Calling a Cosmologist

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Boac
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Calling a Cosmologist

#1 Post by Boac » Sun Apr 26, 2020 8:09 am

OK - an interesting prog on Hubble the other night on't tele. Raises, of course, questions:

1) How is the Hubble steered? Is it propellant or gyro precession?
2) Is it allowed to maintain its attitude as it orbits? It will be facing the earth for part of each orbit if not?
3) OK, allowing for 'journalese', the prog described the 'latest' kit looking 12.5 Billion light years 'back' in the Universe. Amazing. Is that 'history' all around the earth or just in one space direction? IE is the assumed expansion of the universe centred on a point or everywhere?
4) This is really where my brain hurts.... if uni-directional, and Hubble looks 'the other way', what is it seeing in terms of universe history? If it 'looked' 12.5 billion light years in that direction, it is presumably seeing galaxies that are x billion years older than ours as they were 12.5 Billion years ago? There would, presumably, be a cross-over point where we could start seeing galaxies as old or older than ours and see what happened to them - gulp! Time to lie down. That is without bringing in distortion of the speed of light, of course...................

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Re: Calling a Cosmologist

#2 Post by TheGreenGoblin » Sun Apr 26, 2020 10:25 am

Boac wrote:
Sun Apr 26, 2020 8:09 am
OK - an interesting prog on Hubble the other night on't tele. Raises, of course, questions:

1) How is the Hubble steered? Is it propellant or gyro precession?
2) Is it allowed to maintain its attitude as it orbits? It will be facing the earth for part of each orbit if not?
3) OK, allowing for 'journalese', the prog described the 'latest' kit looking 12.5 Billion light years 'back' in the Universe. Amazing. Is that 'history' all around the earth or just in one space direction? IE is the assumed expansion of the universe centred on a point or everywhere?
4) This is really where my brain hurts.... if uni-directional, and Hubble looks 'the other way', what is it seeing in terms of universe history? If it 'looked' 12.5 billion light years in that direction, it is presumably seeing galaxies that are x billion years older than ours as they were 12.5 Billion years ago? There would, presumably, be a cross-over point where we could start seeing galaxies as old or older than ours and see what happened to them - gulp! Time to lie down. That is without bringing in distortion of the speed of light, of course...................
Call me a Cosmologist? You can call me TheGreenGoblin! :p

On the question reference the cross over point, yes that cross over point will come as there are untold galaxies still not seen yet, but eventually because of the faster than light expansion of space itself, some of the furthest galaxies will never been seen because they will be too far away, and getting further all the time, even with their electromagnetic radiation streaming out at the speed of light

This interesting video by Prof. Kipping sums some of it up very well and takes you an interesting thought journey as well (long and thought provoking... first go to the second video if you want the short beautiful answer. I like it bigly)...
expansion of the universe centred on a point or everywhere?
Everywhere.... but we are the centre of the universe observable to us... (the observable universe). Confused! Go to the last video for the quick and very interesting answer.



Here is a beautiful, quick summary for the impatient...

Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#3 Post by TheGreenGoblin » Sun Apr 26, 2020 10:43 am

For a while some astronomers thought that they might have seen a star older than the observable universe...

https://www.space.com/how-can-a-star-be ... verse.html

But then they realized that they hadn't given the error margins in these difficult measurements...
Though you remain
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"To be alive
You must have somewhere
To go
Your destination remains
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Re: Calling a Cosmologist

#4 Post by TheGreenGoblin » Sun Apr 26, 2020 10:45 am

For the Haynes type manual details on ISS guidance systems and ops (and so much more) see here...

http://www.spaceref.com/iss/elements/sm.html
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Your destination remains
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Re: Calling a Cosmologist

#5 Post by Boac » Sun Apr 26, 2020 11:10 am

I still think the answer to 4) is 42, but any ideas on 1) and 2)?

