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Author Topic: Space Thread  (Read 77504 times)
calapine
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Reply #910 on: October 07, 2017, 12:50:50 PM

A little more about the ISS. The station maintains an (almost) circular orbit around Earth at a height of ~400 km.


Yet if one consults a map to find it's position, the result looks something like this:


(The projected track of 5 orbits)

The answer to "Why?" should, but might not be, obvious. Especially if you are like me and spatial understanding of 3D spaces isn't your forte.


I found this visualisation helpful:




The "Sinus-curve-orbit" is resulting from the fact that a maps are just 2D projections of a globe.

The "track drift" to the West is due the earth rotating below the station. (If someone can phrase this better PM me and I will edit gladly!)

And that's that!  smiley
« Last Edit: October 07, 2017, 12:54:01 PM by calapine »

Restoration is a perfectly valid school of magic!
Strazos
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Reply #911 on: October 09, 2017, 02:19:38 AM

So why the roughly-45% orbit? I'd have thought it would be more parallel to the equator or something.

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Bungee
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Reply #912 on: October 09, 2017, 03:15:45 AM

So why the roughly-45% orbit? I'd have thought it would be more parallel to the equator or something.

Look at the picture above the animation. They basically get to be over every part of the planet within just a few orbits. Also, is parallel to the equator even possible outside geostationary orbits? I think it pretty much has to be right on the equator or any rotation of it (like that ISS orbit).

Freedom is the raid target. -tazelbain
calapine
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Reply #913 on: October 09, 2017, 10:23:31 AM

I have a cold from hell (including puking), so I have to do this in parts because it's actually quite challenge to verbalise an answer without resorting to an "Just BECAUSE, Timmy! Now please be quiet and let my mommy drive!!" answer. And just sitting at the desk makes nausea worse.

Also, is parallel to the equator even possible outside geostationary orbits?

Sure can do! It's actually almost the opposite: Any equatorial orbit that isn't at 35,786 kilometres wont be a geostationary orbit.


Centripetal force equation:



If you hop into the role of a spaceship captain and want to achieve a stable, circular orbit your goal to equate everything right of the "=" to the Centripetal Force "F" which is provided by gravity.

In essence Orbit Radius "R" and Velocity "V". For a geostationary orbit (= You appear motionless to ground observers) angular velocity is determined by the need follow the rotation of the Earth. Leaving Radius "R" as the only adjustable variable, which for earth works out at 35,786 km.

I hope that makes sense.



Look at the picture above the animation. They basically get to be over every part of the planet within just a few orbits.

That is reason a) yes. Reason b) is orbital mechanics.

For b) the quick "Shut up, Timmy!" answer is: Because you can't (directly!) launch into an orbit with an inclination (=angle between the orbit and the equator as reference plane. See image below. 0 inclination is an equatorial Orbit, what Strazos asked.) lower than latitude of your launch site. Cape Canaveral is at 28.5, Baikonur at 45.6, ISS inclination (the title Strazos guessed pretty close at 45) is 51.6 degree, so it works out. Now you can do a plane change, but this is like, super expensive. Which brings up to the next WHY? which i'll do later.


« Last Edit: October 09, 2017, 10:59:23 AM by calapine »

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calapine
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Reply #914 on: October 09, 2017, 10:51:54 AM

Urgh. I just noticed something:

So why the roughly-45% orbit? I'd have thought it would be more parallel to the equator or something.

If I misunderstood your question (language barrier and so) and you meant something like I pictured below:



Than the answer is: that's not possible. The plane of a natural orbit must always go through the center of mass. (Unless you constantly maintain thrust...)

off to bed again

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Strazos
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Reply #915 on: October 09, 2017, 02:27:02 PM

So basically, it has to cross the equator at some point. Is it possible to orbit along the equator, though not necessarily with a geostat orbit? ie - path along the equator, but at a speed faster than earth's orbit?


