totm nov 2023 SpaceX Discussion Thread

[tater]

 

[zolotiyeruki]

 

7 hours ago, mikegarrison said:

I would like to see the analysis behind that claim. On the surface, one might think that even a single re-use must save money, but I'm sure it depends a lot on how expensive it is to design parts to be re-used, to do refurbishments, to have a barge and a landing pad, to add landing legs, to reserve fuel for landing (especially including all the fuel needed to lift the landing fuel instead of the payload)....

Recovery adds fuel cost (a few $100ks), but that's not huge in the context of a $62 million launch.  The extra fuel costs for RTLS must be less than the cost difference of recovering via ASDS (otherwise, why bother RTLSing?).  Cost of refurbishment is completely unknown.  You're only saving the cost of building a F9S1--SpaceX will still fully test it, you still have to pay for fuel, launch personnel, FAA paperwork, all the work to integrate the payload, etc.  Let's say that building S1 is half of the launch cost.  $31 million will pay for a lot of fuel, refurbishment, time at sea, and landing legs.

As for the payload issues, or concerns that the additional fuel for recovery will prevent F9 from lofting certain payloads, SpaceX already have an answer:  just fly it expendable.

Edited September 13, 2019 by zolotiyeruki

[sevenperforce]

1 hour ago, zolotiyeruki said:

Recovery adds fuel cost (a few $100ks), but that's not huge in the context of a $62 million launch.  The extra fuel costs for RTLS must be less than the cost difference of recovering via ASDS (otherwise, why bother RTLSing?).  Cost of refurbishment is completely unknown.  You're only saving the cost of building a F9S1--SpaceX will still fully test it, you still have to pay for fuel, launch personnel, FAA paperwork, all the work to integrate the payload, etc.  Let's say that building S1 is half of the launch cost.  $31 million will pay for a lot of fuel, refurbishment, time at sea, and landing legs.

I agree. I don't know whether Tory is factoring in hidden costs or development investments or anything else, though.

Tory also seems to be making subtle digs about the fact that Boeing and Lockheed are publicly traded and SpaceX is not. Though really he has little ground to stand on in that arena. There is no evidence that SpaceX is getting significant private-investor bailouts.

1 hour ago, zolotiyeruki said:

As for the payload issues, or concerns that the additional fuel for recovery will prevent F9 from lofting certain payloads, SpaceX already have an answer:  just fly it expendable.

Of course this runs into Tory's point about how the fleet average must be ten flights. Flying expendable is a nasty datapoint. This would be more of an issue if not for the fact that even when flying with RTLS recovery, F9B5 has a ridiculous amount of throw to GTO. There really aren't any regular commercial payloads available that F9B5 with ASDS recovery cannot throw to GTO (or at least near-GTO).

Also, I just realized that Tory said fly-back recovery requires a fleet average of ten flights. ASDS recovery reserves more performance, which means more expensive payloads, which presumably means a fleet average much lower than ten.

[mikegarrison]

2 minutes ago, sevenperforce said:

Tory also seems to be making subtle digs about the fact that Boeing and Lockheed are publicly traded and SpaceX is not. Though really he has little ground to stand on in that arena. There is no evidence that SpaceX is getting significant private-investor bailouts.

I took that mainly as being aimed at Blue Origin, though of course SpaceX was started with a lot of private capital.

[magnemoe]

4 hours ago, sevenperforce said:

I agree. I don't know whether Tory is factoring in hidden costs or development investments or anything else, though.

Tory also seems to be making subtle digs about the fact that Boeing and Lockheed are publicly traded and SpaceX is not. Though really he has little ground to stand on in that arena. There is no evidence that SpaceX is getting significant private-investor bailouts.

Of course this runs into Tory's point about how the fleet average must be ten flights. Flying expendable is a nasty datapoint. This would be more of an issue if not for the fact that even when flying with RTLS recovery, F9B5 has a ridiculous amount of throw to GTO. There really aren't any regular commercial payloads available that F9B5 with ASDS recovery cannot throw to GTO (or at least near-GTO).

Also, I just realized that Tory said fly-back recovery requires a fleet average of ten flights. ASDS recovery reserves more performance, which means more expensive payloads, which presumably means a fleet average much lower than ten.

Pretty sure he calculates the cost for ULA to develop an fly-back first stage who will require an entire new rocket. 

SpaceX got very lucky with their falcon9, 9 engines let you land on the center one and use 3 for braking burns making it very easy to make reusable. 
5 engines could also work here but fewer would make this very hard. 
Also not using SRB as that would throw first stage to fast and far. 

