NASA has admitted in an internal circular that there are "significant threats" to the performance of its Ares I crew launch vehicle (CLV), as Flight has learned that the preliminary design review for the CLV first stage has slipped by up to six months.
The Ares I first stage is based on the Space Shuttle's four-segment reusable solid rocket motor (RSRM), but with five segments. Initially intended to be largely unchanged from the RSRM, its insulation, throat diameter, propellant chemistry and geometry, and number of segments had all been changed by December 2006. NASA sources also say that, due to ascent stresses, areas of the segment casing are to be modified for strengthening.
The first stage is being designed to lift the CLV's upper stage, the Orion crew exploration vehicle (CEV) and its launch abort system to 129.5km (80.4 miles) before staging. The first manned flight is planned by March 2015.
The Ares I programme has been dogged by rumours of inadequate performance and blamed for repeated redesigns of the Orion's crew and service modules driven by the need to reduce mass. NASA has refuted the rumours and maintained that the Ares I CLV is capable of meeting requirements.
But now the agency's November internal circular says: "There are significant threats to the performance to be worked as the project works towards [PDR]."
The PDR delay is referenced in a report by CLV first-stage office deputy manager Thomas Williams. While unavailable for comment, Williams says in the report: "First-stage element analysis [ending January 2008 leads to] PDR data drop 16 February, [followed by first-stage] PDR on the 20th. [The design analysis cycle] DAC-2 element data drop is 1 April, [then] PDR data drop is on 15 May, [followed by full vehicle] PDR 22 July ."
This differs from the multi-programme integrated milestones in NASA's fiscal year 2008 budget, covering the period 1 October 2007 to 30 September 2008. That shows Ares I first-stage PDR in the first quarter of FY2008 - in other words between October and December 2007.
The project office began its Ares I initial capability level one system definition review (SDR) on 10 September, completing it on 30 October. This SDR came mid-cycle during the DAC-2 design analysis cycle for the CLV first stage.