SpaceX FH: STP-2 : LC-39A : June 25, 2019 - DISCUSSION

[su27k]

https://twitter.com/spaceflightnow/status/1141286545334382592

Is there a fairing attached here? And maybe this will sound stupid, but could it be a "dummy" fairing, with nothing in it? Remember the other day we saw a fairing without markings on it in the HIF?

That would be my guess, one of the benefits of having some used fairing lying around.

[Alexphysics]

Yes, I think there's no payload inside and  it's just a dummy fairing. It might be a pair of flight-proven fairing halves and they put them on it to test the loads during integration, erection on the pad and the static fire and things like that.

[ketivab]

Yes, I think there's no payload inside and  it's just a dummy fairing. It might be a pair of flight-proven fairing halves and they put them on it to test the loads during integration, erection on the pad and the static fire and things like that.

Is there a fairing attached here? And maybe this will sound stupid, but could it be a "dummy" fairing, with nothing in it? Remember the other day we saw a fairing without markings on it in the HIF?

This photo from Julia would favor the "dummy fairing" speculation. No mission patch visible on the fairing.

https://twitter.com/julia_bergeron/status/1141310662750146561

[ZachS09]

Eric Ralph discusses various possible reasons for centre core recovery being so far downrange:

A SpaceX surprise: Falcon Heavy booster landing to smash distance record
By Eric Ralph
Posted on June 19, 2019

In an unexpected last-second change, SpaceX has moved Falcon Heavy Flight 3’s center core landing on drone ship Of Course I Still Love You (OCISLY) from 40 km to more than 1240 km (770 mi) off the coast of Florida.

https://www.teslarati.com/spacex-surprise-falcon-heavy-booster-landing-distance-record/

Let's hope that third time's a charm for the center core. Technically, the Arabsat 6A center core DID stick the landing, but it's kind of controversial when it comes to both landing and towing back to port.

So, I'd constitute the Arabsat 6A center core landing as a 50:50 success/failure.

[RocketLover0119]

Fairing is indeed a dummy fairing:

https://spaceflightnow.com/2019/06/18/falcon-heavy-stp-2-launch-preps/

(Scroll down to live updates)

[Orbiter]

Rough weather going over LC-39A now.

[ZachS09]

Rough weather going over LC-39A now.

Is rough weather a possible factor of delaying any static fire? Not just this one.

[Orbiter]

Rough weather going over LC-39A now.

Is rough weather a possible factor of delaying any static fire? Not just this one.

Yes, absolutely. Can't have a lightning warning in effect to fuel the rocket. In Florida, you get those quite often in June (basically every day).

[kdhilliard]

Fairing is indeed a dummy fairing:
https://spaceflightnow.com/2019/06/18/falcon-heavy-stp-2-launch-preps/
(Scroll down to live updates)

Thanks!  And the reason for the fairing is given in that article:

The fairing is a "non-flight" component, and was added for the static fire at the request of the Air Force to collect acoustic data.

[gongora]

https://twitter.com/exploreplanets/status/1141493728495845376

Here's Our First Look at LightSail 2 Installed on SpaceX's Falcon Heavy Rocket

[Elthiryel]

Do we know what are the three different deployment orbits planned for this mission?

Yes, we do.

300 km x 860 km x 28.5 deg
720 km x 720 km x 24 deg
6000 km x 12000 km x 43 deg

https://forum.nasaspaceflight.com/index.php?topic=30544.msg1939713#msg1939713

[billh]

Do we know what are the three different deployment orbits planned for this mission?

Yes, we do.

300 km x 860 km x 28.5 deg
720 km x 720 km x 24 deg
6000 km x 12000 km x 43 deg

https://forum.nasaspaceflight.com/index.php?topic=30544.msg1939713#msg1939713

Wow! They really are putting S2 through its paces!

[ZachS09]

Do we know what are the three different deployment orbits planned for this mission?

Yes, we do.

300 km x 860 km x 28.5 deg
720 km x 720 km x 24 deg
6000 km x 12000 km x 43 deg

https://forum.nasaspaceflight.com/index.php?topic=30544.msg1939713#msg1939713

Wow! They really are putting S2 through its paces!

Don't forget the passivation burn that inserts Stage 2 into a disposal orbit. That's another part of "being put through its paces".

Quick question for F9 experts: how many times can MVac be reignited on a typical mission with different orbits? Not including STP-2.

[wannamoonbase]

Do we know what are the three different deployment orbits planned for this mission?

Yes, we do.

300 km x 860 km x 28.5 deg
720 km x 720 km x 24 deg
6000 km x 12000 km x 43 deg

https://forum.nasaspaceflight.com/index.php?topic=30544.msg1939713#msg1939713

Wow! They really are putting S2 through its paces!

Don't forget the passivation burn that inserts Stage 2 into a disposal orbit. That's another part of "being put through its paces".

Quick question for F9 experts: how many times can MVac be reignited on a typical mission with different orbits? Not including STP-2.