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Re: Calling a Cosmologist

#6 Post by TheGreenGoblin » Sun Apr 26, 2020 11:19 am

Boac wrote:
Sun Apr 26, 2020 11:10 am
I still think the answer to 4) is 42, but any ideas on 1) and 2)?
1) Gyroscopic precession (gyros are solar powered)... see here



2) The ISS's attitude is constantly adjusted by an equivalent of an onboard computerized automatic pilot using the gyro's (that can be manually overridden onboard if necessary), or manually from the earth, with the command centres being in the USA and Russia. The attitude is normally optimized to maximize the incoming solar illumination of the solar power arrays (on the day light side of the earth).

Fill yer boots for a fuller story here..
The ISS orbits Earth at an altitude that ranges from 370 to 460 kilometers
(230 to 286 miles) and a speed of 28,000 kilometers per hour (17,500 miles
per hour). Owing to atmospheric drag, the ISS is constantly slowed. Therefore,
the ISS must be reboosted periodically in order to maintain its altitude. The ISS
must sometimes be maneuvered in order to avoid debris in orbit. Furthermore,
the ISS attitude control and maneuvering system can be used to assist in
rendezvous and dockings with visiting vehicles, although that capability is not
usually required.
Although the ISS typically relies upon large gyrodynes, which utilize
electrical power, to control its orientation (see “Guidance, Navigation, and
Control”), when force that is beyond the production capability of the gyrodynes
is required, rocket engines provide propulsion for reorientation.
Rocket engines are located on the Service Module, as well as on the
Progress, Soyuz, and Space Shuttle spacecraft.
The Service Module provides 32 13.3-kilograms force (29.3-pounds
force) attitude control engines. The engines are combined into two groups
of 16 engines each, taking care of pitch, yaw, and roll control. Each Progress
provides 24 engines similar to those on the Service Module. When a Progress
is docked at the aft Service Module port, these engines can be used for pitch
and yaw control. When the Progress is docked at the Russian Docking Module,
the Progress engines can be used for roll control.
Besides being a resupply vehicle, the Progress provides a primary method
for reboosting the ISS. Eight 13.3-kilograms force (29.3-pounds force)
Progress engines can be used for reboosting. Engines on the Service Module,
Soyuz vehicles, and Space Shuttle can also be used. The Progress can also be
used to resupply propellants stored in the FGB that are used in the Service
Module engines. The ESA ATV and JAXA HTV will also provide propulsion and
reboost capability.
https://www.nasa.gov/pdf/167129main_Systems.pdf
Though you remain
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To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#7 Post by Boac » Sun Apr 26, 2020 11:39 am

I will review your videos, thanks - when I have time in this busy day.....
we are the centre of the universe observable to us.
- had to re-read that as I thought for one moment you had gone 'Copernican' on us. :))

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Re: Calling a Cosmologist

#8 Post by TheGreenGoblin » Sun Apr 26, 2020 11:40 am

Boac wrote:
Sun Apr 26, 2020 11:39 am
I will review your videos, thanks - when I have time in this busy day.....
we are the centre of the universe observable to us.
- had to re-read that as I thought for one moment you had gone 'Copernican' on us. :))
Glad you are busy... :-bd :)
Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#9 Post by Boac » Sun Apr 26, 2020 12:14 pm

Presumably. oh wise one (May I call you 'Sage', as long as you don;'t invite Dominic...) presumably you and your colleagues have been able to locate the origin of the 'Big Bang' by studying expansion vectors? Do we know where, apart from Milton Keynes, it is?

I have, by the way, reviewed my calculations on 'the answer' and have now refined it to 41.99 recurring.

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Re: Calling a Cosmologist

#10 Post by TheGreenGoblin » Sun Apr 26, 2020 12:44 pm

Boac wrote:
Sun Apr 26, 2020 12:14 pm
Presumably. oh wise one (May I call you 'Sage', as long as you don;'t invite Dominic...) presumably you and your colleagues have been able to locate the origin of the 'Big Bang' by studying expansion vectors? Do we know where, apart from Milton Keynes, it is?

