The International Space Station (ISS) was designed during the Space Shuttle era, but NASA had to come up with alternatives when the Shuttle was retired in 2011. So far, only a few private vehicles have been certified to the station, but the long-delayed Dream Chaser should join the list in 2024. NASA has previewed the demo mission, which will see Sierra Space's reusable space plane visit the ISS with literal tons of cargo.
Sierra Space first revealed the Dream Chaser in 2016, based on the HL-20 concept spacecraft developed at NASA’s Langley Research Center. The Dream Chaser is designed to launch atop a conventional rocket—for the 2024 demo mission, it will launch with a Vulcan Centaur rocket from Space Launch Complex 41 at Cape Canaveral. This is a non-reusable rocket, which will drop into the ocean after seeing the space plane safely on its way. A fairing will cover the Dream Chaser during launch, but this covering will be jettisoned after atmospheric density drops.
Once in space, Dream Chaser will deploy its wings and solar panels, which will be mounted to the wings and cargo module. That non-reusable cargo module, known as Shooting Star, is a key component of Dream Chaser. This 15-foot module attaches to the back of the spacecraft, adding 10,000 pounds of cargo capacity. The optional cargo bay can be pressurized for transporting sensitive equipment and experiments. In the initial test, Dream Chaser will only be carrying 6,500 pounds of cargo, but future missions are cleared to carry as much as 11,500 pounds of cargo. By comparison, the SpaceX Dragon can only haul about 7,000 pounds of cargo to the ISS.
Having gone through certification with two commercial vehicles so far, NASA has nailed down what it wants to see from Sierra Space before it gives Dream Chaser a green light. Before reaching the ISS, the spacecraft will need to demonstrate several important capabilities. These "far-field demonstrations" include demonstrating attitude control, translational maneuvers, and abort procedures. Then, the spacecraft will move into the station's approach ellipsoid, a 2.5-by-1.25-by-1.25-mile bubble around the station where only approved vehicles are permitted. Here, the near-field demo will consist of following commands from ground control and the station to move to and hold position at various distances.
With the maneuvering demos complete, Dream Chaser will wait 38 feet away while the station's Canadarm2 removes and docks the Shooting Star module. Dream Chaser itself will then be attached to the station, where it will stay for about 45 days. When the time comes to leave the station, Dream Chaser's design allows it to land in as little as 11 to 15 hours. The spacecraft will land on a runway in Space Shuttle style at Kennedy’s Launch and Landing Facility. Once the demo flight is in the books, Sierra Space can begin commercial flights just in time for NASA to wind down the ISS. However, Dream Chaser has also been designed with the upcoming Lunar Gateway station in mind.
