

SpaceX aims big with massive new rocket - someperson
http://www.flightglobal.com/news/articles/spacex-aims-big-with-massive-new-rocket-377687/?

======
ballooney
If we're playing 'guess-the-acronym', I'm going to depart from something Mars-
based and suggest that the 'C' is to do with 'Cryogenic', and that now that
they are more confident with engines they might be switching to a harder, but
much higher performance, fuel combination like liquid oxygen with liquid
hydrogen.

Whereas LOX+Kerosene has a Specific Impulse (crudely the amount of 'go' you
get from a pound of propellent) of about 340s, LOX+Hydrogen engines have an
Isp of about 450. That's really a huge increase in terms of what you can
launch with a given size of rocket.

Tom Mueller, the head of propulsion at SpaceX, previously worked for TRW (the
company that did the US's ICBMs in the 50s) and while there he worked on a
LOX+Hydrogen engine, the TR106 ( <http://en.wikipedia.org/wiki/TR-106> ),
which was a beast.

It's harder to work with - both propellants are very cryogenic - but any
rocket engine designer will be very aware that LOX+Hydrogen is hovering at the
top of the evolutionary ladder looking mighty attractive for those that have
the resources to take it on - a position Space X find itself in as they become
more mature and heavyweight. They're already looking at it for their
replacement Upper stage vacuum engine for Falcon 9 - the Raptor (
<http://en.wikipedia.org/wiki/Raptor_(rocket_stage)> ).

Also, almost any Mars mission would involve a lot of heavy lifting into low
earth orbit to construct a vehicle that would transport people there and back.
A space vehicle that can support several people for say 2 years, and move
itself to and from Mars, is going to by way bigger than anything that can be
launched by a single rocket all at once. A big heavy-lifter whose engines have
a much improved Isp (which rather relaxes the expensive mass saving measures
you need in the rest of the rocket to launch a given payload, or alternatively
lets you launch a much heavier payload for the same vehicle) is consistant
with a mars road map.

I doubt they would undertake something like this _just_ for Mars - developing
rocket engines is hecka expensive. SpaceX got started by inheriting most of
the cancelled FastTrac project from Nasa (
<http://en.wikipedia.org/wiki/Fastrac_(engine)> ) and indeed still outsource
their turbopumps (the hardest bit of an engine) to Barber Nichols, who did the
design for Fastrac. That was a great move on their part - starting with a
blank sheet would have been madly expensive and very slow - a working baseline
engine design is a very high-dimensional optimisation problem, before you even
get to cutting metal. My point is, if they're now starting clean-sheet engine
design, I'm sure they must have in mind some way for it to pay for itself
because it's a hugely costly business.

We live in interesting times!

~~~
nkoren
Hydrogen brings absolute oodles of troubles with it. For upper stages, where
it is much more critical to minimise the wet weight, that trouble is generally
worthwhile. For lower stages, not so much -- it's generally FAR more cost-
effective to just build a heavier stages which will do the same job, but with
lower ISP. In the past, SpaceX has always made the (correct, IMHO) decision to
optimise the cost-efficiency of their rockets, rather than the propulsion
efficiency, and hopefully they won't stray from that path.

(They've said in the past that they're working on a LH2 upper stage already,
so if you see them building up a cryogenic capacity, that would explain why).

Also, I kinda miss the days when they could get away with calling their next
generation rocket the "BFR", and no true geek needed to even _ask_ what that
stood for.

~~~
ballooney
Indeed, as I say it's very much harder to work with, but it's worth a revisit
with 2012 technology, I think. I also am involved with oxygen+hydrogen rocket
propulsion research but can't really discuss it much here. But things have
come on a bit in the last 30 years :)

Re: 'BFR', well I have a few hypotheses about 'MCT' in a similar vein but I
reasoned they might be a little bit blue for HN!

Edit: A better reason for first stage hydrogen occured to me over a cup of
tea:

> "SpaceX has always made the (correct, IMHO) decision to optimise the cost-
> efficiency of their rockets, rather than the propulsion efficiency, and
> hopefully they won't stray from that path."

I think the economics change when you try and go reusable in the way that they
are. Lox Hydrogen engines and tankage _might_ be more expensive, which is
obviously a factor in an expendable vehicle, but if you reuse the vehicle, and
have to keep enough fuel back to land, as SpaceX plan, I think actually the
equation goes far more back towards optimising for propulsion efficiency in
order to get the cost efficiency. The launcher cost metric is basically
dollars per kg into orbit, and for a given _reusable_ rocket, lox+hydrogen
will get many more kgs into orbit than lox+kerosene - you need to keep much
less fuel back in reserve to land the various rocket stages, and the extra
fuel you can use on the ascent is also a lot more thrusty per unit mass. I
wouldn't be surprised, assuming you sell at a dollar/kg price, if lox+hydrogen
ended up being much more profitable in reusables than lox+kerosene, everything
else being equal. I have not done the sums though.

~~~
nkoren
I admit to having a bit of an attitude about LH2; for 25 years after they
developed the SSME, NASA maintained an attitude that if "it ain't hydrogen,
it's crap". No non-hydrogen developments were funded during that time, and not
coincidentally, no new first-stage engines ever reached flight status. Until
SpaceX came along and developed its own hydrocarbon engines, we were reduced
to buying hydrocarbon engines from the Russians. During that time I developed
a heck of a bias towards hydrocarbons -- but I have to grant that it's
certainly possible that advances in LH2 have balanced out the negatives since
then.

You're correct that as you go reusable, the economics shift away from capital
costs to operating costs. However, it seems to me that when you consider first
stages from a _systemic_ perspective, it's not obvious that it's any cheaper.
Yes, Hydrogen gives you much more impulse, and so for a given degree of
propulsion, you can use less fuel by weight. However, LH2:

1\. Costs 4x as much as kerosene by weight

2\. Is only 11% as dense as kerosene, requiring much larger and heavier (and
highly insulated) tankage to hold it, and larger and heavier turbopumps,
combustion chambers, and everything else that puts weight on a rocket. So
while your wet weight may still be less, your dry weight is generally quite a
bit higher. T/W is always lower than for hydrocarbon systems.

3\. This much greater bulk increases your drag losses if you're operating in
an atmosphere; lower T/W increases your gravity losses.

4\. Although hydrogen doesn't suffer from coking on the combustion surfaces
the way that hydrocarbon engines do, it embrittelises (is that a word?)
everything it touches, making between-flight inspections a _much_ more crucial
and delicate process. There are hydrocarbon engines which have been fired
thousands of times between rebuilds, for hundreds of hours of firing time.
Show me a hydrogen engine is even 10% as durable.

Of course when you're in orbit, neither drag nor gravity loses matter, and the
nature of the Rocket Equation dictates that every ounce of gross weight
_really_ matters. So LH2 makes undoubted sense there. But the exact inverse is
true when you're launching off the ground. Unless some fundamental
breakthroughs have occurred which I'm not aware of (always possible), I will
remain very surprised if SpaceX is pursuing cryogenic first stages.

~~~
ballooney
All valid and I'm enjoying the discussion but I would address the points as:

1) Sure at the moment, and it will be difficult to match economies of scale
with the oil industry, but the amount of research money going into hydrogen
production at scale is enormous. It's only getting cheaper, and while 'The
Hydrogen Economy' has been promised since the 70s and hasn't yet arrived, it's
definitely coming. I'm sort of thinking about this debate in a 10+ years out
sense rather than right now, I admit.

2&3\. Sure, but that only becomes a smaller problem as rockets get bigger
(i.e. very heavy launchers such as this one being proposed) and the
cube/square law works in your favour (i.e. tank volume increases faster than
frontal area to which the drag is proportional). T/W is often limited anyway
by payload constraints rather than rocket engineering constraints, especially
in manned systems. Doesn't matter if the vehicle can do 5G off the tower, the
people inside it can't.

4) 'Embrittels' I would guess? Anyway, it occurs in _most metals_ but
certainly not all metals and very certainly not "everything it touches". This
is the clue for the way out of this problem. I obviously couldn't show you a
hydrogen engine with the same track record as no operational hydrogen oxygen
engines have been built with a clean sheet using what we know today. That
said, a few are being designed precisely as we speak for very long life
operation in reusable vehicles. I don't think the chickens have come in to
roost yet.

~~~
nkoren
I'm enjoying the conversation too! Your point about the scaling properties
making LH2 more favourable for larger vehicles is something I hadn't properly
appreciated in those terms, but is certainly correct. As far as T/W goes, I
think that you do need to be able to pull 3G off the tower, and moreover do it
with _one_ propulsion system (or cluster of identical systems). Again from a
systems-engineering point of view, the point where a launch vehicle design
jumps the shark is where you're strapping together completely disparate types
of rockets to get the desired effect. I don't think that an LH2 engine has
ever actually done this, although the the X-33 designs perhaps could have
worked. (I always thought that the Venturestar was emblematic of everything
that can go wrong with an LH2-driven design, since it basically turned into a
(non-)flying kitchen sink exposition. But the DC-Y was elegant enough; I would
have loved to see somebody make an honest attempt at that.)

So basically, it sounds like there are three things required to make a
cryogenic first stage/RLV viable:

1\. A market for large payloads -- large enough to allow the scaling laws to
work out in LH2's favour -- with sufficient frequency to pay off the
development costs. As such, this doesn't exist yet, but it's certainly
conceivable that someday it could.

2\. New types of LH2 engine designs, which are much more durable than SSMEs
(which I guess would be the current benchmark of LOX/LH2 durability? Or would
that be RL-10s?) Presumably with some substantial revolutions in materials
sciences. This may be well underway already (as you allude), but is not public
info yet.

3\. New, cheaper ways of generating hydrogen. As long as the lowest-cost
method is steam reformation, then hydrocarbons will, by definition, be
cheaper. If that's the case, then you'd end up in a curious situation where
LH2 might only be economical in the _middle_ of the spectrum. In an ELV which
is primarily concerned with capital costs, hydrocarbons clearly are more more
cost-effective, since they're much easier to develop and build. On the other
hand, in an RLV which achieves true airline-like operations -- where the cost
of fuel begins to become a meaningful concern, which it currently is not --
then hydrocarbons win again. That might only leave a thin band in the middle
where LH2-based designs are the most cost-effective. On the other hand, a new
low-cost hydrogen-generation technique (eg., bacteria that exhale it) could
change the game.

So yes, I guess I'd echo your sentiment that this is something that could be
relevant in a decade, if all three of those items develop in the right way.
Definitely promising enough to merit some R&D, but not yet assured or
inevitable.

~~~
ballooney
Agree on all counts, especially 2. Funny you should mention the [LOX/LH2
Single Stage To Orbit] DC-Y! If you can only have one stage, Hydrogen is also
very attractive. I agree with you that someone should make a proper go of it
because it's possible and it makes a lot of sense. It was actually this
realisation that prompted me to change career and work where I now do. (I am
British, work in propulsion research, especially Oxygen (be it stored liquid
or from the air...) with Hydrogen, am interested in reusable space vehicles,
and I think wings are A Good Thing, and I live in the city where you did your
MBA. As a fellow space enthusiast that's hopefully enough for you to figure it
out :D ).

~~~
nkoren
Oho! That is indeed a _very_ legitimate and exciting piece of technology which
you're working on! Lucky you!

(Just to be clear, I'm not remotely an actual rocket scientist. I'm a
transport planner / urban designer who specialises in Personal Rapid Transit
systems, and starts companies on the side for fun; I've just spent an
inordinate amount of time in pubs with fairly eminent rocket scientists, and
have acquired an Opinion or two along the way. Plus, I need to keep one foot
planted firmly in that world, so that once I've made my fortune elsewhere, I
can move on to colonising the inner solar system without delay...).

Personally, I've always tended to be more of a VTVL guy, but anyone who can
make wings work certainly has my support. In the case of of Reaction Engines /
Skylon, I have to confess a bit of skepticism -- not from a technical point of
view (the credentials and capabilities of the team are superb), but from a
business-plan point of view. I've done various offhand models to get it to
work, and the financing costs always kill it. It only works if you presuppose
A.) an existing launch market of about 250-500 Skylon-class payloads per year,
and B.) that SpaceX or Blue Origin haven't succeeded in lowering launch costs
with their flyback boosters etc.

In contrast, SpaceX has a much more bootstrap-able evolutionary path, which
allows them to largely avoid financing costs, and to theoretically get their
customer prices closer to their marginal costs much more quickly. My feeling
has always been that Reaction Engines ought to focus more on the possibilities
for aviation, since it is a large enough market that it could absorb the R&D /
finance costs much more easily. Once you're turning a profit in that market,
then use it to bootstrap Skylon.

All IMHO, of course!

------
robbiep
_possible payload range of the new rocket is 150-200t to low Earth orbit
(LEO). A vehicle of that size would easily eclipse NASA's proposed Space
Launch System, which will eventually be capable of launching 130t to LEO_

This really allows you to begin to grasp the economics of what Musk _et al_
are doing -

* The Space Launch System has been funded to the tune of $17Bn through to 2017 (Wiki)

* SpaceX got through the Falcon 1 and Falcon 9 development to where we are now (Viable launch system with paying clients) on around ~$1Bn

Even assuming that they have to start the development from scratch, new
tooling, new plant and equipment, you could extrapolate out at a stretch that
perhaps it would cost a cool $3Bn (And likely well under this) if they are
planning on having some form of prototype 'MCT' up and running in around 3
years

so that would be around 1/6th the cost of a bloated government program for an
extremely heavy lift capability, _potentially_ re-usable if they are able to
complete the engineering of that little monkey, making production of a space
elevator within the realms of possibility (and maybe making earth rocket
launches redundant!) as well as cheap heavy launch capability to mars.

The solar system is getting a lot smaller, it seems.

~~~
jacquesm
> making production of a space elevator within the realms of possibility

Rocketry has little to do with a space elevator, the materials science for a
space elevator does not even exist.

~~~
robbiep
you're right, they are completely different fields.

However one of the more likely methods of construction (from this distant
point anyway) would be a launch of lots of material, tie it all to some
asteroid or other large counterweight that has been put in space a good
90,000+km away, and then unspool it all to the surface, which would require a
good and cheap heavy launch capacity

(I suppose you could say if we are going to do such an undertaking as build a
space elevator, with all the billions it may entail, then launch costs to get
it going will probably be the least of our worries, but as far as I see it,
every little bit helps!)

~~~
jacquesm
The problem is not the principle of the thing, the problem is that a part of
it would have to be made of unobtanium.

Earths gravity is such that you'd need a material for the tether that is
stronger than any material that we are currently aware of.

So there is no point in getting any of the mechanisms in place or developed in
any detail until there is a material that can withstand the forces in play.
Right now, sad but true, an earthbound space elevator is science-fiction.

~~~
robbiep
It kind of depends on which experts position paper you read on it - I point
you in the direction of

10.1016/j.actaastro.2012.01.008 (Towards the Artsutanov's dream of the space
elevator: The ultimate design of a 35 GPa strong tether thanks to graphene,
N.M. Pugno)

For someone that is exploring the materials we will likely use in any attempt
at an elevator.

Yes, we can't make the materials today. Like, _right now_. Or even next month,
especially in the quantities needed. But we also can't make the rockets that
might make it more accessible. And, more than likely, the first space elevator
will be built on the moon, not on earth, which will definitely require heavy
lift and would probably be a proving ground for the technology and materials.

So yes, science fiction, but so is pretty much everything else that spaceX
wants to do.

They always say the future is just around the corner and in this case they
might just be true. Or at least, as you can tell, I hope it to be true.

------
sbierwagen
"Elon Announces He Might Be Building A New Rocket, Provides Absolutely No
Details At All."

6m's pretty big, though. Falcon 9 is 3.66m. Ares V (the space shuttle
replacement) is 10m. Saturn V was 10.1m.

I'm really not sure why they're not using RP-1, though. What's the alternative
propellant? LH2 has all sorts of problems.

~~~
cdash
My guess is that they will be using a methane engine.

~~~
Gravityloss
That's an interesting point.

Methane is sort of halfway between kerosene and hydrogen. No operational space
launcher has used it, though, as far as I know, some engines like the venerabe
RL-10 hydrogen upper stage work horse have been modified to run on it on a
test bench.

