SpaceX Tests Raptor Engine

Isolation of U235 is not cheap, and likely never will be.
>but da ore is cheap
Kill yourself my man

U-238 turns into Pu-239

...

Breeding Pu-239 is generally accepted to be several times more expensive than isotopically separating U-235.

And you're filling a thread about exciting real news with tangential crackpot garbage about how nice it would be to live in a world where nukes were free and nobody minded if you set them off.

>Fucking Magic
Exactly. Call us when you invvent magic.

This test only involved a small-scale model, and the engine itself has nothing revolutionary, the only new thing being that it's fueled by methane, a fuel with inferior performances than hydrogen. As for the "it will be yuuuuuge part", making large engines is never usually a problem, paying for them is, so I'll take this seriously when 70% of SpaceX's earning won't come directly or indirectly from the government.

Another non-event brought to you by Elon Entertainment, Inc.

>nukes are so expensive, the US could never afford to make tens of thousands of them

you are dumb

This gets my juices flowing.

solar sails for infinity ISP

>This test only involved a small-scale model,
Full-scale engine.

>and the engine itself has nothing revolutionary,
Highest combustion chamber pressure ever achieved (thanks to the multistage full-flow staged combustion turbopumps). First fluid-bearing (i.e. non-wearing, for long-life reusability) turbopumps on a large-scale rocket engine. Fast-response throttleability for flyback landing. Highest specific impulse achieved with a hydrocarbon fuel.

>the only new thing being that it's fueled by methane, a fuel with inferior performances than hydrogen.
A fuel with inferior specific impulse, but superior density impulse and thrust-to-weight, along with handling advantages such as being liquid at the same temperatures as oxygen, making space storage much more feasible.

This is probably the first rocket engine suitable for airliner-like, gas-and-go reusability, and the first rocket engine suitable for use after long trips in space without severely reduced performance figures.

>From 1940-1996, the United States spent a minimum of $5.5 trillion on its nuclear weapons program.[2] The lack of data for some programs and the difficulty of segregating costs for programs that had both nuclear and conventional roles mean that in all likelihood the actual figure is higher. This figure does not include $320 billion in estimated future-year costs for storing and disposing of more than five decades' worth of accumulated toxic and radioactive wastes and $20 billion for dismantling nuclear weapons systems and disposing of surplus nuclear materials. When those amounts are factored in, the total incurred costs of the U.S. nuclear weapons program exceed $5.8 trillion.[3]
>...
>The amount spent through 1996—$5.5 trillion—was 29 percent of all military spending from 1940 through 1996 ($18.7 trillion).
>...
>[2] Except where noted, all cost figures in this paper have been adjusted for inflation and are expressed as constant fiscal 1996 dollars.
>...
>[3] A subsequent estimate based on Atomic Audit and using its methodology, found that costs through 2005 were $7.5 trillion in adjusted 2005 dollars.

-- nti.org/analysis/articles/costs-us-nuclear-weapons/
>Seen in the year-by-year breakdown listed below, the total amounts (in nominal dollars) that NASA has been budgeted from 1958 to 2011 amounts to $526.178 billion
>...
>...when measured in real terms (adjusted for inflation), the figure is $790.0 billion

-- en.wikipedia.org/wiki/Budget_of_NASA

Nice would-be specs which have nothing to do with the prototype tested.

Im sure you have the numbers that shows that all other launch providers dont get most of their capital from government-related launches.....

Ah yes, the old reusability meme, number one obstacle that prevented us from going to Mars ever, and the claim that these very specifics internal details are any relevant. Had a good lol, m8.

>the old reusability meme, number one obstacle that prevented us from going to Mars ever
Well, yeah. Number one obstacle for doing anything manned in space is high orbital launch costs. The main reason for high orbital launch costs is the lack of efficient reusability.

Arianespace gets annual subsidies in the vicinity of €100M. Their annual revenues are around €1.4B, about 90% of that are commercial launches. So that's about 8% government financed.

Well, that sounds like a heaping load of bullshit. What your source?

*17%

I'm guessing this:
>Arianespace gets annual subsidies in the vicinity of €100M.
...is direct, open, specific, as-labelled operating subsidies for commercial launches of Ariane 5 alone.

