Author Topic: Orbits Q&A  (Read 176743 times)

Offline kevin-rf

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Re: Orbits Q&A
« Reply #160 on: 01/24/2014 04:16 pm »
Now curious what could cause the constraint... Earth sensor, space/radiation environment, rf subsystem? interesting...
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Offline Proponent

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Re: Orbits Q&A
« Reply #161 on: 01/24/2014 05:28 pm »
... looks more like a traditional Hoffman transfer.

Nitpick:  Hohmann rather than Hoffman.

Offline sdsds

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Re: Orbits Q&A
« Reply #162 on: 01/24/2014 06:27 pm »
Can someone explain the rational to me the non standard path TDRS-L just took to GTO?

Looks like they did a single US burn to a 185 x 24,919 km x 26.5 parking orbit, then raised the perigee with a second US burn to  5357 x 36522 km x 25.5 deg.

FWIW 5357 x 36522 km x 25.5 deg. looks like 1500 m/s to GEO.

Quote
Since it does not appear the second burn was at the apogee, this would not be a bi-elliptic, looks more like a traditional Hoffman transfer.

Yes, but note it is named after http://en.wikipedia.org/wiki/Walter_Hohmann, not e.g. http://en.wikipedia.org/wiki/Abbie_Hoffman.
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Offline kevin-rf

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Re: Orbits Q&A
« Reply #163 on: 01/25/2014 06:49 pm »
My first edition Revolution for the Hell of It was a prized possession as a youth... Easy to confuse the two as one grows old ;) 
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Offline Avron

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Re: Orbits Q&A
« Reply #164 on: 02/19/2014 01:33 am »
re-posting :

Quote from: Avron on Today at 05:59 AM
What the best generic orbit inclination for Earth- Mars departure?

There's an Orbit Q&A in the Q&A section. Please repost that there. This thread is titled: "SpaceX FX/FXX/BFR Speculation Thread" - a hilarious title, but you can be sure we're not going to have four pages talking about orbits.

=-------------------------------

there is a lot of discussion as to where said FX/FXX/BFR  should be build and I guess launched.. if the launch site is not optimum, then all the other items for any site are of no value/



Offline gosnold

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Re: Orbits Q&A
« Reply #165 on: 03/11/2014 07:08 pm »
I have a question on electric propulsion and inclined GTO. Since you need a plane change from inclined GTO to GEO and to do this you need to burn at the nodes (and in opposite directions at ascending and descending nodes), how do you do it with electrical propulsion since your thrust is so low?

Offline Jim

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Re: Orbits Q&A
« Reply #166 on: 03/11/2014 07:32 pm »
I have a question on electric propulsion and inclined GTO. Since you need a plane change from inclined GTO to GEO and to do this you need to burn at the nodes (and in opposite directions at ascending and descending nodes), how do you do it with electrical propulsion since your thrust is so low?

Chemical GTO plane changes are done near apogee vs the node, simultaneously occurring with the perigee raise.
One of methods, (there are many burn profiles) electrical propulsion uses continuous burning and adjusts the flight path angle depending on the position in the orbit.  At perigee, it almost 90 degrees to the flight path so as to reduce inclination and not raise apogee.  At apogee, it is to raise perigee but with some angle to help remove inclination.  The high efficiency of the EP allows for inefficient burn "locations"

Offline baldusi

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Re: Orbits Q&A
« Reply #167 on: 03/12/2014 10:20 am »
Btw, electric burn profiles are a continuous function and usually require more delta-v than chemical, but this ia more than made up by the SEP extra efficiency (which is around one order of magnitude).

Offline sdsds

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Re: Orbits Q&A
« Reply #168 on: 03/29/2014 06:35 pm »
Some basic questions about "distant retrograde orbits" (DROs) around the Moon:

1- Are DROs coplanar with the orbit of the Moon around the Earth?
1b- Are DROs even planar?
2- How (if at all) is the "stability" of a DRO linked to the delta-v costs for orbit insertion and trans-Earth injection?
3- Are DROs elliptical, or do they in general have some other shape?
4- Is there a known way to calculate minimum delta-v costs between two DROs?
5- For that matter, what parameters are used to specify a particular DRO?

Thanks in advance for any answers, or pointers to answers!
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Offline set321go

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Re: Orbits Q&A
« Reply #169 on: 05/15/2014 03:52 pm »
Hypothetically speaking

What is the procedure for registering/buying an orbit for a Geostationary Satellite?

If I already have a satellite in a geostationary orbit when my satellite retires to I have to give the orbit back?

