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#400 by Prunesquallor on 06 Sep, 2016 23:15
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Someone correct me if I'm wrong but wouldn't a circular polar orbit place the cubesat in sunlight all the time and also place the extended solar panels in a minimum drag configuration?
Best to all,
Shell
I recommended a sun-synchronous orbit but then deleted the comment because Cannae's image of their orbit doesn't look sun-synchronous.
Generally, CubeSats don't get to choose their orbits. They hitchhike to wherever the main payload is going (or get ejected into the Space Station orbit).
Sent from my iPhone using Tapatalk -
#401 by Rodal on 06 Sep, 2016 23:16
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Someone correct me if I'm wrong but wouldn't a circular polar orbit place the cubesat in sunlight all the time and also place the extended solar panels in a minimum drag configuration?
Dr. Rodal, love your breakdown, you rock math.
Best to all,
Shell
Thanks for the rocking
To be in constant Sunlight all the time,a Sun-synchronous orbit (SSO) is required that combines altitude and inclination in such a way that the satellite passes over any given point of the planet's surface at the same local solar time.
Typical sun-synchronous orbits are about 600–800 km in altitude, with periods in the 96–100 minute range, and inclinations of around 98° (i.e. slightly retrograde compared to the direction of Earth's rotation: 0° represents an equatorial orbit and 90° represents a polar orbit). Since they are not exactly 90° they are not purely polar orbits.
These orbits, (near 90 degrees inclination) are not minimum drag, as the atmosphere opposes the motion of the spacecraft even in a polar orbit. Rather, maximum drag is associated with low orbits, and to minimize atmospheric drag the best thing is to use higher orbits.
The market for such orbits is much smaller and they require higher thrust from the rocket to put them in orbit (*), so to me it sounds like a much more expensive proposition, than sending a Cubesat to a geocentric low-inclination circular orbit at 240 kmQuote from: WikipediaThe Sun-synchronous orbit is mostly selected for Earth observation satellites that should be operated at a relatively constant altitude suitable for its Earth observation instruments, this altitude typically being between 600 km and 1000 km over the Earth surface. Because of the deviations of the gravitational field of the Earth from that of a homogeneous sphere that are quite significant at such relatively low altitudes a strictly circular orbit is not possible for these satellites. Very often a frozen orbit is therefore selected that is slightly higher over the Southern hemisphere than over the Northern hemisphere. ERS-1, ERS-2 and Envisat of European Space Agency as well as the MetOp spacecraft of EUMETSAT are all operated in Sun-synchronous, "frozen" orbits.
(*) Compared to the advantage of launching near the Equator for a low inclination orbit to take advantage of the Earth's rotation. (Anything on the surface of the Earth at the equator is already moving at 460 meters per second (1670 kilometers per hour ) ).
Spaceflight Services plans a dedicated 2017 launch for sun sync.
http://www.spaceflight.com/spaceflight-purchases-spacex-falcon-9-rocket-to-provide-more-frequent-cost-effective-rideshare-availability-for-small-satellite-industry/
Credit: communication from NSF Member HMXHMXQuoteSpaceflight’s 2017 Sun Synch Express mission manifest includes satellites as small as 5 kg 3U CubeSat up to 575 kg satellite. Over 20 satellites will be deployed during the mission, with commercial customers pursuing a range of endeavors and government-sponsored scientific research originating from six different countries. The manifest is nearly at capacity.
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#402 by dustinthewind on 06 Sep, 2016 23:39
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Shell, is an off-set antenna a loop or hoop that is suspended away from the wall or top or bottom caps?
Well what you drew FL looks a lot like what I drew before. I think it is supposed to be about 1/4 wavelength from the wall where the electric field is maximum. I believe the perimeter of the loop, where the wires separate and form the circle, should be 1/2 wavelength long, but that depends on how long the wavelength is in the wire. I was just curious if it was the same concept as I had posted here: https://forum.nasaspaceflight.com/index.php?topic=39772.msg1536201#msg1536201 . Seems like it might be. Maybe if the perimeter is smaller there wouldn't be a problem but if larger there might.
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#403 by sghill on 06 Sep, 2016 23:47
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Will recalculate with 150 miles tomorrow (Is it US Miles
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I reckon it's either that or nautical miles
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#404 by Bob Woods on 07 Sep, 2016 00:03
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One would have to assume there are enough batteries on board to maintain constant power to the thruster even during occultation and non-optimal array pointing.
