The $843 million spacecraft SpaceX plans to land on the International Space Station at the end of the decade will be a superpowered version of its Dragon capsule, which is used today to transport astronauts and cargo into orbit, the company revealed Wednesday.
NASA awarded SpaceX the massive contract to develop the US Deorbit Vehicle (USDV) last month. It won the award — over the only other applicant, Northrop Grumman — in part because the design used so much field-proven hardware, NASA said in a source selection statement released Tuesday.
NASA was seeking proposals that would maximize the use of the flight legacy, as reliability will be key, Dana Weigel, NASA’s program manager for the ISS, said during a news conference Wednesday. But even with the significant incorporation of the Dragon architecture, about half of the USDV will be entirely new, and 100 percent of the deorbit functionality will be new to that spacecraft, she said.
The goal of the USDV is to perform a series of critical burns that will occur during the last week of the station’s life, but NASA plans to launch the spacecraft about 18 months before those burns occur. It will attach to the front port of the ISS, where it will remain as the ISS slowly “descends” toward Earth, Weigel said. The agency will keep the crew on board as long as possible to maintain the station’s trajectory, but they will eventually leave for the last time about six months before re-entry.
The USDV will go into action when the station reaches an altitude of about 220 kilometers above Earth. It will perform a series of burns to set the station on a precise de-orbit trajectory over a period of about four days before performing a final re-entry burn. The parts of the station that do not burn up in the Earth’s atmosphere will land in an uninhabited part of the ocean that has not yet been determined. This is the same ejection 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 guide the station through increasing amounts of atmospheric drag. As Sarah Walker, SpaceX’s director of Dragon mission control, explained, “The thing that I think is the most complex and challenging thing is that this [final] burn must be powerful enough to drive the entire space station while resisting the torques and forces caused by the increasing atmospheric drag on the space station to ensure that it will eventually end up in its intended location.
SpaceX’s final design is a spacecraft that will have six times the usable fuel on board and three to four times the energy generation and storage of the Dragon capsules. The end result, at least according to a rendering released by SpaceX earlier Wednesday, is what looks like a conventional dragon with a massive trunk attached to its end.
That trunk will hold all the extra fuel, power generation and avionics needed to complete the mission, Walker said. This includes 30 additional Draco thrusters in addition to the 16 already in the capsule’s standard configuration. The massive final burn should help ensure that the debris footprint is small – and there will likely be some debris ranging from the size of a microwave oven to small sedans.
NASA officials said the agency 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 provided from Roscosmos possibilities are not ready for the size of the station. NASA issued a request for proposals last fall.
The award comes now because spacecraft of such complexity can take years to develop, Weigel said.
But the contract is unlike SpaceX’s other big wins for NASA. Unlike its station crew and cargo contracts, in which NASA simply buys services for vehicles that SpaceX owns and operates, the Deorbit Vehicle contract turns that on its head: SpaceX will design and deliver the vehicle to NASA , but it will be the space agency’s responsibility to provide the launch, control the spacecraft and actually return the ISS back to Earth.
The agency will begin the missile delivery process about three years before launch in a separate invitation. Assuming ISS operations end in 2030, the station will come down sometime next year.
Agency officials said they want to ensure overlap with commercial space station providers in low Earth orbit, though they acknowledged that any number of variables could prevent a smooth transition. This includes the development schedules of a handful of commercial companies that have stations under development, such as Axiom Space, Voyager-led Space Starlab or Blue Origin and Sierra Space’s Orbital Reef venture. NASA is currently authorized to operate the station until 2030; after that date, it will need to seek government approval and cooperation with other partner space agencies, said NASA Associate Administrator Ken Bowersox.
