Solar Sails

EarthWolf · 2004-08-12 17:41:41

Hello,

Recently, there has been the news of both the Japanese and NASA flying solar sails into orbit. How fast could solar sails propel a spacecraft to Mars? Would they be faster than chemical engines?

Cordially,

EarthWolf

GCNRevenger · 2004-08-12 18:53:29

Optical solar sails would be pretty slow, on the order of at least a year and a half, perhaps as long as three years one way. Very tight mass restrictions too... solar sails are better suited to small probes to the outter planets and beyond.

RobS · 2004-08-13 01:33:59

The future potential of solar sailing for cargo delivery seems pretty high if we can figure out how to deploy huge sails in space. That probably requires more experience in orbit than humanity has now. It may also require orbital construction ability.

At 1 astronomical unit from the sun, sunlight exerts 4.7 micronewtons of force per square meter. That's 4.7 millionths of a newton. A newton is the force necessary to accelerate 1 kilogram by 1 meter per second. A reflective surface doubles the solar force.

To scale that up, a square kilometer has a million square meters, so a square kilometer of solar sail would feel 9 newtons of solar force. That's about two pounds of pressure.

The trick is the mass of such a sail. It is already possible to make sails with the mass of 1 kilogram per 100 square meters (10 grams per square meter). Thinner than that and you can't fold them up, then deploy them. It may be possible to make much thinner sails in space, however, and there is one possible terrestrial manufacturing trick that could make them thinner: manufacture a plastic that will evaporate away on exposure to ultraviolet light and aluminize it. Such a sail will be thick and heavy enough to deploy, but after a few months in orbit the plastic will be gone, just leaving the aluminum.

No one can yet imagine how to deploy a 1 square kilometer sail. The best most folks talk about right now is 100 meters in diameter and a sail mass of 80 kilograms. Such a sail could send a 48 kilogram (105 pound) payload to Mars in 725 days. I found that data via a Google search.

But larger sails should be possible if a research program is initiated that includes deployment of models in orbit. You have to start about 1,000 miles up, by the way, because upper atmospheric drag is a more powerful force on a sail than sunlight below that altitude. So this doesn't help from low Earth orbit. You need a way to move your cargo up to a medium altitute orbit.

If a 1 square kilometer sail could be made that masses 10 tonnes (10 grams/sq meter) it could push a 5 tonne payload to Mars in 725 days (that's just scaling up the example 100 times). If you could make it half as massive through evaporation of the plastic, the 1 square kilometer, 5 tonne sail could deliver 10 tonnes to Mars in 725 days. Double the sail size to 2 square kilometers and the 10 tonnes gets there closer to 1 year after leaving Earth. That's probably feasible in thirty years, if we concentrated on the technology. Some experts talk about solar sailing of crews, and consider that the hab is 25 tonnes; it would need a 5 square kilometer, 25-tonne sail (though the people couldn't get on board until it had spiraled out of the van Allen radiation belts, which would take a few months). Solar sails may be particularly useful for cargo flights to Mercury, where the more intense sunlight increases the sail's effectiveness.

One article I found via Google also gave this interesting fact: if we could make a sail and payload combination with a combined mass of 1 kilogram per 600 square meters (just 1.6 grams per square meter) then the sunlight on the sail would exert a force equal to the sun's gravity on the sail! Such a sail could escape the solar system directly. In *Entering Space* Zubrin talks about a 1000 tonne manned interstellar vehicle with a sail 343 kilometers in radius and just 0.001 micron thick, therefore also massing 1000 tonnes, starting 0.1 AU from the sun. Sunlight would start accelerating it outward at 18 gees (not sure how such a thin sail could handle that!) and the ship would escape the solar system at 1 percent the speed of light. If the sail were illuminated by lasers it could achieve an even higher speed.

So the technology has a lot of future potential. By the time we have moved from exploring Mars to settling Mars, solar sailing cargo ships may be an important element in interplanetary transportation, since they should be much cheaper than other propulsion systems.

-- RobS

SpaceNut · 2004-08-13 05:54:47

See the other topic for other details on solar sails.

