[HN Gopher] How to Spot NASA's Solar Sail Demonstration Streakin...
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How to Spot NASA's Solar Sail Demonstration Streaking Through the
Night Sky
Author : Brajeshwar
Score : 121 points
Date : 2024-09-11 16:36 UTC (2 days ago)
(HTM) web link (www.smithsonianmag.com)
(TXT) w3m dump (www.smithsonianmag.com)
| rob74 wrote:
| 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...
| sholladay wrote:
| That is bigger than many city apartments.
| scoot wrote:
| Not really... apartments have volume.
| sans_souse wrote:
| Ok but how many school busses is that?
| croisillon wrote:
| about half an olympic swimming pool
| sobellian wrote:
| I'm going to need that in smoot-manhattans per cubit.
| skykooler wrote:
| About one medium-sized school bus long on each side.
| dylan604 wrote:
| it's one half of a JWST
| mdl_principle wrote:
| 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.
| cdaringe wrote:
| 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...
| michelb wrote:
| It also works fine with whatever 'reader mode' your browser may
| have.
| lordfrito wrote:
| 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=...
| cbsks wrote:
| I found a few pictures:
|
| https://www.nasa.gov/mission/acs3/
|
| https://www.nasa.gov/smallspacecraft/what-is-acs3/
| lordfrito wrote:
| 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.
| Out_of_Characte wrote:
| >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.
| d4mi3n wrote:
| 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.
| lordfrito wrote:
| > 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.
| digging wrote:
| > It's getting harder to tell real programs from fictional
| programs
|
| ...Is this a real concern of yours? I've never experienced such
| ambiguity
| mrguyorama wrote:
| >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
| dylan604 wrote:
| >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
| abeppu wrote:
| 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?
| teraflop wrote:
| 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.
| Alupis wrote:
| Is there any indication of how much thrust/acceleration they
| expect from this, and over what time scale?
| graboy wrote:
| 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/downloa
| ds/Sm...
| Alupis wrote:
| 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
| db48x wrote:
| 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.
| abeppu wrote:
| > 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?
| zardo wrote:
| > 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.
| jahnu wrote:
| My intuition is failing me here. How does that work since
| there is no body of water like a boat has to push off?
| zardo wrote:
| 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.
| teraflop wrote:
| 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.
| jahnu wrote:
| Thanks, that makes complete sense!
| alnwlsn wrote:
| Raise and lower your orbit, I guess. Any unbalanced force on
| something in orbit will do one of the two.
| bloopernova wrote:
| 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/
| dave333 wrote:
| How can the sail control its orientation? Without that it would
| just get pushed around "at random."
| dave333 wrote:
| 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.
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(page generated 2024-09-13 23:00 UTC)