Question: How many passenger service flights did the only other counterpart of the supersonic aircraft Concorde complete?

Context paragraphs:
Handley Page HP.115: The Handley Page HP.115 was a British delta wing research aircraft built by Handley Page to test the low-speed handling characteristics to be expected from a supersonic airliner of slender delta configuration.  It formed part of the British supersonic aircraft research programme, carried out in the 1960s and sponsored by the Ministry of Supply, that eventually produced the Concorde.

Supersonic transport: A supersonic transport (SST) is a civilian supersonic aircraft designed to transport passengers at speeds greater than the speed of sound.  To date, the only SSTs to see regular service have been Concorde and the Tupolev Tu-144.  The last passenger flight of the Tu-144 was in June 1978 and it was last flown in 1999 by NASA.  Concorde's last commercial flight was in October 2003, with a November 26, 2003 ferry flight being its last airborne operation.  Following the permanent cessation of flying by Concorde, there are no remaining SSTs in commercial service.  Several companies have each proposed a supersonic business jet, which may bring supersonic transport back again.

Tupolev Tu-144: The Tupolev Tu-144 (Russian: Tyполев Ту-144 ; NATO reporting name: Charger) is a retired jet airliner and commercial supersonic transport aircraft (SST).  It is one of only two SSTs to enter commercial service, the other being the Anglo-French Concorde.  The design was a product of the Tupolev design bureau, headed by Alexei Tupolev, of the Soviet Union and manufactured by the Voronezh Aircraft Production Association in Voronezh, Russia.  It conducted 55 passenger service flights, at an average service altitude of 16,000 m and cruised at a speed of around 2,000 km/h (Mach 1.6).

Supersonic aircraft: A supersonic aircraft is an aircraft able to fly faster than the speed of sound (Mach number 1).  Supersonic aircraft were developed in the second half of the twentieth century and have been used almost entirely for research and military purposes.  Only two, Concorde and the Tupolev Tu-144, ever entered service for civil use as airliners.  Fighter jets are the most common example of supersonic aircraft.

KAI T-50 Golden Eagle: The KAI T-50 Golden Eagle (골든이글) is a family of South Korean supersonic advanced trainers and light combat aircraft, developed by Korea Aerospace Industries (KAI) with Lockheed Martin.  The T-50 is South Korea's first indigenous supersonic aircraft and one of the world's few supersonic trainers.  Development began in the late 1990s, and its maiden flight occurred in 2002.  The aircraft entered active service with the Republic of Korea Air Force (ROKAF) in 2005.

Wallace D. Hayes: Wallace D. Hayes (b. September 4, 1918 – d. March 2, 2001) was a professor of mechanical and aerospace engineering at Princeton University and one of the world's leading theoretical aerodynamicists, whose numerous and fundamental contributions to the theories of supersonic and hypersonic flow and wave motion strongly influenced the design of aircraft at supersonic speeds and missiles at hypersonic speeds.  This greatly enhanced the development of supersonic flight and supersonic aircraft design.

Supercruise: Supercruise is sustained supersonic flight of a supersonic aircraft with a useful cargo, passenger, or weapons load performed efficiently, which typically precludes the use of highly inefficient afterburners (reheat).  Many well known supersonic military aircraft are not capable of supercruise as they are only able to maintain supersonic flight in short bursts (typically with afterburners) while they cruise at subsonic speeds.  Aircraft such as the SR-71 Blackbird are designed to cruise at supersonic speed with afterburners enabled.

Droop-nose: The droop-nose configuration is a distinctive feature of some supersonic aircraft, most notably both Concorde and the Tupolev Tu-144.  When these aircraft were in service, the pilot would lower the nose cone to improve visibility of the runway and taxiways.  When in flight, the nose would be raised.  Concorde also had a moving visor that would slide into and out of the nose.  The Tu-144's visor was part of the nose and did not retract.

Avion de Transport Supersonique Futur: The Avion de Transport Supersonique Futur (ATSF) also known as "Alliance" was a concept design for supersonic aircraft considered by British Aerospace and Aérospatiale.  The plane was to be based on the experience learned from the supersonic Concorde, and was to fly at Mach 2 or higher.  Preliminary designs were produced, with some wind-tunnel testing of small-scale models, but development apparently stalled in the early 2000s.

Quiet Supersonic Technology: The Quiet Supersonic Technology, also known as QueSST is a project in development by NASA and Lockheed Martin that is aimed to be a quieter replacement for the Concorde.  After design review, the next stage is to test models in a wind tunnel.  The ground noise is expected to be around 60 dB(A), about 1000 times quieter than current supersonic aircraft.  This is achieved by using a long, narrow airframe and canards to keep the shock waves from coalescing.

Supporting paragraphs: Supersonic aircraft Tupolev Tu-144
Answer: 55