Japan launches Solar Sail
at last someone did it!

noosfractal · 2005-11-02 00:36:18

Interesting paper on solar sails by Zubrin ...

http://www.pioneerastro.com/Projects/USSIT/ussit.html

From the summary ...

Solar sails have long been theorized as capable of sailing interplanetary and interstellar space. Conventional solar sail designs use aluminized plastic support membranes to form the sail, which limit their characteristic accelerations to ~0.001 m/s2, because the plastic dominates sail mass. Such a sail is limited to travel within our solar system for missions lasting less than 10 years. By eliminating the plastic substrate after sail deployment, it is possible to increase the sail acceleration three-hundred fold. This sail can venture anywhere in our solar system within a year. Introducing perforations in the sail, similar to an antenna mesh but at a very small nano-scale, can reduce sail mass such that accelerations of 0.5 to 5 m/s2 are feasible. At these accelerations, a spaceship could visit the Oort cloud beyond our planetary system (~10,000 AU) within several decades. If these perforations were eventually made of carbon nano-structures rather than out of a nano-grid of aluminum, accelerations of 10 to 100 m/s2 may be possible, enabling interstellar travel to  Centauri in less than a century. In its nearest-term and most conservative form, the utltra-thin solar sail will revolutionize outer solar system exploration. In its ultimate form, it will give humanity the stars. We therefore conclude that the development of ultra-thin solar sail technology must be aggressively pursued.

_

John Creighton · 2005-11-02 11:38:48

I had no idea solar sails could go that fast. Still it will be quite an engineering task to build an meuver such large structures.

SpaceNut · 2005-11-02 11:50:49

At 1 astronomical unit from the sun, sunlight exerts 4.7 micronewtons of force per square meter. That's 4.7 millionths of a newton. A newton is the force necessary to accelerate 1 kilogram by 1 meter per second. A reflective surface doubles the solar force.

Sound like we need some sort of concentrator or collector device something simular to a frensel lense to redirect the solar wind on the sail with a greater force.

SpaceNut · 2005-11-02 12:43:55

We all know how Cosmos 1 failed to make it to orbit due to rocket stage not firing but most have forgoten that the Japanese space agency did get a sail to orbit but that was over a year ago and we have heared nothing of it since.

Japan Deploys Solar Sail Film In Space

Of course nasa has been working on them for some time as well:

Solar sail completes first crucial tests

SpaceNut · 2005-11-07 09:59:28

More work as done by Nasa:
NASA ground-tests solar sails for space

"Blue lights beneath the system help illuminate the four triangular quadrants of the solar sail developed by ATK Space Sysems of Goleta, Calif.
The solar sail and boom system developed by L'Garde Inc. of Tustin, Calif., is fully deployed during testing. "

Marshall Space Flight Center engineers and their industry partners have finished ground tests on a pair of futuristic solar sails that one day could push spacecraft around the solar system with nothing but sunlight.

Austin Stanley · 2005-11-15 11:03:46

Speed is all relative, deploy a very large sail close to the sun and deep inside it's gravity well, and you could get going very fast indeed. I read a book about interstellar travel that postulated some systems that could get up to .2C

That close to the sun you get alot more light pressure, and you may be able to get some slingshot effect as well. If you deploy a large static mirror to augment the Sail, your acceleration could potentialy be more limited by the rate you wished to accelerate at then what you could do. Prolonged 9G acceleration is possible using this method.

----

Aha! Found the book, It's "Prospects for Interstellar Travel" by "John H Mauldin" if you can find it, pick it up!

::Edit::
ISBN: 0877033447

Stormrage · 2005-12-04 07:17:45

What happens when there isn't enough sun light? Has far has i know sunlight near pluto is faint.

Austin Stanley · 2005-12-06 19:38:46

What happens when there isn't enough sun light? Has far has i know sunlight near pluto is faint.

For interstellar travel you have already built up most of your speed long before you get to Pluto, or infact before you have even passed Mars or Earth's orbit. Accelerating at multiple G's for a couple hundread million kilometers lets you build up LOTS of speed. Stopping at your destination remains a problem, however.

