Solar Sail Speeds

EarthWolf · 2005-03-25 07:21:28

Hello,

From what I saw online, the Japanese space agency had launched a prototype solar sail, last year. ( I think ) Does anyone know how much faster a solar sail spacecraft would be than a conventionally propelled one?

Cordially,

EarthWolf

GCNRevenger · 2005-03-25 09:44:28

None. It would actually be much slower, or at least as long as you were being pushed only by UV/Vis-to-IR sunlight.

dicktice · 2005-03-25 10:26:14

Aw, come on, GCNR: Constant acceleration vs burn-and-then-coast the rest of the way, not faster?

GCNRevenger · 2005-03-25 11:03:40

Thats right actually, you would get there faster, since you don't waste months and years ever-so-slowly climbing in and out of orbit.

A solar sail has such extremely low acceleration, it would literally take it years to get anywhere.

dicktice · 2005-03-25 14:47:31

I wouldn't limit myself to only one form of propulsion. My imaginary solar sailing ship would have the equivalent of a steam engine and paddle wheels, to get in and out of port. And it would open up the twin hemispheres of space above and below the ecliptic. Don't tell me that they are of no interest.

GCNRevenger · 2005-03-25 16:59:25

That won't work very well. A solar sail vehicle relies on the rest of the ship being as light as possible, but if you are using reaction mass engines for orbital insertion/departure, then you will be lugging lots of fuel & engine weight that you otherwise wouldn't be. The size of the sail you would need to effect much bennefit starts to become very large in that case, and infact would slow you down, not speed you up, because of its weight.

Solar sails are good for one thing and one thing only, and that is to launch light weight things into the outer solar system, or even out of the solar system entirely. Otherwise, a sail pushed by sunlight is pretty worthless. You might as well use an ion engine instead.

There are a huge multitude of ideas for propulsion schema that beat The Rocket Equation out there, tons and tons... physists love that kind of thing no matter how hair-brained it sounds, and will yell it from the rooftops to the gullible media for attention (and funding) for it... Trouble is, most of the ideas are bad.

dicktice · 2005-03-25 23:17:15

All it takes (like true love) is only one good idea per problem, but for it catch on, the "gullible press" will need to be cuddled and coddled into following progress, any progress at all, re. solar sails, ion engines, tether, etc. propulsion schemes. The latest, on cold fusion, finds instant coverage (whatever you may think about its plausibility) because the press has been primed and ready for the next disclosure, such as New Scientist for instance. By the way, I see solar sails, in addition to long term transport, as backup propulsion, not necessarily crewed, manufactured in space from concentrate and deployed to whatever extent required in an emergency and, of course, disposable.

GCNRevenger · 2005-03-25 23:30:08

Even then, as a backup system it would have to be extremely light weight to not ruin the ships' efficency too much. If it were very light, it wouldn't offer much push, and it would be pretty useless on a heavy reaction-mass ship. Since the ship will also be traveling at high speeds, the solar sail probobly wouldnt' be enough to effect much in the way of a course correction. The ship will also probobly be tailored for short transit times, and hence won't have supplies for the multi-year trip a solar sail would require.

A better emergency backup system would just be to send a rescue ship.

Austin Stanley · 2005-03-26 03:11:58

While I do agree with the assement that Solar Sails are so slow as to be completely unusable as either a primary or a back-up method of transportation for manned vessles, I do not think that the same necessarily applies to unmanned vessles. Which lack the strict time constraints of manned vessles.

A solar sail has the extream advantage of not carrying it's fuel source, this makes extreamly long durration flights possible. For example a mission to explore the asteriod belt would require a vehicle which could manuver for decades. No conventional engine can provide this duration of performance, only some sort of ion engine would come close, and even it would eventualy run out of reaction mass.

Another possible example is as a reusable ferry for cargo to Mars or some other destination. Now while it could take 5 years or more for the supplies to arrive, the vessle would be unbeatable in it's simplicty and reusibility. A NTR or Chemical ferry would require large amounts of refuling at either ends and would be much larger and much more complex. A NEP (ion drive) vehicle would also be much larger and more complex, have little to no advantage in speed and would still eventualy require refuling of it's reaction mass. Both sorts of vehicles would probably not be able to slow to Mars or Earth orbital velocity requiring a there cargo to make a tricky high speed orbital rendevous with little option for abort if something when wrong.

