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NASA Chat: Sailing Among the Stars
August 19, 2010

Blue tinted image of a solar sail A blue-tinged image of a fully unfurled solar sail. (NASA/MSFC/D. Higginbotham)
Artist concept of a solar sail in space Artist's rendering of a four-quadrant solar sail propulsion system, with payload. NASA is designing and developing such concepts, a sub-scale model of which may be tested on a future NMP mission. (NASA)

More Information
NASA Link: Nanosail-D
Gallery: Nanosail-D
Image: Solar Sail Concept
Wikipedia: Solar Sail
This fall, NASA researchers will move one step closer to sailing among the stars.

Engineers at NASA have designed and built NanoSail-D, a "solar sail" that will test NASA's ability to deploy a massive but fragile spacecraft from an extremely compact structure. Much like the wind pushing a sailboat through water, solar sails rely on sunlight to propel vehicles through space. The sail captures constantly streaming solar particles, called photons, with giant sails built from a lightweight material. Over time, the buildup of these particles provides enough thrust for a small spacecraft to travel in space.

One of NanoSail-D's several mission objectives is to demonstrate the capability to deploy a large sail structure from a highly compacted volume without recontacting the spacecraft. The mission also will demonstrate and test the de-orbiting capabilities of solar sails.

NASA hopes to one day use thin membranes to de-orbit satellites and space debris. Finally, engineers hope to successfully demonstrate solar sailing. While NanoSail-D's relatively low altitude means drag from Earth's atmosphere may dominate any propulsion from the sun, the nanosatellite remains a small first step towards eventually deploying solar sails at higher altitudes.

On Thursday, Aug. 19, principal investigator NanoSail-D, Dean Alhorn, at NASA's Marshall Space Flight Center in Huntsville, Ala. answered your questions about the NanoSail-D mission and solar sails in general.

More About Chat Expert Dean Alhorn

Alhorn, a NASA Marshall employee since 1991, is an expert in electro-mechanical systems and the principle investigator for NanoSail-D, slated to launch from Kodiak Island, Alaska, no earlier than Oct. 1. Alhorn has prior flight systems experience with the Chandra X-ray Observatory telescope; the Fast, Affordable, Science and Technology Satellite; and the Suppression of Transient Accelerations by Levitation Experiment. Alhorn continues to perform research in the area of solar sail propulsion technology.

He is a native of Albuquerque, N.M., and holds a Bachelor of Science degree in Mechanical Engineering from the University of New Mexico, and a Master of Science degree from the Massachusetts Institute of Technology.

Chat Transcript

Dean: Hi everyone! Welcome to the chat - we're getting everything finalized and will start answering your solar sails questions in just a few moments.

john: image looks like a kite..can you please let us know about that...

Dean: Hi john. It's supposed to look like a kite because it catches solar photons like a kite catches the wind.

Daniel: Is there a scheduled space-test or a planned space-test, if so what is an estimated date?

Dean: Later this fall. Keep checking at http://www.nasa.gov/marshall for status updates.

deejayh: Will NASA offer a website that will allow ground observers to know when it will pass over their location and be in the light of the sun?

Dean: Santa Clara University has a dashboard that's helpful: http://nanosaild.engr.scu.edu/dashboard.htm But I don't think it has the terminator on there - that's what the light of the sun is called.

MDM: Greetings

Dean: Welcome to the chat!

(Moderator Jason): Hi everyone. Welcome to today's chat. We're working to answer your great questions. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

MonkeyLover: What are the dangers of space debris disabling the "sail"?

Dean: Space debris would tear a quadrant, but the sail material is made to survive small impacts.

MonkeyLover: What are the realistic goals for speed of travel as well as longevity regarding the electronics used, and even the unit itself?

Dean: For NanoSail-D, we deorbit in 70-100 days, therefore speed of travel isn't an issue.

Daniel: How much thrust is this expected to give?

Dean: The solar thrust will be swamped by the atmospheric drag.

William_Oglesby: So first question for when this starts... How much thrust do these sails generate and how much can they haul? would it be potentially useful in cheaping the cost of a trip to mars or the moon?

Dean: It all depends on the sail area divided by the mass of the vehicle - this is known as the areal density. The lower the density, the more thrust you can generate.

mikec: How far do you suspect these solar sails will be capable of traveling? Do you see them being implemented for inter-stellar travel, or just within our solar system?