Unless they don't plan on constant power.
No orbit is perfectly round. Maybe they plan power as they approach perigee, then power off so the systems cool down. -
#405 by Star One on 07 Sep, 2016 00:25
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Someone correct me if I'm wrong but wouldn't a circular polar orbit place the cubesat in sunlight all the time and also place the extended solar panels in a minimum drag configuration?
Dr. Rodal, love your breakdown, you rock math.
Best to all,
Shell
Thanks for the rocking
To be in constant Sunlight all the time,a Sun-synchronous orbit (SSO) is required that combines altitude and inclination in such a way that the satellite passes over any given point of the planet's surface at the same local solar time.
Typical sun-synchronous orbits are about 600–800 km in altitude, with periods in the 96–100 minute range, and inclinations of around 98° (i.e. slightly retrograde compared to the direction of Earth's rotation: 0° represents an equatorial orbit and 90° represents a polar orbit). Since they are not exactly 90° they are not purely polar orbits.
These orbits, (near 90 degrees inclination) are not minimum drag, as the atmosphere opposes the motion of the spacecraft even in a polar orbit. Rather, maximum drag is associated with low orbits, and to minimize atmospheric drag the best thing is to use higher orbits.
The market for such orbits is much smaller and they require higher thrust from the rocket to put them in orbit (*), so to me it sounds like a much more expensive proposition, than sending a Cubesat to a geocentric low-inclination circular orbit at 240 kmQuote from: WikipediaThe Sun-synchronous orbit is mostly selected for Earth observation satellites that should be operated at a relatively constant altitude suitable for its Earth observation instruments, this altitude typically being between 600 km and 1000 km over the Earth surface. Because of the deviations of the gravitational field of the Earth from that of a homogeneous sphere that are quite significant at such relatively low altitudes a strictly circular orbit is not possible for these satellites. Very often a frozen orbit is therefore selected that is slightly higher over the Southern hemisphere than over the Northern hemisphere. ERS-1, ERS-2 and Envisat of European Space Agency as well as the MetOp spacecraft of EUMETSAT are all operated in Sun-synchronous, "frozen" orbits.
(*) Compared to the advantage of launching near the Equator for a low inclination orbit to take advantage of the Earth's rotation. (Anything on the surface of the Earth at the equator is already moving at 460 meters per second (1670 kilometers per hour ) ).
Spaceflight Services plans a dedicated 2017 launch for sun sync.
http://www.spaceflight.com/spaceflight-purchases-spacex-falcon-9-rocket-to-provide-more-frequent-cost-effective-rideshare-availability-for-small-satellite-industry/
Credit: communication from NSF Member HMXHMXQuoteSpaceflight’s 2017 Sun Synch Express mission manifest includes satellites as small as 5 kg 3U CubeSat up to 575 kg satellite. Over 20 satellites will be deployed during the mission, with commercial customers pursuing a range of endeavors and government-sponsored scientific research originating from six different countries. The manifest is nearly at capacity.
It's a good bet then it could be on this. -
#406 by Rodal on 07 Sep, 2016 01:01
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That was an article from a year ago (September 2015)....
Spaceflight Services plans a dedicated 2017 launch for sun sync.
http://www.spaceflight.com/spaceflight-purchases-spacex-falcon-9-rocket-to-provide-more-frequent-cost-effective-rideshare-availability-for-small-satellite-industry/
Credit: communication from NSF Member HMXHMXQuoteSpaceflight’s 2017 Sun Synch Express mission manifest includes satellites as small as 5 kg 3U CubeSat up to 575 kg satellite. Over 20 satellites will be deployed during the mission, with commercial customers pursuing a range of endeavors and government-sponsored scientific research originating from six different countries. The manifest is nearly at capacity.
It's a good bet then it could be on this.
This flight claiming a sun sync orbit is no longer on the SpaceX manifest
http://www.spacex.com/missions
Anybody know whether SpaceX has launched to sync orbits with a Falcon 9 before?
We know that SpaceX has launched into a supersynchronous elliptical Geostationary transfer orbit, (which is not a synchronous orbit) , instead it is an orbit with a somewhat larger apogee than the more typical Geostationary transfer orbit (GTO) typically utilized for communication satellites.
This technique was used, for example, on the launch and transfer orbit injection of the first two SpaceX Falcon 9 v1.1 GTO launches in December 2013 and January 2014, SES-8.
