SpaceX Falcon Heavy : Arabsat 6A : LC-39A : April 11, 2019 - DISCUSSION

[Comga]

Wow, OCISLY will nearly be 1,000 km downrage from LC-39A for this one. That'll mean the core stage will be traveling like 3.5 km/s at MECO. Going to be an extremely toasty first stage if they get that one back.

I expect a boostback burn to shed some of the core stage's downrange velocity, as on the demo mission.

Some of our expert modelers could simulate this to get believable numeric answers, but landing 1000 km downrange suggest no "boostback" or post-staging-braking burn to shed velocity.  Just a longer reentry burn as LouScheffer suggested.

Orbiter may be right that this would result in an "extremely toasty first stage".

edit: Homonym.....

[ZachS09]

If this Falcon Heavy launches at night (e.g. 11 PM Eastern), it should be spectacular to see all the boosters boosting back to their respective landing targets, given that the engine plumes will collide with each other.

I mean, we've only seen a single-stick booster do so on a regular Falcon 9 mission, but not three of them at nearly the same time.

[envy887]

If this Falcon Heavy launches at night (e.g. 11 PM Eastern), it should be spectacular to see all the boosters boosting back to their respective landing targets, given that the engine plumes will collide with each other.

I mean, we've only seen a single-stick booster do so on a regular Falcon 9 mission, but not three of them at nearly the same time.

The center core boosts back a bit later and much further downrange than the sides.

[Comga]

If this Falcon Heavy launches at night (e.g. 11 PM Eastern), it should be spectacular to see all the boosters boosting back to their respective landing targets, given that the engine plumes will collide with each other.

I mean, we've only seen a single-stick booster do so on a regular Falcon 9 mission, but not three of them at nearly the same time.

The center core boosts back a bit later and much further downrange than the sides.

The plumes wont be visible, or easily visible, because they won't be illuminated by the Sun in the middle of the night.
The really dramatic tableaus have been just before sunrise or just after sunset where the upper reaches are still sunlit.

Early March won't even have much moonlight.  The new moon is March 6 11 AM EST.

[ZachS09]

That's not what I meant.

To prove my point, here's a photo from the Iridium-NEXT F3 mission, which launched an hour and a half before sunrise.

And quoting Bob Montanero from when he took photos of the ZUMA launch: "Separation of the first and second stage created a surreal multicolored light show of intermixing exhaust gases in the night sky as the two stages maneuvered away from each other."

http://www.lunarcabin.com/Rocket_Launches/zuma.html

When I said "nearly the same time", I was already aware that the center core continues burning for ~30 seconds after the side boosters separate.

[Orbiter]

Wow, OCISLY will nearly be 1,000 km downrage from LC-39A for this one. That'll mean the core stage will be traveling like 3.5 km/s at MECO. Going to be an extremely toasty first stage if they get that one back.

No toastier than usual, I think.  Instead, the re-entry burn will be longer to bring the stage down to the same entry speed as usual.

Yes, this takes more fuel that could otherwise be used for boosting the payload, but they can still get a significantly higher staging velocity and get the stage back.  Conversely, if they could in any way accept a toastier re-entry, they could have given better orbits to the heavy satellites they recently launched in recoverable mode.   From this I conclude they are already at the toastiness limit, and hence a longer re-entry burn will be the option used on the heavy.

A potential flaw in this argument is that the heavy center core is special, anyway, and maybe has some special features for increased toast resistance.  But this goes against SpaceX's drive for maximum commonality, and if possible would likely be ported to the single core.  So I'm still voting for a longer re-entry burn and an otherwise nominal entry.

A landing at around ~70W would indeed suggest at least a moderate boostback burn from the sims I've seen, so your argument appears to be correct.

[ChrisC]

In anticipation of continued DM-1 delays, SpaceX could decide to swap the next two LC-39A missions and have this Falcon Heavy mission go first, which could even mean moving to the left from the March 7th date (posted below, just after I posted this).

To what extent are all of the pieces of this mission in place at the Cape?  From this forum:
Center core: at McGregor as of Jan 1st
Side booster: at the Cape per NSF core spotting thread
Side booster: at the Cape per NSF core spotting thread
Second stage: ?
Payload: ? (expected at Cape on Feb 5th, see below)
Payload fairing: ? (en route? see below)
FCC license:  applied for
FAA license: ?

I'm not going to try to parse the booster numbers.

The payload is the one I'm really wondering about.

