Posts by John Robson

Re: "subscriptions that enhance the EV experience"

Sometimes it's actively cheaper not to have to make choices on the production line.

If you suddenly can't afford that new car then they can sell it to someone else who really wanted heated seats.

If you buy a second hand car then a low cost, without visiting a dealer and giving them your car for a week, upgrade might be just the ticket.

If you're getting a high performance model then yes, the mass matters - but that's not for fuel efficiency, anything but in fact.

Re: Enough already

So you drive without rest, and with a full bladder... Why not drink the wine on route as well?

Re: "subscriptions that enhance the EV experience"

Well when you put it like that - I mean, how much does a seat heater and relay weigh?

Must be on the order of a few grammes.

Do you keep that spare wheel in the car, or the puncture repair kit, or the warning triangle, the parcel shelf, the rear seats (given that the vast majority of journeys are single occupant).

Do you ever carry a jumper, or wear clothes?

Do you carry any drink or snacks?

The fuel consumption argument is complete hogwash and you know it - you just can't think of a good reason to be able to upgrade your vehicle after purchase.

Re: "subscriptions that enhance the EV experience"

Primary functions - I'm with you. Comfort... consider it a discount for not using those features rather than a charge for using them.

Re: "What else are you going to do while waiting for it to charge?"

A handful of times a year I make a journey that requires DC charging - that number will drop with my next vehicle, simply because the range available nowadays is a significant uplift from ~three years ago.

Parasitic load is pretty much irrelevant on a long journey (the only time when charging stops are needed)

Moving air out of the way takes ~15-20kW at motorway speeds.

Adding tens of watts for a streaming setup will make no measurable difference.

Where it *is* relevant is while the car is parked and otherwise idle - And a few solar cells would be a good addition to *any* car (EV or ICE) to maintain the 12V system between uses.

And starship/superheavy seemed to deal with that acoustic energy... The structural margins were quite impressive (see the backflips).

The damage was primarily to the pad, not the booster... the ship is so far away that it's not at much risk.

Re: Car

The cameras were far more expensive and valuable than the car...

Re: I suspect

Their data suggested that the concrete would survive one launch.

As it turns out that data was wrong.

Current theory is that the ground under the foundation is what gave way... just let that sink in (pun absolutely intended) for a moment.

Re: I suspect

Well it never separated because it never got to that point - that requires no questions at all.

It lost control because they lost hydraulics, which are already obsolete - they aren't even on the next booster.

Loss of engines, not really something they care about.

They should *really* care about the FTS, and I expect we'll have some exciting tests of that at ground level to verify it, because the rocket had *far* more structural strength than had been anticipated.

They also need to be concerned about the rapid excavation and significant ballistic trajectory of the excavated material - though again, there is no intention to launch without a rather different pad surface - a (rather substantial) steel "upwards facing" shower head. That should survive much better, but a static fire sequence might be required to demonstrate the performance.

Re: Good thinking that man

Their models showed that the concrete could survive one launch - they were wrong.

Current theory is that the thrust from the engines likely compressed the ground under the concrete, leaving it unsupported and therefore able to crack.

Of course the fact that it ran for 5-6 seconds on the pad didn't help, that's far longer than would typically be seen.

Re: Good thinking that man

Well we know they have slowed production because they can't use them fast enough.

Re: Good thinking that man

The FTS should have done more - it clearly needs an upgrade. 40 seconds is *far* too long between termination and disintegration.

The RUD was caused by the RTS, which was triggered because they had lost gimbal control due to hydraulic power unit failures.

They had had some engine issues (three were stopped rather than ramping to full power before the launch, others lost communications later), but they don't yet have evidence that there was any damage from the concrete which is pretty wild.

Re: Good thinking that man

It's not looking bad in terms of reliability - despite having large chunks of concrete thrown at them the vast majority of the engines were still generating alot of thrust.

When you're in the process of designing something, do you consider the final product to be unreliable?

Here we have a company with more than a little experience in building rocket engines, building a rocket engine - I therefore need more than "oh there are some issues with prototypes" to declare it unreliable.

