Author Topic: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion  (Read 402906 times)

Offline allio

  • Member
  • Posts: 6
  • Dublin, Ireland
  • Liked: 8
  • Likes Given: 2
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #740 on: 01/02/2018 01:24 AM »
First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?
« Last Edit: 01/02/2018 01:29 AM by allio »

Online Comga

  • Senior Member
  • *****
  • Posts: 4012
  • Liked: 1342
  • Likes Given: 1088
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #741 on: 01/02/2018 02:42 AM »
First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?

Not exactly
Most of the mass being carried by by the first stage, or the core in the case of Heavy, is the fueled second stage. Others can give you the numbers, but in general having a very light payload  doesnít change things dramatically until well into the second stage burn.
Looked at it another way, running at 92% thrust cuts it by about a half million pounds. The payload is not 100,000 pounds less than the advertised maximum. Even at the max acceleration before staging itís a smaller effect than the throttling. 
(Sorry for the archaic units. Trying to use one for all and I know the thrust in pounds.)
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline CyndyC

Here's a reminder of the thrust profile, tweeted way back in July. Took a minute to find again but I knew I'd seen it somewhere

https://twitter.com/elonmusk/status/890810308326940672
"Joy to the world!" -- G.F. Handel

Offline allio

  • Member
  • Posts: 6
  • Dublin, Ireland
  • Liked: 8
  • Likes Given: 2
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #743 on: 01/02/2018 03:31 AM »
there is abou 135000 lbs difference between max payload and that tesla :)

I may have overstated the throttling earlier :) but maybe not, as a quick read indicates that the fully loaded shuttles would be running at 65% thrust by max q, with the SRB's deigned to derate their thrust to 66% through propellant design after 50 seconds as well. And that's for a full load.

I believe the shuttle and falcon max q points are similar(13-14km).

at max q i'd expect the boosters in the FH configuration to have burned over half their fuel, with the core down by a third of it's fuel, at which point that 135k lbs in the nose becomes a much greater ratio of the remaining weight of the craft, which in turn adversely affects TWR forcing more throttling etc.

I thought throttling was used to maintain a specific TWR so as not to accelerate too early in the flight where the atmosphere is thicker where overspeed can lead to instability, extra structural loading and heating from excess aerodynamic resistance etc.

I would imagine that the core booster will throttle down earlier to offset the light payload.

anyway. just my basic understanding of rocketry

cyndy- That tweet references how the rocket thrust profile will work in general, not how the individual mission thrust profile will be deployed.

Offline Stan-1967

  • Full Member
  • ****
  • Posts: 491
  • Denver, Colorado
  • Liked: 260
  • Likes Given: 170
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #744 on: 01/02/2018 05:11 AM »
there is abou 135000 lbs difference between max payload and that tesla :)

I believe the shuttle and falcon max q points are similar(13-14km).

at max q i'd expect the boosters in the FH configuration to have burned over half their fuel, with the core down by a third of it's fuel, at which point that 135k lbs in the nose becomes a much greater ratio of the remaining weight of the craft, which in turn adversely affects TWR forcing more throttling etc.

I thought throttling was used to maintain a specific TWR so as not to accelerate too early in the flight where the atmosphere is thicker where overspeed can lead to instability, extra structural loading and heating from excess aerodynamic resistance etc.

I would imagine that the core booster will throttle down earlier to offset the light payload.

anyway. just my basic understanding of rocketry


I think you have the right concept about how throttling is used to manage Max-Q, heating, & loading, however you are in error regarding the importance you assign to the weight of the Tesla in comparison to the largest theoretical payload FH can carry when you focus on the 135k lbs difference. 

Keep in mind there is no payload on the FH manifest that exceeds 8t ( 17.6k lbs ).  The largest payload that Delta V Heavy can lift to GTO is around 14.2t ( 31.4k lbs), & FH hopes to enter the market for this payload class.  That is the ballpark maximum foreseeable payload for FH.    Also understand that the existing F9 or FH PAF can only accomodate up to 24k lbs.   The max payload of FH may never be used.