The Merlin 1D's used for RTLS go through 4 burns in a flight.  They don't seem to mind starting them. 

For S2, it likely comes down to how long the stage is viable once on orbit and how much TEA/TEB they have on board. 

So far we know about 6 hours and 4 burns, 3 changes in orbital plane is pretty cool, looking forward to seeing this one fly.

[LouScheffer]

It would appear that core stage will have a much higher apogee on STP-2 than on Arabsat.

From the Arabsat webcast, the core staged at 100 km altitude, coasted for about 220 seconds (3:35 to 7:15),  then started the entry burn.  The entry burn starts at about 60 km altitude, so we can find the vertical speed a separation that results in these numbers (h  = 100,000 + v*t - 1/2*g*t^2 = 60,000, where t = 220 seconds).  It's about 900 m/s vertical.  The cutoff speed was 10730 km/hr = 2981 m/s.  So the horizontal speed is sqrt(2981^2-900^2) = 2841 m/s horizontal.   During the 220 second coast, the stage will travel 220*2841 meters = 625 km downrange, the bulk of the travel.  The rest is the distance from takeoff to cutoff (a few hundred km) and the distance after the entry burn, which can't be much since the glide angle will not be great.  So all is consistent.

For STP-2 to get 300 km further downrange in the same amount of time is not possible.  To get 300 km further in 220 seconds would require more than 1,000 m/s additional x velocity.  The FH test saved 30 seconds of fuel for after booster separation and got something like 2650 m/s.  Arabsat 6 burned for 64 seconds after booster sep and got 2980 m/s, or an incremental 330 m/s.  This is pretty close the limit - if the center core went full thrust for 30 seconds (to minimize gravity losses), then throttled down to 40% (the lowest we've heard of) for the next 120 seconds, then it would have 72 seconds of fuel left.  That's only 8 seconds more than Arabsat, so it's already pretty close to maxed out.   Maybe they can squeeze 100 m/s more at staging, but that's about it, absent wild strategies like shutting core engines down during the side booster burn, which I doubt they are ready to try yet.

So how do you get 300 km further downrange, if you can't increase the horizontal velocity?  The only way is to increase the apogee, so your coast is longer.  To go 300 km more, at a slightly smaller 2800 m/s, you need to coast for 107 more seconds.  To do this, you need to increase the vertical velocity by 107*g/2,  or about 535 ms.  Your new vertical speed is 900+535 or 1435 m/s.  This gives a horizontal speed of roughly sqrt(3000^2-1435^2) = 2635 m/s.   You could iterate to improve this consistency but given how rough these figures are I doubt it's worth it (except to SpaceX).

With this extra vertical speed, the stage will coast higher.  Starting from the 100 km staging, 143.5 seconds later it will peak out at 203 km, as opposed to the (calculated) 141 km of Arabsat.

So overall, I'm guessing:
  - The cutoff speed will be similar, at most a little better (<100 m/s better)
  - The coast will be much longer (about 107 seconds longer).  So landing at 11:47 or so.
  - The apogee of the core will be much higher (200 km-ish, rather than the 140 km-ish of Arabsat)

EDIT:wording

[Alexphysics]

It would appear that core stage will have a much higher apogee on STP-2 than on Arabsat.

From the Arabsat webcast, the core staged at 100 km altitude, coasted for about 220 seconds (3:35 to 7:15),  then started the entry burn.  The entry burn starts at about 60 km, so we can find the vertical speed a separation that results in these numbers (h  = 100,000 + v*t - 1/2*g*t^2 = 60,000, where t = 220 seconds).  It's about 900 m/s vertical.  The cutoff speed was 10730 km/hr = 2981 m/s.  So the horizontal speed is sqrt(2981^2-900^2) = 2841 m/s horizontal.   During the 220 second coast, the stage will travel 220*2841 = 625 km downrange, the bulk of the travel.  The rest is the distance from takeoff to cutoff (a few hundred km) and the distance after the entry burn, which can't be much since the glide angle will not be great.  So all is consistent.

For STP-2 to get 300 km downrange in the same amount of time is not possible.  To get 300 km further in 220 seconds would require more than 1,000 m/s additional x velocity.  The FH test saved 30 seconds of fuel for after booster separation and got something like 2650 m/s.  Arabsat 6 burned for 64 seconds after booster sep and got 2980 m/s, or an incremental 330 m/s.  This is pretty close the limit - if the center core went full thrust for 30 seconds (to minimize gravity losses), then throttled down to 40% (the lowest we've heard of) for the next 120 seconds, then it would have 72 seconds of fuel left.  That's only 8 seconds more than Arabsat, so it's already pretty close to maxed out.   Maybe they can squeeze 100 m/s more at staging, but that's about it absent wild strategies like shutting core engines down during the side booster burn, which I doubt they are ready to try yet.

