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Jamie M
Guest

Sun Jan 06, 2019 7:45 am   



Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie


Guest

Sun Jan 06, 2019 9:45 am   



On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Quote:
Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104


If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.

Quote:

That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie


Jamie M
Guest

Mon Jan 07, 2019 4:45 am   



Hi,

One simple modification, is to make the artificial guide stars
totally passive and extremely lightweight hollow pyramids:

https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Pyramid.svg/1280px-Pyramid.svg.png

with the apex pointed towards the telescope and illuminate them from the
telescope for the dual purpose of solar sail positioning them by aiming
the laser off center of the apex, as well as using them as an
illuminated guide star. They could be stacked like cups compactly if
they are hollow with no base, and deployed from the telescope to its
field of view. Ideally the required average illumination for guide star
use would equal the average illumination required for solar sail
positioning to maintain the cup within the telescopes field of view, and
not falling back towards the sun. If the average laser power is too
high, more hollow pyramids could be deployed to lower the average laser
power per cup (ie 100 cups would have 1% duty cycle from the laser on
average).

To implement the idea of a coded aperature on the artificial guide star
that the telescope views objects through, perhaps the cubesat could be
a light sensitive transparent material and a laser image projected onto
it from the telescope which temporarily would darken the cubesat to form
a variable coded aperature pattern. If that didn't work then the
artificial guide star should have an active 2d coded aperture, that
could be powered and have data sent via the wireless laser power
transmission from the telescope.

cheers,
Jamie


On 1/6/2019 6:57 PM, Jamie M wrote:
Quote:
On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only doing
high sensitivity imaging during the time the telescope and artificial
star cubesat are falling towards the sun. Batteries would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie




That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ


That is having a coded aperture between the telescope and the object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie


Jamie M
Guest

Mon Jan 07, 2019 4:45 am   



On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
Quote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only doing
high sensitivity imaging during the time the telescope and artificial
star cubesat are falling towards the sun. Batteries would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie



Quote:


That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie


Jamie M
Guest

Mon Jan 07, 2019 5:45 am   



Hi,

One more option that could increase the pointing resolution
by effectively averaging many guide star measurements, would be to
deploy 100,000+ very small retroreflective artificial guidestars,
ie 1 gram each, dispersed around the telescope, and then use a high
power laser pulse at a high repetition rate while using the telescope
and in a 2 arc minute by 2 arc minute field of view, have at least 10
retroreflections from the passive artificial guide stars visible.

That could give more light and pointing accuracy than a single laser
from one guide star perhaps, however the cloud of artificial guide stars
would dissipate over time, so multiple batches might need to be
released. If a known area of sky will be viewed, the artificial guide
stars could be released in a smaller field of view and then far fewer
would need to be deployed too.

cheers,
Jamie


On 1/6/2019 8:10 PM, Jamie M wrote:
Quote:
Hi,

To allow for the artificial guide stars to be used over the
whole 360 degree field of view, for artificial guidestars that
are in the 180 degree field of view of the telescope looking away
from the sun should have slightly larger mass to cross section area,
so that they fall towards the sun slightly faster than the telescope,
and have a miniscule laser correction applied from the telescope
to keep them in the field of view.

For artificial guidestars that are in the 180 degree field of view of
the telescope looking towards the sun, the artificial guidestars should
have a slightly smaller mass to cross section area, so that they fall
towards the sun slightly slower than the telescope, and have a
miniscule laser correction applied from the telescope to keep them
in the field of view.

cheers,
Jamie


On 1/6/2019 7:58 PM, Jamie M wrote:
Hi,

Just one more optimization:

The telescope field of view could approach 360 degrees
(the whole sky) if the telescope can aim independently
of the sun shade, ie they would decouple after launch,
with the sun shade blocking the sun and providing electricty
over small wires to the telescope.

cheers,
Jamie



On 1/6/2019 7:52 PM, Jamie M wrote:
Hi,

To further simplify the telescope design, and allow for the
artificial guide stars to maintain their position in the
telescope field of view at an arbitrary distance, the telescope could be
launched from earth, removing earth's orbital velocity of 30km/s, and
having an apogee of approx 10 AU, so the life of the telescope
would be: plugs into google: sqrt(pi^2 * (5 AU)^3 /(G(m_sun+m_saturn)))

5.58 years *2 = 10 years

The telescope would fall into the sun after about 10 years, and would
require no propellant or thrusters, it would only require a relatively
small solar panel to power control moment gyroscopes. The artificial
guide stars could be passively released from a stack, or actively
controlled if a larger power source is available.