Even the flight tests we have seen have had good success:

- Star hopper (July 2019)

- Star hopper (August 2019)

- SN5

- SN6

- SN8 (failure from a loss of methane pressure in header tank)

- SN9 Finally an engine issue. One engine didn't relight - (now changed process so that they light three and shut one down)

- SN10 (helium ingestion from the fuel tank caused a hard landing)

- SN11 Methane leak in an R1 caused a hard start - (now changed to the R2 which has substantially less opportunity for leaks)

- SN15

21/23 engines operated correctly, with both failure cases severely mitigated.

When we get some decent news out about S24/B7 I expect we'll find that the booster was missing substantial pieces of the failed engines - and there were still no major (i.e. cascading) failures.

Is it human rated - no, is it viable as a launch system... I'd say yes.

It wasn't an engine failure which caused the RUD

Re: Most powerful

Saturn V was ~35MN (no question about it's launch status)

N1 was ~45MN (It certainly launched, though it didn't get as far (distance or time wise) as this test)

Superheavy is rated at ~75MN

Given that the stack mass is ~5,000kg, it must have had over 50MN to lift off (it didn't scream off the pad, so I'd guess it was closer to 60M than 70MN - I've not actually looked at the acceleration yet)

Re: Good thinking that man

"Well yeah, they tend to go off bang, so mass production is important. It's not a good conclusion to say they'll be making this version of the Raptor engine a lot. They may finally figure out that they need to go back to a clean white board again and start something new that will work consistently and reliably enough to put on a manned rocket."

Really?

How many have gone off with bang when you exclude tests to destruction (where the aim is to make it go bang).

The raptor 2 isn't an unreliable engine... Can't quite call it merlin levels of reliability yet, because we haven't seen any non-prototype flights.

Re: Good thinking that man

Only in the numbers, not in the accounting practice.

There are going to be alot of these engines made... they are designing them for mass production for good reason.

Re: Good thinking that man

They *are* designing and building these as a mass production item.

To launch enough people and materials (not in that order) to colonise mars is going to take a huge number of launches - They are looking at sending a *thousand* starships to Mars in a transfer window... that's a *huge* number, and each ship will need ~8 launches of a superheavy (seven with fuel tankers) - even with significant reuse, it's still going to be a lot of engines that need to get made.

The R2 is designed for manufacture in a way that other engines haven't been, last year NASA stated that spaceX were producing seven Raptor 2 engines each week... Compare that with the manufacturing rate for the BE4, or the RS25e.

They are deliberately choosing to run a "hardware rich" development cycle - which results in very visible test results, rather than hiding the calculations and simulations and running those exhaustively and then tentatively (because you're afraid of breaking it) firing a prototype. SpaceX already have the next hardware ready to test, so it doesn't matter if you blow this one up (assuming you get good test data whilst you do it)

The design is to put the water for the not quite deluge water system through the plate, so that the plate is cooled and then the water is put in the way of the flamey bit.

Re: Good thinking that man

Yes.

So how much of the cost of your canned beverage is the design cost of an aluminium can?

The marginal cost is the cost to make one engine for spaceX now. The amount already spent on design is not relevant to the *cost* (rather than price) of the launch.

Re: Good thinking that man

So in that case all the buildings must be fully allocated to the first engine, and all the other engines get a free ride?

When do you stop amortising, or rather when do you plan to stop amortising.

If you intend to produce a million of something then you don't say after 100 that 1% of the tooling costs are attributed to each thing.

The rest of the stack *is* mostly stainless steel - perfectly capable of holding both oxygen and methane at cryogenic temperatures (just one reason they aren't using hydrogen).

Yes there are ancillaries, but the turbo pumps are part of the engine. There are a handful of pressure tanks, and plumbing - but the vast majority of the stack is two massive propellant tanks - You might have missed that I allocated ~$10m to the "rest" of the rocket, not alot of that is taken up by steel costs.

Yes - Musk is a natural optimist, but by aiming for ambitious goals, even if he falls short he's still ended up with more progress than others.

However since the prototypes of the raptor 1 were under $1m four years ago... I don't think the final price per engine (remember the simplified design of the R2, and the focus on design for manufacture) will be $2.5m - It might end up at $300k rather than 250... but that's still substantially less the $100m for the RS25e

"NASA announced May 1 it had awarded a contract to Aerojet valued at $1.79 billion to produce 18 RS-25 engines."

Re: They may call it a success...

Yes, but given that it looked like there was a serious hydraulic failure, and given that the electric gimbal is substantially simpler than the hydraulic gimbal... I wouldn't worry about the gimbal capability.

