

The Future of Space Launch Is Near - speeq
http://justatinker.com/Future/

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stevep98
Great article. I've not heard about any of the other traditional rocket
builders pursuing reusable rockets recently. If SpaceX is successful in their
goal of reusability, they will be able to undercut everybody else. But, they
will have no incentive to reduce prices significantly until they have
competition.

~~~
jccooper
Yeah, no one else has made any announcements wrt re-usability. It seems odd,
but I guess that's why they call it "dino-space".

Ariane 6 seems to be in response to the SpaceX challenge, at least; they aim
to halve the cost per kg through cheaper and common upper/lower stage
components. Which is good, but still not competitive with F9, much less a
reusable version. At one point they almost made it all-solids in the first two
stages, plus boosters, which would have totally doomed any future attempts at
re-usability. The final design uses a F9-style common component liquid core,
so they could maybe do the same thing as SpaceX later. They are still stuck
with solid boosters, though, in a pork-provision move for Italy.

I've got to imagine that ULA is quietly looking into it. But it's quite
possible they're just hoping SpaceX will eventually implode of its own
internal contradictions and they can go back to their nice little government-
launch monopoly. Or maybe they've decided they can't do it without absurd
expense, based on their internal development costs. Or maybe they just hope to
coast on their existing contracts for a while, and deal with it later once
SpaceX has taken all the lumps.

NASA, via SLS, sure isn't looking at re-usability anymore. Lower cost to orbit
via research should be their main task, if you ask me, but Congress would
rather have them fly giant rockets a couple times a decade, apparently.

The Russians, well, are not much into changing things up. (They've been
running Soyuz and Proton, their current launch families, since the sixties!)
And their recent aerospace development programs have been less than
impressive. But they have a real industry to protect, so one would hope they
have a strategy.

I think that everyone's waiting for SpaceX to make it work, and then they'll
get to copying. My long-term guess is that this'll kill several of the
incumbents, a few will make the transition eventually, but most of SpaceX's
competition will come from new entrants. In the meantime, SpaceX will be free
to reap the profit from the margin between what it costs them and what their
old-fashioned competitors can do. And/or capture the whole darn market. And/or
grow it with lower prices. Maybe all of the above.

~~~
Solarsail
"Dino-space" is a term I hadn't heard before... Is this a newer version of the
"Old-space" that people were talking about in 2005? As for re-usability on the
existing designs, there were many impressive concepts for that floating around
in the 80's, before they were all killed off for the Shuttle. But more
recently it's not like they're just protecting what they've always had,
fending off the little guy. The EELV program was rather innovative, and rather
successfully reduced costs and probably improved launch reliability using some
fairly unusual approaches to vehicle design. They worked out sub-optimally,
because commercial demand was weaker than predicted (and never materialized
for Delta IV), and Boeing wasn't exactly about to sell at a loss to boost
sales. I've heard a few people argue, since the ULA merger, that ULA as a
company doesn't really have the money to try to re-do the EELV's anymore, only
somewhat breaking-even while SpaceX gets actual investments. Tho that might be
disgruntled greybeards complaining...

Ariane 5 went expendable specifically to make it feasible to build, where
Sanger and similar SSTO re-usable spaceplanes were too far-fetched to build.

~~~
shasheene
I really like the Atlas V re-usability proposal:
[http://www.ulalaunch.com/uploads/docs/Published_Papers/Evolu...](http://www.ulalaunch.com/uploads/docs/Published_Papers/Evolution/EELVPartialReusable2010.pdf)

After stage separation, it detach the entire engine block (where most of the
cost is), and a helicopter captures the parachute mid-flight! (See figure 2
from the PDF)

~~~
tankenmate
The issue with this though is it goes most of the way back to the STS; i.e.
multi-month turn around instead of days/weeks. It saves manufacturing time and
materials costs (not entirely due to fatigue checking etc), but does little
for integration and turn around costs.

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Animats
Werner von Braun originally wanted to use reusable boosters about the size of
Space-X's Falcon, launch huge numbers of them, and build a big space station.
See his 1952 book, "The Mars Project". (That was written before we found out
that Mars barely has an atmosphere.)

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blisterpeanuts
The article suggests that SpaceX does _not_ use specialized, radiation
hardened onboard computers, but rather they use triple redundant off-the-shelf
computers.

Why wouldn't they use radiation hardened computers, though? Are they that much
heavier and more expensive than the more commonly available components? Out of
a $40 million spacecraft, the difference of a few thousand dollars or even a
hundred thousand dollars seems rather trivial, in exchange for a more reliable
avionics system.

~~~
rzimmerman
At least for Falcon, I imagine radiation-hardened components probably aren't
much of a gain. A rocket's operational lifetime is on the order of an hour.
Triple- or 5-redundant computers are really effective for shorter missions
like this because loss of one computer (due to radiation damage) doesn't have
a long-term impact like it would on a deep space mission. At least that's my
guess.

