Status: Retired 1992. First Launch: 1991-01-28. Last Launch: 1992-03-13. Number: 2 . Thrust: 200.00 kN (44,960 lbf). Gross mass: 14,000 kg (30,000 lb). Height: 4.10 m (13.40 ft). Diameter: 1.16 m (3.80 ft). Apogee: 300 km (180 mi).
Lockheed was awarded a five year contract in November 1985 worth at that time $ 490 million that included integration of the rocket. Four test vehicles were built. First launch was made on 28 January 1991 from Kwajalein Atoll against an Aries sounding rocket. A second test on 13 March 1992 against a Minuteman I was considered successful enough that no further tests were planned. Further development of the technology was to be accomplished by the Orbital Sciences' Aries test vehicle with spectacularly poor results.
Historical Essay © Andreas Parsch
In November 1985, Lockheed was awarded a contract to develop and test the ERIS (Exoatmospheric Reentry Interceptor Subsystem) ballistic missile interceptor as part of the ground-based missile defense system within the SDI (Strategic Defense Initiative) program. ERIS was to become an upper-tier system, complemented by the lower-tier HEDI (High Endoatmospheric Defense Interceptor).
The ERIS test missiles consisted of the second and third stage (Aerojet General M56A1 + Hercules M57A1) of surplus LGM-30A-B Minuteman I ICBMs, which boosted the hit-to-kill interceptor vehicle into space. Sensor and guidance technology of the ERIS KKV (Kinetic Kill Vehicle) was based on the experience won by the earlier HOE (Homing Overlay Experiment) tests. Because of technology improvments the ERIS KKV, which used an inflatable octagonal "kill enhancer", was significantly smaller and lighter than the HOE KKV.
All ERIS tests used Orbital Sciences Aries missiles as delivery vehicles for the target RV (Reentry Vehicle). On the first intercept attempt on 28 January 1991, the target RV deployed two balloon "decoys" on each side, but the KKV was preprogrammed to home on the center target (i.e. the warhead). The RV was successfully destroyed at a closing speed of more than 13.4 km-s (44000 fps) at an altitude of 270 km (145 nm). In the second test on 13 March 1992, the target RV deployed a single decoy balloon and the KKV had to make the warhead-decoy decision by itself. Although the seeker logic of the ERIS KKV reportedly identified warhead and decoy correctly, no hit was scored because target detection was a bit late (partially because of preplanned test requirements), giving the KKV not enough time to manoeuver to the intercept point.
Despite the partial failure of the second test, the ERIS test program was considered fully successful, and two of the originally planned four tests were cancelled. Because of the changed world situation after the end of the Cold War, the SDI program was somewhat reoriented in the early 1990s towards what was then called GPALS (Global Protection Against Limited Strikes), and ERIS itself was not directly developed into an operational system. However, experience and technology developed during ERIS was put to use in the current missile defense programs, like THAAD (Theater High-Altitude Area Defense) and the GBI (Ground-Based Interceptor) missile of the GMD (Ground-Based Midcourse Defense) system (formerly NMD; National Missile Defense).Specifications
I have no data about the exact physical characteristics of the ERIS test vehicles. For data on the Minuteman I 2nd and 3rd stage motors, refer to the LGM-30 Minuteman page.Main Sources
 Missile Defense Agency Website
 Mark Wade: Encyclopedia Astronautica
 Chronology of Missile Defense Tests
Flight test vehicle for Exoatmospheric Re-Entry Interceptor Subsystem, an anti-ballistic missile hit-to-kill interceptor warhead. The ERIS vehicle itself consisted of surplus Minuteman ICBM second and third stages. Four test vehicles were built. First launch was made on 28 January 1991 from Kwajalein Atoll against an Aries sounding rocket. A second test on 13 March 1992 against a Minuteman I was considered successful enough that no further tests were planned. Further develoment of the technology was to be accomplished by the Orbital Sciences' Aries test vehicle with spectacularly poor results.
During the mission the TRW team monitored a mission telephone com channel real time in Redondo Beach. Participants recall the intense, "nail biting" anxiety as they waited the approximate 30 minutes it took for the RV to reach the nominal intercept point, over the Pacific and closer to Hawaii than to Kwajalein Atoll. Launch of the Minuteman I target from Vandenberg AFB came at 1803:00.3, launch of the ERIS interceptor at 1824:24.2, and kinetic intercept over Pacific at 1832:08.2.
This second test or ERIS against a Minuteman I was considered successful enough that no further tests were planned. A second launch attempt on 11 May 1991 had been scrubbed after launch of the target missile but before launch of the interceptor. Further develoment of the technology was to be accomplished by the Orbital Sciences' Aries test vehicle with spectacularly poor results.