Author Topic: Mission to the Gravitational Focus  (Read 23332 times)

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Mission to the Gravitational Focus
« on: 12/09/2011 11:04 AM »
http://www.centauri-dreams.org/?p=785

This would make for one awesome telescope. We could directly image exoplanets in very high resolution. I read that with a Hubble-sized telescope, you would theoretically  be able to make out features only a few hundred meters in size on a planet orbiting Alpha Centauri, if you exploit the gravitational lens of the sun.

So NASA, the next time you plan flagship missions, think about getting a telescope out to 550 - 1000 AU!

How to do it? I believe nuclear electric propulsion would be up to the task. It could get a probe to cover that distance in twenty years of flight or so. Or a close flyby of the sun and then sailing on the solar wind. That may work as well.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline Tass

  • Full Member
  • ***
  • Posts: 352
  • Liked: 59
  • Likes Given: 138
Re: Mission to the Gravitational Focus
« Reply #1 on: 12/09/2011 11:44 AM »
Trouble is that it looks in one specific direction, and steers very slowly. You have to move the probe around the sun at 500AU to change view.

Maybe it we, in a decade or so, have a really good candidate for an earth-like exoplanet, then it may be worth considering sending a probe to the specific point were it is in focus.

A big expensive mission, but much easier (and faster) than sending a probe to the actual planet.

Offline Warren Platts

Re: Mission to the Gravitational Focus
« Reply #2 on: 12/09/2011 01:32 PM »
Yeah, but Alpha Centauri would be a good candidate anyways because it will always (on human time scales) be the closest planetary system.
"When once you have tasted flight, you will forever walk the earth with your eyes turned skyward, for there you have been, and there you will always long to return."--Leonardo Da Vinci

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6580
  • Liked: 862
  • Likes Given: 132
Re: Mission to the Gravitational Focus
« Reply #3 on: 12/09/2011 02:15 PM »
So NASA, the next time you plan flagship missions, think about getting a telescope out to 550 - 1000 AU!

Just for scale...the Voyagers are currently at about 100 and 120 AU from the sun.

Offline STS-200

  • Member
  • Posts: 90
  • UK
  • Liked: 9
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #4 on: 12/09/2011 02:29 PM »
http://www.centauri-dreams.org/?p=785
How to do it? I believe nuclear electric propulsion would be up to the task. It could get a probe to cover that distance in twenty years of flight or so. Or a close flyby of the sun and then sailing on the solar wind. That may work as well.

You would be better off with one of these:

Fission fragment drive - a hypothetical 10t probe on a 10 year flight, using 180kg fuel.

Definitely at home in the "Advanced Concepts" section!
"Nothing will ever be attempted if all possible objections must first be overcome."

Offline sanman

  • Senior Member
  • *****
  • Posts: 3513
  • Liked: 403
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #5 on: 12/09/2011 11:59 PM »
Pardon my ignorance, but what does FOCAL stand for again? Is it an acronym?

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6580
  • Liked: 862
  • Likes Given: 132
Re: Mission to the Gravitational Focus
« Reply #6 on: 12/10/2011 12:04 AM »
Pardon my ignorance, but what does FOCAL stand for again? Is it an acronym?

The point of focus is called the focal point.

Offline sanman

  • Senior Member
  • *****
  • Posts: 3513
  • Liked: 403
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #7 on: 12/10/2011 12:14 AM »
Fine, I know that - but why is FOCAL capitalized here? It just makes it look like it's an acronym which stands for something.

Offline sanman

  • Senior Member
  • *****
  • Posts: 3513
  • Liked: 403
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #8 on: 12/10/2011 12:34 AM »
So using the example of Kepler 22b, which is said to be 600 light years from Earth, could it be imaged using the FOCAL mission approach?

Would there have to be a prolonged exposure time in order to image that planet?

Offline KelvinZero

  • Senior Member
  • *****
  • Posts: 3308
  • Liked: 403
  • Likes Given: 92
Re: Mission to the Gravitational Focus
« Reply #9 on: 12/10/2011 10:39 AM »
So using the example of Kepler 22b, which is said to be 600 light years from Earth, could it be imaged using the FOCAL mission approach?

Would there have to be a prolonged exposure time in order to image that planet?
The article seems to claim it could make pretty much any object appear to be a ‘mere‘ 550 au away. sounds like a huge gain but surely you still need an impressive telescope.

I find this heartening just because it is one more interesting target we have yet to visit. We can just keep pushing the range of our robotic probes with each generation and there is always some new thing to make the extra range worthwhile.

Offline Tass

  • Full Member
  • ***
  • Posts: 352
  • Liked: 59
  • Likes Given: 138
Re: Mission to the Gravitational Focus
« Reply #10 on: 12/10/2011 12:38 PM »
So using the example of Kepler 22b, which is said to be 600 light years from Earth, could it be imaged using the FOCAL mission approach?

Would there have to be a prolonged exposure time in order to image that planet?
The article seems to claim it could make pretty much any object appear to be a ‘mere‘ 550 au away. sounds like a huge gain but surely you still need an impressive telescope.

I find this heartening just because it is one more interesting target we have yet to visit. We can just keep pushing the range of our robotic probes with each generation and there is always some new thing to make the extra range worthwhile.

The article seems to be written by someone who does not know terribly much about optics. I'll try to do some calculations when I have time.

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #11 on: 12/10/2011 01:30 PM »
I read that with a sufficiently large light collector (a rotating tether which is reeled out), you could make out features the size of cars on planets orbiting Alpha Centauri ...

... so I suppose that even with a Hubble-sized telescope, you could directly image Kepler-22b and perhaps make out continents, clouds and oceans, if they existed.
« Last Edit: 12/10/2011 01:31 PM by DLR »
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline Tass

  • Full Member
  • ***
  • Posts: 352
  • Liked: 59
  • Likes Given: 138
Re: Mission to the Gravitational Focus
« Reply #12 on: 12/10/2011 02:25 PM »
By a quick calculation it seems that a diffraction limited pixel of the picture at 600 AU will extend over about 30 millimeter, corresponding to 2 kilometers of the object if it is 600 light years away.

But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc. To get a useful signal to noise ratio in a realistic time one will probably have to drop resolution quite a bit.

Still seeing continents, and maybe finer detail would not seem unrealistic.

Offline sanman

  • Senior Member
  • *****
  • Posts: 3513
  • Liked: 403
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #13 on: 12/11/2011 12:03 AM »
Perhaps this sounds ignorant, but could one perhaps try to arrange for syzygy or colinearity with the Sun and Jupiter to improve the gravitational focus even further? Or is Jupiter's mass just not significant enough? At least it could help in blocking the Sun's disc, I suppose.


Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6580
  • Liked: 862
  • Likes Given: 132
Re: Mission to the Gravitational Focus
« Reply #14 on: 12/11/2011 12:26 AM »
But with an aperture to focal length ratio of about 65000 the intensity will be terrible,...

The math for this works out reasonable.  If the surface is as bright as Earth, a day-time shot would require about 41 seconds of exposure time at ISO 100 (unless I did that wrong).  Assuming the scope is tracking the planetary motion, a push-broom could be used to track planetary rotation making that exposure time work for that level of resolving power.

Offline sanman

  • Senior Member
  • *****
  • Posts: 3513
  • Liked: 403
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #15 on: 12/11/2011 01:06 AM »
So you mean that the space telescope could be very finely adjusting its angle, to keep its gaze fixed on an exo-planet like Kepler 22b for some necessary exposure duration, like say one minute?

If the space telescope is out there at a distance of 550 AU from the Sun, then is it traveling in an orbital trajectory around the Sun? Or is it sort of motionless and stationary while it aims at its exo-planet target?

Offline Lee Jay

  • Elite Veteran
  • Global Moderator
  • Senior Member
  • *****
  • Posts: 6580
  • Liked: 862
  • Likes Given: 132
Re: Mission to the Gravitational Focus
« Reply #16 on: 12/11/2011 01:32 AM »
I would suppose that the Sun's gravitational acceleration at such distance is so small that you could, if you'd like to, hold position there if you had an engine strong enough to get you there in the first place.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #17 on: 12/11/2011 02:03 AM »
If the space telescope is out there at a distance of 550 AU from the Sun, then is it traveling in an orbital trajectory around the Sun?
To get to 550+ AU in a reasonable time, it will be on an escape trajectory. Fortunately it doesn't have to stop there, the gravitational lens works at greater distances, and IIRC being farther away helps with some of the difficulties caused by having a star in the middle of your telescope.