Not counting subsidies hidden as government launches paying higher prices, or vehicle development (which is largely funded up-front by government, at a lavish standard and with no expectation of repayment), land giveaways, services provided free of charge, money provided as "investment", non-Arianespace-specific subsidy programs, etc.

Unlike SpaceX Arianespace publish financial statements. Their revenues are no secret.
The ESA subsidies are also well known. They vary from year to year. Sometimes Arianespace makes a profit then they get nothing. Sometimes they don't then they get subsidy. The €100M figure is an average and well known in the industry. The rest is primary school level math.

Exemplary subsidy numbers can be found here:
seradata.com/SSI/2015/05/arianespace-revenues-up-41-and-it-even-makes-a-profit-after-its-usual-cash-injection/
parabolicarc.com/2012/04/25/arianespace-makes-profit-with-large-esa-subsidy/

>subsidies hidden as government launches paying higher prices
I already accounted for that in the 17% figure by taking 10% off the revenues and adding it to subisidies. Also, unlike in the US, European government launches aren't mandated by law to be launched only by a European LSP. The German DoD, e.g., will launch recon sats with SpaceX. So Arianespace wins government contracts by competitive bidding.

>or vehicle development (which is largely funded up-front by government, at a lavish standard and with no expectation of repayment)
Arianespace buys the launch vehicles. So what's in ESA's budget as expenditure for launcher development comes via Airbus Safran Launchers as costs to Arianespace. And the costs of the Soyuz rocket come as revenue for the manufacturers of the Soyuz rocket. So that's completely accounted for.

>land giveaways
what?

>services provided free of charge
name them

>money provided as "investment"
what do you mean?

>non-Arianespace-specific subsidy programs
Which should by accounted to Arianespace's costs why exactly?

>Unlike SpaceX Arianespace publish financial statements. Their revenues are no secret.
But they are nonsense numbers from la la land. Arianespace is owned by its subsidizing governments and by its suppliers, which are also subsidized. As a corporate entity, its expenses are the same as its profits: payments to its owners.

You would expect it to operate on a near-zero, but non-negative "profit" basis until right before it was shut down.

>You would expect it to operate on a near-zero
And that's exactly what it does. Arianespace gets these ~€100M subsidies so that it breaks even.
No LSP can survive without government money. But Arianespace is by far the least subsidized.

>Arianespace is by far the least subsidized.
You're talking about Arianespace the corporate legal entity, not Arianespace, the overall system that produces and operates launch vehicles.

The corporate entity buys heavily-subsidized vehicles from other parts of the system, and rents heavily-subsidized facilities, and is subsidized directly itself.

Reasoning from the direct subsidies alone leads to vacuous arguments.

How would your argument stand if Arianespace got its vehicles provided to it for free? Would you not count these free vehicles as a subsidy? Why is it different if the vehicles provided to it are just very heavily subsidized?

>Of the $5.8 trillion, just seven percent ($409 billion) was spent on developing, testing, and building the actual bombs and warheads.

IT SAYS IT RIGHT IN UR FUCKING ARTICLE
Just 7 percent was for the bombs! And thats starting from scratch, tens of thousands of fancy military nukes that have to be able to sit around for decades, be durable, fission/fusion/fission bombs etc.

>nukes alone make a spaceship that uses nukes
retard, a nuclear powered spaceship will cost at least as much as nukes AND their delivery systems.

energy in general

>Number of employees 321

Thats really all you gotta see about arianespace to know whats going on there.
They are just the commercial entity to sell launches to the private sector.

Just by going from public to private, you achieve cost reductions of over 10 fold.
Then add on automation, the use of computers, 3d modelling in design, etc

You would have to be insane to think building NPPP vehicles would cost hundreds of billions.

You would have to be insane to think that NPP would just work, without a lengthy development program and a huge number of open-air tests of very dirty low-yield fission bombs, or that providing adequate security for a private system using so many bombs is even feasible, let alone cost-effective.

Compare: a single-use NPP vehicle, which takes 1500 tons payload to Earth escape, vs. a fully-reusable chemical rocket which runs on LOX/LNG and takes 100 tons to LEO (and therefore needs maybe 50 launches to assemble a 1500-ton-payload departure).

50 loads of LOX/LNG, even for something triple the size of Saturn V, will cost far less than 800 nuclear bombs, and the development of the highly-reusable chemical rocket will be far simpler, and more incrementally beneficial, than that of the NPP vehicle.

I do think it's worth developing advanced nuclear propulsion, but not for use on and around Earth.

>The corporate entity buys heavily-subsidized vehicles from other parts of the system
prove it

>rents heavily-subsidized facilities
As does every LSP. It's not like 6 different active launch complexes plus 30 inactive plus 3 pending reactivation in Florida and 5 different active launch complexes plus 35 inactive in Vandenberg are any cheaper to operate and maintain or even remotely as cheap for the US taxpayer as the the 3 active launch pads (just pads, not complexes), 3 inactive and 1 under construction in Centre Spatial Guyanais are for European taxpayers.

>is subsidized directly itself.
Yeah, by ~€100M annually. Which is peanuts compared to what the US, China, Russia, India or Japan do.

>Just by going from public to private, you achieve cost reductions of over 10 fold.
>Then add on automation, the use of computers, 3d modelling in design, etc
That's not an argument supporting nuclear over chemical. If anything the reduction might be enough so that the huge capital costs make chemical feasible for private entrepreneurs but still leave nuclear as too expensive.

...

>>The corporate entity buys heavily-subsidized vehicles from other parts of the system
>prove it

>I am not interested in conversing reasonably. I view this as a contest and intend to proceed adversarially, despite the lack of a referee or impartial judge, and position myself as both judge and opponent.

They do integration and launch, too. And they do it very well. For example the Soyuz never failed when operated by Arianespace. It did though when operated by Russia. Arianespace buys its launch vehicles. These costs are being subtracted from their revenues. Bottom line they lack on average about ~€100M annually to break even, which is why they get that from ESA.

Sounds unrealistic, unless there are more investment, a big amount. This going nowhere.

>make unsourced claim
>refuse to provide proof when asked for
>claim other side isn't interested in reasonable conversation instead
Bad form, Peter. Bad form, indeed.

In 20 years the solar system could be ours.

>Violating the NAP by not letting me own recreational nukes

That the consolidated European aerospace industry (Airbus), and the production of launch vehicles in particular, is heavily subsidized and only semi-private at most, is common knowledge and not disputed by reasonable people.

Go be garbage somewhere else.

This

Do you remember what the cost and schedule predictions of the space shuttle looked like before it actually got built?

...

...

The shuttle was a job project from the start. At least it got the russians to abandon their moon program.

> a single-use NPP vehicle
Why is it single use, when with it's massive Isp & thrust its taking that payload to mars then returning? And ofc a vehicle that small would just be the first test vehicle, you can scale it up significantly without increasing the fissile material needed.

>(and therefore needs maybe 50 launches to assemble a 1500-ton-payload departure).
Building a vehicle in one piece in a ground based shipyard will always be vastly easier and cheaper than building it in orbit.

>and a huge number of open-air tests of very dirty low-yield fission bombs
These nukes would be very clean, using a minimum of plutonium, as they would be optimized for cost, not for size/yield.
The dirtiest part of nukes have always been the fallout from dirt kicked up.

Sure yes I agree that for the foreseable future there won't be any nuclear pulse vehicle made, and the private sector will never be allowed to engage in the regulatory free work needed to make it cost competitive/superior to conventional vehicles.
But a man can dream can't he?

Have you heard about Nuclear salt-water rocket.

it really doesn't matter what "engine" they use at this point, the problem of this shitpiece always been the fuel tanks

still waiting for proof of the original claim

You dont need to enrich it fully.Ten percent ot tweenty percent enriched uranium gives you the solar system

This guys know stuff.Another advantage is methanes ability to self pressure the tanks.So we ditch the helium bottles.

>Number one obstacle for doing anything manned in space is high orbital launch costs
That's nowhere near true. Payloads usually cost between 5 and 10 times the cost of the launch. This is especially true for scientific/human spaceflight payloads. Communication sats usually have a standardised bus and quasi-standardised equipment (communication, propulsion, etc), while you have to develop everything from zero otherwise. Development of all subsystems and testing is what costs, by far, the most money and demand the most man-hours.

So, no, cost of launcher is really not the main worry for a manned mars mission. All the musk is ever going to achieve is making life slightly more comfortable for boring telecom multinationals such as SES or Intelsat thanks to a moderate discount on GTO launches.

But that wouldn't sell very well on twitter

Not him, but SpaceX claims to have a backlog of 70 launches for 10 billion $. That's about... 146 millions $ per flight. Very far for the 70 millions or so that are advertised. How is that possible? No rocket science, the government buys spacex launches at a monstruous prize so that spacex can stay afloat on the commercial market. It's indirect subsidies. Then you have direct subsidies, like US states giving elon free money so he builds his factories there.

And despite all that, they barely manage to make any profit. At their current commercial prizes, SpaceX wouldn't last a month without subsidies.

>prizes
(prices* of course)

Nigga, that's dumb.
The water is going to put out the flame.

Nope salt water has ten percent enruched Uranium and that undergoes fission and kaboom just near the nozzle.Water evaporates and is so fast that it leaves the solar system forever.Now you got other cycle and dont do this at home.

>Why is it single use, when with it's massive Isp & thrust its taking that payload to mars then returning?
If it returns, then it has to blow up that many more bombs in and around Earth's atmosphere.

>Building a vehicle in one piece in a ground based shipyard will always be vastly easier and cheaper than building it in orbit.
Why? It's way easier to move big things around in zero-g.

And it's not "building", it's "assembling". Docking. Snapping together.

>These nukes would be very clean, using a minimum of plutonium, as they would be optimized for cost, not for size/yield.
No, they would be very dirty, because they're designed for low yield.

You seem to have some very confused ideas about nukes. It's the primary stage that's the most expensive, made of plutonium, tritium, and high-precision explosives. The fusion stage is made of cheap stuff like enriched uranium and lithium deuteride, and it's set off by the overwhelming energy of the primary, so precise construction isn't nearly as important.

Plutonium-239 is itself a very nasty radioisotope you don't want to release, so the first requirement for having a clean nuke is lots of fusion generating lots of neutrons to make sure the Pu-239 all undergoes fission (although fission fragments are no picnic either, so you want fission to provide as little energy as possible). The dirtiest bombs are generally the smallest-yield ones, since they can't go below the minimum size of a primary or make much use of fusion, and achieve small yield by being inefficient (having only a small amount of their plutonium undergo fission).

I know. In reality NASA is SpaceX's most important "customer" by far.
The thing is Arianespace is far less dependent on government launches. They're the ones most aligned towards the commercial launch market, precisely because European governments could never spend that much money on space. Plus European government payloads are not restricted to use European launchers only. They've used European, American, Russian and Indian launchers so far, which forces Arianespace to remain competitive. And they are and have been for decades. With a 50% share of the commercial market, which they consitently hold, they're market leader.

>>Number one obstacle for doing anything manned in space is high orbital launch costs
>That's nowhere near true. Payloads usually cost between 5 and 10 times the cost of the launch.
First of all, that's an exaggeration. Secondly, payloads only cost so much because launch costs so much.

To suggest that you could lower launch costs to thousands instead of millions of dollars, and increase launch availability from "order it two years in advance and pray" to "order it when they payload's ready, launch it next week", and people would still only launch billion-dollar science projects is absurd.

People would launch cheaply-built stuff into space to test it. They'd set up assembly lines, and launch thousands of copies of things, instead of running a big R&D project just to build one thing.

>then it has to blow up that many more bombs in and around Earth's atmosphere.

No we have aerobraking for the return, so it would need a small fraction of the bombs, and this pusher plate probably makes a good heatshield too.

>lower launch costs to thousands instead of millions of dollars, and increase launch availability from "order it two years in advance and pray" to "order it when they payload's ready, launch it next week",
To claim that this will happen with any chemical rocket is even more absurd tb'h

Medium-term it's a 30% discount *at most*. Sure, this is totally going to make testing irrelevant, and development of highly-critical subsystems such as life support for a manned mission will magically go down as well. Insurance will be made useless, and while we're at it, let's even envision that post-launch costs (which can be 50% of the mission's cost) will decrease too. Why not, the world of Musk fanboys has so little to do with reality anyway.

Launch costs aren't what is preventing us from going to mars.

>Medium-term it's a 30% discount *at most*.
>Medium-term the cost savings on a fully-reusable rocket is the 30% discount negotiated on a launch already coming in November for a rocket partway through its incremental development from expendable to partially-reusable *at most*.
Jesus Christ.

>First of all, that's an exaggeration. Secondly, payloads only cost so much because launch costs so much.
Not that user, but it's not an exaggeration. And no, payloads don't cost that much because of launch costs but because they have to work reliably for many years without any maintenance at all in a very harsh environment which can't be fully replicated for testing on Earth.

