SpaceX Falcon Heavy Discussion (Thread 6)

[ugordan]

it's a ridiculus idea, but what's the C3 for a low energy transfer to the innermost portion of pluto's orbit?


The window will almost never be open, but technically it's an apples to apples comparison.

The C3 numbers I got were from the New Horizons trajectory analysis with launch period around the time it actually launched (2006) and arrival time of 2015. Pluto was just past perihelion at 2015, but it crossed the orbital plane of Neptune roughly then so probably the 150+ C3 is the lowest practical transfer. As time goes on, this will only increase as Pluto moves farther from the Sun and leaves the general plane of the other planets.

[Paul451]

Please note: SpaceX doesn't mention what trajectory FH uses to inject 3,500 kg to Pluto. As such, it is probably incorrect for you to assume that SpaceX meant direct injection to Pluto. Nor did SpaceX mention the transit time. So your examples of transit times of 13 years and 9 years are probably not appropriate either.

That's pretty much what I said in my original post, that such a number can only work if several planetary flybys are executed, Jupiter being a guarantee. As such, the figure is useless for any kind of performance consideration as you can massage even an Atlas V to reach a number like that once you start assuming elaborate and prolonged flyby trajectories and not a direct flight.

Do you see how you are allowing only two alternatives: Direct flight -- or -- "several" "elaborate and prolonged" flybys which are "useless for consideration". No pragmatic middle-ground.

It is that kind of false dichotomy, those kind of artificial constraints, that leads to bad choices like SLS, or the continual blocking of depot-centric proposals.

[ugordan]

Please note: SpaceX doesn't mention what trajectory FH uses to inject 3,500 kg to Pluto. As such, it is probably incorrect for you to assume that SpaceX meant direct injection to Pluto. Nor did SpaceX mention the transit time. So your examples of transit times of 13 years and 9 years are probably not appropriate either.

That's pretty much what I said in my original post, that such a number can only work if several planetary flybys are executed, Jupiter being a guarantee. As such, the figure is useless for any kind of performance consideration as you can massage even an Atlas V to reach a number like that once you start assuming elaborate and prolonged flyby trajectories and not a direct flight.

Do you see how you are allowing only two alternatives: Direct flight -- or -- "several" "elaborate and prolonged" flybys which are "useless for consideration". No pragmatic middle-ground.

It is that kind of false dichotomy, those kind of artificial constraints, that leads to bad choices like SLS, or the continual blocking of depot-centric proposals.

No, it's not a "false dichotomy". I provided a rationale in the previous posts for it and there is a good rationale for why FH cannot launch 3500 kg to Pluto using only a direct, single Jupiter flyby based on the performance curve posted a couple of posts above. I'm not going to waste any more time elaborating on that just to dispel your notion of a "pragmatic middle-ground". It's much easier to throw words like this around than actually do some BOTE numbers.

I literally have no idea what any of this has to do with SLS or propellant depots. If you think a prop depot is a fair and reasonable assumption for that performance figure, you have just reiterated my original comment about virtually any kind of hidden assumption that could have gone into that SpaceX number and since it's hidden, it's useless for us and people should not be taking that number at face value - as, in fact, a certain member here did when figuring out FH Psyche throw mass.

[soyuzu]

There is only so much a kerolox upperstage can do and the lower Isp over hydrolox is not doing it any favors when it comes to really high C3 - which is why Delta IV is included in the graph for reference.

Actually a BOTE calculation shows this is not the case. To many's surprise, the only reason Delta IV Heavy catches up with FH in deep space mission is because DCSS is much smaller than FH S2.

F9 S2 has about 110t useable propellants with 4.5t burn out mass, while DCSS 5m has 31t and 3.5t for each. If we fractionally scale down F9 S2 to 31t, it will have an empty mass of about 1.27t (I understand it's hard to keep same fraction when scale down, but don't forget the super low TWR of DCSS).

Now put them on the first stages of Delta IV Heavy with 800kg payload, i.e. the intersection on LSP figure. With same Booster delta-V, their difference of total delta-V is depend totally on upper stage delta-v. The mini F9 S2 have start mass of 31.8t, burn-out mass of 2.07t, Isp of 348s, which gives a delta-v of about 9320m/s, while DCSS, having a burn-out mass of 4.3t, Isp of 462.5s, which gives a delta-v of 9080m/s. I.e. mini F9S2 outperforms DCSS by more than 200m/s.

More calculation shows when the mass is above 1500kg, DCSS slaughters. However, below 1000kg, mini F9S2 performance quite a bit better. It is not "lower Isp over hydrolox is not doing it any favors when it comes to really high C3 ",  but actually"High Isp over High density is not doing it any favors when it comes to really high C3 "
 Low-density hydrolox is invincible in a smaller range of mission profile, but not the case for extreme high or low delta-V.

