SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[Yggdrasill]

9 fully visible pairs of non-gimbal-non-throttle Raptor ports (one for fuel & one for oxidiser each) means a ring of at least 18, possibly 19 or 20 depending on lens focal length.
8 angled ports on the thrust puck matches the expected 8 gimbalable-and-throttleable Raptors in the centre cluster.
So somewhere between 26 and 28 raptors still seems to be the target as of that particular dome being completed. No guarantees that dome hasn't since been quietly scrapped for a newer design, though.

It's also possible they make a "final" design for the Super Heavy, and then just close off the ports they don't need for the specific vehicle. That way they get experience making as close to production-intent parts as soon as possible.

And if they suddenly decide to change the number of Raptors for some reason, they can just modify the thrust puck accordingly.

Like if BN3 is supposed to have 18 Raptors, and BN4 is supposed to have 22 Raptors for a more ambitious test, and BN3 is a total failure, they might be able to easily close off the four extra ports on the thrust puck for BN4 and repeat the BN3 test. Or if BN3 performs above all expectation, they could go for the full 28 on BN4 for an even more ambitious test.

All the number of ports really says is that the vehicle will have *no more than* that number of Raptors.

[philw1776]

Since the Starship will be expended, I think it's likely they'll only fly with 3 SL Raptors. They can add the 3 vacuum Raptors when they try to land the Starship.

Hopefully they successfully land the Super Heavy, so the test might only expend three Raptors.

They are trying to land starship. It'll just be in the ocean, but the landing profile will be the same as it would have been for a landingpad. So they will need those raptors.

No they do not need "those raptors" meaning Rvacs to land. 3 sea level engines are more than enough and include engine out redundancy.
They DO need the Rvacs to reach orbit as the Starship needs to carry enough propellant to achieve 9.x Km/sec orbital velocity allowing for gravity losses. Carrying the needed propellant mass means more Newtons force needed to move the Starship 2nd stage up to orbital velocity.

[Space_Puzzle]

According to this picture taken by Mary maybe BN3 will have more than 18 Raptor SL ?

9 fully visible pairs of non-gimbal-non-throttle Raptor ports (one for fuel & one for oxidiser each) means a ring of at least 18, possibly 19 or 20 depending on lens focal length.
8 angled ports on the thrust puck matches the expected 8 gimbalable-and-throttleable Raptors in the centre cluster.
So somewhere between 26 and 28 raptors still seems to be the target as of that particular dome being completed. No guarantees that dome hasn't since been quietly scrapped for a newer design, though.

Did SN5/6 have 3 raptor ports eventhough they only used 1?
If that's the case, BN3 could also fly with less engines than it has ports.

[hkultala]

Since the Starship will be expended, I think it's likely they'll only fly with 3 SL Raptors. They can add the 3 vacuum Raptors when they try to land the Starship.

Hopefully they successfully land the Super Heavy, so the test might only expend three Raptors.

Vacuum raptors have nothing to do with landing. It's the SL engines which are used for landing.

The vacuum engines are needed to get
1) Enough thrust
2) Good specific impulse.

Without any payload, Starship might be able to reach orbit with just 3 sea level engines, and might even have enough fuel left for the landing burn.

However, the flight profile would be quite different than on operational flights. Either it would have quite bad T/W ratio, and the Superheavy would lift it to more lofted trajectory to make it stay in the air for long enough to accelerate to orbital speed, or it would be only partially fueled and then the staging would happen later than normally. Or more probably, a little bit of both.

Reaching orbit with SL engines in place of the vacuum engines (so just total 6 SL engines) would be easy, just some payload capacity would be lost. My quess is in this option - as they do not really need the vacuum version yet, they can concentrate on improving the SL version and then making the  "high thrust dumb version" and make the vacuum versions later when they start flying to higher orbits/trajectories where isp matters more.

And it probably makes more sense to make the vacuum engines based on the "high thrust dumb version" anyway as that version will also have slightly improved isp, and the higher pressure will also mean less flow separation issues if the vacuum engines need to be operated in the atmosphere in an emergency situation to perform an abort in case of Superheavy failure.

[Yggdrasill]

They DO need the Rvacs to reach orbit as the Starship needs to carry enough propellant to achieve 9.x Km/sec orbital velocity allowing for gravity losses. Carrying the needed propellant mass means more Newtons force needed to move the Starship 2nd stage up to orbital velocity.

