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Fourth SpaceX Rocket Successfully Landed on A Drone Ship (theverge.com)
Saturday a SpaceX rocket completed the company's fourth successful landing at sea (watched by over 100,000 viewers on YouTube and Flickr). Saturday's landing means Elon Musk's company has now recovered more than half the rockets they've launched. An anonymous Slashdot reader quotes Saturday's report from The Verge:
Tonight's landing was particularly challenging for SpaceX... The Falcon 9 had to carry its onboard satellite -- called JCSAT-16 -- into...a highly elliptical orbit that takes the satellite 20,000 miles out beyond Earth's surface. Getting to GTO requires a lot of speed and uses up a lot of fuel during take off, more so than getting to lower Earth orbit. That makes things difficult for the rocket landing afterward...there's less fuel leftover for the vehicle to reignite its engines and perform the necessary landing maneuvers.
CEO Elon Musk said the company is aiming to launch its first landed rocket sometime this fall...SpaceX's president, Gwynne Shotwell, estimates that reusing these landed Falcon 9 vehicles will lead to a 30 percent reduction in launch costs.
SpaceX named their drone ship "Of Course I Still Love You."
CEO Elon Musk said the company is aiming to launch its first landed rocket sometime this fall...SpaceX's president, Gwynne Shotwell, estimates that reusing these landed Falcon 9 vehicles will lead to a 30 percent reduction in launch costs.
SpaceX named their drone ship "Of Course I Still Love You."
They slow down mostly through aerodynamic drag. No chute or similar device. The rockets only come on in the last 20 seconds or so to do the final braking.
During reentry the first stage uses the rocket bells as a heat shield, and during the worst part of it they burn three engines to literally push the atmosphere out of the way "entry burn" to ease the heating until it gets down into the lower atmosphere where drag can slow it. For the ship landings, those are the only two burns, total less than 60 seconds with only 3/1 engines firing.
The first stage and the second stage disconnect.
The first stage flips around end to end, and makes a burn to kill most of its velocity.
Then as it is entering the thicker parts of the atmosphere and it would be destroyed by drag and heating otherwise, rapidly slows at high G using the engines to around mach 1, and turns the engines off.
It is at this time steering using fins attached to the top of the rocket.
Once it gets ~10-20 seconds before landing, it lights an engine or three (details vary) and uses the thrust from these vectored in order to precisely land on the barge (along with the fins in the initial portion).
http://www.spacex.com/sites/sp... is a nice diagram.
At the top of it's trajectory, it is out of the atmosphere. As it is about to hit the atmosphere, it burns with three engines for about 20 seconds so that hitting the atmosphere doesn't shred the rocket. It then lets atmospheric drag slow the rocket the rest of the way. It controls its direction with aerodynamic surfaces called grid fins during this phase. Finally, as it approaches the landing platform, it does a one engine burn so that its velocity hits zero at the precise moment when the legs touch down.
The idea is to use the atmosphere to do most of the work slowing down the rocket. However, it needs to not be destroyed entering the atmosphere at velocities that are too high, nor be destroyed hitting the barge at terminal velocity. So engines are used in those two phases.
It has 4 (not 8) grid fins, small cold gas thrusters, and gimbaled engines, all controlling the rocket. They experimented with parachutes (dropping in the ocean instead of of landing on a ship) but never managed to slow down enough to make them work. It's hitting the outer atmosphere at about 2km/second! The has several problems, for example the rocket spinning up in the airflow centrifuging the remaining fuel to the side of the tank, so engines would stop, the steering find moving more than expected and running out of hydraulic fluid just before landing, etc. Even when practicing powered "landing" on the ocean surface before they had a landing ship, the did not even recover small parts because the rocket would be destroyed by waves and sink before they could get to it. The nearly empty first stage is also lighter than the minimum thrust of one of the 9 engines, so if the landing burn is started too early, it will be going back up before reaching zero altitude. Too late, and it will not have stopped before reaching zero altitude. There also has been a problem with one leg not locking into place and toppling over after landing. They now cool the RP-1 (kerosene) to -6C and the liquid oxygen to 50 degrees above absolute zero to make them denser, to get more performance out of the rocket without making the tanks bigger. This makes launch timing very critical since fuel needs to be pumped into the rocket very fast just before launch, without freezing pipes and quickly heads up while in the rocket where it can't be cooled and can't fit in the tank if warmed up. (boil-off only cools it to the boiling point of oxygen which is already to warm to fit in the tank). beginning 2017 SpaceX will start testing a version with 3 of these rockets connected, with all 3 cores landing separately, 2 on land, and the middle on on the ship in the ocean. Next month, SpaceX will present there plans for an even bigger rocket, that will fly to will fly to Mars, land on Mars, re-fuel, fly back to earth and land again, and also be fully reusable.
When a commercial company pays another commercial company to build a commercial satellite and pays to have that satellite launched by yet another commercial company it involves "funny money" and there is no economic benefit?
All three of those commercial companies are profitable.
Space-X raced to build a better launch system because there is substantial demand for launching satellites and by building a better launch system they are able to lower costs, charge less and increase demand.
Space industry amounted to $335 billion last year. Most of that is commercial satellites, which are quite profitable. Do you think AT&T bought DirecTV so they could lose money?