Using Scramjets to Launch Satellites
Scramjets are one of the most elegant engine designs imaginable, having no moving parts and capable of speeds of more than ten times the speed of sound. Pulsar Aerospace is collaborating with Hypersonix Launch Systems with the goal of bringing to fruition the SPARTAN system, a scramjet based satellite launch system.
The Pulsar fly-back rocket is designed to be a first stage booster for the scramjet among other uses. Dr Michael Smart, founder of Hypersonix Launch Systems, is acting as an advisor to Pulsar Aerospace.
Scramjets are perfect for sustainable space
You can read more about the scramjet design that will be used by Hypersonix Launch Systems here, but we'll give you a brief overview so that you can get a sense of why it will make such a difference for sustainable access to space.
The fuel a scramjet carries on board is hydrogen. Unlike a rocket though, it collects the oxygen from the atmosphere along the way. Because of the hypersonic speeds at which it travels, by shaping and compressing the air with shockwaves, it heats the air up as it enters the engine. Then, simply adding the hydrogen to the oxygen inside the engine causes combustion, firing it out the exhaust and generating thrust. The exhaust is almost exclusively made up of the combination of hydrogen and oxygen, i.e. water vapour.
This design is also very elegant. Whereas jet engines require compressors to get the air to the correct temperature and pressure for combustion, the Hypersonix scramjet underbody is precisely angled to direct and shape shockwaves to progressively heat and compress the air and funnel it into the combustion chamber, without the need for any moving parts.
How this enables reusability like never before
Getting a payload to go fast enough to get into orbit requires an enormous amount of energy. Not only that, fuel used to accelerate it, also needs to be accelerated, which requires more fuel, creating a sort of viscous circle. As a general rule of thumb about 85%-90% of the mass of a rocket is the fuel. The other 10%-15% is the engine and structure, and if it is designed extremely well, there will be a small amount of spare weight for the satellite. Engineers can only achieve this if they work very hard to use extremely light and strong materials for the engine and structure. They tread a very narrow margin between 1) being too fragile to handle the stresses of the flight, and 2) being stronger, but too heavy to have any spare weight available for the payload. This is a major reason why rockets are usually discarded after use; they are so finely tuned that they suffer too much wear from the launch. The other reason is that there isn't enough spare weight to carry the return fuel or to add flight capability to fly itself back.
The answer to the Tyranny of the Rocket Equation
NASA Astronaut Don Petit wrote a famous article and gave a TED talk entitled, The Tyranny of the Rocket Equation. He explains the above conundrum and asks us to consider whether there is another way.
Scramjets are a game changer in addressing this problem.
Now, knowing all of this, consider the fact that the major ingredient of rocket fuel is the oxygen, or some variation of it. Generally the oxygen weighs in the region of six times as much as the other fuel. What if, even for a section of the journey, we didn't have to carry that oxygen with us, but we could collect it along the way, say, like a scramjet? That's a large weight saving.
We could use that weight saving to send up a bigger payload, but if we did that, we're still stuck with the problem of a single use rocket as described earlier. Instead, Hypersonix Launch Systems is using that weight saving to achieve full reusability rather than larger payloads, by adding robustness throughout the system. This way, there will be less wear and tear, and components can be built to last. Having that larger margin allows us to make many flights before any significant refurbishment or maintenance is required. This in turn allows us to operate more in the way that commercial airlines operate, where, between flights they simply refuel and do a system check, with periodic maintenance work.
The SPARTAN satellite launch system:
- Rocket (Up to Mach 5)
- Reusable, fly-back capability
- Scramjet (Mach 5 to Mach 10)
- Reusable, glide back capability
- Rocket (Mach 10 to equivalent of Mach 25)
- Currently not reusable. Burns up on re-entry (no space junk)