The field of view of the telescope could approach 180 degrees of the sky
(limited by the size of the sun shade).

cheers,
Jamie



On 1/6/2019 7:34 PM, Jamie M wrote:
Hi,

One simple modification, is to make the artificial guide stars
totally passive and extremely lightweight hollow pyramids:

https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Pyramid.svg/1280px-Pyramid.svg.png


with the apex pointed towards the telescope and illuminate them from
the
telescope for the dual purpose of solar sail positioning them by aiming
the laser off center of the apex, as well as using them as an
illuminated guide star. They could be stacked like cups compactly if
they are hollow with no base, and deployed from the telescope to its
field of view. Ideally the required average illumination for guide
star
use would equal the average illumination required for solar sail
positioning to maintain the cup within the telescopes field of view,
and
not falling back towards the sun. If the average laser power is too
high, more hollow pyramids could be deployed to lower the average laser
power per cup (ie 100 cups would have 1% duty cycle from the laser on
average).

To implement the idea of a coded aperature on the artificial guide star
that the telescope views objects through, perhaps the cubesat could be
a light sensitive transparent material and a laser image projected onto
it from the telescope which temporarily would darken the cubesat to
form
a variable coded aperature pattern. If that didn't work then the
artificial guide star should have an active 2d coded aperture, that
could be powered and have data sent via the wireless laser power
transmission from the telescope.

cheers,
Jamie


On 1/6/2019 6:57 PM, Jamie M wrote:
On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat
would
have to be even further away. It is hard to imagine, what earth or
sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar
panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission
from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase
the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the
telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only
doing
high sensitivity imaging during the time the telescope and
artificial star cubesat are falling towards the sun. Batteries
would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie




That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ


That is having a coded aperture between the telescope and the
object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a
large
next generation satellite.

cheers,
Jamie






Jamie M
Guest

Mon Jan 07, 2019 5:45 am   



Hi,

Just one more optimization:

The telescope field of view could approach 360 degrees
(the whole sky) if the telescope can aim independently
of the sun shade, ie they would decouple after launch,
with the sun shade blocking the sun and providing electricty
over small wires to the telescope.

cheers,
Jamie



On 1/6/2019 7:52 PM, Jamie M wrote:
Quote:
Hi,

To further simplify the telescope design, and allow for the
artificial guide stars to maintain their position in the
telescope field of view at an arbitrary distance, the telescope could be
launched from earth, removing earth's orbital velocity of 30km/s, and
having an apogee of approx 10 AU, so the life of the telescope
would be: plugs into google: sqrt(pi^2 * (5 AU)^3 /(G(m_sun+m_saturn)))

5.58 years *2 = 10 years

The telescope would fall into the sun after about 10 years, and would
require no propellant or thrusters, it would only require a relatively
small solar panel to power control moment gyroscopes. The artificial
guide stars could be passively released from a stack, or actively
controlled if a larger power source is available.

The field of view of the telescope could approach 180 degrees of the sky
(limited by the size of the sun shade).

cheers,
Jamie



On 1/6/2019 7:34 PM, Jamie M wrote:
Hi,

One simple modification, is to make the artificial guide stars
totally passive and extremely lightweight hollow pyramids:

https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Pyramid.svg/1280px-Pyramid.svg.png


with the apex pointed towards the telescope and illuminate them from the
telescope for the dual purpose of solar sail positioning them by aiming
the laser off center of the apex, as well as using them as an
illuminated guide star. They could be stacked like cups compactly if
they are hollow with no base, and deployed from the telescope to its
field of view. Ideally the required average illumination for guide star
use would equal the average illumination required for solar sail
positioning to maintain the cup within the telescopes field of view, and
not falling back towards the sun. If the average laser power is too
high, more hollow pyramids could be deployed to lower the average laser
power per cup (ie 100 cups would have 1% duty cycle from the laser on
average).

