Less than a month after SpaceX successfully landed a Falcon 9 booster stage in Cape Canaveral, it will attempt to one-up the historic feat. On Sunday, the company will attempt another landing, this time on an Autonomous Spaceport Drone Ship off the coast of California.
The mission to deliver a NASA/NOAA/CNES joint science mission, “Jason-3,” is currently scheduled for launch at 10:42 a.m. PST on January 17 from Vandenberg Air Force Base in California. (Updates can be found here.)
It may be the NFL playoffs, but Sunday’s launch and landing are worth watching!
The flexibility enabled by sea landings is critical to the future of reusable rockets, a technology that could reduce the cost of spaceflight by a factor of 100, according to SpaceX founder, Elon Musk.
Read on to learn some of the mechanics and benefits of sea landings.
Drone Ship Landing Mechanics
To date, SpaceX has had little luck landing boosters at sea. The company’s last two attempts ended in explosive near-misses.
As it turns out, stabilizing a 150-foot-tall rocket stage travelling at 2,900 mph can be a bit tricky.
Following first stage engine cutoff, thrusters trigger to flip the stage into position for retrograde burn. The retrograde burn starts, powered by three of the rocket’s nine Merlin engines, correcting the stage’s angle and reducing its velocity.
As the booster enters position and approaches the drone ship, two of the three engines shut down, and four landing legs deploy. The remaining engine burns, slowing the booster to zero velocity while four hypersonic grid fins control the rocket’s lift vector. (See video)
The target is small. The landing area of the drone ship is 150×250 feet while the leg span of the Falcon 9 booster stage is 60 feet. The margin of error is less than one leg span in the shortest direction.
Drone Ship Landing Benefits
It’s possible Jason-3 may be better suited for a ground landing due to the fact that its destination is low Earth orbit, but according to a company spokesperson, SpaceX did not receive approval for a land-based landing in time for the launch, hence the decision to land on the drone ship.
Even so, sea landings are beneficial to the company’s reusable booster model.
Sea landings save fuel. Due to the parabolic arc rockets take to reach space (see image below), returning for a land-based landing requires extra fuel to get back to (or close to) the launch pad. In a recent blog post, SpaceX founder, Elon Musk describes this maneuver:
“…the rocket is moving super fast away from the launch site, so it has to do a screeching U-turn with nitrogen attitude thrusters, then fire the engines to create a reversed ballistic arc, then reorient again for atmospheric entry and have the engines pointed in the right direction for the landing burn.” – Elon Musk
That’s a lot of fuel consumed.
Sea landings enable SpaceX to direct a mobile landing barge underneath the rocket, cutting the distance and fuel required to land. More fuel means more mission capability.
Two types of payloads will generally benefit from barge landings: those that are heavy, and those with destinations beyond low Earth orbit.
Heavy payloads will generally require more fuel to reach orbit. Similarly, payloads headed for more distant orbits, like the SES-9 communications satellite SpaceX will launch to geostationary orbit later in January, require greater launch velocities to reach such altitudes.
Because decelerating and landing a booster stage for these types of launches requires more fuel, barge landings will generally be more practical.
Also a factor for land-based landings is Federal Aviation Administration approval. SpaceX must be able to prove its booster stages will not harm people or property during landings. This may become simpler as the technology becomes more reliable.
Rocket version, performance requirements, environmental concerns and other factors also play into whether a booster is capable of land-based landings, according to SpaceX.
What to Watch
Also this week, as soon as today, SpaceX will test-fire the engines of the Falcon 9 booster that successfully landed at Cape Canaveral Air Force Station back in December. The test will demonstrate the capability of reusing boosters, a critical step to reducing launch costs.
The New England Patriots take on the Kansas City Chiefs in the Divisional Round at Gillete Stadium this Saturday afternoon at 4:35 p.m. EST. Go Pats!
Special Thanks to AmericaSpace.com for helping me with the mechanics of drone ship landings!