Falcon 9 attempts ocean platform landing

It could also be a matter of "expected" vs "actual."

For efficient re-usability, you need at least three things. The first is reliable launches that don't have lots of delays. The second is reliable recovery. The third is efficient readying for another launch.

That last one is trickier than people think. It was the main thing that stopped shuttles from launching faster, for instance. It took months of work to verify that all the systems were as reliable as they were before launch. It will be interesting to see how SpaceX handles that.

One thing that concerns me about reusing it is how do you account for unknown components failing or wearing down in quality after repeated use? Does SpaceX have the metallurgy capacity or experience to deal with cases that no one has ever encountered (reusing a rocket multiple times)?

I'm worried that one small tear or some mold or rust will increase the risk.

I always wonder why they don't launch a rocket from a plane at around 60,000 feet, wouldn't that cheapen the cost rather than launching it form ground zero?

There's been Russian military use of grid fins on supersonic rockets and missiles for many decades. It's my understanding that supersonic flow is not a problem, rather transonic (mercifully a relatively short period on either an accelerating or decelerating rocket) behavior is the problem.

How to do it will also be easier to learn about because it would presumably be done and published either openly or as a patent. People working in the field would know how to do it lowering the barrier to entry - hopefully making the high costs to study and research today pay dividends to the rocket industry. You are correct it would increase the cost to do similar research. Hopefully though the economy of the sector will be so much larger one off rearch focused launches can be easily done with the excess capital... At least that's my hope.

They are low profile since they can be folded against the body of a missile/rocket.

They also have good aerodynamic properties at hypersonic speeds.

http://en.wikipedia.org/wiki/Grid_fin for more info

Watching their example video I'm guessing they act as steerable "fins" where the working area of the fin is spread across a number of "vanes". Not clear if there are two degrees of freedom or just one for each one.

As the rocket travels through the air each one can be rotated on its axis perpendicular to the body of the rocket. If all are rotated the same way they would impart a spin, if two were rotated one way and other two rotated the opposite direction they would simply slow the rocket down. If two adjacent ones are counter rotated the provide drag on one side (imparting a pitch change).

I was thoroughly impressed when I saw the video, that is a really cool technique.

* Grid fins work well at subsonic and high super sonic speeds (but poorly around Mach 1) lowering drag at high mach numbers.

* Grid fins require less structure to support / actuate them per unit control force

* Grid fins are more easily stowed (unneeded during launch, would cause significant drag forces if not stowed)

An interesting mental model is a biplane (well, a grid of 20 not just 2) of really small leading edge slats. That's obviously not exactly how they work, but for seven word summary, not bad.

They're originally a "Russian thing", for a decade or so it seemed like every missile they designed had grid fins.

They're an example of high optimization. Around certain speeds they work REALLY well and weigh practically nothing and the control forces are very low. On the other hand they're little more than speedbrakes around other airspeeds.

Here's a Falcon 9R flight using the grid fins:

https://www.youtube.com/watch?v=DgLBIdVg3EM

I assume to get the accuracy down. Once they prove they can hit that target reliably, they'll be trusted to try over land (where missing can have much bigger consequences).

Because if they fail badly and the rocket slams down hard, the remaining fuel and oxidizer in the tank is going to blow up like a very respectably sized bomb. It won't quite demolish a city block, but you certainly don't want to be anywhere near it.

Until they can be sure they can reliably control it during descent, they are choosing their landing sites so that even in the very worst case, it can't come down on top of someone. This pretty much means it has to come down in the Atlantic.

I can think of several reasons, but the most significant is that the launch takes place over the ocean.

If they don't have the precision to land on a tiny barge at sea (in calm seas), they don't have the precision to safely land anywhere reasonable. The worst case with a botched ground landing is something like dropping a blockbuster on a random, possibly populated area. The FAA won't allow them to attempt a non-sea landing until they've demonstrated several sea landings (along with much technical documentation).

Much easier to get FAA approval, and less propellant is required compared to reversing course completely to land near the launch site on land.