Also this most recent one is supersynchronous instead of sun sync:
http://www.spacex.com/news/2016/05/27/thaicom-8-mission-photos
This 2015 user's guide for SpaceX has them launching from Vanderbeg for sun synch orbits, using either a "Falcon 9 or Falcon Heavy"
http://www.spacex.com/sites/spacex/files/falcon_9_users_guide_rev_2.0.pdf
The Falcon Heavy is not yet operational:
<<Following the Falcon 9 CRS-7 failure investigation in 2015, repeated rocket development delays, and given a very busy Falcon 9 launch manifest in 2016, the first Falcon Heavy launch is now expected in early 2017>> -
#407 by Star One on 07 Sep, 2016 01:07
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That was an article from a year ago (September 2015)....
Spaceflight Services plans a dedicated 2017 launch for sun sync.
http://www.spaceflight.com/spaceflight-purchases-spacex-falcon-9-rocket-to-provide-more-frequent-cost-effective-rideshare-availability-for-small-satellite-industry/
Credit: communication from NSF Member HMXHMXQuoteSpaceflight’s 2017 Sun Synch Express mission manifest includes satellites as small as 5 kg 3U CubeSat up to 575 kg satellite. Over 20 satellites will be deployed during the mission, with commercial customers pursuing a range of endeavors and government-sponsored scientific research originating from six different countries. The manifest is nearly at capacity.
It's a good bet then it could be on this.
This flight claiming a sun sync orbit is no longer on the SpaceX manifest
http://www.spacex.com/missions
One has to wonder whether with such a launch they can get the necessary altitude for a sun sync orbit.
Anybody know whether SpaceX has launched to sync orbits before?
We know that SpaceX has launched into a supersynchronous elliptical Geostationary transfer orbit, (which is not a synchronous orbit) , instead it is an orbit with a somewhat larger apogee than the more typical Geostationary transfer orbit (GTO) typically utilized for communication satellites.
This technique was used, for example, on the launch and transfer orbit injection of the first two SpaceX Falcon 9 v1.1 GTO launches in December 2013 and January 2014, SES-8.
If the manifest for the launch was almost full as they seemed to indicate I wonder why it has disappeared. -
#408 by HMXHMX on 07 Sep, 2016 01:27
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That was an article from a year ago (September 2015)....
Spaceflight Services plans a dedicated 2017 launch for sun sync.
http://www.spaceflight.com/spaceflight-purchases-spacex-falcon-9-rocket-to-provide-more-frequent-cost-effective-rideshare-availability-for-small-satellite-industry/
Credit: communication from NSF Member HMXHMXQuoteSpaceflight’s 2017 Sun Synch Express mission manifest includes satellites as small as 5 kg 3U CubeSat up to 575 kg satellite. Over 20 satellites will be deployed during the mission, with commercial customers pursuing a range of endeavors and government-sponsored scientific research originating from six different countries. The manifest is nearly at capacity.
It's a good bet then it could be on this.
This flight claiming a sun sync orbit is no longer on the SpaceX manifest
http://www.spacex.com/missions
One has to wonder whether with such a launch vehicle (Falcon 9) they can get the necessary altitude for a real sun sync orbit.
Anybody know whether SpaceX has launched to sync orbits before?
We know that SpaceX has launched into a supersynchronous elliptical Geostationary transfer orbit, (which is not a synchronous orbit) , instead it is an orbit with a somewhat larger apogee than the more typical Geostationary transfer orbit (GTO) typically utilized for communication satellites.
This technique was used, for example, on the launch and transfer orbit injection of the first two SpaceX Falcon 9 v1.1 GTO launches in December 2013 and January 2014, SES-8.
Also this most recent one is supersynchronous instead of sun sync:
http://www.spacex.com/news/2016/05/27/thaicom-8-mission-photos
This 2015 user's guide for SpaceX has them launching from Vanderbeg for sun synch orbits, using either a "Falcon 9 or Falcon Heavy"
If they really need a Falcon Heavy to execute a real sun-synch, such a launch vehicle (Falcon Heavy) is not yet operational:
<<Following the Falcon 9 CRS-7 failure investigation in 2015, repeated rocket development delays, and given a very busy Falcon 9 launch manifest in 2016, the first Falcon Heavy launch is now expected in early 2017>>
A sun sync mission would not require a FH vehicle; F9 can can easily perform it. -
#409 by Rodal on 07 Sep, 2016 01:34
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Yes ,as noted, as claimed in their 2015 User's Guide, but has SpaceX actually successfully launched a real sun synch mission before?
