Phobos 4 was built in 2001 as an attempt to regain the altitude record for the highest altitude achieved in the UK, held by the SRA team. The construction and launch of Phobos 4 was featured in a Discovery Channel documentary as part of the "Detonators" series about the professional use of pyrotechnics.
The rocket was a hybrid of components and design elements from the Phobos 2 and Phobos 3 rockets, utilising the same 75mm diameter booster as Phobos 3, mated to a 54mm diameter second stage based on the booster of Phobos 2. The 2-stage rocket was simulated to reach around 22,000 feet in altitude and used an innovative forward bulkhead ignition system for the second stage motor
The rocket launch was unsuccessful due to a structural failure of the inter-stage joint at Max-Q. The rocket reached a maximum recorded speed of over 1050 mph, before the joint failed, sending the sustainer spiralling. The rocket reached an altitude of 8900 feet - a long way short of the planned altitude.
The booster recovered successfully, as did the payload section of the sustainer. The forward bulkhead ignition system was also proven to be successful.
As with so many things, more is often learnt from a failure than a success. The flight of Phobos 4 became a catalyst in re-focusing MARS on to the Deimos project, proving that the high performance hybrids under development by MARS, could provide a far cheaper and more readily available way of breaking records.