Author Topic: What advanced concepts are you interested in  (Read 18895 times)

Offline Moe Grills

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Re: What advanced concepts are you interested in
« Reply #60 on: 06/02/2011 07:56 PM »
   There is a 'silver bullet' of sorts, proverbially speaking, in the near-future development' of advanced solar cells that DO NOT need silicon;
and DO NOT need solar cells/panels centimeters thick; and ARE NOT
limited to 20-30 percent photon-energy to electrical energy conversion.

For instance; Professor Shanhui Fan and his Stanford University team
are at work developing a promising ultra-thin solar-cell technology
that will involve the use of polymer thin film, instead of silicon;
and will increase the photon capture (and containment; my words)
by at least 10X.
  And the ultrathin solar-cells would be roughly about the wavelengths of
red or infrared light (about 0.75 micrometers?).

  To put it all in perspective: if you want a spacecraft or space station to have 100 meters square of solar panels anywhere from 1-4 centimeters thick (silicon density: 2700 kg/m^3) then the mass of the silicon alone would be anywhere from 2.7 -10.8 tonnes. And that doesn't
include the mass of the support frame, etc.

 All that for at most 28-42 KW near one A.U.

Compare that to the potential ultra-thin solar-cells that could be made
by ultrathin layers of polymer film solar-cells of say on less than one micrometer thickness.
 Less than a 1,500 kg of that material, and you are talking about enormous lightweight solar-panels of a surface area exceeding 10 million meters squared.

  And Professor Shanhui mentions a 10X increase in photon collection/retention with this material, compared to silicon.
 Silicon solar panels have a double handicap it seems: one, they have
what appears to be a photon capture retention property that is less than 10 percent of what actually strikes the panels; and, second,  the low percentage of photons captured by silicon-cells have a poor energy conversion rate from photon energy to electrical energy.
 
The ultra-thin solar panels would appear to have an efficiency that would leave
silicon solar cells in the dust.

http://www.news.stanford.edu
« Last Edit: 06/02/2011 08:04 PM by Moe Grills »

Offline Moe Grills

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Re: What advanced concepts are you interested in
« Reply #61 on: 06/02/2011 08:38 PM »
   I'm sorry, the Stanford news URL doesn't seem to work for me.
If someone could locate a reliable URL for Professor Shanhui Fan's
team, it would be appreciated.

 As for the space travel and space-exploitation potential for his team's work?
One thing sticks out: 10^6 + meters square of ultrathin, ultralight solar-cell photon capture area is?...it would be a proverbial orbiting Hoover dam.... without the all those turbines, water and megatons of concrete.

And, except for the necessary structural frame needed, orbital avionics, high-energy microwave transmitters, the booster needed to park it in GEO, etc, it would be of remarkably low mass.

Now if only the treehuggers wouldn't stand in the way.


Offline clongton

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Re: What advanced concepts are you interested in
« Reply #62 on: 06/02/2011 08:50 PM »
I'm interested in perfecting the process to increase the purity of fused silica.

The windows on the shuttle are made of a composite of aluminum silicate glass and fused silica glass, in 3 separate panes; an outside thermal pane, a center optical pane that is approximately 3 & 1/2 inches (89 mm) thick and an interior pressure pane that is part of the cockpit pressurization system. So there is plenty of precedent for its use in spacecraft.

Fused silica, if pure enough, would enable the practical development of the nuclear lightbulb NTR engine, using uranium hexafloride gas as the reactant and LH2 as the propellant. This engine would be safe enough for ground launch and would provide *enormous* thrust and an isp in the tens of thousands of seconds. That would be a true game changer in propulsion.

