totm nov 2023 SpaceX Discussion Thread

[AtomicTech]

Neat!

We're another step closer to seeing S20 and B4 fly!

[CatastrophicFailure]

Hmm... someone mentioned nuclear... could you run a NTR on methane? Or even methane/LOX? Sure, it wouldn't be as efficient as hydrogen, but would surely be better ISP than Raptor could ever do, with the simplicity of using the same propellant(s).

[Rakaydos]

The majority view on NSF is that The Engine to Surpass Raptor is probably a second-generation FFSC methalox engine, using all the lessons and materials developed for Raptor 2 but unrestricted by Raptor's form factor, which was locked in years ago. Particularly optimizing "thrust per dollar"  with the goal to make it so the cost to travel to mars is within the reach of at least a million people who want to go.

 

Also some speculation of Oxygen-rich methalox mixtures.

Edited November 17, 2021 by Rakaydos

[wumpus]

7 minutes ago, Rakaydos said:

The majority view on NSF is that The Engine to Surpass Raptor is probably a second-generation FFSC methalox engine, using all the lessons and materials developed for Raptor 2 but unrestricted by Raptor's form factor, which was locked in years ago. Particularly optimizing "thrust per dollar"  with the goal to make it so the cost to travel to mars is within the reach of at least a million people who want to go.

 

Also some speculation of Oxygen-rich methalox mixtures.

I was shocked by how little delta-v superheavy booster created, so have to wonder if an air-augmented booster would make sense (leave original raptor in Starship).  Not sure how effective air-augmented methalox is, but unlikely to hurt.  Cutting fuel costs seems a long way out, but the was spacex moves, they might be there by the time the engine design is completed.

[Flying dutchman]

4 minutes ago, wumpus said:

I was shocked by how little delta-v superheavy booster created, so have to wonder if an air-augmented booster would make sense (leave original raptor in Starship).  Not sure how effective air-augmented methalox is, but unlikely to hurt.  Cutting fuel costs seems a long way out, but the was spacex moves, they might be there by the time the engine design is completed.

It is primarily designed for rtls though.

[Beccab]

18 minutes ago, Flying dutchman said:

It is primarily designed for rtls though.

Not even primarly, it will always either be RTLS or expended (plus early sea landing tests without recovering the booster). It's designed to have that delta v, as it needs the fuel for one or more boostback burns and has MECO earlier to reduce heat loads on it during reentry (at roughly Falcon 9 altitude, kilometer more kilometer less)

That is to say, more delta v would not help as using it would have more downsides than improvements

Edited November 17, 2021 by Beccab

[JoeSchmuckatelli]

18 minutes ago, wumpus said:

air-augmented booster

I never even thought about something like this - but the Falcon booster stays below 50 miles...  Is there a way to use atmospheric 02 in the initial stage of the launch and landing profile?  I always figured that the amount of time spent in the thickest part of the atmosphere was so short it wouldn't be efficient, but then I'm light on technologies.

[tomf]

3 minutes ago, JoeSchmuckatelli said:

I never even thought about something like this - but the Falcon booster stays below 50 miles...  Is there a way to use atmospheric 02 in the initial stage of the launch and landing profile?  I always figured that the amount of time spent in the thickest part of the atmosphere was so short it wouldn't be efficient, but then I'm light on technologies.

I expect that the fact it flies up in one direction and down in the other would make designing air intakes pretty tough to start with.

[wumpus]

15 minutes ago, tomf said:

I expect that the fact it flies up in one direction and down in the other would make designing air intakes pretty tough to start with.

Since you'd have to operate in vacuum, it would presumably work fine without the extra air (my understanding is that the air isn't an oxidizer, just adds to expansion).  You'd need to close the intakes, but that hardly sounds like the biggest design issue (or they'd be in use already, if only in sub-launched craft).

The whole idea is to scale up the Isp a little bit, and expect the fuel use to scale (more or less linearly) with the Isp (for first stages with reasonably heavy stages above them).

24 minutes ago, Beccab said:

Not even primarly, it will always either be RTLS or expended (plus early sea landing tests without recovering the booster). It's designed to have that delta v, as it needs the fuel for one or more boostback burns and has MECO earlier to reduce heat loads on it during reentry (at roughly Falcon 9 altitude, kilometer more kilometer less)

That is to say, more delta v would not help as using it would have more downsides than improvements

I'll have to get realism overhaul up and running (now that KSP development is over) and figure out what a 3-stage starship would be like.  First stage would be air-augmented RTLS, second stage would be starship-like, but only as fast as it can go without heat tiles (ideally landing in Florida after taking off in Boca Chica), and finally Starship (now starting with a higher delta-v).

