It would make sense to primary batteries, to the point of being the overwhelmingly obvious choice. However, they aren't even using plain lithium-ion:
http://www.rocketlabusa.com/ab...

"Rutherford adopts an entirely new propulsion cycle, making use of brushless DC motors and high performance Lithium Polymer batteries to drive its turbo pumps."

Lithium polymer batteries being a form of lithium ion batteries that have an electrolyte with a bunch of added gelling additives, or an actual polymer electrolyte, trading some of their capacity for flexibility in form factor and leak-proofness that makes them better for things like cell phones. I don't know why they'd choose these batteries, but it's what their website says they're using.

The minimum amount of energy required to pump a given quantity of propellant against a given chamber pressure is fixed, and not low. Doing it in a shorter period of time only makes the *power* requirements *higher*. You also need enough batteries to supply your power demands with the batteries partially discharged, so the effective energy density is reduced.

For a rough, BOTE calculation: they claim a thrust of 4600 lbf and specific impulse (vacuum, presumably) of 327 s. Mass flow rate is something like 6 kg/s. Very roughly approximating the combined LOX and RP-1 density as 1 g/cm^3, assuming a Merlin 1D-like chamber pressure of 9.7 MPa, pumping with 100% efficiency takes 62 kW per engine. Realistically, more like 100-200 kW, or 1-2 MW total.

Also, the rocket's not going at anything close to 30 gravities. All 9 first stage engines at peak thrust could only push about 600 kg at that acceleration.

Fuel cells can achieve high energy density due to using tanks of fuel, but their power density may not be up to driving a fuel pump for a launch vehicle. They are also limited in fuels. This rocket appears to use some form of semi-liquid monopropellant.

They state they use lithium polymer batteries on this page: http://www.rocketlabusa.com/ab...
This is a rather odd choice. The main advantages of LiPo are rechargability and ability to be formed into thin cell-phone-friendly shapes, and they make tradeoffs to achieve these advantages compared to other lithium-ion and non-rechargable lithium batteries. LiPo batteries aren't a huge improvement over alkaline batteries in energy density, and are a few times worse than lithium metal batteries. An oxygen tank and lithium-air "battery" (actually a type of metallic fuel cell) might be a relatively good choice.

If you throw it away, you are guaranteed to have nothing. If you bring it back for reuse, you have a great deal of very expensive hardware that you no longer need to build for the next launch. Just reusing it once allows that hardware to launch 50% more mass over its lifetime than it would have if operated as an expendable vehicle. They anticipate much longer lifetimes.

First...that doesn't in any way make staged rockets "a thing of the past". Second, the first stage doesn't go anywhere near low orbit, let alone the moon.

I'm pretty sure the large object that went overboard was the first stage's engine/octaweb section.

The range safety charges should be almost impossible to detonate by fire or impact, and there was an announcement that they were "safed" during descent, but I wonder if there might be a contingency for setting them off in situations like this...not to destroy the vehicle, but to make sure there aren't any surviving bits of high explosive strewn around.

More than that: since the minimum thrust is greater than the vehicle weight, slowing it down would actually mean a shorter landing burn. The faster the stage is falling, the higher it starts the landing burn and the more time it has to correct its descent.

Note that they don't fully extend the legs until just before landing...this might be to reduce drag and ensure it has enough descent speed to make the landing.

No, it comes out of the entire second stage mass, only about 20% of which is payload/structure. With that mass fraction, each kilogram of payload you sacrifice means there's 4 kg of second stage propellant you no longer need, so you can load an extra 5 kilograms of propellant onto the first stage. They anticipate around a 30% payload reduction due to reuse, eliminating most of the cost of a new launch vehicle in return.

Those test vehicles weren't coming back after launching a second stage on its way to orbit, and could carry a bunch of extra ballast. For the later hoverslam tests, they still lifted off with a T/W ratio of 1, hovered for a bit to burn off fuel, then started their descent under power before their T/W went above 1. The returning first stage starts its landing burn with a T/W ratio of more like 2-2.5.

The center core would never get far from Florida, even in completely expendable operation. However, getting cold would not be a problem if it could make orbit: RP-1 will stay liquid in LEO, and LOX will boil off over time if not insulated and shielded from the sun and Earth or actively cooled. However, they'd last long enough: the upper stage uses the same propellants and has the capability to restart after periods of coasting to do place multiple payloads in different orbits, perform additional high orbit maneuvers, etc.

With a light enough payload/low energy trajectory, and especially with crossfeeding, you can leave the center core with more propellant at separation than the side cores had. So there is a range of launches where they can bring all three cores back. It's not yet clear how useful that range is, and it's not doable for missions to geostationary orbit: http://www.reddit.com/r/IAmA/c...

It may be that they just didn't want to model the ASDS.

They use a pneumatic separation system. No consumables, fewer munitions for people to have to work around, greatly reduced mechanical shock during separation, etc.

The engines can start and restart multiple times, as demonstrated by the hot fire tests and multiple burns during flight. I don't think they use pyro valves or anything of the sort anywhere. There's been talk of refueling on the ASDS and having the stage fly itself back to land, so they're hoping for something very close to gas and go.

That was about aerodynamic control surfaces doing funny things at supersonic speeds. The rocket was moving slowly enough to very nearly make a good landing, it just didn't quite null out enough of its horizontal motion to stay upright.

Jokes aside, it was probably good that they got a crash landing on the barge that early, because it illustrated how badly some people were exaggerating the dangers involved. The rocket was almost completely empty of fuel, and while it made a big fireball and smeared the rocket itself across the deck of the barge, it caused very little damage. The detractors of bringing the first stage back to land would have you think it'd be more like the last Antares launch: https://lh6.googleusercontent....

The point isn't that it would be safe, it's that there's a wide range of hazardous concentrations that wouldn't affect a canary. Canaries were only useful for detecting presence of poisonous gases or a dangerous lack of oxygen. Presence of flammable gases was detected by instruments such as Davy lamps, not canaries.

And a lot more than 3.4 times as difficult to reach. There's no shortage of deuterium on Earth, and no reason to go out there to get it.

Of course, this is good news should we ever need to put a fusion power plant on Mars, but there's many other much more immediate uses for the water, like virtually any sort of industrial activity.