The SpaceX launch company is scaling back expectations for an unprecedented rocket landing on a floating ocean platform, comparing the feat to "trying to balance a rubber broomstick on your hand in the middle of a windstorm."
The experiment is scheduled to take place on Jan. 6, when SpaceX sends a two-stage Falcon 9 rocket and its uncrewed Dragon cargo capsule toward the International Space Station on a resupply run. After stage separation at an altitude of roughly 60 miles (100 kilometers), the Falcon's first stage is slated to relight its rocket engines and go through a complex series of maneuvers to put itself down on a 300-foot-long (90-meter-long) "autonomous spaceport drone ship" in the Atlantic Ocean.
"The odds of success are not great — perhaps 50 percent at best," SpaceX said in a statement explaining the effort. "However, this test represents the first in a series of similar tests that will ultimately deliver a fully reusable Falcon 9 first stage."
For decades, launch vehicles have traditionally dropped away their rocket stages, leaving them behind to burn up while the rest of the vehicle ascended to orbit. That's the way it worked for the Saturn 5 back in the days of Apollo, and the way it works for virtually all modern-day rockets. Even the space shuttle jettisoned its external fuel tank for destruction, although its solid rocket boosters fell into the sea and were recovered for refurbishment.
Although suborbital rocket ships have been known to blast off and land again in recent years, no rocket stage has ever flown itself back to a controlled landing after sending a payload to orbit. SpaceX plans to do it using a series of three rocket engine burns, helped along by the use of hypersonic control fins.
The retro rocket firings are meant to slow the 14-story-tall rocket stage's descent from a supersonic speed of 2,900 mph (1,300 meters per second) to less than 5 mph (2 meters per second). Just before landing, four landing legs would spring open — and the rocket would settle onto the thruster-stabilized drone ship for eventual return to shore.
For a larger version of the graphic and a full explanation of the launch profile and its significance, check out 'The Future of Space Launch Is Near' by John Gardi and Jon Ross.
SpaceX has previously tested some of the technologies for a "soft splashdown" of the Falcon first stage, but the company has not yet been able to recover the stage intact — and next month's launch attempt marks the first time that the landing ship will come into play.
"During previous attempts, we could only expect a landing accuracy of within 10 kilometers," or 6 miles, SpaceX said. "For this attempt, we’re targeting a landing accuracy of within 10 meters [33 feet]."
A different kind of land-based rocket experiment ended in a spectacular failure in August, when an uncrewed SpaceX F9R test rocket went awry and had to be blown up during a flight test of the self-landing system. SpaceX said the failure was traced to a problem with a sensor that would not have arisen on an operational Falcon 9 rocket.
Why do it?
The point of the exercise is to bring the cost of spaceflight down dramatically. Today, the commonly quoted figure for the cost of sending payloads to low Earth orbit is $10,000 a pound ($22,000 a kilogram). SpaceX's billionaire founder, Elon Musk, says making rockets fully recoverable and reusable could reduce that cost by 99 percent.
That cost reduction is a key part of Musk's long-range strategy to send colonists to Mars and turn humanity into a multiplanet species — as an "insurance policy" in case a killer asteroid, climate catastrophe or global pandemic threatens civilization on our home planet.
Although rockets that land themselves are a big part of Musk's vision for the future, mission success will not depend on whether or not the Falcon 9 first stage sets down safely on the drone ship. The key task is to deliver more than 3,700 pounds (1,680 kilograms) of scientific experiments, hardware and supplies to the space station. This is the fifth of 12 scheduled cargo runs covered by SpaceX's $1.6 billion resupply contract with NASA.
The Falcon 9 launch is currently scheduled for 6:18 a.m. ET Jan. 6 from Cape Canaveral Air Force Station in Florida. It had been set for Friday, but problems with a static-fire test at the launch pad forced a delay. Liftoff will be webcast via SpaceX and NASA. A series of NASA briefings about the mission is scheduled to be webcast on Jan. 5, starting at noon ET.
Update for 12:15 p.m. ET Dec. 18: This report has been updated with the postponement of the launch attempt to Jan. 6.