I have, by the way, reviewed my calculations on 'the answer' and have now refined it to 41.99 recurring.
I am a humble amateur astronomer with a good math's background and in interest in these matters. :))

I loathe Cummings. Nor am I a sage, but I can tell you this, the notion of the centre of a universe arising from a singularity is essentially meaningless as space is expanding from an infinite number of points throughout the universe, but will not be expanding at the same rate everywhere due to gravitational effects, dark matter, dark energy etc. etc.

The Big Bang wasn’t a normal explosion starting from a single point in space. Space itself was expanding, with everything in the universe moving away from everything else. Think of an expanding raisin loaf in the oven. Today we observe a universe that appears fairly isotropic; that is to say, it looks basically the same in every direction. No vectors or a QDM that leads back to the big NDB at the 'centre of the universe'.
Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#11 Post by Boac » Sun Apr 26, 2020 12:51 pm

Come on guys and girls - someone must know how Hubble is steered?

EDIT: You know what they say? "If you want a job done properly, do it yourself"

https://www.nasa.gov/content/goddard/hu ... rol-system

Not precessionary but torque.

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Re: Calling a Cosmologist

#12 Post by TheGreenGoblin » Sun Apr 26, 2020 1:28 pm

Boac wrote:
Sun Apr 26, 2020 12:51 pm
Come on guys and girls - someone must know how Hubble is steered?

EDIT: You know what they say? "If you want a job done properly, do it yourself"

https://www.nasa.gov/content/goddard/hu ... rol-system

Not precessionary but torque.
You are slow Boac today, I trust you are not tarrying in Shoreham? Answered by me some posts back and explicitly stated in the video posted.... =)) =))
Although the ISS typically relies upon large gyrodynes, which utilize
electrical power, to control its orientation (see “Guidance, Navigation, and
Control”), when force that is beyond the production capability of the gyrodynes
is required, rocket engines provide propulsion for reorientation.
Control moment gyroscope - Gyrodine

:p ;)))

Gyrodine wars...

Gyrodine - Control Moment Gyroscope.JPG
A control moment gyroscope (CMG) is an attitude control device generally used in spacecraft attitude control systems. A CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor’s angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the spacecraft.
Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#13 Post by Boac » Sun Apr 26, 2020 1:51 pm

You are slow Boac today,
not me, Sir - sharp as a Tennis Ball. ISS? :-B

Did you say somewhere you had passed your medical.......?

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Re: Calling a Cosmologist

#14 Post by TheGreenGoblin » Sun Apr 26, 2020 2:11 pm

Boac wrote:
Sun Apr 26, 2020 1:51 pm
You are slow Boac today,
not me, Sir - sharp as a Tennis Ball. ISS? :-B

Did you say somewhere you had passed your medical.......?
I did....

Medical.JPG
Medical.JPG (36.22 KiB) Viewed 312 times
The limitations section also says something about needing to shake addled brain before looking at the sky.
Though you remain
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"To be alive
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Your destination remains
Elusive."

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Re: Calling a Cosmologist

#15 Post by Boac » Sun Apr 26, 2020 2:35 pm

Well, as I said, you can relax 'cos I have shown you how HUBBLE attitude is controlled. :-bd

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Re: Calling a Cosmologist

#16 Post by TheGreenGoblin » Sun Apr 26, 2020 3:29 pm

Boac wrote:
Sun Apr 26, 2020 2:35 pm
Well, as I said, you can relax 'cos I have shown you how HUBBLE attitude is controlled. :-bd
;)))
Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#17 Post by TheGreenGoblin » Mon Apr 27, 2020 7:43 am

