A Space & astronomy forum. SpaceBanter.com

Go Back   Home » SpaceBanter.com forum » Space Science » Technology
Site Map Home Authors List Search Today's Posts Mark Forums Read Web Partners

Sun Synchronous Orbit



 
 
Thread Tools Display Modes
  #1  
Old April 17th 13, 10:13 AM posted to sci.space.tech
Smit Kamal
external usenet poster
 
Posts: 5
Default Sun Synchronous Orbit

On Monday, June 3, 1996 12:30:00 PM UTC+5:30, Frank Crary wrote:
In article , Pat wrote:
...the reason i heard sun synchonicity
was desired was not measuring building heights (which can be measured
at any time of day given the known sun angle, but rather to minimize
shadow changes in the photo so as to maximize photo-analysts chances
of spotting new construction or new building features.


I disagree. You can not do equally good height measurements at
any time of day. What's the length of a shadow at noon, on
the equator, on June 21? You'd need very good resolution to
measure the length of a nonexistent shadow... To get an
accurate measurement of height, you need shadows that are
much longer than the resolution of the image. How much
longer depends on the desired accuracy, but longer
shadows certainly help and that is a motive for sun-synchronous
orbits with early morning passes. As Henry pointed out, it
isn't the only reason as far as the Earth is concerned. I
guess I'm too used to thinking of observations of other planets...

Frank Crary
CU Boulder

hye,
I was reading about sun synchronous orbits and i had a lot of confusion reg
arding that topics so i was looking into various group pages which discusse
d this topic.I was wondering if a satellite is in sun synchronous orbit and
if it completes 14 orbits per day then will the satellite be passing over
one particular location on the earth twice a day.ie 7 am in morning and 7 p
m at evening or will it pass over one location on the earth only once.
The inclination of the orbit can be taken as around 98 degrees and time per
iod as 101 minutes.Altitude will be around 800 kms.
Please help if possible

  #2  
Old April 18th 13, 01:05 AM posted to sci.space.tech
Alain Fournier
external usenet poster
 
Posts: 49
Default Sun Synchronous Orbit

On 04/17/2013 5:13 AM, Smit Kamal wrote:
On Monday, June 3, 1996 12:30:00 PM UTC+5:30, Frank Crary wrote:
In article , Pat wrote:
...the reason i heard sun synchonicity
was desired was not measuring building heights (which can be measured
at any time of day given the known sun angle, but rather to minimize
shadow changes in the photo so as to maximize photo-analysts chances
of spotting new construction or new building features.


I disagree. You can not do equally good height measurements at
any time of day. What's the length of a shadow at noon, on
the equator, on June 21? You'd need very good resolution to
measure the length of a nonexistent shadow... To get an
accurate measurement of height, you need shadows that are
much longer than the resolution of the image. How much
longer depends on the desired accuracy, but longer
shadows certainly help and that is a motive for sun-synchronous
orbits with early morning passes. As Henry pointed out, it
isn't the only reason as far as the Earth is concerned. I
guess I'm too used to thinking of observations of other planets...

Frank Crary
CU Boulder

hye,
I was reading about sun synchronous orbits and i had a lot of confusion reg
arding that topics so i was looking into various group pages which discusse
d this topic.I was wondering if a satellite is in sun synchronous orbit and
if it completes 14 orbits per day then will the satellite be passing over
one particular location on the earth twice a day.ie 7 am in morning and 7 p
m at evening or will it pass over one location on the earth only once.
The inclination of the orbit can be taken as around 98 degrees and time per
iod as 101 minutes.Altitude will be around 800 kms.
Please help if possible



It is amusing to see a reply to a post 17 years later.

The answer is basically only once. You can separate the orbit in two
halves. On the first half, let's say the satellite is heading
northwards, and on the second half it is heading southwards. On the
northward half orbit the satellite will always pass at a given latitude
at the same local time. So if the satellite passes over your head at 7
am while the satellite is heading north, then on its northern bound half
orbit it will pass over your head every day at 7 am and at no other time.

What about, on its southern bound half orbit 12 hours later? Exactly
twelve hours later, the satellite, which you said completes 14 orbits
per day will have completed exactly 7 orbits and will be over the same
latitude on its northern bound half orbit, not on its south bound half
orbit.

If instead of 14 orbits per day, you have an odd number of orbits per
day. Let's say 15 orbits per day. Then the satellite can pass over your
head in the south bound half orbit about 7.5 orbits after passing over
your head in the north bound orbit. But that would happen only at one
specific latitude. Why only at one specific latitude?