~~~
tankenmate
The first stage never steps outside the van allen belt so it would never get
much in the way of serious radiation; the second stage would possibly go
outside for GTO or SSTO.

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slashnull
Okay, but, doesn't it, like, at least double the amount of fuel needed for a
launch?

Also, there is something about using the same engine on every stage to gather
more data per launch, but iirc different engine profiles are used for
different velocities and air densities long the launch. I wonder what's the
efficiency loss of using a single engine profile for the whole launch.

~~~
jccooper
Probably not. You only need a few seconds of propellant for landing: a mostly-
empty stage weighs much less than a full one, and even one engine is enough to
slow it down real fast. I've done some really rough guess-numbers before,
landing on 5-10% of a full propellant load needed for landing.

It's probably not even as bad as that, since they certainly fly with some
performance reserve already, at least several percent, and most payloads are
probably not max-weight. The landing propellant in many cases may be entirely
free, mass-budget-wise. They do add some additional mass for the legs and
fins, in addition to any extra propellant they need, so it's not free, but the
first stage is not as performance-sensitive as higher stages (see: rocket
equation), so they can get away with it. I don't see 'em getting second stages
back any time soon, though, and I think they've given up on that, at least for
F9.

WRT engines, the efficiency based on air density is mostly a function of the
nozzle, and the upper-stage Merlins have a nozzle extension to deal with this.
Higher-efficiency fuels (i.e LH2) are historically preferred for upper stages,
since they are more performance-sensitive, so SpaceX is losing some
performance there. But LH2 is super-cryogenic and a beast to work with, and an
entirely different engine. SpaceX's thing is that they are willing to
sacrifice maximum efficiency for reasonable cost, so they decided to make that
tradeoff. It seems like a good plan so far.

~~~
TylerE
Also, much of the power of stage 1 is spent moving air out of the way. That
helps rather than hinders on the way down.

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kirk21
I am sure they did the math but at first I thought that landing legs would be
unnecessary if you have a system that 'catches' the rocket on the ground.
Since the rocket can hover, it would be possible to grab the rocket with a
structure/claw.

The weight of the legs is probably quite low so this might have been the
easiest solution.

~~~
jccooper
A single Merlin engine, even at low throttle, has quite a bit more thrust than
a (nearly) empty F9-1 stage has weight. Thus, it cannot hover; once it slows
to 0, it quickly starts going up again.

Thus the landing profile is the "hover-slam": the engine is started at the
exact point in time necessary to reach a "landable speed" (from 0-several m/s)
at the ground, and is cut off when it gets to the target.

While modern avionics are quite good, it's still coming in pretty fast and
from far away and will have some variance in location and speed, just because
that's the real world. Probably they don't quite know how much yet, but it
could easily miss the target by multiple meters and a few meters/s. And that's
a heck of a condition to build some sort of giant grabbing apparatus for.

Perhaps once they're routinely landing on land, they may be able to determine
they can hit the target well enough to build a grabbing contraption. Or maybe
it's too hard. Or maybe they'd rather keep their infrastructure to a minimum:
a concrete pad is a lot cheaper to build and easier to operate, and SpaceX
wants to do a lot of flights.

Besides, the 4000lb of the legs is on a 40,000lb rocket.

~~~
Gravityloss
I haven't checked the data, but being a pintle injector engine, there's
potential for the Merlin to throttle quite deeply. Maybe they haven't done
that yet.

~~~
jccooper
It's published to be able to run at 70%, which is quite nice. But 70% is still
way too much to match stage weight.

It's been said to be capable of 60% (or maybe 40%, depending on how you
interpret a three-character tweet). But even that is still not enough: the
stage is 40k lb empty and a Merlin D at sea level is 165k lb thrust. You'd
need to get it to 25-33% to hover nearly-empty.

(Keep in mind most SpaceX numbers involve a fair amount of guesswork and
Kremlinology, and they're always changing, but they should be ballpark
accurate.)

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mrfusion
Has anyone looked at only using a solid rocket booster to get to orbit? Would
that be cheaper, perhaps only needing a singe stage plus orbital insertion?

Even if unsafe could it still make sense for unmanned launches, supplies,
cargo?

~~~
Solarsail
All solid LV's haven't really been cheaper than liquids in the general case,
the motors themselves tend to be quite expensive. Also, a single SRB is never
sufficient, even with 0 payload a very large solid doesn't have the
propellant-mass ratio to get even close to orbit. Something like Pegasus or (I
think) Athena 1 were 3 stage designs. Being solid helps simplify the ground
support infrastructure and launch pad, whose costs don't scale down well. With
an all-solid, something like the Kodiak launch complex is feasible, an
extremely simple assembly building + pad.

~~~
mrfusion
Interesting. So how did they help the shuttle?