[JoeSchmuckatelli]

37 minutes ago, tomf said:

I expect that the fact it flies up in one direction and down in the other would make designing air intakes pretty tough to start with.

Yeah - now that I've had time to read a bit 

"It might be envisaged that such an increase in performance would be widely deployed, but various issues frequently preclude this. The intakes of high-speed engines are difficult to design, and require careful positioning on the airframe in order to achieve reasonable performance – in general, the entire airframe needs to be built around the intake design. Another problem is that the air thins out as the rocket climbs. Hence, the amount of additional thrust is limited by how fast the rocket climbs. Finally, the air ducting weighs about 5× to 10× more^{[citation needed]} than an equivalent rocket that gives the same thrust. This slows the vehicle considerably towards the end of the burn"

Looks like it won't be a match for SX /SS

[cubinator]

1 hour ago, CatastrophicFailure said:

Hmm... someone mentioned nuclear... could you run a NTR on methane? Or even methane/LOX? Sure, it wouldn't be as efficient as hydrogen, but would surely be better ISP than Raptor could ever do, with the simplicity of using the same propellant(s).

It was calculated some time back that the regular propellants in a Starship would give more delta-V with NTR than hydrogen, due to density. 

[JoeSchmuckatelli]

Unless, of course, they redesign the booster with several side mounted / circumferal air augmented boosters replacing the outer raptors for lift and keep three gimbaling raptors for landing? 

[mikegarrison]

7 hours ago, JoeSchmuckatelli said:

You don't rename the engine because you got better at building it.

Names are for marketing, and you can rename something with no change at all if you think it will help the marketing.

[Flying dutchman]

2 hours ago, Beccab said:

Not even primarly, it will always either be RTLS or expended 

Thats what I meant by primarily. 

[sevenperforce]

19 hours ago, tater said:

A definite taste of N1 with the engine-bell-hugging shield, although presumably without the doesn't-actually-work bits.

I am sure @kerbiloid appreciates. I suppose some design choices are made because they are just good.

17 hours ago, mikegarrison said:

On 11/14/2021 at 1:22 AM, tater said:

The GSE on the launch table seems to be rigged for starting the outer engines. That just the outside ring of fixed engines. Not never restarted, not restarted in flight. They don't gimbal, and once the booster hits MECO, the next time they are used is the next liftoff. The best part is no part, leave the igniters on stage 0.

I have no idea whether this applies to a Raptor engine, but I will mention that sometimes airplane engines operate close enough to the flameout margin that they turn the ignitors on in flight. It's much easier to restart a flame that partially goes out than to restart an engine after the flame is completely out.

Raptor uses a blown-plasma augmented spark igniter. Well, two of them. They are quite small and screw directly into the side of the combustion chamber. There is no TEA-TEB being squirted up into the combustion chamber through the engine bell, as with the ground-started Merlin 1D.

Plus, Elon says there will be additional close-out covers added to the  outside of the engine skirt, so it wouldn't make sense to have ignition from the GSE.

17 hours ago, tater said:

For Raptor from what he has said (Tim Dodd interview/tour), it sounds like the Rboosts are simpler because they don't throttle (much?), don't gimbal at all. SL are what we have seen, throttle to ~40%, gimbal. And the vac engines that they have right now that also work at SL (no gimbal, unsure on throttle).

I think lacking the gimbal mount probably saves weight, but doesn't make any difference to the rest of the engine. The RBoosts have a different, simpler, higher-thrust set of guts because they don't throttle.

The RVacs can definitely throttle. They have to be able to throttle in order to provide pitch and yaw by differential thrust. 

4 hours ago, Rakaydos said:

The majority view on NSF is that The Engine to Surpass Raptor is probably a second-generation FFSC methalox engine, using all the lessons and materials developed for Raptor 2 but unrestricted by Raptor's form factor, which was locked in years ago. Particularly optimizing "thrust per dollar"  with the goal to make it so the cost to travel to mars is within the reach of at least a million people who want to go.

Also some speculation of Oxygen-rich methalox mixtures.

They have a very good oxygen-rich preburner so they should have no trouble scaling it up to make it an ORSC engine, and ORSC gives you a slightly denser fuel mix to boot. Perhaps using only a single preburner and turbopump would make the engine lighter.

But then you lose three main advantages of FFSC: lack of ox/fuel hot seals, variable mixtures and efficiently-sized preburners, and gas-gas combustion efficiency.

