Image courtesy of X PRIZE.
The history of spaceflight has had its unfortunate share of accidents and fatalities. The continued progression of spaceflight has its risks, especially when the boundaries of what's possible continue to be pushed. The vast majority of these accidents, however, occurred during orbital spaceflights. These flights require a vehicle to get to low Earth orbit, most often the ISS, which is 250 miles above the Earth, over four times higher than the Hermes Spacecraft, a suborbital spacecraft, will fly.
The dynamics of a suborbital vehicle are completely different than an orbital vehicle; it doesn't have to travel as fast, so it doesn't require as much fuel. The vehicle stays a lot cooler, and is much easier to control upon re-entry into the atmosphere. The vehicle can also be structurally stronger because it can afford to weigh more. The vehicle doesn't stay airborne or out of the atmosphere as long, reducing exposure to radiation or the vacuum of space. For all of these reasons the Hermes can be much less complex, and developed at a high highly reduced cost, while still achieving a greater safety factor than its orbital counterparts.
Modular Propulsion System Futron, a well respected decision management solution company, performed a design reliability study on orbital vehicles and concluded that the majority of failures occurred due to propulsion issues. While this study was for orbital vehicles, it makes sense to heed its warnings and apply the same lessons learned and recommendations to a suborbital vehicle. The study found that simplicity and redundancy were the keys to a successful design.
STAR Systems has developed a Modular Propulsion System (MPS), which is our technical term for a multi-motor rocket system. Each motor employs a simple design and is called a core. These cores are easy to fabricate, test, and replicate. The MPS is made up of several cores, which are each an exact copy of each other. Once installed, the MPS provides the rocket ride which takes our passengers into space. Once your trip is over, the cores be ejected, provided maintenance, and reinstalled, ready for the next flight. This system can be thought of as how model rockets work, or gun cartridges.
Being a modular design has several advantages. The MPS greatly increases our mission success, which is getting you and your payloads into space. If there is a problem with one motor during a flight, that motor can be shut down and in that situation, the worst case scenario is that flight will achieve a slightly lower altitude than normal. If a potential problem with a motor is observed during our pre-flight checks, that specific motor can be swapped our prior to launch. Instead of canceling your flight for the day, you wont even know there was a delay. Our modular design allows us to rapidly produce our motors, ultimately bringing our production costs down. It also allows our test program to progress rapidly as our motors are smaller, and changes can be implemented quickly.
Some famous examples of a multiple-chamber designs, all of which have excellent design reliability include the Saturn 1, Soyuz, and now SpaceX. Most suborbital competitors are utilizing a single engine design. We consider our MPS to be not only be the ultimate safety factor, but also our competitive advantage.
Hybrid Rocket Propulsion System
Each of the motor cores in the Hermes Spacecraft is a hybrid motor. In a hybrid motor, the propellant and oxidizer are separated by state, whereas for a solid or liquid motor, all propellant is in their respective state. STAR Systems' motors use a solid fuel (HTPB - rubber) and a liquid oxidizer (Nitrous Oxide). There are several safety advantages in using a hybrid design. They are easy to store and handle since both the propellant and oxidizer are inert separately. Our motors are also environmental benign and create non-toxic byproducts. Hybrids can also be shut down, restarted, and throttled as needed for both the mission and to safe the motors in the event of a problem. The fuel is much easier to examine prior to launch to ensure a high level of quality control on the fuel grain manufacture. All of these factors, combined with STAR Systems Modular Propulsion System made a hybrid motor a clear choice for the Hermes Spacecraft.
All of our astronauts will be wearing their fitted space suits while they take their ride on the Hermes. Over the past several years new and innovative suits have been developed, improving both safety and function. Gone are the bulky suits NASA astronauts currently use, your suit will feel natural and provide maximum mobility while keeping you safe from an unexpected loss of cabin pressure or exposure to the space environment.
Our build-a-little,test-a-lot process ensures that we have fully tested all features of the Hermes Spacecraft before you fly on it. Our prototype was created specifically to work out and improve any design issues that were found. Our Modular Propulsion System was designed to be easy to manufacture so that dozens of revisions could be made and tested of our rocket motors. With each test firing, we received real time feedback which is then incorporated into the next version. Each subsystem is going through this level of testing. This cycle of testing is critical to ensuring the Hermes Spacecraft works right, every time.