« Last Edit: 06/02/2011 08:56 PM by clongton »
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Offline Robotbeat

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Re: What advanced concepts are you interested in
« Reply #63 on: 06/02/2011 10:19 PM »
Nanotechnology, nuclear fusion, imaging a life-bearing exoplanet, an interstellar mission (unmanned or manned).
Very good list. :)

You might also be interested to know that there are a couple groups looking for exoplanets around Alpha Centauri. While large gas giants (like in the movie from which your... ummm... avatar image comes from) are not considered likely, many think near-Earth-mass planets (perhaps in the habitable zone!) may indeed exist around some of the three stars of the nearest star system...
http://oklo.org/2009/06/07/alpha-centauri-market-outperform/
and especially:
http://seedmagazine.com/content/article/the_long_shot/
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #64 on: 06/05/2011 04:16 PM »
SolarKinetic Pulse Propulsion could provide cheap access to space, if the sailbots are cheap enough.  Not just LEO, but really the entire Solar System.

About the cost of the sailbots--the 30cm square of aluminized kapton costs almost nothing, so the main cost is the control chip.

If the control chips can be mass produced at a cost of under $1 per chip, this adds up to under $100 per kg to GTO, or under $70 per kg to LEO.

Offline KelvinZero

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Re: What advanced concepts are you interested in
« Reply #65 on: 06/06/2011 03:58 AM »
SolarKinetic Pulse Propulsion could provide cheap access to space, if the sailbots are cheap enough.  Not just LEO, but really the entire Solar System.

About the cost of the sailbots--the 30cm square of aluminized kapton costs almost nothing, so the main cost is the control chip.

If the control chips can be mass produced at a cost of under $1 per chip, this adds up to under $100 per kg to GTO, or under $70 per kg to LEO.

This reminds me a bit of my slightly kooky "beamed regolith propulsion" launcher :)

The idea was to deliver cargoes of super fine regolith dust from the moon to LEO. The dust is dispersed like a long column of smoke in the path of a suborbital craft. Because this dust is moving at orbital velocity, or even faster if it still retains its velocity from the trip from the moon, it can apply a force against the heatshield of the craft accelerating it to orbital velocity.

It is also a lot like the overhead magnetic monorail idea. I can't really claim that because it is just an orbital ring without the elevator/tower. It really only differs from the solar kinetic idea in that the chain of satellites apply force magnetically, like a magnetic train track, so they are reusable but I guess must be much more massive. Because the could be used to both accelerate and decelerate craft they don't need their own method of gaining momentum, they are really just a momentum battery for outgoing and incoming craft.

(note: I do believe rockets are the answer for now but these ideas are fun to play with. For right now I just want to see ongoing research into something like an evolvable reusable TSTO, and kept as just a series of prototypes rather than forced to be a workhorse like the shuttle. We have to keep building the next version. )
« Last Edit: 06/06/2011 04:05 AM by KelvinZero »

Online aero

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Re: What advanced concepts are you interested in
« Reply #66 on: 06/06/2011 05:26 AM »
I've always liked the Scifi idea of force fields. Have no idea how to start the construction of one but a force field having the strength of a steel cylinder with no or very little mass would sure improve the mass ratio of solid rockets. Of course Vasimr already uses a magnetic field for its rocket nozzle so that is a kind of force field.
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Offline Nascent Ascent

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Re: What advanced concepts are you interested in
« Reply #67 on: 06/06/2011 06:32 AM »
I'm interested in perfecting the process to increase the purity of fused silica.

The windows on the shuttle are made of a composite of aluminum silicate glass and fused silica glass, in 3 separate panes; an outside thermal pane, a center optical pane that is approximately 3 & 1/2 inches (89 mm) thick and an interior pressure pane that is part of the cockpit pressurization system. So there is plenty of precedent for its use in spacecraft.

Fused silica, if pure enough, would enable the practical development of the nuclear lightbulb NTR engine, using uranium hexafloride gas as the reactant and LH2 as the propellant. This engine would be safe enough for ground launch and would provide *enormous* thrust and an isp in the tens of thousands of seconds. That would be a true game changer in propulsion.



Chuck,

Is this because any impurities in the quartz/silica would not be transparent to the UV radiation and hence heat up uncontrollably and damage the window?

-Jim
“Why should we send people into space when we have kids in the U.S. that can’t read”. - Barack Obama

Offline clongton

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Re: What advanced concepts are you interested in
« Reply #68 on: 06/06/2011 10:08 AM »
I'm interested in perfecting the process to increase the purity of fused silica.

