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

[PM3]

According to SpaceX website, total mission duration will be ~ 6 hours, and there will be a ~ 3 hours coast before passivation. This means that DSX will be deployed ~ 3 hours after liftoff. Would this help to select one of the two options?

[soltasto]

Yes, we can get an approximation by getting the usual time between liftoff and SES-2 for a normal GTO mission, then adding the semi periods of the various intermediate orbits by using the obital period forumla: T/2 = pi*sqrt((a^3)/(G*M)) with a being the Semi major axis of the orbit. I would need a piece of paper to do that but I am only from mobile now so I will do it tonight if no one else does it before then!

[soltasto]

Alright did some math:

Liftoff to SES-2 (300km x 860km x 28.5°): 27.5 min (at least, Arabsat-6 time)
SECO-2 to SES-3 (720km x 720km x 24°): 49.5 min
Option 1:
SECO-3 to SES-4 (720km x 12000km x 24°): 119.1 min
SECO-4 to passivation (6000km x 12000km x 43°): 180 min
Mission time to DSX deploy: 196.1 min = 3.27 hours (at least)
Total mission time: 376.1 min = 6.27 hours (at least)

Option 2:
SECO-3 to SES-4 (720km x 6000km x 24°) 79.6 min
SECO-4 to passivation (6000km x 12000km x 43°) 180 min
Mission time to DSX deploy: 156.6 min = 2.61 hours (at least)
Total mission time: 336.6 min = 5.61 hours (at least)

So I would bet on the second one, assuming the FH has enough performance to do it, but would think it has.
But there isn't much difference since we only know approx times.

Adjusting the Liftoff to SES-2 time (pi/1.6 rad revolution and 300km x 860km orbit) gives me 30 min travel time instead, so almost no difference.

We either have to wait for more accurate timings or some hints from someone who knows.

[FutureSpaceTourist]

https://twitter.com/spacex/status/1121974223566561281

Falcon Heavy center core booster completed a static fire test at our rocket development facility in McGregor, Texas ahead of its next mission → spacex.com/stp-2

[LouScheffer]

The DSX satellite looks pretty light.  The paper Design and Systems Engineering of AFRL’s Demonstration and Science Experiments says it masses less than 600 kg.  This should give FH plenty of performance.  Arabsat went into a transfer orbit that required LEO+2960 m/s.  Reducing the mass from 6465 to 600 kg provides a lot more performance.  With the usual assumptions (107t fuel, 5.5 empty mass + residuals, ISP=348), about 2125 m/s more, so a total of LEO+5085 m/s available.  This should be enough to put the satellites in final orbit, and then actively dispose of the stage. So I wonder why they are not doing that?  Maybe they don't want to put the droneship out so far and stress the second stage.  Maybe the second stage cannot light 5 times?

The below calculations use the law of cosines: if you have one vector of length a m/s, and you want a vector of length b m/s at an angle of theta away, you need dv = sqrt(a^2+b^2-2*a*b*cos(theta))

So they start with a 28.5^o LEO, and release the first satellites.  Then they need about 600 m/s to do a 4.5^o plane change to 720x720x24^o, and release the second set.

Next, assume they go to a 720x6000x24^o, coast to the top, then boost to a 6000x12000x43^o.  This is not the most efficient (better to do the plane change at 12000 km, and also better to do some of the plane change with each burn) but it's a worst case.  Also it's the shortest time to final satellite release, which may be preferable for reliability.

720x720 -> 720x6000, both 24^o, takes 956 m/s.  (7497.5 m/s in LEO, need 8453.5 m/s)
720x6000x24^o -> 6000x12000x43^o takes 2264 m/s.  Going 4845.3 at top of transfer orbit, need 6205.6 at bottom of final orbit, plane change of 19^o.

Now they drop of DSX in its orbit.  So far they have used 600 + 956 + 2264 = 3820 m/s after LEO.

Now (in theory) they should still have plenty of delta-V left to dispose of the stage.  At the top of a 6000x12000 orbit, speed is 4179 m/s.   To reduce this to a 0 x 12000 orbit, need to reduce the speed to 3343 m/s, or remove 836 m/s.  They should easily have this left over.

NOTE added later:  This neglects that first (orbital) burn and plane change are done with more mass, and the mass of the dispenser.   So the margin might not be there...

[gongora]

The original requirements had them carrying a significant amount of ballast throughout the mission.  We really don't know the amount of ballast they may or may not be carrying now.

