Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 425753 times)

Offline dodo

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #240 on: 12/05/2017 06:08 PM »
Lifting the apoapse out of the inner solar system is a lot easier, and even that will take multiple fortuitous gravity encounters, most likely with earth.

I am trying to imagine, without much success, where periapsis and apoapsis would be, if (I believe) the Earth-Mars trip is only a short arc of a much longer heliocentric orbit.

Offline envy887

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #241 on: 12/05/2017 06:54 PM »
Lifting the apoapse out of the inner solar system is a lot easier, and even that will take multiple fortuitous gravity encounters, most likely with earth.

I am trying to imagine, without much success, where periapsis and apoapsis would be, if (I believe) the Earth-Mars trip is only a short arc of a much longer heliocentric orbit.

If the trajectory is a Hohmann transfer, the periapsis is at Earth's orbit, and apoapsis is at Mars' orbit.

Faster transfers raise the apoapsis, but periapsis always lies on Earth's orbit. This is true even if the transfer is inclined out of the ecliptic - gravity always take you back the same place, at least until the orbit is perturbed.

Offline Steve D

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #242 on: 12/05/2017 07:05 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

Offline gongora

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #243 on: 12/05/2017 07:06 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.

Online woods170

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #244 on: 12/05/2017 07:14 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.
They will be recovered (that is: SpaceX will attempt recovery). Sources at KSC have spotted all three cores in the HIF sporting landing legs. SpaceX doesn't put landing legs on cores they intend to expend.

Offline Steve D

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #245 on: 12/05/2017 07:25 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.
They will be recovered (that is: SpaceX will attempt recovery). Sources at KSC have spotted all three cores in the HIF sporting landing legs. SpaceX doesn't put landing legs on cores they intend to expend.


Cool. That didn't sound right to me but we also thought this was just an LEO flight. Going for escape velocity I wasn't sure if they would have to expend the boosters or not.

Offline envy887

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #246 on: 12/05/2017 08:23 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.
They will be recovered (that is: SpaceX will attempt recovery). Sources at KSC have spotted all three cores in the HIF sporting landing legs. SpaceX doesn't put landing legs on cores they intend to expend.


Cool. That didn't sound right to me but we also thought this was just an LEO flight. Going for escape velocity I wasn't sure if they would have to expend the boosters or not.

An expendable Falcon Heavy could launch about 13 Roadsters to Mars transfer. No problems going with recovery for this light payload.

Offline Eagandale4114

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #247 on: 12/06/2017 04:25 AM »
Quote from: /u/TheRealWhiskers
If this isn't already known, the TEL has been on the pad for at least two days now in the 'post-launch' configuration. They have the two F9 side hold-down clamps removed and sitting at the east edge of the pad complete with the white supporting structure beneath them partially covered in soot. Of course, in my infinite wisdom, I drove 1,500 miles and forgot to bring the cable to transfer pictures from my DSLR.

Quote from: /u/TheRealWhiskers
It's a bit difficult to tell through all of the other pad structure getting in the way, but it looks like all 6 hold downs are now in place. I'll admit I'm not 100% sure what to look for as in TSM's so I can't help much there.
I also forgot to mention, this morning and into the early afternoon the south HIF door was raised about 15 feet for a fork lift to move in and out. I snapped some pictures through the moving bus window but my camera didn't do a stellar job. It may get a lot better with some editing, but you can clearly see the top ends of the FH center core, a side booster with nose cone, and another F9 core.
Edit: FH S2 may have been present but blocked from view by a large white crate sitting in the doorway. It was definitely not attached to the center core.

No pictures yet, as he forgot his camera to computer cable but we should get some soon.

Reddit link
« Last Edit: 12/06/2017 04:26 AM by Eagandale4114 »

Offline Lars-J

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #248 on: 12/06/2017 04:38 AM »
All 6? I assume he knows that there will be *8* (eight) hold downs for FH.

Offline robert_d

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #249 on: 12/06/2017 09:04 AM »
How close to first roll-out then? Any chance for the 'money shot' with Falcon 9 on the pad at the same time as the Falcon Heavy? Too far apart? Are the pads far enough apart that they could risk the Heavy on the pad at the lift off of the Falcon 9?

Offline codav

All 6? I assume he knows that there will be *8* (eight) hold downs for FH.
Yes, eight hold-down clamps (three for each side booster, two for the center core) and two compression bridges. The latter don't hold the boosters down, they just provide structural support for the center core.
« Last Edit: 12/06/2017 09:35 AM by codav »

Online Johnnyhinbos

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #251 on: 12/06/2017 09:48 AM »
With triple the cores and therefore way more densified LOX required, do we know if a launch (or static fire) can be held without scrubbing to rechill the LOX?

Or enough for a recycle - as in, is there in the very least six cores, plus two second stage’s worth of densified LOX available at LC-39A?

Edited for semantics
« Last Edit: 12/06/2017 09:50 AM by Johnnyhinbos »
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Offline AncientU

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #252 on: 12/06/2017 12:47 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.
They will be recovered (that is: SpaceX will attempt recovery). Sources at KSC have spotted all three cores in the HIF sporting landing legs. SpaceX doesn't put landing legs on cores they intend to expend.


Cool. That didn't sound right to me but we also thought this was just an LEO flight. Going for escape velocity I wasn't sure if they would have to expend the boosters or not.

An expendable Falcon Heavy could launch about 13 Roadsters to Mars transfer. No problems going with recovery for this light payload.