[Eric Hedman]

Forbes article:

https://www.forbes.com/sites/jonathanocallaghan/2019/01/29/spacex-reveals-potential-launch-date-for-its-next-falcon-heavy-rocket/#5ac572015e5a

[Chris Bergin]

NET March is only what SpaceX want to go with at this stage:

https://twitter.com/NASASpaceflight/status/1090736978251915264

[Alexphysics]

In anticipation of continued DM-1 delays, SpaceX could decide to swap the next two LC-39A missions and have this Falcon Heavy mission go first, which could even mean moving to the left from the March 7th date (posted below, just after I posted this).

To what extent are all of the pieces of this mission in place at the Cape?  From this forum:
Center core: at McGregor as of Jan 1st
Side booster: at the Cape per NSF core spotting thread
Side booster: at the Cape per NSF core spotting thread
Second stage: ?
Payload: ?
FCC license:  applied for
FAA license: ?

I'm not going to try to parse the booster numbers.

The payload is the one I'm really wondering about.

Payload fairing for this mission may be on the road. There's been a rare sighting of a pair of fairing halves being moved to Florida and at this time I doubt they are for PSN-6 so it's most likely they are for Arabsat 6A.

[docmordrid]

In anticipation of continued DM-1 delays, SpaceX could decide to swap the next two LC-39A missions and have this Falcon Heavy mission go first,
>

ISTM that risks even further delaying both Crew Dragon DM launches should ArabSat 6A suffer a pad-damaging oppsie.

[scr00chy]

In anticipation of continued DM-1 delays, SpaceX could decide to swap the next two LC-39A missions and have this Falcon Heavy mission go first,
>

ISTM that risks even further delaying both Crew Dragon DM launches should ArabSat 6A suffer a pad-damaging oppsie.

You could say that about any launch, not just FH. There is always some risk the pad will get damaged. I don't think they worry too much about these things when planning launches.

[woods170]

In anticipation of continued DM-1 delays, SpaceX could decide to swap the next two LC-39A missions and have this Falcon Heavy mission go first,
>

ISTM that risks even further delaying both Crew Dragon DM launches should ArabSat 6A suffer a pad-damaging oppsie.

What's your point?

The scenario you picture is no worse than Atlas 551 having a pad-damaging oopsie that risks further delay to Boeing's Crewed Flight Test.

[StuffOfInterest]

I doubt a Heavy can be stacked while another stick is completely assembled in the garage.  If it was just another single stick then I could see it being done.  To get the Heavy assembled, I believe they would have to completely demate the stages and payload to move them out in order to have space for the side boosters to be placed before moving them onto the TE.  For that reason more than any other I wouldn't expect to see the launches swapped unless there was going to be a multi-month delay for DM1.

[wannamoonbase]

Agreed, nothing getting in the way of DM-1 and that milestone check from NASA.

39A has a lot going on between the DM’s and the FH’s.

Could see them trying to get the FH in as soon as possible after DM-1 lifts off.  What I’m saying is March seems realistic.

[Roy_H]

NASA seems to be determined to delay DM1 as long as possible. I think it would be a mistake for SpaceX to delay Arabsat because of conflict with DM1. If DM! is delayed to March (now likely), I think it is in SpaceX best interest to launch Arabsat and get it out of the way, who knows how long it will be before DM1 flies?

[zubenelgenubi]

To what extent are all of the pieces of this mission in place at the Cape?  From this forum:
Center core: at McGregor as of Jan 1st
Side booster: at the Cape per NSF core spotting thread
Side booster: at the Cape per NSF core spotting thread
Second stage: ?
Payload: ?
Payload fairing: ? (en route? see below)
FCC license:  applied for
FAA license: ?

The payload is the one I'm really wondering about.

According to this up-thread, satellite delivery is requested for February 5 (see bold):

Welcome back regulations.gov 

January 16, 2019

On behalf of Volga-Dnepr Airlines, Lockheed Martin Space kindly requests that the United States Department of Transportation (DOT) review and approve the exemption application from VOLGA-DNEPR AIRLINES LLC for an exemption (Docket OST-2019-0006) from the provisions of 49 U.S.C. §§ 40109(g) and 41703(c) of an intra-CONUS transport of ArabSat-6A commercial satellite from Moffett Field, Mountain View, CA to the NASA Shuttle Landing Facility, Titusville,
FL.

We understand that the government shutdown and furlough of many federal employees has impacted the DOTs approval process and would unpretentiously request specific approval of the Volga-Dnepr’s AN-124 transport scheduled for 5 February 2019. This transport is for the Arabsat-6A spacecraft...
<snip>

[LouScheffer]

Time for the obligatory back-of-the-envelope calculations for this mission.  Start with the basics for other missions, all from SpaceX webcasts - altitude at stage separation, speed at stage separation, horizontal speed (see next paragraph), distance of the landing pad from the launch, the time of separation, and the landing time.