The windows on the shuttle are made of a composite of aluminum silicate glass and fused silica glass, in 3 separate panes; an outside thermal pane, a center optical pane that is approximately 3 & 1/2 inches (89 mm) thick and an interior pressure pane that is part of the cockpit pressurization system. So there is plenty of precedent for its use in spacecraft.

Fused silica, if pure enough, would enable the practical development of the nuclear lightbulb NTR engine, using uranium hexafloride gas as the reactant and LH2 as the propellant. This engine would be safe enough for ground launch and would provide *enormous* thrust and an isp in the tens of thousands of seconds. That would be a true game changer in propulsion.



Chuck,

Is this because any impurities in the quartz/silica would not be transparent to the UV radiation and hence heat up uncontrollably and damage the window?

-Jim

The UV that the shuttle windows experience is not strong enough to damage them, not even close. But that would not be the case for the nuclear lightbulb NTR engine. In that case, the integrity of the transparent containment could be compromised by the impurities.
« Last Edit: 06/06/2011 10:09 AM by clongton »
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Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #69 on: 06/06/2011 10:44 AM »
SolarKinetic Pulse Propulsion could provide cheap access to space, if the sailbots are cheap enough.  Not just LEO, but really the entire Solar System.

This reminds me a bit of my slightly kooky "beamed regolith propulsion" launcher :)

The idea was to deliver cargoes of super fine regolith dust from the moon to LEO. The dust is dispersed like a long column of smoke in the path of a suborbital craft. Because this dust is moving at orbital velocity, or even faster if it still retains its velocity from the trip from the moon, it can apply a force against the heatshield of the craft accelerating it to orbital velocity.

I used to ponder variations on this theme of using orbital impactors, but there are numerous problems stemming from the relatively low impact velocity.  By the time the target vehicle is reaching orbital speed, the impact velocities will be below 3km/s.  The specific impulse isn't all that much better than a chemical rocket, so the entire scheme only makes sense if the mass of the impactors comes from in situ resource utilization--meaning a huge investment to get the scheme started up.

The deal killing problem, though, is the space junk problem.  The impact velocities are insufficient to guarantee vaporization upon impact with a gas puff, and the ejecta from a solid-solid impact will leave a stupendous amount of orbital space junk.

In order to eliminate the space junk problem, you need much higher impact velocities.  One commonly proposed solution is to use a mass driver of some sort, but there are two problems with this.  First, we have never produced a mass driver with anywhere near the sorts of muzzle velocities required--our best EM accelerators have only reached on the order of a km/s.  Second, this requires a stupendously powerful mass driver in orbit or on the Moon.  This is an incredible initial investment required.

In contrast, solarkinetic requires no mass driver to reach impact speeds of 60km/s.  This means no incredible initial investment, other than waiting about 3 years for the first sailbots to complete their orbital cranking treks.  This 3 year wait isn't really so much time, compared to development time for any radically new launcher concept.

The impact velocities of 50+km/s guarantee complete vaporization, and the exhaust will have 40+km/s velocity relative to Earth.  Even if there are some bits of solid ejecta swept up in the exhaust stream, it will have Earth escape velocity.  SolarKinetic produces no space junk problem.

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It is also a lot like the overhead magnetic monorail idea. I can't really claim that because it is just an orbital ring without the elevator/tower. It really only differs from the solar kinetic idea in that the chain of satellites apply force magnetically, like a magnetic train track, so they are reusable but I guess must be much more massive.

Yes, it needs to be MUCH more massive.  It requires a huge initial investment of many orders of magnitude launch mass compared to the payload.  Like any other scheme involving a huge initial investment, it only makes sense if there are going to be an extremely high number of launches.

SolarKinetic is unique in that its initial investment is an order of magnitude LESS mass than its payload capacity.  The incredibly high impact velocities mean that 1 ton of sailbots can lift 10 tons of payload to GTO, or 14 tons of payload to LEO.