[sevenperforce]

4 hours ago, wumpus said:

Not sure how effective air-augmented methalox is, but unlikely to hurt.  Cutting fuel costs seems a long way out, but the was spacex moves, they might be there by the time the engine design is completed.

The booster needs higher T/W more than it needs higher efficiency. Air-augmentation can increase static thrust a little but the thrust multiplication really only kicks in once you're high-subsonic or supersonic, and by that time Superheavy will be outside of half the atmosphere and it will have lost about a quarter of its liftoff weight.

Also, you can't very well just add a duct system to Superheavy as it is. The length of an air augmentation duct needs to be on the order of its diameter in order to allow sufficient space for air-exhaust mixing and expansion.

What you could do -- I suppose -- is create ram air inlets about halfway up the LOX tank with ducts that penetrate the LOX tank and open at outlets between the inner and outer ring of Raptors. Just like a boat-tail bullet, Superheavy has a region of low pressure at its base during flight, low pressure that will cause parasitic drag and suck plume recirculation up between the engines, robbing them of some of their exhaust efficiency. If you had a ram air duct pushing compressed air out there, it would mix with the engine plumes and increase efficiency, and also reduce parasitic drag. But I am guessing that the added weight and the structural issues in the LOX tank wouldn't be worth it.

 

3 hours ago, cubinator said:

It was calculated some time back that the regular propellants in a Starship would give more delta-V with NTR than hydrogen, due to density. 

Yeah, the mass ratio is just so so different.

I wonder what would happen if you moved the common bulkhead down and kept the SL Raptors in the  middle but replaced the RVacs with methane-based NTRs. You would lost some mass ratio but would the methane nukes make up for it?

3 hours ago, JoeSchmuckatelli said:

Unless, of course, they redesign the booster with several side mounted / circumferal air augmented boosters replacing the outer raptors for lift and keep three gimbaling raptors for landing? 

A small spaceplane with air-augmented Raptors (preferably variable-mixture-ratio) would work for an SSTO. All the better if you carried extra methane and transpiration cooling, because if you did it properly the transpiration cooling system could double as a fuel injector for a shock combustion ramjet....

[JoeSchmuckatelli]

23 minutes ago, sevenperforce said:

air-augmented Raptors

How do you air-augment a Raptor?  

[tater]

 

First orbital flight January

Working on a large space telescope.

[StrandedonEarth]

49 minutes ago, JoeSchmuckatelli said:

How do you air-augment a Raptor?  

Oh, we have plenty of those...

[JoeSchmuckatelli]

Also "we intend to have a high flight rate next year"

'Hopefully a dozen... maybe more'

 

Huzzah!

 

46 minutes ago, StrandedonEarth said:

Oh, we have plenty of those...

Fine, Smart ...

...

Augmented.

 

Edited November 18, 2021 by JoeSchmuckatelli

[sevenperforce]

1 hour ago, JoeSchmuckatelli said:

How do you air-augment a Raptor?  

Wrap a duct around it.

Raptor is a fairly decent engine for air augmentation. It has a high O/F ratio so its propellant is reasonably dense, but it has a high specific impulse so it can operate in AA mode up to a theoretical maximum of 3.7 km/s. It has a terrific T/W ratio which helps counteract the extra weight of the duct system. It's just a little oversized for air augmentation purposes. A mini-Raptor with a thrust closer to that of the Merlin 1D would work better.

[JoeSchmuckatelli]

1 hour ago, tater said:

 

First orbital flight January

Working on a large space telescope.

This really is worth listening to - the part about why steel over carbon fiber is great, too. 

"Stainless Steel and I should get a room, or something"

(The CC feed is a hoot, btw).

 

... The part where the SX 'non' enthusiast came on to question Starlink's adverse impact on astronomy was really well done.  (She had that 'gonna get a glib corporate answer face'... and then he knew the main risk and addressed it head-on)

He does have to deal with his share of 'kook' questions - but overall its a good watch.

...

I wonder if Jeff can explain his own rocket nearly so well...

(BO better be taking notes).

Edited November 18, 2021 by JoeSchmuckatelli

[tater]

Hopefully a dozen SS launches next year.

Plan is a highly insulated prop depot SS. Fill it, then Lunar (or Mars) ship docks to it and fills up in one go.

[JoeSchmuckatelli]

18 minutes ago, tater said:

Plan is a highly insulated prop depot SS. Fill it, then Lunar (or Mars) ship docks to it and fills up in one go

I found that part to be a 'loose' plan.  As in 'we have a LOT of technical details to work out, but this is our current best-guess'.

[tater]

That's always been the obvious solution, particularly once vehicles actually have crew on them.