Low cost to low orbit

The options for getting satellites into orbit has grown significantly in the last couple of years with an increasing number of players in the space launch market. One area that is growing very quickly is the market for the launch of micro satellites into low earth orbit. The recent successful launch by Rocket Lab from Mahia Peninsula in New Zealand has added another player to the rapidly growing market. Their rocket, is no ordinary old rocket, it’s a new innovative design aimed at reducing cost and increasing efficiency, this includes 3D printing parts and an electric powered pump.

But this isn’t the only area where innovation is occurring, generally in the rocket world, one of the biggest areas is in propulsion, and the advancements that may make it possible to use a single stage rocket to put payloads into orbit will be dramatically reducing the cost of space launches even further.

The centre of this innovation is the aerospike engine which seeks to eliminate the need for multiple stages by having an engine that is efficient at sea level as well as in the outer atmosphere. The traditional rocket engine exhaust is in the shape of a bell, this is to ensure all of the gases exert a pressure in the right direction, which propels the rocket. To be efficient, the shape of the bell needed at sea level is different to the shape of the bell needed at high altitude. That is because as air pressure decreases, the exhaust gases are not contained by the edge of the exhaust bell, in other words, at higher altitude you need a bigger bell. This is why most rockets have multiple stages so they can get rid of the first engine once its efficiency is reduced and then fire up the second stage, which is optimised for the extremely low pressure of the upper atmosphere. Also getting rid of the heavy fuel tanks and engine weight of the first stage also mean there’s less stuff to push into space so there’s a weight saving as well.

If you want to save money on getting into space then you can reuse the rockets, like SpaceX does and the Space Shuttle programme did with the Solid Rocket Boosters, or you can figure out how to burn less fuel. One way is to have a smaller weight through building parts from strong lightweight materials and taking advantage of modern manufacturing techniques, like RocketLab are doing. Another way is to build a new type of engine that burns less fuel and can go all the way to orbit – so you don’t need the extra weight of a second stage engine and the complexity of systems to separate the first stage and fire up the second stage. The aerospike engine makes this a real possibility.

XRS2200 aerospike engine from X-33 programme being tested (credit: NASA via Wikipedia)

The way this engine works is by allowing the shape of the exhaust pattern to change as the air pressure decreases. It does this through a number of ways, the first is that instead of having one source for the hot gases as in the traditional exhaust bell, the aerospike engine has a whole row of sources that start directing the gases in the right direction before they get to expand in the exhaust. The picture above has 20 of these on each side of the engine. So the air pressure at sea level keeps the exhaust flow quite tight, as the air gets thinner higher up the exhaust flow expands a bit but is kept going in the right direction by the shape of the spike (the metal bit in the middle). So unlike the traditional engine which loses efficiency as it goes higher, the aerospike doesn’t.

So why aren’t these engines being used now, instead of the other sort? It’s because they are hard to build and haven’t really had a lot of testing. They were considered for the main engine on the shuttle programme but lost out to the RS-25. The engine design was also considered by NASA for the X-33 programme (a linear aerospike XRS2000 engine is depicted above) but this programme was cancelled. A number of commercial ventures are aiming at using the aerospike engine including Firefly and Arca. The Arca setup is due to begin testing this year and if successful could be quite revolutionary for low cost space access.

Haas 2CA single stage to orbit rocket from http://www.arcaspace.com

Arca are claiming to be able to launch a satellite for $1 million, significantly cheaper than other offering on the market. They ar aiming for the 1 to 50kg market which they think will be worth over $5 billion in the next decade. Arca plan to test the engine this year and launch the suborbital Demonstrator 3 rocket also this year. If they have success, this will be the first successful flight test to space of the aerospike engine. If anything can be learned from the Rocket Lab experience is that Arca might very well succeed.

Rocket Lab did one flight test last year where they got the rocket to space, then yesterday tested the second rocket and successfully delivered a payload. Arca also aim to test the full Haas 2CA rocket and begin commercial operations by the end of this year.

The space launch market is rapidly changing with faster times from design to implementation to market occurring. It might be over dramatic to say that it looks like low cost space access is about to go exponential, but it looks that way.