The thrust profile for the Tesla will not be radically different than what will be used for FH GTO launches.

Online hkultala

  • Full Member
  • ****
  • Posts: 663
  • Liked: 181
  • Likes Given: 120
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #745 on: 01/02/2018 06:06 AM »
there is abou 135000 lbs difference between max payload and that tesla :)

No, there is not.

The 63 tonne number in spacex web site is for LEO (total delta-v about 9km/s), and even that number is notional as there actually currently is no a payload adapter capable of holding that mass.

The roadster will go to non-optimal trajectory that goes near Mars(over 13km/s needed).
On optimal trajectory, FH payload to Mars is about 17 tonnes.







I may have overstated the throttling earlier :) but maybe not, as a quick read indicates that the fully loaded shuttles would be running at 65% thrust by max q, with the SRB's deigned to derate their thrust to 66% through propellant design after 50 seconds as well. And that's for a full load.

I believe the shuttle and falcon max q points are similar(13-14km).
[/quote]

FH should initially accelerate much faster than STS, as it has considerable higher T/W ratio at liftoff.

On the other hand, to make booster RTLS use less delta-v, FH will have higher trajectory than STS, making it also rise from the dense air to the thinner air earlier.

Offline Tonioroffo

  • Full Member
  • *
  • Posts: 125
  • Belgium
  • Liked: 82
  • Likes Given: 98
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #746 on: 01/02/2018 06:53 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Offline MattMason

  • Full Member
  • ****
  • Posts: 921
  • Space Enthusiast
  • Indiana
  • Liked: 625
  • Likes Given: 1101
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #747 on: 01/02/2018 07:18 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
"Why is the logo on the side of a rocket so important?"
"So you can find the pieces." -Jim, the Steely Eyed

Offline CJ

  • Full Member
  • ****
  • Posts: 801
  • Liked: 569
  • Likes Given: 179
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #748 on: 01/02/2018 08:06 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.

That's not necessarily true. There's a lot of commonality between FH and F9, so depending on what the failure is, it might cause an F9 stand down, in the same way that the F9R destruct at McGreggor caused an F9 stand down until they were sure the cause wasn't something that would affect a flight F9. 

Offline gadgetmind

  • Full Member
  • *
  • Posts: 115
  • Liked: 109
  • Likes Given: 236
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #749 on: 01/02/2018 08:31 AM »
On that occasion the KORD control system did indeed diagnose an engine failure on one side, it did shut down the symmetrically opposite engine to compensate, and then it all got complicated ...

Thanks for the link. Interesting that they kept changing the control system to *not* shut down engines willy nilly even when things went very bad as they didn't want to destroy the pad. OK, they still destroyed the pad, but it was a good plan despite this.

Offline Ictogan

  • Full Member
  • *
  • Posts: 102
  • Germany
  • Liked: 52
  • Likes Given: 67
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #750 on: 01/02/2018 10:12 AM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
And what makes you so certain there's <1% chance of an explosion on the pad? Would you have said the same about F9 prior to AMOS-6?

Offline sevenperforce

  • Full Member
  • ****
  • Posts: 760
  • Liked: 192
  • Likes Given: 225
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #751 on: 01/02/2018 12:11 PM »
I see a lot did posts concerning "when can it explode to not damage towers/endanger infra" but what about the aftermath?  If we do get late New Year fireworks, are we automatically looking at (long) stand down for the entire F9 family?  I would think months of delays for Crew effort?  Or am I wrong?

Even with my limited understanding of launch mechanics, I know that an FH failure won't sideline any F9 flights. The worst case (explosion on pad; <1% chance) means that Commercial Crew flights may be delayed since they must use LC39A. The F9 is its own tried and true vehicle. FH is a new vehicle--thus, the test flight to rack up flight data.
And what makes you so certain there's <1% chance of an explosion on the pad? Would you have said the same about F9 prior to AMOS-6?
Falcon 9 has had 46 launch attempts, with at least one static fire per launch attempt, plus one additional post-recovery static fire for most of the 20 recovered boosters. So we have well over 100 launch and ignition sequences, which means a single explosion during prop loading (AMOS-6) is still statistically <1%.