However, pointing will be a challenge. If you actually manage to get km scale resolution on something light years away, you are going to need really precise and stable pointing to make use of it. Your target planet will also be moving at tens of km/s in it's orbit, and the star it orbits will probably be moving tens or hundreds of km/s relative to the sun.

We should keep in mind that the theoretical capabilities being discussed here are from spherical cow land. Achieving them in the real world would present tremendous challenges. However, you could fall short by many orders of magnitude and still do a lot better than conventional telescopes.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26447
  • Minnesota
  • Liked: 6357
  • Likes Given: 4634
Re: Mission to the Gravitational Focus
« Reply #18 on: 12/11/2011 02:23 AM »
Kilometer-scale resolution... If we can get resolution to even 100km or 1000km/s, we could study continents and possibly (if we get good spectral data) lifeforms if there are any pervasive on the surface in detail significantly greater than the single-point-of-light we have now and are likely to have for quite a long time (before a mission of this scale is done). The nice thing about a project like this is that it can be used to study planetary systems 10lightyears-100lightyears at reasonably good resolution that would be out of reach for even first-generation interstellar missions. There are at least 10,000 stars within 100 light years, compared to only ~10 within about 10 light years. Much better odds of finding good planets to study in detail. It would be interesting to read the details of someone doing serious analysis of this idea. This hand-waving is likely to be not too useful.
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 Sparky

  • Full Member
  • ***
  • Posts: 378
  • Connecticut
  • Liked: 0
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #19 on: 12/11/2011 07:15 AM »
Getting out there quickly could be done with a solar sail. Once beyond the 550au point, the sail can double as your reflector.

Online rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mission to the Gravitational Focus
« Reply #20 on: 12/11/2011 08:36 AM »
Getting out there quickly could be done with a solar sail. Once beyond the 550au point, the sail can double as your reflector.

You could get out there with a solar sail. But forget about using a solar sail as an optical reflector. A reflector for a telescope is a precision optical instrument, whereas a solar sail is just a very large area of reflecting foil.
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Online rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mission to the Gravitational Focus
« Reply #21 on: 12/11/2011 08:39 AM »
Trouble is that it looks in one specific direction, and steers very slowly. You have to move the probe around the sun at 500AU to change view.

Maybe it we, in a decade or so, have a really good candidate for an earth-like exoplanet, then it may be worth considering sending a probe to the specific point were it is in focus.

A big expensive mission, but much easier (and faster) than sending a probe to the actual planet.

The kepler mission also looks into one specific direction. This would still be good enough for a survey of extraterrestrial planets in a small, previously chosen area of the sky. And you could give the probe some tangential velocity using a jupiter flyby to slowly scan a strip of sky.
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #22 on: 12/11/2011 10:02 AM »
NASA studied a thousand AU probe in the late 80's. With a 1MW reactor and ion drives, it would have covered 1000AU in fifty years.

Scale up the nuclear reactor to higher power levels, and you can still be faster.

Aren't the Russians planning a 12MW reactor? I suppose a space tug this powerful could carry a telescope to 550 - 1000 AU in a reasonable time frame?
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline Tass

  • Full Member
  • ***
  • Posts: 352
  • Liked: 59
  • Likes Given: 138
Re: Mission to the Gravitational Focus
« Reply #23 on: 12/11/2011 11:48 AM »
Trouble is that it looks in one specific direction, and steers very slowly. You have to move the probe around the sun at 500AU to change view.

Maybe it we, in a decade or so, have a really good candidate for an earth-like exoplanet, then it may be worth considering sending a probe to the specific point were it is in focus.

A big expensive mission, but much easier (and faster) than sending a probe to the actual planet.

The kepler mission also looks into one specific direction. This would still be good enough for a survey of extraterrestrial planets in a small, previously chosen area of the sky. And you could give the probe some tangential velocity using a jupiter flyby to slowly scan a strip of sky.

For a given definition of "specific", one which was not the one used here.

Kepplers field of view is comparatively huge. Even at 600ly the object is only some 60000-70000 times bigger than the detector (meaning a 200m detector just to cover an earth-like planet). Your field of view is going to be little more than a single planet, not even a full solar system, let alone interstellar distances to survey more than one star at once. The chance of two stars in the same galaxy lying lined up well enough to fit them both is negligible.

If you have a tangential velocity then the strip covered will be way too narrow to hit anything at all in this galaxy. It has to be specifically steered to look at a certain point of interest.

If this solar lens thing works as well as it could in theory then you could theoretically do a Kepler type survey of the stars in a distant galaxy, and I don't mean Andromeda here. This is truly insane magnification.

But with an aperture to focal length ratio of about 65000 the intensity will be terrible,...

The math for this works out reasonable.  If the surface is as bright as Earth, a day-time shot would require about 41 seconds of exposure time at ISO 100 (unless I did that wrong).  Assuming the scope is tracking the planetary motion, a push-broom could be used to track planetary rotation making that exposure time work for that level of resolving power.

Ah right. Regular telescopes have a hard time seeing planets because a planet is much smaller than the resolution, so it only contributes a little bit of the light at a pixel. Not so in this case. Although we we lose a lot of light by only having a ring to gather it, we can also do way better than ISO 100 here. Great. 

We should keep in mind that the theoretical capabilities being discussed here are from spherical cow land. Achieving them in the real world would present tremendous challenges. However, you could fall short by many orders of magnitude and still do a lot better than conventional telescopes.

Definitely. All of it.

Motion I believe should be counterable. It should also be possible to correct for the sun being oblate. I don't know whether unpredictable turbulences in the sun are going to alter its gravitational field enough to smear the picture. 

 
« Last Edit: 12/11/2011 11:59 AM by Tass »

Online rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mission to the Gravitational Focus
« Reply #24 on: 12/11/2011 12:05 PM »
NASA studied a thousand AU probe in the late 80's. With a 1MW reactor and ion drives, it would have covered 1000AU in fifty years.

Scale up the nuclear reactor to higher power levels, and you can still be faster.

Aren't the Russians planning a 12MW reactor? I suppose a space tug this powerful could carry a telescope to 550 - 1000 AU in a reasonable time frame?

I would like to see giant nuclear reactors just as much as any other space enthusiast. But the political reality is that anything that involves reactors is not going to happen, at least from the US and europe. The best you can hope for is a RTG or some other (stirling?) radioisotope generator to power the telescope at 500au.

Fortunately you don't need nuclear electric propulsion to get to 500au. A solar sail could be used, or some other form of solar propulsion like solar electric or mini magnetospheric plasma propulsion. The problem with the latter is that you can only create radial outward forces. But for getting to 500au this is not a problem.

For using solar sails, see for example
http://intrance.org/paper/200410_Vancouver_Dachwald_Sail.pdf
or
http://interstellar.jpl.nasa.gov/interstellar/ISP_Space2K_v4.pdf
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Online rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mission to the Gravitational Focus
« Reply #25 on: 12/11/2011 12:41 PM »
Trouble is that it looks in one specific direction, and steers very slowly. You have to move the probe around the sun at 500AU to change view.

Maybe it we, in a decade or so, have a really good candidate for an earth-like exoplanet, then it may be worth considering sending a probe to the specific point were it is in focus.

A big expensive mission, but much easier (and faster) than sending a probe to the actual planet.

The kepler mission also looks into one specific direction. This would still be good enough for a survey of extraterrestrial planets in a small, previously chosen area of the sky. And you could give the probe some tangential velocity using a jupiter flyby to slowly scan a strip of sky.

For a given definition of "specific", one which was not the one used here.

Kepplers field of view is comparatively huge. Even at 600ly the object is only some 60000-70000 times bigger than the detector (meaning a 200m detector just to cover an earth-like planet). Your field of view is going to be little more than a single planet, not even a full solar system, let alone interstellar distances to survey more than one star at once. The chance of two stars in the same galaxy lying lined up well enough to fit them both is negligible.

Ok. Thanks for the correction. So the magnification is much better than I expected. So what you really want is a bunch of small telescopes looking towards the sun on a rotating tether, to cover a large area.

If you get there using a large solar sail, you could have multiple small telescopes spread over the area of the (slowly rotating) sail. I am thinking of something like the IKAROS sail, but scaled up to a diameter of several km.

