Imagine if you had developed, built and flown a spacecraft that successfully traversed the cosmos but upon landing, spun out of control or hit something that destroyed the ship. Such nightmare scenarios are exactly what NASA engineers are developing sophisticated software technology to avoid.
NASA is currently testing one of the more important components of such software - the algorithms that incorporate the spacecraft's trajectory, speed and landing information to guide a ship to a safe arrival. The latest algorithm, known as Fuel Optimal Large Divert Guidance algorithm (G-FOLD) is being flight-tested in conjunction with Masten Space Systems at the Mojave Air and Space Port in California.
According to NASA, G-FOLD, invented at the agency's Jet Propulsion Laboratory, "autonomously generates fuel optimal landing trajectories in real time and provides a key new technology required for planetary pinpoint landing. Pinpoint landing capability will allow robotic missions to access currently inaccessible science targets. For manned missions, it will allow increased precision with minimal fuel requirements to enable landing larger payloads in close proximity to predetermined targets," NASA said.
G-FOLD incorporates key information such as the maximum and minimum thrust magnitude; thrust pointing direction; glide slope to avoid surface contact during flight; and the maximum velocity to avoid supersonic flight.
"Spacecraft accumulate large position and velocity errors during the atmospheric entry phase of a planetary mission due to atmospheric uncertainties and limited control authority. The powered descent phase, which is the last phase of Entry, Descent, and Landing, is when the lander makes a controlled maneuver to correct for these errors. This maneuver must be computed onboard in real-time because the state of the lander cannot be predicted at the start of powered descent phase," NASA stated.
Current powered-descent guidance algorithms used for spacecraft landings are inherited from the Apollo era. These algorithms do not optimize fuel usage and significantly limit how far the landing craft can be diverted during descent, NASA said.
For the current test, NASA said it used Masten's XA-0.1B Xombie vertical-launch, vertical-landing experimental rocket. To simulate a course correction during a decent to Mars, the Xombie was given a vertical descent profile to an incorrect landing point. About 90 feet into the profile, the G-FOLD flight control software was automatically triggered to calculate a new flight profile in real-time and the rocket was successfully diverted to the "correct" landing point some 2,460 feet away.
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