Roy good questions Yes it s actual thrust data from the Columbia mission STS 107 However you can t directly measure thrust Rather it s calculated from other parameters such as chamber pressure Also the thrust curve is generally corrected to constant sea level or constant vacuum thrust In actuality the physical thrust would be constantly changing even if engine thrust was constant which it s not for the SRBs I include below some more info I was preparing to post Because of the frequent confusion on this point I uploaded a thrust time graph for the SRBs I also revised the thrust numbers in the article to reflect this SRB sea level liftoff thrust is 2 8 million pounds each Each SSME produces 393 000 pounds sea level thrust at 104 power level Thus the shuttle total liftoff thrust is 393 000 3 2 800 000 2 6 779 million pounds force or 3 075 million kgf or 30 16 MN Using these numbers the SRBs provide 82 6 of liftoff thrust This is confusing because many sources just blindly copy the 3 3 million pound thrust number some even erroneously adding sea level or liftoff thrust There are six possible thrust numbers for the SRB Sea level liftoff thrust Sea level peak thrust Sea level average thrust Vacuum liftoff thrust Vacuum peak thrust Vacuum average thrust The problem is most references don t state which they are using This is why references state SRB thrust from 2 65 million lbs probably sea level average thrust to 3 4 million lbs probably vacuum peak thrust When comparing SRB thrust to say Saturn V F 1 engine thrust you must consider the different characteristics of each engine type The F 1 is not throttlable so excluding altitude variations always produces the same thrust At sea level this is 1 5298 million lbs per engine or 7 649 million lbs thrust total By comparision the SRB thrust changes over the burn time see chart Space shuttle total sea level liftoff thrust is 6 779 million pounds force or about 88 6 of the Saturn V In theory you could compare the SRB thrust at T 20 sec which is somewhat higher but that wouldn t be liftoff thrust