To implement the idea of a coded aperature on the artificial guide star
that the telescope views objects through, perhaps the cubesat could be
a light sensitive transparent material and a laser image projected onto
it from the telescope which temporarily would darken the cubesat to form
a variable coded aperature pattern. If that didn't work then the
artificial guide star should have an active 2d coded aperture, that
could be powered and have data sent via the wireless laser power
transmission from the telescope.

cheers,
Jamie


On 1/6/2019 6:57 PM, Jamie M wrote:
On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only doing
high sensitivity imaging during the time the telescope and artificial
star cubesat are falling towards the sun. Batteries would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie




That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ


That is having a coded aperture between the telescope and the
object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie




Jamie M
Guest

Mon Jan 07, 2019 5:45 am   



Hi,

To further simplify the telescope design, and allow for the
artificial guide stars to maintain their position in the
telescope field of view at an arbitrary distance, the telescope could be
launched from earth, removing earth's orbital velocity of 30km/s, and
having an apogee of approx 10 AU, so the life of the telescope
would be: plugs into google: sqrt(pi^2 * (5 AU)^3 /(G(m_sun+m_saturn)))

5.58 years *2 = 10 years

The telescope would fall into the sun after about 10 years, and would
require no propellant or thrusters, it would only require a relatively
small solar panel to power control moment gyroscopes. The artificial
guide stars could be passively released from a stack, or actively
controlled if a larger power source is available.

The field of view of the telescope could approach 180 degrees of the sky
(limited by the size of the sun shade).

cheers,
Jamie



On 1/6/2019 7:34 PM, Jamie M wrote:
Quote:
Hi,

One simple modification, is to make the artificial guide stars
totally passive and extremely lightweight hollow pyramids:

https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Pyramid.svg/1280px-Pyramid.svg.png


with the apex pointed towards the telescope and illuminate them from the
telescope for the dual purpose of solar sail positioning them by aiming
the laser off center of the apex, as well as using them as an
illuminated guide star. They could be stacked like cups compactly if
they are hollow with no base, and deployed from the telescope to its
field of view. Ideally the required average illumination for guide star
use would equal the average illumination required for solar sail
positioning to maintain the cup within the telescopes field of view, and
not falling back towards the sun. If the average laser power is too
high, more hollow pyramids could be deployed to lower the average laser
power per cup (ie 100 cups would have 1% duty cycle from the laser on
average).

To implement the idea of a coded aperature on the artificial guide star
that the telescope views objects through, perhaps the cubesat could be
a light sensitive transparent material and a laser image projected onto
it from the telescope which temporarily would darken the cubesat to form
a variable coded aperature pattern. If that didn't work then the
artificial guide star should have an active 2d coded aperture, that
could be powered and have data sent via the wireless laser power
transmission from the telescope.

cheers,
Jamie


On 1/6/2019 6:57 PM, Jamie M wrote:
On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only doing
high sensitivity imaging during the time the telescope and artificial
star cubesat are falling towards the sun. Batteries would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie




That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ


That is having a coded aperture between the telescope and the object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie



Jamie M
Guest

Mon Jan 07, 2019 5:45 am   



Hi,

To allow for the artificial guide stars to be used over the
whole 360 degree field of view, for artificial guidestars that
are in the 180 degree field of view of the telescope looking away
from the sun should have slightly larger mass to cross section area,
so that they fall towards the sun slightly faster than the telescope,
and have a miniscule laser correction applied from the telescope
to keep them in the field of view.

For artificial guidestars that are in the 180 degree field of view of
the telescope looking towards the sun, the artificial guidestars should
have a slightly smaller mass to cross section area, so that they fall
towards the sun slightly slower than the telescope, and have a
miniscule laser correction applied from the telescope to keep them
in the field of view.

cheers,
Jamie


On 1/6/2019 7:58 PM, Jamie M wrote:
Quote:
Hi,

Just one more optimization:

The telescope field of view could approach 360 degrees
(the whole sky) if the telescope can aim independently
of the sun shade, ie they would decouple after launch,
with the sun shade blocking the sun and providing electricty
over small wires to the telescope.

cheers,
Jamie



On 1/6/2019 7:52 PM, Jamie M wrote:
Hi,

To further simplify the telescope design, and allow for the
artificial guide stars to maintain their position in the
telescope field of view at an arbitrary distance, the telescope could be
launched from earth, removing earth's orbital velocity of 30km/s, and
having an apogee of approx 10 AU, so the life of the telescope
would be: plugs into google: sqrt(pi^2 * (5 AU)^3 /(G(m_sun+m_saturn)))

5.58 years *2 = 10 years

The telescope would fall into the sun after about 10 years, and would
require no propellant or thrusters, it would only require a relatively
small solar panel to power control moment gyroscopes. The artificial
guide stars could be passively released from a stack, or actively
controlled if a larger power source is available.

