Developing a fully reusable launch vehicle is on SpaceX's (News - Alert) to-do list of big ideas for making space flight cheaper, as this video illustrates. Last week, the company released a short video – below – of its Grasshopper vertical takeoff and landing (VTVL) test vehicle taking its first test flight hop (pardon the pun) from the company's rocket testing facility in McGregor, Texas.

The September-21 flight took all of about three seconds of flight time with the vehicle rising up about six feet before settling back down on to its concrete pad. Grasshopper is built using a Falcon 9 rocket first stage, a single Merlin-1D engine, four steel landing legs, and steel support structure.  

The next major testing milestone expected in the coming months is to bring the vehicle off the pad to hover at 100 feet before landing.

Information gained from Grasshopper flights will be used to develop a fly-back reusable first stage for the company's Falcon 9 rocket, a goal the company believes is obtainable by finding the right balance with enough fuel and hardware for a controlled landing without adding too much weight to cut down on the amount of payload put into orbit.

Being able to partially or fully reuse rocket stages would substantially cut the cost of launches. A Falcon 9 launch currently costs in the neighborhood of $54 million, but only a small fraction of that – perhaps under million or so – is the for the RP-1 and liquid oxygen fuels. 

Flying back half of the two stage Falcon 9 rocket would presumably result in a substantial cut in launch costs.

A reusable Falcon 9 second stage presents more interesting challenges since it leaves earth's atmosphere on its mission to put payloads into orbit, and effectively becomes a (very short flight) orbiting spacecraft.  The second stage would have to deploy a heat shield for reentry so it wouldn't simply disintegrate when it hit the atmosphere.

Once it finished reentry, it would then re-ignite its single engine and deploy landing gear to land.

Making the Falcon 9 second stage reusable may require the use of a hypersonic inflatable atmospheric decelerator (HIAD). The idea uses an inflatable heat shield that can be much larger than the diameter of a capsule or rocket to protect a vehicle. A larger heat shield means more surface area to more effectively slow down while distributing the heat load across the larger surface; think of how a bigger sale catches the more wind.

NASA demonstrated a HIAD over the summer with a suborbital test launch out of Wallops Island, Virginia and may conduct a test from the International Space Station (ISS) at some point in the future. 

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