SpaceX Falcon Heavy Discussion (Thread 6)

[woods170]

https://www.nbcnews.com/mach/science/nasa-s-17-billion-moon-rocket-may-be-doomed-it-ncna991061

"I'll never forget being at Marshall with the leadership team the day that SpaceX announced the Heavy," said Lori Garver, NASA's deputy administrator from 2009 to 2013. She recalls NASA officials telling her: "Lori, you have got to tell your friend Elon he can't do that. He's in our lane. You made us get out of low-Earth orbit, so we've given him that lane, but this is our lane. We build the big rockets."

Some NASA p*ke actually said that to Lori?

Sheesh...

Lord I hope that character doesn't work for NASA anymore because "stuck-in-the-1960's" folks like that are the last things NASA needs right now.

[kevinof]

Reminds me of a conversation I had with a lobster fisherman north of Boston. He claimed that "that piece of the ocean was his to fish and his only, because he had fished there for the last 30 years!".

I hope, and would expect that Nasa has moved on from this. Maybe I'm being naive.

https://www.nbcnews.com/mach/science/nasa-s-17-billion-moon-rocket-may-be-doomed-it-ncna991061

"I'll never forget being at Marshall with the leadership team the day that SpaceX announced the Heavy," said Lori Garver, NASA's deputy administrator from 2009 to 2013. She recalls NASA officials telling her: "Lori, you have got to tell your friend Elon he can't do that. He's in our lane. You made us get out of low-Earth orbit, so we've given him that lane, but this is our lane. We build the big rockets."

[wannamoonbase]

He may have just said....."hold my beer!"....and Jeff may have said it as well....

I imagine that he was motivated. 

The NASA folks are concerned about their jobs like anyone else.  However, instead of clinging to what worked before they should be working on new technologies, not trying to build things like SLS.  Which they clearly aren't structured to do well.

I think Elon make a decision to pursue FH to push the SpaceX team and raise the expectations of industry. 

I think the more FH flies and shows its legs then it will get more orders for flights. 

A beast like the FH ready to go for $90 million.

[Spindog]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

[Spindog]

And by that I mean in something other than Kerbal.

[TrueBlueWitt]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

[envy887]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

[whitelancer64]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

4 / 5 cores would require rework of the launch pad and a new thrust plate for the T/E. It's just more hassle than it is worth, especially with BFR / Starship coming along soon.

[Spindog]

Clearly you'd need a greatly strengthened core stage and a lot of infrastructure changes. I think that it would make sense to use the core stage a something akin to a second stage by throttling down very early and planning to expend the core since it would end up too fast and high. That way you could minimize any upgrades to the second stage. But certainly an upgraded 2nd stage could help. So, it would seem that you could get very close to or exceed SLS performance by doing this without using any H2 stages? I know Elon would rather move to Starship but NASA wants an affordable moon program sooner and they're very wait and see about Starship so maybe those could fill a gap. I wonder what was in SpaceX's proposal.

[clongton]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Ahem. iCPS.

[rakaydos]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Elon has mentioned such a plan was a backup if BFR didn't work out. This was before Starship/Superheavy got so much momentum.

As others have said, it has a lot of problems of it's own. Starship is hands down the better choice.

[gongora]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

It's been discussed here over and over again.  Here's the first four threads I found with a quick search.  Please don't get started on that topic in this thread.
https://forum.nasaspaceflight.com/index.php?topic=44879.0
https://forum.nasaspaceflight.com/index.php?topic=40503.0
https://forum.nasaspaceflight.com/index.php?topic=36662.0
https://forum.nasaspaceflight.com/index.php?topic=25282.0

[Proponent]

I'd guess this is because aircraft use nautical miles, presumably because ships use nautical miles.  It would be helpful if everyone would switch to metric....

Can't remember offhand where statute miles come from, but clue in the name, probably a tradition codified into law at some point, most likely for surveying (i.e. where does Lord X's property end and Baron Y's property begin).

I believe the original idea behind what is now called a statute mile is that it was 1000 ("mille" in Latin) double steps of a Roman soldier.

