SpaceX Raptor engine - General Thread 4

[rsdavis9]

Well, for a start, it contains water that freezes in the tanks.
This was the cause of a couple of in-flight failures earlier in the testing programme.
As a result, they had to install a complex filtration system on V2 starships.
I'm not sure how this is done differently (if at all) on V3.

Did we see anything like that in the oxygen tank of the B18 wreck? I don't think so, and it was ripped wide open.

That is a very good point. Although I would have thought the filters would be around the engine inlets which are not that clearly visible to me so I'm still not entirely convinced. I hope someone asks Elon just to clarify.

I don't think the inlet filters would go away, just the scaffolded full tank filters that had been on v2 boosters.
Unless those should be unnecessary? I think keeping some minimal amount of filters is preferable...

Did we ever see verification of those filters? They were hypothesized by csi starbase? Basically a filter the size of the whole tank to catch the solid co2.

[spacenut]

Can the current R3 throttle?  Or are they just going to cut off engines to throttle down on Starship.  I know they are doing it for Superheavy by cutting off engines. 

[SpaceLizard]

Well, for a start, it contains water that freezes in the tanks.
This was the cause of a couple of in-flight failures earlier in the testing programme.
As a result, they had to install a complex filtration system on V2 starships.
I'm not sure how this is done differently (if at all) on V3.

Did we see anything like that in the oxygen tank of the B18 wreck? I don't think so, and it was ripped wide open.

That is a very good point. Although I would have thought the filters would be around the engine inlets which are not that clearly visible to me so I'm still not entirely convinced. I hope someone asks Elon just to clarify.

I don't think the inlet filters would go away, just the scaffolded full tank filters that had been on v2 boosters.
Unless those should be unnecessary? I think keeping some minimal amount of filters is preferable...

Did we ever see verification of those filters? They were hypothesized by csi starbase? Basically a filter the size of the whole tank to catch the solid co2.

I don't think we ever saw the filters themselves no, just the speculated brackets to hold them in one of the recovered booster wrecks that got cut up at Massey's.

[SpaceLizard]

Can the current R3 throttle?  Or are they just going to cut off engines to throttle down on Starship.  I know they are doing it for Superheavy by cutting off engines.

I would assume they can throttle, why wouldn't they?

[DanClemmensen]

Can the current R3 throttle?  Or are they just going to cut off engines to throttle down on Starship.  I know they are doing it for Superheavy by cutting off engines.

I would assume they can throttle, why wouldn't they?

Raptor 1 and Raptor 2 can apparently throttle down to 40% max. I thought we assumed that Raptor 3 can also do this. The lower limit is set by the way the turbopumps operate at lower-than-max rpm. Turbine design is a black art, and rocket engines must be designed for maximum efficiency at their highest thrust, which I suspect constrains the design space for throttled operation.

[Slarty1080]

Can the current R3 throttle?  Or are they just going to cut off engines to throttle down on Starship.  I know they are doing it for Superheavy by cutting off engines.

I would assume they can throttle, why wouldn't they?

Raptor 1 and Raptor 2 can apparently throttle down to 40% max. I thought we assumed that Raptor 3 can also do this. The lower limit is set by the way the turbopumps operate at lower-than-max rpm. Turbine design is a black art, and rocket engines must be designed for maximum efficiency at their highest thrust, which I suspect constrains the design space for throttled operation.

I thought the sea level engines were throttleable but the vacuum engines were not?

[DanClemmensen]

Can the current R3 throttle?  Or are they just going to cut off engines to throttle down on Starship.  I know they are doing it for Superheavy by cutting off engines.

I would assume they can throttle, why wouldn't they?

Raptor 1 and Raptor 2 can apparently throttle down to 40% max. I thought we assumed that Raptor 3 can also do this. The lower limit is set by the way the turbopumps operate at lower-than-max rpm. Turbine design is a black art, and rocket engines must be designed for maximum efficiency at their highest thrust, which I suspect constrains the design space for throttled operation.

I thought the sea level engines were throttleable but the vacuum engines were not?

