"During previous attempts, we could only expect a landing accuracy of within 10km. For this attempt, we’re targeting a landing accuracy of within 10 meters."
I thought previous landing accuracy was more than 10km. Regardless, it's highly impressive that they are working to improve the accuracy by 1000x. I'm curious if this accuracy improvement is a combination of the grid fins and the autonomous spaceport drone ship (with the ship constantly communicating with the Falcon to be an "easier" target).
This is an absolutely huge test. Musk's entire vision for SpaceX[0] involves cheap, reusable spaceflight, simply because there’s no other way to colonize a different planet without it. According to Musk, abandoning “disposable” rocket technology would result in a 100 fold reduction of the cost of rocket launches[1]. While it might not be that significant, I fully believe than NASA could utilize the minute budget it has much better without throwing away millions of dollars of technology every launch.
Based on that, landing this rocket perfectly is the proof Musk needs to show the world he can launch that rocket again in 10 hours, essentially turning rocket launches into a daily—not monthly—occurrence.
Musk’s vision aside, it would be so cool to land a fucking rocking on floating object in the middle of the ocean. It’s basically a reverse missile maneuver. They’re not ramming the object, they’re just gently touching down, but with all the more accuracy.
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.
The shuttle is in no way comparable with the SpaceX solution. The shuttle was notoriously slow for turn around because it was a massively complicated machine that had to be man-rated. A Falcon 9 first stage is a much simpler machine. On top of that, the shuttle had to go through re-entry, with all of the G forces, and thermal shock associated with that. The Falcon 9 first stage has neither of these problems.
The Falcon 9 still has to deal with heat cycles, vibration, and soot/chemicals byproducts from the engines. The heat cycles and vibration lead to work hardening and cracking or softening of components. Soot can and will get into everything and destroy bearings and connectors.
Even the spray from the ocean combined with the heat from the latent heat in the craft can lead to accelerated corrosion.
They're shooting for a final touchdown speed of 2m/s which seems fairly slow but that's still a lot of mass to stop very quickly. The ocean helps soften touchdown for sure.
It would not surprise me if the turn around procedure was to r&r the entire bottom third of the craft and (possibly) the fuel tanks. The removed components could get inspected and rebuilt and flown again.
It won't be anywhere near the scale of the shuttle turn around but it won't be as simple as hosing it off and fueling it up.
SpaceX has of course considered all of these things and it will be an amazing thing for space travel if they pull it off.
Exactly. SpaceX has completely designed this rocket around easy readiness tests. That's why the rocket was switched from a parachute landing, to a VTOL device[0].
They basically want this to be a smart rocket. Something that can just launch payloads into and out of orbit, and come home like a good dog after a long day of work.
Well, either they tear apart and inspect the engine in between launches or they don't. If they don't, their turnaround will be way faster, but there is a greater chance of failure, and if there is a failure, a much lower chance of figuring out the reasons.
The engines are fired up, shut down and then re-lit again for many dozens of cycles during testing. Plus it's re-started 3 times during landing manoeuvers on top of the launch burn, so it's definitely capable of re-use without being stripped and cleaned. How many times I don't know, but like I said they run the engines though a lot of cycles during testing so they should have a good handle on that.
> so it's definitely capable of re-use without being stripped and cleaned. How many times I don't know
I'm confident SpaceX themselves would have tested multiple engines to failure with many, many re-light, shutdown, re-light cycles so they have a good understanding of what's going to happen when they try to re-use one of these things.
There is no way they'd be going to all this trouble to design a rocket that can come back, all the trouble of giving it someplace to land if they were not already confident the engine can be used at least a few times.
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?
Launching at 60k feet doesn't buy you many advantages except there's less atmospheric drag up there - it's about the speed, not so much the altitude. But you'd gain the problem of hauling a ~500 ton rocket up to 60k feet, and you'd anyway have to launch that plane from ground zero.
Damn I can't wait for this. Its going to be great. Will be interesting to see how the grid fins go. I'm wondering if there could be any trouble from generating too much load from drag while they are in supersonic flow as opposed to high subsonic flow and hypersonic flow where they are known to work fine.
If i were to guess, I would imagine they are going to deploy the fins after or during the 2nd burn / the retro propulsion burn, so that they can only open them after the reach their target speed.
Course I'm probably wrong since I have no idea just where in the powered return flight plan they are supersonic, and they could actually be using the drag from the fins to 'slow down faster' and have engineered the fins to deal with the drag load. Which wouldn't surprise me, but will impress me if its the case.
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.
Its very interesting how they get to use commercial flights to do landing tests. If 50 years from now rockets are reusable and there is competition, they'll be depending on the cost saving of reuse. Any new competitor will be at a significant disadvantage. It's development that is dirt cheap by todays standards, but will be considered expensive in the future.
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.
SpaceX does not file patents. [1] The assumption is that the protection offered by the patent is outweighed by the downside of giving your competitor a roadmap of how you did it. My guess is that just knowing it can be done will be a huge part of enabling someone else to develop similar technology.
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.
On the second video they show them gimbaling towards the rocket and down as well as rotating so I think they have at least 2 degrees of freedom to aide in control alongside the engine gimbal.
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.
On a completely unrelated side note; the cattle grazing (or running?) in the foreground was quite a contrast to the modern, huge rocket landing itself in the background.
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.
In addition to this, it will be required for the middle booster of the Falcon Heavy, which has its first flight next year and which will be too far away from land at separation for a boost back.
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).
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.
> 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.
If you are like me and wondering what makes Vandenberg AFB (California) so good then, well it turns out it's great for polar orbits specifically. Draw a line south from Vandenberg AFB and you don't hit land until Antarctica.
KSP actually models this well; try putting something into a retrograde orbit and compare how easy it is compared to putting it into a regular orbit. If you fly both well, you'll have less left-over delta-v in the craft that you put into a retrograde orbit (if it makes it to orbit at all).
Alternatively, just switch to "orbital speed" on your navball while sitting on the launchpad. That's what you benefit from if you are launching west-to-east, but what you have to overcome if you launch into a retrograde orbit.
In Florida (28 degrees north) the earth surface travels at 400 m/s eastwards. (earth circumference * cos(28) / day)
A spacecraft that would launch from the ground and start westwards, would, after gaining the first 400 m/s relative to its starting point only be stationary relative to the earth's center. Then after 800 m/s, it would travel at 400 m/s westwards. Say if your orbital velocity is 8.0 km/s.
Your total delta vee would be 8.4 km/s.
In comparison, an eastward flying rocket would start from 0.4 km/s , and would need rocket propulsion only for the remaining 7.6 km/s. A 10% saving compared to the westward rocket!
In reality it's a bit more complex as you don't launch straight east or west anyway, and ISS is at a 50 degree inclination etc...
Exactly, and this is maximized by putting launch sites close to the equator. This is one reason why the European Space Agency launches from South America, by the way:
> Kourou lies at latitude 5°3', just over 500 km north of the equator. Its nearness to the equator makes it ideally placed for launches into geostationary transfer orbit as few changes have to be made to a satellite’s trajectory.
> Launchers also profit from the ‘slingshot’ effect, that is the energy created by the speed of the Earth’s rotation around the axis of the Poles. This increases the speed of a launcher by 460 m per second. These important factors save fuel and money, and prolong the active life of satellites.
When you next launch a rocket in KSP, click on the speed indicator right before or after take-off to switch it from "surface" to "orbital". You'll see that the rocket already has a horizontal velocity from the rotation of Kerbin, even before it starts accelerating.
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.
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).
They lease a bunch of agricultural land, and the entity they lease the land from (city of McGregor) doesn't want to ruin the land by leaving it in the hands of a bunch of rocket scientists, so they are required to hire a farmer to manage it.
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?
This is where you can really tell that SpaceX is a private company. If something has a chance of going wrong, and they can avoid live-streaming it, they will.
Why is SpaceX not using a shuttle design? From a layman's perspective, having something that basically works like an aeroplane would be much easier to get reusable, or am I missing something here?
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.
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).
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.
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"
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.
I always wonder how much fuel this rocket needs for landing and if this reduces the maximum payload compared to the disposable Falcon 9. Find they ever release that information?
> 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.
But the point is that by making the stage re-usable, you significantly cut your cost/kg, meaning that even with a decreased capacity it's more cost effective, as you could do several launches rather than just one to lift whatever.
Of course, also bear in mind that this isn't technology just for the Falcon 9 - this is the test-bed. Once we have the systems in place for a reusable first stage, this can be applied to the heavy (which of course uses falcon 9's), and other future generations of craft.
Until we've got SSTO spaceplanes or space elevators, this is pretty much as good as it gets.
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.
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.
Wow. I really hop they nail this landing (if not this timw then next time). A very interesting read, ill have to make a calendar entry tobkeep an eye on the news!
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.
Falcon 9 stages are stored on their sides unpressurized, see any of the numerous roll out videos, and factory images. There are launchers that require pressurization for handling (atlas 5?) but falcon is not one. Musk has mentioned this as a cost reduction and simplification withyou respect to encumbent providers, don't have a link unfortunately.
Bingo it's all about dynamic pressure: to be reusable the hull of the rocket has to land intact and not having undergone plastic deformation of any kind, so it's as close to "factory condition" as possible.
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.
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.)
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.
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 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.
So just to be clear, these rockets are going into space, then somehow coming all the way back down and landing? It seems fantastical that such a rocket could have a controlled descent from space and then land vertically (considering how the shuttle does it for example). How will it control decent speed? Will they carry enough fuel to control the entire descent and land?
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.
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.
curious why don't they deploy parachutes or floatables and then slowly do a controlled descent using the rockets? I mean is this most efficient way of landing the rocket, essentially going backwards on re-entry? What if the rocket catches a gust of wind and flips on its side? Bad weather?
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.
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.
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.
I thought previous landing accuracy was more than 10km. Regardless, it's highly impressive that they are working to improve the accuracy by 1000x. I'm curious if this accuracy improvement is a combination of the grid fins and the autonomous spaceport drone ship (with the ship constantly communicating with the Falcon to be an "easier" target).