SpaceX Falcon 9 v1.1 - SES-8 - DISCUSSION THREAD

[Roy_H]

Thank you, SBerger. So they want to start with almost a full day of sunlight on their solar panels.

I don't understand the statement about drift time, as it is the same distance from Canaveral to the GEO slot over Thailand regardless of the time of day.

[SBerger]

As you likely know, if you launch at a particular time of day, and perform a particular sequence of propulsive events, you will reach full GEO orbit over a particular point above the earth.  I don't have the knowledge to say what that would be for a given flight.  If that point is not where the satellite operator wants to be, they have to 'move' (drift) the satellite to the desired position.  Usually by slightly, and temporarily, changing the orbital altitude (lower -via a retro burn - to move East, the opposite to move West).  Such a maneuver obviously consumes onboard satellite propellant that the operator would prefer to reserve for other requirements such as N-S station keeping. 

[Avron]

I see no issue with the thread title.. and normally I am up in arms about some of the titles.. However, when I heard that there was a turkey involved someplace I was not trilled.. however, when I did see the image I loved it.. very tasteful or tasty  I was wondering if the use of new battery tech, mitigates any real positives in terms of launch time.

[Lar]

I love all rockets.

I am just waiting for the day when someone deploys a non rocket launch system. THEN maybe you'll see some bias from Chris. But I doubt even then... He'll just modify the above to "I love all rockets and space elevators" or what have you

[Halidon]

I love all rockets.

I am just waiting for the day when someone deploys a non rocket launch system. THEN maybe you'll see some bias from Chris. But I doubt even then... He'll just modify the above to "I love all rockets and space elevators" or what have you

Just so long as it's not "I love rockets and nuclear bombs going off under a giant iron plate."

[darkenfast]

I'd love to see nuclear bombs going off under a giant plate, as long as I'm not downwind! But, about that erector: it seems to be using a different lifting mechanism that is similar to the one at Vandenberg. So while the erector itself may not be set up for Falcon Heavy, there seems to have been an upgrade in capability for some reason. Is it just the slightly increased weight of the 1.1?

[ChrisWilson68]

I'd love to see nuclear bombs going off under a giant plate, as long as I'm not downwind! But, about that erector: it seems to be using a different lifting mechanism that is similar to the one at Vandenberg. So while the erector itself may not be set up for Falcon Heavy, there seems to have been an upgrade in capability for some reason. Is it just the slightly increased weight of the 1.1?

It's not just an upgrade -- they built a whole new erector for F9 v1.1 at the Cape.  The v1.0 erector was discarded.

Perhaps the new erector was built with a design to be upgradable to FH configuration.  It may be that only the bottom plate needs to be replaced for FH while the vertical portion of the new erector remains the same.

[Jim]

Thought I'd try again. Jim's response pointing out the obvious environmental differences didn't help much as it still doesn't answer why. It did make me think of one possible reason, maybe the satellite can lock on to it's navigational stars easier if it is in earth's shadow. Right? Wrong? Anybody know why launching into the dark side of the earth is better than daylight?

It isn't launching into the "dark side of earth".   It going in a high orbit where there is no shadow

Comsats don't use star trackers.

My post answered the "why".

The position of the transfer orbit with respect to the final orbital slot (and ground stations) of the spacecraft drives the timing of the launch as well as solar angles on the spacecraft (for power and thermal considerations) in the transfer orbit. 

[LouScheffer]

Thought I'd try again. Jim's response pointing out the obvious environmental differences didn't help much as it still doesn't answer why. It did make me think of one possible reason, maybe the satellite can lock on to it's navigational stars easier if it is in earth's shadow. Right? Wrong? Anybody know why launching into the dark side of the earth is better than daylight?

It isn't launching into the "dark side of earth".   It going in a high orbit where there is no shadow

In the final orbit, yes.  But in the transfer orbit, there will be eclipses.  To get the shortest eclipses, you want the perigee at midnight and the apogee at noon.  Since there is some chance of being in the transfer orbit for some time (if there is a problem they are trying to sort out), I could certainly see comsat operators wanting to launch into the most power-positive orbit they could get.  This would imply doing the GTO injection burn near local midnight, which seems consistent with the SpaceX launch window.

[Jim]

In the final orbit, yes.  But in the transfer orbit, there will be eclipses.  To get the shortest eclipses, you want the perigee at midnight and the apogee at noon.  Since there is some chance of being in the transfer orbit for some time (if there is a problem they are trying to sort out), I could certainly see comsat operators wanting to launch into the most power-positive orbit they could get.  This would imply doing the GTO injection burn near local midnight, which seems consistent with the SpaceX launch window.

Covered that here "solar angles on the spacecraft (for power and thermal considerations) in the transfer orbit. "

The shadow comment wrt star trackers

[docmordrid]

Thought I'd try again. Jim's response pointing out the obvious environmental differences didn't help much as it still doesn't answer why. It did make me think of one possible reason, maybe the satellite can lock on to it's navigational stars easier if it is in earth's shadow. Right? Wrong? Anybody know why launching into the dark side of the earth is better than daylight?

