The correction made in the article (5000 tons => 5000 lbs) shows the importance of having mental visualizations for basic numerical concepts.
5000 lbs of cargo is about an SUV. I can imagine a rocket carrying that up.
5000 tons of cargo is... a giant Wal-mart parking lot full of SUVs (2000 of them). Stacked, they'd make a tower of metal a few miles high. (How? Figure 6 feet tall x 2000 = 12000+ feet.)
Can you imagine a rocket carrying that up and dropping it off at the space station? Nope.
When numbers are just symbols, mistakes like this are easy to make.
Strictly, any man-made vessel that can maneuver independently can be docked, one only needs a larger vessel or facility that can receive it. That any man-made vessel can be docked follows from the fact that it is man-made: some sort of contraption was used to hold it during manufacture, and then it was removed. So long as I can make a vessel big enough to reproduce that environment, I can dock the smaller vessel.
The need for the ability to independently maneuver comes from the legal nature of the issue. At some point, legal responsibility for the vessel transfers from the captain or pilot to the dockmaster. In conventional shipping, that point is when the bow crosses the plane of the dock's gate.
When a vessel is berthed, some mechanism bridges the gap between the facility and the vessel, like ropes, or, in the case of the Dragon Cargo, a robotic arm manipulated from the station.
Docking = A coupling device that actively 'grabs' the other vessel and allows passage between them.
Berthing = A passive process where the vessel is maneuvered into place and bolted onto the other vessel.
The advantage of berthing is that it allows for a larger opening between the two vessels (since the port doesn't need to have all the mechanics necessary to do the 'grabbing' bit).
* The 3-engine deorbit burn worked; previously it was screwed up by uncontrolled roll preventing the engines from getting fuel
* The 1-engine landing burn, previously separately demonstrated by the Grasshopper and F9R test vehicles, worked for a rocket coming down from orbit
The remaining items:
* 3-engine burn to take the rocket back to the Cape from downrange
* Making everything safe enough to dare landing at the Cape, without killing anyone or destroying all the expensive ground equipment that's nearby.
My impression was that with the CASSIOPE attempt, the 3-engine burn was successful but the following 1-engine burn was cut short by the roll.
In the landing burn, it's powering 1 engine for maybe 10 seconds. So that's less than half a percent of the initial fuel mass - something that would make a potential failure a lot less dangerous.
However, even if we assume 30 as the ratio of loaded vs. dry mass, which is better, for example, than Titan II first stage, which has pretty good mass ratio, we need to add the mass of landing legs - something unique for the Falcon. Suppose legs halve the mass ratio, making it 15.
9 engines are capable of lifting the dry first stage, the fuel in it, and the second stage plus payload. That means 9 engines can lift much more than 15 times the dry mass of the first stage. Dividing the thrust by 9 makes the thrust much more than necessary to support the dry stage.
In other words, even the thrust of a single Merlin engine is more than enough to brake the dry weight of the first stage. That means when first stage lands the engine is throttled - spending less mass of fuel per second than it does when Falcon lifts off. The better mass ratio of the first stage, the smaller flow of fuel is needed to decelerate it - so less fuel is needed to brake. It's not enough to count seconds of thrust - how big the thrust is should also be taken into account.
Even with only one engine at 70%, the thrust to weight ratio is greater than 1. That means the rocket can't hover, they just have to time the burn perfectly so the speed reaches 0 at the moment it reaches the ground.
Nasa overview of liquid engine throttling:
"Data upload from tracking plane shows landing in Atlantic was good! Several boats enroute through heavy seas." -- https://twitter.com/elonmusk/statuses/457307742495993856
Which is pretty amazing. Apparently the telemetry continued for 6 seconds as it fell over.
"Flight computers continued transmitting for 8 seconds after reaching the water. Stopped when booster went horizontal." -- https://twitter.com/elonmusk/statuses/457311780943822848
One thought which had occurred to me was maybe they needed to get people working on the upcoming Orbcomm OG2 launch which is currently scheduled for May. When you think about all the time and energy which goes into fabricating the rocket along with all nine Merlin engines, it really hits home how significant of an achievement making reusable rockets will be when SpaceX pulls it off. You have to think that at some point in the not-too-distant future it would be absolutely crazy to launch a rocket where you knew you were going to lose the first stage.
That said, the ability to 'tag along' additional testing without jeopardizing the main mission is a huge win for SpaceX. The cost of the launch (about $100M according to their web site) is paid for by the contract. Getting flight test data as well is pretty priceless.
Finally, even if the seas were calm it would be unlikely they would put a ship in the area as it would put people at risk of having a chunk of rocket and fuel crashing into them. They might have gotten better video though. If I were there I would have tried to figure out how to borrow a predator drone to have it loitering right there to film the arrival.
Regardless, I'm really glad that the mission went off mostly without a hitch. I can't wait to see when SpaceX glues all of the pieces together and has a truly reusable rocket platform.
Maybe they technically could have waited until Saturday, but there is no way they would scrap one of their windows for a tertiary objective.
During the post launch news conference (https://www.youtube.com/watch?v=8G2pRVQ1JhA) Elon said he was pessimistic about a successful recovery of the stage for this launch. However, he said SpaceX is "connecting the dots" and seemed optimistic that they are making good progress (for example, they successfully canceled the roll this time). The rough timeline he mentioned was that they will probably recover a stage sometimes this year, with fully successful recoveries (i.e. capture, refuel, and ready to launch again within hours) sometime early 2015.
As to longer term plans, it's not clear they will relaunch the first booster they get back, even if seawater exposure weren't an issue. More likely, they'll disassemble it, and see how the parts handled the stress of a full launch and re-entry, looking for wear that could endanger a second launch of the same booster. If there are any unpleasant surprises like that lurking, it's a lot cheaper to find out this way than in a launch with a payload at risk.
But they would sure like to know that it behaved properly after they lost contact, and they'd like to know if anything was damaged before it hit the water.
But still, they really would be better off if they had it to pull apart.
Lack of news of recovery makes me think they lost the stage in rough seas. I think we would have heard if it was recovered.
It would be cool if they did :).
I don't know if the whole footage is up yet, but this is a nice summary: https://www.youtube.com/watch?v=3fDzvdEfSgc
working. If they get the 1st stage reusable it brings the bootstrap costs down significantly.
or is spacex still using expendable stages ?
Any technological venture is helping to solve poverty in the long run. Even if the venture does nothing to help inequality, the new technology is almost guaranteed to raise society's collective standard of living.
What SpaceX and their sub contractors have accomplished in the last 12 years is nothing short of amazing.
I think Orbital also has used the NK-33 and NK-43, which were all built in the 60s and 70s. Refurbished can also just mean "something that was sitting around for a long time and needed to maintenance to get up to working". Anything that sits around for 40 years is going to need some kind of work done on it before it's put in service.
Either way, SpaceX doesn't use them.
Huh? As Wikipedia says:
"In order to control quality and costs, SpaceX designs, tests and fabricates the majority of its components in-house ..."