As for in-system travel, solar sails are not realy optimal in the outer solar system. Trips to Mars are and some of the asteriod belt are about the outer limit because after that it takes a LONG time to get to anywhere. If you just wanted to do a fly-by or could aero-capture in one of the Gas giants I suppose a probe could make a dip into the inner system to build up speed first. But I think a nuclear-electric would probably end up being more efficent at this point. It's trip would certianly be shorter.

Dook · 2005-12-06 20:08:40

Stopping at your destination remains a problem, however.

After your 20 year interstellar trip just unfurl the sail and use it to slow you down as you approach the foreign sun.

Stormrage · 2005-12-24 11:16:55

I was just thinking about them i thought about something. Solar Sails are useless. They probably won't be able to carry humans or cargo but there is a good use for them. Intestallar probes like Voyager 1 and 2 (can they actually be called intestallar since they are close to leaving the solar system?).

Computer technology has evolved a thousand times since the 70s. We can get powerful computers in small sizes. This means we can get more detailed information from them then can ever get from Voyager 1 and 2. Also they would exit the solar system way faster. We would have to send two though. The first one would leave behind pieces of it's self at certain points that would receive signals from the second sail enhance it and send it back to earth.

By the way The Planetary Society are trying again with their Solar Sail. I hope it works. They just need $4 million now.

http://www.planetary.org/programs/proje … 51202.html

GCNRevenger · 2005-12-27 08:26:14

The computers and electronic subsystems already don't take up much mass and aren't really the problem. The real killers are the rest of the vehicle...

-the structure its built out of
-transmitter capable of interstellar communications
-gyroscopes/fuel for effecting attitude control
-the real biggie: enough power for ~50 years of operation
-particle impact shield for the probe chassis

...And everything built sturdy enough enough to resist 40 years of C-fractional cruise, the early and late part of which has to go through the Ort Cloud of Sol and the target star system.

A new breed of RTG generator or a highly "storable" superlight nuclear fission plant, neither of which will be light weight, would be a must since regular RTGs don't have that kind of service life.

I also bet that regular radio transmission will be too slow, and an interstellar probe would need a laser transmitter, which is itself going to be heavy and power hungry.

Stormrage · 2005-12-27 10:03:30

The computers and electronic subsystems already don't take up much mass and aren't really the problem. The real killers are the rest of the vehicle...
-the structure its built out of
-transmitter capable of interstellar communications
-gyroscopes/fuel for effecting attitude control
-the real biggie: enough power for ~50 years of operation
-particle impact shield for the probe chassis
...And everything built sturdy enough enough to resist 40 years of C-fractional cruise, the early and late part of which has to go through the Ort Cloud of Sol and the target star system.
A new breed of RTG generator or a highly "storable" superlight nuclear fission plant, neither of which will be light weight, would be a must since regular RTGs don't have that kind of service life.
I also bet that regular radio transmission will be too slow, and an interstellar probe would need a laser transmitter, which is itself going to be heavy and power hungry.

The sail can be made out of Carbon fibres. They are apparently 200 times thicker then normal sail material but due to it's porous nature weighs the same. This will probably stop it from tearing so easily.
About the transmitter why can't we send another probe that will leave bits of it's self that act like a communication array.

JPL made have a website about interstellar probe. All they need it to go is 200 to 400 AU at the rate of 14 AU/yr.

A new breed of RTG generator or a highly "storable" superlight nuclear fission plant, neither of which will be light weight, would be a must since regular RTGs don't have that kind of service life.

I don't get this one. I thought a solar sail just had to unfurl near the sun and it would be going at a high speed and accelerating at 1 millimeter per second per second. So and RTG wouldn't be needed (besides the protestors would ruin suck out all the fun).

Edit: I forgot the JPL/NASA site
http://interstellar.jpl.nasa.gov/

SpaceNut · 2005-12-27 10:13:42

Possibly this technology would work for the Antenna.. "utilize light weight "paint-on antenna" technology on Techsphere airships for communication, radar, remote sensing and other applications."

