"After that the spacecraft's atmospheric friction will lead to it falling back to Earth, destroying itself in the process. "
Not much of a propulsion system if it can't even keep the spacecraft in orbit...
A small cube sat has become the first spacecraft in Earth’s orbit to fly using only the power of sunlight shining down on its solar sail, after it was successfully deployed on Tuesday. The Planetary Society, a nonprofit focused on space exploration and currently led by Bill Nye (yes, the Science Guy), announced it had …
It has been quite successful and has met its primary goal of being the first solar sailed satellite in orbit. Hopefully in the coming year it'll met and exceed its secondary goal of proving the concept of light propulsion for such small scale systems. Once the initial research is done, there is no point in leaving it to clutter NEO, so it'll gracefully dispose of itself.
One would generally consider learning to crawl before running to be a good thing.
It had to have its momentum wheel spun up so it could move high enough before it could deploy the lightsail.
One: Was the leccy for the wheel supplied by battery or solar panel?
Two: How does a momentum wheel enable a change in orbit? Is there a reaction-mass thruster we have not been told about here?
Three: Lightsails are not solar panels. Go on, be honest, where does the onboard power really come from?
Four: No longer moving fast enough to sustain orbit for more than a year, it deploys its lightsail. This will be used to check basic system functions, presumably steering effects, but cannot prevent orbital decay. That is hardly "powered by", either, just another manoeuvring thruster. (a boost from LEO to escape velocity would have been expected under that monicker, and would have equally de-cluttered the neighbourhood.)
"Lightsail-assisted" is what we are really talking about here. Roll on LightSail 3, I say.
It does have solar panels, batteries are for when it's got the Earth between it & the Sun & they wouldn't have lasted the 3 weeks or so since launch otherwise.
The momentum wheel is for attitude control. Can't use gas jets etc as there's no room for fuel & that could affect the sails as well.
Now it's deployed the next year is to attempt to change it's orbit using just photons from the sail. The momentum wheel will be used to tack, just like a traditional wind sail - so when it's orbit takes it towards the sun it's edge on so it has no effect & when going away from the sun it's full on to get the full benefit of the photons.
Thanks, that's the questions about the onboard power and solar panels answered.
We all know what the momentum wheel is for.
"the next year is to attempt to change it's orbit using just photons from the sail. The momentum wheel will be used to tack." is pretty much what I said.* The changes it can make to the orbit are trivial, no more than a bit of manoeuvring, this lightsail simply does not rate "powered" by. I hope the next one will.
* But take care with the sailing analogies. "Tacking" is a technique for sailing overall into the wind, not just crosswind or downwind. A good Bermuda rig can tack faster than the wind is blowing, you can think of its sail as a force amplifier. Lightsails behave more like Newtonian flat plates, they can sail across the photon wind to some extent but they cannot tack back towards the sun. There is a way to manoeuvre a lightsail inbound, by reducing its orbital velocity, but that ain't tacking neither.
It was launched on a falcon heavy and then deployed from Prox1 a larger space craft just a few weeks ago.
The last few weeks have seen the team working to detumble the craft, get the solar panels opened and finally yesterday deploy the sail.
At each turn they have seriously taken their time to ensure they fully understood what the spacecraft was doing, what it was telling them on its passes over the four official tracking stations and how its attitude control systems (momentum wheel and torsion bars) actually operates in space. They've been very cautious to ensure the whole experiment can be conducted.
So no the timing of the deployment has nothing to do with its existing momentum.. in fact quite the reverse.
It it's lightsail powered, that's the whole and only point of the experiment in the first place..
The experiment is to raise the orbit apogee and not lengthen it's perigree (actually I believe it's perigree is due to shorten) repeatedly over a month after which time the atmosphere breaking effect on each orbit will counteract any lightsail benefit.. it will then take a further 11 months to deorbit..
And why will they deorbit so quickly... Partly because they don't think the attitude control will be accurate enough to do more than that and Pauly because that was within the launch permissions they were granted.
As far as boosting it out of Leo rather then letting it fall..... Sounds really reasonable... Why use the force of gravity... when you could use expensive (to build and launch) boosters and a whole different and incredibly expensive guidance system to avoid hitting anything in GEO orbit.......
The problem, as the other commentard pointed out and y'all keep conveniently ignoring, is that all that the light sail is doing could be done ballistically. Of course, we're hearing they didn't but we're also hearing that the light sail can't get it out of orbit to truly show it's actually moving the darned thing. It can't even keep it in orbit beyond a year, based on the way the article is written.