I suspect they could be throttled, since the power heads are identical. Whether or not there is a use case for throttling them is a different issue. If there is never a reason to throttle them, they might have components or controls missing, I suppose. With basically zero insight or info, my guess is that they are throtteable to allow for steering via differential thrust as a backup to gimballing the non-vac engines.

[catdlr]

https://twitter.com/SpaceRhin0/status/2005947171141451856

Rhin0
@SpaceRhin0
Yesterday evening we saw 10 Raptor 2's heading in the direction of the scrap yard...

This is likely clearing out stock from the hangar as these (at least mostly) don't appear to be flown engines.

[DanClemmensen]

Rhin0
@SpaceRhin0
Yesterday evening we saw 10 Raptor 2's heading in the direction of the scrap yard...

This is likely clearing out stock from the hangar as these (at least mostly) don't appear to be flown engines.

Too bad they couldn't sell them to ULA...

[TheRadicalModerate]

I don't think the inlet filters would go away, just the scaffolded full tank filters that had been on v2 boosters.
Unless those should be unnecessary? I think keeping some minimal amount of filters is preferable...

Did we ever see verification of those filters? They were hypothesized by csi starbase? Basically a filter the size of the whole tank to catch the solid co2.

If you have ice (both wet and dry) accumulating in the LOX tank, is there a way to purge it without having infrastructure to do so?

For right now, we would expect tankers to be dryable back on Earth, along with Pez dispensers.  HLS Starships--for now--are single-use.

But depots will be receiving multiple loads of prop, all contaminated with ices.  Presumably, the depot itself is mostly protected by the tankers' filters.

How 'bout a Mars Starship, to be used for Earth return?  If you purge the tanks just by venting them and waiting for the ices to sublime, you likely wind up with more CO2 in the tank than you started with.  There's no He or N2 supply to do purges, unless it's imported at some non-trivial expense, at least not until there's a pretty sophisticated air-separation plant on the surface.

Even for Earth-Mars-Earth, you're only dealing with two loads of prop before servicing.  Maybe that's an acceptable load of ices?

The last application that gets talked about would be a reusable LEO-LLO-LEO shuttle for crews, which are supplied by D2.  This is an interim step to provide commercial cislunar crew services before Starship is crew-certified for launch and EDL. 

Such a shuttle would never get serviced throughout its lifetime, but it also spends lots of time in vacuum, from which the ices can presumably be dried.  But that requires completely emptying the LOX tank.  Will that be viable from an attitude control standpoint?  Can the header tanks hold enough LOX during the drying process?

[SpaceLizard]

Unless Raptor 3 fixed the icing problem. I can't remember, have we seen anything yet to confirm or deny that?

[Vettedrmr]

But depots will be receiving multiple loads of prop, all contaminated with ices.

Not sure how this is related to Raptor engines, but why will the depots be getting contaminated loads?  AIUI the prop payloads are just that, payloads, not used during launch.  So how would they be contaminated?

[meekGee]

But depots will be receiving multiple loads of prop, all contaminated with ices.

Not sure how this is related to Raptor engines, but why will the depots be getting contaminated loads?  AIUI the prop payloads are just that, payloads, not used during launch.  So how would they be contaminated?

Is the tanker payload fuel stored separately?
If yes (and I assume it is) then no problem.

[Vettedrmr]

But depots will be receiving multiple loads of prop, all contaminated with ices.

Not sure how this is related to Raptor engines, but why will the depots be getting contaminated loads?  AIUI the prop payloads are just that, payloads, not used during launch.  So how would they be contaminated?

Is the tanker payload fuel stored separately?
If yes (and I assume it is) then no problem.

I can't see any reason, nor have I heard any speculation, for SpaceX to design a completely new ship configuration to stretch the tanks to take up the payload bay.

[TheRadicalModerate]

But depots will be receiving multiple loads of prop, all contaminated with ices.

Not sure how this is related to Raptor engines, but why will the depots be getting contaminated loads?  AIUI the prop payloads are just that, payloads, not used during launch.  So how would they be contaminated?

Is the tanker payload fuel stored separately?
If yes (and I assume it is) then no problem.

