During a de-orbit burn, a pre-calculated ∆V (delta V, change in velocity) will be used to decrease the Orion MPCV's altitude. The Orion MPCV's Orbital Maneuvering System (OMS) engines provide a combined thrust force of 53,000 Newtons. The Orion MPCV has a mass of 25,848 kg when fully loaded. 

CALCULATION: 

Calculate how long a de-orbit burn must last in seconds to achieve the Orion MPCV's change in altitude from 391.6 kilometers to 96.5 kilometers at perigee. 

Use the equations and conversions provided to find the required burn time. Equations to use:  

1.    Newton's Second Law: F = ma Where: a = acceleration is in meters per second squared  (ms2) units F = force is in Newtons 1N = 1(kg−m/s^2) M = mass is in kg units Solve for a = F/m  

2.   Determination of ΔV (DeltaV): Find the change in altitude (Original Perigee - New Perigee) Use the conversion factor of (0.379[ms]/1km) . This conversion factor is the approximation of orbital velocity for the altitude difference, only valid for Earth's gravity and atmospheric drag for the altitudes of this problem.