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How to Spot NASA's Solar Sail Demonstration Streaking Through the Night Sky (smithsonianmag.com)
138 points by Brajeshwar 27 days ago | hide | past | favorite | 41 comments



Another option for those who don't want to download the app: https://www.heavens-above.com (also works for many other satellites).

Set your location in the upper-right corner, then select the ACS3 on the main page.


The good thing about NASA is that they always also give you the metric measurements (and sometimes, as a bonus, some real-world thing they're comparable to). To quote https://blogs.nasa.gov/smallsatellites/2024/08/29/nasa-compo...:

> From above, the sail will appear as a square, with an area of approximately 860 square feet (80 square meters) – about half the size of a tennis court.

Not bad for a device the size of a microwave...


That is bigger than many city apartments.


Not really... apartments have volume.


Not according to the paperwork I’ve signed. ;)


it's one half of a JWST


Ok but how many school busses is that?


About one medium-sized school bus long on each side.


Or just one square school bus.


about half an olympic swimming pool


I'm going to need that in smoot-manhattans per cubit.


I remember being fascinated by the concept of sailing the sea of stars. Mostly because I read Sunjammer by Arthur C Clarke at an impressionable age lol.

https://fiction.scoutlife.org/the-sunjammer/


Perhaps a really naive question: what can you do with a solar sail in orbit?

I've always heard these as mentioned in the context of very long distance trips (heading away from the sun). But if you're orbiting the earth, how do you take advantage of this? In general, how do you use a solar sail to do anything other than head away from the sun?


The sail doesn't have to be oriented directly perpendicular to the sun. By angling it, you can gain momentum in other directions, just like a sail on a boat doesn't have to push you directly downwind.

When in orbit around earth, thrust in the direction of your orbit (prograde) causes you to gain energy and altitude, and retrograde thrust does the opposite.


> just like a sail on a boat doesn't have to push you directly downwind

I'm not a sailor, but doesn't this rely on the force of water on the keel, to avoid being pushed laterally?

> When in orbit around earth, thrust in the direction of your orbit (prograde) causes you to gain energy and altitude, and retrograde thrust does the opposite.

For station-keeping purposes, when should you prefer a solar sail as versus PV panels and an ion drive?


> I'm not a sailor, but doesn't this rely on the force of water on the keel, to avoid being pushed laterally?

The analogy with sailing is actually kind of weak.

Since you get elastic collisions with photons on the sail, you can (approach) applying force at 90 degrees from the direction of the light. Unlike with actual sailing, you can never have an "upwind" force component.


Huh, now that I think about this, it makes me realize solar sails might be able to be used to drop material directly into the sun? Angle it for maximum retrograde acceleration in a solar orbit, and twenty years later the cargo impacts the sun? That's normally a very difficult task.


My intuition is failing me here. How does that work since there is no body of water like a boat has to push off?


It's true that the mechanism is different, but this still works (to a limited extent) even without any external object to transfer momentum to, just using the momentum of the photons themselves.

I can't be bothered to draw a diagram, but imagine that the sun is to the "north", and the solar sail is at a 45-degree angle running NE/SW. Incoming photons heading south reflect off the sail and leave to the west. So the photons experience a net momentum change to the NW, pushing the sail to the SE, which is not directly away from the sun.


Thanks, that makes complete sense!


The sail is a mirror. Subtract the momentum vector of the incoming light from that of the reflected light and you have the momentum change applied to the sail.


Is there any indication of how much thrust/acceleration they expect from this, and over what time scale?


625 micro-newtons [1]. Total weight of craft is 16kg [2]. That works out to 3.4 m/s gained per day.

[1] The "Solar Sail" wikipedia page says 800m x 800m is about 5N. This is 80m^2.

[2] https://ntrs.nasa.gov/api/citations/20210017923/downloads/Sm...


Interesting data. This[1] seems to suggest that this relatively small solar sail would be able to reach the moon from earth's orbit after ~3 years (I could be horribly misinterpreting this data!). That seems impressive, given how "simple" this method is.

However, it strikes me as difficult to use this the deeper into space we go. I would assume the further from the sun you go, the less thrust you receive from the sail. Also, how do you slow down and stop? Maybe you don't...

