SpaceX Falcon 9 : AMOS-17 : August 6, 2019 : DISCUSSION

[RocketLover0119]

My first ever attempt at a streak shot during yesterday's launch 

[gongora]

Has anyone found the TLEs for AMOS 17 yet?

I'd like to know the delta-v to GTO for this mission.

There seems to be a problem with the satellite catalog right now.  None of yesterday's launches are there yet.

[andrewsdanj]

Has anyone found the TLEs for AMOS 17 yet?

I'd like to know the delta-v to GTO for this mission.

There seems to be a problem with the satellite catalog right now.  None of yesterday's launches are there yet.

I'm sure I heard the migty John Insprucker state '2.6 km/s added to get from parking orbit to transfer orbit' (or words to that effect) during the orbit raising burn, if that helps for now.

[LouScheffer]

I'd like to know the delta-v to GTO for this mission.

There seems to be a problem with the satellite catalog right now.  None of yesterday's launches are there yet.

I'm sure I heard the migty John Insprucker state '2.6 km/s added to get from parking orbit to transfer orbit' (or words to that effect) during the orbit raising burn, if that helps for now.

From above in the thread - using this info, likely delta-V is about 1700 m/s, not much different if they chose super-synchronous or inclination reduction.

On the webcast, John said they would add 2.6 km/sec to the orbital speed, more than enough to reach GEO apogee.  I'm guessing they used the rest to reduce inclination.  You can do slightly better with a super-synchronous apogee but it's only a few m/s and likely not worth the extra complexity.  Inclination reduction is also consistent with the final measured Earth-relative velocity of 35295 km/hr.

So my guess is 220 km x 36000 km, inclined 22^o.  1700 m/s to get to GEO.

[gongora]

https://twitter.com/planet4589/status/1159233901270917120

TLE data flowing again. 3 of  4 expected objects from the Ariane launch in  213-241 x 35557 - 35788 km x 4.5 deg geotransfer orbit. Both expected objects from the SpaceX AMOS 17 launch in 221 x 35750 km x 26.1 deg geotransfer orbit.

I can't find them, but I just poke around looking and Jonathan probably pulls everything

[LouScheffer]

https://twitter.com/planet4589/status/1159233901270917120

TLE data flowing again. 3 of  4 expected objects from the Ariane launch in  213-241 x 35557 - 35788 km x 4.5 deg geotransfer orbit. Both expected objects from the SpaceX AMOS 17 launch in 221 x 35750 km x 26.1 deg geotransfer orbit.

I can't find them, but I just poke around looking and Jonathan probably pulls everything

This is odd.  Such an orbit is only about 2.5 km/s from LEO, but John definitely said 2.6 km/sec.  I'm surprised there is not a bigger inclination reduction, or a higher apogee.

[scr00chy]

Yeah, seems kinda meh, compared to Intelsat 35e which was heavier (6761 kg), flew on a Block 4 rocket but still reached 296 x 42742 x 25.85°.

[edkyle99]

Yeah, seems kinda meh, compared to Intelsat 35e which was heavier (6761 kg), flew on a Block 4 rocket but still reached 296 x 42742 x 25.85°.

I don't find this surprising.  Block 5 introduced changes to improve reusability, which likely increased dry mass.  Also, I believe that Intelsat 35e used a Block 3 first stage and Block 4 second stage, with the first stage probably designed from the start to be expended.

 - Ed Kyle

[ZachS09]

Using https://gtocalc.github.io/, inputting the 221 by 35,750 kilometer orbit inclined 26.1 degrees gives the sat 1,784 m/s of delta-v to GEO.

[Alexphysics]

Arbasat 6A was about the same mass and went to GTO-1500. It kinda shows why FH still has some value for these kind of GTO sats.

[abaddon]

Could be the difference between a minimum residual shutdown versus a targeted orbit insertion.

[ZachS09]

Could be the difference between a minimum residual shutdown versus a targeted orbit insertion.

It could have been a Guidance-Controlled Shutdown in my humble opinion. If it were a Minimal-Residual Shutdown, the apogee would have been over 45,000 kilometers given that Block 5 has more power than Block 4. I also didn't hear from SpaceX that they would try to burn until depletion.

[abaddon]

Yes, that’s what I’m saying.

[Alexphysics]

Regarding targeted shutdown vs minimal residual shutdown: Towards the end of the webcast behind Kate Tice there's a view of the LOX tank and you can see it still had a some amount of LOX inside it so it had some more performance left. I know they don't literally drain the tanks but I remember back when they showed views of the LOX tank that when the tank was almost dry you could see the bottom of it and in this case it was not visible so the amount of LOX could have been enough to get more performance out of the second stage.

[mn]

Can anyone explain why they would choose guidance controlled vs minimum residual?

I had asked this before and the answer I got was roughly 'payload specific requirements'.

Does anyone have any reasonable explanation of what kind of requirements could be different between different payloads going to the same target orbit for the same purpose.

Are there additional risks with minimum residual that some customers don't want to take?

And another question: considering the final orbit, could they have tried a ASDS landing?

[LouScheffer]

Something literally does not add up about this trajectory:

They are starting from a roughly 200 km parking orbit (actually it looks roughly like 165 x 235, and they do the second burn 1/4 way around when they are at 200 km, but that makes no difference here).  Speed is 7789 m/s.  We know they ended up in a 221 x 35750 km orbit.  Speed at the bottom of such an orbit is 10226 m/s.

