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#800
by
Space Ghost 1962
on 04 Jan, 2018 18:10
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Someone mentioned here that under a certain scenario, the S2 might need to fire for a Mars course correction quite a while after launch.
Too early for a significant course correction.
Where it is heading isn't Mars but Mars-like in distance/reach, so you don't need a course correction at all to get there.
What you could do is at furthest range do a burn to insure that the payload+F9US wasn't captured by the earth-moon system, but that would be chancy because it isn't the right geometry at the moment for various reasons.
Seems to me this would be an excellent opportunity to gather some more data points for the performance of the S2 engine under unique conditions.
The F9US would have to be outfitted for long duration. No signs of that at the moment.
And they'd have to have tracking assets to allow such, and that does not yet appear to be arranged for.
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#801
by
Brian45
on 04 Jan, 2018 18:24
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Well, it was just a thought. Eventually SpaceX will need to develop and/or ensure the capability of firing the engine after extended periods (days, weeks, months?) in space, so maybe someone at SpaceX said - what the heck, what do we have to lose?
Have they ever done this, firing the engine after a long period?
Again, just a thought. Maybe a little off-topic though.
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#802
by
kevinof
on 04 Jan, 2018 18:34
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Batteries won't last that long and there's no other way to generate power.
Well, it was just a thought. Eventually SpaceX will need to develop and/or ensure the capability of firing the engine after extended periods (days, weeks, months?) in space, so maybe someone at SpaceX said - what the heck, what do we have to lose?
Have they ever done this, firing the engine after a long period?
Again, just a thought. Maybe a little off-topic though.
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#803
by
ChrisC
on 04 Jan, 2018 18:35
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FYI, someone who monitors the Facebook SpaceX group tells me they are saying that Playalinda Beach will be closed for the FH launch. So, that's third hand information, but I thought it worth mentioning here because I have seen no such report here, just that we don't know yet either way.
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#804
by
envy887
on 04 Jan, 2018 19:15
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1 - Do we know if this is going to a direct TMI (or Mars-distance orbital injection) or whether they'll coast in earth orbit for a bit?
2 - I would assume for publicity purposes that Elon will have arranged an epic live video shot of the Tesla payload separating from the upper stage. Or do we think that they'll just have it remain attached to stage 2 for total simplicity?
1. They won't coast because they need to stay in range as long as possible to get tracking from Florida assets nothing elsewhere.
2. Very likely it'll remain with F9US because it's easier to track, has active control/telemetry for the life of the stage, and deals with disposal of stage.
Consensus seems to be direct injection and no separation, but there's no a lot of evidence either way. Only: longest S2 coast was for DSCOVR (30 min) & it would require S2 modifications for significantly longer; and no obvious hardware on the roadster (solar panels, comm antennas) to support a mission apart from the S2. Of course there could be surprises.
Attitude controls for a Tesla? 
If they inject directly into heliocentric orbit the apoapsis will be significantly out of the ecliptic and very far away from Mars. This might not be a bad thing, but it's not really a Mars-like orbit.
All GTO launches coast for about 1/4 orbit and relight over the equator. SpaceX obviously has the necessary tracking assets to do this, and even streams live video from the S2 over Africa, well out of range of the Florida stations. I see no reason why the TMI burn wouldn't also occur over Africa.
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#805
by
1
on 04 Jan, 2018 20:45
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If they inject directly into heliocentric orbit the apoapsis will be significantly out of the ecliptic and very far away from Mars. This might not be a bad thing, but it's not really a Mars-like orbit.
All GTO launches coast for about 1/4 orbit and relight over the equator. SpaceX obviously has the necessary tracking assets to do this, and even streams live video from the S2 over Africa, well out of range of the Florida stations. I see no reason why the TMI burn wouldn't also occur over Africa.
I imagine the equator is of little use for this launch, because the Earth is tilted a good 23ish degrees from the plane of the ecliptic.
As such, I assume SpaceX won't do much more than wait until the Earth rotates the rocket near the plane of the ecliptic and then just go for direct injection. Could probably zero out that 4 degree difference pretty easily if they really wanted to; but I too think that they'll deliberately send the stage slightly off-plane so they can guarantee that it will never hit Mars.
If they do need to go to an intermediate parking orbit, I think 23.5 degree is what they'd need to aim for.
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#806
by
Heinrich
on 04 Jan, 2018 20:55
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In case the above post (by 1) is right, what will the approximate launch time?
(Would be nice to know whether it will be within or outside of office hours)
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#807
by
atsf90east
on 04 Jan, 2018 21:05
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If Zuma is delayed until Sunday will the FH static fire at LC39A still happen on Saturday, or will it be pushed back until Zuma launches from LC40 so that manpower is not stretched too thin?