It isn't launching into the "dark side of earth".   It going in a high orbit where there is no shadow

Comsats don't use star trackers.

My post answered the "why".

The position of the transfer orbit with respect to the final orbital slot (and ground stations) of the spacecraft drives the timing of the launch as well as solar angles on the spacecraft (for power and thermal considerations) in the transfer orbit.

Alphasat uses star trackers

http://blogs.nature.com/news/2013/07/europe-launches-massive-laser-communications-satellite.html

[AJA]

Jim could better explain how paranoid the spacecraft people are about battery conditioning (up to and including charging to the last possible second and keeping prelaunch battery temperatures as cold as possible).

As cold as possible? Really? In conventional experience, battery life goes down with temperature, and there's no reason why this should be different for spacecraft battery chemistries. Still governed by the Nernst and Arrhenius equations. Did you mean to say keep them as low as possible in their optimal range?


Or is it a case of 'you can always heat the batteries if needed, but hyperthermal damage is bad'?

Since there is some chance of being in the transfer orbit for some time (if there is a problem they are trying to sort out), I could certainly see comsat operators wanting to launch into the most power-positive orbit they could get.  This would imply doing the GTO injection burn near local midnight, which seems consistent with the SpaceX launch window.

I'm not saying getting into the most power positive orbit you can isn't done, or that it's a bad thing...but if your apogee is at noon, doesn't it then leave you susceptible to a large duration of communication whiteout (when the satellite is around apogee), thanks to that great ball of fire at 1 AU? Or would the S/C antenna point off-nadir and allow some ground station where it isn't local noon to pick it up?

[Jim]

Alphasat uses star trackers

http://blogs.nature.com/news/2013/07/europe-launches-massive-laser-communications-satellite.html

that isn't a standard comsat

[Jim]

1.  As cold as possible? Really? In conventional experience, battery life goes down with temperature, and there's no reason why this should be different for spacecraft battery chemistries. Still governed by the Nernst and Arrhenius equations. Did you mean to say keep them as low as possible in their optimal range?

2.  I'm not saying getting into the most power positive orbit you can isn't done, or that it's a bad thing...but if your apogee is at noon, doesn't it then leave you susceptible to a large duration of communication whiteout (when the satellite is around apogee), thanks to that great ball of fire at 1 AU? Or would the S/C antenna point off-nadir and allow some ground station where it isn't local noon to pick it up?

1.  It is to remove heat from battery charging

2.  The spacecraft would be using omni antenna during transfer orbits.

[Nomadd]

 It might just be a slight difference in terminology, but I wouldn't say battery "life" goes down with temperature, but battery capacity. And that's probably not a factor since as soon as you start a considerable draw it will probably heat back up and have almost the same capacity as if it had started warm. End result would be the battery starting the mission at a more optimal temperature than if it had started warm from charging. (All guesswork based on other fields. Not pretending to know the numbers from sats)

[Joffan]

In the final orbit, yes.  But in the transfer orbit, there will be eclipses.  To get the shortest eclipses, you want the perigee at midnight and the apogee at noon. 

The initial transfer orbit is not necessarily 24-hour period. The second transfer orbit is definitely not. So whatever perigee "time" you set up with the initial boost out of LEO will not endure.

We're not at an equinox, so the intended equatorial apogee would never be in eclipse anyway.

[Lekolite]

Sorry to pick more nits on the article, but I don't see the actual launch time listed anywhere. I see countdown start at 4:07 local, but even that is buried way down in the text.  Shouldn't scheduled liftoff be close to the top of the article? 

Apologies in advance if I'm just blind.   

[ChefPat]

Sorry to pick more nits on the article, but I don't see the actual launch time listed anywhere. I see countdown start at 4:07 local, but even that is buried way down in the text.  Shouldn't scheduled liftoff be close to the top of the article? 

Apologies in advance if I'm just blind.   

Welcome to the board. The 66 minute launch window opens at 17:38 local time.

[Lekolite]

Wow, I've been an L2 member for over a year, didn't realize that was my first post! I apologize to Chris and all NSF contributors that it was negative.  For the record I was trying to help improve the article, not tear it down.
I did find the launch time through the consolidated launch thread. 

[mheney]

More on the launch time - if you want your equator crossing to be at local midnight for the GTO burn (and getting the spacecraft into the light and generating power as early as possible), you'd launch a bit before 6 pm local (1/4 of an orbit; your launch site is the northernmost point in the orbit for a due north launch.  (We're using "true solar time" here).  Factor in 8-10 minures of powered flight before orbit injection, and the fact that the launch site is not necessarily centered in the time zone, and the fact that it's not critical to hit the GTO *precisely* at local midnight, and you get some play in the launch window. 

But the driver is that once the GTO burn is complete, you want to separate from stage 2 and deploy the solar arrays as close to sunrise as possible, and then not cross back into shadow again on the ride uphill.