SpaceX FH : Falcon Heavy Demo : Feb 6, 2018 : Discussion Thread 2

[geza]

And lunar Dragon is no longer pursued... BFR is everything!

[envy887]

LOX boiloff and batteries.

I question batteries being an issue if you've got tons of margin, and a ton gets you 200kWh of battery. (yes, it's not quite this simple, and you'd need thermal managment for the battery).

Is the issue not actually LOX boiloff depleting LOX, but LOX warming and autogenously pressurising the tanks to the point it needs vented, meaning it's now just vented a lot of helium and can't properly maintain pressure as the burn goes on?

Wouldn't LOX boiloff on a coast to GEO be worse than LOX boiloff in LEO?

No, deep space is colder than LEO because the Earth is relatively warm and fills ~1/2 the sky.

[JonathanD]

Will they throttle down for Max Q?  With such a small payload it seems like they'd be going awfully fast in thick atmosphere.

[IanThePineapple]

Will they throttle down for Max Q?  With such a small payload it seems like they'd be going awfully fast in thick atmosphere.

Of course, the whole thing would tear apart if they didn't, probably even if they had a heavy payload too.

[envy887]

Will they throttle down for Max Q?  With such a small payload it seems like they'd be going awfully fast in thick atmosphere.

The payload is a trivial amount of the whole stack mass at Max-Q. But yes, they will throttle down. F9 does and it accelerates a lot slower.

[andrewsdanj]

Will they throttle down for Max Q?  With such a small payload it seems like they'd be going awfully fast in thick atmosphere.

Of course, the whole thing would tear apart if they didn't, probably even if they had a heavy payload too.

That early on, payload mass is still a very small fraction of total mass. 64 tons or 640 kg, you're still talking a handful of percent difference.

[cebri]

Musk: looks like development of BFR is moving quickly, and won’t be necessary to qualify Falcon Heavy for crewed spaceflight.

This sounds VERY encouraging.

It's moving the goal post to the right. Replacing one objetive with another. Expect more delays and mission cancellations.

[geza]

Except for the two persons, who lost their mission...

[karki]

Except for the two persons, who lost their mission...

Or they got moved to a BFR at the same price with a delay.

[DigitalMan]

Except for the two persons, who lost their mission...

Or they got moved to a BFR at the same price with a delay.

Loren tweeted more on that.  SpaceX could bring back crew on FH if BFR progress slows.

[envy887]

Don't direct GEO missions require 4 upper stage burns?
1) S2 ascent
2) GTO injection
3) GEO circularization
4) raise S2 to graveyard orbit?

Or might the RCS/tank venting be enough to move the S2 to graveyard?

[jpo234]

Except for the two persons, who lost their mission...

Or they got moved to a BFR at the same price with a delay.

And a much more comfortable ride.

[.Scott]

Really a double whammy tomorrow evening ( UTC/GMT Time) since not only first Falcon Heavy launch but at 19:58 UTC ,a newly discovered Apollo type asteroid ,  2018 CC, will flyby Earth at about half the distance between Earth-Moon. Its estimated size is anywhere from 9 to 30 metres and was only discovered on the 4 February 2018. Its inclination is about 8.6 degrees and its velocity is around 6 km/sec  with respect to Earth.

And there's 2018 CB in the area as well.  But I wouldn't worry.  I'm sure Elon carries collision on his Tesla.
He's in good hands with AllSpace.

[Negan]

Except for the two persons, who lost their mission...

Or they got moved to a BFR at the same price with a delay.

And a much more comfortable ride.

Maybe a ride all the way to the Moon's surface or at least LLO.

[MKremer]

Would 6 hour coast mean LOX is no longer densified?

Doesn't matter.

The other two burns (ascent, circularization/plane adjustment/phase/apsides) will consume volume.

Thermal management of the stage, needed for the long life/coast will keep prop temps within the restart "box" of parameters.

Could this be why Musk described this S2 as a 'Frankenstage', because of the thermal management additions to a "stock" S2?