Techsphere To Fly Antenna Technology On High Flying Airships

GCNRevenger · 2005-12-27 11:49:03

The sail could be strengthend by carbon nanofibers, but I am not worried about the strength of the sail so much, since minor damage to it is unimportant. The real killers are going to be the particle impact shield, and you might need radiation shielding around the electronics too for the superlong soak in the cosmic rays.

Dropping communications bouys doesn't change the total distance needed to communicate with Earth, infact it would only help a little while introducing huge chances of failure, and since there is no sunlight to accelerate or decelerate a sail in the interstellar void, there is no way to "drop" anything. It would need propulsion to slow down and trail the probe, which it doesn't have... direct communication with Earth is the only option.

The JPL probe is for studying the void itself, hence the probe only needs to leave the Heleopause at the edge of our solar system, not to reach another. I am talking about a probe capable of actually reaching other star systems and return knowledge about them on the order of 12 light years distant. This would require a probe to operate for ~70 years at 0.2C cruise speed, the vast majority of which would be without sunlight for propulsion or power. This range would permit missions to the nearest 30 stars from Earth.

The RTG power plant isn't to provide electricity for propulsion, its for providing electricity to operate the probes' electronics. An RTG is a "nuclear battery," and is used on all probes that do much of anything beyond our asteroid belt. If we can't learn to deal with the eco-wacktivists, then we might as well give up on this "space" business and consign ourselves to go extinct when the Sun goes supernova. They've already started preaching against fusion!

The trouble is, the Plutonium fuel has too short of a half-life to support a 70 year mission, and so either a different medium-lived nuclear fuel would be needed that you would need alot more of it, or else you would need a genuine fission reactor. RTGs have the annoying drawback that they can't be throttled or shut down, but a fission reactor can, and if you need it to run a long long time you just add more Uranium.

The fission plant also offers one big advantage, that if it were built with a "surge" mode or a short-term high-power storage system (maybe have attitude gyros perform double-duty as flywheels?), it could pump alot of power into a transmitter for sending data home to Earth. Another option, which I am not too confidant about, would be to not power the probe during the cruise phase at all, and "paint" a portion of the sail with thin-film (like gallium arsenide cells) photovoltaic cells and just hope the thing "wakes up" at its destination after being frozen at -270C for three quarters of a century.

Current computer chips, by the way, can't... developing ones that can (and be able to handle 70 years of cosmic rays) might be hard if they are going to be relativly fast by today's standards. And they will need to be, since this probe will absolutely have to be able to carry out its entire mission without direction from Earth due to the communications lag (24 years round trip), so some fairly sophisticated intelligence would be a must. High-performance computing would be useful to effect highly efficient data compression too for communication.

The problem with using the sail as a giant communications dish is that its the wrong shape as its perfectly flat, and communication with radio I think might be off the table. A laser would have lousy energy efficiency compared to a microwave generator, but much more of that energy would actually reach Earth. The laser could be useful for the probe too, to aquire spectroscopy and range/topography data about targets of interest.[/i]

Stormrage · 2005-12-28 12:03:45

Well the nearest solar system is Alpha Centauri is 4.36 light years away it will only take 21.8 years at 0.2 C. The mission will last about 45 years which is lower then 70. The half life of Plutonium is 87/88. Thats more then enough for the trip to α Centauri. But getting 0.2 C is really hard so we do need laster longing fuel. Plutonium 239 and Uranium 233 last long enough are they good candidates?
Or we could just bypass the fuel problem by increasing the efficiency. According to Wikipeida most RTGs have an efficiency of 3-7%. If we can increase it more we will solve the fuel problem and we can use less of it

By the way we really don't have to worry about Ecowarriors. Yes they will cause a fuss but they can't do much to stop it going. Most people don't give a shit about space. You just have to tell them even in the worst case secnario there won't be anything dangerous.Besides NASA,ESA and othe space agencies are government run not companies who need to keep a good public image.

The computer chips be covered with radiation shielding polyethylene.

