The U.S. space race is heating up again.

SpaceX rival United Launch Alliance (ULA) is reportedly a target for a potential takeover by several interested parties.

One of these interested parties is believed to be Blue Origin, an aerospace firm owned by Amazon (AMZN  ) founder Jeff Bezos who has a well-documented rivalry with SpaceX owner Elon Musk.

ULA, jointly owned by aerospace majors Lockheed Martin (LMT  ) and Boeing (BA  ), has - according to the Wall Street Journal - received additional bids from private equity group Cerberus Capital Management and Textron, which makes Bell helicopters as well as Cessna planes.

ULA Up For Sale

Financial details of the offers were not known. But in 2015, Aerojet Rocketdyne Holdings bid $2 billion for ULA.

It is thought that ULA has effectively been up for sale for much of the year. Online tech journal Ars Technica reported in November that its joint owners were close to selecting a buyer from three unnamed bidders.

Blue Origin has an existing relationship with ULA to supply its BE-4 rocket engines to ULA's Delta IV and Atlas V rockets.

While these two vehicles are being retired to make way for the new Vulcan Centaur rocket it will also be powered by the BE-4 engine, making a merger between the two companies a seemingly good fit.

ULA was formed by Boeing and Lockheed in 2006 and, for many years, enjoyed a monopoly on supplying launch services to NASA and Department of Defense and has notched up more than 150 successful missions and has around 70 missions booked for the new Vulcan rocket.

Commercial Space Race

Its dominance in the launch services industry, however, has been eroded by new entrants into the market such as Musk's SpaceX, partly driven by Pentagon directives to seek a broader range of launch providers, and also by rising demand among commercial satellite companies.

Cerberus, meanwhile, owns Stratolaunch which conducts hypersonic tests for air-launched rockets.

Shares in Amazon were up 0.8% at $153.30 in early trade on Thursday, while Musk's Tesla (TSLA  ) was 2.5% higher at $253.41. Lockheed Martin added 0.7% to $445.75 and Boeing gained 1.4% to $263.87.