[Xd the great]

5 hours ago, magnemoe said:

Pretty sure he calculates the cost for ULA to develop an fly-back first stage who will require an entire new rocket. 

SpaceX got very lucky with their falcon9, 9 engines let you land on the center one and use 3 for braking burns making it very easy to make reusable. 
5 engines could also work here but fewer would make this very hard. 
Also not using SRB as that would throw first stage to fast and far. 

And F9 has a powerful second stage. 800kN, enough dv to support reusing first stage.

ULA launchers using weak RL-10s cannot get enough thrust.

Which means Vulcans require first stage to do so much more work. Either flying high and get little atmo for slowing down, or fly low and need a lot of propellant to go back for a runway landing.

Edited September 13, 2019 by Xd the great

[magnemoe]

1 hour ago, Xd the great said:

And F9 has a powerful second stage. 800kN, enough dv to support reusing first stage.

ULA launchers using weak RL-10s cannot get enough thrust.

Which means Vulcans require first stage to do so much more work. Either flying high and get little atmo for slowing down, or fly low and need a lot of propellant to go back for a runway landing.

This is correct, the RL-10 on the other hand has very good ISP who is that you want from an for the upper stage. 
They had the option to use two engines on upper stage but this was not used before they wanted an manned capsule who required  a flatter trajectory. 

Falcon 9 needs an powerful engine on second stage as they stage so early, its also the engine they had who probably influenced this, for reuse they also needed to stage pretty early. 

[mikegarrison]

8 hours ago, Xd the great said:

ULA launchers using weak RL-10s cannot get enough thrust.

Way more ISP, though. It's a tradeoff most KSP players should understand. Centaurs are not really ideal for LEO, but they have been used very successfully for most of our deep space missions. The ISP advantage really pays off for those.

6 hours ago, magnemoe said:

They had the option to use two engines on upper stage but this was not used before they wanted an manned capsule who required  a flatter trajectory.

Not used recently. They have used dual-engine centaurs before.

Edited September 13, 2019 by mikegarrison

[tater]

Yeah, Centaur is an awesome rocket stage. The only problem with RL-10 is honestly the retail price, but it's a fantastic rocket engine.

[Nothalogh]

2 hours ago, tater said:

Centaur is an awesome rocket stage

It's practically the only reason why ULA is in business, the Centaur upper stage is their bread and butter.

[sevenperforce]

22 hours ago, Xd the great said:

And F9 has a powerful second stage. 800kN, enough dv to support reusing first stage.

ULA launchers using weak RL-10s cannot get enough thrust.

Which means Vulcans require first stage to do so much more work. Either flying high and get little atmo for slowing down, or fly low and need a lot of propellant to go back for a runway landing.

In order to be as cost-effective as possible, a launch company needs a "dial-a-rocket" model. Otherwise you end up with a far more expensive launch vehicle than needed for most missions. ULA accomplishes this because most of its launch vehicles are not 2-stage-to-orbit, but 2.5-stage-to-orbit, with parallel (usually solid) boosters.

The solid boosters themselves don't contribute much in terms of absolute dV; their real advantage is to amp up TWR (not unlike F9B5 did with the final uprate on the Merlin engines) so gravity losses on the core stage are lower, giving the core greater speed at staging. Putting the bulk of the work on the core allows a low-thrust upper stage, which means a less heavy upper stage, which helps with mass ratio and obviates the famously horrible TWR of hydrolox engines.

It's a great model, but it simply isn't amenable to amending into a fly-back-booster model. Look at the comparison. The original Falcon 9 could throw 9 tonnes to LEO, whereas the Atlas V 401 can throw 9.7 tonnes to LEO. Pretty comparable. Yet for the original Falcon 9, the upper stage packed 5.3 km/s and the lower stage packed 3.6 km/s, while for the 401, the Centaur packs 4.4 km/s and the Atlas CCB packs 5.6 km/s. The Falcon 9 upper stage was, in comparison to its lower stage, 87% beefier than the Centaur.

Of course the Falcon 9 has evolved tremendously; for the same payload, it now packs 7.6 km/s into the upper stage while the lower stage has the same dV as before. SpaceX can "dial-a-rocket" by simply adjusting the recovery profile: RTLS has a lower operations cost than ASDS recovery, and near-shore ASDS recovery has a lower operations cost than distant recovery.

Since the ULA model puts so much weight on the core, the only thing that really makes sense is downrange recovery of the engines alone. It's telling that they require an expandable heat shield just to try.

14 hours ago, mikegarrison said:

Way more ISP, though. It's a tradeoff most KSP players should understand. Centaurs are not really ideal for LEO, but they have been used very successfully for most of our deep space missions. The ISP advantage really pays off for those.

