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It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s (28328 km/hr using the units you mentioned)
• OMS-2 delta-v: 96.8 ft/s (106 km/hr)

And the orbital parameters (units are nautical miles given as altitudes, all numbers are approximate)

• Main engine cutoff: Apogee 118 nm, Perigee 31 nm

• Post OMS-2: Apogee 124 nm, Perigee 84.9 nm

Sources:

• Space Shuttle Mission Summary
• STS-135 Space Reporter's Handbook

Two quibbles with the question:

• 17500 is roughly orbital speed in miles per hour, not km/h
• It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s (28328 km/hr using the units you mentioned)
• OMS-2 delta-v: 96.8 ft/s (106 km/hr)

And the orbital parameters (units are nautical miles given as altitudes, all numbers are approximate)

• Main engine cutoff: Apogee 118 nm, Perigee 31 nm

• Post OMS-2: Apogee 124 nm, Perigee 84.9 nm

Sources:

• Space Shuttle Mission Summary
• STS-135 Space Reporter's Handbook

It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s (28328 km/hr using the units you mentioned)
• OMS-2 delta-v: 96.8 ft/s (106 km/hr)

Source: Space Shuttle Mission Summary

It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s (28328 km/hr using the units you mentioned)
• OMS-2 delta-v: 96.8 ft/s (106 km/hr)

And the orbital parameters (units are nautical miles given as altitudes, all numbers are approximate)

• Main engine cutoff: Apogee 118 nm, Perigee 31 nm

• Post OMS-2: Apogee 124 nm, Perigee 84.9 nm

Sources:

• Space Shuttle Mission Summary
• STS-135 Space Reporter's Handbook

It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s
• OMS-2 delta-v: 96.8 ft/s

Source: Space Shuttle Mission Summary

It's probably best not to discuss it in terms of "leaving the Earth's atmosphere". The shuttle never really did, the atmosphere in some form goes out very far indeed.

However we can look at some times, velocities and burns.

For STS-135 these are the important times (given in minutes and seconds from liftoff)

• Solid rocket booster staging: 2:03
• Main engine cut-off: 8:23.8
• OMS-2 perigee-raising burn: 37:45

And the corresponding velocities

• Main engine cut-off: 25817 ft/s (28328 km/hr using the units you mentioned)
• OMS-2 delta-v: 96.8 ft/s (106 km/hr)

Source: Space Shuttle Mission Summary