Offline Cinder

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Re: What advanced concepts are you interested in
« Reply #70 on: 06/06/2011 11:57 AM »
I've always liked the Scifi idea of force fields. Have no idea how to start the construction of one but a force field having the strength of a steel cylinder with no or very little mass would sure improve the mass ratio of solid rockets. Of course Vasimr already uses a magnetic field for its rocket nozzle so that is a kind of force field.
Not sure if its strength is at that level, but there is such a tech restricted to inch-scales due to power requirements.

Offline KelvinZero

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Re: What advanced concepts are you interested in
« Reply #71 on: 06/09/2011 11:19 AM »

Yes, it needs to be MUCH more massive.  It requires a huge initial investment of many orders of magnitude launch mass compared to the payload.  Like any other scheme involving a huge initial investment, it only makes sense if there are going to be an extremely high number of launches.

SolarKinetic is unique in that its initial investment is an order of magnitude LESS mass than its payload capacity.  The incredibly high impact velocities mean that 1 ton of sailbots can lift 10 tons of payload to GTO, or 14 tons of payload to LEO.

Good points.. I know what Jim would say about the suborbital rendezvous though. Version 1.0 could just be about raising orbits. I like that the weight to begin testing it is minuscule since you would begin by navigating a single sail into a retrograde orbit.

Reminds me a bit of my 'solar butterflies' idea... ;D

Im still sort of in love with that orbital ring, but for a distant future where there is so much urban sprawl in LEO that the ring also serves as their subway. Its certainly not happening anytime soon.

Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #72 on: 06/09/2011 02:31 PM »
SolarKinetic is unique in that its initial investment is an order of magnitude LESS mass than its payload capacity.  The incredibly high impact velocities mean that 1 ton of sailbots can lift 10 tons of payload to GTO, or 14 tons of payload to LEO.

Good points.. I know what Jim would say about the suborbital rendezvous though. Version 1.0 could just be about raising orbits.

Things are greatly simplified by the fact that a certain amount of slop is acceptable and there is no need to match velocities.  This reduces the problem to that of a suborbital missile colliding with a spacecraft--an already demonstrated capability.  In this case, the the spacecraft cooperatively navigate themselves onto a particular path defined by the ground based navigation beams.  This provides precision down to about 20cm.

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I like that the weight to begin testing it is minuscule since you would begin by navigating a single sail into a retrograde orbit.

Yes, although the mass you need to launch to test sailbot prototypes is more than that.  To minimize mass and cost, the sailbots can only receive signals.  They can't transmit signals, so you need some other method of receiving feedback on a prototype's location and status.  The 30cm x 30cm dimensions are big enough for existing space junk sensor systems to track location in LEO, but you really want high resolution feedback on attitude to determine how well the control systems are working.

After testing in Earth orbit to prove the control systems, you could launch sailbots to test BEO capabilities.  The small size of the sailbots mean that there's not really a practical way to track these things in BEO.  So you'll want to play things conservatively with test sailbots scheduled to return after progressively longer and longer journeys.

There are also other aspects of testing which I've thought about.  For example, how do you test the thruster?  My original idea was to use simple direct impacts for momentum--each impact causing a crater so most of the momentum was actually from the crater ejecta.  But there are various problems with this, including testing.  A 60km/s impact velocity is an order of magnitude greater than the highest speeds available for solid-solid hypervelocity impact testing.

However, 60km/s is within the capabilities of solid-gas impact testing.  The Giant Planet Facility was used to test the Galileo atmospheric entry probe's heat shield.  To test this thruster, two solid-gas impacts need to be considered.  The first is the impact between the gas puff and the sailbot.  It must consistently vaporize the sailbot within a range of impact attitudes and off-axis errors.  The second is the impact between the resulting plasma and the thrust bell.  The thrust bell is essentially a heat shield, just with a concave shape to redirect the for increased impulse.

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Reminds me a bit of my 'solar butterflies' idea... ;D

What is your solar butterflies idea?

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Im still sort of in love with that orbital ring, but for a distant future where there is so much urban sprawl in LEO that the ring also serves as their subway. Its certainly not happening anytime soon.

There are numerous ideas which could make sense after a sufficient space infrastructure is in place.  An orbital ring has various problems, but they could be overcome.  For example, there is a requirement to match transverse velocities.  That's significantly more challenging than simply intercepting the orbital ring path.  The tolerances are also challenging.  The ring needs to be a perfectly smooth circle or the vehicle and ring destroy each other.