My research so far has indicated this is managed by the ITU (http://en.wikipedia.org/wiki/International_Telecommunication_Union) but not a whole lot more information

Offline mheney

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Re: Orbits Q&A
« Reply #170 on: 05/15/2014 05:18 pm »
Doing a quick google on "Geostationary slot assignment", I quickly found this report:
Governing the Geostationary Orbit
Orbital Slots and Spectrum Use
in an Era of Interference   
(Jan 2014)

at http://www.ifri.org/downloads/noteespacegpenent.pdf

In it, on p. 46, it reads
Quote
"The number 18.1 of the ITU Radio Regulations states that: “No transmitting station may be established or operated by a private person or by any enterprise without a license issued in an
appropriate form and in conformity with the provisions of these Regulations by the
Government of the country to which the station in question is subject.”

So that suggests that you'd apply for a slot through the Government of Canada (based on your location in Vancouver).

Offline IanH84

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Re: Orbits Q&A
« Reply #171 on: 06/26/2014 03:22 pm »
Procedures in the US and Canada are similar. You start by specifying your target orbital position and frequency bands, submit it to the Federal Communications Commission (FCC) in the US or Industry Canada (IC) in Canada. Both agencies allow for satellites at the same location to be listed on the same application. Once the application has been received, the federal agency reviews it and submits it to the ITU if they find it acceptable. The ITU will then review it to ensure that new satellites are not at risk for colliding or interfering with existing ones.

Here are the full pages from each agency, I'll paraphrase a few notes from them
http://transition.fcc.gov/connectglobe/sec8.html
http://www.ic.gc.ca/eic/site/smt-gst.nsf/eng/sf01385.html

Both agencies have a timeline that requires applicants to actually build and launch satellites after approval to prevent anticompetitive warehousing of frequency spectrum assignments.

Frequency assignments are handled differently between the two countries:

-IC specifies that frequencies are reserved on a first-come, first-served basis, with applications received simultaneously (within one second of each other) having the band divided equally between the applicants.

-The FCC publishes a public notice and a request for comments when applications are received. Typically, there is a time frame (usually 30 days) in which other entities wishing to provide service on the same frequency spectrum must submit their proposals in order to be considered.


In the US, a one-time fee of $115,625 per operational statement (satellite or co-located satellites in the same orbital position,) I don't see an equivalent fee for Canada. There is an annual fee for operation, IC provides a table in the second link below of fees charged by various countries.

All values are in Canadian Dollars:
-Canada
--$666,667/year for C/Ku band
--$291,667/year for C band
--$375.000/year for Ku band

-US (for all bands)
--$242,693 for a geosynchronous satellite
--$301,491 for a satellite in any other orbit

http://transition.fcc.gov/fees/factsheets/owe-ib.pdf
http://www.ic.gc.ca/eic/site/smt-gst.nsf/en/sf10291.html#sec3


Yes, end-of-life procedures are required. Guideline 7 specifically addresses this, but I'll summarize the whole thing for you.

The UN Office for Outer Space Affairs Space Debris Mitigation Guidelines of the Committee on the Peaceful Uses of Outer Space
offers guidelines to minimize production of space debris and risk to other spacecraft, and neither the IC nor FCC will issue you a permit to operate a satellite if you don't have a plan to follow these guidelines. To summarize them:

1: Limit debris released during normal operations
If possible, don't leave anything but the spacecraft in orbit, if you can't avoid it, minimize the amount of it. There are thousands of pieces of debris including entire discarded stages still in orbit, we don't need any more.

2: Minimize the potential for break-ups during operational phases
"Spacecraft and launch vehicle orbital stages should be designed to avoid failure modes which may lead to accidental breaks-ups."

3: Limit the probability of accidental collision in orbit
Only you can prevent Kessler Syndrome.

4: Avoid intentional destruction and other harmful activities
Whenever possible, don't break up anything that's in orbit. If you have to, do so low enough that debris is not left in a stable orbit. I'm sure most people reading this have seen the diagram of tracked Fengyun-1C debris following the 2007 Chinese anti-satellite missile test, which is exactly the opposite of what you should do if you have to shoot down a satellite.

5: Minimize potential for post-mission break-ups resulting from stored energy
UNOOSA states that "By far the largest percentage of the catalogued space debris population origniated from the fragmentation of spacecraft and launch vehicle orbital stages" and recommends that all propellant be vented and batteries discharged before discarding a spacecraft of launch vehicle stage.

6: Limit the long-term presence of spacecraft and launch vehicle orbital stages in the
low-Earth orbit (LEO) region after the end of their mission

Launch stages and end-of-life spacecraft should be deorbited, and if any parts are likely to survive they should be aimed at unpopulated areas. Toxic or hazardous components should be taken into account (for example, aiming the RTGs from Apollo missions for the deepest areas of the Pacific Ocean.)

7: Limit the long-term interference of spacecraft and launch vehicle orbital stages
with the geosynchronous Earth orbit (GEO) region after the end of their mission

"Spacecraft and launch vehicle orbital stages that have terminated their operational
phases in orbits that pass through the GEO region should be left in orbits that avoid
their long-term interference with the GEO region." Since deorbiting GEO satellites is impractical and orbital lifetime of objects at GEO/GSO altitudes is on the order of hundreds of millions or billions of years , the FCC and IC require that spacecraft reserve enough propellant to boost themselves to at least 200km above GSO at the end of their operational life. In reality, only about 1/3 of spacecraft are in operable condition and able to do this at the end of their life.

Offline mgfitter

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Re: Orbits Q&A
« Reply #172 on: 09/18/2014 05:09 am »
There was a very old discussion on here regarding some really cool low-dV trajectories heading for the Earth Moon LaGrange points. I can't find the thread, but one question that I never saw raised on there, was whether there are any free return trajectories that are compatible with heading for EML1 or EML2?

To be precise, I am wondering if a crew heading for a station based at either location, experienced a complete failure to fire the final braking maneuver -- could they have a trajectory that will still get them home again?    And, for now, I am choosing to ignore any situations where that braking burn is only partially successful, because I expect that would cause some real problems! :)

-MG.
« Last Edit: 09/18/2014 05:10 am by mgfitter »

Offline kevin-rf

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Re: Orbits Q&A
« Reply #173 on: 11/23/2014 01:38 am »
I realize this might be a long shot question, but does anyone know if sun synchronous orbits exist at Venus? I was wondering if it is possible to place and keep a satellite in orbit along the terminator.
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Offline baldusi

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Re: Orbits Q&A
« Reply #174 on: 11/23/2014 12:59 pm »
Wikipwdia stated that Venus was too round for it to provide any meaningful drift.

Offline gbaikie

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Re: Orbits Q&A
« Reply #175 on: 11/24/2014 02:09 pm »
There was a very old discussion on here regarding some really cool low-dV trajectories heading for the Earth Moon LaGrange points. I can't find the thread, but one question that I never saw raised on there, was whether there are any free return trajectories that are compatible with heading for EML1 or EML2?

To be precise, I am wondering if a crew heading for a station based at either location, experienced a complete failure to fire the final braking maneuver -- could they have a trajectory that will still get them home again?    And, for now, I am choosing to ignore any situations where that braking burn is only partially successful, because I expect that would cause some real problems! :)

-MG.

http://hopsblog-hop.blogspot.com/2013/04/cartoon-delta-v-map.html
Which links to:
http://forum.nasaspaceflight.com/index.php?topic=18070.0

But in terms of question, I would say the low delta-v trajectory to  EML1 or EML2 are approaching the Moon so as to not need much braking at the Moon. Whereas free return is approaching Moon in manner which requires significant amount braking- otherwise you around it and return to Earth [going pretty fast back to earth].
So one could do the free return trajectory, and brake less than needed to get to a low lunar orbit, and instead go into high elliptical lunar orbit, which then doesn't require much delta-v to get to or from a highly elliptical lunar orbit to EML1 or EML2. 

« Last Edit: 11/24/2014 02:15 pm by gbaikie »

Offline satwatcher

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Re: Orbits Q&A
« Reply #176 on: 11/24/2014 03:16 pm »
I realize this might be a long shot question, but does anyone know if sun synchronous orbits exist at Venus? I was wondering if it is possible to place and keep a satellite in orbit along the terminator.

I do not know the answer, but the answer is not as easy to compute as it is for the Earth and other bodies.

The problem is that for Venus the first few spherical harmonics that describe the deviations from a sphere (J2, J3 and J4) are about equal in magnitude. For the Earth J2 is about a 1000 times larger than J3 and J4. Because of that, the nodal precession is almost entirely caused by J2 and the impact from J3 and J4 can be neglected.

For Venus the contributions from J3 and J4 can not neglected. In this case you'd have to either take into account the higher order terms when deriving the nodal precession or take the Venus gravity potential and brute force propagate orbits with different inclinations/semimajor axes.

Offline Proponent

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Re: Orbits Q&A
« Reply #177 on: 11/24/2014 05:38 pm »
It just occurred to me to wonder whether, since J2 is so small, solar tidal torque might be important.  The back of an envelope tells me that to get a circular orbit about Venus to precess once per Venusian year, in the best (45º inclination to the plane of Venus' orbit about the sun), the orbital period would have to be two Venusian sidereal years.  That's pretty clearly a non-starter -- an orbit that large surely isn't even bound to Venus, because of solar perturbations.  But what about a highly-elliptical orbit with apocytherian directly sunward (or the opposite)?  Then the satellite would spend most of its time where the solar torque is greatest.

Offline baldusi

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Re: Orbits Q&A
« Reply #178 on: 11/24/2014 05:45 pm »
Please remember that the Venusian day is longer than the Venusian year.

Offline Proponent

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Re: Orbits Q&A
« Reply #179 on: 11/25/2014 10:25 am »
True, but a sun-synchronous orbit is one which precesses once per solar year regardless of the planet's rotation rate.

Tags: inclination 
 

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