Elon Musk’s SpaceX is petitioning the U.S. Patent & Trademark Office to overturn a patent awarded to Blue Origin, the space venture backed by Amazon founder Jeff Bezos — arguing that Blue Origin’s approach for landing a booster rocket at sea is actually nothing new in the field of launching and recovering rockets.

“The ‘rocket science’ claimed in the ‘321 patent was, at best, ‘old hat’ by 2009,” says SpaceX in one of two challenges, filed last week with the U.S. Patent Trial and Appeal Board following the approval of the Blue Origin patent in March. SpaceX cites prior work by researchers and scientists who proposed techniques similar to those in Blue Origin’s patent.

It’s the latest public dispute between Blue Origin and SpaceX, which are among the companies competing for a NASA contract to transport U.S. astronauts to the International Space Station. SpaceX has already launched a series of unmanned supply missions to the ISS. The companies previously battled over a contract to control and operate NASA’s historic Launch Complex 39A at Kennedy Space Center.

Blue Origin applied in June 2010 for the patent, Sea landing of space launch vehicles and associated systems and methods, outlining a system for launching a rocket from a coastal launch site and recovering the booster by landing it vertically, tail-first, on a platform at sea — using the booster engines to control the descent.

Although the patent applies specifically to water landings, Blue Origin has been focusing on vertical takeoff and landing in its rocket development, an approach that SpaceX has been pursuing, as well.

If it stands, Blue Origin’s patent could complicate matters for SpaceX if Musk’s company uses the water-landing approach described in the Blue Origin patent. SpaceX announced in May that it had completed qualification testing for the SuperDraco thruster for its Dragon spacecraft, with capabilities including a propulsive landing on Earth or another planet.

Blue Origin declined to comment on the SpaceX challenge when contacted by GeekWire this morning.

SpaceX’s challenge to the Blue Origin patent was first noted by Slashdot. Read SpaceX’s documents challenging the patent here and here.