The size of the field of view in radians is just the diameter of the telescope divided by the distance from the sun, right? Kind of like a pinhole camera with the pinhole being in the center of the sun, and the screen being the collection area of the spacecraft? That is really some mindboggling magnification...

If this solar lens thing works as well as it could in theory then you could theoretically do a Kepler type survey of the stars in a distant galaxy, and I don't mean Andromeda here. This is truly insane magnification.

So make sure there are some distant galaxies in the field of view and just take a look. At the very least you should be able to validate or invalidate theories about the gravity of the sun.
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Offline clongton

  • Expert
  • Senior Member
  • *****
  • Posts: 10256
  • Connecticut
    • Direct Launcher
  • Liked: 2005
  • Likes Given: 619
Re: Mission to the Gravitational Focus
« Reply #26 on: 12/11/2011 12:46 PM »
I would like to see giant nuclear reactors just as much as any other space enthusiast. But the political reality is that anything that involves reactors is not going to happen, at least from the US and Europe. The best you can hope for is a RTG or some other (stirling?) radioisotope generator to power the telescope at 500au.

The US and Europe are eventually going to have to get over their childish fear of nuclear power if they are ever going to do anything significant in space beyond the inner solar system. This fear reminds me of a child being unwilling to give up its bottle in order to drink its milk from a cup.

Getting out past Mars by any significant amount will make SEP impractical without arrays that are tens or hundreds of square kilometers in area and those would be completely unwieldy. Nuclear power is the only way forward, unless someone here thinks matter-antimatter is safer? Yes, nuclear is dangerous, but *anything* powerful is dangerous. So what? Learn to safely control the danger and get on with it. As a species, are we still bottle-fed infants?

Using a constantly thrusting nuclear powered ion engine would put this telescope on station in no time flat, relatively speaking. We could actually begin imaging exoplanets in our own lifetime. It's either do that or stick with our baby bottle and hope that our grandchildren remember to turn on the switch in 75 years or so.
Chuck - DIRECT co-founder
I started my career on the Saturn-V F-1A engine

Online rklaehn

  • telemetry plumber
  • Full Member
  • ****
  • Posts: 1204
  • germany
    • www.heavens-above.com
  • Liked: 88
  • Likes Given: 147
Re: Mission to the Gravitational Focus
« Reply #27 on: 12/11/2011 01:10 PM »
The US and Europe are eventually going to have to get over their childish fear of nuclear power if they are ever going to do anything significant in space beyond the inner solar system. This fear reminds me of a child being unwilling to give up its bottle in order to drink its milk from a cup.

I completely agree. But the paranoia regarding all things nuclear is so strong that it will be another decade or more before nuclear fission gets seriously considered for power generation, let alone space applications. Maybe the US and europe will wake up when china and india power their entire economies using lithium fluoride thorium breeders, but maybe it will be too late then.

Quote
Getting out past Mars by any significant amount will make SEP impractical without arrays that are tens or hundreds of square kilometers in area and those would be completely unwieldy. Nuclear power is the only way forward, unless someone here thinks matter-antimatter is safer? Yes, nuclear is dangerous, but *anything* powerful is dangerous. So what? Learn to safely control the danger and get on with it. As a species, are we still bottle-fed infants?

It seems so. But I think that it is perfectly possible to get out of the solar system at high speed using solar electric propulsion as long as you don't plan to brake. You can do all your thrusting while close to the sun. Usually you will drop in to below venus orbit for the majority of the thrusting.

Quote
Using a constantly thrusting nuclear powered ion engine would put this telescope on station in no time flat, relatively speaking. We could actually begin imaging exoplanets in our own lifetime. It's either do that or stick with our baby bottle and hope that our grandchildren remember to turn on the switch in 75 years or so.

I fear that it's the latter. My hope is that it will be possible to start colonizing the inner solar system with just solar power. People living on the moon, mars, phobos or on a near earth asteroid will not have any irrational fear of nuclear power, since they will have all kinds of real dangers to worry about...
Try the ISS 3D visualization at http://www.heavens-above.com/ISS_3D.aspx

Offline Seer

  • Member
  • Full Member
  • **
  • Posts: 250
  • Liked: 5
  • Likes Given: 1
Re: Mission to the Gravitational Focus
« Reply #28 on: 12/11/2011 03:06 PM »
The magnification factor for visible light is 10^8. There is a scientis called Maccone
who has

written articles & books about the gravitational lens. For alpha centauri the theoretical maximum resolution is 3 meters with a 12m telescope. I imagine the practical maximum is 1 km if only due to pointing stability.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #29 on: 12/11/2011 05:09 PM »
I don't know whether unpredictable turbulences in the sun are going to alter its gravitational field enough to smear the picture. 
From what I gather, optical effects of the solar corona are also a big concern.

Claudio Maccone has done a great deal of work on this. You can find some presentations and papers google. He also wrote a book: http://www.amazon.com/Deep-Space-Flight-Communications-Gravitational/dp/3540729429 which is rather pricey ;)

I just noticed he gave a talk at the SETI institute, I haven't watched.

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26447
  • Minnesota
  • Liked: 6357
  • Likes Given: 4634
Re: Mission to the Gravitational Focus
« Reply #30 on: 12/12/2011 04:28 AM »
The US and Europe are eventually going to have to get over their childish fear of nuclear power if they are ever going to do anything significant in space beyond the inner solar system. This fear reminds me of a child being unwilling to give up its bottle in order to drink its milk from a cup.

I completely agree. But the paranoia regarding all things nuclear is so strong that it will be another decade or more before nuclear fission gets seriously considered for power generation, let alone space applications. ...
Not a problem when discussing a probe out to 550 AU. It'll be a while before we're ready.

Still, we're going to need to research fission (or radioisotopic) fragment rockets eventually. They're quite powerful.
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 Tass

  • Full Member
  • ***
  • Posts: 352
  • Liked: 59
  • Likes Given: 138
Re: Mission to the Gravitational Focus
« Reply #31 on: 12/12/2011 05:35 AM »
The size of the field of view in radians is just the diameter of the telescope divided by the distance from the sun, right? Kind of like a pinhole camera with the pinhole being in the center of the sun, and the screen being the collection area of the spacecraft? That is really some mindboggling magnification...

That is the assumption I worked with. However according to Macone you can use of-center light and so expand your field of view at the expense of resolution and intensity. So watching multiple stars are maybe not completely out.

Edit: Here's an interesting slideshow. It lacks the talk obviously, but it is still informative.

Second edit, forgot the link to said slideshow: http://www.cesr.fr/~g-wave05/presentations/optics/Koechlin.pdf
« Last Edit: 12/13/2011 03:27 PM by Tass »

Offline DLR

  • Full Member
  • ****
  • Posts: 494
  • Angus, Scotland
  • Liked: 14
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #32 on: 12/13/2011 11:29 AM »
I think you people are overestimating public opposition against fission reactors.

There are plenty of fission power plants under construction right now. Most in Asia and Russia, but some in the EU too.

Russia is planning to design and launch a space-based fission reactor in the next decade.

Launching a radioisotope power generator (which is kind of routine) is much more hazardous, since those things are stuffed with Plutonium and other nasty transuranics. Not so a "virgin" reactor: just U-235 and U-238. 

Anyway, this is not the topic of this thread. I brought it up because nuclear electric propulsion is probably the most mature technology when it comes to high-performance propulsion. A solar fryby + solar sail propulsion is completely untested. Fission reactors and electric engines on the other hand have been flown before.
"Bei der Eroberung des Weltraums sind zwei Probleme zu lösen: die Schwerkraft und der Papierkrieg." - Wernher von Braun

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26447
  • Minnesota
  • Liked: 6357
  • Likes Given: 4634
Re: Mission to the Gravitational Focus
« Reply #33 on: 12/13/2011 02:47 PM »
I think you people are overestimating public opposition against fission reactors.
I agree, in the long-term (which is necessarily what this thread is about).
Quote
Russia is planning to design and launch a space-based fission reactor in the next decade.
I would bet they've been planning to design and launch a space-based fission reactor since Sputnik (they have actually done that, mind you, but the performance hasn't been spectacular).