Mission    Alt  Speed Speed   Hor Dist Time  Time
            Km  km/hr m/sec   m/s   km  sep  land
----------  --  ----   ----  ---- --- ---- -  ---
X-37        70  5865   1629  1176    0 2:30  8:15  Full telemetry from first stage
Telstar-18  67  8174   2271  1972  650 2:39  8:30
Intelsat35  73  9480   2633  2380    - 2:47     -  Expended
FH (side)   61  6875   1910  1542    0 2:34  7:58
FH center   86  9540   2652  2400  350 3:06  8:19


After stage sep, X-37 went up for 115 sec, down 115 sec to same altitude (70 km).  So vertical speed was 115*9.8 = 1127 m/s.  This speed will coast upward an additional 115^2*9.8/2 = 65 km, consistent with the webcast (reported 136 km ~= 70 km + 65 km).  To first order, this approximate vertical speed can be applied to all missions, since they all take about the same time to land.  Use this to calculate the horizontal velocity at separation in the table above.

So SpaceX gets a min of 240 seconds of pure coast, and a max of 330 seconds until landing.  But the last part of landing is more or less vertical, and assuming about 300 seconds of coast gives good estimates.  Consistent with GTO, 1972 m/s * 300 seconds = 592 km downrange coast.  This plus about 70 km downrange at burnout is about what we see, 650 km.

The FH center core catcher was at 350 km; so FH did not cancel all the horizontal speed but cancelled most of it.  (Not boost-back, but boost-not-so-far-forward.)  Assuming turn-around at 150 km, land at 200 km further, gives an effective 667 m/s forward for 300 seconds.  But it started at 2400 m/s horizontal, so SpaceX applied about 1700 m/s reverse speed.

One F9 engine eats about 270 kg/sec.  So a single engine landing burn is about 6t (8.1t max, but it’s throttled during much of this time).  Re-entry = 20 sec x 3 engines = 16200 kg.  Call it 17000 kg, just in case.

Then assuming empty = 27t, landing = 6t, re-entry burn = 17t, then normal GTO re-entry starts at 50t. So the FH center core boost-back of 1700 m/s must have started at 87t  = (50t*exp(1700/311/9.8)). 

Now how can they best use this fuel?  They need to use part of it to increase the speed of the payload, then the rest to get down to normal GTO entry conditions, which are 1972 m/s and 50t total mass.  So the separation speed (horizontal) must meet two conditions, where x is the mass at staging, and 125t the mass of the second stage + payload:

2400 + 311*9.8*ln((87+125)/(x+125))  speeding up
1972 + 311*9.8*ln(x/50)  (slowing down)

These two curves cross at x=64.4t and v = 2742 m/s.

So FH will stage at 2742 m/s horizontal, coasting 2742 m/s * 300 sec = 823 km downrange.  Added to 150 km start, this is nearly what we see.  Separation speed will be about sqrt(2742^2+1127^2) or 2965 m/s.

So expect 9 seconds more boost (3:15), 2965 m/s (10670 km/hr) at sep, and a re-entry burn lasts 38 instead of 20 seconds.

EDIT: add Intelsat-35 expendable for comparison
EDIT:  Calculation was inconsistent.   Assumed -1000 m/s for boostback to meet nominal GTO entry conditions, but only ended up with 700 m/s more forward velocity.   Corrected these calculations.

[LouScheffer]

And now we can re-do the estimates for the final orbit.  Compare to Intelsat-35, which massed 6.7t and added 2550 m/s from LEO.

Reducing the payload to 6t from 6.7t adds about 180 m/s.  From the above post, the further downrange landing of the center core adds about 340 m/s.  So a total of 520 m/s more than Intelsat 35, or about 3070 m.s from LEO.

This could give a hugely super-synchronous apogee of 241,000 km.  This is theoretically minimum delta-V to GEO, but it's operationally awkward so I don't think they will do that.

Alternatively, they can apply the delta-V to inclination reduction, to get a 250x36000x15^o with 1583 m/s remaining to get to GEO.  I think this is the most likely result, though they could also choose intermediate orbits with some inclination reduction and a super-synchronous apogee.

EDIT: Changed numbers to more recent values from corrected calculation above.  Conclusions are essentially unchanged.

[envy887]

Couldn't they coast after SECO2 and use that delta-v in a third burn to raise perigee and decrease inclination? That would probably get them closer to GEO, even if they did the 3rd burn after only a few hours and well short of apogee.