John clearly states "we're going to add about 2.6 km/second" at 46:48 of the SpaceX archived webcast, or roughly T+26:48.  These three speeds form a triangle with sides 7789, 10226, and 2600.  So now we can calculate the change in inclination, using the law of cosines.  The far end is 2600, and we want the angle between the 7789 and the 10226 vector.   2600^2 = 7789^2 + 10226^2 - 2*7789*10226*cos(theta).

So we ask google "acos((2600^2-7789^2 -10226^2)/ (-2*7789*10226)) in degrees"  and get 5.8 degrees.  So they final inclination should be 28.5^o (the Cape) - 5.8^o = 22.7^o, or less since the first two burns usually remove a small amount of inclination, 0.5 to 1 degree typically.

But the reported inclination is 26^o.  What's going on here?  It's hard to imagine the orbital speeds are wrong - the Earth's mass, gravitational constant, and radius are pretty constant.  The law of cosines seems hard to argue with.  That leaves John's statement, which was quite specific.  Even if you take the smallest value that he could have rounded up to 2.6 km/sec, 2550 m/s, you still get 4.8 degrees of inclination reduction, which was more than observed.  And there appeared to be no underburn, since right after the GTO insertion was the call "nominal orbit".

Any suggestions or double-checks would be appreciated.  My guess is that John was wrong, since the physics don't lie.

EDIT:  Add specifically which times in which webcast for John's statement.

[mn]

Something literally does not add up about this trajectory:

They are starting from a roughly 200 km parking orbit (actually it looks roughly like 165 x 235, and they do the second burn 1/4 way around when they are at 200 km, but that makes no difference here).  Speed is 7789 m/s.  We know they ended up in a 221 x 35750 km orbit.  Speed at the bottom of such an orbit is 10226 m/s.

John clearly states "we're going to add about 2.6 km/second" at 26:48 of the webcast.  These three speeds form a triangle with sides 7789, 10226, and 2600.  So now we can calculate the change in inclination, using the law of cosines.  The far end is 2600, and we want the angle between the 7789 and the 10226 vector.   2600^2 = 7789^2 + 10226^2 - 2*7789*10226*cos(theta).

So we ask google "acos((2600^2-7789^2 -10226^2)/ (-2*7789*10226)) in degrees"  and get 5.8 degrees.  So they final inclination should be 28.5^o (the Cape) - 5.8^o = 22.7^o, or less since the first two burns usually remove a small amount of inclination, 0.5 to 1 degree typically.

But the reported inclination is 26^o.  What's going on here?  It's hard to imagine the orbital speeds are wrong - the Earth's mass, gravitational constant, and radius are pretty constant.  The law of cosines seems hard to argue with.  That leaves John's statement, which was quite specific.  Even if you take the smallest value that he could have rounded up to 2.6 km/sec, 2550 m/s, you still get 4.8 degrees of inclination reduction, which was more than observed.  And there appeared to be no underburn, since right after the GTO insertion was the call "nominal orbit".

Any suggestions or double-checks would be appreciated.  My guess is that John was wrong, since the physics don't lie.

While I admit the math is way over my head, I nevertheless find the discussion fascinating.

So how much v do we expect to get from a 1 minute burn?

(and BTW there's a small typo in your post, the statement in the webcast is at 26:48 (not 46:48)
Edit: never mind on the typo: that's T+26:48, I can't seem to find the original SpaceX webcast so I can't see the time in the video)

[OneSpeed]

Something literally does not add up about this trajectory:

I've attached the AMOS-17 telemetry below. Assuming the parking orbit was 166 x 232, and the burn started at 199 kms, the instantaneous plane change ΔV requirement would be 325 m/s. However, as the burn progresses, the apogee raises. At the end of the burn, the instantaneous plane change requirement reduces to only 67 m/s. The integrated plane change ΔV requirement would be somewhere between these values, depending on how constant the yaw angle is.

Simply raising the apogee from 232 to 35750 at 199 kms requires 2,470 m/s, so perhaps John meant that the plane change cost 130 m/s, for a scalar total of 2,600m/s?

[LouScheffer]

Yeah, seems kinda meh, compared to Intelsat 35e which was heavier (6761 kg), flew on a Block 4 rocket but still reached 296 x 42742 x 25.85°.

I don't find this surprising.  Block 5 introduced changes to improve reusability, which likely increased dry mass.  Also, I believe that Intelsat 35e used a Block 3 first stage and Block 4 second stage, with the first stage probably designed from the start to be expended.

 - Ed Kyle

Whatever the explanation is, it's not this.  Amos-17 separated at 9520 km/hr (2644 m/s)  and 79.6 km.  Intelsat 35e separated at 9480 km/hr (2633 m/s) and 73.6 km.  The lesser mass of Amos-17 (6500 kg vs 6770 kg) only accounts for about 3 m/s of the 11 m/s delta.  So at least in this case, the Block 5 first stage has higher performance than the Block 4. 

[LouScheffer]

How well do we really know the mass of AMOS-17?  If it was really 7000 kg instead of 6500, then the performance would be in line with other launches.

As a wild guess as to what that extra 500 kg might be, sometimes the military will host their GEO payloads on commercial comsats.  This might be particularly appealing to the Israeli military, which unlike the US does not have its own dedicated GEO satellites.