Well let's imagine the orbit has zero eccentricity and passes exactly
over the poles (which is impossible but it will help understand) and
that the satellite has an odd number of orbits per day, let's say 2n+1
orbits per day. If it passes over you on the equator on its north bound
half orbit, then half a day later, the satellite will have done n + 1/2
orbits, it will therefore be over the equator on its south bound half
orbit, exactly over your head. But if you aren't on the equator, let's
say you are in the norther hemisphere, then half a day later, the
satellite will be in the southern hemisphere, not over your head. So you
see, that in such an (impossible) sun synchronous 90 degree circular
orbit, the satellite goes twice a day over the same point over the
equator. It also goes 2n+1 times a day over the poles, but for other
points under its path, only once a day. For a real sun synchronous
orbit, the points where the satellite passes over head twice a day got
to be placed in such a way that it takes exactly 12 hours to do n orbits
plus the remaining "half orbit". But because of eccentricity, the said
"half orbit" has to be a half orbit in time, but does not have to be a
half orbit in distance, so the points where this works aren't
necessarily over the equator.


Alain Fournier

  #3  
Old April 18th 13, 01:06 AM posted to sci.space.tech
Steve Willner
external usenet poster
 
Posts: 1,172
Default Sun Synchronous Orbit

In article ,
Smit Kamal writes:
I was wondering if a satellite is in sun synchronous orbit and
if it completes 14 orbits per day then will the satellite be passing over
one particular location on the earth twice a day.ie 7 am in morning and 7 p
m at evening or will it pass over one location on the earth only once.


Twice a day, once going northbound and once southbound. Imagine
yourself near the Sun looking back at the Earth with the satellite
going round. From that perspective, the Earth rotates once in 24
hours, and a given spot on Earth (at least a spot not near either
pole) passes under the satellite path twice.

--
Help keep our newsgroup healthy; please don't feed the trolls.
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA

  #4  
Old April 22nd 13, 08:36 PM posted to sci.space.tech
David Spain
external usenet poster
 
Posts: 2,901
Default Sun Synchronous Orbit

On 4/17/2013 8:05 PM, Alain Fournier wrote:
On 04/17/2013 5:13 AM, Smit Kamal wrote:
It is amusing to see a reply to a post 17 years later.

[...snip...]
Alain Fournier


Smit,

So what's life like around HR4550? Is your planet earth-like? And if so
or even if not, how many Earth-like planets in your system?

Hopefully I'm still around in the year 2030 to read your reply....

;-)

Dave


  #5  
Old April 23rd 13, 11:16 AM posted to sci.space.tech
David Spain
external usenet poster
 
Posts: 2,901
Default Sun Synchronous Orbit

HR4550 (aka. Groombridge 1830)...

Oh well I misread this map, I thought you had to determine distance by
projecting down into the circled plane. No, apparently this is a 3D
projection. I should have looked at the table at the end....


http://www.atlasoftheuniverse.com/50lys.html


So I'm stuck with Sirius... Maybe Smit in on a space platform orbiting
Sirius... :-)


Dave



  #6  
Old April 23rd 13, 03:59 PM posted to sci.space.tech
Alain Fournier
external usenet poster
 
Posts: 49
Default Sun Synchronous Orbit

On 04/17/2013 8:06 PM, Steve Willner wrote:
In article ,
Smit Kamal writes:
I was wondering if a satellite is in sun synchronous orbit and
if it completes 14 orbits per day then will the satellite be passing over
one particular location on the earth twice a day.ie 7 am in morning and 7 p
m at evening or will it pass over one location on the earth only once.


Twice a day, once going northbound and once southbound. Imagine
yourself near the Sun looking back at the Earth with the satellite
going round. From that perspective, the Earth rotates once in 24
hours, and a given spot on Earth (at least a spot not near either
pole) passes under the satellite path twice.


As I said in an other post, if it passes exactly over your head while
northbound, it is unlikely to past exactly over your head while southbound.

Of course, because not all days are 24 hours according to apparent solar
time, if the satellite passes exactly over your head, it is unlikely to
pass again exactly over your head 24 hours later. So one can assume less
precision and then yes, there will be one orbit where it will pass "not
too far" from your location on the southbound leg, but in that case "not
too far" could be about 13 degrees of longitude for a satellite doing 14
orbits per day.


Alain Fournier


  #7  
Old March 24th 14, 03:35 PM posted to sci.space.tech
[email protected]
external usenet poster
 
Posts: 1
Default Sun Synchronous Orbit

On Tuesday, April 23, 2013 8:29:41 PM UTC+5:30, Alain Fournier wrote:
On 04/17/2013 8:06 PM, Steve Willner wrote:

In article ,


Smit Kamal writes:


I was wondering if a satellite is in sun synchronous orbit and


if it completes 14 orbits per day then will the satellite be passing over


one particular location on the earth twice a day.ie 7 am in morning and 7 p


m at evening or will it pass over one location on the earth only once.




Twice a day, once going northbound and once southbound. Imagine


yourself near the Sun looking back at the Earth with the satellite


going round. From that perspective, the Earth rotates once in 24


hours, and a given spot on Earth (at least a spot not near either


pole) passes under the satellite path twice.




