The $843 million spacecraft that SpaceX is designing to bring down the International Space Station by the end of the decade will be a supercharged version of its Dragon capsule used today to ferry astronauts and cargo into orbit, the company announced Wednesday.
NASA awarded SpaceX the massive contract to develop the U.S. Deorbit Vehicle (USDV) last month. It won the prize — over the only other bidder, Northrop Grumman — in part because its design uses so much flight-proven hardware, NASA said in a source selection statement released Tuesday.
NASA was looking for proposals that maximized the use of flight heritage, because reliability will be key, Dana Weigel, NASA’s ISS program manager, said during a press briefing Wednesday. But even with the significant integration of the Dragon architecture, about half of the USDV will be entirely new and 100 percent of the deorbit functionality will be new to this spacecraft, she said.
The USDV’s goal is to perform a series of critical burns that will occur in the last week of the station’s life, but NASA plans to launch the spacecraft about 18 months before those burns occur. It will dock at the forward port of the ISS, where it will remain as the ISS slowly “drifts” toward Earth, Weigel said. The agency will keep the crew on board as long as possible to maintain the station’s orbit, but they will ultimately depart for the final time about six months before reentry.
The USDV will come into view when the station reaches an altitude of about 220 kilometers above Earth. It will perform a series of burns to prepare the station for a precise deorbit trajectory over a period of about four days before performing a final reentry burn. The parts of the station that do not burn up in Earth’s atmosphere will land in an uninhabited part of the ocean, yet to be determined. This is the same disposal method the station has used for other large spacecraft, such as Northrop Grumman’s Cygnus or Japan’s HTV cargo capsule.
The mission is complex, and SpaceX will need to develop a vehicle powerful enough to navigate the station through increasing amounts of atmospheric drag. As Sarah Walker, SpaceX’s director of Dragon Mission Management, explained, “What I find most complex and challenging is that this [final] “The fire must be powerful enough to fly the entire space station, while at the same time resisting the torques and forces caused by increasing atmospheric drag on the space station, to ensure it ultimately ends up in its intended location.”
SpaceX’s final design is a spacecraft that carries six times the usable propellant and three to four times the power generation and storage of Dragon capsules. The end result, according to a rendering released by SpaceX earlier Wednesday, is what appears to be a conventional Dragon with a giant trunk on the end.
That trunk will house all the extra propellant, power generation and avionics needed to complete the mission, Walker said. That includes 30 additional Draco thrusters, in addition to the 16 already on the standard capsule configuration. A massive final burn should ensure the debris footprint is small — and there will likely be some debris, ranging from the size of microwave ovens to small sedans.
NASA officials said the agency had agreed with the station’s other partners — Roscosmos, the European Space Agency, the Japan Aerospace Exploration Agency and the Canadian Space Agency — to request a deorbit vehicle from private industry after realizing that the capabilities provided by Roscosmos were inadequate for the station’s size. NASA issued a request for proposals last fall.
The award is coming now because developing a spacecraft of this complexity could take years, Weigel said.
But the contract is different from SpaceX’s other big wins for NASA. Unlike the space station crew and cargo contracts, in which NASA simply buys services for vehicles that SpaceX owns and operates, the deorbit vehicle contract flips that around: SpaceX will design and deliver the vehicle to NASA, but it will be the space agency’s responsibility to arrange the launch, operate the spacecraft and actually bring the ISS back to Earth.
The agency will begin the rocket procurement process in a separate tender about three years before launch. Provided ISS operations end in 2030, the station would land sometime the following year.
Agency officials said they would like to see an overlap with commercial space station providers in low Earth orbit, though they acknowledged that a number of variables could prevent a seamless transition. That includes the development schedules of the handful of commercial companies that have stations in development, such as Axiom Space, the Voyager Space-led Starlab or the Blue Origin and Sierra Space venture Orbital Reef. NASA currently has approval to operate the station through 2030; after that date, it would need to seek government approval and cooperation from the other partner space agencies, NASA Deputy Administrator Ken Bowersox said.