A sun sync mission would not require a FH vehicle; F9 can can easily perform it. -
#410 by SeeShells on 07 Sep, 2016 02:24
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#411 by dustinthewind on 07 Sep, 2016 02:25
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Doesn't it also take extra power to rotate the orbit 90 degrees over 3 months so that the orbit stays sun synchronous?...
Yes ,as noted, as claimed in their 2015 User's Guide, but has SpaceX actually successfully launched a real sun synch mission before?
A sun sync mission would not require a FH vehicle; F9 can can easily perform it.
Ok I am mistaken. quote from: https://en.wikipedia.org/wiki/Sun-synchronous_orbit "Sun-synchronous orbits can happen around other oblate planets, such as Mars. A satellite around the almost spherical Venus, for example, will need an outside push to be in a sun-synchronous orbit."
So it appears it is the oblateness that allows them to do such an orbit with out the need for extra power. Never mind then. -
#412 by HMXHMX on 07 Sep, 2016 02:29
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Yes ,as noted, as claimed in their 2015 User's Guide, but has SpaceX actually successfully launched a real sun synch mission before?
A sun sync mission would not require a FH vehicle; F9 can can easily perform it.
Don't know myself but it is no different that inserting into any other orbit, except for deltaV and launch azimuth constraints. It's really not an issue. -
#413 by Rodal on 07 Sep, 2016 02:48
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OK but direct insertion launching into Sun-synchronous orbits (SSO) is different from other orbits, in that SSO require high injection accuracy. The launch window needs to occur at the time of day when the launch site location is aligned with the plane of the required orbit. To launch at another time would require an orbital plane change manoeuvre which would require a large amount of propellant....
Yes ,as noted, as claimed in their 2015 User's Guide, but has SpaceX actually successfully launched a real sun synch mission before?
A sun sync mission would not require a FH vehicle; F9 can can easily perform it.
Don't know myself but it is no different that inserting into any other orbit, except for deltaV and launch azimuth constraints. It's really not an issue.
There is also the issue of approval.Was this Sun Synch Express mission officially approved to launch? Did it ever appear in the SpaceX manifest?
The high inclination of SSO orbits causes satellites with similar semi-major axes but differing right ascension values to have intersecting orbit planes near both poles. Avoidance maneuvers are not uncommon among high value active SSO satellites to avoid other active satellites and orbital debris.
An older USAirForce satellite, DMSP-F13, blew up in February 2015 after a battery failed, creating tens of thousands of pieces of small debris and a potential problem for other satellites operating in sun-synchronous polar orbits. ( https://spaceflightnow.com/2015/05/13/dmsp-satellite-debris-expected-to-remain-in-orbit-for-decade/ )
One way to reduce the frequency of avoidance maneuvers and the risk of collision is to place active satellites in strategic orbits and restrict the amount of allowable drift from that original orbit.
_________________________
Several announcements about SpaceX going to launch a Sun Synch Orbit (SSO), but apparently (?) SpaceX has NOT launched a single SSO yet (?):
SSO missions still on SpaceX manifest:
Argentina's SAOCOM:
http://www.spacex.com/press/2012/12/19/spacex-signs-argentinas-space-agency-two-falcon-9-launches
<<Originally, the launch was announced for 2010 (1A) and 2011 (1B), but later due to delays in satellites development both launches were postponed for 2012 and 2013.Further delays pushed the launches date back tentatively towards 2014 and 2015. As of February 2016, SAOCOM 1A was later scheduled for launch in December 2016 and SAOCOM 1B in December 2017. As of April 2016 the scheduled launch dates for 1A and 1B are were further pushed back to October 2017 and October 2018. Falcon-9 rockets will be used for the launches>>
Taiwan NSPO satellite AKA Formosat-5
The news reports about it are from 2010 (And, yet, it is still on the SpaceX manifest.)
http://www.spacex.com/press/2012/12/19/spacex-and-national-space-organization-nspo-sign-contract-launch
<<Formosat-5 is slated to launch as early as December 2013 from SpaceX's launch site on Omelek Island at the U.S. Army Kwajalein Atoll (USAKA) in the Central Pacific, about 2,500 miles southwest of Hawaii.>>
That's 3 years ago...
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#414 by FattyLumpkin on 07 Sep, 2016 03:16
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dustinthewind, yes to your question, and could the hoop not also be suspended from the bottom? And while we're at it what about the from the side?