Dean: They're probably just within our solar system for the next decade.

iEvolved: I probably should've read more in-depth about the project, but what is the main objective for the NanoSail-D?

Dean: To demonstrate the ejection of the satellite for another satellite, without recontact, to demonstrate sail deployment, and to deorbit the satellite within a reasonable time.

michael: What are new discoveries of photon behavior?

Dean: That's not my area - I build the units. :) You'd have to ask an astrophysicist!

Daniel: Are you using arogel for the insulation?

Dean: No, no aerogel. It could be used on something else, but not NanoSail-D.

john: are their any videos of how this all works...

Dean: Yes! Try this Web site for video and images: http://www.nasa.gov/mission_pages/smallsats/nanosaild.html.

William_Oglesby: Could you potentially launch a solar sail vehicle from the ISS or would the atomospheric drag escaping LEO make it illogical due to the time nessecary to haul a medium to heavy weight craft out into space?

Dean: ISS is too low of an altitude - needs to be at least 1,100 km.

mikec: Does the current design allow for meneuvering like a sailboat? Are there supplemental thrusters to assist with meneuvering?

Dean: No, and no. We have no ACS control (attitude control). This is a first step.

Quest_1: Why are y'all launching from Kodiak Isalnd, Alaska, of all places?

Dean: We got manifested by the SERB board - Space Experiments Review Board - to be ejected from FASTSAT to launch on the Minotaur launch vehicle.

michael: Why did you build it in that shape?

Dean: The cube set has a defined dimension to fit inside a P-POD. The sail size is determined by the amount of volume.

lostdumb: What is sail material? and total weight of craft?

Dean: Sail material in CP1 - it's a polymer with aluminum coating. Total mass is 3.85 kgs.

MonkeyLover: People are mentioning traveling within our solar system; which is why I was wondering what speeds you feel are within the realm of possibility for these sails =)

Dean: NanoSail-D is small. A larger system might be able to reach the point where Voyager is currently in 10 years.

mikec: If this is to be used to deorbit space junk, will the sail be used as a net to capture these objects?

Dean: NanoSail-D would be a subsystem on a future larger satellite to aid in deorbit.

(Moderator Jason): We're working to get through all of the great questions you've asked us. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

kyler: In terms of accedemics how long does it take to get where you are including pre reqs and or community colledge?

Dean: It took me six years - 4.5 in undergrad and two in graduate school. Don't give up! :)

Daniel: Is it possible to launch from ISS if you launched a vehicle from the ISS and then from there launch the sail with an acceptable price range?

Dean: ISS is too low for sails.

William_Oglesby(Q) If you need to ascend to 1,100km isn't this impractical for use? It needs to be quite large to haul anything major to begin with doesn't it? So You'd have to haul this stuff up on heavy payload rockets which we're short on, and it'd cost a small fortune every time we launched something.

Dean: No, since NanoSail-D is small, small sail vehicles are lighter and don't need as large of rockets. Since they don't require fuel, the overall up mass is less.

john: I watched the video on http://www.nasa.gov/mission_pages/smallsats/nanosaild.html... it's amazing

Dean: Yes, it is. You should have seen it in person!

Dell_Conagher: Will you actually be able to measure the thrust on the sail, or is this more of a test of deployment?

Dean: Test of deployment. We're still too low of altitude. It MIGHT, but it will be hard.

Daniel: If the sail works like a sail, how do you predict the currents used to propel it?

Dean: The solar photons is a constant stream.

AnthonyRusso: As fossil fuels are probably not going to get humans to Mars, do you feel the sail or nuclear energy is the better choice to reach Mars and beyond?

Dean: Yes, sails are a practical method, but not for awhile.

lostdumb: Ah, so you envision every satellite eventually to have one of these attached, to remove satellite from orbit after it servicable lifespan?

Dean: That's a possibility. It's simpler and has fewer safety hazards, as opposed to chemical deorbit.

john: Does this mean that sails fly higher than ISS?

Dean: Yes, to be practical for thrust. For deorbit, any altitude is fine.

john: Of course i would love to see this in person.. how can i see that?

Dean: Unfortunately, we're locked and loaded and ready to be shipped to Kodiak. Best we all have is the video!

