How Sierra Space Protects America’s Next Space Plane, Dream Chaser

by Sawyer Rosenstein

Dream Chaser, the so-called “mini shuttle”, is set to bring back the capability of returning experiments and equipment from the International Space Station (ISS) through Earth’s atmosphere for an eventual runway landing.

As much as the vehicle resembles NASA’s Space Transportation System, better known as the space shuttle, it’s actually based on a different NASA design. NASA’s Vehicle Analysis Branch at the Langley Research Center in Virginia originally studied the lifting body design known as the HL-20. NASA researched the vehicle for more than 15 years before transferring the research to the then Sierra Nevada corporation, now Sierra Space, in 2006.

However, in discussion with NSF, representatives from Sierra Space tell us there’s still plenty of inspiration taken from the shuttle program, particularly its thermal protection system (TPS).

Sierra Space is providing NASASpaceflight access into the build and design of the first-ever commercial spaceplane. Its current iteration of Dream Chaser is the DC-100, with the first vehicle in the fleet taking the name Tenacity.

The vehicle is covered with more than two thousand individual tiles according to the company. That’s compared to approximately 24,000 for a single space shuttle vehicle.

A render of the Dream Chaser Tenacity in orbit. Credit: Sierra Space

Part of that has to do with vehicle size. In comparison, Dream Chaser is also around ¼ the size of the orbiters. The company is also using larger tiles compared to shuttle. Each Dream Chaser tile, while slightly different in size based on its location on the vehicle, is approximately 10 by 10 inches, compared to the 6 by 6 inch tiles used by NASA.

Similar to the shuttle, each tile on the vehicle is a unique design. “[Each tile] differs in size, shape, thickness, and density,” Sierra Space said. However, they note some significant differences.

Each of the tiles on Tenacity are made of a stronger material than what was used on each of NASA’s orbiters, although still silica-based.

Most of the white material seen aboard the space shuttle is a thermal blanket rather than tiles. As newer orbiters were built, the vehicles tended to use more of the thermal blanket in a way to reduce vehicle weight.

EXCLUSIVE: Work continues on installing thermal tiles. The difference between the white and black tiles is distinct. Credit: Sierra Space

On Dream Chaser, it’s both black and white tiles. Sierra Space told NSF the main difference between the two is a special additive to the outer glass coating.

Another significant difference is that the vehicle consists primarily of the two types of tiles, black and white. The Space Shuttle had portions of the orbiter that needed to be reinforced to handle the heat of reentry including the nose and the leading edge of the wings. In those locations, NASA used special tiles made of reinforced carbon carbon (RCC) to withstand the higher temperatures.

In comparison, we’re told Dream Chaser has no RCC-type panels on the vehicle. “Standard tiles can withstand up to 2,600° F (1,420° C) for multiple reentry cycles, and specialized ones can go higher for single use,” the company told NSF.

EXCLUSIVE: An up-close look at the thermal protection system on Tenacity. Credit: Sierra Space

The tiles serve multiple purposes. In addition to protecting the vehicle during reentry, it will also help normalize the temperature within the craft while in direct sunlight. Temperatures can get as hot as 250° F (120° C) during orbital daylight. The tiles can help to maintain a steady temperature for experiments, and eventually humans, inside.

Tenacity and future Dream Chaser cargo missions to the ISS will fly under the Commercial Resupply Services-2 round of NASA contracts. Sierra Space would be the third and final company to fly under this contract. Northrop Grumman’s Cygnus resupply vehicle along with SpaceX’s Cargo Dragon v2 complete the contract. Dream Chaser is expected to provide a minimum of seven uncrewed cargo missions under this contract.

One unique design factor with this variant of Dream Chaser is the foldable wings. This not only allows for a smaller vehicle profile when docked to the ISS but allows it to fit inside any five-meter payload fairing.

For now, the vehicle is set to launch atop United Launch Alliance’s (ULA) newest vehicle, Vulcan, in particular the 542 variant (flying with a 5-meter payload fairing, four Northrop Grumman GEM-63XL solid rocket boosters, and a dual-engine Centaur upper stage).

While that vehicle has yet to fly, its first flight is expected to launch Astrobotic’s Peregrine lunar lander to the Moon, with the Dream Chaser Demo-1 flight currently scheduled to fly aboard the rocket’s second flight. ULA CEO Tory Bruno currently says the debut flight of Vulcan is targeting Q4 2023 with Tenacity flying in 2024.

A render of Dream Chaser with the Shooting Star cargo module. Credit: Sierra Space

Dream Chaser is expected to carry up to five metric tons of pressurized cargo and a half metric ton of unpressurized cargo to the ISS. That’s in part due to the attached Shooting Star cargo module.

Crews can access the Shooting Star via the aft hatch, berthing to the space station. Once opened, crews can then use this to access the Dream Chaser vehicle itself, and provides a normal cabin environment for astronauts to work.

This portion of the vehicle is not reused and will be disposed of prior to Dream Chaser’s reentry. Sierra Space says they are offering this as a service to help dispose of garbage or other items no longer needed in space or on Earth.

However, the primary Dream Chaser vehicle will become only the second cargo vehicle in use today to offer “down mass” capability, in other words the ability to bring experiments and equipment back to Earth.

EXCLUSIVE: Crews work inside the Dream Chaser vehicle. Credit: SIerra Space

The vehicle will be able to return 1.75 metric tons and can land on most conventional runways. It’s currently scheduled to land at the Launch and Landing Facility at NASA’s Kennedy Space Center. The company also says the largest g-force any payload would experience on reentry would be only 1.5 Gs.

Regarding reusability, the TPS will still require some work between flights of each space plane. Space shuttle tiles were injected with dimethylethoxysilane between flights to help waterproof the tiles.

When speaking to NSF, Sierra Space confirmed, “the tiles are planned to be re-waterproofed between missions similar to Shuttle.”

EXCLUSIVE: An overview of the main Dream Chaser vehicle covered in tiles, including the vertical stabilizer. Credit: Sierra Space

Tenacity, along with its Shooting Star attachment, will soon be sent to the NASA Glenn Research Center in Ohio where it will undergo thermal vacuum testing along with vibration and acoustic testing.

Following that, the vehicle will then be delivered to the Kennedy Space Center in Florida for final tests and processing prior to launch.

(Lead image: Crews work on the thermal protection system for Dream Chaser. Credit: Sierra Space provided to NSF)

Related Articles