~~~
Solarsail
The shuttle used them as early-flight boosters. Same trick used by Ariane V,
Titan III / IV, Delta II / III / IV, endless other big vehicles... They are
much cheaper to develop per thrust than liquids (They are expensive per size,
but scale up to higher thrusts well), and you often want most of your thrust
early on rather than later. Solid boosters you ditch after 30s or a minute
raise your T/W ratio so you don't loose as much fuel to gravity losses, and
get your more efficient but less powerful liquids into the upper atmosphere.
Both Ariane V and Shuttle typify this, with almost all liftoff thrust from the
solids, and a small, expensive hydrogen-burning engine continuing to most of
orbital velocity. For the shuttle, this was aimed at reusablility, they could
do most of their work on expensive engines, and not need to pay that cost
every flight. Ariane did it so it could make near-orbit with only engines it
lit on the pad, for reliability sake. (Planned for the Hercules spaceplane,
which wouldn't have used the upper stages that satellites would eventually
use.)

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tempestn
Can anyone point me to more information on this line from the article,
regarding the space shuttle: "But the final design, modified to accommodate
Air Force requirements, ended up being only a partially reusable launch
system."?

What exactly were these "Air Force requirements"?

~~~
InclinedPlane
In short: it needed to be capable of doing a once around polar orbit launch,
which meant that when it came around back on the next orbit it would be
several hundred miles away from the landing strip in Vandenberg. So it needed
a huge cross range flight capability, which meant very large wings. Large
wings meant more weight and a stronger airframe (also more weight), as well as
a more complex and difficult thermal protection system. It raised the cost and
complexity of the vehicle a great deal, though it wasn't the only reason why
the Shuttle didn't meet its design goals.

~~~
jccooper
And it never even flew that mission profile.

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knappador
Someone use drones already. Whoever is using drones to launch many air-
breathing components that return on their own and launch stages that glide in
after re-entry wins. The rest of this stuff has obvious gigantic weight
disadvantages.

Current gas turbines are not optimized for pure thrust-to-weight or else why
are military engines outperforming civilian in thrust-to-weight? Turbofan-to-
turbo-jet for high Isp in atmospheric flight and then fly everything back on
its own. Firefly's rocket has a max thrust of 90klb on the main while a big
gas turbine pulls 100klb easy. While we're talking about Isp and re-usability,
the entire first stage of a rocket could be gas-turbine powered and the
engines just peel away and fly home after they're done. The engine needs gas.
The gas takes space. Put the gas in a wing. Wing glides the engine home after
launch. Easy as 1,2,3-a-bunch-of-engineering. Go!

~~~
ceejayoz
You're advocating for air launch, not drones - the Falcon 9 / Dragon is
already an unmanned drone craft.

It has been successfully tried -
[http://en.wikipedia.org/wiki/Pegasus_%28rocket%29](http://en.wikipedia.org/wiki/Pegasus_%28rocket%29)
\- but my understanding is payloads are pretty severely limited. You can see
the size of the Pegasus launcher is much, much smaller than a Falcon 9 - it's
certainly not going to work for SLS/Falcon Heavy/MCT-sized payloads.

 _edit:_ For ground-launch with jets as the first stage, I really don't think
that's going to work.

[http://en.wikipedia.org/wiki/Thrust-to-
weight_ratio#Jet_and_...](http://en.wikipedia.org/wiki/Thrust-to-
weight_ratio#Jet_and_rocket_engines) indicates the SR-71's engine had a
thrust-to-weight ratio of 5.2. SpaceX's Merlin has a thrust-to-weight of 150.
There might be room for improvement, but 30-fold? I doubt it.

~~~
knappador
T:W for rockets vs air-breathing are really skewed by fuel consumption. Falcon
9's Merlins will burn ~25-30k lb fuel (70% launch mass is 1st stage gas?) per
minute (180s total 1st stage time) vs ~1k lb fuel per F119. The jet engine
will scorch the rocket in effective T:W for it's short atmospheric burn.

More modern F119 has a T:W of about 8. With ceramics and pure focus on re-heat
and specific thrust, you can get over T:W of 10 likely. There may be other
tricks on fuels besides jet fuel that might even allow more focus on re-heat,
making the T:W even higher without necessarily affecting fuel consumption.

Going COTS with F119 is interesting, but ceramics might make some game-
changers. Ceramic turbine blades and afterburner pipes will drastically lower
the weight vs Nickel superalloy parts while lower cost and manufacturing
complexity. Turbine blades are really impressive, but it's all cost.