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#808
by
russianhalo117
on 04 Jan, 2018 21:13
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If Zuma is delayed until Sunday will the FH static fire at LC39A still happen on Saturday, or will it be pushed back until Zuma launches from LC40 so that manpower is not stretched too thin?
They could do it as currently scheduled but there a risk factor with ZUMA soon rolling to SLC-40 for PI. Will know sooner rather than later if they officially bump ZUMA to Sunday.
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#809
by
Celestar
on 04 Jan, 2018 21:22
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Batteries won't last that long and there's no other way to generate power.
There's something else on board that has some relatively huge batteries ...
Celestar
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#810
by
Space Ghost 1962
on 04 Jan, 2018 21:28
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If they inject directly into heliocentric orbit the apoapsis will be significantly out of the ecliptic and very far away from Mars. This might not be a bad thing, but it's not really a Mars-like orbit.
Yes expect direct injection -
am very interested in how much C3 a kerolox cluster vehicle can impart.If they launch in the late evening during December, they can direct inject close to optimal with Earth's orbital velocity in a "Mars-like" transfer orbit, a little above the plane. If they launch during the day, it'll be closer to the ecliptic but more out of plane with Mars, and likely an launch azimuth above 90.
All GTO launches coast for about 1/4 orbit and relight over the equator. SpaceX obviously has the necessary tracking assets to do this, and even streams live video from the S2 over Africa, well out of range of the Florida stations. I see no reason why the TMI burn wouldn't also occur over Africa.
Yes closer to the equator obviously will be better, but I wonder if only Florida tracking will be used for this launch.
In that case if they coast then they'll be over the horizon and have to use those other assets.
There are some advantages to keeping it all in the range. Especially for a new vehicle.
If Zuma is delayed until Sunday will the FH static fire at LC39A still happen on Saturday, or will it be pushed back until Zuma launches from LC40 so that manpower is not stretched too thin?
We don't know the issues that remain with the vehicle. Could be they need more time anyways. Which could also stretch static fire, as well as after static fire. Frankly I'm already amazed its assembled and having been erected at the pad so quickly. This isn't something that goes fast. Ever.
If Zuma is delayed until Sunday will the FH static fire at LC39A still happen on Saturday, or will it be pushed back until Zuma launches from LC40 so that manpower is not stretched too thin?
They could do it as currently scheduled but there a risk factor with ZUMA soon rolling to SLC-40 for PI. Will know sooner rather than later if they officially bump ZUMA to Sunday.
Speaking of the slowest of slow boats ... will this thing ever go? A real "high touch" mission ... <groan>.
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#811
by
1
on 04 Jan, 2018 21:34
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In case the above post (by 1) is right, what will the approximate launch time?
(Would be nice to know whether it will be within or outside of office hours)
My WAG is that a direct injection launch in late January (approximately one month later) would happen somewhere around 22:00 Florida time. This is nothing more than running with the approximation that the "tipping over" of the northern hemisphere during southern solstice is centered at local midnight. After a month, that point should be about two hours earlier going with the normal 4 minute/day differential between sidereal time and civil time. Complete guess on my part; so don't plan your schedule around that.
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#812
by
kevinof
on 04 Jan, 2018 21:39
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I doubt there are any batteries in the car and anyway they would need to be heated someway to get them to work good (I should know!). You would also need to connect it to the S2 which is not something they would do for a one shot deal.
Batteries won't last that long and there's no other way to generate power.
There's something else on board that has some relatively huge batteries ...
Celestar
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#813
by
LouScheffer
on 04 Jan, 2018 23:08
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In case the above post (by 1) is right, what will the approximate launch time?
(Would be nice to know whether it will be within or outside of office hours)
My WAG is that a direct injection launch in late January (approximately one month later) would happen somewhere around 22:00 Florida time. This is nothing more than running with the approximation that the "tipping over" of the northern hemisphere during southern solstice is centered at local midnight. After a month, that point should be about two hours earlier going with the normal 4 minute/day differential between sidereal time and civil time. Complete guess on my part; so don't plan your schedule around that.
My guess would be about 6:00 PM (18:00) local time. My reasoning is this: injection is most efficient when exactly the opposite of the intended target. To get maximum throw, they need the target to be tangent to the Earth's orbit. This puts the opposite point at about 18:00 local time. This is only true for direct injection - with a parking orbit, the earth departure burn needs to happen about 18:00 local time (in the probe's time zone) but the launch can be anytime.
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#814
by
Skylab
on 04 Jan, 2018 23:15
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#815
by
Lars-J
on 04 Jan, 2018 23:27
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That's just ... wildly inaccurate.