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Trippy
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Reply #916 on: October 09, 2017, 02:33:03 PM

It takes more fuel to get it over the equator cause the US and Russia don't have any launch sites there. Also it won't traverse as much of the earth if it's orbiting around the equator longitudinally.

https://www.quora.com/How-does-the-ISS-orbit-the-earth
calapine
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Reply #917 on: October 09, 2017, 02:48:45 PM

So basically, it has to cross the equator at some point. Is it possible to orbit along the equator, though not necessarily with a geostat orbit? ie - path along the equator, but at a speed faster than earth's orbit?

Yes to all points.

Edit: If someone who can explain the concepts better than me follows this thread please post. :)

Edit2: The link Trippy posted is perfect, really. Recommended reading.
« Last Edit: October 09, 2017, 03:30:55 PM by calapine »

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Polysorbate80
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Reply #918 on: October 09, 2017, 05:00:45 PM

So basically, it has to cross the equator at some point. Is it possible to orbit along the equator, though not necessarily with a geostat orbit? ie - path along the equator, but at a speed faster than earth's orbit?



Orbits are counterintuitive.  If you want to circle the earth faster, you have to slow down your orbital speed.  As you lose speed, your orbital altitude will decrease and you circle the earth quicker.  Such an orbit is unstable; eventually gravity will pull you down unless you accelerate periodically to maintain your altitude.

If you accelerate, you'll orbit at a higher altitude, and actually take longer to complete the circle.  Accelerate too much, you achieve escape velocity and stop orbiting.
« Last Edit: October 09, 2017, 07:09:42 PM by Polysorbate80 »
Count Nerfedalot
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Reply #919 on: October 10, 2017, 12:31:37 AM

also interesting is the French launch site is closer to the equator than either the US' or Russia's, which not only makes equatorial orbits (like the geosynchronous so popular for so many things) a little bit cheaper/less fuel because they can start out with less inclination to compensate for, but also double plus bonus they get a little more boost from the angular momentum of the earth's spinning itself, being fastest at the equator.

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Reply #920 on: October 10, 2017, 05:56:09 AM

In places like the US or Russia, I'm always surprised more stuff isn't damaged in transit between these sensitive production facilities and being loaded onto the rockets.

Doubly so for launches out of French Guyana - that's either a long set of flights, or a perilous boat ride.

Fear the Backstab!
"Plato said the virtuous man is at all times ready for a grammar snake attack." - we are lesion
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calapine
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Reply #921 on: October 10, 2017, 07:35:00 AM

In places like the US or Russia, I'm always surprised more stuff isn't damaged in transit between these sensitive production facilities and being loaded onto the rockets.

Doubly so for launches out of French Guyana - that's either a long set of flights, or a perilous boat ride.

It occurs, but rarely.

The worst recent accident happend still during the manufacturing phase:





 swamp poop ACK! Oh ho ho ho. Reallllly?

As for transport: Sats to Baikonour and French Guyana come per plane, for the Cape road or plane, AFAIK. All special airtight containers.

Example:





Transporting of the rocket is another issue, every manufacturer coming up with different solutions.

That Falcon 9 looks a flying asparagus is because the diameter was choose to be just-about road transportable. I have read the 3.6 meters are the maximum to still pass below interstate underpasses and such on the way from California to Florida.




Proton: Again form follows function



What looks like boosters on the first stage are actually strap-on tanks. The center tank (which carries the oxidiser, not the fuel) has a diameter of 4.1m, the maximum allowed by Soviet/Russian rail. The fuel tanks are attached once the launcher reaches Baikonur.



Ariane 5: With a diameter of 5.4 meters nly ship transport is really practicable.


« Last Edit: October 10, 2017, 07:38:40 AM by calapine »

Restoration is a perfectly valid school of magic!
Sir T
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Reply #922 on: October 10, 2017, 07:49:46 AM

Reminds me that NASA were advertising earlier this year for an "earth protection officer". Basically someone whose job it is to work internationally ensure that no contamination gets onto any probes going to space and especially Mars or wherever. If Earth born bacteria got onto Mars no-one knows what could happen. Also her responsibilities would be to ensure no space pathogen got onto earth from something coming down from space.

IN actuality ist sthe same woman for the last 20 years, but they had to advertise with the change in the administration.