Boac wrote:
Sun Apr 26, 2020 2:35 pm
Well, as I said, you can relax 'cos I have shown you how HUBBLE attitude is controlled. :-bd
Perhaps you could have been of some help to these folks then... ;)))
In December 1998 NASA launched the Mars Climate Orbiter spacecraft, which then took nine months to travel from Earth to Mars. Once it arrived at Mars, a mismatch of metric and imperial unitsf caused a complete mission failure and the loss of the spacecraft. Spacecraft use flywheels, which are basically massive spinning tops, for stability and control. The gyroscopic effect means that, even in the friction-free vacuum of space, the craft can effectively push against something and move itself around. But, over time, the flywheels can end up spinning too fast. To fix this, an angular momentum desaturation (AMD) event is performed to spin them down, using thrusters to keep the spacecraft stable, but this does cause a slight change in the overall trajectory. A slight but significant change. Whenever the thrusters are used, data is beamed back to NASA about exactly how powerful the bursts were and how long they lasted. A piece of software called SM_FORCES (for ‘small forces’) was developed by Lockheed Martin to analyse the thruster data and feed it to an AMD file for use by the NASA navigation team. This is where the problem occurred. The SM_FORCES program was calculating the forces in pounds (technically, pound-force: the gravitational force on one pound of mass on the Earth), whereas the AMD file was assuming the numbers it received were in Newtons (the metric unit of force). One pound of force is equal to 4.44822 Newtons, so, when SM_FORCES reported in pounds, the AMD file thought the figures were the smaller unit of Newtons and underestimated the force by a factor of 4.44822. The Mars Climate Orbital crashed not because of one big miscalculation when it arrived at Mars but because of many little ones over the course of its nine-month journey. When it was ready to go into orbit around Mars, the NASA navigation team thought it had been moved off course only slightly by all the angular momentum desaturation events. They expected it to glance past Mars at a distance of 150 to 170 kilometres from the surface, which would clip the atmosphere just enough to start to slow the spacecraft down and bring it into orbit. Instead, it was heading directly for an altitude of just 57 kilometres above the Martian surface, where it was destroyed in the atmosphere.
- from Humble Pi

wheels within wheels.JPG
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Your destination remains
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Re: Calling a Cosmologist

#18 Post by Boac » Mon Apr 27, 2020 8:03 am

Yes, I think I can,even if it is bit late - it is not strictly a 'gyroscopic' effect but a 'torque' reaction as I understand it. Maybe that is where they went wrong? As for metric/imperial - a good reason for measuring things in cm as it makes them bigger?

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Re: Calling a Cosmologist

#19 Post by TheGreenGoblin » Mon Apr 27, 2020 8:19 am

Boac wrote:
Mon Apr 27, 2020 8:03 am
Yes, I think I can,even if it is bit late - it is not strictly a 'gyroscopic' effect but a 'torque' reaction as I understand it. Maybe that is where they went wrong? As for metric/imperial - a good reason for measuring things in cm as it makes them bigger?
True as highlighted in the video above.

The gyroscope does what a gyroscope does, attitude control and the following...
A control moment gyroscope (CMG) is an attitude control device generally used in spacecraft attitude control systems. A CMG consists of a spinning rotor and one or more motorized gimbals that tilt the rotor’s angular momentum. As the rotor tilts, the changing angular momentum causes a gyroscopic torque that rotates the spacecraft.
Though you remain
Convinced
"To be alive
You must have somewhere
To go
Your destination remains
Elusive."

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Re: Calling a Cosmologist

#20 Post by Boac » Mon Apr 27, 2020 9:02 am

I think you are still confusing torque with gyroscopic principles? Hubble had gimballed gyros but I understood that its attitude CONTROL was effected by changes in rotor torque and the use of the earth's magnetic field. Whether the 4 'reaction Wheels' were also part of its gyro attitude monitoring system or separate is not clear. I don't think Hubble has any reaction control system using thrusters.

It is worth reading about the Actuators in my link.

I would also take issue with the terms 'gyrodynes' used by NASA in your link (wash my mouth out with Lysol as the Chump would propose....) - the definition of a 'gyrodyne' is

"an aircraft that uses a powered rotor to take off and manoeuvre, but uses autorotation when cruising"

What a grand distraction from the woes of COVID!

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