as a sail? Maybe. I wonder if it would stay 'deployed'/keep its shape under really energetic impacts though.

Yes it would, and that is precisely the reason. Interstellar dust does little damage to a solar sail because the sail is thin enough for dust to pass through without imparting a significant amount of energy. (A spacecraft body, on the other hand, could need potentially mission-killing amounts of shielding.) The bigger concern is actually at perihelion since the environment very near the sun is not (last time I checked) understood well enough to know if the dust density is survivable.