Plastic is an appealing alternative: Compared to aluminium, polyethylene is 50% better at shielding solar flares and 15% better for cosmic rays.
That's how Shielding Project researcher Raj Kaul, working together with Barghouty, came to invent RXF1. RXF1 is remarkably strong and light: it has 3 times the tensile strength of aluminium, yet is 2.6 times lighter - impressive even by aerospace standards.
"Since it is a ballistic shield, it also deflects micrometeorites," says Kaul, who had previously worked with similar materials in developing helicopter armor. "Since it's a fabric, it can be draped around molds and shaped into specific spacecraft components." And because it's derived from polyethylene, it's an excellent radiation shield as well.
Some "galactic cosmic rays are so energetic that no reasonable amount of shielding can stop them," cautions Frank Cucinotta, NASA's Chief Radiation Health Officer. "All materials have this problem, including polyethylene."

They've already started preaching against fusion!

Here is a qoute from Men In Black that describes Human beings.

A person is smart. People are dumb, panicky.

GCNRevenger · 2005-12-28 12:51:05

I'm thinking about a one-way trip at the maximum practical solar sail speed to the nearest thirty stars using the same (or similar) model of probe, which will require a range of about 12 light years or a ~65 year transit time followed by a five year science mission, for a total of 70 years of operation. Call it 100 years and you only need to reach ~0.12C. The first few years and the last five will require moderate and high power outputs respectively for attitude adjustment (gyros, start and finish) and sensors/transmitters (spectrometers, cameras, laser etc).

The problem with choosing a nuclear fuel for an RTG is that it must have a fairly short half life in order to decay quickly enough to make power, but slow enough so that most of it is retained over the 70-100 year mission life. It must also be able to yeild an insoluble ceramic for launch safety, and preferably be only an alpha emitter. Isotopes with superlong half lives like Pu-239 or U-233 decay too slowly to make practical RTG fuel, but I am sure fuels do exsist with half lives ~500-1000yrs. Making an RTG more efficient is also not very realistic, since the only way to squeeze a much higher efficiency is to use moving parts rather than solid-state thermocouples. Thermocouples have the big advantage of operating for very, very long times reliably, and are probobly the only option for cruise-mode power for an RTG or fission.

In any event, RTGs probobly don't have enough power output to operate a transmitter strong enough to reach Earth from 12 light years away. Cassini, which has the biggest arrays of RTGs yet flown, will produce a mere half a kilowatt or so by the end of its service life. For power, this leaves three options:
-RTG for cruise only with solar at destination (solar pannels survive?)
-All solar, hoping that the vehicle survives unpowerd (unreliable)
-Nuclear fission with low-power and high-power modes (heavy)

That sounds like good impact armor, but can it stand up to dust grains traveling 0.1-0.2C? And, since the chips will have to soak in the radiation for a very long time then the corresponding dose is higher too, requiring really good shielding. How much will it weigh? And, will these superhigh energy cosmic rays be a show-stopper? Computer chips being relativly light weight, redundancy with automatic failure-bypass would increase chances.

...And yes, they have started to preach against fusion. The Sierra Club in Canada lobbied against the Canadian siting for an experimental tokamak reactor that is supposed to resemble what a real power plant would be like. Their reasoning? The slightly radioactive Trintium (Hydrogen-3) byproduct and the reactor vessel/shielding becomming slightly "hot" from the neutron flux. Pathetic.

Austin Stanley · 2005-12-29 01:19:13

GCRN's right after propulsion, reliability is the #1 problem for an interstellar spacecraft. Face it, we have a VERY hard time building things right now that can last for 50+ years. Much less a century or more.

In my view, some sort of hibernation for the spacecraft only makes sense. If we are still talking about the mirror driven solar salior I was talking about before, than there really isn't anything for the craft to DO for all that time it spends in deep space. Interstellar void is just that, void. There really isn't anything intresting that we would want the probe to look at untill it starts to get fairly close to it's destination. So having sensors and electronics on and transmiting data back realy doesn't make any sense, and would add enormous amounts of mass. And communication to the craft is likewise pointless since the solar sail would have no ability to manuver untill it began to reach it's destination, and it's ability would be limited even then.