There's also that whole exercise from the previous year of seeing if it could launch Orion + and underfueled SM around the Moon and the constraints there worked out to be around 15.5-16 metric tonnes which is consistent with the LSP figure for C3 of around 0. So we have a data point on low C3, we have implicit data for not being able to launch 6000 kg directly to over 80 (km/s)^2 C3 and we have implicit data that the curve is consistent with FH+Star 48 just barely being able to launch Clipper to a L+3 year Earth flyby trajectory. And yet we're supposed to believe that the performance curve does something magical and actually goes back up to 3500 kg at a minimum of 150 C3?

Back in 2017, when Musk claimed the performance of FH has been increased by 20%, he also put this under the prerequisite of "a structal reinforcement".  Current LSP curve actually fits the Payload capability of pre 2017 FH, with a bit difference may come from burn to deplete and instruction shutdown. In contrast, Simulation in L2 at that time also proves the possibillity of 64t LEO, etc. can be achieved if the centre core can throttle down arbitarily.

So the Mars and Pluto number you doubt, the incabability of FH to launch Clipper and the LSP curve actually may just because they are performance of different vehicles. The most efficient way of increasing FH's capability can have nothing to do with an upper stage, but just by realize the structal reinforcement.

[wannamoonbase]

I'm surprised no one has posted in this FH thread about Dragon XL yet.

It seems like consensus is reusable side boosters and expendable center core, correct?

It's been sometime since I've seen numbers for the following. 

However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well? 

[baldusi]

I'm surprised no one has posted in this FH thread about Dragon XL yet.

It seems like consensus is reusable side boosters and expendable center core, correct?

It's been sometime since I've seen numbers for the following. 

However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well?

According to the NASA Launch Services Program, assuming a c3=-0.5, FH expendable does 6.7 tonnes, while fully expendable it does 15.1 tonnes. I would assume that Dragon XL should mass somewhere between 10 to 20 tonnes. So I would tend to assume an expendable. But, may be if it can do 13 tonnes with booster recovery, they might be able to achieve that. May be.

[omelet1978]

I'm surprised no one has posted in this FH thread about Dragon XL yet.

It seems like consensus is reusable side boosters and expendable center core, correct?

It's been sometime since I've seen numbers for the following. 

However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well?

According to the NASA Launch Services Program, assuming a c3=-0.5, FH expendable does 6.7 tonnes, while fully expendable it does 15.1 tonnes. I would assume that Dragon XL should mass somewhere between 10 to 20 tonnes. So I would tend to assume an expendable. But, may be if it can do 13 tonnes with booster recovery, they might be able to achieve that. May be.

I read that Musk stated that recovering the side Falcon 9 boosters and then expended the Falcon Heavy Center Core would only cause a 10% loss of payload. I'll have to look for the quote. I think that is what the smart bet would be for this though...SpaceX is not going to want to lose 2 Falcon 9 rockets every time they launch a cargo mission since they can re-use them for other launches.

Just my two cents...

[Robotbeat]

I'm surprised no one has posted in this FH thread about Dragon XL yet.

It seems like consensus is reusable side boosters and expendable center core, correct?

It's been sometime since I've seen numbers for the following. 

However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well?

According to the NASA Launch Services Program, assuming a c3=-0.5, FH expendable does 6.7 tonnes, while fully expendable it does 15.1 tonnes. I would assume that Dragon XL should mass somewhere between 10 to 20 tonnes. So I would tend to assume an expendable. But, may be if it can do 13 tonnes with booster recovery, they might be able to achieve that. May be.

The figures on that page are still pretty pessimistic.

[woods170]

I'm surprised no one has posted in this FH thread about Dragon XL yet.

It seems like consensus is reusable side boosters and expendable center core, correct?

It's been sometime since I've seen numbers for the following. 

However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well?

According to the NASA Launch Services Program, assuming a c3=-0.5, FH expendable does 6.7 tonnes, while fully expendable it does 15.1 tonnes. I would assume that Dragon XL should mass somewhere between 10 to 20 tonnes. So I would tend to assume an expendable. But, may be if it can do 13 tonnes with booster recovery, they might be able to achieve that. May be.

The figures on that page are still pretty pessimistic.

