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#20
by
Zed_Noir
on 04 Oct, 2013 07:27
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It says in the news article that the spacecraft will be parked in an undisclosed location in Florida until the shutdown lifts, because Astrotech is unavailable. Why is that? I thought Astrotech was a private company with it's facilities off-base.
I thought it was going to Spacex facilities and with KSC shutdown access is only via the south gate which might not be able to take the transporter.
Does that mean the SpaceX core transporter also could not access SLC-40 as well? Since it's bigger than the SES-8 transporter.
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#21
by
sdsds
on 04 Oct, 2013 08:35
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For the SES-8 mission, most of the Falcon 9's performance will go into putting the spacecraft in an orbit over 80,000 km altitude at apogee. Some of the rocket's performance will also lower the orbit inclination from about 28 degrees (the lattitude of Cape Canaveral) to a little under 21 degrees, also reducing the amount of fuel that the satellite will require to get to its final orbital slot.
Wow that's high! For comparison on the Intelsat 22 launch ILS targeted a 65,000 km apogee (with a 3,791 km perigee and an inclination of 28.5 degrees). Optimally these apogees should be directly above the equator, even with the orbit inclined to the equatorial plane, right? So what did Elon mean when he said, "We can technically do [GTO missions] without a restart, we can do them as a single burn, but it means the satellite has to do more work to change the plane of its orbit to equatorial." If the decision were made to use only a single burn of the Falcon upper stage (without a restart) then could the spacecraft still be delivered to an orbit with that apogee, but not with the apses at the equator? How much of a penalty would that impose?
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#22
by
StarryKnight
on 04 Oct, 2013 14:26
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Eer,
I can't speak as to whether SpaceX was attempting to do a re-entry of the second stage. But SES wanted SpaceX to demonstrate the relight because a second burn of the upper stage is needed for the SES-8 mission.
sdsds,
Yes it's very high. There's a possibility that the Thaicom-6 mission may be even higher. But I understand they may still be looking at other apogee altitudes.
Yes, apogees have to be nearly above the equater. The penalty can be pretty large if it is too far off. I don't know what Elon may have been refering to. You quote him as saying a plane change (i.e. inclination). So that doesn't mean the apogee is not above (or nearly above) the equator. It means that the upper stage won't be able to knock down the inclination much. For a launch out of the cape, without the rocket reducing inclination, you'll end up with about a 28 degree inclination orbit (the latitude of the launch site). As I noted earlier, the inclination on the SES-8 mission is targeted to be just under 21 degrees. So that's 7 degrees of inclination that the satellite does not have take out by the time it's done with its own delta-v maneuvers.
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#23
by
Chris Bergin
on 04 Oct, 2013 15:12
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Speaking of which, Thaicom-6 is another Orbital bird, so we'll do the same coverage for that mission too (LV in SpaceX section. Spacecraft in this section).
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#24
by
kevin-rf
on 04 Oct, 2013 15:21
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Just make sure they orient the bird the right way
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#25
by
baldusi
on 04 Oct, 2013 16:32
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Is it pure chance or a cheap Falcon 9 means a lot of good business chances for OSC satellites?
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#26
by
StarryKnight
on 04 Oct, 2013 16:45
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It's probably just a coincidence that the first two commercial GEOs on a Falcon 9 are Orbital built spacecraft. In both instances, the end customer (SES and Thaicom) purchased the launch vehicle, not Orbital. The reasons for them to do this were some combination of the cost of the launch (including insurance) and the performance obtained by launching into a very high supersynch mission (which directly relates to a higher spacecraft on-orbit maneuvering life, OML).
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#27
by
jimvela
on 04 Oct, 2013 16:51
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Is it pure chance or a cheap Falcon 9 means a lot of good business chances for OSC satellites?
A SpaceX that is successful in providing reliable, lower-cost launches is good for *EVERY* spacecraft builder and spacecraft operator.
I can't wait to see the first of the S/C that I've worked on launch on a Falcon...
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#28
by
Arthree
on 04 Oct, 2013 17:00
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If the decision were made to use only a single burn of the Falcon upper stage (without a restart) then could the spacecraft still be delivered to an orbit with that apogee, but not with the apses at the equator? How much of a penalty would that impose?
A single-burn GTO injection can (and would) result in an orbit with perigee/apogee over the equator. The advantage to a 2-burn method is that by waiting for the launch vehicle to pass over the equator, inclination can be lowered at the same time that apogee is increased, which leaves the payload in an orbit that requires less delta-v to transfer out of into GEO.
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#29
by
StarryKnight
on 04 Oct, 2013 17:48
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A single-burn GTO injection can (and would) result in an orbit with perigee/apogee over the equator.
Only if that single injection burn also stradles the equitorial plane. Performing a prograde burn will increase the height of the orbit 180 degrees from where the vehicle is when the burn is performed. So if you start with a 28 degree inclinatioin and wait until the the vehicle is at the southern most point of the orbit to do a burn, the apogee will occur over the northern most point of the orbit. Usign this type of burn is how you can get into a Molniya orbit (though that's a 63.4 inclination, 40,000 km apogee).
You are correct about burns for inclination changes have to occur as the vehicle passes the equitorial plane. That is to say to at least do the burn efficiently. An out of plane burn in other places in the orbit can also impact the inclination, but the effect is reduced relative to a burn above the equator.
[Edited to correct Molniya orbit info.]
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#30
by
antonioe
on 04 Oct, 2013 18:42
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Von Karman is regularly quoted as having once said "given enough power, ANYTHING can fly" (aerodynamically speaking...)
I guess the orbital mechanics equivalent is "given enough DV ANY orbit is good"...
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#31
by
StarryKnight
on 04 Oct, 2013 18:50
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I once had a boss who said "I can get you to any orbit you want using 3 burns." Of course this ignores the current state of technology since in the extreme cases you'd need more powerful/fuel efficient engines than have been imagined by anyone except the best science fiction writers.
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#32
by
Arthree
on 05 Oct, 2013 01:32
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A single-burn GTO injection can (and would) result in an orbit with perigee/apogee over the equator.
Only if that single injection burn also stradles the equitorial plane
There is no requirement for the injection burn to ever pass through the equator in order to get an apo/perigee over the equator. Burning towards or away from the center of the orbit will affect both the eccentricity of the orbit and the location of the apo/perigee, and it is this method that would be used in a direct-ascent GTO launch profile.
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#33
by
StarryKnight
on 05 Oct, 2013 01:54
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A single-burn GTO injection can (and would) result in an orbit with perigee/apogee over the equator.
Only if that single injection burn also stradles the equitorial plane
There is no requirement for the injection burn to ever pass through the equator in order to get an apo/perigee over the equator. Burning towards or away from the center of the orbit will affect both the eccentricity of the orbit and the location of the apo/perigee, and it is this method that would be used in a direct-ascent GTO launch profile.
Correct. That was my point later on about the efficiency. A burn centered a few degrees from the eclipse doesn't cost too much in terms of propellant. But burning 30 degrees away costs a lot.
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#34
by
jacqmans
on 09 Oct, 2013 09:09
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SES-8 ARRIVES AT CAPE CANAVERAL FOR SPACEX FALCON 9 LAUNCH
08.10.2013
55th SES satellite to serve Asia-Pacific from 95 degrees East
Luxembourg, October 8th, 2013 – SES S.A. (NYSE Euronext Paris and Luxembourg Stock Exchange: SESG) is pleased to announce that the SES-8 satellite has arrived at the Kennedy Space Center in Cape Canaveral (Florida). The satellite will now be processed for a November launch on board a SpaceX Falcon 9 booster.
SES-8 has been manufactured by Orbital Sciences Corporation. The satellite features up to 33 Ku-band transponders (36 MHz equivalent). SES-8 will be co-located with NSS-6 at the orbital location of 95 degrees East to provide growth capacity over Asia-Pacific. The spacecraft’s high performance beams will support the rapidly growing markets in South Asia and Indo-China, as well as provide expansion capacity for DTH, VSAT and government applications.
Martin Halliwell, Chief Technology Officer of SES, stated: “SES looks forward to the maiden launch of an SES satellite on board the Falcon 9 rocket operated by SpaceX. When co-located with NSS-6 at 95 degrees East, SES-8 will not only provide incremental high performance capacity for multiple applications, it will also create greater reliability and additional security for customers. As such, the SES-8 satellite is an integral part of SES’ growing presence in Asia-Pacific.”
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#35
by
QuantumG
on 15 Oct, 2013 02:48
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#36
by
MP99
on 03 Nov, 2013 20:31
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http://www.orbital.com/SatellitesSpace/Communications/SES-8/
Apparently, that's orbiting some exo-planet that has the same land/water masses as Earth, but has its Arctic Circle around 45
o North (IE with a 45
o axial tilt, and pictured at Northern Winter Solstice).
And it's picking up signals from some alien spacecraft nowhere near the exo-planet's surface, and broadcasting them back somewhere that's nowhere near the exoplanet's surface.
Also, you'd think the solar panels would work better if pointing at the exo-planet's star on at least one axis.
[Although reflections on the solar panels do suggest a second star that is eclipsed from the exo-planet, but is illuminating the satellite.
]
aint she pretty?
Depends if you think form follows function and what alien conspiracists speculate it's function is supposed to be.
LOL.
cheers, Martin
PS anyone spot anything else that I've missed?
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#37
by
AJA
on 23 Nov, 2013 08:42
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Can someone explain to me how you can raise the perigee AND lower the apogee (or vice versa) with the same burn? Or even multiple burns in the same direction (i.e. all of them being prograde or retrograde)?
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#38
by
deltaV
on 23 Nov, 2013 14:44
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Can someone explain to me how you can raise the perigee AND lower the apogee (or vice versa) with the same burn? Or even multiple burns in the same direction (i.e. all of them being prograde or retrograde)?
Let's suppose you're in a circular orbit. Do a single burn thrusting away from the center of the Earth, as if trying to raise the orbit the intuitive but wrong naive way. Immediately after the burn the altitude will clearly increase so apogee must have increased. To first order this burn only changes the direction of velocity, not its magnitude. The vis-viva equation therefore says that the semi-major axis (i.e. average of perigee and apogee) has not changed. We deduce that perigee must have decreased.
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#39
by
Roy_H
on 24 Nov, 2013 14:18
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I am not a rocket scientist, and am finding this an interesting education on orbital mechanics. So if I understand correctly, the most cost effective maneuvers for SES-8 from the delivered orbit would be burns directly away from earth at perigee to circularize the orbit, and at apogee in a northern or southern direction to change the plane of orbit. The north/south burns would not be directly north or south, but at some optimal off angle, and they would have to be done when the perigee coincides with crossing the equator. Did I get this right? To take this a little farther, I assume it best to do the plane change first so it is an equatorial orbit, is this done in a single burn?