~~~
InclinedPlane
Methane is about half-way between Kerosene and Hydrogen in terms of Isp but
it's far closer to Kerosene in density, which is critically important for
overall achievable rocket stage performance (weight ratios). Liquid methane
has about half the density of Kerosene but liquid Hydrogen has about 1/12th
the density. Moreover, liquid Hydrogen is a super cryogen whereas liquid
methane has a higher boiling point than LOX so handling, materials, and
insulation requirements for LCH4 are comparable to LOX.

------
benzofuran
I was thinking the same thing - either Moon or Mars Crew / Cargo / Colony
Transporter. It's an exciting time around these parts, and as I understand it
the Merlin concept is pretty scaleable.

Perhaps the new fuel he's speaking of is some sort of hypergolic mixture
(Hydrazine etc) that can be used for just about everything once the vessel
arrives somewhere without much available oxygen.

------
danieldrehmer
A few days before this article, a redditor reported a conversation where Elon
Musk tells his friend that Dragon is just an appetizer for what he called
"Mars Colonial Transport"... MCT?

[http://www.reddit.com/r/space/comments/11bpvi/elon_musk_just...](http://www.reddit.com/r/space/comments/11bpvi/elon_musk_just_informed_my_friend_that_dragon_is/)

------
someperson
This was submitted 11 hours ago
(<http://news.ycombinator.com/item?id=4661364>), but only got 9 upvotes so was
probably missed by many people. I sincerely believe this is strong Hacker News
material that wasn't successful due to an unfortunate submission time, so it's
worth resubmitting. This news deserves quality HN discussion.

------
someperson
> Musk declined to say what 'MCT' stands for, and declined to answer further
> questions on the project.

There's some speculation [1] that MCT stands for Mars Crew Transporter (or
Mars _Cargo_ Transporter).

(The comments on [1] are very interesting, speculating on Musk's aims for a
rocket that currently doesn't have that much value to private industry)

[1] [http://nextbigfuture.com/2012/10/spacex-developing-larger-
en...](http://nextbigfuture.com/2012/10/spacex-developing-larger-engine-
to.html)

~~~
robbiep
aaah my dreams are coming true. How exciting, even from this far off
speculative point.

------
masklinn
> During an April interview, SpaceX president Gwynne Shotwell discussed a
> project with similar characteristics, describing engines with "more than 1.5
> million pounds" of thrust.

For comparison, 6.7MN (1.5 million pounds) was roughly the thrust of Saturn
V's F-1 engines (it had 5 on first stage and that many J-2 — at a mere 4.4MN
each — on second stage), and it had an LEO payload quite a bit under those
asserted here (120t).

Going beyond that means SpaceX is going to compete with the Zenit's RD-171
(~8MN), which is the current holder of "most powerful liquid-fuel rocket
engine" title (the shuttle boosters are the holder of "most powerful rocket
engine" title at more than 12MN each).

The Merlin page[0] seems to confirm that, suggesting the Merlin 2 is planned
for around 8.5MN. That's absolutely enormous.

You still have to wonder how many of these things they'll put on a rocket to
get it to push the expected 200t to LEO: the original Energia only lifted 100t
to LEO with 4 zenit boosters (so 4xRD-170) and its own engines (4xRD-0120 at
2MN each), there were plans to have a 200t-lifting Energia… by strapping _8_
zenits to it

[0] <http://en.wikipedia.org/wiki/Merlin_(rocket_engine)#Merlin_2>

------
Gravityloss
How many launches per year?

I don't see the economics here. Not with expendable, not with reusable.

Plus, if you have fewer big engines, you can't land on them as their thrust is
too high.

------
TeMPOraL
SpaceX - because screw FTL, we'll just build a better rocket. ;).

Jokes aside, they're doing really impressive job and I'm very happy to see
visible progress in what I thought was a stale industry.

------
teeja
Given Musk's vision for the future, MCT clearly means Mars Colonization
Transport.

------
JulianMorrison
Are they building Sea Dragon?

------
bejar37
Eaoq

