SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion Thread 1

[joek]

If that is so and it causes so much pain to the control of the descending booster, wouldn't it be easier to just put the cone on top of a regular (or a shortened one) inter-stage? I know it would be a little heavier, but being on the boosters, I believe it would not translate in a huge loss to de capability of rocket.

No indication that there is enough "pain" to require an alternative solution.  SpaceX obviously feels they have sufficient avionics smarts and control authority that an alternative construct is sub-optimal.  Validation is most certainly one of the items on the list for this test flight.

[Yeknom-Ecaps]

SpaceX - Falcon Heavy - Fueling Test 01-13-2018


USLaunchReport
Published on Jan 13, 2018

Was there really a fueling test on 1/13? No venting seen in video.

[Ben the Space Brit]

Re.: Fuelling test - Could they have filled/drained the RP1 tanks or do they have to also do the LOX tanks for some safety or engineering reason?

[john smith 19]

No, Atlas V was designed from the beginning to do the 3 core heavy.  They just never finished the foreward attachment points and the pad GSE.

The two strapons would occupy where the solids would go.

I think this demonstrates (once again) that it's fairly easy to design in something from day one (side by side boosters), but trying to get something to do something it was not really designed for at a later date is very much more challenging, as SX have been finding.

[OneSpeed]

Any information or informed speculation on the launch window (UTC) for Falcon Heavy?

I think someone else drew a chart for this earlier (forgot who), but basically - If the idea is to launch the roadster on a direct transfer orbit, then 6pm (local) is the optimal time. But they probably want to launch during daylight, so my bet would be mid-to-late afternoon. (Which would still work, since the upper stage could coast until TMI)

So 3-5pm local time would be my educated guess. (20:00-2300 UTC)

Here are some hypothetical trajectories for a Falcon Heavy Demo Mission launched on February 1st 2018.
The first image shows the general planetary arrangement on that day, viewed from Earth's north pole. Earth has moved through 43.5° or 42.6 days since its summer solstice at 0°.

The second image zooms to Earth at the same time. I've superimposed two trajectories, direct injection in red, and a TMI burn from LEO in sky blue. Both burns produce the same ∆V and trajectory to Mars. The direct injection burn SECO is about 2h45m before midnight eastern time, so launch would be about 9pm. The TMI burn from LEO would be at 6pm, but the launch to LEO could be earlier, depending on the maximum S2 coast time. The Iridium-4 second engine startup 2 (SES2) was 52 minutes into flight, so a 40 minute coast has been demonstrated. This implies the launch could be as much as 1/2 an Earth orbit before the TMI burn, as early as 6am local.

The third image is a closer zoom.

The choice between direct injection and TMI from LEO could come down to how lofted the launch trajectory will be. If the Special Temporary Authority (STA) referenced by Gongora here: https://forum.nasaspaceflight.com/index.php?topic=42705.msg1719795#msg1719795 still applies: https://apps.fcc.gov/oetcf/els/reports/STA_Print.cfm?mode=current&application_seq=80084&RequestTimeout=1000 the ASDS coordinates are: 'North  29  0  20  West  77  7  55  Autonomous Drone Ship, within 10 nautical miles 18.52'. The fourth image shows those coordinates on Google Maps, 342kms from LC-39A.

If the ASDS is that close to shore, then I suspect a launch trajectory not unlike Formosat-5, which injected a very light payload directly to a 720km circular orbit. Direct injection simplifies what is already a complicated enough demonstration mission, because no S2 restart is required. The quoted FH payload to Mars is 16.8mT, but the direct injection to such a high velocity by a FH with only 92% available thrust may well have determined the very light demo mission payload.

[StuffOfInterest]

No, Atlas V was designed from the beginning to do the 3 core heavy.  They just never finished the foreward attachment points and the pad GSE.

The two strapons would occupy where the solids would go.

I think this demonstrates (once again) that it's fairly easy to design in something from day one (side by side boosters), but trying to get something to do something it was not really designed for at a later date is very much more challenging, as SX have been finding.

For SpaceX, I see this as more of a sign of their Agile (big 'A' on purpose) approach to development.  The rough engineering was done for the rocket to go from single stick to triple stick.  Some incremental changes were required to go from the single stick to side booster configuration, but a full new iteration of the rocket was required to make a working center core.  The same can be applied as the rockets have moved through their "blocks" as experience allows them to make changes as they go to improve the rocket. 

Much of this could have been engineered up front, but the costs would have been much, much more and required far more testing ahead of the first flight.

[Jim]

Much of this could have been engineered up front, but the costs would have been much, much more and required far more testing ahead of the first flight.

Not really

[Jim]

No, Atlas V was designed from the beginning to do the 3 core heavy.  They just never finished the foreward attachment points and the pad GSE.

The two strapons would occupy where the solids would go.

I think this demonstrates (once again) that it's fairly easy to design in something from day one (side by side boosters), but trying to get something to do something it was not really designed for at a later date is very much more challenging, as SX have been finding.

Not really

[AncientU]

Think of the tail service mast at base of the core.  It is on the opposite side of the TEL.  Now take another core and make it the left booster.  The attach points of the booster to the core are on the right side of the booster.   Now, duplicate the left booster and to attach it to the core, it has to rotated 180 degrees.  This now puts TSM on the TEL side of the vehicle.

Titan had right and left boosters.  Delta IV Heavy had three unique cores, that is why it was expensive

It's these sorts of quite subtle design points that make the whole "Let's make a big rocket by clustering a bunch of common stage together" idea quite a bit trickier IRL than it seems on paper.