(Sure, there are 3 cores and 8 hold-downs, but everything else is way off)
EDIT: Looks like it is a closeup of a design for a FH model and its 3d printed pad hold downs. Here is a video clip a launch of a single core model:
https://twitter.com/joebarnard/status/924506150254665729
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#816
by
envy887
on 05 Jan, 2018 02:41
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If they inject directly into heliocentric orbit the apoapsis will be significantly out of the ecliptic and very far away from Mars. This might not be a bad thing, but it's not really a Mars-like orbit.
All GTO launches coast for about 1/4 orbit and relight over the equator. SpaceX obviously has the necessary tracking assets to do this, and even streams live video from the S2 over Africa, well out of range of the Florida stations. I see no reason why the TMI burn wouldn't also occur over Africa.
I imagine the equator is of little use for this launch, because the Earth is tilted a good 23ish degrees from the plane of the ecliptic.
As such, I assume SpaceX won't do much more than wait until the Earth rotates the rocket near the plane of the ecliptic and then just go for direct injection. Could probably zero out that 4 degree difference pretty easily if they really wanted to; but I too think that they'll deliberately send the stage slightly off-plane so they can guarantee that it will never hit Mars.
If they do need to go to an intermediate parking orbit, I think 23.5 degree is what they'd need to aim for.
Good point. They would still need a second burn to reduce inclination to 23.5 degrees, but it would happen over the Atlantic somewhere, before reaching Africa. Or just inject directly and stay 4+ degrees out of plane.
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#817
by
envy887
on 05 Jan, 2018 02:44
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In case the above post (by 1) is right, what will the approximate launch time?
(Would be nice to know whether it will be within or outside of office hours)
My WAG is that a direct injection launch in late January (approximately one month later) would happen somewhere around 22:00 Florida time. This is nothing more than running with the approximation that the "tipping over" of the northern hemisphere during southern solstice is centered at local midnight. After a month, that point should be about two hours earlier going with the normal 4 minute/day differential between sidereal time and civil time. Complete guess on my part; so don't plan your schedule around that.
My guess would be about 6:00 PM (18:00) local time. My reasoning is this: injection is most efficient when exactly the opposite of the intended target. To get maximum throw, they need the target to be tangent to the Earth's orbit. This puts the opposite point at about 18:00 local time. This is only true for direct injection - with a parking orbit, the earth departure burn needs to happen about 18:00 local time (in the probe's time zone) but the launch can be anytime.
Shouldn't that be midnight local time? For a Hohmann transfer, apoapsis and periapsis are on opposite sides of the sun, and the tangent to Earth is on the far side from the Sun.
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#818
by
Johnnyhinbos
on 05 Jan, 2018 02:58
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Okay, so... and it ain’t going to be me due to the 12 SpaceX limit poll thread - but maybe it’s time for an unofficial poll - will the Tesla payload separate from the Falcon Heavy second stage?
I say yes - here’s my logic...
- Payload adapter. If you examine the photos, there seems to me to be separation mechanisms. Why add if not separating?
- Fairing. Even though not fully installed in the photos, why go through the expense to put in a fairing separation system if the payload will stay attached to the second stage?
(Okay, fine, that second point is easily arguable. Proof of concept, weight, photo op - there, I did it for you)
Regardless - my vote is separation. I simply don’t see it any other way. I can only see Elon wanting the Tesla in a slow tumble away from camera. Sorry - it’s just the only way I see it...
Edit/Lar: no such poll limit... this doesn't seem a good topic for a poll though.
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#819
by
LouScheffer
on 05 Jan, 2018 03:10
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My guess would be about 6:00 PM (18:00) local time. My reasoning is this: injection is most efficient when exactly the opposite of the intended target. To get maximum throw, they need the target to be tangent to the Earth's orbit. This puts the opposite point at about 18:00 local time. This is only true for direct injection - with a parking orbit, the earth departure burn needs to happen about 18:00 local time (in the probe's time zone) but the launch can be anytime.
Shouldn't that be midnight local time? For a Hohmann transfer, apoapsis and periapsis are on opposite sides of the sun, and the tangent to Earth is on the far side from the Sun.
You want to leave Earth at midnight local time, but the way to do that is to burn at 18:00 local time, then the Earth bends the trajectory around 1/4 turn. To see this, imagine a super long and skinny orbit around the Earth with a 40,000,000 km apogee. If the long axis of this orbit is tangent to the Earth's orbit, then the perigee is at the trailing edge of Earth, or about 18:00 local time. Since firing at perigee is the most efficient time, that's where the injection should be.
(Sure, there are 3 cores and 8 hold-downs, but everything else is way off)