I should also point out that there has been an interplanetary solar sail already flown (being flown right now)... The Japanese IKAROS. You probably already knew that, but I'm just pointing that out. Granted, it only went in to about Venus orbit, but the fission reactors we've flown so far are nowhere even CLOSE to the performance necessary for a mission to 550AU.
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 Chandonn

  • Extreme Veteran
  • Full Member
  • ****
  • Posts: 1226
  • "Pudding!!! UNLIMITED Rice Pudding!!!"
  • Lexington, Ky
  • Liked: 4
  • Likes Given: 9
Re: Mission to the Gravitational Focus
« Reply #34 on: 01/19/2012 03:00 PM »
I've been giving this proposed mission a lot of thought.  Now, getting out to 550 AU may well be out of our reach for now.  So I was thinking about something more doable, but I don't have the math figures to see if it's even feasible.

We know that every sizable mass will produce a noticeable gravitational lensing effect.  As the sun's gravitational focus is well beyond our technological reach at present, what about Jupiter?  True, it won't produce anywhere near the lensing effect that the sun will.  But where would be its focus and how much of an improvement would that get us?

Offline Robotbeat

  • Senior Member
  • *****
  • Posts: 26447
  • Minnesota
  • Liked: 6357
  • Likes Given: 4634
Re: Mission to the Gravitational Focus
« Reply #35 on: 01/19/2012 03:32 PM »
I've been giving this proposed mission a lot of thought.  Now, getting out to 550 AU may well be out of our reach for now.  So I was thinking about something more doable, but I don't have the math figures to see if it's even feasible.

We know that every sizable mass will produce a noticeable gravitational lensing effect.  As the sun's gravitational focus is well beyond our technological reach at present, what about Jupiter?  True, it won't produce anywhere near the lensing effect that the sun will.  But where would be its focus and how much of an improvement would that get us?
Jupiter's gravitational focus would be even further away than the Sun's.
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 Andrew_W

  • Full Member
  • ****
  • Posts: 763
  • Rotorua, New Zealand
    • Profiles of our future in space
  • Liked: 11
  • Likes Given: 11
Re: Mission to the Gravitational Focus
« Reply #36 on: 01/19/2012 07:09 PM »
Jupiter's gravitational focus is at about 5000 AU:
http://www.physicsforums.com/showthread.php?t=101614
I confess that in 1901 I said to my brother Orville that man would not fly for fifty years.
Wilbur Wright

Offline TakeOff

  • Full Member
  • ***
  • Posts: 330
  • Liked: 71
  • Likes Given: 92
Re: Mission to the Gravitational Focus
« Reply #37 on: 01/26/2015 09:48 AM »
A good start might be to dive in close to the Sun and there blast off a high thrust engine to make maximum use of the Oberth effect in apohelium. Solar Probe Plus will have a top speed of 200 km/s. The dive would require the orbital speed of Earth to be canceled, which is done either by a flyby of Jupiter or like Solar Probe Plus, by several flybys of Venus.

I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling. It would only need to work for hours or days. Could nuclear weapons be used to give a shove when the Oberth bonus is at its maximum?

For the multi-decadal journey from there on, nuclear electric ion propulsion would be great. The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

It is a mission which seems doable this century, and it is an interstellar mission of sorts. It could be used to reconnaitre a star before a truly interstellar mission is sent there, and also to communicate with such an interstellar probe using the same phenomenal magnification.

But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

(Old thread, but unfortunately interest seems to be too low to start another one on the same topic)

Offline Bynaus

  • Full Member
  • ***
  • Posts: 363
  • Planetary Scientist
  • Switzerland
  • Liked: 248
  • Likes Given: 143
Re: Mission to the Gravitational Focus
« Reply #38 on: 01/26/2015 09:59 AM »
Jupiter's gravitational focus is at about 5000 AU:
http://www.physicsforums.com/showthread.php?t=101614

Lets hope we find a Jupiter-sized planet in the Oort cloud, then... :)

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5035
  • Liked: 736
  • Likes Given: 502
Re: Mission to the Gravitational Focus
« Reply #39 on: 01/26/2015 10:49 AM »
I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling.

Are you perhaps thinking of nuclear-electric propulsion?  A nuclear-thermal rocket cools itself by dumping heat into its exhaust.

Quote
The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

For a weak gravitational field like the sun's, the angle (in radians) by which a ray of electromagnetic radiation is deflected as it passes the sun is 4GM/(c2b), where G is the universal gravitational constant, M is the mass of the sun, c is the speed of light and b is the impact parameter, the distance of closest approach of the ray.  This is independent of frequency, so everything will focus at the same point.

Quote
But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

Why bother with a rotating tether?  Just go to the focus and look back at the sun with a coronograph (i.e., a telescope having a little dot in its center to block out the light of the sun itself).  Image the ring of light around the sun and then process the image to remove the massive distortion.

It seems to me that the real limiting factor with the gravitational-lens telescope is that you can look only at one very small part of the sky, namely the part that's opposite the sun.
« Last Edit: 01/26/2015 10:52 AM by Proponent »

Offline TakeOff

  • Full Member
  • ***
  • Posts: 330
  • Liked: 71
  • Likes Given: 92
Re: Mission to the Gravitational Focus
« Reply #40 on: 01/26/2015 11:34 AM »
I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling.

Are you perhaps thinking of nuclear-electric propulsion?  A nuclear-thermal rocket cools itself by dumping heat into its exhaust.

Quote
The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

For a weak gravitational field like the sun's, the angle (in radians) by which a ray of electromagnetic radiation is deflected as it passes the sun is 4GM/(c2b), where G is the universal gravitational constant, M is the mass of the sun, c is the speed of light and b is the impact parameter, the distance of closest approach of the ray.  This is independent of frequency, so everything will focus at the same point.

Quote
But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

Why bother with a rotating tether?  Just go to the focus and look back at the sun with a coronograph (i.e., a telescope having a little dot in its center to block out the light of the sun itself).  Image the ring of light around the sun and then process the image to remove the massive distortion.

It seems to me that the real limiting factor with the gravitational-lens telescope is that you can look only at one very small part of the sky, namely the part that's opposite the sun.
Great answer! (Especially since you bring good news).

Combining the gravitational lens with a coronagraph and why not a diffraction disk(1) too, and of course an interferometer, would be a triple whammy with too much of everything, thank you. But I fear, I don't know I just fear, that there is a limit to the resolution achievable in telescopes, because space itself contains gas which scatters light. If the light is scattered before it hits the telescope, there's no telescope technology which can fix that. There might be a limit of resolution beyond which better telescopes don't help.

1) http://www.colorado.edu/news/releases/2015/01/23/new-space-telescope-concept-could-image-objects-far-higher-resolution

Now to the aiming issue:
If one aims the first FOCAL telescope towards the center of the Milky Way, isn't it dense enough that always something would be in sight? If we first aim it at Sagittarius A-star (the super massive black hole), or at the center of the Andromeda galaxy, but it then drifts off because of the galactic orbit of the Sun or something, wouldn't one even then just glide over to other (a bit less, but still) interesting random objects in that general direction? One would hardly miss everything. And even then, I suppose that at least a tiny spot of the microwave background would be very well mapped.

Would continuous propulsion perpendicular to the trajectory, once in the focus, with a nuclear electric engine, be enough to keep a chosen target in line with the precision required?

Is there a show stopper for this idea?
« Last Edit: 01/26/2015 12:06 PM by TakeOff »

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #41 on: 01/26/2015 11:39 AM »
a couple of additional points.

(1)  If the thing was pointed in the direction of alpha centauri you would have three targets for the price of one. possibly more depending on whether any other interesting but more distant stars were in the general direction. But proxima, AC A and AC b are within spitting distance of each other. You could definitely hit those three without worrying about traversing along the 550 au orbital.

(2) if there were a probe sent to AC or whatever a relay station at 550 AU lensing would also amplify the telemetry, data and comms signals so that the transmitter size on the probe could be reduced to reasonable size.

http://www.centauri-dreams.org/?p=10123
« Last Edit: 01/26/2015 11:46 AM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

Offline TakeOff

  • Full Member
  • ***
  • Posts: 330
  • Liked: 71
  • Likes Given: 92
Re: Mission to the Gravitational Focus
« Reply #42 on: 01/26/2015 11:47 AM »
A FOCAL type mission would be the mission of the century. 2-3 decades preparation and then 5 or so decades travel time. Every decade a new mission should be sent to aim at another target: The galactic center, Andromeda, the most distant galaxy known, an interesting exoplanet, nearest Sun-twin star (to study its sunspot cycle and activity for our own protection) et c.