Now if we are talking about a more conventional probe, powered by a high-tech fusion engine, the answer becomes much simpler. The engine will have to fire for a signifigant portion of it's journey, during which it will have ample excess energy to spend on heating, sensors, and communication. Keeping such an engine "idling" during the transit would not consume a great amount of fuel in comparision to the amounts it would spend during the propulsive parts of it's mission.

-----

As for how to acomplish a hibernation, well I have no easy answers to this. But since we are no where near ready to build an interstellar probe, we have some time to solve the issue. However, I think solar power will have to be used to some extent, since it is the only power source we have that will be able to able to go from passive to active and warm up other more powerful sources, such as a nuclear reactor.

-----

Another issue is the targeting of the probe. If hitting a target inside our system is difficult, hitting another STAR is quite several orders of magnitude more difficult. Stars move as well you know, some quite rapidly. LHS 52 is approaching us at ~300km/s. Any stellar probe, which most likely can only manuver during the opening stages of it's journey, may have a hard time indeed hitting such a distant target.

GCNRevenger · 2005-12-29 11:34:32

Who says we can't do this today? I didn't say it would be easy, but the technology is aproximatly available right now if we put some effort into it.

A high-energy fusion drive has the simple drawback that it is going to be rough on its componets, while a solar sail with few/no moving parts and no high-temperature systems should be far far easier to make reliable. The high temperatures and neutron flux associated with a fusion reactor and its magnetic "nozzle" seems like it would be difficult to make it run for tens of years.

My big questions are:
-Can any probe made of any material launched by today's rockets survive 0.1-0.2C flight with the risk of dust impacts for ~100yrs? Is this a show stopper? Minor damage to the sail from debries impacts shouldn't be a big problem, and perhaps the sail could be retracted during cruise, but this would present a failure mode at the destination.

-I am fairly confidant that multiply redundant computer systems could survive the radiation soak; include half a dozen or more complete computer systems, any of which can use eachothers' componets. The question here is software, can it be made "smart" enough to return information well enough automatically to be worthwhile?

-Communications: are any available laser or phased array microwave transmitters powerful enough and accurate enough to send useful amounts of information back to Earth without an unreasonable power or mass demand?

-Navigation: can we "hit" another star accuratly enough such that the sail probe could decelerate at least into a very excentric orbit around the target star? Considering that the acceleration near the end of the probes' departure will be small, which would be ideal for fine course correction.

No chemical or mechanical energy storage mechanisms exsist that can be reliably switched on after a 100yr soak in the cosmic rays and ~3K temperatures, some sort of low power source would be required to operate the probes' attitude control, starfinder, and at least minimal computing power as it aproaches the target star system. Solar arrays would need a really large area to be able to operate at all the edge of a star system.

For this reason some sort of nuclear power is probobly nessesarry, and if you have nuclear power then you can power the probe through the cruise phase at least minimally. I think that this might be important for onboard self-help systems to keep the probe in working shape through the cruise phase.

Also, due to the extreme distance from Earth, a great deal of power is needed to operate a transmitter able to reach ~12 light years. This probobly means that RTG power for the whole mission is out.

This narrows down the power options to:
-RTG cruise with solar at destination
-Nuclear fission throughout

Nuclear reactors can, in theory, be built with a fairly high level of reliability: a core cooled by liquid metal feeding a bank of thermocouples and radiators, pumped by a combination of convection and/or cycling electromagnets, would have no solid moving parts at all except for the core control mechanism which is outside the core and would not have to move much. Concerns here are the switch for the magnetic pump, the core control mechanism, and damage to the cooling radiators (particular a coolant leak).

If a reactor could be operated by convection alone at very low power levels, that would really help, since the electromagnetic pump (and its switch) would only have to operate for the years at the destination. I am not overly worried about the control mechanism, since all thats needed is rotary motion, and then only very very slowly except for a low/high power mode switch.