If you actually read the article, it's much ado about nothing.
What NotBob and the other commentard are so blithely ignoring is a little thing called "research". The LightSail project is a proof of concept, not a final product. It may not be able to get out of orbit, but it can adjust its orbital position, to a degree. Which is kind of the point.
"...there is no point in leaving it to clutter NEO, so it'll gracefully dispose of itself."
N.E.O. is irretreivably cluttered already. One more little blob wouldn't make much of a difference.[As everyone mutters while throwing their plastic straws into the rivers. :) ]
If the idea is to prove the concept of star-sails being practical and viable then the object should have done something *useful* such as zip past Puto or catch up to Halley. There are millions of radiometers sitting happily, and damned cheaply, on planet Earth that demonstrate the idea of light having momentum; even I have one of those This thing is just a waste of time, money, energy and resources.
It is marketing hype of vapourware, nothing more.
I applaud the effort but I'm not convinced that all they have done is just deploy a sail in space. Is there any data to show that the trajectory before sail deployment has changed? I would have sent it up on a trajectory away from earth and captured data showing acceleration due to sail deployment. All I can see on the dashboard is some mundane data that doesn't tell us much about how the sail is contributing to it's velocity. Perhaps there is more data hidden away?
They are going to change the shape of the orbit, but they won't be sailing off to the Andromeda Galaxy or anything. The reaction wheel is to change the angle of the sail to the incoming sunlight so that they can make an elliptical orbit. Details are all on their website if you poke around a bit. I must admit the website seems to be more difficult to find stuff on than it used to be.
It's not being pushed along my mass anyway, says this annoying nerf physics pendant. Which makes the paperclip analogy even more wrong. It's being pushed by momentum transfer. Photons have zero mass, but they do have momentum.
(The y have zero _rest_ mass, to be properly pedantic. Although I'm sure I'll be pedantically obliterated somehow anyway.)
Because everyone, dogs included, would need a spacesuit, increasing the mass required to be moved against gravity. It is thus better to put the people and other creatures in a pressurised capsule and move the capsule up the elevator to dock with an airlock enabling the travellers to float forward into the reception area.
Unless we have learned to tame gravity along with the materials to make the elevator then they can walk off the capsule.
Now you're just being silly. Lots of people in suits, weight being an issue - why the answer is obvious! The space ski-lift!
Simply extend ramp up the slopes of Everest, past the summit and into space. Equip all astronauts with skis - and have them pulled up to orbit.
Tonnes of gluhwein to be available as apres space - and I'd have thought fondue was a pretty practical microgravity food.
You know it makes sense!
Might be feasible on Mars. Certainly possible on the moon, but then a rail launch might work there anyway.
Not feasible on Earth:
1) No current material is strong enough.
2) Everything has to be lifted to orbit and then cables extended down and up. Launch cost prohibitive.
3) How do you anchor the bottom end of cable?
4) Cost of ongoing maintenance / operational life.
An atomic powered plane / spaceship hybrid is more feasible. The Space Elevator is just a nice idea for a story. Just because his idea of Geosynchronous / Geostationary satellites was economic and possible doesn't mean all his ideas work.
1) True but emphasis on 'current'
2) Not true. Just nip out to the asteroids and drag back a rock into geosynchronous orbit. Use the rock as raw materials for your carbon nano-tube/unobtanium composite cables.
3) Easy, there isn't any weight (by definition) on the cable at the bottom, so just tie it off with bit of string. In fact it's probably sensible to use a temporay tether - in bad weather you could raise the cable up a few 10s of km to avoid damage. You can always use a balloon as a ferry for the last stretch.
4) Economics + maintenance is just economics. If people want to move stuff off earth in sufficient quantities, or feel elevator rides are better than rockets, it will pay for itself. If not it won't , but we will still have it (see Concorde/Channel Tunnel/most Victorian railways etc).
For everyone who posts such an answer to such objections, they should go out there and build a mobile phone with their bare hands. CPU and all.
While some things are "possible", they are not practical. See even SpaceX having to modify their designs when real world problems appear.
A space elevator on earth hits too many problems. Most other smaller planets? Go ahead and propose it, it's probably doable.
Well certain groups in society get the advanced toys well before the rest of us. Military, police, coastguards, mountain rescue, fire services, boat owners, radio hams would all be examples.
First mobile telephone I ever used was in about 1990. It was similar to a linesman's 'phone or a field telephone but deeper because it had a lead-acid battery in the bottom half. Talk time was the same as standby time, all of twenty minutes. I used to recharge it overnight, say eight hours but I guess it might have reached full charge in under that time. So I'd need 24 spares and 24 trickle chargers to keep that thing working all day. I wasn't near a source of power though.