But nautical miles are a particular subdivision of the earth's circumference, and map square latitudes are based on them, which simplifies navigation for ships and planes--and missile trajectories. (The squares shrink in longitude as you approach the poles though; hope I'm not getting mixed up here, but I probably am...)

That's right: a nautical mile is meant to correspond to 1' (1 minute) of arc on the earth's surface, hence the earth's circumference is (360)(60) = 21,600 nautical miles.  Nowadays, though, the nautical mile is usually defined as 1852 m.

P.S.  If you measure angles in grads (100 grads = 90^o), then 0.01 grad corresponds to 1 km.  But that's a part of the metric system which, like decimal measures of time, has never really caught on.

[Proponent]

Likewise, the Atlas 5 manual says:

A park orbit perigee altitude of 167 km (90 nmi) is assumed for the reference cases.

OK, looking at the Atlas V user's guide, I see where you're coming from.  MECO1 often occurs in a 167 x XXX-km orbit.  Assuming that's at perigee (though it might conceivably not be), re-ignition and insertion probably occur at a slightly higher altitude.  I doubt it makes much difference in the estimation of Stage 2's parameters, though.

[nicp]

Has anyone looked at a 36 engine or 45 engine 4 or 5 core Falcon Superheavy?

Stretching S2 on current is much more bang for buck. S2 really the limiting factor.

More boosters helps a lot more than a bigger upper stage, but would require serious changes to the center core and especially to the ground infrastructure.

A larger upper stage would mainly help when recovering the boosters. For expendable max payload, especially to very high energies, it doesn't help so much. A 3rd or kick stage is probably better value for the money there.

Why not _really_ stretch the S2 and shorten the core stage (which is custom anyway, not a standard F9). Have the standard F9 boosters burn out at the same time as the short core. The short core and boosters aren't so far from land and you have a super big S2...

P.S A custom S2 as well as the custom core? Not gonna happen, I know, never mind Starship and all that...
P.P.S I did try to post this earlier from my phone and it evaporated. Apologies if this appears twice.

[ugordan]

Why not _really_ stretch the S2 and shorten the core stage (which is custom anyway, not a standard F9). Have the standard F9 boosters burn out at the same time as the short core.

That's the opposite of what you actually want to do with this "2.5-stage" launch architecture. You want the boosters to provide as much as possible of initial lift and the center core throttling down as soon as possible (it's a tradeoff to a certain extent vs gravity losses) so that by the time the boosters separate, the center core still has as much fuel as possible left and it has only *its* dry mass to push further along.

If you burn out all three cores at the same time, you've wasted energy accelerating the dead weight of the side boosters to the same burnout speed as the core. You're no longer getting effectively a 3-stage vehicle, but a 2-stage vehicle with an oversized first stage and a correspondingly undersized 2nd stage. Yes, you'll still be going faster at MECO than a single-stick, but the delta-V gain will not be as impressive as the staggered staging approach.

Stretching the S2 makes much more sense in the context of maximizing FH throw weight because the higher velocity at MVac ignition means it would not suffer as heavily in gravity losses as it would on a single-stick F9 where it starts off much slower.

[nicp]

Why not _really_ stretch the S2 and shorten the core stage (which is custom anyway, not a standard F9). Have the standard F9 boosters burn out at the same time as the short core.

That's the opposite of what you actually want to do with this "2.5-stage" launch architecture. You want the boosters to provide as much as possible of initial lift and the center core throttling down as soon as possible (it's a tradeoff to a certain extent vs gravity losses) so that by the time the boosters separate, the center core still has as much fuel as possible left and it has only *its* dry mass to push further along.

If you burn out all three cores at the same time, you've wasted energy accelerating the dead weight of the side boosters to the same burnout speed as the core. You're no longer getting effectively a 3-stage vehicle, but a 2-stage vehicle with an oversized first stage and a correspondingly undersized 2nd stage. Yes, you'll still be going faster at MECO than a single-stick, but the delta-V gain will not be as impressive as the staggered staging approach.

Stretching the S2 makes much more sense in the context of maximizing FH throw weight because the higher velocity at MVac ignition means it would not suffer as heavily in gravity losses as it would on a single-stick F9 where it starts off much slower.