A far less challenging system could be a satellite with a scoop to simply catch a suborbital payload.  This only works if you don't mind the payload delivered in paste form, of course.

Offline KelvinZero

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Re: What advanced concepts are you interested in
« Reply #73 on: 06/10/2011 10:28 AM »
Solar butterflies was just various speculations about the sorts of megascale engineering you could do with a flock of solar sails that do nothing but control their own angle, especially if self reproducing. I imagined a single element looking sort of like a butterfly with a tiny body.

Paste form is quite a disadvantage :)

The orbital ring can accelerate you as gently as you like, take a suborbital craft up to at least twice orbital velocity, and also reverse this, taking an incoming craft back to earth velocity.

Why is matching transverse velocity hard? That means sideways right? :)
I see it as essentially landing on a runway except there is no weather up there. There would probably be a tram with a cable that latches on when you get to within a few meters or hundred meters so the suborbital craft does not need to carry heavy magnets. Docking with that I guess would be a bit like inflight refueling.

The ring would not need to be a solid piece. An accident would only wipe out the tram,  a few segments and possibly not even the craft given it is on a cable.

What other ideas do you see as becoming practical with a large infrastructure? Beamed power would be a complementary addition. I never liked space elevators, rotovators only a little better.

Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #74 on: 06/10/2011 03:37 PM »
Solar butterflies was just various speculations about the sorts of megascale engineering you could do with a flock of solar sails that do nothing but control their own angle, especially if self reproducing. I imagined a single element looking sort of like a butterfly with a tiny body.

These sailbots look like a square sheet of aluminized kapton, with a small control circuit.  Ideally, the circuit itself is directly printed on the kapton, perhaps using LCD screen manufacturing technology.  The sail is kept flat and stable by rotating it.  The control circuit only needs to modulate the reflectivity of an off-center zone in order to control attitude.

The number of sailbots involved are not suitable for megascale engineering.  Ten million of these sailbots, suitable for boosting 140 tons of payload to LEO, still only have a total sail area of one square kilometer.

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Paste form is quite a disadvantage :)

It's good enough for bulk cargo like fuel, water, aeroponic nutrients, 3d printer feedstock, and so on.  Not bad for something that's doable in the near term with a modest investment.

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The orbital ring can accelerate you as gently as you like, take a suborbital craft up to at least twice orbital velocity, and also reverse this, taking an incoming craft back to earth velocity.

Accelerating beyond orbital velocity would require some sort of high power propulsion system.  Decelerating down to Earth is an already solved problem--the atmosphere helps!

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Why is matching transverse velocity hard? That means sideways right? :)
I see it as essentially landing on a runway except there is no weather up there.

It's certainly a solvable problem, but one which requires careful tolerances.  It's not as easy as landing on a runway because runways are wide.  And they don't explode if you slam down on them too hard.

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There would probably be a tram with a cable that latches on when you get to within a few meters or hundred meters so the suborbital craft does not need to carry heavy magnets. Docking with that I guess would be a bit like inflight refueling.

This requires a high speed tram with a propulsion system suitable for accelerating it to 8km/s relative to the track.  This might be the most practical method of solving the various issues, but of course it requires solving its own issues.

The alternative is for the spacecraft to directly interface with the orbital ring, which only requires some form of braking.

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The ring would not need to be a solid piece. An accident would only wipe out the tram,  a few segments and possibly not even the craft given it is on a cable.

Unfortunately, an accident would cause an explosion of debris, and half of the nearby ring is screaming toward the debris at 8km/s.  The initial cloud of debris is mostly only a threat for a some seconds, as gravity pulls it down to Earth.  But in the meantime, many kilometers of orbital ring will be shredded by it--and THIS will result in a stupendous amount of space junk in orbit.  This secondary debris will repeatedly return to the path of the orbital ring.  Each bit of debris will pass near the ring twice every 90 minutes until it hits.

The bottom line is that the orbital ring is doomed, and you've got a nasty clean up problem before you can consider creating a new orbital ring.