The other option, a long-lived RTG for cruise coupled with solar arrays for science/communications power has some advantages and disadvantages: solar arrays are able to provide more power for less mass then a multi-tonne reactor (which runs ~5-6MT for 100kWe), and RTGs are the most reliable portable power souce available. However, solar arrays might have to be articulated to point at the destination star, which presents a pretty serious failure mode. Will the deployment and aiming system work after a century at 3K?

Or, would simply painting part of the sail with thin-film cells (or its own mini-sail deployed at destination) and skip articulation be practical? There is also the concern that the cosmic radiation will damage the cells, which is a question that must be addressed before relying on them.

An idea about the antenna system, could painting the sail with flat antennas and operating them as a phased array be power efficent enough? Certainly a phased array several kilometers across could generate a very focused microwave beam and could point it at Earth without moving parts even if the sail isn't. The big question mark there is how does the power bill stack up to a laser transmitter?

Another thought, if its not practical to operate a nuclear reactor at any power level for the whole cruise, an RTG could be used to provide startup power, but the reactor by itself is going to be pretty heavy. Maybe too heavy.

SpaceNut · 2005-12-29 14:18:30

The combining of some systems such as the antenna and solar cells as well as the sail seems possible. This is the work that is ongoing for In-flight demonstration of innovative combined antenna/solar array

I agree that in cruise mode once the solar wind is no longer boosting the speed that the sail should be retracted and that the sail upon entering the target solar system should be able to do this over and over again until it slows down enough to go into orbit about its sun.

GCNRevenger · 2005-12-29 15:09:35

Retracting the main sail might be awfully hard, particularly if it is spin-stableized, and make the thing light weight. Total mass is absolutely critical to keeping mission times under the century mark, and the mechanism to retract the sail will have to work perfectly after 100yrs at three Kelvin. The easiest way to maximize the probe's chance of survival is to minimize as many mission-critical mechanical componets as possible. Eliminating a "roll up" system and making the sail perminantly deployed is probobly a good way to save mass.

Come to think of it, the high mass that a nuclear reactor, even designed to operate only ~5-10yrs, will probobly be untennable without a sail of unrealistic proportions. The 100 kilowatt SP-100 reactor would clock in around ~5MT, which will weigh as much as most of the rest of the probe, sans sail. Closer to 6-7MT with extra Uranium and redundant cooling systems.

It has absolutely got to weigh as little as possible, which probobly means that the nuclear reactor is too heavy. This leaves us with only one option, a long-lived RTG coupled for cruise with solar cells for mission power.

The question mark then is how to deploy the solar cells? Paint them on the sail and design an electrical bus that can handle the changing load? Or paint them onto a deployable boom and have it deploy by spring loading or inflation so it remains protected during cruise? To make sure the power supply is uniform, some sort of power storage device will be needed that can survive the 100 year soak. A flywheel would be high on my list since they won't corrode like batteries nor need a radiation-sensitive membrane like fuel cells.

Or stick with the traditional mechanical deployment and articulation, and hope that the thing works after 100 years in the cold soak better than Galileo's antenna worked after five?

One idea to add, if the solar cells are light enough, they could perhaps generate enough electricity to operate a high-Isp ion engine for course correction?

Or suppose we go all out and build a massive sail so that the probe can be equipped with a fission reactor and sail retraction mechanism, it could use its ion engine to correct its trajectory if it were off course and would miss the target star system alltogether.

As far as antennas go, the only practical way to have one big enough to reach Earth would be a phased array antenna painted onto one side of the sail, which permits you to have an array measured in square kilometers, rather than meters if it were a part of the solar arrays.

Edit: If you want to stick with plain old Pu-238 for RTG power, and just pack lots of it so you have some left by the time you reach your destination, then you are going to have excess power during the cruise phase. Just how much thrust do you really need to make course corrections if you have ~50 years of firing time?

With an extremely (I'm not kidding, something flashlight sized) small ion engine of some kind firing for a very, very long time could give the vehicle a substantial "nudge" I would think. This would require attitude control and starfinders to keep working throughout the cruise phase however.

Perhaps the ion engines could be employed in clusters to effect ultraslow/ultrafine attitude control too.

