How Does Dream Chaser Compare To The Space Shuttle?
Dream Chaser is a modern day spaceplane approaching its first launch expected to happen late this year. Decades prior, the Space Shuttle was launching consistently and proving itself as an extremely capable and impressive launch system. While by no means perfect, over the course of around 30 years, the spacecraft launched 135 times.
These missions were crucial in the construction and placement of key space infrastructure still in use today such as the International Space Station or Hubble Telescope. With this in mind, it brings up the question of what exactly is Dream Chaser’s plan and how does this modern spaceplane compare. Here I will go more in-depth into some of the biggest differences between the two, the similarities they share, what to expect in the near future, and more.
The Differences
One aspect of the Space Shuttle that made it so effective was its massive size and specifically its payload bay. A fully assembled shuttle was 184 feet tall and weighed 4,500,000 pounds. The bay was 15 feet (4.6 meters) in diameter and 60 feet (18.3 meters) long; large enough to fit a school bus or 50,000 pounds of payload. This unique capacity allowed entire telescopes or station segments to fit with ease.
Dream Chaser, on the other hand, is not aiming for the same payload capacity as the Shuttle. Dream Chaser is 30 feet, or 9 meters long—roughly ¼ the total length of the space shuttle orbiters. In terms of payload capacity, Dream Chaser is partially configurable which changes its capabilities depending on the mission. With the help of the Shooting Star service module, (a transport vehicle attached to the back of the spaceplane) Dream Chaser can deliver up to 5,500 kg of pressurized and unpressurized cargo to the space station. Looking inside reveals that there is space for things like food, water, supplies, and science experiments, rather than large structures.
In reality, Dream Chaser is not meant for large payload missions but instead consistent crew travel and payload delivery. Dream Chaser was originally designed as a crewed spaceplane, in part under NASA’s Commercial Crew Program, capable of carrying up to seven astronauts to and from the space station and other low Earth orbit (LEO) destinations. This number is quite similar to the Shuttle which carried between two and eight astronauts on each mission. Right now, Sierra Space is trying to first launch an uncrewed Dream Chaser to the ISS. Assuming this initial mission is successful and followed by many others, we can expect work on actual crewed Dream Chaser launches.
This leads to the next difference which has to do with Dream Chaser’s variants. Not long ago it was revealed that the Dream Chaser spaceplane would feature at least three different designs for various mission profiles and goals. Rather than try to make one spacecraft that could do it all, Sierra Space decided to separate Dream Chaser into multiple designs meant to excel at their respective tasks. This eventually led to Dream Chaser 100 or DC100, DC200, and DC300. DC100 is the uncrewed variant currently being worked on by the company and is about to launch. DC200 is the crew version that features a host of engines on the back for an abort capability and other tasks. Finally, DC300, an upgraded Dream Chaser meant for missions not only to LEO but also MEO and GTO.
One last key difference has to do with the heat shield application and material. In the past, the Space Shuttle struggled with this design quite a bit. Often times missions could be delayed solely by the work needed to replace damaged tiles across the body of this massive shuttle. The TPS was a system of different protection types, not just silica tiles. They were in two basic categories: tile TPS and non-tile TPS. The main selection criteria used the lightest weight protection capable of handling the heat in a given area. However, in some cases, a heavier type was used if additional impact resistance was needed. Much of the shuttle was covered with LI-900 silica tiles, made from essentially very pure quartz sand. The insulation prevented heat transfer to the underlying orbiter aluminium skin and structure.
In contrast, Sierra Space is quoted saying, “SNC engineers have been able to update the TPS tiles from what was used during NASA’s shuttle program with more innovation, better technology, and utilizing lessons learned. They use more modern manufacturing techniques to increase strength and reduce cost. Another difference between the tiles is Dream Chaser tiles are about 10 inches by 10 inches, while those on the shuttle were six inches by six inches. Dream Chaser tiles are stronger and lighter weight than those used during the shuttle program and meet all Micro-Meteroid Orbital Debris (MMOD) requirements to ensure safe entry, descent, and runway landings for crewed or cargo missions. These among other changes are intended to make the tiles even more reliable and easier to refurbish.