Along the way there would be several spin offs. Radio telescopy, interferometry in pocket launchable format, heliophysics both for the near flyby and for adjusting the signal for coronal distortions, spacecraft design for century lifetime with respect to energy supply, upgradability and self-repairs from radiation and micro impact damages. (Radio communication with Earth should be easy since it has a big radio telescope directed our way.)

And it is directly useful as a precursor for the first interstellar probes to be launched in the 22nd century. "Long term" is very popular if one asks people in general. FOCAL would provide a long term vision with step wise tangible progress along the way.

Offline TakeOff

  • Full Member
  • ***
  • Posts: 330
  • Liked: 71
  • Likes Given: 92
Re: Mission to the Gravitational Focus
« Reply #43 on: 01/26/2015 12:00 PM »
a couple of additional points.

(1)  If the thing was pointed in the direction of alpha centauri you would have three targets for the price of one. possibly more depending on whether any other interesting but more distant stars were in the general direction. But proxima, AC A and AC b are within spitting distance of each other. You could definitely hit those three without worrying about traversing along the 550 au orbital.
I don't do the math, but I'm not sure that is true. The gain is so enormous that even the angular distance between Centauri A and B might be huge for a solar gravitational lensing telescope. I think one would have to pick one of them and cannot turn enough to go from one to the other.

To catch more than one object with one such telescope, I think that objects which are naturally gravitationally lensed by galactic clusters, or with good timing by microlensing, could be candidates. Or just a dense mess like a galactic core. Or of course a transiting planet, then you either observe the star, or the planet, they do line up regularly.
« Last Edit: 01/26/2015 12:03 PM by TakeOff »

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #44 on: 01/26/2015 12:29 PM »
I think AC a and AC b are within the distance from Sol to Uranus. you may have a point with Alpha Proxima even though they are .16 light years apart but it is harder to imagine AC a and AC b would necessitate anything more than a mere flick of an attitude thruster. I meant only that you would not have to wait for the scope to make a appreciable fraction of one orbit to reposition.
When antigravity is outlawed only outlaws will have antigravity.

Offline aceshigh

  • Full Member
  • ****
  • Posts: 587
  • Liked: 164
  • Likes Given: 16
Re: Mission to the Gravitational Focus
« Reply #45 on: 01/26/2015 02:11 PM »
problem is getting to 1000 AU from the Sun.

That's 0.015 light years away.

Even New Horizons would take some 100 years to get there (can anybody do the math?)

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #46 on: 01/26/2015 02:41 PM »
If some of the near term prospects for faster transport work out this will not be a problem.

I consider NEP VASIMR short term. i consider the Slough Fusion rocket near term. Even M2P2.

if these do not happen it will only be because of political will and funding. It will not be a technology show stopper that prevents any of these from happening.
When antigravity is outlawed only outlaws will have antigravity.

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2389
  • Claremore, Ok.
  • Liked: 371
  • Likes Given: 10
Re: Mission to the Gravitational Focus
« Reply #47 on: 01/26/2015 02:52 PM »
A good start might be to dive in close to the Sun and there blast off a high thrust engine to make maximum use of the Oberth effect in apohelium. Solar Probe Plus will have a top speed of 200 km/s. The dive would require the orbital speed of Earth to be canceled, which is done either by a flyby of Jupiter or like Solar Probe Plus, by several flybys of Venus.

I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling. It would only need to work for hours or days. Could nuclear weapons be used to give a shove when the Oberth bonus is at its maximum?

For the multi-decadal journey from there on, nuclear electric ion propulsion would be great. The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

It is a mission which seems doable this century, and it is an interstellar mission of sorts. It could be used to reconnaitre a star before a truly interstellar mission is sent there, and also to communicate with such an interstellar probe using the same phenomenal magnification.

But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

(Old thread, but unfortunately interest seems to be too low to start another one on the same topic)

Well, since you want to dive close to the sun in the first place, why not a Nuclear Fusion drive?  you're going to wind up preheating the fuel to a fairly high temp, so pumping the fuel into the fusion chamber should not be an issue, simply open a valve.

The heat should be high enough that pushing it over the edge to fusion shouldn't require much energy, and with magnetic constrictionthe fuel will be under such high compression, it'll be close to fusion in the first place!
My God!  It's full of universes!

Offline Nilof

  • Full Member
  • ****
  • Posts: 877
  • Liked: 349
  • Likes Given: 529
Re: Mission to the Gravitational Focus
« Reply #48 on: 01/27/2015 03:13 PM »
A good start might be to dive in close to the Sun and there blast off a high thrust engine to make maximum use of the Oberth effect in apohelium. Solar Probe Plus will have a top speed of 200 km/s. The dive would require the orbital speed of Earth to be canceled, which is done either by a flyby of Jupiter or like Solar Probe Plus, by several flybys of Venus.

I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling. It would only need to work for hours or days. Could nuclear weapons be used to give a shove when the Oberth bonus is at its maximum?

For the multi-decadal journey from there on, nuclear electric ion propulsion would be great. The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

It is a mission which seems doable this century, and it is an interstellar mission of sorts. It could be used to reconnaitre a star before a truly interstellar mission is sent there, and also to communicate with such an interstellar probe using the same phenomenal magnification.

But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

(Old thread, but unfortunately interest seems to be too low to start another one on the same topic)

Well, since you want to dive close to the sun in the first place, why not a Nuclear Fusion drive?  you're going to wind up preheating the fuel to a fairly high temp, so pumping the fuel into the fusion chamber should not be an issue, simply open a valve.

The heat should be high enough that pushing it over the edge to fusion shouldn't require much energy, and with magnetic constrictionthe fuel will be under such high compression, it'll be close to fusion in the first place!

Any temperature you'll reach with sunlight alone will be many, many orders of magnitude below that required for fusion.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline aceshigh

  • Full Member
  • ****
  • Posts: 587
  • Liked: 164
  • Likes Given: 16
Re: Mission to the Gravitational Focus
« Reply #49 on: 01/27/2015 05:01 PM »
If some of the near term prospects for faster transport work out this will not be a problem.

I consider NEP VASIMR short term. i consider the Slough Fusion rocket near term. Even M2P2.

if these do not happen it will only be because of political will and funding. It will not be a technology show stopper that prevents any of these from happening.

what's your concept of "near term"? And what is the latest news about Slough's Fusion rocket?

Offline nadreck

Re: Mission to the Gravitational Focus
« Reply #50 on: 01/27/2015 05:24 PM »
My take on the ideal vehicle to get you to the focal point:

3.5 separate main propulsion systems:

Solar sail
Solar Thermal hydrogen high thrust near the sun
Nuclear Electric hydrogen ion (for braking which occurs for most of the flight)

So the solar sail gets deployed close as the probe 'rounds the bend at solar perihelion (5Giga meters say) and is spin stabilized, it is let go when the probe has to start braking (probably about 20 AU out from the sun but depends on Nuclear electric ion engine thrust to vehicle weight ratio and to the top speed of the probe).

For the highest impact I suggest that the solar sail includes central panel that is deformed later but has a point on the probe as its focus to heat hydrogen that cools the solar heat collector, if any MHD benefit can be added to the hydrogen that is heated this way by the ion engine, then go for that too. Plan the thrust to probe weight ratio to not exceed the acceleration to the sail and shrouds from the solar sail. As soon as the hydrogen budget for this is used up deform the reflector on the sail, continue to add thrust with the nuclear electric until it would run the craft into the sail or until when braking needs to start.


It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #51 on: 01/27/2015 06:16 PM »

what's your concept of "near term"? And what is the latest news about Slough's Fusion rocket?

i categorize as near term technologies that could work now if someone would throw all the components together in an integrated system or that appear to be approaching that state of TRL where it is rational to assume the current progress to that state will be uninterrupted by show stopping physics or technological implementation problems.

I do not take into account politics and funding.

VASIMR only needs a power source to work and those power sources are all available except fusion. it can be powered by batteries and solar panels. it can be powered by fission. NOW. Fusion in the near future. Available power is adequate. suitable Nuclear reactors are essentially available now from several companies including GE and Hitachi needing only to clear regulatory hurdles.