[1] https://spacemath.gsfc.nasa.gov/weekly/5Page26.pdf


Sure, the amount of acceleration you get decreases as you get further from the nearest star, but that’s ok. Remember that you keep all the velocity you gained along the way, when you’re in space. You can be going pretty fast by the time you turn your sail to face the star at your destination.


Raise and lower your orbit, I guess. Any unbalanced force on something in orbit will do one of the two.


This website is a so distracting with ads I couldn’t focus and had to close it. Too bad—i did want that content. Ya ya i have ad blocking but over vpn my dns settings change. Must… fix…


It also works fine with whatever 'reader mode' your browser may have.


Related: this little object spins because the darker part absorbs light while the lighter part reflects light — or so people initially thought!

https://en.m.wikipedia.org/wiki/Radiometer


So I wanted to take a look at the actual craft they built, but all I can find are a bunch of nice CGI animations. Usually there are photos of the fully assembled satellite sitting in a test lab somewhere prior to launch.

Anyone have a link to actual pictures of the probe?

Also -- what's happening to science when more and more articles seem to have CGI artists renditions instead of pictures of the real thing. I get that those with ADHD need some stimulation to keep them interested in science funding -- but as a skeptic I find the boring "real" photos far more interesting. It's getting harder to tell real programs from fictional programs with clickbait titles and pretty graphics i.e. "NASA has designs for a working warp drive"

/rant

edit: OK so I finally found an image of the final assembled satellite prior to launch here [0]

[0] https://pbs.twimg.com/media/GL2pPKZW4AAXK1P?format=jpg&name=...



Thanks for this, no photo of the completed satellite but it's something. It's a shame you have to dig deeper into the NASA website to find the images-- should be on the main mission page.


>no photo of the completed sattelite

That's the completed sattelite in the second link. The 'solid' booms are very similar to how a tape measure rolls out and remains rigid. Solar spacecraft are half sail by mass and half sattelite.


I realize you said it in jest, but as someone with ADHD generalizations like this hurt. Many of us love science and we have enough day to day difficulties to contend with.

That said, I can think of a few reasons for not releasing a photo:

1. Solar sails are flimsily and fragile. The photo would likely not be representative of the craft in action.

2. The labs building these things may not have a professional photographer available.

3. A prototype craft might just look like junk. Wouldn’t be surprised if they want to iterate on the design a bit before they solidify the public’s vision of what a solar sailing craft looks like.


> as someone with ADHD generalizations like this hurt

Apologies -- I was mainly referring to the "overstimulated generation" of kids and their effect on media becoming more clickbaity with fancy/fake images. It was a poor choice of mine to summarize this idea using the word ADHD.


>Also -- what's happening to science when more and more articles seem to have CGI artists renditions instead of pictures of the real thing

I'm sorry for joining the pile-on but why do you believe this is "new"? Artists interpretations and renderings have been the norm for space media since before NASA. It makes sense, since it's so hard to get the film crew out to Jupiter, and the craft all folded up on it's launch platform is usually less interesting to normal people than seeing the instrument as it will be in space

>but as a skeptic... It's getting harder to tell real programs... working warp drive

Skeptic? I promise you that everything put onto a rocket is real. Keep in mind that every single project anyone has ever had to get funding for will inevitably have a CGI rendering or artists interpretation because you need something to put on the first powerpoint slide when you pitch it to the funding board. This is not limited to NASA


>Also -- what's happening to science when more and more articles seem to have CGI artists renditions

In case you weren't aware, pretty much everything in advertising in a render as well. If the car is not moving in a commercial shot from a camera car/drone, it's more than likely 3D rendered. Those close up interior shots or the camera zooming from outside to the interior, yup, those are 3D rendered. A large portion of product shots (like furniture) online are 3D rendered as well. This has been happening for a long time too


> It's getting harder to tell real programs from fictional programs

...Is this a real concern of yours? I've never experienced such ambiguity


How can the sail control its orientation? Without that it would just get pushed around "at random."


From wikipedia: Attitude control is achieved by a relative shift between the craft's center of pressure and its center of mass. This can be achieved with control vanes, movement of individual sails, movement of a control mass, or altering reflectivity.


"the spacecraft began flying without attitude control"




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