GCNRevenger · 2005-12-29 20:48:53

Yes, seeing it come together...

A large solar sail (kilometer scale) carrying a probe weighing in around 5-10MT launched aboard the big SDV rocket and set on an escape trajectory tward the Sun. An adapter/bus would guide the sail on the proper trajectory after EDS burnout/seperation. Nearing the sun, the bus would provide last-minute guidence update and seperate, then the sail would deploy via inflatable booms lined with a polymer that hardens under UV radiation (already tested). It would then leave the Solar system at ~0.12C and head to the target star system.

Enroute, the RTG will be producing more power then needed for navigation, which will be fed to very small super-reliable ion engines to effect limited course correction as needed to increase the odds of "hitting" the target star system. Fuel might be in the form of Cesium or Mercury instead of the regular Xenon or Argon to minimize the chance of loss via leakage. Upon reaching the destination system, the vehicle would decelerate using the stars' light and enter an orbit around it to begin a ~5-10yr study of the system.

Power would be by a "jumbo" RTG with extra Plutonium-238 tailored to provide minimum power for the probe to navigate and run gyroscopes. Mission power would be provided by thin film solar cells "painted" on the sail, and current moderated by using the gyroscopes as a storage buffer.

Communication would be effected by a phased array antenna created by "painting" antenna nodes on one side of the sail to return data, with the antenna doubling as a radar array for locating bodies not visible by camera or for radar mapping of bodies of interest.

The vehicle would be controlled by a fairly sophisticated computer system with multiple backup processors, storage systems, and software where all componets are regularly checked for health and damaged componets bypassed. The computers should be smart enough to guide itself to targets, catagorize and employ proper instrumentation on bodies of interest, and retain enough processing power to operate the phased array antenna.

The "nose" of the vehicle would be coverd with a thick plate of impact-resistant material for blocking C-fractional dust particle impacts, with boron-doped polyethylene or hydrogen-doped carbon nanofiber shielding for sensitive electronic componets. No componet on the vehicle should have integrated circuts locally except the main computer wherever possible, with cameras and star trackers (which will be redundant) having their own shielded casings. Wiring to the solar cells and antenna arrays would multiply redundant, and the sail itself would be strengthend with carbon nanofiber to minimize the chance of major damage. If possible, sail wiring might be made with superconducting wire, if it could be kept cool enough to operate, to hold down system mass.

Edit: Radiation testing could be done by blasting the probe with a particle accelerator, which could generate the same dose of radiation as a 100yr cruise in a shorter amount of time. Zap the thing and make sure it keeps on ticking.

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#1 2004-08-12 17:41:41

Re: Solar Sails

#2 2004-08-12 18:53:29

Re: Solar Sails

#3 2004-08-13 01:33:59

Re: Solar Sails

#4 2004-08-13 05:54:47

Re: Solar Sails

#5 2005-11-02 00:36:18

Re: Solar Sails

#6 2005-11-02 11:38:48

Re: Solar Sails

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Re: Solar Sails

#8 2005-11-02 12:43:55

Re: Solar Sails

#9 2005-11-07 09:59:28

Re: Solar Sails

#10 2005-11-15 11:03:46

Re: Solar Sails

#11 2005-12-04 07:17:45

Re: Solar Sails

#12 2005-12-06 19:38:46

Re: Solar Sails

#13 2005-12-06 20:08:40

Re: Solar Sails

#14 2005-12-24 11:16:55

Re: Solar Sails

#15 2005-12-27 08:26:14

Re: Solar Sails

#16 2005-12-27 10:03:30

Re: Solar Sails

#17 2005-12-27 10:13:42

Re: Solar Sails

#18 2005-12-27 11:49:03

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#19 2005-12-28 12:03:45

Re: Solar Sails

#20 2005-12-28 12:51:05

Re: Solar Sails

#21 2005-12-29 01:19:13

Re: Solar Sails

#22 2005-12-29 11:34:32

Re: Solar Sails

#23 2005-12-29 14:18:30

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#24 2005-12-29 15:09:35

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#25 2005-12-29 20:48:53

Re: Solar Sails

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