MonkeyLover: Beautiful answer. Thanks :) In theory, could a sail be built large enough to haul materials to...oh...say, Mars?

Dean: Yes, solar sail technology is inherently safe, as opposed to a rocket or chemical propulsion.

MonkeyLover: Why do I get the feeling this is some sort of side-project for reaching the speed of light ;)

Dean: This is a real project, which required blood, sweat, tears, and time. Speed of light is unobtainable with NanoSail-D.

lostdumb: If this test is successful, what are future plans for testing other aspects of the technology?

Dean: I'm researching a follow-on concept called FeatherSail.

michael: Do you plan to build a space ship with Nano Sail-Ds?

Dean: It's possible, but no plans for that. We might use the deployment concept for a future project. There was a recent conference on solar sails that I was at recently. Here's http://www.citytech.cuny.edu/isss2010

(Moderator Kim): We're working to get through all the great questions you've asked. Keep them coming! To submit your own question, please type it in the box at the bottom of the window and click the "Ask" button on the right side og the box. Thanks for your patience as we answer your questions.

AnthonyRusso: Is there any nagative to the enviornemtn from using sails at all? Any inherent larger dangers than fossil fuels or nuclear?

Dean: Not that I know of. You still have to have chemical propulsion to get to orbit.

Dell_Conagher: Will the very small amount of atmosperic drag affect deployment, compared to deployment at an altitude that a interplanetary sail would use? Or is the difference pretty negligible?

Dean: Atmospheric drag won't affect deployment of the sails. After deployment, the drag will be greater at lower altitudes. 1,100 kms is a good altitude where the drag is low enough.

carolinad28: How far away from the sun could the sail travel?

Dean: Once it gets going, as far as it wants, although the thrust diminishes the farther you are away from the sun.

MonkeyLover: That was in jest :P The entire "photon-harnessing" idea is fascinating and I'm sure everyone appreciates your effort. Is the "FeatherSail" a smaller/lighter version? What would the advantages be?

Dean: FeatherSail is a preliminary design that should be about 4x the size of NanoSail-D. Advantage is attitude control using sail position.

unity: Is there a "terminal velocity" in space that the NanoSail will reach, much like a falling object in Earth's atmosphere?

Dean: Again, we're too low and yes, there's probably a theoretical limit - not sure what that would be.

William_Oglesby: You said earlier that a larger sail could haul us out to the distance of Voyager in ten years I believe? It's currently around 10,625,447,387 miles from the sun. so lets say 1billion miles a year, 2,739,726 so these sails could haul at an average speed of 114,155mph? really? that's very impressive vs a rocket.

Dean: Yes, because a rocket has only thrust for a short period of time. A sail has a small thrust for a much greater period of time. And, it can pick up speed until the thrust is negligible from the sun.

William_Oglesby: have you considered talking to Elon Musk or Space X about some of these technologies and building them into there spacecraft?

Dean: Elon was all for us launching in 2008, on the 3rd launch of Falcon-1. We even tried to get the second unit on the 4th launch. Unfortunately, the 3rd launch had a failure and never made it to orbit.

unity: Because of inertia, the sail will just keep sailing between stars (points of photonic emission). Is that right? Is it possible to "tack" and use other manoeuvers to get the sail to where we want it to go?

Dean: Yes, you can tack it just like you tack a ship in water.

mikec: does the solar sail have photocells in it to power any onboard electronics?

Dean: Not NanoSail-D, but that's a concept for future designs. The Japanese currently have a sail in space that has solar (photo) cells in the sails.

William_Oglesby: Additionally at the speed I mentioned earlier a trip to mars could be achieved in 17days. but you can't make a return mission with this monolithic energy force can you? or is there a way to use the solar sails in a reversed direction to pull you into the sun?

Dean: The speed - small thrust - is achieved over time and you can return by tacking, like a ship.

Dell_Conagher: Will Nanosail-D be providing science during the time between the deployment test, and the analysis of the deorbiting effects? Or will atmopheric drag start the deorbiting almost immediately?

Dean: It will take some time for the atmospheric drag to start causing deorbiting. We don't have a science instrument onboard.

Daniel: If this were to be used to travel to Mars, how would it land presuming it would be traveling at such high velocities?