They don't really *need* the vacuum Raptors to reach orbit, though they would of course be nice to have.

For instance, a centaur upper stage with one RL10 has 0.44G* of acceleration, Starship with 3x 200 ton Raptors and 1350 ton mass has 0.44G. So they aren't that different in that regard. Though the first stage of the Atlas V does burn for a longer time, which helps the upper stage get past more of the gravity losses before firing up, so you probably would want to compensate by reducing the propellant load to some extent.

I don't really know what they will prioritize, though.

1. Not expending three additional Raptors.
2. Getting additional data on vacuum Raptor performance in space.

I guess if they have the vacuum Raptors to spare, they will use them.

* Edit: Sorry, that's actually without payload. A single engine Centaur may actually carry as much as 18.8 tons of payload. In that case the acceleration is 0.23G. Starship with 3x SL Raptors and no payload has almost twice the T/W.

[Yggdrasill]

Vacuum raptors have nothing to do with landing. It's the SL engines which are used for landing.

The vacuum engines are needed to get
1) Enough thrust
2) Good specific impulse.

Without any payload, Starship might be able to reach orbit with just 3 sea level engines, and might even have enough fuel left for the landing burn.

I wasn't saying the vacuum Raptors had anything to do with the landing. Just that if they hold off on installing the vacuum Raptors until they try landing (and recovering) the Starship, they won't have to intentionally expend any vacuum Raptors.

If we say they cost $1 million each, that's a $3 million saving by dropping them from this test flight. That's not huge of course, but these flights aren't making SpaceX any money. And having to replace them for a new flight might actually delay the test program, if availability is a challenge.

[StarshipTrooper]

Vacuum raptors have nothing to do with landing. It's the SL engines which are used for landing.

The vacuum engines are needed to get
1) Enough thrust
2) Good specific impulse.

Without any payload, Starship might be able to reach orbit with just 3 sea level engines, and might even have enough fuel left for the landing burn.

I wasn't saying the vacuum Raptors had anything to do with the landing. Just that if they hold off on installing the vacuum Raptors until they try landing (and recovering) the Starship, they won't have to intentionally expend any vacuum Raptors.

If we say they cost $1 million each, that's a $3 million saving by dropping them from this test flight. That's not huge of course, but these flights aren't making SpaceX any money. And having to replace them for a new flight might actually delay the test program, if availability is a challenge.

An interesting side note, using vacuum raptors on starship may fulfill some portion of a $67 million dollar contract with the DOD to create a second stage raptor engine.

https://spacenews.com/air-force-adds-more-than-40-million-to-spacex-engine-contract/

[Robotbeat]

Since the Starship will be expended, I think it's likely they'll only fly with 3 SL Raptors. They can add the 3 vacuum Raptors when they try to land the Starship.

Hopefully they successfully land the Super Heavy, so the test might only expend three Raptors.

Not according to NSF article

I trust our reporters, but I'd really like confirmation that this (that Super Heavy WILL be expended, not just most likely expended) is actually well-sourced information. Several other folks have said the FCC document mentions Super Heavy being expended and splashed, when in fact it refers specifically to landing and "touchdown", which is very different language than the "splashdown" used for Starship in the same section.

And in case someone misreads this: I would bet money that Super Heavy will be expended this flight (i.e. that there won't be anything solid to land it on). But we do not have sourced information that *says* they will expend it. From what I can telling, this is something we are *inferring*, and we cannot yet 100% rule out that they may still hold out hope for landing the booster on something.

[su27k]

Given SpaceX changes the plan on a weekly basis, there's not much point to be "100% sure" about anything, since it may very well change next week. I think it is enough for us to know that they're gearing up for the ability to expend multiple SuperHeavy's (ramp up Raptor production, pair new SuperHeavy with Starship), whether they actually expend them can be left as a surprise...

[Robotbeat]

Given SpaceX changes the plan on a weekly basis, there's not much point to be "100% sure" about anything, since it may very well change next week. I think it is enough for us to know that they're gearing up for the ability to expend multiple SuperHeavy's (ramp up Raptor production, pair new SuperHeavy with Starship), whether they actually expend them can be left as a surprise...

I am simply insisting that unsourced inferences (regardless of how likely) not be accidentally upgraded to sourced “fact” without some kind of confirmation.

[Alberto-Girardi]

Since the Starship will be expended, I think it's likely they'll only fly with 3 SL Raptors. They can add the 3 vacuum Raptors when they try to land the Starship.