Online Robotbeat

  • Senior Member
  • *****
  • Posts: 27138
  • Minnesota
  • Liked: 7107
  • Likes Given: 4936
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #752 on: 01/02/2018 12:42 PM »

Also understand that the existing F9 or FH PAF can only accomodate up to 24k lbs.  .
This is not correct.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2806
  • Liked: 454
  • Likes Given: 397
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #753 on: 01/02/2018 12:51 PM »
First time poster.

Regarding the 92% thrust.

Is this not simply because it's an LV capable of lifting 16000kg to MTO that is in fact only lifting off with a 1500kg payload. An LV that can hoist 60000kg off the pad only lifting 1500kg (or whatever the weight of the tesla + mounting is) would go into a massive over g situation within seconds lifting that light a load. As it is I would imagine the 92% will only be until it clears the pad, then a massive throttle down until well past max q and throttling down all the way up. A lot of rockets auto throttle to constant 5g acceleration for structural reasons IIRC. This baby in its maiden config will have plenty of horses to spare.

Or am I wrong on that?

Edit: Does anyone know if there is extra ballast in the payload to counteract this? Or what the actual final payload weight actually will be?

You need to consider payload as a portion of gross lift of mass. Expecting the early stages of flight to be noticeably different due to the small payload is akin to being able to spot a HGV accelerating more quickly just because the driver lost some weight.
Waiting for joy and raptor

Offline Kaputnik

  • Extreme Veteran
  • Senior Member
  • *****
  • Posts: 2806
  • Liked: 454
  • Likes Given: 397
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #754 on: 01/02/2018 12:53 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?
Waiting for joy and raptor

Online ZachS09

Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

It's possible that both side boosters will be retired after landing while the center core COULD be reused for one reflight before retirement.
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Online hopalong

  • Member
  • Posts: 84
  • Milton Keynes
  • Liked: 36
  • Likes Given: 28
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #756 on: 01/02/2018 01:07 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

I suspect between unlikely and zero.
SpaceX will want to take them apart after recovery to look for any cracks and alike in the load bearing structure and it has already been stated that future Heavies will be block 5 based.   

edited for spelling
« Last Edit: 01/02/2018 01:10 PM by hopalong »

Online wannamoonbase

  • Elite Veteran
  • Senior Member
  • *****
  • Posts: 2765
  • Denver, CO
    • U.S. Metric Association
  • Liked: 568
  • Likes Given: 971
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #757 on: 01/02/2018 01:27 PM »
Apologies in case this has been done to death, but am I correct in thinking that the initial FH side boosters are b3 and the core is b4?
What are people's thoughts on the likelihood of each of these cores flying again?

Iíve been thinking about this for awhile and I think itís possible this FH team of 3 cores gets another flight. 

The 2 Block 3 Cores have been significantly reworked since their first flight, maybe theyíve been reworked enough to be considered fresh.  The core certainly is.

SpaceX could offer a new or existing FH customer to jump the queue with a FH ride.  They have spent a huge amount of money on developing FH and building this specific article.  If they can generate more revenue from this vehicle I think theyíll book a flight, after the Dragon 2 demo and LC39A has an open window.
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline Oersted

  • Member
  • Full Member
  • ****
  • Posts: 794
  • Liked: 394
  • Likes Given: 239
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #758 on: 01/02/2018 01:59 PM »
Only with SpaceX do you get people speculating about further flights of a launch vehicle that is about to embark on a perilous first flight... Sign of confidence!

Offline meekGee

  • Senior Member
  • *****
  • Posts: 7899
  • N. California
  • Liked: 4145
  • Likes Given: 843
Re: SpaceX FH : Falcon Heavy Demo : early 2018 : Discussion
« Reply #759 on: 01/02/2018 02:05 PM »
Only with SpaceX do you get people speculating about further flights of a launch vehicle that is about to embark on a perilous first flight... Sign of confidence!

The mission patch shows a guy whistling in the wind while standing under a ladder - they're that confident.
ABCD - Always Be Counting Down

Tags: