SOFTWARE ACQUISITION
FOR CAPABILITY
Precision-guided munitions fly to the sound of dif ferent GPS signals.
by Paul Manz and Thomas Blenk O
n Oct. 12–14, 2021, the Joint Program Executive Office for Armaments and Ammu- nition’s (JPEO A&A) Assured Precision Weapons and Munitions team and its partners successfully executed the first-ever network-assisted M-code GPS precision- guided munition live-fire developmental test at Yuma Proving Ground in conjunction
with Project Convergence 2021.
Until recently, most precision-guided munitions used an encrypted GPS reference signal called P(Y)-code to help them accurately fly to and engage an enemy target. (P-code is precise code. P(Y)-code is encrypted code to protect against spoofing.) Now, after many decades of using P(Y)- code GPS signals, precision-guided munitions are migrating to a new, enhanced military GPS signal called M-code. M-code GPS has many benefits, including improved GPS jamming resis- tance, improved ability to determine enemy spoofing of GPS signals and enhanced cryptography for improved security.
OFF TO A HOT START Te ability to use any form of GPS, including M-code GPS, is based on the user or platform being able to “see” GPS, “hear” GPS and know what is being heard is “truth” in a timely manner.
Seeing GPS means the user or platform—in this case, a precision-guided munition—must have direct view of sufficient overhead GPS satellites to determine its location in simplistic terms of X, Y and Z coordinates. Sufficient GPS satellites mean a weapon or precision-guided munition must always see at least four GPS satellites, noting that seeing more than four satellites that are widespread across the sky results in even better positioning accuracy. Te information (such as satellite location, timing and “health” information) from GPS satellites seen by the weapon can be used to hot-start the precision-guided munition. Tis pre-loaded hot-start information allows the precision-guided munition to more rapidly see and hear GPS signals after launch and help in determining if those signals are truth or spoofed signals.
While a precision-guided munition at the highest point of its flight usually has an unobstructed direct view of all GPS satellites in the sky from horizon to horizon (sometimes eight satellites or more), ground-based indirect-fire artillery and associated precision-guided munitions being fired may sometimes initially see less than the required minimum four GPS satellites. Tis could happen if the weapon is located in vertically-challenging terrain, such as a deep valley
CODE WORD
https://asc.ar my.mil
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