M2P2 is nearly as ready as VASIMR. I say this because all of the elements have been tested. working earthbound prototypes have been built. But a integrated space worthy system has not been considered to the degree VASIMR has if at all. you cannot find schematics of a flight article. but this should be fairly simple to do if someone decides to do it. thus M2P2 could be done in a short period of time anytime someone says the word.

Fusion appears to be viable within the decade. a number of private efforts and private-public partnerships have competing designs (which is a good thing.) several of these designs have data that suggests proper scaling increases will result in the critical break even which is just one step away from operational implementation. 

latest Slough information i could find:

http://www.helionenergy.com/?page_id=199
« Last Edit: 01/27/2015 07:43 PM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

Offline ChrisWilson68

  • Senior Member
  • *****
  • Posts: 3473
  • Sunnyvale, CA
  • Liked: 2020
  • Likes Given: 2343
Re: Mission to the Gravitational Focus
« Reply #52 on: 02/03/2015 10:01 AM »
I wonder what high thrust engine would be suitable? Nuclear thermal has about 4 times higher exit velocity than chemical rockets (if I'm not mistaken). But radiative cooling is a serious problem near the Sun, nuclear thermal needs cooling.

Are you perhaps thinking of nuclear-electric propulsion?  A nuclear-thermal rocket cools itself by dumping heat into its exhaust.

Quote
The gravitational focus is an endless line so there's no need to slow down. At different distances, different radio frequencies are magnified the most, so going on outwards is a benefit.

For a weak gravitational field like the sun's, the angle (in radians) by which a ray of electromagnetic radiation is deflected as it passes the sun is 4GM/(c2b), where G is the universal gravitational constant, M is the mass of the sun, c is the speed of light and b is the impact parameter, the distance of closest approach of the ray.  This is independent of frequency, so everything will focus at the same point.

Quote
But with an aperture to focal length ratio of about 65000 the intensity will be terrible, made even worse by the fact that one can only use a ring shaped aperture and not the full disc.
This "ring issue" is addressed by using two dishes, one at each end of a rotating tether. That way the telescope would in effect be ring shaped.

Why bother with a rotating tether?  Just go to the focus and look back at the sun with a coronograph (i.e., a telescope having a little dot in its center to block out the light of the sun itself).  Image the ring of light around the sun and then process the image to remove the massive distortion.

It seems to me that the real limiting factor with the gravitational-lens telescope is that you can look only at one very small part of the sky, namely the part that's opposite the sun.
Great answer! (Especially since you bring good news).

But I fear, I don't know I just fear, that there is a limit to the resolution achievable in telescopes, because space itself contains gas which scatters light. If the light is scattered before it hits the telescope, there's no telescope technology which can fix that. There might be a limit of resolution beyond which better telescopes don't help.

Gas scattering light doesn't limit resolution, it simply diminishes brightness.  If we can see an object at all with ordinary telescopes, it has plenty of brightness to make an extremely high resolution image at the gravitational focus.

Offline gosnold

  • Full Member
  • ***
  • Posts: 366
  • Liked: 82
  • Likes Given: 735
Re: Mission to the Gravitational Focus
« Reply #53 on: 02/03/2015 08:11 PM »
Gas and dust scattering is a problem for coronographs, because it introduces parasitic light that comes from the same direction as the desired signal. It may diminish the brightness of the target a bit, but it will mostly raise the noise floor, making it harder to detect the target.

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2389
  • Claremore, Ok.
  • Liked: 371
  • Likes Given: 10
Re: Mission to the Gravitational Focus
« Reply #54 on: 07/03/2015 09:41 PM »
Assuming for a moment that an optical version of the VLA radio telescope could be constructed and launched to the Gravitational Focus area, would there be a sufficient improvement in optical acuity to justify such an array?

     I was considering a 10 kilometer diameter array of smaller optical telescopes all tethered to a central point/control and processing hub, using multiple tethers, say about ten legs, each having five smaller optical telescopes spaced evenly along each leg of the tethers, for a total of fifty smaller telescopes, plus a central aiming telescope at the hub.

     The whole array would be rotating at about .01 G of acceleration and would use reaction control wheels to both aim and steady the telescopes.  If required to rotate the whole array, the telescopes and tethers would be reeled in to the central hub after closing the optical ports, the master attitude control wheels would be used to turn the whole array to the desired attitude and the telescopes and tethers would be reeled out to their new stations.

      Essentially I am suggesting an optical synthetic aperture array that would give the rough equivalent to an optical telescope with a ten kilometer mirror.

just a thought...
My God!  It's full of universes!

Offline Nilof

  • Full Member
  • ****
  • Posts: 877
  • Liked: 349
  • Likes Given: 529
Re: Mission to the Gravitational Focus
« Reply #55 on: 07/04/2015 01:29 AM »
One thing which would be very interesting (but very difficult) would be having a Neutrino detector out there. Gravity is the only force which is practical for bending the path of Neutrinos. Having an array of neutrino detectors at the lensing point distance could in theory allow for an imaging neutrino telescope. That could be a pretty big deal, since Neutrinos usually come from interesting sources, and completely ignore any interstellar gas or dust. It should be able to see a background from the big bang nucleosynthesis era and observe the effects of inflation much more directly.

Now, actually building something of the sort would be a massive undertaking and would likely involve highly capable robots building detectors using ice from local comets. It'd be limited to looking at small patches of sky and would mostly see noise unless each individual detector is made absolutely gigantic.
« Last Edit: 07/04/2015 01:32 AM by Nilof »
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #56 on: 07/04/2015 01:54 AM »
WRT the VLA idea just using the gravity lensing effect multiplies the power by millions and millions of times.  I do not see how the added complexity and points of failure for no certain benefit would be justifiable.

http://www.centauri-dreams.org/?p=785

http://www.centauri-dreams.org/?p=10123

(mind the paywall:  )

http://physicsworld.com/cws/article/print/2004/jun/10/gravitational-lensing-brings-extrasolar-planets-into-focus

http://www.icarusinterstellar.org/sun-gravitational-lens/

the HST if placed at the gravitational focus could resolve a mercury sized planet at 1000 light years distant (and theoretically at least at any distance) at the same resolution level and detail it could looking at mercury in our own solar system. 
When antigravity is outlawed only outlaws will have antigravity.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #57 on: 07/04/2015 02:12 AM »
the signal amplification and presumably the resolving power of a light would be multiplied by 10^8th power.

10^8 is 10 times itself 8 times.

that's a magnification factor of... ten times ten times ten times ten times ten times ten times ten times ten times ten.

thats 100,000,000.

thats 100 million times the original resolving power of the telescope or reception threshold or transmitting power of a radio communications system.

Would a VLA really be necessary?
« Last Edit: 07/04/2015 02:14 AM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

Offline Paul451

  • Full Member
  • ****
  • Posts: 1167
  • Australia
  • Liked: 571
  • Likes Given: 494
Re: Mission to the Gravitational Focus
« Reply #58 on: 07/04/2015 03:35 AM »
WRT the VLA idea just using the gravity lensing effect multiplies the power by millions and millions of times.  I do not see how the added complexity and points of failure for no certain benefit would be justifiable.

The reason was in the links you included. Gravitational lens telescopes have the resolving power of the same telescope at that distance from the sun (ie, 550-1000AU). HST resolves Pluto to about 4 pixels at a mere 40AU. Therefore if you want anything more than a single pixel (actually a sub-pixel) image of an exo-planet, you need a large array.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #59 on: 07/04/2015 03:45 AM »
granted you could learn more from a VLA but even with one pixel if there are contrasting areas on the planet you can deduce such things as snow, ice caps, clouds, continents, oceans, major forests, major deserts maybe even city lights and forest fires. With four you can do more still. Of course you can do a lot more with better and better resolution but you don't need much to uncover a wealth of information. Some of the very impressive big seeming detail revealing pictures of distant stars began with just 8 (5?) pixels (in width) and end up looking like medium res pictures of our sun from good earth bound telescopes.

« Last Edit: 07/04/2015 04:07 AM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #60 on: 07/04/2015 04:28 AM »
 Additionally while larger more advanced scopes than hubble may be necessary there are at least a couple of upcoming scopes expected to find terrestrial class planets in the habitable zone without being a VLA.  courtesy of Astronomer Jadestar on another forum:

Quote
We shouldn't have too wait long for confirmation of a planet around Proxima or Alpha Centauri A or Alpha Centauri B. Between TESS (transits), E-ELT and TMT (radial velocity) and WFIRST and potentially Exo-S (direct imaging) we will be looking at these stars closely in the next 15 years. And that's just the NASA missions, ESA also has several exoplanet missions.