I guess in the end what any engine decision comes down to is the cost to deliver a cargo to some destination. While alot of research still needs to be performed on solar sails, they potentialy could perform quite well in this catagory. A solar sail has the potential to be a very cheap and reliable method of transport. No exotic or hazerdous materials are required (xenon, plutonium, uranium) neither is any complex machinery (reactors, turbopumps). The only disadvantage is there speed.

And speed is realy only a question of sail size/mass versus the size of your cargo. If you can get the sail light enough, make it large enough, and keep the cargo resonable you could realy zip. Indeed, I once read a study about a interstelar probe which launched near the sun which developed several G's of exceleration for an extended period of time.

There are also solar dynamic vehicles which operate in a similar manner to NTR, using large mirrors to reflect sunlight to heat the propellent. They can supposedly achive similar performance, but are slightly more restricted in there use (you can't use them in a planets shadow obviously).

dicktice · 2005-03-26 21:23:26

I seem to remember sugesting using the solar sail itself as such a mirror. I'd forgotten. Another variation on the theme was discussed last year, I think, based upon hydrogen ion cloud formation about the space vehicle, contained by an electromagnetic field. Needs to be updated by (?) of us, before we complete the thread, now that it's been brought up again, eh?

RobS · 2005-03-26 23:12:28

In the Case for Mars by Robert Zubrin, page 243, he describes a solar sail of one square kilometer area and 10 microns thickness (1/4 the thickness of a trash bag) massing ten tonnes. He says at Earth's distance from the sun the sail would experience 10 newtons or 2 pounds of force on it and would be able to accelerate by 30 km/sec over a year's time. If it had a ten-tonne cargo, the acceleration over a year's time would be 15 km/sec. That's about the delta-v needed to go from medium Earth orbit (you can't start in low Earth orbit; too much atmospheric drag ona 1 sq km sail) to Mars orbit in about a year. Thinner sails than 10 microns should be possible, too.

Regarding the idea of accelerating the entire vehicle with a chemical "kick" stage, even if the kick stage did its thing and dropped away, it might not be able to help a solar sail much. The problem is that a 1 sq km sail, to be light, has to be rather flimsy. If it's designed for two pounds of solar thrust, 2,000 pounds of chemical thrust might tear it apart. If it's designed for 2,000 pounds of thrust, it may be rather heavy to serve as a solar sail.

-- RobS

dicktice · 2005-03-27 19:31:28

This is the other form of "Solar sailing" I vaguely remember posting some time ago (updated here) which would derive propulsion from Solar Wind protons, rather than Solar radiation photons.

Mini-magnetospheric plasma propulsion
WikipediaMini-magnetospheric plasma propulsion.
Mini-magnetospheric plasma propulsion (M2P2) is a form of spacecraft propulsion, a way to make a magnetic sail. A major problem with magnetic sails is that they would have to be superconductive. To circumvent this problem, NASA has attempted to develop a system using a conductive plasma constrained by the magnetic field, a sort of synthetic magnetosphere.
This mechanism creates an electromagnetic loop or mini-magnetosphere extending out from the spacecraft, using a cloud of plasma to conduct the current to create the magnetic field. The solar wind is deflected (being made of protons, it has mass) and the reaction accelerates the spacecraft. The thrust can be in any direction at right angles to the solar wind, allowing efficient changes of orbit.
One advantage is that no reaction mass is depleted or carried in the craft. The "fuel" is the gas needed to maintain the cloud. It therefore can generate thrust for long periods of time without refueling. One can calculate a "specific impulse" for this system by computing the amount of "fuel" consumed per newton of thrust. This is a figure of merit usually used for rockets, where the fuel is actually reaction mass. The "specific impulse" of such a system is about 200 kN·s/kg (200 times better than the space shuttle main engine). The system requires on the order of a kilowatt of power per newton of thrust, easily supplied by a nuclear reactor.
A unique advantage, not shared by magnetic or solar sails, is that the sail spreads automatically as the solar wind becomes less dense. In simulations, the system generates the same thrust anywhere within the heliopause. The solar and magnetic sails have a thrust that falls off as the square of the distance from the sun.
Another unique advantage is that the system requires no large mechanical system to catch solar protons or maintain the magnetic field. This reduces its total mass.
The basic mechanism looks like a coffee can with both ends open. Gas is emitted from a valve in the coffee can. The coffee can confines the gas long enough for some electronics to strike an arc through the gas. Then a low voltage (low electrical pressure) high-current (lots of electrons) electric current is pushed through the arc. The magnetic field from this current "traps" the plasma of the arc. The conductive plasma finds it hard to move in the magnetic field because whenever it cuts the magnetic field, eddy currents form opposing magnetic fields and stop the motion. The magnetic field naturally wants to expand. This causes the arc to grow, and confines the ionized gas in the arc. This process is called "blowing the arc."
Blowing the arc is something like blowing a large soap bubble. The arc is fragile. If the electric current at some point becomes too low, the magnetic field decreases, gas deionizes and escapes, and the current and magnetic field decrease even more.
A tank of gas is required to replace the ions of the cloud that leak from the magnetic field. The prototype uses argon for the plasma, but the researchers hope to develop helium plasmas as the technology improves. An argon plasma has more massive ions, which are easier to contain because they move more slowly for a given electric current and magnetic field. Radon gas would be still more massive and would have at least a slight tendecy to be self ionizing. Helium would mass less, and therefore might yield more velocity per kilogram. However, more of it leaks from present designs.
Electric power is required to keep the cloud ionized, and keep the current flowing. The magnetic field and current requirements are small enough that they could be powered by solar cells on unmanned vehicles.
For mission capabilities and maneuvers see magnetic sail. Magnetic sails are not at all like rockets. They can maneuver using planetary magnetic fields and plasmas other than the solar wind.
A prototype is being developed at the University of Washington (http://www.ess.washington.edu/Space/M2P2). It has been successfully tested on Earth, but not deployed in space. Also, a beam-powered variant called MagBeam.
(http://www.ess.washington.edu/Space/magbeam/)