The count of failure modes probably goes down.

Re: They may call it a success...

I'm not entirely convinced that the RTS wasn't fired substantially before the eventual explosion - punching a couple of holes in the tanks, but the tanks simply held together far better than might have been anticipated.

Re: They may call it a success...

Very different failures.

And do remember that SpaceX have experience with running 27 engines at a time already...

Re: Good thinking that man

$3m each - you got a citation on that cost?

The target price (and I am fully aware that we aren't there yet) is ~$250k.

In 2019 the marginal cost of each engine (i.e. the cost to build one, ignoring the design costs etc) was stated to be "approaching $1m".

I suspect that R2 is rather cheaper than R1, but they are still (almost) prototypes, so $1m is probably too high, but certainly not by a factor of 4.

The rest of the stack is mostly steel pressure vessel, so is probably on the order of $200k for materials.

I'd be expecting ~$50m as a first order approximation for these prototypes (the ~$900k of fuel is less than a rounding error)

A fully expendable, fully developed, ship would have ~40 engines ($10m planned) so probably an all up cost of $15-20m

Re: Good thinking that man

They made an engineering decision to try to do without - partially because of the challenges of the local environment, partly because of the eventual design goals for SH/SS.

In the same manner they decided to leave the grid fins extended during ascent - the potential issues resulting from the technically unstable centre of lift being outweighed by the benefits of reduced mass and complexity.

There are quite a few decisions they make which might look odd, but without being in their meetings it's very hard to say that they're mistakes.

They thought the pad would survive one launch - they were wrong - but the rest of stage zero has held up very well indeed from what we can see. There are some dents in the outer walls of the tank farm (remember there is a serious amount of insulation between that dented wall and the internal wall), and there is going to need to be some more concrete work (I hope that the base of the pillars can be tied back together without having to dismantle the OLM entirely), and then the actively cooled steel base/diverter will be added.

Given the amount of debris which was flying around, I was somewhat surprised that so *few* engines had issues - and some amateur analysis I've seen suggests that one of the failures was in the hydraulic unit (which is already an obsolete component)

merely 1.2?

800cc used to be common.

I far prefer having an electric motor though, just need more small cars now that the technology is well established (but as your "mere 1238" comment shows that's a long standing issue)

Re: Those are rookie numbers

It could - but I imagine that they need to be able to perform an emergency landing with basically everything they took off with.

The difference is so thin that I suspect it's closer to an engineering decision (given this max takeoff weight this is the most we can ever be expected to land with, so we'll engineer to that) than a fundamental limit on landing performance.

Re: Those are rookie numbers

Yes - it's still very energy dense.

But if your engine weighs as much as your fuel (easily possible in many applications)

Sticking with aviation... 737 Max engines (random newish plane) are about 4 tonnes each, and they carry up to ~20 tonnes of fuel. So that's actually probably 1/3rd engine and 2/3rds fuel (don't usually fully fuel an aircraft)

They also tend to be able land with just a shade under max takeoff weight - Modern Airliners suggests the difference is only 4 tonnes, and they burn (Quora, sorry no good source) about 8 tonnes of fuel during takeoff (don't know how far they include as takeoff). So the weight difference is pretty small - I imagine that the max landing weight is merely an engineering challenge.

There is no reason that the batteries should take any "aircraft time" to recharge - you simply load on replacements as you do cargo and charge at leisure.

And of course that's ignoring the other downsides of liquid fuels.

Re: Those are rookie numbers

So after just 25 cycles the battery has already beaten the liquid fuel.

You could have just gone for matter itself which has an energy density of 1.5e13Wh/kg.

Your precious petrol has a couple of serious disadvantages

- you can only access 30% of that energy usefully

- you need a fairly heavy conversion engine

So it's not actually 12kWh/kg if you want to use it in a vehicle... and it gets worse and worse with a small fuel tank.

Particulalry since one of the failures was in one of the central cluster of three.

I wonder if they'd have lit three of the "second ring" instead, or if their restart supplies are tied to individual engines.

Re: Starship hasn't had the most successful history?

Quite possible - and that's sort of why they have an interesting actively cooled flame diverter ready to install.

So the "not quite a deluge system" water will go via the flame diverter to stop it being melted.