Dean: Alternate system for landing is necessary.

carolinad28: how does the sail "maneuver" itself on "incoming traffic"? That is, avoiding collision with other space objects?

Dean: NanoSail-D doesn't have attitude control and can't maneuver. Future concepts will have need of this ability.

(Moderator Jason): We're still working on answering all the questions you've asked. If you haven't seen yours yet, give us a few minutes to get to all of your questions. To submit your own question, please type it in the box at the bottom of the window and click the 'Ask' button on the right side of the box. Thanks for your patience as we answer your questions.

unity: Is it possible to design "sails" out of materials that would allow NASA to "sail" into Jupiter's core, for example, and return valuable data on the way (through?)?

Dean: No, gravity would crush the craft!

lostdumb: Does converting some of the photon energy to electricy reduce the kinetic energy imparted to the sail? i.e. is a sail that has solar cells on it less efficient?

Dean: Converting solar energy to electricity reduces the thrust by about half.

MonkeyLover: 114k MPH! THAT'S what I'm talking about :D If the FeatherSail is larger and more manueverable that seems like an extremely logical solution to our somewhat immediate space-travel needs. What kind of operational longevity do you feel is possible for the units?

Dean: I'd say it depends upon the design and thus the cost. Do you have some spare change? :D I'd love to move out with it.

mikec: Perhaps this was already stated, and perhaps I overlooked it online, but what are the dimensions of the sail, unfolded? And what are the dimensions of the unfoled package?

Dean: It's 10 square meters, about 3.1 meters square and about 100 square feet. The stowed dimensions are 10 cms x 10 cms x 38 cms - - about the size of a small loaf of bread. A detailed fact sheet will be posted soon. http://www.nasa.gov/mission_pages/smallsats/nanosaild.html.

Daniel: How much electrical energy could be gained if using this as a generator of sorts?

Dean: Depends upon the size and efficiency of the solar sail.

unity: Economically, is it possible to get to, say Titan, by sailing out there, placing the craft in orbit through turns of the sail, and then maintain position using the sun's rays rather than expendable rocket fuel?

Dean: Yes, possibly. Sounds like a neat trip. :)

(Moderator Kim): Keep the questions coming! Dean is enjoying the chat.

Daniel: Using electromagnetic pulses to to transfer energy to earth, is it possible that this would be a viable means of energy?

Dean: I don't think so - the amount of size you'd need would be better used for interplanetary travel. Good idea, though!

MonkeyLover: LOL! I've got...$11.45 in my pocket :D Who do I pester to you get you these funds? Let's do it!

Dean: Ask Congress! :)

lostdumb: lol any plans for a 'solar windmill' in the works? since direct electrical conversion by photocells is still ineficient, would a solar windmill be more efficient?

Dean: If you have a chain long enough to reach the generator here on Earth! :)

William_Oglesby: Could you also use some kind of focus like a giant magnifying glass or something that can rotate to control direction of such a craft and even itensify/decrease power easier then just relying on the monolithic direction?

Dean: You don't need monolithic direction - tacking works just fine. There are concepts for beamed energy propulsion, but that's not my area of expertise.

unity: It may be that information like this cannot be shared with this audience, but I'm assuming a sail made of gold foil (extremely thin)-am I correct?

Dean: Gold foil would be too costly. CP1 is the material that's been engineered for this purpose.

lostdumb: Well, i was referring to a solar windmill on a spacecraft, lol

Dean: Ah! That's a good idea. It would take awhile to spin up (pun intended!)

lostdumb: This concept has been around for a long time, good to see it finally being tested :D

Dean: Johannes Kepler thought of it over 400 years ago - before my time.

john: how much it costs?

Dean: Nanosail-D project cost approximately $2 million. That included two units, integration costs, and manpower.

unity: Gold foil might be costly, but, reflectively, wouldn't it work the best?

Dean: Not sure - need to look at the alpha and emissivity parameters.

William_Oglesby: I'm not a big fan of asking congress such things... hmm I'm quite facisnated by the idea now of space X and Dragon getting on with this and using sails to haul themselves out to planets at extrememly cheap costs.. hmmm I dunno, just something to get us back out to the planets and not stuck in LEO. the question would be then what's the smallest cheapest rocket that could get us up high enough to get going.

