Someone mentioned here that under a certain scenario, the S2 might need to fire for a Mars course correction quite a while after launch.
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.
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.
Quote from: Surfdaddy on 01/04/2018 05:20 pm1 - 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.Quote from: cscott on 01/04/2018 05:41 pmConsensus 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?
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?
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.
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.
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?
Batteries won't last that long and there's no other way to generate power.
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.
Quote from: atsf90east on 01/04/2018 09:05 pmIf 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.
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)
Quote from: kevinof on 01/04/2018 06:34 pmBatteries 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
Quote from: Heinrich on 01/04/2018 08:55 pmIn 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.
Quote from: envy887 on 01/04/2018 07:15 pmIf 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.
Quote from: 1 on 01/04/2018 09:34 pmQuote from: Heinrich on 01/04/2018 08:55 pmIn 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.
Quote from: LouScheffer on 01/04/2018 11:08 pmMy 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.
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.