As I said in an other post, if it passes exactly over your head while

northbound, it is unlikely to past exactly over your head while southbound.



Of course, because not all days are 24 hours according to apparent solar

time, if the satellite passes exactly over your head, it is unlikely to

pass again exactly over your head 24 hours later. So one can assume less

precision and then yes, there will be one orbit where it will pass "not

too far" from your location on the southbound leg, but in that case "not

too far" could be about 13 degrees of longitude for a satellite doing 14

orbits per day.





Alain Fournier


could you please explain the eclipse patterns in the sunsynchronous orbits which are not experiencing van allen radiations and the altitude is around 800km.

  #8  
Old March 25th 14, 07:21 PM posted to sci.space.tech
Smit Kamal
external usenet poster
 
Posts: 5
Default Sun Synchronous Orbit

On Tuesday, April 23, 2013 3:46:27 PM UTC+5:30, David Spain wrote:
HR4550 (aka. Groombridge 1830)...
Hye Dave

Thankyou for your help.
I was asking about satellites at an altitude of 800 kilometres which is in sun sychronous orbit.


Oh well I misread this map, I thought you had to determine distance by

projecting down into the circled plane. No, apparently this is a 3D

projection. I should have looked at the table at the end....





http://www.atlasoftheuniverse.com/50lys.html





So I'm stuck with Sirius... Maybe Smit in on a space platform orbiting

Sirius... :-)





Dave


  #9  
Old March 25th 14, 07:21 PM posted to sci.space.tech
Smit Kamal
external usenet poster
 
Posts: 5
Default Sun Synchronous Orbit

On Tuesday, April 23, 2013 8:29:41 PM UTC+5:30, Alain Fournier wrote:
On 04/17/2013 8:06 PM, Steve Willner wrote:

In article ,


Smit Kamal writes:


I was wondering if a satellite is in sun synchronous orbit and


if it completes 14 orbits per day then will the satellite be passing over

Thankyou Alain!!!

Your reply was pretty helpful
one particular location on the earth twice a day.ie 7 am in morning and 7 p


m at evening or will it pass over one location on the earth only once.




Twice a day, once going northbound and once southbound. Imagine


yourself near the Sun looking back at the Earth with the satellite


going round. From that perspective, the Earth rotates once in 24


hours, and a given spot on Earth (at least a spot not near either


pole) passes under the satellite path twice.




As I said in an other post, if it passes exactly over your head while

northbound, it is unlikely to past exactly over your head while southbound.



Of course, because not all days are 24 hours according to apparent solar

time, if the satellite passes exactly over your head, it is unlikely to

pass again exactly over your head 24 hours later. So one can assume less

precision and then yes, there will be one orbit where it will pass "not

too far" from your location on the southbound leg, but in that case "not

too far" could be about 13 degrees of longitude for a satellite doing 14

orbits per day.





Alain Fournier


  #10  
Old March 26th 14, 04:18 AM posted to sci.space.tech
David Spain
external usenet poster
 
Posts: 2,901
Default Sun Synchronous Orbit

On 3/25/2014 2:21 PM, Smit Kamal wrote:
On Tuesday, April 23, 2013 3:46:27 PM UTC+5:30, David Spain wrote:
HR4550 (aka. Groombridge 1830)...
Hye Dave

Thankyou for your help.
I was asking about satellites at an altitude of 800 kilometres which is in sun sychronous orbit.



Smit,

Sorry I was not being very helpful.

I was joking about your response time.
Either you are very busy, have an extremely slow USENET service, or are
very far away.

However if the latter, at one month shy of 1 year for a response, puts
you at slightly 0.5 light-year away, so you've moved significantly
closer! You are no longer at Sirius but somewhere in the Oort Cloud!

Just kidding (I think), if not, I'll see your response in February
2015.... :-)

Dave


 




Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
an efficient orbit to fly a space craft from the L1 lagrange point from earth to mars sun-synchronous orbit? kelvin Space Shuttle 1 November 11th 05 04:21 AM
An efficient orbit to fly a space craft from the L1 lagrange point to mars sun-synchronous orbit? kelvin Technology 2 November 10th 05 09:01 PM
reccomendations on an efficient orbit to fly a space craft from the L1 lagrange point from earth to mars sun-synchronous orbit? kelvin Space Station 1 November 8th 05 03:56 PM
an efficient orbit to fly a space craft from the L1 lagrange point from earth to mars sun-synchronous orbit? kelvin Astronomy Misc 0 November 8th 05 03:48 PM
What's a sun-synchronous orbit? Ultimate Buu Technology 0 July 24th 03 09:45 AM


All times are GMT +1. The time now is 11:41 AM.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2024, Jelsoft Enterprises Ltd.
Copyright ©2004-2024 SpaceBanter.com.
The comments are property of their posters.