At the same time, putting a fully-loaded Falcon 9 upper stage into LEO wildly outperforms putting a fully-loaded Centaur into LEO, because it's simply so much bigger.

14 hours ago, mikegarrison said:

Not used recently. They have used dual-engine centaurs before.

Not on Atlas V.

21 hours ago, magnemoe said:

Falcon 9 needs an powerful engine on second stage as they stage so early, its also the engine they had who probably influenced this, for reuse they also needed to stage pretty early. 

Interestingly, Russian-derived launch vehicles (like CNSA and ISRO) may actually be more amenable to first-stage reuse than the ULA model. Rather than strapping on more core boosters, they typically add liquid kick stages to achieve their dial-a-rocket performance. Look at Fregat on the various Soyuz versions, for example.

[tater]

 

[kurja]

1 hour ago, sevenperforce said:

The solid boosters themselves don't contribute much in terms of absolute dV; their real advantage is to amp up TWR (not unlike F9B5 did with the final uprate on the Merlin engines) so gravity losses on the core stage are lower, giving the core greater speed at staging. 

Delta vee being literally change of velocity, how does one have a system that does little for dv while increasing speed..?

[Ultimate Steve]

Just now, kurja said:

Delta vee being literally change of velocity, how does one have a system that does little for dv while increasing speed..?

At the very beginning of the flight, if you have a twr of 1.2, 5/6 of the delta-v expended is going towards countering gravity. This quickly changes once the gravity turn is started. Increasing takeoff twr does help.

[tater]

31 minutes ago, kurja said:

Delta vee being literally change of velocity, how does one have a system that does little for dv while increasing speed..?

@Ultimate Steve answered it well, but think of the gravity drag this way. If the engines could throttle such that the TWR of the rocket was always exactly 1, you could make an arbitrarily large rocket with infinite dv, but you'd never leave the pad.

Edited September 14, 2019 by tater

[sevenperforce]

2 hours ago, kurja said:

Delta vee being literally change of velocity, how does one have a system that does little for dv while increasing speed..?

Great answers already from @Ultimate Steve and @tater, but an additional explanation would look at the uprating on the Falcon 9 Block 5 itself. There is no difference in propellant capacity between B3, B4, and B5, and in fact the B5 actually has slightly greater dry mass than its B3 and B4 predecessors, but the B5 has greater throw to LEO and beyond because the engines burn at higher thrust.

Prior to the gravity turn, every second spent climbing costs you 9.8 m/s off your final velocity. Adding more propellant does not add linearly to your final stage because of the tyranny of the rocket equation, but adding more thrust does produce linear gains that propagate all the way up. If you can uprate your engines enough to shave 10 seconds off the pre-turn climb, then you stage at 98 m/s faster, which is 98 m/s less that your upper stage has to produce.

That's why adding those inefficient SRBs to the bottom of the Atlas V and Delta IV is so very effective.

[kurja]

Good answers, thanks guys.

[CatastrophicFailure]

Some very informative replies upthread.  @kurja don’t just take their word for it (although you certainly could), you can validate all this yourself in KSP.

It’s also worth noting, tho, that adding thrust does reach a point of diminishing return when dealing with that pesky atmosphere. At some point your air drag losses will exceed your gravity losses if you just keep piling on thrust. 

[sevenperforce]

3 minutes ago, CatastrophicFailure said:

...adding thrust does reach a point of diminishing return when dealing with that pesky atmosphere. At some point your air drag losses will exceed your gravity losses if you just keep piling on thrust. 

Depends on what happens to the dry mass associated with that extra thrust. With the Falcon 9, there was no addition to dry mass required to uprate the engines, and so the gains were essentially free. With the Atlas V, the added mass of the SRB casings is jettisoned at burnout, so there's no worry there either. The original Atlas that put John Glenn into orbit jettisoned its outboard engines once their thrust was no longer needed.

However, if you try to replicate in KSP by simply adding more engines, you will run into dry mass losses before you run into drag losses. Real-life engines and tanks are much lighter than in KSP.

In real life, I think piling on more thrust (more SRBs, etc.) would cause structural problems with your launch vehicle before the gravity drag advantage would be outweighed by the air drag disadvantage. 

[tater]

2 minutes ago, sevenperforce said:

The original Atlas that put John Glenn into orbit jettisoned its outboard engines once their thrust was no longer needed.

Makes me wonder if a 3 BE-4 Vulcan could be a thing, dumping the outboard 2, original Atlas style---but at a lower staging velocity (with the same collection via parachute as "smart reuse").