Small series production is already being done with comsats to reduce payload cost down to about 2-3 times the launch costs. And that's just manufacture. Operating it over its 15+ years lifetime costs additionally.

The debate is much older than Veeky Forums. Launch costs will only come down with expanded production of launchers. But this will only be feasible with an expanded market for payloads. It's demand driven not supply driven. And it grows rather slowly. If you want space to be more accessible by reduced launch costs the best thing you can do is invest in commercial satellite operations to increase volume there, not launchers as these would follow increased demand automatically. But first there has to be the demand.

>payloads don't cost that much because of launch costs but because they have to work reliably for many years (because of launch costs) without any maintenance at all (because of launch costs) in a very harsh environment which can't be fully replicated for testing on Earth (and we can't access directly for testing because of launch costs).
How thick can you be?

How can there be demand for something that doesn't exist? Every successful entrepreneur builds the product first, and the demand comes later

Is there massive demand for going to space in the world? Yes, make it affordable and it'll happen.

Yeah, how thick are all the experts when random internet guy knows so much better?

>Because of the high cost of spacecraft, a dramatic reduction in launch cost alone will not substantially lower spacecraft program costs. Although launching a pound of payload to LEO currently costs about $3,000, procuring that pound of payload typically costs much more. For example, representative U.S. spacecraft bussess of types first launched between 1963 and 1978 cost between $130,000 and $520,000 per pound dry, including amortized program overhead costs. Procurement of the mission payloads carried on those busses cost about 50 percent more—about $200,000 to $800,000 per pound. Reducing launch costs from $3,000 to $300 per pound of payload, a goal of the Advanced Launch System program, would reduce the total cost of procuring and launching a dry spacecraft (half bus, half mission payload) by less than 2 percent.

>A spacecraft bound for a high orbit or another planet requires an upper stage, which when fueled is typically more than twice as heavy as the spacecraft but costs less. Even so, a payload consisting of a Centaur upper stage (about $2,250 per pound) and a spacecraft weighing a third as much (half bus, half mission payload) might cost from $40,000 to $160,000 per pound.
Reducing launch costs to $300 per pound would reduce the total cost of procuring and launching such a payload by only 2 to 6 percent.

-- Affordable Spacecraft: Design and Launch Alternative, Background Paper, OTA, 1990

Right there, black on white: a 90% reduction in launch costs equates to 2-6% reduction of overall costs.

>how thick are all the experts when random internet guy knows so much better?
"The experts" are often employed to crank out bullshit pseudologic to justify profiteering and big-budget careerism.

>Every successful entrepreneur builds the product first, and the demand comes later
No, every successful entrepreneur builds the product for which there is demand. Like Edison and the light bulb. The unsuccessful ones build the product for which there's no demand. Like the head-mounted toilet paper dispenser.

...

>How can there be demand for something that doesn't exist?
Finding that out is the hard/luck/risk part of innovation.

Also: what kind of trash searches out "expert support" on the internet, cherry picks a bit out of context, and doesn't provide a link to the source?

princeton.edu/~ota/disk2/1990/9003/9003.PDF

The bit you quoted is part of the preamble of the document, framing the problem that spacecraft themselves are currently costly, therefore improving launch costs *entirely without changing anything about the spacecraft* would have a relatively small effect on overall costs.

The document as a whole strongly supports the idea that reduced launch costs can be used to reduce spacecraft costs.

>The document as a whole strongly supports the idea that reduced launch costs can be used to reduce spacecraft costs.
No it doesn't. It discusses alternative concepts of payload design, not launcher design, precisely because it makes immediately clear where the cost reduction has to come from. Alternative launchers for example for the concept of allowing payloads to be five times as heavy for the benefit of reducing payload cost are taken for granted.

>Also: what kind of trash searches out "expert support" on the internet, cherry picks a bit out of context, and doesn't provide a link to the source?
And what kind of complaint is that? I provided the source. I backed up my claim while your side of the argument didn't. Yet somehow I'm the bad guy? How silly and childish is that?

>Plutonium-239 is itself a very nasty radioisotope you don't want to release

No it isn't, its a mildly radioactive alpha emitter. Theres nothing super special about it. When its blasted into the atmosphere by its own explosion it is not a risk to anyone.

cool, hope they can get it into use.