So how do you get 300 km further downrange, if you can't increase the horizontal velocity?  The only way is to increase the apogee, so you coast longer.  To go 300 km more, at a slightly smaller 2800 m/s, you need to coast for 107 more seconds.  To do this, you need to increase the vertical velocity by 107*g/2,  or about 535 ms.  Your new vertical speed is 900+535 or 1435 m/s.  This gives a horizontal speed of roughly sqrt(3000^2-1435^2) = 2635 m/s.   You could iterate to improve this consistency but given how rough these figures are I doubt it's worth it (except to SpaceX).

With this extra vertical speed, the stage will coast higher.  Starting from the 100 km staging, 143.5 seconds later it will peak out at 203 km, as opposed to the (calculated) 141 km of Arabsat.

So overall, I'm guessing:
  - The cutoff speed will be similar, at most a little better (<100 m/s better)
  - The coast will be much longer (about 107 seconds longer).  So landing at 11:47 or so.
  - The apogee of the core will be much higher (200 km-ish, rather than the 140 km-ish of Arabsat)

A higher apogee makes also sense if you look at the orbits the payloads are going to go. The insertion orbit will probably be the initial 300x860km at 28.5°. This would mean the second stage will have to be around 300km in altitude at MECO with the apogee at the other side of the Earth at 860km in altitude. So instead of a lower altitude at SECO like on Arabsat 6A, this time the second stage will have to go higher to 300km so it makes sense the center core will also go higher up to push the second stage higher too.

[intelati]

My modest contribution from Playalinda beach yesterday around 4 pm.
Not the best quality compare to the traditional profi reporters here, but its my first personal "close" encounter with FH so I'm pretty excited. 

Loving the contrast between the used boosters and the clean core. 

[Steven Pietrobon]

Do we know what are the three different deployment orbits planned for this mission?

Yes, we do.

300 km x 860 km x 28.5 deg
720 km x 720 km x 24 deg
6000 km x 12000 km x 43 deg

https://forum.nasaspaceflight.com/index.php?topic=30544.msg1939713#msg1939713

I calculate 597.8 m/s from the first to second orbit and 2829.9 m/s from the second to third orbit. Total delta-V is 3427.7 m/s.

http://www.sworld.com.au/steven/space/orbit.zip

Delta-V calculator by Steven S. Pietrobon. 22 Jun 2019.
Enter negative perigee height to exit program.
Enter negative height for geosynchronous altitude.

Enter initial perigee height (km): 300
Enter initial apogee height (km): 860
Enter required inclination change (deg): 4.5
Enter required perigee height (km): 720
Enter required apogee height (km): 720

Burn at   860.0 km: theta1 =  4.50 deg, dv1 =  586.6 m/s
Burn at   720.0 km: theta2 =  0.00 deg, dv2 =   36.5 m/s
dv =  623.1 m/s

Burn at   860.0 km: theta1 =  3.68 deg, dv1 =  484.3 m/s
Burn at   720.0 km: theta2 =  0.82 deg, dv2 =  113.5 m/s
dv =  597.8 m/s

Enter initial perigee height (km): 720
Enter initial apogee height (km): 720
Enter required inclination change (deg): 19
Enter required perigee height (km): 6000
Enter required apogee height (km): 12000

Burn at   720.0 km: theta1 =  0.00 deg, dv1 = 1507.4 m/s
Burn at 12000.0 km: theta2 = 19.00 deg, dv2 = 1440.6 m/s
dv = 2947.9 m/s

Burn at   720.0 km: theta1 =  4.25 deg, dv1 = 1625.8 m/s
Burn at 12000.0 km: theta2 = 14.75 deg, dv2 = 1204.1 m/s
dv = 2829.9 m/s

[LouScheffer]

[First orbit]         300 km x 860 km x 28.5 deg
[second orbit]     720 km x 720 km x 24 deg

I calculate 597.8 m/s from the first to second orbit [...]

http://www.sworld.com.au/steven/space/orbit.zip

Delta-V calculator by Steven S. Pietrobon. 22 Jun 2019.
Enter negative perigee height to exit program.
Enter negative height for geosynchronous altitude.

Enter initial perigee height (km): 300
Enter initial apogee height (km): 860
Enter required inclination change (deg): 4.5
Enter required perigee height (km): 720
Enter required apogee height (km): 720

[...]

Burn at   860.0 km: theta1 =  3.68 deg, dv1 =  484.3 m/s
Burn at   720.0 km: theta2 =  0.82 deg, dv2 =  113.5 m/s
dv =  597.8 m/s

Seems correct, but this is not the way SpaceX will do this, I think, since number of burns is a tighter limit than delta-V.   This can be done with one burn - as the 300 x 800 orbit crosses 720km, a single burn can re-direct into a 720x720 at any inclination.   The magnitude of this burn will require full 3D trig to figure out, though.  I suspect it's comparable.

[TorenAltair]

I wonder if the flight profile represents the way that the DoD conducts or wants to conduct its launches: launch in one direction, then after first stage separation change orbit/inclination multiple times and drop the sat(s) some time before the end of the whole second stage mission to make things harder for an observer.