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#415 by Monomorphic on 07 Sep, 2016 13:25
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SpaceX isn't launching anything until they can figure out why their second stages keep exploding.
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#416 by Star One on 07 Sep, 2016 14:10
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SpaceX isn't launching anything until they can figure out why their second stages keep exploding.
That goes without saying I would have thought. -
#417 by JohnFornaro on 07 Sep, 2016 14:47
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I'd like to point out that the Cannae picture [that was] posted is their futuristic Space Freighter for deep space work, NOT the cubesat they are sending up.
Thanks for that.So they are using miles instead of kilometers to specify an orbit?
Hah! The early space standards were all American! Note that the various constants and what have you, are Mother Nature's and do not fit in with SAE or SI units. But still, it would be nice if the simplest of information could be shared by the Cannae people.
The key factor, besides altitude, in Jose's calcs, I think, is the efficiency of the solar panels, and this is dependent on the chosen orbit of the sat, as well as the sat's ability to optimize the panels to face the Sun. Keep in mind that there will also be stationkeeping requirements, which encourages one wonder how they plan on achieving all this.Someone correct me if I'm wrong but wouldn't a circular polar orbit place the cubesat in sunlight all the time and also place the extended solar panels in a minimum drag configuration?
That is correct, but note that the term "parallel to the orbital velocity vector" has many answers, since "parallel" can rotate about its vertical axis and still be parallel. The illustration is incorrectly oriented for a helio-synch orbit, for the most part.
See the chart in the oracle for the direction of the velocity vector:
https://en.wikipedia.org/wiki/Orbital_state_vectors
One crucial peice of info not provided in the thread as of the moment, is whether or not the Cannae cubesat has been placed in a geosynch orbit, where I believe that it would have better than 50% solar cell efficiency.Typical sun-synchronous orbits are about 600–800 km in altitude...
Which, solo dicendo, is much higher than the advertised orbit. And SpaceX hasn't yet launched such an orbit, according to, well, their manifest.As discussed in my post, if you don't keep the solar panels parallel to the orbital velocity vector at all times...
Right, but... were you assuming a helio-synch orbit in your calcs? How did you get the 50% efficiency factor?
Sounds like the future launch of this sat is speculative. -
#418 by Rodal on 07 Sep, 2016 14:56
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As discussed in my post, if you don't keep the solar panels parallel to the orbital velocity vector at all times...
Right, but... were you assuming a helio-synch orbit in your calcs?
NO, not at all.
As it was clear clear to SeeShells and Monomorphic (who deserve the credit for suggesting a SSO orbit] I did not assume, in my calculations, anything even close to a Sun-Synchronous Orbit
How did you get the 50% efficiency factor?
I implicitly assumed (but let's make it explicit now) a low-to-moderate inclination circular orbit at 240 km altitude:Quote from: RodalPower available from sunlight (from news that Theseus is anticipated to require less than 1.5 U volume and will use less than 10 watts of power) = 10 watts
Effective power available taking into account that solar panels will be experiencing eclipse ~ 50% of the time
P=(1/2) 10 watts (*) and considering that solar panels must be kept always parallel to the orbital velocity vector, at all times)
I'll edit my original post to make that low-to -moderate inclination orbit assumption explicit to read:
mille grazieQuotePower available from sunlight (from news that Theseus is anticipated to require less than 1.5 U volume and will use less than 10 watts of power) = 10 watts
Effective power available , assuming a common low-to-moderate inclination circular orbit at 240 km altitude, and hence taking into account that solar panels will be experiencing eclipse ~ 50% of the time, and considering that solar panels must be kept always parallel to the orbital velocity vector, at all times)
P=(1/2) 10 watts (*)
=5 watts -
#419 by JohnFornaro on 07 Sep, 2016 15:41
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... if you don't keep the solar panels parallel to the orbital velocity vector at all times...
Right, but... were you assuming a helio-synch orbit in your calcs?
NO, not at all.
HAH! 'Cause I was assuming an SSO! I just couldn't see the sat stationkeeping in the shadow on battery power and only 50% efficiency for recharging and at that low-ish altitude.
Just for laffs, in an SSO, you can minimize drag by orienting the panels parallel to the orbital velocity vector, AND you can minimize solar efficiency by ensuring that the panels point away from the Sun!
On the serious side, the sat would be a success if it could keep itself in orbit, and be able to report data back to Earth.
It seems clear that the launch is speculative.
)