The Similarities
While there are a lot of differences between the two, they still share some key similarities. The most obvious being a runway landing. The approach and landing phase began when the orbiter vehicle was at an altitude of 3,000 m (10,000 ft) and traveling at 150 m/s. The orbiter followed either a -20° or -18° glideslope and descended at approximately 51 m/s (167 ft/s). The speed brake was used to keep a continuous speed, and crew initiated a pre-flare maneuver to a -1.5° glideslope at an altitude of 610 m (2,000 ft).
The landing gear was deployed 10 seconds prior to touchdown, when the orbiter was at an altitude of 91 m (300 ft) and traveling 150 m/s. A final flare maneuver reduced the orbiter vehicle’s descent rate to 0.9 m/s, with touchdown occurring at 100–150 m/s, depending on the weight of the orbiter vehicle. After the landing gear touched down, the crew deployed a drag chute out of the vertical stabilizer, and began wheel braking when the orbiter was traveling slower than 72 m/s. After the orbiter’s wheels stopped, the crew deactivated the flight components and prepared to exit. It was said that on a regular mission, the forces put on the body as the craft decelerated through the atmosphere were only 1.7 Gs.
Sierra Space is confident that Dream Chaser can return critical cargo at less than 1.5 g’s using the same runway landing method. So far there have been a few drop tests for this exact process. For example, in one instance, as the helicopter made its second try on the launch zone, all systems were green, and the Dream Chaser began its test flight. The spaceplane entered a steep 70-degree dive, quickly gaining airspeed to intercept the flight path for its normal Earth return. The Dream Chaser then flawlessly performed a series of aerodynamic ‘test inputs’ designed to produce real-world data to validate control system parameters. Finally, the Dream Chaser deployed its landing gear, flared and touched down on the Edwards runway. This process will not only allow reuse opportunities but its intended to speed up the process of reviewing the spacecraft and getting it ready for the next mission.
However, not only is the landing similar, but so is the launch. Between T−6.6 seconds and T−3 seconds, while the RS-25 engines were firing but the SRBs were still bolted to the pad, the offset thrust would cause the Space Shuttle to pitch down 650 mm (25.5 in) measured at the tip of the external tank; the 3-second delay allowed the stack to return to nearly vertical before SRB ignition. This movement was nicknamed the “twang.” At T−0, the eight frangible nuts holding the SRBs to the pad were detonated, the final umbilicals were disconnected, the SSMEs were commanded to 100% throttle, and the SRBs were ignited. By T+0.23 seconds, the SRBs built up enough thrust for liftoff to commence, and reached maximum chamber pressure by T+0.6 seconds. At this point, the spacecraft and its boosters would lift off.
In Dream Chaser’s case, while the spacecraft won’t be providing any help in the form of thrust, it does need a dedicated rocket to get it into orbit. By itself, Dream Chaser would not get very far at all. Once in space, however, it can maneuver accordingly. Uniquely, Dream Chaser can fly on any suitable launch vehicle, in other words, a rocket that can fit the spacecraft inside its fairings. At its core, the Dream Chaser spaceplane is a multi-mission vehicle capable of supporting a variety of LEO needs. It can be customized for both domestic and international customers via vehicle configuration, launch site, destination, landing site, duration, and a host of other variables. Sierra Space has already entered into agreements with multiple international space agencies. Together they are developing technologies, applications, and missions for Dream Chaser-based space systems.
Recently we learned that the first launch of Dream Chaser Tenacity has been delayed from this summer to no earlier than December 2023. NASA updated its internal schedule to show that Sierra Space’s Dream Chaser spacecraft will now berth to the International Space Station late this year. While not ideal, it’s the first ever launch and is bound to be delayed some. Hopefully, in the coming months, the company provides more updates and gets ready for some final testing in preparation.
Conclusion
Sierra Space is trying to revamp what a spaceplane is capable of and meant to do. Dream Chaser shares quite a few similarities and differences with the Space Shuttle, all of which are intended for the future goal of this spacecraft. We will have to wait and see how it progresses and the impact it has on the space industry.