The only reasonable solution that comes to my mind is to greatly overengineer the ring so it can shrug off and absorb debris impacts.

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What other ideas do you see as becoming practical with a large infrastructure? Beamed power would be a complementary addition. I never liked space elevators, rotovators only a little better.

I assume you mean launch systems.  I prefer systems that don't require a large infrastructure (like solarkinetic pulse propulsion), or ones where the large infrastructure is on the ground (like laser thermal or some sort of gun launch).

One variant of gun launch which I like is a kinetic storage ring machinegun.  The first part of the system is a solid bullet version of a particle accelerator.  Imagine a 20km diameter storage ring consisting of a 4cm diameter pipe.  Within this storage ring are a bunch of long thin darts.  Several accelerator coils are used to incrementally accelerate the darts--they coast between the coils.

After some hours or days, the ring of darts have been accelerated up to 10+km/s.  For launch, they are diverted to a gun barrel that curves upward.  This barrel is aimed at the launch vehicle, which accepts momentum from the impacts using a thick pusher shield.  This system could be useful for large volume heavy lift.

Unlike beam powered rockets, this storage ring system could build up the required kinetic energy over hours or days.  Unlike a mass driver system, only a few accelerator coils are required and they have extremely high usage cycles (almost continuous).

Online aero

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Re: What advanced concepts are you interested in
« Reply #75 on: 06/10/2011 06:26 PM »
I've always liked the Scifi idea of force fields. Have no idea how to start the construction of one but a force field having the strength of a steel cylinder with no or very little mass would sure improve the mass ratio of solid rockets. Of course Vasimr already uses a magnetic field for its rocket nozzle so that is a kind of force field.
Not sure if its strength is at that level, but there is such a tech restricted to inch-scales due to power requirements.
Do you happen to know if that tech will shield against radiation, and if so, what levels of radiation?
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Offline KelvinZero

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Re: What advanced concepts are you interested in
« Reply #76 on: 06/11/2011 02:32 AM »
Unfortunately, an accident would cause an explosion of debris, and half of the nearby ring is screaming toward the debris at 8km/s.  The initial cloud of debris is mostly only a threat for a some seconds, as gravity pulls it down to Earth.  But in the meantime, many kilometers of orbital ring will be shredded by it--and THIS will result in a stupendous amount of space junk in orbit.  This secondary debris will repeatedly return to the path of the orbital ring.  Each bit of debris will pass near the ring twice every 90 minutes until it hits.

I don't see it happening that way. As you say any elements moving at 8km/s relative to the ring would remove themselves immediately. The arc of any fragment travelling from a point on the ring has to travel halfway around the world before it possibly intersects the ring again. Therefore any fragment with less than orbital velocity should be removed by that point. Since the ring is in as low an orbit as possible (and having no forward surface this can be lower than for any usual satellite), any trajectory which is not extremely exact will intersect deep into earths atmosphere and be removed. Most of the extremely exact trajectories that do survive would be essentially inline with the ring and have low  relative velocities.

Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #77 on: 06/11/2011 02:37 AM »
FWIW, I've just conceived of a superior alternative to solarkinetic pulse propulsion, which I call "picokinetic pulse propulsion".  Picokinetic doesn't require development of small 1g solar sails.  Instead, it uses 200g picosats with plain old chemical propulsion.

I won't describe the method of getting the picosats up to very high impact velocities.  I'll just reveal that this method doesn't require any sort of powerful infrastructure (like a honking huge mass driver or ISRU), and it doesn't require any fancy propulsion systems (like solar sails or VASIMR).

Picokinetic pulse propulsion only uses 5000 picosats to boost a 20 ton client vehicle, rather than over a million sailbots for solarkinetic.  This has a huge impact on the potential for cheap access to space.  If the 200g picosats can be mass produced at under $4 each, costs to LEO can be under $1000 per ton.