[magnemoe]

5 hours ago, sevenperforce said:

In order to be as cost-effective as possible, a launch company needs a "dial-a-rocket" model. Otherwise you end up with a far more expensive launch vehicle than needed for most missions. ULA accomplishes this because most of its launch vehicles are not 2-stage-to-orbit, but 2.5-stage-to-orbit, with parallel (usually solid) boosters.

The solid boosters themselves don't contribute much in terms of absolute dV; their real advantage is to amp up TWR (not unlike F9B5 did with the final uprate on the Merlin engines) so gravity losses on the core stage are lower, giving the core greater speed at staging. Putting the bulk of the work on the core allows a low-thrust upper stage, which means a less heavy upper stage, which helps with mass ratio and obviates the famously horrible TWR of hydrolox engines.

It's a great model, but it simply isn't amenable to amending into a fly-back-booster model. Look at the comparison. The original Falcon 9 could throw 9 tonnes to LEO, whereas the Atlas V 401 can throw 9.7 tonnes to LEO. Pretty comparable. Yet for the original Falcon 9, the upper stage packed 5.3 km/s and the lower stage packed 3.6 km/s, while for the 401, the Centaur packs 4.4 km/s and the Atlas CCB packs 5.6 km/s. The Falcon 9 upper stage was, in comparison to its lower stage, 87% beefier than the Centaur.

Of course the Falcon 9 has evolved tremendously; for the same payload, it now packs 7.6 km/s into the upper stage while the lower stage has the same dV as before. SpaceX can "dial-a-rocket" by simply adjusting the recovery profile: RTLS has a lower operations cost than ASDS recovery, and near-shore ASDS recovery has a lower operations cost than distant recovery.

Since the ULA model puts so much weight on the core, the only thing that really makes sense is downrange recovery of the engines alone. It's telling that they require an expandable heat shield just to try.

At the same time, putting a fully-loaded Falcon 9 upper stage into LEO wildly outperforms putting a fully-loaded Centaur into LEO, because it's simply so much bigger.

Interestingly, Russian-derived launch vehicles (like CNSA and ISRO) may actually be more amenable to first-stage reuse than the ULA model. Rather than strapping on more core boosters, they typically add liquid kick stages to achieve their dial-a-rocket performance. Look at Fregat on the various Soyuz versions, for example.

This, the centaur and the Ariane 5 upper stage is both pretty low trust, high isp but pretty light, the dry weight is also low while Falcon 9 upper stage is much heavier. This does not matter much for LEO missions but give better performance if you want lots of dV rather than heavy payload. 

An Soyuz would require an complete rebuild to be reusable to. 
 

[kurja]

59 minutes ago, CatastrophicFailure said:

Some very informative replies upthread.  @kurja don’t just take their word for it (although you certainly could), you can validate all this yourself in KSP.

Oh I've discovered the concept in ksp before, it was just that the wording seemed oxymoronic - "there is no increase to delta v but the end speed is higher"

[Racescort666]

6 hours ago, sevenperforce said:

Since the ULA model puts so much weight on the core, the only thing that really makes sense is downrange recovery of the engines alone. It's telling that they require an expandable heat shield just to try.

This is essentially the crux ULA has. It’s probably pure speculation to say that the Falcon 9 was designed from the beginning for recovery but Falcon 9’s flight profile is much more amenable to fly-back recovery. The Atlas V stages at almost 2X the velocity and has a much more lofted flight profile. ULA would likely have to develop an entirely new rocket to do the same thing as SpaceX and they’d probably converge on the same design. (They might be calling Vulcan a new rocket but it’s basically an Atlas derivative.)

Off topic (kinda): I just want to say “whew” 17 pages of SpaceX thread finally caught up on. They blocked the KSP forum at work so now I can’t catch up on my lunch break.

[tater]

https://www.businessinsider.com/yusaku-maezawa-zozo-ceo-resigns-sells-yahoo-spacex-starship-flight-2019-9

Quote

Yusaku Maezawa, a key investor in SpaceX's next-generation rocket system, called Starship, plans to sell a 30% stake in his online fashion-retail company, Zozo, to Yahoo Japan.

As part of the $3.7 billion tender offer, Maezawa will resign as CEO of Zozo, receive about $2.3 billion in cash, and maintain a 6% stake in the company he founded, according to Forbes.

...

Maezawa also indicated he'd fly on a less ambitious space mission before SpaceX's privately funded circumlunar voyage.

"Training to go into space will to take up much of my time," Maezawa said, according to Forbes.

 

[Xd the great]

5 hours ago, tater said:

https://www.businessinsider.com/yusaku-maezawa-zozo-ceo-resigns-sells-yahoo-spacex-starship-flight-2019-9

 

And please send Elon along as a tourist guide.