It's even possible that we get a positive detection through the ESPRESSO spectrograph at the VLT (Very Large Telescope at the European Souther Observatory in Chile.

It will be able to detect Earth sized planets around nearby stars by measuring radial velocity. With a radial velocity precision better than 10cm/s, an Earth mass planet in the habitable zone of a low mass star can be detected.

ESPRESSO will be installed at the VLT and go into operation next year
When antigravity is outlawed only outlaws will have antigravity.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #61 on: 07/04/2015 05:13 AM »
If required to rotate the whole array, the telescopes and tethers would be reeled in to the central hub after closing the optical ports, the master attitude control wheels would be used to turn the whole array to the desired attitude and the telescopes and tethers would be reeled out to their new stations.
Only very fine aiming is needed... with the sun as your lens, there's only one direction to point.

To aim at a different target, you'd have move the whole telescope around the sun, which is going to be very slow at 500+ AU. This is one of the big downsides of the whole concept, it only makes sense if you have one target that you already know you *really* want to look at.

Quote
Essentially I am suggesting an optical synthetic aperture array that would give the rough equivalent to an optical telescope with a ten kilometer mirror.
The whole point of going to the gravitational focus is you effectively get a *sun sized* aperture (ok, it's more complicated than that, but you should get the idea...) edit: or maybe not, see Paul451 post.

An interferometer of the sort you suggest would be incredibly difficult to do. Unlike radio, you can't just record the data and correlate it later. The light path between your telescopes must maintained accurately on a scale similar to the wavelength of light your are observing, meaning a few hundred nanometers for visible.
« Last Edit: 07/04/2015 05:21 AM by hop »

Offline Paul451

  • Full Member
  • ****
  • Posts: 1167
  • Australia
  • Liked: 571
  • Likes Given: 494
Re: Mission to the Gravitational Focus
« Reply #62 on: 07/05/2015 05:07 AM »
To aim at a different target, you'd have move the whole telescope around the sun, which is going to be very slow at 500+ AU.

However, you will want to scan within a target system. (And track the target planets as they orbit.)

(Hmmm, what kind of lateral movement would be required to target exo-planets around Alpha Centauri A and B? (And Proxima?))

This is one of the big downsides of the whole concept, it only makes sense if you have one target that you already know you *really* want to look at.

Yeah. It's best thought of as a cheap interstellar probe, not an expensive observatory.

Stormbringer,
The published resolution for HST is 0.05 arcseconds. At 550AU, that gives you a resolution of 20 thousand km. That's actually better than I thought. (For Earth-sized planets, you can use tricks like using telescope slew to let the target drift across pixel boundaries to increase information content, in addition to using the natural rotation of the object to selectively mask/reveal features.)

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #63 on: 07/05/2015 01:59 PM »
One of the biggest questions critics of this concept bring up (in my opinion out of tune with the state of the art and nearing propulsion technology) is the length of time it would take us to get out there to that distance.

I think that we have tech now to quadruple or quintuple the Voyager probe's speed. If Voyager had the speed now possible due to advances in ion propulsion and other things it would already be there. Going from memory here: It's over 1/4 there now using old school tech. It is 17 light hours away. it took Voyager 36 years to get where it is but...It got there and it's still working.

Voyager 1 and 2's real time odometer and trip meter are right here:  http://voyager.jpl.nasa.gov/where/

:)

If some of the just out of reach technology developments appear short term as is probable this could turn into a 5 or ten year trip time.
When antigravity is outlawed only outlaws will have antigravity.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #64 on: 07/05/2015 06:41 PM »
(Hmmm, what kind of lateral movement would be required to target exo-planets around Alpha Centauri A and B? (And Proxima?))
Once you are outside of the lensed region, shouldn't it just be the angle between the targets, projected on a 550(+) AU radius circle?
D = ~3500 AU = 9.5 AU/deg = 0.0026 AU / arcsec = roughly the earth / moon distance.... which doesn't actually seem that bad. With the incredible magnification, any targets of opportunity you passed over while slewing would be good science.

Alpha centaur A and B vary between 2 and 22 arcsec, while Proxima is a whopping 2.2 degrees away.

Of course, if you got to 550 AU in a reasonable time, you'll be moving outward at tens of AU per year.

Quote
The published resolution for HST is 0.05 arcseconds. At 550AU, that gives you a resolution of 20 thousand km.
So a diffraction limited single telescope in the tens of meters range would really be very good.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #65 on: 07/05/2015 09:48 PM »
Hubble's resolution has been bested by newer scopes -even based ground scopes of smaller sizes in some cases. Hubble is not SOTA now. It's old. Still spectacularly useful; but old.
When antigravity is outlawed only outlaws will have antigravity.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #66 on: 07/06/2015 03:01 AM »
Hubble's resolution has been bested by newer scopes -even based ground scopes of smaller sizes in some cases. Hubble is not SOTA now. It's old. Still spectacularly useful; but old.
Well... sort of. You see lots of "OMG BETTER THAN HUBBLE" press releases, and they aren't usually lies, but if you read the fine print you generally find the claim only applies to some very specific application or requires very rare conditions. For many applications, Hubble is still state of the art.

In terms of resolution, Hubble is fairly close to diffraction limited, so a single telescope with a similar size mirror can't do much better. Interferometers can achieve higher resolution, but they aren't really equivalent in other respects.

All that said, if you were going to go to the trouble of flying a telescope to 550 AU, you'd probably want to start with a bigger mirror than Hubble. "like Hubble but with a larger mirror" would unequivocally be better than Hubble.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #67 on: 07/06/2015 03:57 PM »
Well you may be right; but I have had "conversations" with an advanced astronomy student of the sort that is already doing "field work" by going to work studies at such places as Australian facilities and NASA facilities. She is preparing to do a work study thing at NASA this year. She is based in WU normally. She posted several articles on work done with existing scopes that due to advances in signal processing and other technological tricks and techniques can surpass Hubble's resolution at least at some tasks.

and it's not all popular science article noise, bad editing, hype and misunderstandings by media authors either because she is in the loop with a lot of the first sources in those articles and often provides more information than the articles themselves manage.
When antigravity is outlawed only outlaws will have antigravity.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #68 on: 07/06/2015 10:33 PM »
on another note let's put this thing there:  http://www.astronomynow.com/news/n1406/26atlast/?#.VZsBH_lVhBd
When antigravity is outlawed only outlaws will have antigravity.

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2389
  • Claremore, Ok.
  • Liked: 371
  • Likes Given: 10
Re: Mission to the Gravitational Focus
« Reply #69 on: 07/07/2015 05:21 PM »
the signal amplification and presumably the resolving power of a light would be multiplied by 10^8th power.

10^8 is 10 times itself 8 times.

that's a magnification factor of... ten times ten times ten times ten times ten times ten times ten times ten times ten.

thats 100,000,000.

thats 100 million times the original resolving power of the telescope or reception threshold or transmitting power of a radio communications system.

Would a VLA really be necessary?

Not at first, granted, but later when you want more data at say, 13 billion light years away?  Then you wouldn't mind having a VLA.
My God!  It's full of universes!

Offline A_M_Swallow

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 8077
  • South coast of England
  • Liked: 247
  • Likes Given: 94
Re: Mission to the Gravitational Focus
« Reply #70 on: 07/07/2015 10:44 PM »
Would an ion thruster supply sufficient delta-v and thrust to provide the telescope's station keeping?

Offline JasonAW3

  • Senior Member
  • *****
  • Posts: 2389
  • Claremore, Ok.
  • Liked: 371
  • Likes Given: 10
Re: Mission to the Gravitational Focus
« Reply #71 on: 07/08/2015 12:01 AM »
Would an ion thruster supply sufficient delta-v and thrust to provide the telescope's station keeping?

Likely, but aiming and stabilization would likely work better with reaction wheels.  Gross movement could be handled by the job thrusters, but you'd want to cover your optics when using them, much like Hubble does during a hardware upgrade.
My God!  It's full of universes!