I get that (and I was pretty much joking - side boosters taller than core? Not impossible, but it would look wrong and therefore probably is).
But as I understand it, it isn't really practical to stretch F9 or FH much, it's just too slender so wishing for a bigger S2 is just that, a wish. So I had the odd idea of shrinking the core (I didn't originally think all the way to 'stage at the same time').
I assume the relative heights of the first and second stages of F9 (F9. Not FH) are optimized for maximum payload - that is complicated of course by the various (RTLS, ASDS, expended) modes of the first stage. But the ratio of lengths of F9 stage1 vs stage 2, as optimal as it may be, presumably is not necessarily optimal for FH.

I'm being silly, I just thought a short core stage for FH might be a fun thought experiment. But we know it won't work.

EDIT: A daft idea. Note to self - don't post interesting ideas after a couple of pints of Guinness.

[Slarty1080]

Why not _really_ stretch the S2 and shorten the core stage (which is custom anyway, not a standard F9). Have the standard F9 boosters burn out at the same time as the short core.

That's the opposite of what you actually want to do with this "2.5-stage" launch architecture. You want the boosters to provide as much as possible of initial lift and the center core throttling down as soon as possible (it's a tradeoff to a certain extent vs gravity losses) so that by the time the boosters separate, the center core still has as much fuel as possible left and it has only *its* dry mass to push further along.

If you burn out all three cores at the same time, you've wasted energy accelerating the dead weight of the side boosters to the same burnout speed as the core. You're no longer getting effectively a 3-stage vehicle, but a 2-stage vehicle with an oversized first stage and a correspondingly undersized 2nd stage. Yes, you'll still be going faster at MECO than a single-stick, but the delta-V gain will not be as impressive as the staggered staging approach.

Stretching the S2 makes much more sense in the context of maximizing FH throw weight because the higher velocity at MVac ignition means it would not suffer as heavily in gravity losses as it would on a single-stick F9 where it starts off much slower.

If this second FH launch has 10% more thrust than the first launch, this should give some scope for optimising the throttle settings. Why not let the side boosters run full throttle continuously and let the central booster do all of the throttling back for the whole stack at Qmax and whenever else they need to throttle down?

This way the side boosters would burn out earlier and could be jettisoned earlier and the central stage would have more fuel at this point than if all the boosters had been throttled to the same extent.

There may well be limits to the degree of throttling possible (so some throttling might still be needed on the side boosters) but the point remains.

[AC in NC]

I'd never noticed these Standoffs on the Nozzles before but presume it was discussed and I just missed it.  Probably not much to say about them but an interesting detail.

Quite impressed with how tight and buttoned up the greenish-hued base is compared to the first returns with all that missing cork or whatever.

[OccasionalTraveller]

So would a stretched centre core actually be better? Yes, probably it would. However, it's challenging logistically - I suspect Stage 1 is as long as is feasible to transport by road. The longer it gets, the greater the radius of the arc needed to take corners, so the wider the roads to be: at some point there is no route available to get from the factory to McGregor or the launch site that is wide enough/with high enough radius corners. It can't be transported in bits since the entire wall of the stage is a single welded unit, it's not two separate tanks.

The available space at the factory also constrains the maximum length. You can't build a stage that's longer than the longest dimension of the building, and you might have to completely reorganize the space to make a larger core-assembly area.

I think that's why discussion has focused on stretching the second stage. It's not ideal but it's relatively easy to do without disrupting the whole operation. As I understand it, first and second stages are assembled on the same line - so a new stage length somewhere between the current S1 and S2 could be accommodated.

Speculating:

If SpaceX do go for a third stage, rather than stretch S2, the easiest thing to produce and handle would be yet another kerolox stage with an MVac engine. No new propellants or designs required, although some insulation work would still be necessary to extend the stage's lifetime a bit more. The main reason for staging, after all, is to drop the mass of the empty tanks: switching to a higher-Isp engine is a bonus. Adding a second second stage is probably too much fuel and mass, but otherwise it's just a shortened S2.