That is putting it mildly. According to two of my SpaceX sources the LSP figures for FH are flat out incorrect.
For example: NASA LSP claims that Falcon Heavy, in fully expendable mode can throw only 12 metric tons to Mars. SpaceX claims that, in fully expendable mode, FH can throw nearly 17 metric tons to Mars. That is a massive 5 metric ton difference.
Given that SpaceX are the ones that actually build and operate FH I am inclined to believe the SpaceX figures over those of NASA.

[Comga]

I'm surprised no one has posted in this FH thread about Dragon XL yet.
It seems like consensus is reusable side boosters and expendable center core, correct?
It's been sometime since I've seen numbers for the following. 
However, could side booster recover by ASDS do enough to let the center core do ASDS down range as well?

According to the NASA Launch Services Program, assuming a c3=-0.5, FH expendable does 6.7 tonnes, while fully expendable it does 15.1 tonnes. I would assume that Dragon XL should mass somewhere between 10 to 20 tonnes. So I would tend to assume an expendable. But, may be if it can do 13 tonnes with booster recovery, they might be able to achieve that. May be.

The figures on that page are still pretty pessimistic.

That is putting it mildly. According to two of my SpaceX sources the LSP figures for FH are flat out incorrect.
For example: NASA LSP claims that Falcon Heavy, in fully expendable mode can throw only 12 metric tons to Mars. SpaceX claims that, in fully expendable mode, FH can throw nearly 17 metric tons to Mars. That is a massive 5 metric ton difference.
Given that SpaceX are the ones that actually build and operate FH I am inclined to believe the SpaceX figures over those of NASA.

Is it pessimism or conservatism?
A colleague who often interfaces with ULA says that Centaurs generally wind up with a ton or two of propellants on board.
My understanding is that this is where the probabilistic threshold is set, one-sigma, two-sigma, three-sigma, etc. on the fight not running out of propellants.
It's like on the SpaceX COTS-1 flight. 
As I recall, NASA demanded 95% probability that the test payloads could be put in an orbit considered safe for the ISS, which I think meant at a sufficient altitude. 
The determination at the time, IIRC, was that the probability was "only" 90%, so the orbit raising burn was not attempted. 
(I am sure someone will correct whatever details are incorrect, but let's not let that detract from the main point.)
As we all know statistical predictions for processes on which there is little or no data involve many assumptions, and the aggregation of many justifiably conservative assumptions is a very conservative prediction.   

But this last COTS flight is a good data point. 
SpaceX was attempting to recover the booster.
There was a failure, but the main mission was not significantly impacted.
They lost the booster but the payload got to the intended orbit.
My guess is that launching Dragon XL to lunar orbit will be like that.
NASA will not ask or even let SpaceX "run the tanks dry", use up all the margin on the boosters.
SpaceX will get a higher probability that the boosters will be recoverable if nothing goes wrong.
So they will land both side boosters downrange on their pair of ASDSs.

NASA could, however, request and pay for SpaceX to fly the boosters without the reentry and landing equipment, even if that only increases the capacity by a small amount.
It will be their choice.
Given that previous planning was based on the expendable SLS, any Falcon option will be lower cost. 
Even fully expendable. 

[DreamyPickle]

The recent Dragon XL contract validates the decision to build Falcon Heavy: without it SpaceX would have been unable to compete for any contracts related to the Gateway.

[pochimax]

The recent Dragon XL contract validates the decision to build Falcon Heavy: without it SpaceX would have been unable to compete for any contracts related to the Gateway.

But ... all the contracts related to Gateway are possible because of Falcon Heavy previous existence, too.

[TheRadicalModerate]

I have a kind of random question:  Does anybody know why SpaceX so studiously avoids publishing a "mass to TLI" number for FH?  They've got mass to LEO (63.8t), mass to GTO (26.7t), and mass to Mars (16.8t, which I assume is really mass to MTO).  But no TLI.

It's weird.  It's especially weird when ULA is happy to publish TLI numbers for all of its platforms.

Things are even somewhat weirder than that.  If you go to NASA's ELV performance web tool, there are no FH entries for anything with a C3 < -1.8 km²/s².  That includes all LEO and HEEO options, as well.

Anybody know what the deal is?

[FutureSpaceTourist]

Nice animation of extended fairing

[Citabria]

What if the expendable core had fewer Merlins, say 5 with larger nozzles optimized for high altitude (not quite MVac)? Down side is lower take off thrust. Up side is higher ISP at altitude and better mass fraction and less waste. Would there be a net benefit?

[MATTBLAK]

I'd say modifications of that nature aren't really needed. They could alter the throttling profile of the FH a bit more; perhaps operate at a lower throttle setting for a few seconds longer to preserve more propellant when expending the Corestage. Theoretically; the thing FH needs more than anything is an upgraded upper stage. Widening it to 5.2 meters to match the Payload Fairing would give a fairly big bump in available propellants. The next step would be to uprate the Merlin 1D vacuum engine with either more thrust or improve the nozzle for even more Isp. I'm not sure increasing the thrust would be all that feasible, really.