I can't see any reason, nor have I heard any speculation, for SpaceX to design a completely new ship configuration to stretch the tanks to take up the payload bay.

Even if they’re stretched, it’ll still be the same tank. Separate tanks make no sense; they would require two extra domes, which is needless dry mass.

Remember, we’re talking about more than 100t of propellant delivered to LEO.

[Craigles]

. . .
But depots will be receiving multiple loads of prop, all contaminated with ices.  Presumably, the depot itself is mostly protected by the tankers' filters.

How 'bout a Mars Starship . . .

It seems like additional ice mitigation will be essential soon, before HLS. Do any of us know if R3 has heat exchangers that might provide clean autogenous pressurization?

[Vettedrmr]

Even if they’re stretched, it’ll still be the same tank. Separate tanks make no sense; they would require two extra domes, which is needless dry mass.

Remember, we’re talking about more than 100t of propellant delivered to LEO.

Well, there's a performance trade-off there; extra mass of dedicated tanks and the simplicity that brings vs. the extra processing and hardware (which increases mass but let's agree it's less than dedicated tanks), plus disposal of contaminants that common tanks bring.

It'll be interesting to see how SpaceX solves that problem.

[OTV Booster]

. . .
But depots will be receiving multiple loads of prop, all contaminated with ices.  Presumably, the depot itself is mostly protected by the tankers' filters.

How 'bout a Mars Starship . . .

It seems like additional ice mitigation will be essential soon, before HLS. Do any of us know if R3 has heat exchangers that might provide clean autogenous pressurization?

One can only hope.

[meekGee]

Even if they’re stretched, it’ll still be the same tank. Separate tanks make no sense; they would require two extra domes, which is needless dry mass.

Remember, we’re talking about more than 100t of propellant delivered to LEO.

Well, there's a performance trade-off there; extra mass of dedicated tanks and the simplicity that brings vs. the extra processing and hardware (which increases mass but let's agree it's less than dedicated tanks), plus disposal of contaminants that common tanks bring.

It'll be interesting to see how SpaceX solves that problem.

Interestingly - can a tank be partitioned with some sort of bladder or other non pressure bearing partition, to keep the refueling portion pure?

If separate tanks, would tgis much smaller amount of fuel require a full diameter tank and dome?  We're talking 10-20% of ship, it might be less than one ring tall if implemented as full cross-section.  Also - does each tanker carry bith propellants in the right ratios?  Or we have oxy tankers and gas tankers?

[goretexguy]

. . .
But depots will be receiving multiple loads of prop, all contaminated with ices.  Presumably, the depot itself is mostly protected by the tankers' filters.

How 'bout a Mars Starship . . .

It seems like additional ice mitigation will be essential soon, before HLS. Do any of us know if R3 has heat exchangers that might provide clean autogenous pressurization?

One can only hope.

A 30-cm-thick layer of accumulated ices will weigh 10 metric tons or more. I cannot see SpaceX tolerating this amount of dead weight (not even considering the weight of screens and filters) which has the capability of killing engines and affecting balance. (Not to mention issues with rapid reuse, to warm and drain the tanks.)

I have no idea what the weight tradeoffs versus engine heat exchangers and plumbing mods are, but I'd put real money down that they've engineered improvements to the autogenous system.

Math:
Ice volume, assuming a 'pancake' at the bottom of a flat-ended cylinder
  = 3.14 × (4.5 m)² × 0.30 m ≈ 19.08 m³.
Density of water ice
  ≈ 917 kg/m³, dry ice ≈ 1560 kg/m³. (Really cold dry ice can be 10% denser, to 1.7 gm/cm³)
Average density of ices
  = (917 kg/m³ + 1560 kg/m³)/2  = 1238.5 kg/m³
  = 1238.5 kg/m³ × 0.5  (50% solid, 50% void)
  = 619 kg/m³
Guesstimated mass of accumulated ices = 19.09 m³ × 619 kg/m³ ≈ 11,817 kg.

Depending on the actual volume of ices and the density, the mass can change significantly.