SpaceX is building a souped-up version of its cargo Dragon spacecraft to deorbit the International Space Station and perform a controlled re-entry and breakup in a remote part of the ocean after the laboratory is set to retire in 2030, NASA and company officials said Wednesday.
The ISS Deorbit Vehicle (DV) will be a one-of-a-kind, custom-built spacecraft that will be required to ensure the space station re-enters the atmosphere at the right point and orientation, ensuring that any debris that can withstand the 3,000-degree heat will crash-land harmlessly at sea.
In late June, NASA awarded SpaceX a contract worth up to $843 million to build the orbiter, which will be owned and operated by the space agency. The heavy-lift rocket needed for launch has not yet been selected, but NASA Administrator Bill Nelson has requested a total of about $1.5 billion from Congress to carry out the entire orbiter operation.
And that’s no small matter. The space station, comprised of multiple pressurized modules where visiting crew members live and work, has a long axis of 218 feet. Mounted perpendicular to the long axis, the lab’s solar panel power and cooling truss extends 310 feet from end to end, longer than a U.S. football field.
The entire laboratory complex has a total mass of 925,000 pounds (about 473,000 kg) and is moving through space at about 17,100 miles per second (about 84 football fields).
To carefully lower its altitude for a controlled reentry, the DV will carry approximately 35,000 pounds of propellant powering 46 Draco rocket engines, 30 of which will be mounted on an extended fuselage section to perform most of the deorbit maneuvers.
“Once we decide to deorbit the station, we will launch the US DV about a year and a half before the final reentry burn,” he said. Dana WeigelISS program manager at the Johnson Space Center.
“We’ll dock the ship, do a series of checks, and once we’re satisfied that everything looks healthy and we’re ready, we’ll let the ISS drift down.”
The final space station crew will remain on board until periodic thruster firings and the ever-increasing “drag” in the extreme upper atmosphere bring the laboratory down to an altitude of approximately 205 miles. This milestone will be reached approximately six months before the final re-entry procedure.
Once the ISS, which is uncrewed by then, reaches an altitude of about 140 miles, the DV will “do a series of burns to prepare us for that final out-of-orbit,” Weigel said. “And then four days later, it will do the final re-entry burn.”
The space station’s large but relatively flimsy solar panels will be the first to rupture and burn, along with antennas, radiator panels and other appendages.
Larger components (modules and the lab’s massive power cage) will also break apart in the infernal high-speed descent, but pieces the size of a small car are expected to survive the ocean splashdown along its narrow 1,200-mile-long “footprint.”
The remote areas of the South Pacific Ocean offer uninhabited landing zones, although a final destination has not yet been determined.
“To achieve a fully targeted entry, a deorbit vehicle would need six times the usable propellant and three to four times the power generation and storage space of today’s Dragon spacecraft,” said Sarah Walker, a senior manager at SpaceX.
“It needs enough fuel on board to not only complete the primary mission, but also to operate in orbit with the space station for about 18 months. Then at the right time, it will perform a complex series of actions over several days to deorbit the International Space Station.”
Some kind of deorbiting spacecraft is needed because even at the space station’s current altitude of 260 miles, trace amounts of atmosphere are still present. As the station flies through this wispy material at about 5 miles per second, collisions with these particles slow the craft down ever so slightly in a phenomenon known as atmospheric drag.
Throughout the life of the program, periodic thruster firings were performed by engines on Russian modules or attached to Progress cargo ships to increase the laboratory’s altitude as needed to offset the effects of drag. More recently, Northrop Grumman’s Cygnus cargo ships added a modest repowering capability.
Without these carefully planned launches, the station would eventually crash-land into the lower atmosphere.
The station flies over every point on Earth between 51.6 degrees north and south latitude, covering the entire planet between London and the tip of South America. In an uncontrolled reentry, any station debris that survives the re-entry heating could crash anywhere in that region.
While the likelihood of hitting a populated area is relatively low, something as large as the space station has never fallen back to Earth and re-entered our atmosphere before, and NASA doesn’t want to take any risks.
NASA and its station partners—the space agencies of Europe, Russia, Canada, and Japan—had planned from the beginning to deliberately launch the laboratory into the atmosphere at the end of its life, where it would disintegrate over a desolate patch of ocean.
Initially, it was planned to use thrusters on multiple Russian Progress cargo ships to lower the laboratory’s altitude and enable a targeted drop to Earth.
“Early in the station planning, we considered deorbiting using three Progress vehicles,” Weigel said. “But the Roscosmos segment was not designed to control three Progress vehicles simultaneously. So that posed a bit of a challenge.
“Also, the capacity wasn’t really what we needed for the size of the station. So we decided together to have the U.S. industry take a look at what we could do on our side for deorbit.”
Last year, NASA sought industry bids, and two companies responded: SpaceX and Northrop Grumman. The agency announced last week that SpaceX had won the contract.
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