There have been suggestions from time to time to make the upper stage LOX/Methane and put a single Raptor engine on it - but throttle that engine down a bit, operationally. I don't see the value of that, unless Starship were to either fail or be dramatically delayed. I'm not seeing either prospect as likely to happen. So 'tweaking' FH to have a bit more upper stage propellant, along with some minor engine tweaks would be relatively cheap and easy. Having a booster that could throw 20 metric tons towards the Moon or Mars could be useful.

[envy887]

I'd say modifications of that nature aren't really needed. They could alter the throttling profile of the FH a bit more; perhaps operate at a lower throttle setting for a few seconds longer to preserve more propellant when expending the Corestage. Theoretically; the thing FH needs more than anything is an upgraded upper stage. Widening it to 5.2 meters to match the Payload Fairing would give a fairly big bump in available propellants. The next step would be to uprate the Merlin 1D vacuum engine with either more thrust or improve the nozzle for even more Isp. I'm not sure increasing the thrust would be all that feasible, really.

The Falcon S2 is already quite large. A bigger upper stage, even with a bit more thrust, would not really help the performance of expended FH that much. Adding 60% more propellant would be around a 5% payload to TLI increase by my calculations.

[Citabria]

What if the expendable core had fewer Merlins, say 5 with larger nozzles optimized for high altitude (not quite MVac)? Down side is lower take off thrust. Up side is higher ISP at altitude and better mass fraction and less waste. Would there be a net benefit?

I'd say modifications of that nature aren't really needed. They could alter the throttling profile of the FH a bit more; perhaps operate at a lower throttle setting for a few seconds longer to preserve more propellant when expending the Corestage.

My point is to minimize everything on the expended core. Obviously they'll delete legs and fins, re-entry shields, engine re-start hardware, etc. With only 5 Merlins they could lighten the thrust structure. They could bring the booster attach struts back on the boosters, not leave them on the core. Maybe the 5 Merlins would not need throttling, so more hardware saved there.

Sure, it's all hand-waving, but it would be interesting to see estimated performance numbers with such mods.

[wannamoonbase]

What if the expendable core had fewer Merlins, say 5 with larger nozzles optimized for high altitude (not quite MVac)? Down side is lower take off thrust. Up side is higher ISP at altitude and better mass fraction and less waste. Would there be a net benefit?

I'd say modifications of that nature aren't really needed. They could alter the throttling profile of the FH a bit more; perhaps operate at a lower throttle setting for a few seconds longer to preserve more propellant when expending the Corestage.

My point is to minimize everything on the expended core. Obviously they'll delete legs and fins, re-entry shields, engine re-start hardware, etc. With only 5 Merlins they could lighten the thrust structure. They could bring the booster attach struts back on the boosters, not leave them on the core. Maybe the 5 Merlins would not need throttling, so more hardware saved there.

Sure, it's all hand-waving, but it would be interesting to see estimated performance numbers with such mods.

FH is a beast, with an expended core the performance numbers must be incredible. 

No doubt SpaceX could tweak somethings to get numbers even better.  However, SpaceX has always looked for consistency and a simple path forward.

If they needed even more performance they would just run fully expendable and keep the vehicle, software, handling and prep consistent.

A fully expendable FH would be a pretty amazing mission to see.

[rsnellenberger]

What if the expendable core had fewer Merlins, say 5 with larger nozzles optimized for high altitude (not quite MVac)? Down side is lower take off thrust. Up side is higher ISP at altitude and better mass fraction and less waste. Would there be a net benefit?

I'd say modifications of that nature aren't really needed. They could alter the throttling profile of the FH a bit more; perhaps operate at a lower throttle setting for a few seconds longer to preserve more propellant when expending the Corestage.

My point is to minimize everything on the expended core. Obviously they'll delete legs and fins, re-entry shields, engine re-start hardware, etc. With only 5 Merlins they could lighten the thrust structure. They could bring the booster attach struts back on the boosters, not leave them on the core. Maybe the 5 Merlins would not need throttling, so more hardware saved there.

Sure, it's all hand-waving, but it would be interesting to see estimated performance numbers with such mods.

I’d be curious whether there’d be any benefit in a flight profile that exploits the 3-engine restart capability by (for example) shutting them down in parallel with a usual throttle down (IIRC, to 40%?) in the other six engines, and then some combination of restarting the three and/or shutting down the six after booster separation.

All other things being equal...