The field of view of the telescope could approach 180 degrees of the sky
(limited by the size of the sun shade).

cheers,
Jamie



On 1/6/2019 7:34 PM, Jamie M wrote:
Hi,

One simple modification, is to make the artificial guide stars
totally passive and extremely lightweight hollow pyramids:

https://upload.wikimedia.org/wikipedia/commons/thumb/9/91/Pyramid.svg/1280px-Pyramid.svg.png


with the apex pointed towards the telescope and illuminate them from the
telescope for the dual purpose of solar sail positioning them by aiming
the laser off center of the apex, as well as using them as an
illuminated guide star. They could be stacked like cups compactly if
they are hollow with no base, and deployed from the telescope to its
field of view. Ideally the required average illumination for guide star
use would equal the average illumination required for solar sail
positioning to maintain the cup within the telescopes field of view, and
not falling back towards the sun. If the average laser power is too
high, more hollow pyramids could be deployed to lower the average laser
power per cup (ie 100 cups would have 1% duty cycle from the laser on
average).

To implement the idea of a coded aperature on the artificial guide star
that the telescope views objects through, perhaps the cubesat could be
a light sensitive transparent material and a laser image projected onto
it from the telescope which temporarily would darken the cubesat to form
a variable coded aperature pattern. If that didn't work then the
artificial guide star should have an active 2d coded aperture, that
could be powered and have data sent via the wireless laser power
transmission from the telescope.

cheers,
Jamie


On 1/6/2019 6:57 PM, Jamie M wrote:
On 1/6/2019 12:17 AM, upsidedown_at_downunder.com wrote:
On Sat, 5 Jan 2019 22:18:43 -0800, Jamie M <jmorken_at_shaw.ca> wrote:

Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

If the telescope is parked at Lagrange point 2 (L2), the cubesat would
have to be even further away. It is hard to imagine, what earth or sun
centered orbit it would have.

To handle telescope targets in the ecliptical plane only, a large
number of satellites would be required. For telescope targets outside
the ecliptical plane, a huge number of satellites at different
inclinations would be required.


Hi,

That could be done with a smart orbit of the constellation of cubesats
(which could be useful for other purposes too maybe).

Or maybe a simpler idea is to use a next generation telescope that
uses a large solar sail, not to travel, but just to stay parked at
a certain distance from the sun, ie at 10 AU, a 10,000 kg telescope
would require a 0.59 Newton force to maintain its distance from
the sun with no orbital velocity. It could be powered by a solar panel
feeding an ion engine or a solar sail, in either case it would be
integrated as part of the sun shield.

If a solar panel is used, at 10 AU, a 20% efficiency panel giving
2.7watts per square meter, and the spacecraft requires 20kW of power
that is a 85m x 85m solar panel. If a modern space rated solar panel
weighs 2kg/m^2 of collecting area that would weight 14,450kg just for
the solar panels, so to keep the solar panel weight under 4000kg it
should weight at most 0.72kg/m^2 of collecting area.

Then the cubesat guidestars, say 100kg, would only require a 0.006
Newton force to stay in proximity to the telescope. I think the
cubesats could be powered by microwave or laser energy transmission
from
the telescope, to avoid them requiring having solar panels or RTG
nuclear reactors, since the cubesats would stay in the field of view
of the telescope and within a specified range. That would increase the
solar panel requirements on the telescope, so it would be best to use
a 40kW nuclear reactor on the telescope, which would power the
telescope
and all cubesats via wireless power transmission.

(0.006N force of gravity on a 100kg mass at 10 AU from the Sun)

If an ion engine gives 0.25 N thrust for 7kW, and can be throttled
down to 0.5kW ie:

https://en.wikipedia.org/wiki/NEXT_(ion_thruster)

Then three of those ion thrusters could provide propulsion for the
telescope and one ion thruster for the cube satellites.

It has a specific impulse over 4000s so at a force of 0.006N, a
100kg cubesat should use 0.12ug of propellant per second, or about
10grams of propellant per day, 3.78kg of propellant per year.

If the thruster is rated for 10 years operation, that would require
less than 36kg of propellant to counter the force of gravity at 10 AU
for 10 years. Which would give the cube satellites a 64kg dry mass.

For the telescope, using slightly more than two full throttle ion
thrusters, providing 0.59 Newtons of force, about 100 times the fuel
would be required than each cubesat, so 378kg of propellant per year
for the telescope. Or 3780kg for 10years of propellant, which would
give the telescope a 6220kg dry mass. The propellant used would
decrease as well over time as the spacecraft mass decreased.

The extra complexity of ion engines providing non uniform thrust
could defeat the purpose of high accuracy artificial guide stars,
so I guess they could be operated only when a specific cube satellite
isn't being used as a guide star.

This could be accomplished for the telescope and cubesats by running
the ion thrusters at 50% duty cycle at twice the thrust, and only doing
high sensitivity imaging during the time the telescope and
artificial star cubesat are falling towards the sun. Batteries
would be needed to
keep the solar panel size the same in that case of 50% dutycycle at
twice the thrust.

Instead of the 85m x 85m solar panel on the telescope, a 20kW nuclear
reactor could be used too: (ie four Topaz 2 10kW reactors)

https://en.wikipedia.org/wiki/TOPAZ_nuclear_reactor

cheers,
Jamie




That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ


That is having a coded aperture between the telescope and the
object(s)
being imaged.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a
large
next generation satellite.

cheers,
Jamie





Martin Brown
Guest

Mon Jan 07, 2019 2:45 pm   



On 06/01/2019 06:18, Jamie M wrote:
Quote:
Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104


I think what they are trying to do is a variant of the holographic
correction of the shape of the segmented mirror after launch and that
the press release has garbled it into "guide star".

The technique was pioneered at Jodrell Bank to fine tune the big dish in
one of its refurbishments and code derived from that was used to
quantify the abberations on the original Space Telescope and deduce the
corrections needed for COSTAR.

https://core.ac.uk/display/36897832

Can't find any references not behind a paywall.
Quote:

That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.


There was a time when this was done for hard X-rays before narrow angle
glancing incidence imaging was possible.

Quote:
I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie


Parallax would almost certainly prevent using it as a guide star.

Most fields of view contain at least one star bright enough for an
autoguider so outside the atmosphere I don't see what the advantage is.

--
Regards,
Martin Brown

Phil Hobbs
Guest

Mon Jan 07, 2019 6:45 pm   



On 1/7/19 8:19 AM, Martin Brown wrote:
Quote:
On 06/01/2019 06:18, Jamie M wrote:
Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

I think what they are trying to do is a variant of the holographic
correction of the shape of the segmented mirror after launch and that
the press release has garbled it into "guide star".

The technique was pioneered at Jodrell Bank to fine tune the big dish in
one of its refurbishments and code derived from that was used to
quantify the abberations on the original Space Telescope and deduce the
corrections needed for COSTAR.

https://core.ac.uk/display/36897832

Can't find any references not behind a paywall.

That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

There was a time when this was done for hard X-rays before narrow angle
glancing incidence imaging was possible.

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie

Parallax would almost certainly prevent using it as a guide star.

Most fields of view contain at least one star bright enough for an
autoguider so outside the atmosphere I don't see what the advantage is.


It looks like a variant of the usual terrestrial adaptive optics
technique, which uses high-altitude scattering of a laser beam to figure
out the dynamic aberrations due to the turbulent atmosphere. AO systems
usually use Shack-Hartmann sensors to measure local wavefront tilt. SH
sensors are crappy but fast, and easily good enough to take out the
'seeing'. I doubt they'd be good enough for exoplanet detectors
though--you'd need something more like what's used in semiconductor
litho tools, which is usually moire.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC / Hobbs ElectroOptics
Optics, Electro-optics, Photonics, Analog Electronics
Briarcliff Manor NY 10510

http://electrooptical.net
https://hobbs-eo.com

Martin Brown
Guest

Tue Jan 08, 2019 10:45 am   



On 07/01/2019 16:53, Phil Hobbs wrote:
Quote:
On 1/7/19 8:19 AM, Martin Brown wrote:
On 06/01/2019 06:18, Jamie M wrote:
Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

I think what they are trying to do is a variant of the holographic
correction of the shape of the segmented mirror after launch and that
the press release has garbled it into "guide star".


[snip]
Quote:

Parallax would almost certainly prevent using it as a guide star.

Most fields of view contain at least one star bright enough for an
autoguider so outside the atmosphere I don't see what the advantage is.


It looks like a variant of the usual terrestrial adaptive optics
technique, which uses high-altitude scattering of a laser beam to figure
out the dynamic aberrations due to the turbulent atmosphere. AO systems
usually use Shack-Hartmann sensors to measure local wavefront tilt. SH
sensors are crappy but fast, and easily good enough to take out the
'seeing'. I doubt they'd be good enough for exoplanet detectors


+1

Also outside the atmosphere and in microgravity you shouldn't need to
actively tune the system up provided it is moderately rigid.

Interestingly you can do incredibly well on amateur sized instruments by
getting the focus right and taking a video aka Lucky seeing. Basically
by selecting only the sharpest images, register and stacking them.

https://en.wikipedia.org/wiki/Lucky_imaging

It has revolutionised amateur astronomy with cheap webcams and Jupiter
now imaged at high resolution almost 24/7 when it is in the night sky.

Big professional instruments need a lot more terms than just tilt-tip.

Quote:
though--you'd need something more like what's used in semiconductor
litho tools, which is usually moire.


I also thought that the intention for next generation planet hunting
scopes was to aim to null out the central star interferometrically.

It sounded to me like a project derived from this earlier work but it is
hard to tell from the popularised press release:

https://www.researchgate.net/publication/3806379_Space_Interferometry_Mission_measuring_the_Universe

--
Regards,
Martin Brown

Phil Hobbs
Guest

Tue Jan 08, 2019 8:45 pm   



On 1/8/19 4:35 AM, Martin Brown wrote:
Quote:
On 07/01/2019 16:53, Phil Hobbs wrote:
On 1/7/19 8:19 AM, Martin Brown wrote:
On 06/01/2019 06:18, Jamie M wrote:
Hi,

I came across this article mentioning using cubesats or similar
small satellites as a constellation of artificial guide stars for
a next generation space telescope to have a laser feedback signal to
maintain pointing accuracy on telescopes that don't necessarily have
inherent pointing accuracy, ie cheaper telescopes:

http://news.mit.edu/2019/tiny-satellites-guide-telescopes-0104

I think what they are trying to do is a variant of the holographic
correction of the shape of the segmented mirror after launch and that
the press release has garbled it into "guide star".

[snip]

Parallax would almost certainly prevent using it as a guide star.

Most fields of view contain at least one star bright enough for an
autoguider so outside the atmosphere I don't see what the advantage is.


It looks like a variant of the usual terrestrial adaptive optics
technique, which uses high-altitude scattering of a laser beam to figure
out the dynamic aberrations due to the turbulent atmosphere.  AO systems
usually use Shack-Hartmann sensors to measure local wavefront tilt.  SH
sensors are crappy but fast, and easily good enough to take out the
'seeing'.  I doubt they'd be good enough for exoplanet detectors

+1

Also outside the atmosphere and in microgravity you shouldn't need to
actively tune the system up provided it is moderately rigid.

Interestingly you can do incredibly well on amateur sized instruments by
getting the focus right and taking a video aka Lucky seeing. Basically
by selecting only the sharpest images, register and stacking them.

https://en.wikipedia.org/wiki/Lucky_imaging


That idea has been around for a long time, e.g. speckle interferometry
with silver halide plates, but it's sure easier nowadays.

Quote:

It has revolutionised amateur astronomy with cheap webcams and Jupiter
now imaged at high resolution almost 24/7 when it is in the night sky.

Big professional instruments need a lot more terms than just tilt-tip.

though--you'd need something more like what's used in semiconductor
litho tools, which is usually moire.

I also thought that the intention for next generation planet hunting
scopes was to aim to null out the central star interferometrically.


That only works if it's unresolved, I think, so it's better suited to
smaller space-borne telescopes.

Quote:

It sounded to me like a project derived from this earlier work but it is
hard to tell from the popularised press release:

https://www.researchgate.net/publication/3806379_Space_Interferometry_Mission_measuring_the_Universe


Cheers

Phil Hobbs


--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510

hobbs at electrooptical dot net
http://electrooptical.net

Jamie M
Guest

Wed Jan 09, 2019 8:45 pm   



Quote:

That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

There was a time when this was done for hard X-rays before narrow angle
glancing incidence imaging was possible.


Hi,

That is a stationary mask pattern that was used which is integral to the
X-ray telescope.

Imagine if you replace the stationary coded aperature mask pattern with
a transparent LCD screen, ie like this one:

https://www.youtube.com/watch?v=wxjZu7F2GfI

If a space rated version is put in space, between an optical telescope
and the object being viewed, it could have the effect of vastly
improving the resolving power of the telescope by cycling the pixels
from transparent to opaque in a repeatable pattern. Also optionally
colour filtering could be done if using a monochrome CCD on the telescope.

The distance from the telescope to the LCD coded aperature depends on
how wide the LCD is and the pixel size, and the angular resolution of
the telescope, but it would be effective over a large range of distances.

The simplest way for it to be practical would be to have the telescope
and LCD having no orbital velocity, and either falling towards, moving
away, or stationary in relation to the sun.

If one or more LCD's are placed say 1000km to 10000km away from the
telescope, they could each cover a portion of the telescopes field of
view and move into position on the surface of a 1000km to 10000km
diameter sphere around the telescope. As long as the LCD, once in
position between the telescope and object being viewed, maintains
radial position within half a pixel on the LCD (ie 0.1mm approx) it
would work fine.

If the LCD is 1000x1000 pixels and at a given distance from the
telescope, masks a viewed object that appears 500x500 pixels when
viewed from the telescope, then even if the resolving power of the
telescope only can see a 10 pixel blur of the object, by cycling the
LCD pixels in a repeatable pattern (with full blanking for clock
timing with the telescope), then over time the telescope can resolve
a 500x500 pixel image of the object with some computer processing.

The limit to resolving power is in how many pixels are on the LCD.

cheers,
Jamie




Quote:

I think the two ideas of artificial guide stars and coded apertures
could be done by the same small satellite constellation around a large
next generation satellite.

cheers,
Jamie

Parallax would almost certainly prevent using it as a guide star.

Most fields of view contain at least one star bright enough for an
autoguider so outside the atmosphere I don't see what the advantage is.


Jasen Betts
Guest

Thu Jan 10, 2019 6:45 am   



On 2019-01-09, Jamie M <jmorken_at_shaw.ca> wrote:


Quote:
Imagine if you replace the stationary coded aperature mask pattern with
a transparent LCD screen, ie like this one:

https://www.youtube.com/watch?v=wxjZu7F2GfI


you'd have to make it optically flat and deal with diffraction
artifacts from the grid.

--
When I tried casting out nines I made a hash of it.

Martin Brown
Guest

Thu Jan 10, 2019 11:45 am   



On 09/01/2019 19:01, Jamie M wrote:
Quote:


That reminded me of an idea I had before, in this thread from 2014:

https://groups.google.com/forum/#!msg/sci.electronics.design/OzE-XroMuy8/wzH7Xgp_WqgJ

That is having a coded aperture between the telescope and the object(s)
being imaged.

There was a time when this was done for hard X-rays before narrow
angle glancing incidence imaging was possible.

Hi,

That is a stationary mask pattern that was used which is integral to the
X-ray telescope.


At least one was proposed (not sure if it was ever built) that consisted
of a 1-D quadratic residue mask in front of a wider block of detectors.
The spinning satellite would then image the object in radial slices.

They were all big blocks of scintillator with photomultiplier detectors.
The initial design was complete rubbish designed at Saclay in France
where they put their atomic bomb makers out to grass.

http://adsabs.harvard.edu/abs/1983A%26A...120..150D

It was actually for gamma-rays.

They tried to use maximum entropy to tart up the results but basically
as published the thing lacked adequate discrimination and had ghosts.

Quote:
Imagine if you replace the stationary coded aperature mask pattern with
a transparent LCD screen, ie like this one:

https://www.youtube.com/watch?v=wxjZu7F2GfI

If a space rated version is put in space, between an optical telescope
and the object being viewed, it could have the effect of vastly
improving the resolving power of the telescope by cycling the pixels
from transparent to opaque in a repeatable pattern.  Also optionally
colour filtering could be done if using a monochrome CCD on the telescope.


It wouldn't make a blind bit of difference to the resolving power of the
telescope which is determined fundamentally by the longest baseline that
it correlates photons over (typically diameter of its optics).
Quote:

The distance from the telescope to the LCD coded aperature depends on
how wide the LCD is and the pixel size, and the angular resolution of
the telescope, but it would be effective over a large range of distances.


The aperture would have to introduce a uniform phase delay if it was to
work at all. Mainly coded apertures allow you to alter the depth of
field after taking the image data but when everything you are looking at
is effectively at infinity this is not an advantage in astronomy and
merely degrades signal to noise with no benefits at all.

--
Regards,
Martin Brown

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