[scr00chy]

There is supposed to be 5 tons of ballast.

The LSC shall plan and execute a mission that includes the insertion orbits detailed below. The LSC shall also demonstrate a minimum of three upper stage burns and carry 5,000 kg (TBR) of LSC-provided ballast for the entire mission.

Source (PDF)

[gongora]

There is supposed to be 5 tons of ballast.

The LSC shall plan and execute a mission that includes the insertion orbits detailed below. The LSC shall also demonstrate a minimum of three upper stage burns and carry 5,000 kg (TBR) of LSC-provided ballast for the entire mission.

Source (PDF)

You might want to take note of the "TBR" there, and also there have been many changes to the requirements over the last 7 years (one of the deployment orbits is not in that requirements document).

[ZachS09]

This means that the total payload mass at launch will be 7.2 tons.

Makes sense to land the center core really close to the shore (~40 kilometers downrange) since not that much performance is needed besides the four Stage 2 burns.

[gongora]

This means that the total payload mass at launch will be 7.2 tons.

Makes sense to land the center core really close to the shore (~30 kilometers downrange) since not that much performance is needed besides the three Stage 2 burns.

There are four Stage 2 burns.

[LouScheffer]

Yet another possible reason for doing passivation to a graveyard orbit rather than an explicit de-orbit - maybe they need to qualify this procedure since this will be needed for direct-to-GEO missions, where there is not enough performance for an explicit de-orbit,

[Karloss12]

The structural strength and natural frequency checks of the FH is hardly being tested.
I would have thought they would have gone from 6 tonnes for the previous launch to something like 12 tonnes for this launch.
And work the way up to maximum weight.

[OccasionalTraveller]

The structural strength and natural frequency checks of the FH is hardly being tested.
I would have thought they would have gone from 6 tonnes for the previous launch to something like 12 tonnes for this launch.
And work the way up to maximum weight.

You can only launch the payloads that customers book launches for. Well, without adding mass simulators, but that is a waste of resources with obvious space debris/re-entry problems. SpaceX are running a business, not playing Top Trumps: they don't launch unless someone is paying. (The FH Demo excepted, where they couldn't find anyone willing to take the risk of losing their payload.)

SpaceX clearly feel that their computer models and structural tests adequately characterise the launcher's performance, they don't need to actually demonstrate the maximum capability. Not least, they don't actually have any missions on the manifest that need the full advertised capability: everything booked so far is GTO or GEO with mass probably well under 10 tonnes.

There's a good chance that the theoretical LEO capability is never actually demonstrated, that it is only ever used for higher-energy missions.

[Rondaz]

SpaceX’s third Falcon Heavy launch on track as custom booster aces static fire..

By Eric Ralph Posted on May 2, 2019

https://www.teslarati.com/spacex-falcon-heavy-static-fire-third-launch/

[FutureSpaceTourist]

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We're opening our doors in June for you to see @SpaceX's Falcon Heavy rocket launch from @NASAKennedy in Florida. Apply to go behind the scenes, meet experts from @AFspace & much more: go.nasa.gov/2Y9ceJ8

https://twitter.com/nasasocial/status/1125476186363133952

https://www.nasa.gov/social/spacex-falcon-heavy-launch

[FutureSpaceTourist]

https://twitter.com/exploreplanets/status/1126516420106276865

LightSail 2 is officially on the road to launch! Our citizen-funded solar sailing CubeSat has successfully shipped to the Air Force Research Laboratory: http://planetary.org/blogs/jason-davis/lightsail-2-integrated-prox-1.html

[emerrill]

LightSail 2 is officially on the road to launch! Our citizen-funded solar sailing CubeSat has successfully shipped to the Air Force Research Laboratory: http://planetary.org/blogs/jason-davis/lightsail-2-integrated-prox-1.html

It amazes me that payloads are making their way to integration so close to launch. I get that is a benefit standardized sat interfaces, but still...

[Chris Bergin]

But this is very much likely to move to the right as per natural and expectations, so remember what NET means when booking flights!

https://twitter.com/NASASpaceflight/status/1126966130780909568

[OnWithTheShow]

Air Force has officially announced June 22nd as the launch date.

http://spaceref.com/news/viewpr.html?pid=54055

[ZachS09]

Air Force has officially announced June 22nd as the launch date.

http://spaceref.com/news/viewpr.html?pid=54055

And that date might be confirmed following the upcoming static fire.