Launch trajectory is always over water for US launches, so if the rocket fails there are fewer people to hit below.

It's a big win to buy, build, and outfit the barge instead of paying an insurance payment to do the landing on land.

Because the trajectory of where this thing ends up is in the ocean (on purpose -- think about failure modes to see why).

In addition to what everyone else said: location and range safety.

The launch sites they use were built for non-recoverable launch vehicles which are dropped to the sea. The launch sites have a narrow range eastwards, and SpaceX needs to adhere to the restrictions despite being able to land the boosters safely. This means that their rockets will inevitably be going over the sea.

Incremental testing. They don't even have a landing site built yet, nor FAA permits for that. But get a few landings on a barge down and they'll improve confidence in the process a great deal.

1. You launch eastwards so you get the bonus speed from earth's rotation.

2. You launch over the ocean (or other sparsely populated areas) for safety purposes. All rockets so far have dropped stages or engines on the way.

3. To get to orbit, you have to do mostly horizontal acceleration (8 km/s or so). That's why the rocket points eastwards soon after launching, and staging happens already far from the launch site and why the first stage has a lot of horizontal velocity towards east. You don't want to fly a dog-leg as that wastes energy.

Well not your regular cows, they surely belong to a spacex farmer! :D http://www.spacex.com/careers/position/5749

r/spacex think almost certainly not - it's definitely going to be filmed and usually that footage gets released, but previous cams on the test stages didn't transmit live. The actual mission's likely to get the livestream.

OTOH, it would be incredibly cool to cut to the barge and a dainty, Gernsbackian landing. So, who knows?

Because you have to haul up a great big airframe, and you need a landing strip, and you limit your configuration.

With this variety of thing you can strap multiple first-stage rockets together, blast a great big payload into space, and then the first stages return safely for rapid re-use - while your payload stays up.

The space shuttle had a pretty small payload bay, and only came in the one configuration - no flexibility, like this provides.

Also, with a passively slowed vessel, like a shuttle, you have a huge amount of heat to dissipate, which requires thermal tiles (yet more mass and refit each launch), whereas this slows in several burns throughout re-entry, meaning that the thermal stresses are nothing like you have on a shuttle re-entry.

This is for reusing the first stage of the rocket, not the bits that actually go into space.

The shuttle's promise (inexpensive frequent launches) never materialized. Instead it was an incredibly complicated and expensive system to operate, launch, service, and recover. SpaceX's approach is to take the approach that's cost-effective and simple (but no more simple than necessary) and then to try to iteratively improve it to achieve reusable spaceflight. The "works like an airplane" thing is a great strategy if the thing can take off and get to orbit like an airplane, but to this point we (humanity) have not had the technology to produce a single-stage-to-orbit reusable spaceplane. Once we have to stage it and add boosters of various sorts, it quickly has all the same problems as a "traditional" rocket, but with all of the added complexity of a space plane. The Skylon approach purports to tackle this, but at this stage is more fiction than science (funding aside, there's a long way to go).

The Energia (Russian shuttle) program originally planned to have a system like the Shuttle with even more of the rocket returnable to launch site (boosters/core stage (Energia had the "main engines" on the tank rather than the orbiter)) but also abandoned that plan (and indeed the entire program, shortly thereafter).

Yes, you are missing something. Air resistance.

At the velocities rockets go, air resistance is terrible, as it grows with the square of velocity and air density.

Rockets minimize area and drag by huge amounts. This means they could carry more payload per power unit.

Wings are great if you want to go a long distance horizontally through the atmosphere at subsonic speeds.

Most of a rocket's travel is in a ballistic arc that's vertical at takeoff and supersonic. On the upward journey, wings are unwanted drag and weight. On the downward journey, they suffer drag heating and stress. And they don't work on planets with a lighter or no atmosphere. In theory all you have to do is fire the rocket engine that's already there with a comparatively small amount of fuel to slow it from terminal velocity (probably subsonic) to a stop exactly above the ground. We finally have the computer control systems to make that feasible.

People keep designing spaceplanes on paper, but the engines are the limiting factor there.

one of spacex's goals is to make us a multiplanetary species,

with the knowledge and technology we have now that means propulsive is the only way to do it

musk says of the moon, "there's are no runways and no atmosphere"

https://www.youtube.com/watch?v=SOpmaLY9XdI#t=11m30s

why colonise other planets? musk says, "planetary redundancy, backing up the biosphere..there are some risks that are just extremely difficult to mitigate and some risks which we ultimately not be able to mitigate"

https://www.youtube.com/watch?v=SOpmaLY9XdI#t=30m22s

Who knows? Weather and technical issues can scrub a launch, which is why they don't say in their PR materials. But it's scheduled for Friday 19 Dec. 1:22 pm.

https://www.kennedyspacecenter.com/events/2014/december/laun...

> In order to make the Falcon 9 reusable and return to the launch site, extra propellant and landing gear must be carried on the first stage, requiring around a 30 percent reduction of the maximum payload to orbit in comparison with the expendable Falcon 9.

From https://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_...

They have said it takes about 3% of the stage's propellant load. They further say recovery systems (mostly legs and fins) and propellant reduces orbital payload by about 30%, but that their advertised capacity is already 30% under maximum performance to allow them the margin to experiment with recovery systems.

The numbers are all kind of old and fuzzy, but should give you the idea.

http://en.wikipedia.org/wiki/SpaceX_reusable_launch_system_d...

Since they haven't managed to properly film any of the ocean landings, I highly doubt it. But this time we could have good video from the platform itself.

Not a chance. Here's the map: https://mapsengine.google.com/map/u/0/viewer?mid=zp15b_P5ERV...

I think for previous flights they've had couple of ships outfitted for stage recovery, in case they were able to pluck them out of the ocean. Presumably one of those can go pick it up off the barge. Or maybe just tie it down and tow the barge home.

Rockets are extremely weak in any direction other than straight up/down. The reinforcement to allow a Falcon 9 core to even lay on its side unpressurised would probably weigh more than the entire set of recovery hardware (legs, grid fins, extra rcs fuel, etc) to land vertically.

The point is reusability.

Reusable rockets will dramatically lower the cost of rocket launches.

(On the other hand, if you're questioning why rockets are tall & cylindrical, it's because that's the best design for rockets: https://www.quora.com/Spacecraft/Why-are-rockets-tall-and-sl...)

The engine is at the bottom pointing down, so the only way to do a powered soft landing is vertically. Other posts talk about why they're using the engine rather than e.g. parachutes.

Landing it horizontally would require the rocket to be able to coast horizontally, meaning it would have to have wings. I can imagine wings would make the whole thing more complex but even if they nailed that, imagine what it would have to do on the descent. You basically have two choices, either fall straight down and try to control spin, or coast down, trying to control horizontal and vertical speed like an aeroplane. I have the suspicion that when dropping from space it's very hard to get into coasting mode since the air is so thin.

However it is, a rocket that simply falls down instead of coasting like an aeroplane is so much less structurally complex, the only real challenge is controlling its landing which modern computers and their rocket engine make feasible.

Aerodynamically it wants to be aligned along the vertical axis. Similar thing for thrust forces. So at a minimum you want to decelerate all the way down from terminal velocity with the vertical direction aligned to the direction of travel. And that only leaves a narrow window of time after which you could bother concerning yourself with reorienting. And, of course, reusing the main engines saves on complexity a great deal.

The heavy stuff is all at the engine-end, so absent any lift, that's the orientation you get.

Shuttle SRB's hung from parachutes in the nose, but a chute landing is still pretty fast. The hot motors were dunked in salt water at speed... generally worse all round. Solid rockets are one-shot deals that can't be relit.

The Russians have been working on a booster that deploys a wing and glides back home, with a little nose-mounted engine to drive it. But that's been in development hell for over a decade.

It re-uses existing systems (gimballing engines, computers) to effect the recovery. They do add some stuff (legs, RCS, and now fins) but those have nothing like the mass and aero penalties from wings. It also minimizes development cost, since it's a modification of the existing expendable stage and can be tested during revenue flights, rather than development of a whole new vehicle.

Hovering a rocket, btw, is not that hard these days. Look up the Lunar Lander Challenge and/or Masten, Armadillo, Unreasonable Rocket, Morpheus, Mighty Eagle. Big and tall rockets are also easier to hover, given their large moment arm. Think balancing a broom on your hand vs a pencil. (Not that an F9-1 can hover--it's too powerful and too light--but it's a similar operation to do a controlled slowdown.)

Very little, actually. Most of the weight of the rocket is fuel; once it's hit its target altitude, it weighs practically nothing, and takes very little fuel to land.

In all seriousness, try it in Kerbal Space Program (with one of the aerodynamic mods if you want to be more accurate); I don't have hard numbers but I'd guess something like 2-5%. Fuel needed for a particular acceleration is proportional to the mass (duh), so the amount of fuel needed for the same delta-v of an almost-empty first stage is much, much less than for one with a second stage on top.

Estimates are overall payload to orbit is reduced by around 30% with reusability. Dry land landings are more economical for SpaceX, but have further reduced payload to orbit.

I understand the portion of total fuel required can be worked out from that and knowing a little about the rocket specifications.

It was said at some point to be 3%. Anywhere in 2-5% is plausible. Doesn't take much; a nearly-empty stage weighs next to nothing in comparison to a fully-loaded stack. In fact, even with only one engine at minimum throttle, the the F9R-1 stage still has a thrust significantly higher than its weight. Thus the "hover-slam" description of their landing mode: they try to slow down to just above 0 at just the right altitude. Quite a bit of precision required.

One reason, according to Elon Musk, is that parachutes or floatables won't work in the thin atmosphere of Mars. So if Mars is the vision, they must develop something that works there.

Parachutes are hard and have their own failure modes. IIRC even emergency parachutes have taken out some test rockets when they weren't supposed to have been deployed at all.

SpaceX did try parachutes at first, but there were too many down sides.

Parachutes impart heavy stresses on the rocket so aside form the weight of the 'chutes you have to strengthen the rocket, adding even more weight. They also don't allow for landings that are either precise or vertical. In theory you could use 'chutes to slow the rocket for part of the descent, but to land vertically at a precise point you'd still have to add legs and use fuel for a propulsive landing. At which point the 'chutes are adding very little value.

Landing in the sea with floatables means you get a very wet rocket contaminated with saltwater and potentialy flotsam. Seawater plays havock with the hot precision metal parts of the rocket engine. Also again you have to strengthen the rocket to survive the tumble into the sea and wave action.

So using parachutes adds significantly more weight without giving you what you want, and ditching into the sea also means more structural weight and mucks up your engines.

For exactly the same reason that doesn't happen when landing an airplane, it's not efficient, it's complex, it's error prone. Parachutes means you have a recovery zone not a precision landing. Efficiency is all about operational efficiency, and fuel is the cheapest thing in the whole system. Burning a little fuel so that you can have a fully powered, highly controlled, high precision landing means that you are able to recover tens of millions of dollars of spacecraft reliably, and that's far more important than saving a few dollars in fuel. Precisely the same reason why airplanes do powered landings even though they have wings and it would be far, far easier for them to coast to a landing without using parachutes or whatnot.

As for wind, the rocket isn't going to be launched if there's a risk of high wind gusts regardless, and most anything else the vehicle is capable of compensating for with its thrust and fins.

WRT wind tipping the stage: while in flight, it has several control mechanisms to counteract wind, and may have some inherent stability as well.

After landing, it's extremely bottom heavy. Got a bunch of engines and legs down there, and up top a big empty tube. I imagine it's still possible in bad weather, but they'll probably try to avoid that. I imagine it will also be tied down or put on a recovery ship some time after landing.