SpaceX Falcon 9 v1.1 - Thaicom 6 - DISCUSSION THREAD

[Lars_J]

Or the most simple explanation... The numbers in the press kit and/or press release are just wrong. Based on pre-prepared data has changed with a different flight profile.

[bunker9603]

Or the most simple explanation... The numbers in the press kit and/or press release are just wrong. Based on pre-prepared data has changed with a different flight profile.

I agree with Lars-J, the Press Kit had other errors so I think this is the most reasonable explanation.

[sdsds]

I've been burned recently while trying to interpret catalog data, but like a stubborn child I'll reach towards the stove again here:

2 Objects have now been catalogued by USSTRATCOM.
Object A: 2014-002A/39500 at 0051UTC was in 376 x 90039 km x 22.46° (tentatively Thaicom-6)
Object B: 2014-002B/39501 at 2336UTC was in 457 x 91590 km x 22.39°

My spreadsheet shows the Object A orbit is better for the spacecraft (closer to GEO) than the target orbit, though only by 4 m/s.

Also it shows the minimum delta-v between the Object A orbit and the Object B orbit as 288 m/s. Can that be achieved purely with venting?

(On the topic of standard deviation: I think something like https://en.wikipedia.org/wiki/Monte_Carlo_method is implicit.)

288 m/s? My spider senses tell me this should be an error. Could you check your calculations and perhaps post them for review purposes?

Ah, your spider senses are keen! Plus, double-checking rarely hurts. And in this case yes, there was an obvious error. (I had mis-entered the size of the inclination change.) It's not 288 m/s; it's only 10 m/s.

Sorry about that!

[Danderman]

Good job SpaceX!

2 Objects have now been catalogued by USSTRATCOM.
Object A: 2014-002A/39500 at 0051UTC was in 376 x 90039 km x 22.46° (tentatively Thaicom-6)
Object B: 2014-002B/39501 at 2336UTC was in 457 x 91590 km x 22.39°

I am guessing that much of the inclination change from 28 degrees (latitude of Cape Canaveral) and this 22 degree orbit was achieved via some yaw steering during the latter portion of the second stage 2nd burn.

Still..... it costs something to perform that yaw steering, but inclination change at 90,000 km altitude, not so much. Is inclination change at relatively low altitudes really the best use of propellant, or would it have been better, for example, to somehow raise perigee with that prop (if possible)?

[blazotron]

Just a quick checks on clocks by reviewing the video.

at ignition:

17:05:58 displayed on the ground camera (EST) and 00:00 on the screen overlay

at separation:

22:09:13 displayed on the 2nd stage camera (UTC) and 03:00 on the screen overlay

Right there is a 15 second discrepancy between the clocks.

If you look at t-2 minutes in the webcast, the onboard videos are already mis-synced from the ground videos by 15 or 16 seconds, but from those views (which are simulcast during liftoff), it's clear that they are showing the same point in time.  I suspect they are operating the ground and flight cameras on different clock references.  For instance, the ground could be operating on UTC since that seems to match the launch times, and the flight clocks on GPS time since that's an easy reference for a vehicle that has integrated GPS receivers, which happens to be <dramatic pause> 16 seconds ahead right now...
http://www.leapsecond.com/java/gpsclock.htm

[Lars_J]

Good job SpaceX!

2 Objects have now been catalogued by USSTRATCOM.
Object A: 2014-002A/39500 at 0051UTC was in 376 x 90039 km x 22.46° (tentatively Thaicom-6)
Object B: 2014-002B/39501 at 2336UTC was in 457 x 91590 km x 22.39°

I am guessing that much of the inclination change from 28 degrees (latitude of Cape Canaveral) and this 22 degree orbit was achieved via some yaw steering during the latter portion of the second stage 2nd burn.

Still..... it costs something to perform that yaw steering, but inclination change at 90,000 km altitude, not so much. Is inclination change at relatively low altitudes really the best use of propellant, or would it have been better, for example, to somehow raise perigee with that prop (if possible)?

What do you mean by 'yaw steering'? A combined apogee raising and inclination change burn can be achieved by just thrusting in a single vector that accomplishes both at the same time. No steering during the latter part of the burn is required.

It may not be the most efficient way to do the inclination change as low (<400km) as it was done, but the upper stage has limited lifetime and a limited number of restarts, so it tries to get as much of the job done as possible for the satellite to lessen its delta-v to its destination orbit.

[LEGO_Man]

Is inclination change at relatively low altitudes really the best use of propellant, or would it have been better, for example, to somehow raise perigee with that prop (if possible)?

For a given vehicle and desired orbit, there's a single fuel-optimal trajectory which distributes the plane change across all the burns, weighted by how efficient at plane changes that burn is. There's also an optimal supersynchronous apogee, which I assume they chose.

So to go from SLC-40's starting latitude of 28.56°, there was a tiny amount of 'yaw steering' during ascent into the parking orbit (0.9°), a bit of plane change during the perigee burn (5.2°), the majority of the plane change during the apogee burn (~16?°), and a small amount during the perigee burn into GEO (~6?°). Being the fuel-optimal trajectory, any other distribution of inclination changes would be less efficient. The supersynchronous trajectory saved Thaicom-6 300 m/s of ∆v vs. a Hohmann transfer, representing nearly 7 years of GEO stationkeeping.

First, btw.

