Engineers are busy prepping a modified Russian ballistic missile for launch Monday with a $450 million European probe that will measure the tug of Earth's gravity with finer detail than ever before.

The GOCE spacecraft as seen in earlier pre-flight testing. Credit: ESA

The Gravity field and steady-state Ocean Circulation Explorer, or GOCE, is bolted atop a Rockot launcher at Complex 133 at the Plesetsk Cosmodrome in far northern Russia.

Technicians loaded the Rockot with toxic hydrazine and nitrogen tetroxide propellants this weekend. Workers also completed a series of electrical checks on the 95-foot-tall booster, verifying it is ready for the final countdown on Monday.

The Rockot is an SS-19 missile built to deliver nuclear warheads to targets across the globe. Eurockot, a Germany-based launch services firm, will oversee the Monday's launch for the European Space Agency.

Liftoff is set for precisely 1421:17 GMT (10:21:17 a.m. EDT) Monday.

The Russian state commission will give its approval to proceed with launch about six hours before blastoff.

Officials will confirm their readiness for flight 40 minutes prior to launch. The Rockot's automatic launch sequence will begin a half-hour before liftoff.

A view of Rockot booster's frigid launch pad. Credit: ESA

The pad's mobile service tower will be wheeled away from the rocket and locked in launch position four minutes before launch.

Launch was postponed from September after rocket officials discovered a failure in the guidance and navigation system of the Rockot's Breeze KM upper stage. Technicians had to replace the rocket's gyroscope and refurbish its power system, delaying launch to this year.

The silver rocket will turn north from Plesetsk and drop its missile-heritage first and second stages in the Barents Sea within the first five minutes of the flight.

The Breeze KM will ignite to for more than nine minutes to reach a temporary orbit with a high point of 163 miles and a low point of 95 miles, according to Khrunichev, the Russian contractor for the Rockot vehicle.

The upper stage will briefly fire again for 13 seconds at 1539 GMT to climb to a circular orbit with an altitude of 173 miles and an inclination of 96.7 degrees.

The Rockot will deploy GOCE just shy of 90 minutes after blastoff. Officials hope to confirm spacecraft separation moments later after acquiring the first signals from GOCE through a ground station in Kiruna, Sweden.

Controllers will monitor the launch from the European Space Operations Center in Darmstadt, Germany.

GOCE carries an ultra-sensitive sensor to detect subtle variations in Earth's gravity field as it circles the planet in an unusually low orbit just 162 miles high.

Accurate maps of the gravity field will give scientists a crucial reference to compare against ocean circulation and sea level measurements.