Damn' thing wouldn't even let you play snake, connect to the Internet, calculate your GPS co-ordinates etc.
Had a dial, though, and the microphone was next to your mouth and the speaker was next to your ear. Call quality was usually excellent, if it went a bit crackly you just bashed the carbon granules and all was well.
That's only 30 or so years ago (it wasn't a brand new device when I got my mitts on it.)
(Icon - too big to fit in your pocket!)
I said "build it with your bare hands". Beyond "magic" materials, we cannot build a space elevator. Just as without the thousands of people helping, and the specialist factories and machinery, you cannot build an iphone.
Rockets, phones, computers etc are increasing the fidelity of existing skills and technology. They are reaching under the limits of physics.
A space elevator asks to reach the limit of physics.
I never said "impossible". I said "impractical" (and as an example, we are starting to hit the impracticality of nano scale etching processes on silicon chips, so limits exist).
Not really a point whoosh at all.
Nobody is suggesting that one person can build an iPhone by themselves, starting from scratch with nothing more than a sharpened flint and some combustible vegetation.
Nobody is suggesting that one person can build a space elevator by themselves, starting from scratch with nothing more than a sharpened flint and some dry grass.
I would assume that any group of people constructing a space elevator would be allowed to use any of the technologies and materials developed/discovered in the last few thousand years. They will also be allowed to develop new ones.
Modern aeroplanes are made from metal, not wood and fabric. We are allowed to improve things as we go along, that's why we don't use square wheels on our bullock carts any more. I am (mostly) happy to fly in them despite the fact I have never built one in my shed with my own hands.
If your point is that materials strong and light enough to construct an earth-based space elevator break the laws of physics you may well be wrong. If you are saying they can't be manufactured you may be right, but there is a famous quote by Clarke that is applicable here!
But as graphene is not strong enough by a long chalk there is no conceivable material that you could make it from. C-C is 3/4 the strength of the strongest bond you can get and anything else is not going to be in graphenes useful lattice.
So the tether does indeed look impossible,
A stab at the oribital period equation suggests a lunar geosynchronous orbit would be some 681km. (though I've not checked my workings, so there is room for error of many orders of magnitude)
There would likely be some interference from Earth's gravity out there (see https://science.nasa.gov/science-news/science-at-nasa/2006/30nov_highorbit) but it's a lot smaller than i originally thought.
I am quite aware that I couldn't build a mobile phone in my garage from sticky back plastic and straws . In fact the list of things that I take for granted that I have no skills and inadequate knowledge to produce is a lot longer than mobile phones. Given enough iron ore, charcoal, clay and a few years experimentation I might manage a crude paperclip. However luckily man is a) a social animal, b) capable of specialising and c) callable of innovating.
I don't realistically expect to see a space elevator in my lifetime. I doubt my children will see one. But in 3 generations we have gone from horse and cart to the moon, quill pen to streaming downloads, morse code to the internet, so who would bet against astonishing developments in the next 150 years?
1) Blockchain might be strong enough. Has anyone actually mesured the tensile strength yet?
2) Use asteroids, just move one close enough. Just ad a light sail and a tow rope (more blockchain?)
3) 3D printing is the answer to everything.
4) Build it and they will come (and pay)
IKAROS was interplanetary, not Earth orbit. NanoSail-D's launch failed, but its understudy (NanoSail-D2) deployed in LEO a couple years later after a hiccup or two.
"Only the power of sunlight" is a key phrase; NanoSail was battery powered, LightSail is powered by solar cells, the batteries are only there for use during eclipse conditions. This is pure marketing pedantry IMO, and has no place in science.
Wasn't IKAROS also powered entirely by solar cells? It would lose power at regular intervals in its orbit when it wasn't getting enough sunlight. It also sent back enough data to prove that it did get a fair amount of delta-V from the solar sail, and showed that it could manoeuvrer using the sail, IIRC.
To be fair, LightSail 2 cost less than half of what IKAROS cost; but the latter was set (and successfully met) far more ambitious goals.
As tons of photons strike the sail, they apply force (not much - about the same as a paperclip on your hand), but since there's no friction in space this will propel the spacecraft forward at ever-faster speeds.
Stargazers hoping to spot LightSail 2 will need a telescope and you'll have around a year to spot it. After that the spacecraft's atmospheric friction will lead to it falling back to Earth, destroying itself in the process.
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