[Kaputnik]

Very informative first post! Welcome to the forum

[rpapo]

I don't know how one goes about nagging SpaceX about their web site, but the list of completed missions in their manifest still shows Thaicom as having launched in 2013...

http://www.spacex.com/missions#completed-missions-header

[LouScheffer]

Good job SpaceX!

2 Objects have now been catalogued by USSTRATCOM.
Object A: 2014-002A/39500 at 0051UTC was in 376 x 90039 km x 22.46° (tentatively Thaicom-6)
Object B: 2014-002B/39501 at 2336UTC was in 457 x 91590 km x 22.39°

I am guessing that much of the inclination change from 28 degrees (latitude of Cape Canaveral) and this 22 degree orbit was achieved via some yaw steering during the latter portion of the second stage 2nd burn.

Still..... it costs something to perform that yaw steering, but inclination change at 90,000 km altitude, not so much. Is inclination change at relatively low altitudes really the best use of propellant, or would it have been better, for example, to somehow raise perigee with that prop (if possible)?

Sin/cos trig makes the cost of a slight inclination worthwhile.  Instead of a straight apogee raise, suppose you aim in the direction of the inclination change by 0.1 radians (6 degrees). You give up only 0.5% of your desired delta-V (cos(0.1) ~ 0.995) but gain 10% of the total delta-v in  the cross direction (since sin(0.1) ~ 0.1).  This is just an example, and the exact numbers will be optimized for the mission.   But basically on each major burn, it makes sense to reduce the inclination somewhat.

[cambrianera]

Any estimate on the distance from which this photo was taken, and hence the operational time on the second stage?

Diameter of nozzle is 250 cm, distance of nozzle edge from bottom of the tank (where likely the camera is positioned) is 500 cm.
Apparent diameter of earth in this pic is about two times apparent diameter of nozzle.
Distance from earth should be something like 1 earth diameter, about 12000 km.

[ugordan]

Do we think it indicates that the ACS was still working or did they just pick the best shot from several taken while tumbling?  (Not that we will ever know for sure.)

The stage was rotating as can be noticed by the slight interlacing artifacts around Earth's limb.

[hrissan]

Hard to say given the weird fisheye lens geometry they use on those rocket cams.

There must be a optics person who can do the calcs.. the lens cannot have changed from launch.. using the know measurements at launch ( frame grab)  one can get some idea from  the dimension of earth in the video frame grab (i.e. image posted)  will give us the altitude

Roughly, the visible diameter of earth is twice the visible diameter of nozzle.

I guess camera position at the outer rim of the tank by comparing interstage view from http://www.spacex.com/falcon9 and image from Cassiope launch (favourable lighting conditions, attached)

The camera is about 5.5 meters from the end of nozzle, which has diameter around 2.7 meters, so the distance to the Earth is about its diameter or roughly 12000 kilometres.

The camera has vertical fov a bit less than 60 degrees.

Now the guess is what's the moment of the snapshot? Is it on the way up before satellite release or on the way down?

[edkyle99]

Now the guess is what's the moment of the snapshot? Is it on the way up before satellite release or on the way down?

If it was at roughly 12,000 km, it would have been well after satellite release.  I would guess on the way up, but it would take an analysis of sun angles, etc, to provide a basis.

 - Ed Kyle

[Jarnis]

Now the guess is what's the moment of the snapshot? Is it on the way up before satellite release or on the way down?

If it was at roughly 12,000 km, it would have been well after satellite release.  I would guess on the way up, but it would take an analysis of sun angles, etc, to provide a basis.

 - Ed Kyle

How long do the batteries on the stage last? Almost certainly on the way up, as I would expect the batteries to be dry by the time it is swinging back down again, no?

[edkyle99]

How long do the batteries on the stage last? Almost certainly on the way up, as I would expect the batteries to be dry by the time it is swinging back down again, no?

What is it, something like 16 hours to first apogee for this orbit?  I don't know about battery life for this stage, but Centaur batteries are supposed to provide power for up to 24 hours.  Telemetry availability could be another issue.

 - Ed Kyle

[mlindner]

Or the most simple explanation... The numbers in the press kit and/or press release are just wrong. Based on pre-prepared data has changed with a different flight profile.

Completely agree. Please people, more Occam's Razor and less Kerminology and Tin foil hats...

[mlindner]

I don't know how one goes about nagging SpaceX about their web site, but the list of completed missions in their manifest still shows Thaicom as having launched in 2013...

http://www.spacex.com/missions#completed-missions-header

*Year indicates vehicle arrival at launch site.

[rpapo]

I don't know how one goes about nagging SpaceX about their web site, but the list of completed missions in their manifest still shows Thaicom as having launched in 2013...

http://www.spacex.com/missions#completed-missions-header

*Year indicates vehicle arrival at launch site.

That is the column header for future missions.  For completed missions it says "Launch", with no footnote.

[Lar]

I don't know how one goes about nagging SpaceX about their web site, but the list of completed missions in their manifest still shows Thaicom as having launched in 2013...

http://www.spacex.com/missions#completed-missions-header

*Year indicates vehicle arrival at launch site.

That is the column header for future missions.  For completed missions it says "Launch", with no footnote.

I tweeted @spacex about the Thiacom 6 error. One tweet probably won't do much good but if everyone did?   Because, really, it's kind of embarrassing for me when I point people less rabidly fannish at their site and they spot errors like that right away. And it probably also costs SpaceX some credibility... 

(my embarrassment is of course WAY more important than a billion dollar company's credibility! )