Dean: I think Orbital has rockets that might do it (Pegasus?) By that, I mean that an Orbital rocket might take a sail into orbit.

carolinad28: how do you keep track of the sail?

Dean: Via ground-tracking.

michael: How would the recent solar activity affect Nano Sail-D?

Dean: More thrust!

Daniel: How much does it cost to build a sail, excluding research money?

Dean: We'll know when we build FeatherSail.

Dell_Conagher: Are there surprising differences between tacking a sailing ship, and tacking a solar sail?

Dean: Yes, no friction from the water. :)

unity: When a much larger craft may demand it, along the lines of the windmill discussion, could a sail-gyroscope be designed?

Dean: Maybe. I can research that. Any more spare change? ;)

lostdumb: The sun doesnt just emit photons, it emits charged particals, any plans to use them to enhance thrust?

Dean: That's a concept some people have looked into.

MonkeyLover: Are there any other uses, that weren't mentioned, you're excited about and can share with us? And thank you for your time and info *high five* :)

Dean: You're very welcome! As to other uses, I'm working on it.

William_Oglesby: Well anyway thank you very much for answering my questions, I'm a highschool artist inspired by science, so If I seemed completely oblivious to obvious things, my apologies, but this is very inspirational, and all about the side of space travel I find facisnating, I look forward to seeing where this goes. If theres anyway I could help out in getting this going let me know.

Dean: Stay in school and learn your math and science - then apply for an internship at NASA. I'm always looking for bright minds!

Daniel: Would we be able to predict flight course well enough to maintain some form of data-communication between earth and the sail?

Dean: Yes.

dood: Is it powered by solar wind or photons? i'm asking because the article mentions photons. Tks

Dean: It's photons - solar wind is the charged particles. It's the absorption or reflection that generates thrust.

unity: Appearance aside, would it be possible to deploy sails on a ship similar in design to the current shuttle and sail about the solar system much in the same way our forebearer explorers did?

Dean: The shuttle is too heavy - the sail would be too big.

carolinad28: Is this sail going to collect any data from space (in addition to its travel data), if so what in particular?

Dean: No science instruments onboard, only decay data.

lostdumb: A keel and a rudder are crucial for a sailing ship to tack, tacking in space looks like it will be more difficult and slower...true or false?

Dean: Mariner-10 proved that a small wing tip would deflect, so yes, sail or rudder would work.

michael: Thank you for your answering my questions.

Dean: You're very welcome - I'm having fun!

john: whats decay data?

Dean: It's the tracking of the orbit as Nanosail-D deorbits.

atmx: Is using of gravitational slingshot useful for this kind of spacecrafts?

Dean: Possibly!

Daniel: Thank you for your time! Is there a spesific website that is dedicated to this topic?

Dean: Try this URL: http://www.nasa.gov/mission_pages/smallsats/nanosaild.html

unity: If I may ask, what comprises CP1? I am curious because it must have awesome reflectivity.

Dean: It's a plastic, like SaranWrap with a thin coating of aluminum on one side. It's 2-3 microns thick.

Dell_Conagher: Can communication signals be bounced off the sail's surface? Would there be anything useful in that?

Dean: Yes - that's an idea in the works.

john: thanks for answering my questions... quite helpfull...

Dean: You're very welcome. I've enjoyed it.

Janis: How are mathematics integrated? I have my degree in mathematics and I'm working on my MS in computer science. I don't know too much about this particular topic, but ever since forever I've hoped to someday end up at NASA.

Dean: The NASA Academy is for graduate students to intern at NASA - or you could co-op. Try this link: http://academy.nasa.gov/

dood: Will it be possible to predict trajectory using software like the Copernicus, or will it be somehow unpredictable?

Dean: We'll look into it!

MonkeyLover: At that thickness (of the sail) what size object would it take to disable the unit?

Dean: Small particles make small holes. CP1 doesn't shred - you'd need an object half its size to create major problems.

Dan_Wade: How will you follow the sail and track it's progress?

Dean: You can try viewing it from Earth - once it's up there and deployed. I'm using government assets to track the sail. Every object in space is tracked.

(Moderator Kim): Thanks to you for the great questions, and thanks to our expert guest Dean Alhorn. Keep checking http://www.nasa.gov/Marshall for the most recent news and status on the upcoming launch of NanoSail-D.

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