In hindsight it's pretty impressive that SX have gotten away with only needing 2 separate designs and being able to reuse single stick F9 boosters as the boosters, rather than a whole new booster design.

Atlas V Heavy would have only required one design for all three boosters since all cores can handle solid boosters.

Things would have been much different if Altas V had won the lion’s share and heavies of the EELV order.

What 'things' would have been much different?

No ULA?
Competition between Boeing and LockMart?
No Block Buy(s)?
Progressive development of respective B/LM vehicles?
American-made RD-180s?
Reusability from B and/or LM?
Re-development of a commercial market for US?
Difficult environment for SpaceX/Falcon to get a foothold?
No SLS/Orion?

Curious what your alternate universe would have looked like...

[Greg Hullender]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

[gongora]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

They probably gave up on it altogether.  There isn't really a need for it and they're already working on design of a bigger rocket.

[DrRobin]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

They probably gave up on it altogether.  There isn't really a need for it and they're already working on design of a bigger rocket.

Hi Greg! Fancy meeting you  here.  As you probably know, Propellant Cross-feed has been an idea floating around for a very long time. I remember thinking/hoping that the proposals from Boeing to use it for Delta-IV Heavy would come to fruition, but alas, no. For Falcon 9 Heavy, I think I remember Musk saying they had concluded it was not worth the trouble, but when I went looking for the citation, I just found secondary citations like this from from Kerbal https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging (I do like the name Asparagus Staging, which I had not known till reading this reference!). It seems to be one of those clever ideas to increase performance, when the reality usually turns out to be that the best value comes from just building a bigger rocket!

[Rocket Science]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

They probably gave up on it altogether.  There isn't really a need for it and they're already working on design of a bigger rocket.

Hi Greg! Fancy meeting you  here.  As you probably know, Propellant Cross-feed has been an idea floating around for a very long time. I remember thinking/hoping that the proposals from Boeing to use it for Delta-IV Heavy would come to fruition, but alas, no. For Falcon 9 Heavy, I think I remember Musk saying they had concluded it was not worth the trouble, but when I went looking for the citation, I just found secondary citations like this from from Kerbal https://wiki.kerbalspaceprogram.com/wiki/Asparagus_staging (I do like the name Asparagus Staging, which I had not known till reading this reference!). It seems to be one of those clever ideas to increase performance, when the reality usually turns out to be that the best value comes from just building a bigger rocket!

I recall Elon saying "no crossfeed" as well but I don't recall where at the moment...

[macpacheco]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

Makes no sense. BFR/BFS will replace FH altogether and quickly. Falcon 9 might live a little longer but not much more. It will be much more economical due to full reuse.
There very little revenue potential from a FH with crossfeed.
Far more important would be to reuse the upper stage, but that's a tough nut to crack with M1D's ISP.

[uhuznaa]

Did SpaceX give up on crossfeed altogether, or did they just postpone it for now? Does anyone know?

Cross-feeding propellants in such a configuration is both an eminently obvious idea and in practice opens a HUGE can of worms engineering-wise. It would be a logical next step if you needed to squeeze more payload out of FH. But what for? Even now FH is hardly more than "we can't give up on it now, really". The F9 has grown a lot, BFR is the next step and everything in between is something nobody really needs or wants to do hard-to-do things with.

And even with no cross-feed FH has more payload than you can realistically get under the payload fairing as long as you don't have to launch lumps of lead.

[vanoord]

But then why do the boosters have titanium grid fins? I believe these are all 'old' designs.

The nosecones give the side booster odd aerodynamics, so the titanium gridfins give them the extra authority they need.

The tail of an X-15 is the best example of why the single-stick F9s work with relatively small grid fins.

[vanoord]

I recall Elon saying "no crossfeed" as well but I don't recall where at the moment...

I think it was broadly 'we thought about it - but at the moment we don't need it; and in any case it was a lot more complicated than we first thought'?

The performance gains from engine development has, it seems, mostly eliminated the need to develop a more capable version of FH (which crossfeed would be) for now - and the future is covered by BFR (or whatever next-generation single stick SpaceX rocket may get built).

[TrueBlueWitt]

I recall Elon saying "no crossfeed" as well but I don't recall where at the moment...

I think it was broadly 'we thought about it - but at the moment we don't need it; and in any case it was a lot more complicated than we first thought'?

The performance gains from engine development has, it seems, mostly eliminated the need to develop a more capable version of FH (which crossfeed would be) for now - and the future is covered by BFR (or whatever next-generation single stick SpaceX rocket may get built).

Looking at trades, not clear that Raptor based US would be that much more difficult than X-Feed, and would have far better performance and much broader benefits(F9).
Not that there's a business case for either right now with BFR on the Horizon.

[wannamoonbase]

I recall Elon saying "no crossfeed" as well but I don't recall where at the moment...

I think it was broadly 'we thought about it - but at the moment we don't need it; and in any case it was a lot more complicated than we first thought'?

The performance gains from engine development has, it seems, mostly eliminated the need to develop a more capable version of FH (which crossfeed would be) for now - and the future is covered by BFR (or whatever next-generation single stick SpaceX rocket may get built).

Looking at trades, not clear that Raptor based US would be that much more difficult than X-Feed, and would have far better performance and much broader benefits(F9).
Not that there's a business case for either right now with BFR on the Horizon.

I'd say with FH on the horizon.  There's nothing on the books that needs more than the FH.

[Lars-J]

Exactly. FH will already provide more than enough performance for customers. Why spend a lot of effort on technology of questionable use, and also not something that will be also useful on BFR?