Funny how no one is discussing the rocket engine itself.

>I backed up my claim while your side of the argument didn't.
So we're getting specific about what kind of trash you are. Posting other people's opinions, cherry-picked and distorted from papers you clearly haven't read in full, is "backing up your claim", while making good arguments and referencing common knowledge is "not backing up your claim".

>>The document as a whole strongly supports the idea that reduced launch costs can be used to reduce spacecraft costs.
>No it doesn't. It discusses alternative concepts of payload design, not launcher design, precisely because it makes immediately clear where the cost reduction has to come from.
>Alternative launchers for example for the concept of allowing payloads to be five times as heavy for the benefit of reducing payload cost are taken for granted.
"If payloads were allowed to be heavier for the same capability, some could cost substantially less"

Yeah, man. That is totally meant to shoot down the idea that lower launch costs can enable cheaper spacecraft to be built. How do you even twist it around in your head like that?

All four approaches it lists to lowering spacecraft costs revolve around the launch constraints: not using all the available mass (so there's margin for mass creep), using a much bigger launch vehicle (so special custom hardware can be avoided), building small, simple satellites (so they can launch on new small, low-cost launch vehicles or ride as secondary payloads), and building small, rugged satellites (so they can be launched on exotic systems).

You are such garbage. Such a total waste of time to talk to.

This is exactly what I mentioned earlier. Taking a purely adversarial approach to winning the argument, by your own standards, while lying and cheating like a motherfucker. Knowing that you're not arguing honestly, just trying to gratify your own ego by deluding yourself that you convinced some imaginary onlookers that you were right.

>>Plutonium-239 is itself a very nasty radioisotope you don't want to release
>No it isn't, its a mildly radioactive alpha emitter.
It has a half-life of over 24 millennia and bioaccumulates. Alpha emitters are the worst radioisotopes to have in your body. Dust particles are particularly dangerous.

It's active enough to be a serious health risk, but long-lived enough to be an essentially permanent pollutant.

Routinely airbursting hundreds of Pu-239 bombs would make the whole world a carcinogenic mess.

FUSION! WE NEED FUSION!

Seriously though a nuclear fusion engine providing a constant high thrust and ultra high isp, is the key to not only space travel, but power itself.

A clean burning fusion engine could pretty much take us anywhere in the galaxy.

But to get back on topic.
>30mpa

Jesus fucking Christmas is no understatement, And there's supposed to be like 20-30 of these on the first stage?
Musk is litterally making the N1 all over again.

This thing is going to break the record for largest non nuclear explosion on first test flight.

We clearly need to build Michael

Pournelle was right all along

Well yeah, the engine is pretty unremarkable except for meme attributes (reusability, muh mars colonization), so we are discussing the underlying memes

Ah yes, the engine design that requires hand waving in certain places to function.

You can add "it's SpaceX" in the meme list.

Had an engine with the exact same characteristics be tested by China, Roscosmos or ESA no-one would give a shit. (And actually, there many existing russian and european engines which are more capable).

This board is such bullshit

>the engine is pretty unremarkable except for meme attributes
>(And actually, there many existing russian and european engines which are more capable).
Mental illness crew present and accounted for.

? have you read anything?

30% was a one-off, harshly-negociated discount for a launch that a has a great chance of blowing up. Future customers will never directly get that. It is however, what spacex will be able to do medium-term.

If they don't blow up too often, that is, which is a pretty large if

Why would a reused stage blow up?

And here, we have the typical ultra-sheltered american netizen who can't possibly comprehend that other people might be doing better than spacex. 3MN of thrust is nothing exceptional, neither is 382s of specific impulse. The rest are irrelevant internal specifics.

SpaceX follows the paradigm of one-size fits all to use the same engine for both the lower and the upper stage, so it ends up with an engine that indeed does the required trade-off, neither hugely powerful, neither hugely efficient.

It suit SpaceX's delusional ideas perfectly, but the engine itself has indeed nothing exceptional.

>it really doesn't matter what "engine" they use at this point, the problem of this shitpiece always been the fuel tanks

Methane doesn't need helium to pressurise, which is what caused both Falcon 9 RUDs.

highest chamber pressure
highest Isp of any non-LH2 engine
highest thrust to weight
A lower thrust just means you put more engines in the rocket