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calapine
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Reply #923 on: October 10, 2017, 02:55:31 PM

Came across this today, and maybe of interest to some.



Echoes in space - Trailer

It's listed as a 5 week, 3 hours/week course. And free of course. https://eo-college.org/
« Last Edit: October 10, 2017, 02:59:24 PM by calapine »

Restoration is a perfectly valid school of magic!
calapine
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Reply #924 on: October 12, 2017, 05:16:43 AM

Last night's SpaceX lift off from the Cape provided some really stunning visuals visuals. At least the first 30 seconds are must watch, imho:



Watch me!
« Last Edit: October 12, 2017, 05:22:22 AM by calapine »

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calapine
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Reply #925 on: October 14, 2017, 05:39:41 AM

Weekend guessing game. Looks like Paranormal Green Slime, but what is this actually?




« Last Edit: October 14, 2017, 05:48:29 AM by calapine »

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Mandella
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Reply #926 on: October 14, 2017, 08:38:45 PM

Elon Musk just did an AMA over on reddit (where else?).

Nicely technical round of question and answers this time, IMHO. And as an example oh how fast and fluid Elon's plans are, the BFS described at the most recent IAC barely a month ago now has three landing engines planned, changed from two. Not really for safety -- it gives the opportunity to land with a heavier cargo load.
calapine
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Reply #927 on: October 14, 2017, 11:45:29 PM

4 legs, changed from 3. wink

I live tweeted the AMA (sans the fluff talk), see here.

The talk was solely focused on BFR and Mars, and imho, won't convince any sceptics.

Elon was his usual optimistic self. 
Q: How does BFR radiation shielding look like?
A: Radiation damage is not significant for our transit times. Buzz Aldrin is 87.

Yeah well, Buzz spent 12 days, 1 hour in space.

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MahrinSkel
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Reply #928 on: October 14, 2017, 11:56:43 PM

4 legs, changed from 3. wink

I live tweeted the AMA (sans the fluff talk), see here.

The talk was solely focused on BFR and Mars, and imho, won't convince any sceptics.

Elon was his usual optimistic self. 
Q: How does BFR radiation shielding look like?
A: Radiation damage is not significant for our transit times. Buzz Aldrin is 87.

Yeah well, Buzz spent 12 days, 1 hour in space.
Unless he has a working large scale microwave cavity drive squirreled away, or some other constant thrust solution, radiation is absolutely something he needs to plan for.

--Dave

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Mandella
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Reply #929 on: October 15, 2017, 11:09:53 AM

4 legs, changed from 3. wink

I live tweeted the AMA (sans the fluff talk), see here.

The talk was solely focused on BFR and Mars, and imho, won't convince any sceptics.

Elon was his usual optimistic self. 
Q: How does BFR radiation shielding look like?
A: Radiation damage is not significant for our transit times. Buzz Aldrin is 87.

Yeah well, Buzz spent 12 days, 1 hour in space.
Unless he has a working large scale microwave cavity drive squirreled away, or some other constant thrust solution, radiation is absolutely something he needs to plan for.

--Dave

Calapine left out mention of the storm shelter and the fact that fast transit times are means of planning for radiation hazards. The fact is that a few months of interplanetary radiation (barring solar storms) are still within NASA approved lifetime radiation counts. It's hazardous, but certainly less so than, say, a lifetime of smoking, and we've had generation on generation happily subject themselves (and others) to that potential cancer risk, for far less gain.

It *does* mean that there probably won't be any veteran Mars transit crews. Pilots and crews will likely be limited to one or two round trips to keep exposure down.
Lucas
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Reply #930 on: October 20, 2017, 01:52:38 PM

You probably already heard about this, but anyway: Japan's lunar orbiter "Selene" found something....VERY interesting on the Moon:

http://www.dailymail.co.uk/sciencetech/article-4996024/Huge-cave-moon-house-astronauts-Japan-scientists.html

You know, now that we're also entering an era of private exploration, a manned mission that actually goes there and take a look around doesn't seem so far-fetched.

" He's so impatient, it's like watching a teenager fuck a glorious older woman." - Ironwood on J.J. Abrams
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