SpaceX Drone Ship Landing
On April 8, 2016, the Falcon 9 rocket launched the Dragon spacecraft to the international
space station, and the first stage returned and landed on the “Of course I still love
you” droneship.
Curious to know the significance of this landing type?
KEEP WATCHING!!
Of Course I Still Love You (OCISLY) is an autonomous spaceport drone ship (ASDS) that
operates out of Port Canaveral, Florida.
The droneship is a modified barge outfitted with a large landing platform, station-keeping
thrusters and other equipment to allow SpaceX to land boosters at sea on high-velocity missions
that cannot carry enough fuel to allow for a return-to-launch-site landing.
Construction of OCISLY started in early 2015 and was built as a replacement for the original
drone ship “Just Read The Instructions” and The drone ship entered service in June
2015.
OCISLY is built upon a barge – Marmac 304 – and was modified in a Louisiana shipyard.
Modifications include an expanded deck to increase the size of the landing platform,
the installation of 4 thruster engines so the drone ship can autonomously maintain its
position at sea, and blast shielding to protect electrical and engine equipment on deck.
It is equipped with 4 x 300 horsepower azimuth thruster engines that are fitted to each corner
of the landing platform.
When deployed, they allow the drone ship to maintain a precise position whilst at sea.
Elon Musk has stated that the drone ship is capable of maintaining its target position
to within 3 meters, even under storm conditions.
The drone ship can reportedly maintain its target position autonomously, or under remote
control by operators on a support ship.
It’s also fitted with cameras, sensors and other measuring equipment to allow SpaceX
to record and gather data on the landings.
On a number of occasions, it has been shown that the cameras can be remotely adjusted
and moved during landings to provide a better perspective.
Moreover, it is fitted with two satellite antennas for the uplink of data and for communication
with the incoming booster.
A common problem experienced during SpaceX webcasts is the video connection to the droneship
cutting out during the landing.
This occurs because vibrations created by the landing booster violently shake the droneship,
temporarily breaking the connection and up-link to the satellite.
A robot, officially named the Falcon 9 Securing Robot, but universally known as Octagrabber
lives on the droneship and is deployed shortly after a booster landing.
The robot is remotely driven from it’s blast-proof shelter and positioned underneath the Falcon
9.
Four arms then raise up and latch onto the Falcon 9 Octaweb, securing the booster.
OCISLY is equipped with remotely-operated fire fighting hoses that can quickly deluge
the drone ship in water in the event of an explosion or fire caused by a failed landing.
SpaceX drone ships are not designed to autonomously move themselves over long distances.
Instead, a tugboat is used to tow the drone ship to the target position offshore in the
Atlantic Ocean.
The exact position of the drone ship is dependent on mission requirements.
Boosters used on Starlink and geostationary transfer orbit missions typically land between
600 – 675 km downrange.
The furthest drone ship position was 1239 km downrange, set during the STP-2 Falcon
Heavy mission in June 2019.
OCISLY and the tugboat will leave Port Canaveral up to 7 days in advance of the launch date,
with other accompanying support ships leaving later.
After traveling to the landing zone the thrusters and other equipment will be engaged.
Support vessels and the tugboat will then retreat to a safe distance to observe the
landing.
Of Course I Still Love You is unmanned during all landings.
Once the landing is complete, Octagrabber will be deployed to secure the booster and
SpaceX technicians will dis-engage the thrusters and prepare the drone ship for the return
journey.
The tugboat will then tow OCISLY back to Port Canaveral.
You may ask yourself, what is the point of landing SpaceX’s rocket on a barge in the
ocean?
And the main reason is that in certain cases, the first stage simply does not have enough
fuel to come back to the land.
Launching a heavy payload or pulling something into a higher orbit requires that the first
stage does a lot more in terms of generating velocity for the payload before it hands off
the rest of the mission to stage two.
And this is why SpaceX is focusing recently on having more powerful engines and more fuel.
A conventional launch mission will leave the stage with close to as little fuel as possible
by the time it detaches in order to be efficient.
SpaceX wants the first stage to deliver the rest of the rocket closer to the orbit with
enough leftover fuel to boost back and land.
Which is also tough because any fuel left over for landing is just added weight it had
to bring all the way up with it.
Sometimes, it does not have enough fuel or is simply too far down range by the time it
detaches from stage two to make the round trip.
In conclusion, the motivation behind landing on a barge is not necessarily to mitigate
risk or to prove that the feat is possible, but more of a result of logistics.
A drone ship floating on the ocean is a harder target to hit than a large expanse of ground,
since it is smaller and floating on moving water.
Plus, all of SpaceX's ocean landing attempts have resulted in the rocket explosion.
Still, landing at sea can be less tricky than ground landings, and the main reason has to
do with fuel.
To return back to Earth, the Falcon 9 has to use the fuel leftover from takeoff to reignite
its engines in a series of burns.
These burns help to adjust the rocket's speed and reorient the vehicle into the right position
for entering Earth's atmosphere and then landing.
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Different types of landing techniques require different amounts of fuel, though, and that
revolves around how the Falcon 9 launches.
The rocket doesn't travel straight upward into space but follows a parabolic arc up
and away from the launch pad.
Because of this, the rocket has to go through a lot to conduct a ground landing.
The vehicle has to slow down in the direction it's heading, completely turn around, and
then retread the vertical and horizontal distance it's covered to get back to the landing site.
That requires a lot of extra fuel.
Ocean landings aren't as complicated as that.
SpaceX's drone ship can position itself in an ideal place to "catch" the vehicle on its
more natural path back to Earth.
That decreases the distance the rocket needs to travel, as well as the amount of fuel needed
to maneuver the Falcon 9 for landing.
For SpaceX missions that use up lots of fuel, performing a ground landing may not even be
possible.
Rockets that launch heavy payloads or go to a high orbit need extra speed during the initial
ascent, and extra speed needs more fuel.
Those Falcon 9s that have to reach extra high velocities don't have as much fuel leftover
for the landing.
That’s when the drone ship is the best — if not only — option for recovery.
The whole point of landing these rockets is to help save SpaceX money on launch costs.
Right now, most rockets are destroyed or lost after they launch into space, meaning entirely
new rockets must be built for each mission.
SpaceX hopes to recover as many rockets as possible to cut down on the cost of creating
new vehicles.
The Falcon 9 costs $60 million to make and only $200,000 to fuel.
If a recovered rocket doesn’t need too much updating and refurbishment between launches,
reusability could eliminate a good chunk of that manufacturing cost.
SpaceX president Gwynne Shotwell expects reusable rockets to bring down launch costs by about
30 percent, making the company’s vehicles an even cheaper option for clients than it
already is.
However, the true cost of a launch will depend on how many times they can reuse the stage
- which is still up for debate.
But taking some educated guesses and quoting SpaceX officials, reusing just the first stage,
they could possibly get a Falcon 9 launch down to as low ~$18 million per launch, if
they were willing to accept slim profit margins.
However, with SpaceX's competitors still trying to catch up to their current prices, and the
company shifting substantial development work toward Starship and Starlink, prices will
likely remain well above that level for now to help finance those ambitions.
SpaceX sometimes land on the ASDS when they could land back at the pad and the reason
is because, initially, barge landings were about safety and were used for practice before
moving towards landing back at the launch site.
However, even though RTLS has now been proven to work, the booster cannot always land at
the launch site.
The main practical difference is that RTLS trajectory consumes more fuel than ASDS, which
eats into the payload capability.
RTLS loses about 30% total capacity, vs about 15% for ASDS landings.
Barge landings are needed for high mass/high-velocity launches, such as Geostationary Transfer Orbit
missions.
During these types of missions, it's just not physically possible to return to the launch
site.
This is because they put such a high demand on the rocket; the rocket needs to work hard
to raise a heavy bird to the speeds required for high orbits.
To land back at the pad, the speed at stage separation cannot be greater than about 1650
m/s.
If you can land on a ship, there's no need to zero out the booster's lateral velocity,
so stage separation can occur at up to around 1900 m/s.
Put another way, the extra delta V "boostback" expense inflicts a penalty on payload mass.
the process for bringing back boosters that land on the ASDS consists of different aspects,
The first job is to secure the booster.
While the center of gravity is pretty low for the booster, as all the engines and residual
propellant is at the bottom, it can still slide around in rough seas if unsecured or
even fall over In the past, SpaceX would attach the boosters to jack stands, and weld those
to the deck of the barge.
However, this took time and could not be done in rough seas, as it was too dangerous for
the crew.
To resolve this, SpaceX has developed a remote controlled robot, informally named "Octograbber"
or "Roomba", that slides under the booster and attaches to its four hold down points
on the Octaweb to keep it in place.
Once the booster is secured, a tug tows the ASDS back to port.
At the port, the booster is lifted off the barge using a crane, and placed onto a stand
which supports the weight of the booster from the launch hold-down point.
Once on the stand, the legs can be removed or retracted, and then the booster is rotated
to the horizontal, and placed on the back of a transporter, to be taken back to the
launch site.
At the launch site, the stage is inspected, any required maintenance is carried out, and
then a series of test fires are carried out in order to requalify the booster for a relaunch.
Thanks for watching everyone!!
Can you guess Why does half of the Falcon booster look black or dirty after it has landed?
Do you know why Falcon boosters have 4 legs?
Did you learn anything new in this video?
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