You are assuming that the roadster is the only payload.  What about the Hail Mary, try to land second stage clue?
The roadster could be the '(midnight) cherry on top' of a more ambitious payload.
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Offline lrk

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #253 on: 12/06/2017 12:57 PM »
A guy from work was telling me the boosters would not be recovered on this flight. I thought they were. Has there been a change of plans due to the Mars orbit they want to go to?

An early version of an article mistakenly said that and was later changed.  I haven't seen any other information saying the boosters will be expended.
They will be recovered (that is: SpaceX will attempt recovery). Sources at KSC have spotted all three cores in the HIF sporting landing legs. SpaceX doesn't put landing legs on cores they intend to expend.


Cool. That didn't sound right to me but we also thought this was just an LEO flight. Going for escape velocity I wasn't sure if they would have to expend the boosters or not.

An expendable Falcon Heavy could launch about 13 Roadsters to Mars transfer. No problems going with recovery for this light payload.

You are assuming that the roadster is the only payload.  What about the Hail Mary, try to land second stage clue?
The roadster could be the '(midnight) cherry on top' of a more ambitious payload.

I don't see how that is still possible, given that the stage will be on an escape trajectory - unless the Roadster has its own propulsion system attached for the last bit of dV to leave earth orbit. 

Online ugordan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #254 on: 12/06/2017 12:59 PM »
What about the Hail Mary, try to land second stage clue?

I'd like to see them make this stage come back after injecting itself and the roadster into an Earth escape trajectory...

Offline Kaputnik

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #255 on: 12/06/2017 01:28 PM »
What about the Hail Mary, try to land second stage clue?

I'd like to see them make this stage come back after injecting itself and the roadster into an Earth escape trajectory...

It's not beyond the laws of physics for the payload to be separated immediately after TMI, and for the US to promptly rotate and make another burn to bring the apogee back down again. You'd then need to wait a whole orbit (with one more burn at apogee) before starting entry. The limit is likely to be stage lifetime rather than propellant.
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Offline crandles57

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #256 on: 12/06/2017 01:38 PM »
I assume they could make apogee less than Mars' perigee.

If it was an instantaneous delta-V you couldn't avoid perigee being below Earth's apogee. However it doesn't have to be an effective instantaneous delta-V, does it? Couldn't they throttle back the engines for a while til further from Earth then give a final delta-V to make the orbit less elliptical so perigee is sufficiently well above Earth's apogee? Also could passing below Mars be used to give a delta-V to make the orbit less elliptical?

(Still not completely safe as an asteroid could pass close and change its orbit but still fairly safe?

Anyway what if roadster was on a collision course with Earth in a few million years, would it burn up fairly harmlessly or reach the surface?)

Online ugordan

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #257 on: 12/06/2017 01:53 PM »
What about the Hail Mary, try to land second stage clue?

I'd like to see them make this stage come back after injecting itself and the roadster into an Earth escape trajectory...

It's not beyond the laws of physics for the payload to be separated immediately after TMI, and for the US to promptly rotate and make another burn to bring the apogee back down again. You'd then need to wait a whole orbit (with one more burn at apogee) before starting entry. The limit is likely to be stage lifetime rather than propellant.

Let's run some BOTE numbers. Wikipedia says a typical delta-V requirement from LEO to Mars transfer is 4.6 km/s (although another number shows only 0.6 km/s above C3=0 escape, hmm).

Let's say we take the first number, 7.8 km/s + 4.6 km/s = 12.4 km/s for TMI. To get back to a GTO-like trajectory, you need to reduce those 12.4 or so km/s down to around 10 km/s for GTO perigee velocity. That's 2.5 km/s of delta V right there. 2nd number (0.6 km/s of Oberth effect above C3=0) works out to roughly 2 km/s.  And that only puts you into a several hour long orbit.

Theoretically you wouldn't even need to make another burn at apogee, you could set up perigee right at the reentry burn with some cosine losses, but you'd still probably want to do some kind of burn high up if for nothing else but to control the *timing* of the reentry and hence the reentry groundtrack on the Earth as it rotates under you. Highly eccentric orbits can have large differences in orbital period with small delta-V differences.

2 km/s is not a small number for a kerolox stage, hence why I'm pretty skeptical we'll be seeing this happen.

Online speedevil

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #258 on: 12/06/2017 02:21 PM »
I don't see how that is still possible, given that the stage will be on an escape trajectory - unless the Roadster has its own propulsion system attached for the last bit of dV to leave earth orbit.

Which raises a question - is there a nearish term goal for such a kick stage for a few million newton-seconds that might appeal to spacex.
Something broadly similar to a STAR48, perhaps.
A simple tank with two superdracos and three tons or so of propellant would almost be a no-brainer.
Almost, not counting the hypergolic nature of the superdracos.

It seems a bit early for a methalox gas thruster as intended for the BFR to be ready, though that might also almost suit.
Fueling such a thruster on the pad might almost be worse than the hypergols though.

https://en.wikipedia.org/wiki/Green_Propellant_Infusion_Mission which is planned for the third FH launch might be in principle interesting, though there have been no signs of interest in exotic hypergols so far.
It would be moderately amusing if they decided on the basis of what they'd seen from integration of the SPIM mission they decided to use it for a highly capable booster. (which would incidentally eat a little of orbital ATKs market potentially)

Following AMOS-6, they're probably unlikely to be willing to do anything too novel without much more thought than simple robust options would give them.

Something like the above would give a pretty nice boost to FH to higher energy orbits.

In principle, it could also allow the second stage in some cases to reenter at a noticably lower speed after staging earlier, simplifying reentry.

Offline gongora

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Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #259 on: 12/06/2017 02:57 PM »
Recovering the second stage from TMI is really not "relevant discussion".

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