Offline IsaacKuo

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Re: What advanced concepts are you interested in
« Reply #78 on: 06/11/2011 04:24 AM »
Unfortunately, an accident would cause an explosion of debris, and half of the nearby ring is screaming toward the debris at 8km/s.  The initial cloud of debris is mostly only a threat for a some seconds, as gravity pulls it down to Earth.  But in the meantime, many kilometers of orbital ring will be shredded by it--and THIS will result in a stupendous amount of space junk in orbit.  This secondary debris will repeatedly return to the path of the orbital ring.  Each bit of debris will pass near the ring twice every 90 minutes until it hits.

I don't see it happening that way. As you say any elements moving at 8km/s relative to the ring would remove themselves immediately.

The initial explosion debris would shred many kilometers of the orbital ring before it's pulled down to Earth.

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The arc of any fragment travelling from a point on the ring has to travel halfway around the world before it possibly intersects the ring again.

No, it doesn't.  It can return to the ring after any distance.  I don't know where you get this idea that it needs to travel half an orbit first.

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Therefore any fragment with less than orbital velocity should be removed by that point. Since the ring is in as low an orbit as possible (and having no forward surface this can be lower than for any usual satellite), any trajectory which is not extremely exact will intersect deep into earths atmosphere and be removed.

No, the ring will experience much higher drag than a typical satellite.  The problem is that the orbital ring is narrow and has a lot of surface area for a given volume.  Typical satellites are far more compact.  At orbital speeds, even the "sideways" surfaces experience a lot of drag.  Air molecules don't just stand still.  They have transverse thermal motion on the order of the speed of sound.  As such, surfaces which are parallel to orbital motion get "sideswiped" by air molecules.

Given the extremely tight tolerances required to keep the ring perfectly smooth and "straight", it's really not a good idea to have the slightest bit of atmosphere around to interact with it.

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Most of the extremely exact trajectories that do survive would be essentially inline with the ring and have low  relative velocities.

Untrue.  The surviving trajectories are ones along an orange slice.  Any debris headed in either the "forward" direction or to the sides or anywhere in between will survive, and they can have large relative velocities when they return to the ring path (up to 13km/s relative velocity).

The surviving orbits are all of the ones with perigee near the impact point and velocities between 7.5km/s and 10.5km/s.  This includes debris orbits which are greatly inclined compared to the ring.

Offline Andrew_W

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Re: What advanced concepts are you interested in
« Reply #79 on: 06/12/2011 09:58 PM »
1. Aerial propellant Transfer for spaceplanes. A modified A380 could refuel a reusable Lh2/LOX spaceplane large enough to put a 20 tonnes payload into LEO. With operations of airline efficiency, cost could be as low as $100/kg. APT hugely increases the number of launch windows compared to direct ascent from the ground.

2. Hypersonic rotovators. In sun synchonous orbits, combine this with APT spaceplanes and costs to orbit could be as low as $25/kg as payload /spaceplane quadruples.
http://nextbigfuture.com/2009/01/industrial-scale-production-of.html

3. Space tourism, a hotel in the polar dusk to dawn sun synchronous LEO orbit would be in  continuous sunshine.

4. Solar power satellites, these also go into sun synchronous orbit with microwave reflectors in equatorial orbit to send power to rectenna near population centers on the ground.
http://www.earthspaceagency.org/space-articles/space-opinions/the-space-grid-sun-synchronous-orbiting-sbsp-satellites-with-equatorial-orbiting-reflector-satellites-for-earth-and-space-energy.html

5. Stanford torus, again these go into sun synchronous orbit, they are a base for the crews building the Solar power satellites, a home for rich people wanting to move out of Beverly Hills and a destination for tourists.

6. Solar thermal rockets, I'm puzzled that these don't get more study for interplanetary flight, they only need light weight mirrors to collect sunlight and don't waste that sunlight energy the way solar sails do by just bouncing it away, at 1AU from it the sun provides 1 GW of power per square km, H2 propellant will give an Isp of about 1000s, H2O ~400s. Why would anyone even consider the weight cost and complexity of nuclear electric or solar electric?

7. Asteroid mining.

8. The lunar surface based rotating tether covered at the end of this paper:
http://www.niac.usra.edu/files/studies/final_report/1032Pearson.pdf
« Last Edit: 06/14/2011 02:27 AM by Andrew_W »
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

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