Hopefully they successfully land the Super Heavy, so the test might only expend three Raptors.

Not according to NSF article

I trust our reporters, but I'd really like confirmation that this (that Super Heavy WILL be expended, not just most likely expended) is actually well-sourced information. Several other folks have said the FCC document mentions Super Heavy being expended and splashed, when in fact it refers specifically to landing and "touchdown", which is very different language than the "splashdown" used for Starship in the same section.

And in case someone misreads this: I would bet money that Super Heavy will be expended this flight (i.e. that there won't be anything solid to land it on). But we do not have sourced information that *says* they will expend it. From what I can telling, this is something we are *inferring*, and we cannot yet 100% rule out that they may still hold out hope for landing the booster on something.

I agree.

We'll see if they will splashdown or not the SH. SpaceX many time has surprised us, doing things aiming very high or in a unconventinal way, but other time they go more "conventional". I hope to see both SH and SS recoverd, but maybe this isn't really the best thing for this test flight.

[Robotbeat]

Since the Starship will be expended, I think it's likely they'll only fly with 3 SL Raptors. They can add the 3 vacuum Raptors when they try to land the Starship.

Hopefully they successfully land the Super Heavy, so the test might only expend three Raptors.

They are trying to land starship. It'll just be in the ocean, but the landing profile will be the same as it would have been for a landingpad. So they will need those raptors.

No they do not need "those raptors" meaning Rvacs to land. 3 sea level engines are more than enough and include engine out redundancy.
They DO need the Rvacs to reach orbit as the Starship needs to carry enough propellant to achieve 9.x Km/sec orbital velocity allowing for gravity losses. Carrying the needed propellant mass means more Newtons force needed to move the Starship 2nd stage up to orbital velocity.

As far as I can tell, they don’t need the RVacs to reach orbit and land the ship without any payload. Because without payload, they can afford to partially fill Starship and still reach orbit and landing. I haven’t seen any calculations that show otherwise.

What’s the separation mass of SH? 400t? 3400t usable ascent propellant? 340s average ascent Isp for SH? If Starship has 150 tons of dry mass plus landing propellant... 350s ascent Isp... then with 850t usable ascent propellant (1000t total mass on Separation), it gets 10.6km/s delta-v.

3 Raptors each 200t thrust make 600 ton thrust. It’s not uncommon or unreasonable for upper stage engines to have half the thrust as the mass of the full upper stage, so 1000t wet mass being pushed by 600t thrust Raptors is no big problem for gravity losses.

https://www.google.com/search?q=350*9.8*ln%281000%2F150%29%2B340*9.8*ln%28%281000%2B3800%29%2F%281000%2B400%29%29
Heck, even if you set the upper stage (Starship) to a T/W of 1:1, it still gets 9.7km/s delta v.

RVacs are not strictly necessary for reaching orbit on this flight (and people should stop claiming they are required, unless they have a much better argument), but I expect them to use them anyway.

[Robotbeat]

Vacuum raptors have nothing to do with landing. It's the SL engines which are used for landing.

The vacuum engines are needed to get
1) Enough thrust
2) Good specific impulse.

Without any payload, Starship might be able to reach orbit with just 3 sea level engines, and might even have enough fuel left for the landing burn.

I wasn't saying the vacuum Raptors had anything to do with the landing. Just that if they hold off on installing the vacuum Raptors until they try landing (and recovering) the Starship, they won't have to intentionally expend any vacuum Raptors.

If we say they cost $1 million each, that's a $3 million saving by dropping them from this test flight. That's not huge of course, but these flights aren't making SpaceX any money. And having to replace them for a new flight might actually delay the test program, if availability is a challenge.

An interesting side note, using vacuum raptors on starship may fulfill some portion of a $67 million dollar contract with the DOD to create a second stage raptor engine.

https://spacenews.com/air-force-adds-more-than-40-million-to-spacex-engine-contract/

Regular Raptor on the second stage still counts as a second stage Raptor engine...

[oldAtlas_Eguy]

Since they would want to test as much items as they can on this flight without much risk. Testing RVACs in actual vacuum flight profile would be invaluable for the RVAC development. So they will most likely be there just to test them whether they are really needed or not to make orbit.

[cscott]

Agree.  In-vacuum testing of Rvac will make the test worthwhile even if SS frags on re-entry. *Especially* if the SS engines underperform or fail to light, that's useful info on failure modes which only occur in flight conditions.