srmeaney · 2005-03-29 07:26:12

The maths for a solar sail is:

[Imperial] Pressure(solar)=2.5lb/square mile
[Metric] Pressure(Solar)=0.4378kg/square km

Force=Pressure(solar)*Area(sail)
Force/Mass(craft)=acceleration(craft)

SpaceNut · 2005-03-29 08:50:45

And the object is to get something for nearly nothing in terms of propulsion speed.

karov · 2005-03-29 09:48:09

Google for "dusty plasma solar sail"

GCNRevenger · 2005-03-29 10:18:47

The maths for a solar sail is:
[Imperial] Pressure(solar)=2.5lb/square mile
[Metric] Pressure(Solar)=0.4378kg/square km
Force=Pressure(solar)*Area(sail)
Force/Mass(craft)=acceleration(craft)

At what distance from the Sun?

SpaceNut · 2005-04-07 12:14:26

NASA's Marshall Center to Begin Test of 20-Meter Solar Sail Technology That Could Use Sun's Energy for Future Space Missions

NASA engineers and their industry partners are preparing to test two 20-meter (66-feet) long solar sail propulsion system designs -- a critical milestone in development of a unique propulsion technology using the Sun's energy that could lead to future deep space missions.
The systems tests, scheduled for April through July, will be conducted at the NASA Glenn Research Center's Plum Brook Station in Sandusky, Ohio.

srmeaney · 2005-04-08 04:42:50

At what distance from the Sun?

At Earth Orbit. Solar Pressure drops off rapidly by the time you hit the Asteroid Belt. It's only useful for sending stuff to Mars.

If it is viable, someone is downplaying it's usefulness.

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#1 2005-03-25 07:21:28

Re: Solar Sail Speeds

#2 2005-03-25 09:44:28

Re: Solar Sail Speeds

#3 2005-03-25 10:26:14

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#4 2005-03-25 11:03:40

Re: Solar Sail Speeds

#5 2005-03-25 14:47:31

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#6 2005-03-25 16:59:25

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#7 2005-03-25 23:17:15

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#8 2005-03-25 23:30:08

Re: Solar Sail Speeds

#9 2005-03-26 03:11:58

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#10 2005-03-26 21:23:26

Re: Solar Sail Speeds

#11 2005-03-26 23:12:28

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#12 2005-03-27 19:31:28

Re: Solar Sail Speeds

#13 2005-03-29 07:26:12

Re: Solar Sail Speeds

#14 2005-03-29 08:50:45

Re: Solar Sail Speeds

#15 2005-03-29 09:48:09

Re: Solar Sail Speeds

#16 2005-03-29 10:18:47

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#17 2005-04-07 12:14:26

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#18 2005-04-08 04:42:50

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