[Lar]

If your post only makes you smile, please consider putting it in the party thread... I know this mission is a big party, and the parameters are not very normal, but do consider it thank you.

[tvg98]

Elon Musk says the Falcon Heavy has a 50-50 chance of success

“There’s a lot that could go wrong,” Musk admitted. “A really tremendous amount. I really like to emphasize that the odds of success are not super high. I don’t want to jinx it—I’m tempted to say. Because I feel super optimisitc. But I feel as though that optimism has no basis in fact. I feel like we’ve got a two-thirds chance of success, but in reality we only have a 50-50 chance.”

For a typical Falcon 9 launch, the booster can sustain one engine failure out of nine engines, right off the pad. (A single Falcon 9 first stage engine has failed just once in flight). The first stage can even survive two failures if the payload isn’t too heavy or if it's going to geostationary transfer orbit. With the Falcon Heavy, the rocket could lose as many as six engines and still reach orbit—in theory.

Because this is a test flight, Musk said it’s a “softball mission.” This means SpaceX won’t be pushing the envelope in terms of dynamic pressure during the launch. While the potential maximum dynamic pressure for a Falcon Heavy flight is “pretty high,” Musk said the peak dynamic pressure for this launch will be about 15- or 20-percent less than a Falcon 9 going to geostationary orbit.

https://arstechnica.com/science/2018/02/at-the-pad-elon-musk-sizes-up-the-falcon-heavys-chance-of-success/

Some interesting bits and bobs from Eric's article.

[tvg98]

We can finally get a good idea of the timings for each event now that the press kit's here. Some changes that I can see are:

1- Filling RP-1 and LOX begins 15 and 10 minutes earlier, respectively.

2- The engines on the side boosters ignite two seconds before the ones on the core do.

3- MaxQ occurs 10 seconds or so earlier than usual.

4- MECO for the core occurs about 30 seconds after it occurs for the side boosters.

5- The press kit seems to suggest that the side boaster landings may occur simultaneously, with the core stage landing some 15 seconds later!

This will be intense for sure!

Edit: I also noticed that the burn to GTO here seems to be only 30 seconds long compared to the usual 55-60 seconds. Does this suggest a fairly elliptical parking orbit?

[sevenperforce]

6 hours in LEO! That puts TMI at 19:30 EST if they launch at the opening of the window, or 4 orbits after launch.

Speculation: Maybe they do a GEO profile and then just burn longer? I know its inefficient, but the mission has hilarious amounts of margin anyway? Ie. Launch, coast to equator, 2nd burn to GTO, 3rd burn at GEO height that just goes way longer than a GEO insertion?

There is no risk of remaining in LEO after coast, if the coast is after GTO insertion. See Eric Berger's quote of Musk. Eric knows the difference between LEO and GTO, so the 6 hour coast must be 4 orbits in LEO.

To do a 6 hour coast in LEO and then a burn at GEO distance would require 12+ hours of total endurance, which seems unlikly. More likely Musk is calling S1 ascent the 1st burn, S2 ascent the 2nd burn, and TMI after coast the 3rd burn.

https://twitter.com/SciGuySpace/status/960615490803634176

If the GTO burn is successful but the TMI burn from GTO fails, then the Tesla still swings back through a perigee of 180-200 km, which is enough to slowly circularize and end up re-entering.

[Galactic Penguin SST]

We can finally get a good idea of the timings for each event now that the press kit's here. Some changes that I can see are:

1- Filling RP-1 and LOX begins 15 and 10 minutes earlier, respectively.

2- The engines on the side boosters ignite two seconds before the ones on the core do.

3- MaxQ occurs 10 seconds or so earlier than usual.

4- MECO for the core occurs about 30 seconds after it occurs for the side boosters.

5- The press kit seems to suggest that the side boaster landings may occur simultaneously, with the core stage landing some 15 seconds later!

This will be intense for sure!

The timing of the second stage burns (in particular burn 2 at T+28:XX for a dozen seconds) seems to indicate that the first two burns will insert the stage into a standard GTO, cruise to 36000 km high and then do the Earth escape burn there.