SpaceX Raptor engine - General Thread 4

[deltaV]

It's interesting that the $5M price was public since the prices of contracts between two companies are usually kept private. However I guess the reason it's public probably has more to do with Velo3D wanting to show off the contract than with SpaceX so maybe we can't learn anything about space from this.

[FutureSpaceTourist]

Crosspost:

https://twitter.com/nasaspaceflight/status/1840836308966785256

WOW! A Raptor just fired for the longest duration ever and by some margin at McGregor just now.

A full 897 seconds! Nearly 15 minutes!!

Just seeing how long it could keep going for @elonmusk?

nsf.live/mcgregor

[Oersted]

Almost 15 minutes, that is madness... Will the Earth tilt on its axis? (Just kidding)

[dabomb6608]

That is truly an impressive duration. I wonder what kind of records are out there for comparable(ish) rocket engine tests?

[catdlr]

That is truly an impressive duration. I wonder what kind of records are out there for comparable(ish) rocket engine tests?

The January 17 test comes three months after the current series began in October. During three tests last fall, operators fired the engine for durations from 500 to 650 seconds. The longest planned test of the series occurred on November 29 when crews gimbaled, or steered, the engine during an almost 11-minute (650 seconds) hot fire. The gimbaling technique is used to control and stabilize SLS as it reaches orbit.

Source

[Asteroza]

Was that at full throttle for 15 minutes, or minimum throttle for 15, or everything in between?

Is there a use case for 15 minute minimum throttle?

[Gliderflyer]

15 minutes could be close to a lunar landing abort case where you do a full descent, have a problem, and have to go back to low lunar orbit. Not sure what accelerations they are planning for those burns, but 15 minutes is in the ballpark.

[InterestedEngineer]

At full throttle, one engine at 670kg/sec in 15 minutes consumes 600t of fuel.

First of all, that's a lot of fuel for a test stand.

Second, at 6 engines that's 3,600t of fuel.  I can't think of a 6 engine configuration that will have that kind of tankage.

So from that I would guess it was not full throttle.

But anywhere in any gravity well, one wants max thrust for any conceivable burn, up to the point where the load is somewhere north of 3Gs.

So a 15 minute burn doesn't fit any burn profile I can think of.  So perhaps it's "let's see what the wear looks like if we burn as long as the test stand can do it" margin test.

[deltaV]

At full throttle, one engine at 670kg/sec in 15 minutes consumes 600t of fuel.

If you keep the 3 Raptors with sea level nozzles off and use only the 3 Raptors with vacuum nozzles for maximum specific impulse, and then one of the engines malfunctions and shuts down, the remaining 2 engines would take ~15 minutes to use Starship's ~1200 tonnes of propellant. I don't have a specific use case where they'd do this but it seems like a good thing to test.

Edit: if it's true that Raptor Vac doesn't gimbal (https://forum.nasaspaceflight.com/index.php?topic=56086.msg2354874#msg2354874) then this wouldn't work. But it's probably nice to know if there are any long-duration burn gremlins in case they want to try something else in the future.

[Herb Schaltegger]

I wonder if SpaceX is considering a “Falcon Heavy Demo-like” flight for Starship at some point, where they simply burn to depletion for deep space as a publicity/inspiration type flight? A long-duration burn profile avoids the technical risks of vacuum restart and long-duration boil-off mitigation, as well as needing to keep the vehicle powered for more than a few hours.

[steveleach]

At full throttle, one engine at 670kg/sec in 15 minutes consumes 600t of fuel.

First of all, that's a lot of fuel for a test stand.

Second, at 6 engines that's 3,600t of fuel.  I can't think of a 6 engine configuration that will have that kind of tankage.

So from that I would guess it was not full throttle.

But anywhere in any gravity well, one wants max thrust for any conceivable burn, up to the point where the load is somewhere north of 3Gs.

So a 15 minute burn doesn't fit any burn profile I can think of.  So perhaps it's "let's see what the wear looks like if we burn as long as the test stand can do it" margin test.

I might see if I can make a model of a Starship v3 (2300t of propellant) starting with six RVacs at 100% then throttling down and/or cutting off to keep acceleration to a couple of G, with one sea-level Raptor running at 50% throughout for gimbaling.

The lower bound (9 engines at 100% power) is 6 minutes and the upper bound (4 engines at 50%) is 28 minutes, so it feels like there might be solutions with around a 15 minute total burn.

[steveleach]

At full throttle, one engine at 670kg/sec in 15 minutes consumes 600t of fuel.

First of all, that's a lot of fuel for a test stand.

Second, at 6 engines that's 3,600t of fuel.  I can't think of a 6 engine configuration that will have that kind of tankage.

So from that I would guess it was not full throttle.

But anywhere in any gravity well, one wants max thrust for any conceivable burn, up to the point where the load is somewhere north of 3Gs.

So a 15 minute burn doesn't fit any burn profile I can think of.  So perhaps it's "let's see what the wear looks like if we burn as long as the test stand can do it" margin test.

I might see if I can make a model of a Starship v3 (2300t of propellant) starting with six RVacs at 100% then throttling down and/or cutting off to keep acceleration to a couple of G, with one sea-level Raptor running at 50% throughout for gimbaling.

The lower bound (9 engines at 100% power) is 6 minutes and the upper bound (4 engines at 50%) is 28 minutes, so it feels like there might be solutions with around a 15 minute total burn.

Nope, it doesn't seem to work out.

For simplicity I modelled it as 4 phases...

1. Three SL + six Vac Raptors at 100% for 2 minutes, peaking at just under 1.5g
2. Shut down two SL, throttle the third to 50%, keep six RVacs at 100%, for 3 minutes, peaking at just 1.6g
3. Shut down three of the RVacs, keep others at 50%, for 2.5 minutes, peaking at 1.7g
4. Throttle the three RVacs to 50% for another 2.5 minutes (using the remaining propellant), peaking at 1.8g

So about 11.5 minutes to use all the propellant, keeping acceleration under 2g all the way. It just takes too long to burn enough propellant to make a difference to acceleration for it to be worth shutting engines off or throttling down. Any changes I make to the parameters to make it more realistic just use prop faster.

Assumptions...

* Starship v3, three SL Raptor 3s plus six RVac v3s, all with 300t thrust
* Ship dry mass 150t, cargo 150t, max propellant 2300t
* Fuel flow rate 670kg per engine per second

Someone who actually knows how to do this properly should probably check the numbers.

[OTV Booster]

Do we know if it was an R2 or an R3?