<P> Some military weapons use rockets to propel warheads to their targets . A rocket and its payload together are generally referred to as a missile when the weapon has a guidance system (not all missiles use rocket engines, some use other engines such as jets) or as a rocket if it is unguided . Anti-tank and anti-aircraft missiles use rocket engines to engage targets at high speed at a range of several miles, while intercontinental ballistic missiles can be used to deliver multiple nuclear warheads from thousands of miles, and anti-ballistic missiles try to stop them . Rockets have also been tested for reconnaissance, such as the Ping - Pong rocket, which was launched to surveil enemy targets, however, recon rockets have never come into wide use in the military . </P> <P> Sounding rockets are commonly used to carry instruments that take readings from 50 kilometers (31 mi) to 1,500 kilometers (930 mi) above the surface of the Earth . </P> <P> Rocket engines are also used to propel rocket sleds along a rail at extremely high speed . The world record for this is Mach 8.5 . </P> <P> Larger rockets are normally launched from a launch pad that provides stable support until a few seconds after ignition . Due to their high exhaust velocity--2,500 to 4,500 m / s (9,000 to 16,200 km / h; 5,600 to 10,100 mph)--rockets are particularly useful when very high speeds are required, such as orbital speed at approximately 7,800 m / s (28,000 km / h; 17,000 mph). Spacecraft delivered into orbital trajectories become artificial satellites, which are used for many commercial purposes . Indeed, rockets remain the only way to launch spacecraft into orbit and beyond . They are also used to rapidly accelerate spacecraft when they change orbits or de-orbit for landing . Also, a rocket may be used to soften a hard parachute landing immediately before touchdown (see retrorocket). </P>

What idea is being expressed in the following sentence the scientists sent the rocket to mars