Offline indaco

  • Member
  • Posts: 5
  • Liked: 0
  • Likes Given: 0
Re: Mission to the Gravitational Focus
« Reply #72 on: 07/10/2015 08:27 AM »
..
This is one of the big downsides of the whole concept, it only makes sense if you have one target that you already know you *really* want to look at...

Are you certain?

I'm thinking about beamed propulsion, say MagBeam ( https://en.wikipedia.org/wiki/MagBeam) used to launch "relatively" passive, "relatively" cheap and "relatively" mass produced probes, so that you can place some of them on many proper trajectories.

The fact that a probe has to be specialized for a specific target suggest that we need many probes having a relatively low marginal cost per unit.

The expensive task is the MagBeam facility ... but we could reuse it for many scopes and missions, not for gravity lens missions only.   Scale and scope economies: an expensive program but many missions and veichles.

Of course this is for the relatively long term but still much more realistic than interstellar missions. i don't konw is MagBeam is workable, but the literature I've found on the web is relatively reassuring.

Excessive use of the word "relatively" is intentional :-)
Non-native English speaker and non-expert, be patient.

Offline aceshigh

  • Full Member
  • ****
  • Posts: 587
  • Liked: 164
  • Likes Given: 16
Re: Mission to the Gravitational Focus
« Reply #73 on: 07/10/2015 03:06 PM »
sorry for the stupid question, which is just SOMEWHAT related to the thread...

would a HUMAN, with naked eyes (well, he certainly would need a spacesuit visor, so no truly naked eyes here) be able to notice the Sun Gravitational Focus? Obviously not to see a planet around another star... but suppose the human aligned himself and the gravitational focus to see Jupiter, maybe even Earth?

As I understand, in a black hole the effect would be easily noticed by naked eyes, in the few nanoseconds before your eyes are burned to crisps by the gamma rays from the accretion disk.

I guess the lens effect would be only a little larger than the apparent size of the sun seen from 550 AU?

Offline Paul451

  • Full Member
  • ****
  • Posts: 1167
  • Australia
  • Liked: 571
  • Likes Given: 494
Re: Mission to the Gravitational Focus
« Reply #74 on: 07/11/2015 02:47 AM »
would a HUMAN, with naked eyes (well, he certainly would need a spacesuit visor, so no truly naked eyes here) be able to notice the Sun Gravitational Focus?

Anything roughly behind it will be turned into a partial Einstein Ring. The distortion should be pretty obvious, provided you mask the sun.

(There won't be enough light from any exo-planets for their Einstein Rings to be visible with the unaided eye.)

but suppose the human aligned himself and the gravitational focus to see Jupiter, maybe even Earth?

No. It works because the light path from distant objects is nearly parallel by the time it passes the sun. Anything inside the solar system is too close, the light path is too divergent. (Without doing the maths, my guess is that the focal points for objects within the solar system would be light years away from the sun.)

I guess the lens effect would be only a little larger than the apparent size of the sun seen from 550 AU?

Yes, the path of light that focuses at 542AU brushes the edge of the sun. Any closer to the sun and the (theoretical) light path you are looking for would be passing through the sun. The further you are from the sun, the further beyond the sun's surface the focusing light path moves.

At 550AU you will still get some distortion from the sun's corona, but it's apparently usable for higher frequencies. Between 600-1000AU is considered the butter-zone for both optical and radio, close enough to keep your 'scope size (and trip time) reasonable, far enough to minimise distortion. Beyond 1000AU, you'll need larger and larger 'scopes to achieve the same resolution.

Online hop

  • Senior Member
  • *****
  • Posts: 3139
  • Liked: 341
  • Likes Given: 655
Re: Mission to the Gravitational Focus
« Reply #75 on: 04/22/2016 03:37 AM »
Geoffrey Landis pours some cold water on this concept: Mission to the Gravitational Focus of the Sun: A Critical Analysis

As one might expect, having the sun in the middle of your telescope is a Big Problem, but not the only one. If Landis' analysis is correct, the characteristics of the Einstein ring that forms the image of the planet seem to present some pretty fundamental difficulties. It will be interesting to see if there is a response from Maccone.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #76 on: 04/22/2016 08:43 AM »
what i got from that ( i just read the opening blurb) is it's a hard job. not that it's impossible. I have faith that we can make the technical and engineering improvements needed to do it.
When antigravity is outlawed only outlaws will have antigravity.

Offline jebbo

  • Full Member
  • **
  • Posts: 274
  • Cambridge, UK
  • Liked: 56
  • Likes Given: 42
Re: Mission to the Gravitational Focus
« Reply #77 on: 04/22/2016 12:41 PM »
Indeed he pours cold water on the idea:
- Need to go beyond 2200AU to avoid the corona
- Need for starshades to block both the sun and the host star
- Image size around 12km, so difficulty in obtaining full image
- Focal blur means very poor surface resolution
- Gain of 100,000 is fairly low, so it is worthwhile going that far
- Essentially a one target device.  At 550AU to re-target by 1 degree, need to move spacecraft by 10AU.

Ultimately it only feels like a reasonable idea as an interstellar precursor rather than as a sensible exoplanet characterisation exercise.  I can almost see it working with a huge swarm of starwisps that cross the focal plane simultaneously ...

--- Tony


Offline Proponent

  • Senior Member
  • *****
  • Posts: 5035
  • Liked: 736
  • Likes Given: 502
Re: Mission to the Gravitational Focus
« Reply #78 on: 04/22/2016 01:59 PM »
Having scanned the paper, I'd summarize it by saying that it's more than an order of magnitude more difficult than "merely" sending a spacecraft with a good camera to 550 AU, which is how I'd thought of it before.

Offline Proponent

  • Senior Member
  • *****
  • Posts: 5035
  • Liked: 736
  • Likes Given: 502
Re: Mission to the Gravitational Focus
« Reply #79 on: 04/22/2016 02:04 PM »
Having scanned the paper, I'd summarize it by saying that it's more than an order of magnitude more difficult than "merely" sending a spacecraft with a good camera to 550 AU, which is how I'd thought of it before.  I think along the lines of what jebbo suggests that if you were headed out that far for some other reason and could tweak your trajectory so that you'd actually pass the the focus of rays from some object, it might be cool to look back and see the Einstein ring.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #80 on: 04/22/2016 03:53 PM »
As for resolution I read an article yesterday about a new technique that will give upcoming scopes the ability to resolve continents on exoplanets so the limits of scopes and techniques are routinely being broken. 

OTOH this means that a lot of the advantages of a Gravitational Focus telescope are also being reduced.
When antigravity is outlawed only outlaws will have antigravity.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #81 on: 04/22/2016 04:54 PM »
http://nextbigfuture.com/2016/04/stellar-echo-imaging-of-exoplanets.html

Quote
A mission utilizing distributed-aperture stellar echo detectors could provide continent-level imaging of exoplanets more readily than interferometric techniques, as high temporal resolution detection is less technically challenging and more cost effective than multi-kilometer-baseline fringe-tracking, particularly in a photon-starved regime. The concept is viable for detecting exoplanets at more diverse orbital inclinations than is possible with transit or radial velocity techniques.
When antigravity is outlawed only outlaws will have antigravity.

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
Re: Mission to the Gravitational Focus
« Reply #82 on: 04/22/2016 05:20 PM »
BESIDES (<---------Yes i am shouting) we now have a new and even better reason to go even farther and a way to do it faster.

Planet nine is thought to be further out than the minimum 500 AU distance of the beginning of the GF region. We need to send probes there (once we verify it's location.)

And thanks to new propulsion ideas slightly less sketchy than the EM drive (so far...) we could get there three to four times faster than Voyager or Pluto Express (RIP) with one method and possibly at 20 percent c with another.
« Last Edit: 04/22/2016 07:07 PM by Stormbringer »
When antigravity is outlawed only outlaws will have antigravity.

Offline Star One

  • Senior Member
  • *****
  • Posts: 7480
  • UK
  • Liked: 1202
  • Likes Given: 168
Re: Mission to the Gravitational Focus
« Reply #83 on: 04/25/2016 04:56 PM »
This article is very much applicable to this thread.

Starshot and the Gravitational Lens

http://www.centauri-dreams.org/?p=35486

Offline Stormbringer

  • Full Member
  • ****
  • Posts: 1278
  • Liked: 220
  • Likes Given: 80
When antigravity is outlawed only outlaws will have antigravity.

Tags: