SpaceX ISS Deorbit Vehicle: A Dragon on Steroids

The $843 million spacecraft SpaceX is designing to bring down the International Space Station (ISS) at the end of the decade will be a super-powered version of its Dragon capsule that’s used to transport astronauts and cargo to orbit today, the company revealed Wednesday.

NASA Awards SpaceX Massive Contract

NASA awarded SpaceX the massive contract to develop the U.S. Deorbit Vehicle (USDV) last month. It won the award — over the only other bidder, Northrop Grumman — in part because the design leverages so much flight-proven hardware, NASA said in a source selection statement published Tuesday.

Emphasis on Flight Heritage and New Design SpaceX 

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 Wednesday press conference. However, even with the significant incorporation of the Dragon architecture, around half of the USDV will be entirely new, and 100% of the deorbit functionality will be new to this spacecraft.

Function and Timeline of the USDV

The USDV’s purpose is to execute a series of critical burns over the last week of the station’s life. NASA is planning to launch the spacecraft around 18 months before these burns. It will dock to the forward port of the ISS, where it will remain while the ISS slowly “drifts down” to Earth. The agency will leave crew onboard for as long as possible to maintain the station’s trajectory, but they’ll eventually depart for the final time around six months before reentry.

Detailed Deorbit Process

The USDV will come into play when the station reaches an altitude of around 220 kilometers above Earth. It will perform a series of burns to set the station up for a precise deorbit trajectory over a period of around four days before conducting the final reentry burn. The parts of the station that don’t burn up in Earth’s atmosphere will land in a yet-to-be-determined part of uninhabited ocean, following the same disposal method used for other large spacecraft, like Northrop Grumman’s Cygnus or Japan’s HTV cargo capsule.

Technical Challenges and Enhancements

The mission is complex, and SpaceX will have 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 management, explained, “The thing that I think is most complex and challenging is that this [final] burn must be powerful enough to fly the entire space station, all the while resisting the torques and forces caused by increasing atmospheric drag on the space station to ensure that it ultimately terminates in the intended location.”

USDV Specifications

SpaceX’s ultimate design is a spacecraft that will have six times as much usable propellant onboard and three to four times the power generation and storage of Dragon capsules. According to a render released by SpaceX earlier Wednesday, it resembles a conventional Dragon with a massive trunk attached to its end. This trunk will house all the extra propellant, power generation, and avionics needed to complete the mission, including 30 additional Draco thrusters, in addition to the 16 already on the standard capsule configuration. The massive final burn aims to ensure that the debris footprint is small, though there will likely be some debris ranging from the size of microwave ovens to small sedans.

Collaboration and Procurement

NASA officials said the agency jointly agreed with the other station partners — Roscosmos, the European Space Agency, the Japan Aerospace Exploration Agency, and the Canadian Space Agency — to solicit a deorbit vehicle from private industry after realizing that Roscosmos-provided capabilities weren’t up to the size of the station. NASA released a request for proposals last fall. The award is coming now because spacecraft of this complexity can take years to develop, Weigel said.

SpaceX Contract Specifics

The contract differs from SpaceX’s other big wins for NASA. Unlike its station crew and cargo transportation contracts, in which NASA simply purchases services for vehicles that SpaceX owns and operates, the deorbit vehicle contract flips this on its head: SpaceX will design and deliver the vehicle to NASA, but it will be the space agency’s responsibility to procure launch, operate the spacecraft, and bring the ISS back to Earth. The agency will start the rocket procurement process around three years prior to launch in a separate solicitation. Provided that ISS operations cease in 2030, the station would splash down sometime the following year.

Ensuring a Seamless Transition

Agency officials said they were keen to ensure an overlap with commercial space station providers in low Earth orbit, though they admitted that any number of variables could get in the way of a seamless transition. This includes the development schedules of the handful of commercial companies that have stations under development, like Axiom Space, the Voyager Space-led Starlab, or the Blue Origin and Sierra Space venture Orbital Reef. Right now, NASA is cleared to operate the station through 2030; beyond that date, it would need to seek approval from the government and cooperation with the other partner space agencies, said NASA associate administrator Ken Bowersox.