[oldAtlas_Eguy]

The other item here is having 3 more engines give some redundancy in number of engines needed to make orbit. If not all the SL engines light then just having the SL engines means not making orbit. If some combination of VAC and SL engines start whose total is >3 then orbit is very likely to be reached.

[Cherokee43v6]

To me, all this argument about leaving off the RVACs to "save money" or "save weight" or "avoid throwing away engines" smacks of the same type of lack of understanding of what SpaceX is trying to do that all those in that other thread arguing for an SSTO flight of the Starship have.

What is the point of creating one-off frankenvehicles that require extra development expense and are a distraction from doing the work they actually need to do to fly SN/SS operationally?

Leaving off the RVACs means they have to write special software to control the vehicle that then has no application and becomes a dead-end for future development.  It means recalculating how the entire stack behaves with the mass of the RVACs missing from their specific locations.  It means that a significant portion of the data they retrieve has no value towards further development as it comes from a 'one-off special build'.

SpaceX is building an integrated system and things that are not going to be a part of that system are distractions.

[Robotbeat]

Only one person that I can tell argued SpaceX would leave them off. Others, like me, were just correcting the incorrect claim that RVac is *required* to reach orbit. It’s not “all this argument about leaving off RVacs to save weight”

[Nevyn72]

We haven't even begun to see BN3 in any tangible form yet, just some components that may or may not make it to orbital launch pad...

I suspect the static/test fire program with a whole gaggle of Raptors in close proximity to each other will end up being a longer and more problematic process than many are expecting... add into that teething problems with a whole new GSE setup and unfortunately delays are likely to be significant.

By the time the whole stack is ready to fly who knows what landing options may be available for SH offshore. 

[kkattula]

Costs of an SH and SS:

SH
 Engines -> From $30M to $40M depending on number of engines used (18 vs 23)
 Tank -> from $10M to $15M
 Ancillary hardware etc. -> from $10M to $15M
 Totals
    Min = ~$50M
    Max = ~$70M

SS
 Engines -> from $8M to $10M
 Tank and Fairing -> from $10M to $15M due to complexity of the nose cone shape and extra internal piping and header tanks + tiles attachments
 Ancillary Hardware -> from $15M to $20M The fins complications and the tiles
 Totals
    Min = ~$33M
    Max = ~$45M

Cost of flight hardware for orbital flight
   Min =~$83M
   Max = ~$115M

Or about 6 launches or more in a year without any recoveries for a total cost including all non flight hardware costs such as support GSE, tooling and other ground equipment fees and cryo costs. From a total spending of ~$1B.

I'm not convinced the costs will be anywhere near that high.

Raptors were estimated at around $2m each, BEFORE the spool up in production rate. They are likely well below $1M each by now.

Tanks are only a few $100K in stainless steel, and with the  rate they're churning them out, labor costs can't be more than a few million. 

So my guess is $10M to $15M for SS and $20M to $30M for SH.  With those numbers reducing as they make more of them.


However, the unit cost is almost irrelevent, as the big spend is on the infrastructure to build Raptors, Starships & Super Heavies, then test, launch and land them.  If they spend $1B this year and get one orbital launch, did it cost $1B per launch? That sort of calculation is almost meaningless until they reach steady state, if ever. 

I prefer to look at it this way:

  -  They have invested in and established the capacity (infrastructure, supply chains and people) to build Raptor, Starships and Super Heavies. 
  -  That capacity costs almost as much to sit idle as it does to make units.
  -  Using it builds experince and improves quality, at the minor additinal cost of some raw materials and power.
  -  The designs are not finalized yet, so current builds will not be of use when they eventually reach the operational designs.

So it makes sense to keep churning out prototypes and expending them in ways that inform the operational design.  Or even discard them if they've already moved on.  If they splash a SS and SH on the first orbital ettempt? No big deal, the new & improved versions will be just rolling out of the High Bay.

That said, I expect the SH will try to land on one of the drone ships, 20 km off Boca Chica. There could be a lot to learn by examining an intact, dry, booster, and the landing profile is relatively easy. Probably way too soon for one of the oil rigs to be ready though.

On the other hand, getting another droneship to the SS landing area would be very difficult & dangerous, with pretty low probabilty SS will make it that far intact, and be able to do the flip and stick the landing.